Search This Blog

Saturday, September 18, 2010

Pharmaceutical Instruments :

Posted by Anonymous
- Sumit Goel.


The subject of pharmacy deals with the practical application of the science of physics to the medicinal preparations. This part of the section deals with some of the instruments, appliances and apparatus used in a homoeopathic pharmacy and the next part of the section deals with some common laboratory methods employed in the practice of pharmacy.

The study of the pharmaceutical instruments, appliances and apparatus can be broadly studied under the following categories.

1. Those used for preparation of homoeopathic medicines

Comminution - mortar, pestle, chopping board and knife

Succussion - leather pad

Percolation - percolator

Expression - presses

Sifting - sieves

2. Those required for weighing, measuring and storage Balances; Measuring cylinder; Graduated conical glass; Measuring tile; Funnel; Volumetric flask; Burette; Pipette; Official medicine dropper; Beaker; Spatula and spoon; Stirrer.

Glass containers are discussed in the section of 'Preservation and Packaging'.

3. Those used in heating

Burner; Water bath; Sand bath; Wire gauze and tripod stand; Hot air oven; Thermometer

4. Those used in laboratory procedures

Crucible; Evaporating dish; Distillator; Condenser; Retort still; Desiccator; Tray dryer; Pycnometer; Hydrometer; Alcoholometer

Instruments for standardization of homoeopathic medicines are not described in this section.

COMMINUTION

This is the process of reducing a substance to finer particles and maybe described as cutting, slicing, bruising, grinding, pulverizing and triturating.

* Cutting, slicing and chopping can be performed with the aid of a chopping knife and a chopping board or with any sharp instrument.

* In pharmacy, herb-cutter is usually employed for cutting and slicing the plant drugs.

* Contusion or bruising is performed in a mortar.

* Grinding is the process of reducing substances to moderately coarse powders. Pulverization is a term usually applied to grinding to a still fine powder.

* Trituration is the process of reducing the substance to a finer powder than is normally obtained by grinding in a mill and is accomplished with a mortar and pestle aided by the spatula.

Mortar and Pestle

The apparatus used in trituration is the mortar and the pestle, aided by the spatula.

(A) Mortars are available in diverse sizes, shapes and material, but are usually hemispherical in shape and made of agate, iron or steel, porcelain, glass and wedgewood.

* Agate mortars are employed for very hard substances.

* Iron or steel mortar and pestle are utilized for pulverizing and grinding very hard substances, e.g. seeds of Nux vomica, Sabal serrulata. These must be lightly polished and kept perfectly free from rust, as rust decomposes many vegetable juices at once.

* Porcelain mortar and pestle are used for trituration of soft aggregates or crystals. It is commonly used for trituration of powders of approximately uniform particle size. The inside of the mortar and the face of the pestle should be ground and unglazed. This is very important for producing friction, which is essential for the process of trituration. If not, it is unglazed by rubbing wet sand upon their surfaces. The outer surface of the mortar is glazed and hence, less porous as compared to the wedgewood mortar.

* Glass mortar and pestle is primarily used for mercurial preparations and in preparing solutions and suspensions of chemical materials in a liquid. They are also suitable for preparing ointments, which require reduction of soft aggregates of powdered materials or the incorporation of a liquid. Glass also has the advantage of being comparatively non-porous and not staining easily. Glass cannot be used for triturating hard solids.

* Wedgewood mortars are suited well for comminution of crystalline solids or for reduction in particle size of most materials. They are capable of adequately powdering most substances that are available only as crystals or hard lumps. However, it is relatively porous and stains quite easily. It is available with a roughened interior that aids in the trituration process, but requires meticulous care in washing, as particles of drugs may be trapped in the rough surface and cause contamination of materials subsequently triturated in the mortar.

* For trituration of a large quantity, power mortars are also available. This consists of a weighted pestle mounted eccentrically in a ceramic, granite or metal mortar, which is rotated by a motor. The pestle rotates with friction and is free to rise and fall in the mortar, so that its grinding action involves both impact and shear, the material being crushed and rubbed between it and the rotating mortar. Spring loaded scrapers ensure that the material is constantly returned to the grinding area and at the end of the operation, the pestle can be swung clear of the mortar to facilitate emptying and cleaning. Trituration is commercially carried out on a large scale with power motors.

(B) The pestle, mainly of porcelain and wedgewood, accompanying the mortar has a wooden handle, which is fixed into the head of the pestle that is made of the same material as that of the mortar. The fixing has to be properly cemented, as the handle tends to separate from the head due to repeated use. Pestle entirely made up of porcelain or wedgewood is not suitable, as it is easily broken. Also, the wooden handle makes the pestle light and convenient to use.

Mortar and pestle should not be interchanged. If only one mortar is kept for all medicines, it should be washed and cleaned immediately after use. The efficiency of trituration depends largely on the maximum contact between the surfaces of the head of the pestle and the interior of the mortar.

Chopping Board and Knife

Chopping boards should be made of sound, well-seasoned maple, and maybe circular or oval shaped. Marble or glazed porcelain slabs may also be utilized. It may have a central concavity. It is used as a base for cutting, slicing or chopping fresh medicinal plants and their parts.

Chopping knives should be made of good steel, well polished and free from rust, as rust decomposes many vegetable juices at once.

SUCCUSSION

Leather pad

During the process of succussion, it is required to strike the vial or phial against an object that is hard and at the same time elastic. This is important, because the strike of the vial or phial needs to end in a jerk; taking care not to break the glass container. This is achieved by leather that may be cut of such a size that fits on the palm of the hand. This is called a leather pad, having a belt from the edge of the longer side to secure the pad on the palm. Hahnemann, mentions in the instructions for the preparation of his medicines - "The vial used for potentizing is filled two-thirds full and given one hundred strong succussions with the hand against a hard but elastic body, perhaps on a leather bound book."

PERCOLATION

It is a process of extracting the soluble constituents of a drug and preparing the mother tincture by the passage of a solvent (menstruum) through the powdered drug contained in a suitable vessel called percolator for a definite period of time as per directions specified in Pharmacopoeia.

Percolator

The utensil in which the drug is packed is called a percolator, and consists of a suitable cylindrical vessel of glass or a metal like stainless steel or copper, provided with an orifice at the bottom.

Glass percolators are preferred as the metal percolators have the double disadvantage of being more easily attacked by acid or other substances that the menstruum or drug might contain and also the fact that their opacity prevents the observation of the process of percolation. However there are limits to the size of a glass percolator.

The simplest form of a percolator is the conic variety. This however offers too great a width of surface for the menstruum, which, therefore, has a correspondingly smaller course to travel before emerging from the bottom of the percolator. A tapering percolator is a modification of the conic variety. But a cylindrical percolator is more popular, for by means of it, one can exhaust a drug far more thoroughly than in either a tapering or a conic percolator, from the simple fact that each portion of menstruum has to travel through a larger amount of the drug before emerging from the percolator.

A percolating apparatus consists of the percolator and the receiver. The percolator has a body, which contains the packing and a lower narrow portion called the neck that may be connected to the receiver. The saturated solution emerging from the percolator is called the percolate and is collected in the receiving bottle. The percolator is supported on an appropriate stand.

EXPRESSION

It is a process of forcibly separating liquids from solids. A number of mechanical principles have been recognized in the operation of expression - namely the use of spiral twist press, screw press, roller press and the hydraulic press.

Presses Most forms of presses consist of two parts between which the substance is placed and which are made to approach each other by means of lever, screw or some other mechanical power. Presses for plants must be so constructed that they can be taken apart and thoroughly cleansed.

Important in the process of expression is the straining of the expressed liquid through suitable cloth. The mass to be expressed is therefore usually enclosed in a bag of stout cloth (press cloth) before placing it in the press. Such a press cloth can be used directly for expression by forcible straining.

* Wooden press - each press has two wooden parts, each of which consists of one handle. Two hinges connect these two parts to each other. One part has a deep concave coning at the centre, whereas the other has an elevated rounded convex part, so that each of them is fitted with another, when pressed.

* Spiral twist press - the principle of this press is best and most practically illustrated in the usual process of manually expressing a substance contained in a cloth.

* Roller press - this is used for large-scale pressing of oily seeds, fatty substances, etc. Care must be taken to apply the force gradually to the bag containing the material to be pressed.

* Hydraulic press - the spiral twist is not powerful and its action is limited. The screw presses have friction with which to contend. The friction of the screw increases with the intensity of the pressure applied and when a certain limit is reached, all further force applied is wasted and if continued, may result in destruction of the press. The roller press is very limited in its action. The hydraulic press though expensive, is economical, because the greatest power is obtained at the expense of least labour. The principle of a hydraulic press is based on the fact that pressure exerted on an enclosed liquid is transmitted equally in all directions. Tremendous pressures can be developed with hydraulic presses.

SIFTING

Sieves

These are vessels with meshed or perforated bottom for separating fine powders from coarser substances in the mixture. A number of factors must be considered in selecting screening surfaces or sieves. Primary consideration is given to the size and shape of the aperture opening, the selection of which is determined by the particle size that is to be separated. Screens most commonly used are woven wire sieves, bolting cloth, closely spaced bars and punched plates. There are various types of woven wire screens including plain, twilled and braided weave.

Different authorities prescribe different standards for the sieves and their classification. The wire sieves used in sifting powdered drugs are distinguished by numbers that indicate the number of meshes included in a length of 2.54 cm in each transverse direction parallel to the wires. According to HPI, the sieves are made of wires of uniform circular cross-section and are specified as sieve numbers 6, 8, 10, 22, 25, 30, 36, 44, 60, 85, 100 and 200. The sieves that are used today are made up of silk, hair or stainless steel wire.

METROLOGY

This involves weighing and measuring; the former process requires the use of balance and the latter process require the use of the measure, the graduate and the pipette.

Balances

Successful performance of many procedures in pharmacy depends upon a thorough knowledge of the principle of the balance and a correct understanding of its care and use. Weighing is nearly always an important step in trituration and dispensing.

Balance is an instrument devised to determine the relative weights of substances and therefore should be correctly constructed, skillfully used and carefully protected from damage. It must also be periodically checked to obtain accurate results.

Sensitivity of Balance

This corresponds to the smallest mass that makes the pointer move over one division on the scale. If the sensitivity of a balance is 0.1 mg, this means that a mass of atleast 0.1 mg is needed to move the pointer.

Types

The only form of scale with which the mass of a substance is estimated by actual gravity is the spiral balance, consisting of a delicate spring to which is attached the scale pan; the elongation of the spiral when a weight is placed in the pan being marked by the descent of an arrow attached to the lower part of the spiral. This needle moves against a scale, and the elongation of the spring under influence of gravity can be measured and the weight can be determined.

For systematic consideration, pharmaceutical balances may be classified as follows:

* Single beam, equal arm balances

* Single beam, unequal arm balances

* Double beam, unequal arm balances

* Compound lever balances

* One arm balance

COMPONENTS OF AN ANALYTICAL BALANCE

The entire instrument is placed in a glass casing to protect it from dust and to avoid air convection during weighing.

The essential parts of a common balance are -

1. The balance beam: It is a horizontal metal or alloy casting, generally of the form of a thin bar that is capable of turning freely about a sharp agate knife-edge at the middle, which is called the fulcrum. The sharp end of the knife-edge rests on a small plate agate to minimize friction. At the ends of the beam, two similar agate knife-edges are attached with their sharp edges upwards. The knife-edges in balances may be of hard polished steel, but as it is liable to rust from contact with moist air, and since every particle of rust increases the friction, rusted knife-edges oscillate less freely. This impediment to free oscillation is prevented by making the tip of knife-edges of polished agate, a hard mineral that does not rust.

2. The stirrups or pan supporters: These rest on the terminal edges. In the better type of balances, these are provided with agate pieces attached at the lower surfaces of their upper arms. These are furnished with hooks at the lower end, from which the pans are suspended. The distances from the fulcrum to the centre of gravity of the stirrups are called the arms of the balance, which are equal in length.

3. The scale pans: The standard weights and bodies that are to be weighed are placed on the scale pans.

4. The pillar: It is attached to the base plate of the instrument to support the beam when at rest. It is a vertical rod encased within an outer cover and can be lowered or raised by a key or knob at the base, when required. The pillar has an agate at the top, upon which the central knife-edge of the beam rests.

5. The pointer: This is attached at its upper end to the middle part of the beam and the lower end can move freely over a graduated scale attached to the bottom of the pillar. When the beam is horizontal, the pointer should be vertical and its lower end should point to the zero mark of the scale.

6. The arresting arrangement: When the balance is not in use, the pillar supporting the beam is lowered so that the beam rests on another support attached to the outer casing of the pillar as horizontal projections and the undersurfaces of the pans just touch the pan-rests on the baseboard. Thus the knife-edges at the centre of the beam do not always rest on the agate plate and so its sharpness is preserved.

7. The adjusting nuts: At each end of the beam, there is a nut working in a screw. By displacing the position of the nuts, the effective weight on each side can be altered through a small range and thus the weighing accuracy of the balance can be adjusted.

8. The plumb line and leveling screws: The base of the instrument is provided with leveling screws by whose adjustment the pillar is made vertical, so that the balance beam becomes horizontal; the correct adjustment is indicated by the exactly vertical position of the plumb line attached to the instrument. An alternate technique of determining the level is with the help of the spirit level.

9. The Rider: The rider is a small piece of wire weighing 10 mg, made of platinum, gold, stainless steel, etc. and bent twice at about 90 degrees with a loop at the middle. A chemical balance is provided with such a rider for taking fractional weights below 10 mg. For this purpose, the whole of the balance beam is divided by serrated marks into 100 equal parts and marked accordingly. For weights less than 10 mg, the rider is moved by the rider carriage and placed by trial and error method on a suitable position on the beam.

"Reading Zero"

Time is saved in determining equilibrium by watching the oscillation of the needle against the index mentioned on the balance. The index scale on the balance is usually divided into twenty equal lines, ten on either side of the line exactly below the line of suspension. When the beam is in oscillation, pans are said to be balanced if there is an equal deflection on both sides of the reference point on the scale.

The weights

The weight box is a wooden box with hinged lid. The standard weights are kept in the grooves present in the box. The weights used on the scales may be made of iron, brass or aluminum, depending on the capacity, sensitivity and use.

Weighing technique

1. Place the balance in a convenient position for use and ensure its cleanliness. Use a perfectly dry duster for wiping the balance and its parts.

2. Confirm that the instrument is level and adjust if necessary.

3. Check that the pointer is at the null point and make sure it is moving freely.

4. Place a clean sheet of white paper under each pan. These are replaced if spillage occurs, to prevent inaccuracy due to powder adhering to the pan supports.

5. Place the required weights on the left-hand pan. Use forceps while handling the weights.

6. Close the glass casing of the balance to prevent deflection of the pointer due to a wind current.

7. Place the material, appropriate to the amount to be weighed on the right-hand pan. The pointer will be seen to deflect away from the null point after the screw is turned.

8. Adjust the material till the pointer comes back to the null point. This is the amount of the substance that is needed, of the required weight. For determining the weight of the given substance, the same method is followed, but the metric weights are adjusted till the pointer achieves the null point.

9. Return the weights to their right place in the box and clean the balance.

CARE OF THE BALANCE

* It should be placed in a room free from dust and fumes.

* Due care must be taken to protect the balance from injury.

* The balance should be kept permanently in a dry room, the temperature of which is as even as possible, and protected from any acid or corroding vapours. In case it is necessary to weigh a fuming liquid, it should be placed in a well-stoppered bottle while weighing.

* The balance should be kept on a strong base like table so that vibrations do not affect it.

* The balance may not be properly leveled. This is easily detected by looking at the plumb line, which may not be exactly vertical under such conditions or by checking the spirit level. The defect is corrected by adjusting the leveling screws provided at the base of the instrument, till the plumb line is exactly vertical.

* The beam of the balance may not be perfectly horizontal when freed. This is to be adjusted by screwing in or out the nuts provided at the ends of the beam of the balance.

* The stirrups may be displaced. This should be properly placed on the beam before weighings are made.

* The pans need to be clean before weighing is commenced.

* Weights should never be left on the balance and should be transferred to the balance by means of pincers or forceps.

* Under no circumstances should the balance be left to oscillate after weighing is finished and during weighing, it should be brought to a state of rest whenever new weights or new portions of the substance is removed or placed thereon.

Measuring cylinder

These are long, cylindrical shaped calibrated glass containers used for measuring volume or capacity of liquids. The measuring cylinder is allowed to stand on a flat surface, like a table. The eye-level is adjusted to the level of the surface of the liquid. The reading is taken corresponding to the lower part of the meniscus. Measuring glass cylinders are available in different capacities with different least counts.

Graduated conical glass

For the purposes of capacity, conical measures may be used. These are available in different capacities as 10 ml, 50 ml, 100 ml, etc. These may be made of glass or plastic. The diameter of a cylindrical measure is constant and hence the error due to misreading the meniscus is the same at any mark throughout the height. With conical measures, the error is progressively larger with height because of outwardly sloping sides. Another advantage of a cylindrical measuring glass over the conical measure is that the volumes between the gradations can be estimated more precisely. Conical measures have this advantage that it is easier to fill without spilling the liquid on the sides above the required level. It is also convenient to rinse, clean and drain.

Measuring tile

The measuring tile or pill tile is generally made of porcelain or glass, with the painted graduations burnt in during the process of glazing of the porcelain or etched into the glass. It is generally used for measurement of globules and preparation of ointments.

Funnel

Funnel is a conical shaped apparatus intended to facilitate the pouring of liquids into narrow-mouthed vessels. It has an expanded upper conical part and a lower narrow, pipe-like structure. They are chiefly used for transfer of liquid, filtration and for sublimation. They are widely used for supporting filter media. Funnels maybe made of glass, polyethylene, metal, porcelain or any other material that serves the specific purpose. Funnels maybe fluted, grooved or ribbed for the purpose of facilitating the downward flow of the filtrate. Filter funnels can be fitted with a suitable filter media, which may be paper, cloth, sintered glass, sintered metal or asbestos sheet, according to the type of filtration required. The most commonly employed filtering medium on the small scale is the filter paper that is available in various textures and porosity. The selection of a suitable filter medium depends upon the purpose of filtration and the quantity to be filtered. It is desired that a filter medium be inert, allow the maximum passage of liquid while retaining the solid and should be of sufficient mechanical strength to withstand filtration pressure.

Volumetric flask

A volumetric flask is a flat-bottomed glass container, with a long narrow neck. It is accompanied with a stopper, which is usually made of glass or plastic. Flasks may be of different capacities. The capacity of a flask at a particular temperature is usually engraved on its wall. The neck carries a thin circular mark etched glass, which indicates the capacity of the flask. The temperature at which the liquids should be measured is also etched on the flask. It is generally used for preparation of reagents and also for storing standard solutions.

Burette

A burette is a long glass tube of uniform bore (10 - 15 mm diameter) throughout its length and is graduated in fractions of cubic centimeters. One end (upper) of the tube is open and the other end (lower) is drawn to a jet and is fitted with a glass stopcock about 5 - 6 cm above the lowest jet point. The graduation begins a few centimeters from below the upper end and goes downwards to a few centimeters above the stopcock. The uppermost graduation is marked as 'zero' and the lowermost graduation is marked according to the capacity of the burette. The burettes are filled from the top with the liquid to be measured. A burette is a suitable apparatus for delivering variable amounts of a liquid contained in it and the rate of delivery can be controlled by means of the stopcock. Hence, it is generally used for titration in the analytical laboratory. The burette is filled up with the solution to a little above the zero mark. The burette is held vertically and the liquid is allowed to flow out slowly by opening the stopcock lightly, until the lower part of the liquid meniscus coincides with the zero mark. The burette is clamped vertically to a stand. Care must be taken to avoid air bubbles inside the jet or the burette. In such a case, the stopcock is fully opened and the liquid is allowed to run out with a force till the air bubbles are expelled. The liquid is then poured again in the burette to fill upto the zero mark.

For finer measurements, which measure 1 ml in fraction, micro-burettes are used.

Pipette

Pipettes are employed for withdrawing a measured volume of a liquid accurately and its transfer.

The pipettes used in a laboratory, maybe of graduated or volumetric type.

(a) Volumetric - These are used to measure precise volumes, with a high degree of accuracy.

The volumetric pipette may be of two types.

- A pipette with a single graduation mark: the pipette is a glass tube with a cylindrical bulb in the middle, one end of the tube is drawn into a jet, while the other stem carries a thin circular mark etched on it. This mark indicates the volume of the liquid to be measured out by the pipette. The capacity of the pipette, at a particular temperature, is usually engraved on the bulb. Pipettes may be available in different capacities.

- A pipette with two graduation marks.

(b) Graduated - For volumes under 1 ml, graduated pipettes calibrated in units of 0.1 ml or 0.01 ml should be used. Two types of graduated pipettes are available - those that deliver the calibrated volume when the contents are blown out, by mouth or by a teat and those that deliver the calibrated volume when the liquid is allowed to drain out on the side of the receiver. For hygienic reasons, pipettes should not be used by mouth in dispensing and they must never be used in this way for corrosive liquids and other poisons. In such cases, safety bulbs are used.

The given solution, of which a definite quantity is to be measured out, is sucked by mouth into the pipette, until it rises a little above the mark. The forefinger closes the open end. The pipette is now held in a vertical position and the liquid is allowed to run out slowly by slightly relaxing the pressure at the finger until the lowest point of the meniscus just coincides with the mark. The liquid inside the pipette is then transferred into a container by releasing the forefinger and holding the pipette in a slightly inclined position, until the whole of the liquid is emptied.

Official medicine dropper

The pharmacopoeial medicine dropper is 3 mm in external diameter at its delivery end and when held vertically delivers 20 drops of water, the total weight of which is between 0.9 g and 1.1 g at 25oC. In using a medicine dropper, one should keep in mind that few medicinal liquids have the same surface and flow characteristics as water and therefore the size of drops varies materially from one preparation to another. In administering small quantities of liquids, the very convenient drop is used almost always. It should be emphasized that 1 drop ? 1 minim and that 60 drops ? 1 fluid drachm.

Beaker

It is usually made of glass. These are available in different sizes. The mouth of the beaker is generally circular, but some beakers may have a spout or lip in the mouth of the beaker for better drainage of the liquid. It is used for storage of liquids.

Spatula and Spoon

These are usually made of horn, bone, ivory, porcelain, solid hard rubber and stainless steel. Iron spatulas may also be used but should be free from rust. The handle of the spatula is usually heavier than the blade. Hence, when it is kept on the table, the blade does not touch the surface of the table.

During the process of trituration, the powder tends to get packed on the inner sides of the mortar, due to increased pressure exerted by pestle. The object of spatula in trituration is to scrape the triturated powder from the sides of the mortar. The spatula is also used for handling and transfer of powders and in preparation of semi-solid external applications like ointments. Spoon is used to transfer liquid substances from one container to another.

Stirrer

It is generally made of glass, steel or wood. It is a rod having a long handle and a small rounded tip. It is used to stir and mix the liquid.

Burner

For performing chemical tests or experiments involving chemical reactions, application of heat is necessary. Gaseous fuels are very suitable for laboratories. The gases used to produce heat are coal gas, acetylene and natural gas. For burning gas fuels, special devices are required that would allow the gas to burn without danger. Such devices are called burners. Bunsen burner

A Bunsen burner is a simple mechanical device used in laboratories for production of heat and flame by burning gaseous fuel (commonly coal gas). Apart from the great advantage of freedom from soot, the flame of the Bunsen burner is superior to the ordinary flame by reason of its greater heat

Water bath

Water bath is required for the purpose of heating at a low temperature. As water boils at 100oC, the temperature of water bath always remains at the temperature of boiling water. A water bath is a round or pan-shaped vessel, generally made up of copper. The vessel is covered with concentric, reducible, flat, ring-like lids that are made up of copper. The lids are arranged one above another. All the lids are perforated except the one that is placed at the top. A water bath may have a single or multiple perforations for heating purpose. The vessel is partially filled with water and heated by an electric current or heated from below by a Bunsen burner. It is used to calculate the moisture content of drug substances; for indirect heating at low temperature; and for sublimation.

Wire gauze and Tripod stand

It is a dictum that, in heating substances in porcelain or ordinary glass utensils, the direct heat of a Bunsen burner should never be applied, but the flame should be uniformly distributed. The simplest form for the uniform distribution of heat is a sheet of asbestos or of tin, by which the cylindrical flame of the Bunsen burner is spread out to the entire surface of the interposing medium and uniform heat is transmitted from it to the container above. In the laboratory, for the purpose of heating, the substance is placed over the wire gauze. This wire gauze is placed over a three-legged stand, called a tripod stand. A Bunsen burner heats from below the substance. The Bunsen flame will be spread equally if the substance is kept over the wire gauze. Through such gauze, the heat more readily penetrates and at the same time the heat is uniformly distributed. This is due to the fact that the material of the wire is a good conductor of heat and the moment the flame comes in contact with the gauze, each of its filament aid in drawing the heat to every portion of the gauze. If the wire gauze is coated with asbestos, the temperature can be controlled and the surface of the vessel will not have a blackish discolouration.

Hot air oven

The air is ignited in a closed chamber known as hot air oven. It is a small chamber, made of aluminium or stainless steel. Two or more perforated and movable racks are provided within the chamber, having a hinged door. At the top of the chamber, there is a hole, where a thermometer can be inserted for recording the temperature of the air inside. The oven is heated electrically. The materials are heated by keeping them on the shelves of the oven. It is used for the evaporation of the moisture of vegetable drugs or other raw materials.

Thermometer

Thermometers are instruments used for directly measuring the intensity of heat. Most of these instruments are based on the expansive power of certain liquids and gases. It is characteristic of a large number of varieties of matter to expand with a rise in the temperature and in regular proportion to the increase in temperature.

The simplest and commonly used instrument for measuring temperature is the thermometer. They are made up of glass tubes having capillary bores and mercury is the most common liquid used in the thermometer. The expansion of mercury is very delicate and the density of this liquid being much more than water, it would require a much lesser quantity of mercury in the thermometer, thereby reducing the length of the tube.

The temperature is commonly recorded in the following scales

* Celsius - scale divided into 100 degrees (centigrade) with zero degree as the freezing point of water and hundred degrees as its boiling point.

* Fahrenheit - scale divided into 180 degrees with thirty-two degree as the freezing point of water and 212 degree as its boiling point.

Crucible

Crucibles are utensils of various sizes, shapes and materials, according to the objects for which intended. Porcelain crucibles are the most popular of all forms of crucibles. These are comparatively durable, easy to clean and moderate in price. They can be obtained in all sizes. It is used for drying the hard substances in small amounts at a high temperature. For drying at a very high temperature, crucible made of silica is used. Appliances necessary to the successful handling of crucibles are crucible tongs.

Evaporating dish

The simplest form of natural circulation evaporator is the evaporating dish or pan. It consists of a hemispherical, or shallower pan constructed from a suitable material such as porcelain, glass, silica ware, copper or stainless steel. The hemispherical shape gives the best surface / volume ratio for heating and the largest area for disengagement of vapor. The advantage of the evaporating dish is that it is simple, cheap to construct and easy to use, clean and maintain. The disadvantage is that, having only natural circulation, the overall coefficient of heat transfer is poor and solids are likely to deposit on the surface, leading to decomposition of the product.

For practical purposes, the porcelain dish is generally preferred, being more durable and comparatively inexpensive. It is used for evaporation of liquids at high temperature. An important point to remember is that a porcelain dish should never be heated in direct flame, the source of heat being modified by use of wire gauze. A warm evaporating dish should never be placed directly on the counter. If the counter is of wood, the heat may be sufficient to soften the varnish and if it is of marble or metal, the rapid chilling of the evaporating dish may cause a fracture of the dish.

Distillator

For simple distillation in the laboratory, a distillation flask with side arm sloping downwards is used. The temperature at which the vapours distill is observed on a thermometer, inserted through a cork and having its bulb just below the level of the side arm. The flask should be of such a size that it is one-half to two-thirds full of the liquid to be distilled. When large quantities of water are to be condensed, a spray or jet condenser is frequently used, which brings the vapour in direct contact with cooling water.

Condenser

A condenser is fundamentally a heat exchanger. Almost every type of condenser embodies a surface that is kept cold by a stream of water on one side, the vapour to be condensed impinging on the other side. The condenser must be so constructed as to be easily cleaned. The cooling surface must be large because the rate of condensation is proportional to the area of condensing surface. The condensing surface must be a reasonably good conductor of heat because the rate of condensation is proportional to the rate at which the surface conducts away the heat. The film of condensed liquid is a bad conductor of heat and must be removed quickly. The warmer water in contact with the condensing surface must be quickly carried away and replaced by fresh cold water that moves in the counter current direction.

Liebig Condenser

This consists of a long glass tube that is connected with the boiler, be it a retort or flask, thus affording passage to the vapour arising from the boiler. Surrounding this glass tube is a second tube, usually made of glass, through which passes a stream of cold water.

In large processes of distillation, a much longer condensing surface is required and hence giving rise to a modification in the apparatus. This consists of a tube of glass, twisted into a spiral and fitting into a vessel through which water can circulate freely.

Retort still

It is a flask-like round-bottomed apparatus. One of its sides is bent with a long and tapering neck, and bent at an acute angle. It may be used in the laboratory as distilling flask. Hahnemann mentions its use in the preparation of Causticum.

Desiccator

It is used for desiccation, i.e. removing moisture or dehydration of substances at moderate temperature. It is an airtight thick walled hard glass vessel provided with a glass lid fitting perfectly on the upper rim of the desiccator. The desiccator is constricted at the middle. A circular perforated sheet is placed above the constriction and separates the upper from the lower half. The air inside the desiccator is always kept dry by placing some drying agent like fused calcium chloride or concentrated sulphuric acid. The substances to be dried are kept in the upper half.

For quick drying, a vacuum desiccator is used; the vacuum is crested through an adjustable opening at the top of the desiccator, with a vacuum pump.

Tray dryer

This is essentially a hot air oven in which the material is placed in thin layers in trays. There are many variants of design according to the source of heat used and also as a result of added modifications such as vacuum, forced air circulation and thermostatic control. In small laboratory dryers, the material is placed on trays that slide into the drying cabinet; while in large installations, the interior may be designed for the wheeling in of trolleys containing the trays.

Pycnometer

Pycnometer or a specific gravity bottle is a flat-bottomed bulb-like glass bottle with a long tapering neck. A well-ground solid glass stopper with a narrow bore fits the neck. If the bulb is filled with a liquid and the stopper dropped in place, some liquid comes out through the bore and the bottle contains a fixed amount of liquid. The internal volume of the bottle is usually 20 ml, 25 ml or 50 ml. It is a standard bottle and the volume and the temperature at which the volume is exact, are marked on the bottle. A specific gravity bottle should always be held by the neck and never by the bulb. It is used in the determination of specific gravity.

Hydrometer

A common hydrometer consists of three parts - a long narrow graduated stem; a tubular bulb; and a round bulb. The round bulb contains lead shots or mercury, making the apparatus heavy at the bottom. This enables it to hold an upright position when immersed in the liquid. Due to tubular hollow part, it displaces sufficient liquid in which it is dipped and it floats vertically with its stem more or less immersed in the liquid. According to the theorem of Archimedes, a body when immersed in water loses as much weight as the weight of the water it displaces, or in other words, a body displaces its own weight of a liquid. Accordingly as the liquid is lighter or heavier than water, so does the hydrometer sink or rise when immersed in the same. The upper stem is graduated according to the utility of the apparatus. The stem is made thinner for better sensitivity of the hydrometer. Since its weight is constant, it dips more in a lighter liquid than in a heavier liquid, since, while floating, the weight of the displaced liquid must be equal to its weight in every case. It is used for rapid and easy measurement of relative density or specific gravity of liquids.

Alcoholometer

This is a modification of the hydrometer for estimating the strength of alcohol through the specific gravity. Usually, the markings of this form of hydrometer are not in terms of specific gravity, but in the actual percentage of alcohol. The alcoholometer is dipped in a sufficient quantity of alcohol and allowed to float. The graduations on the alcoholometer are such that when the alcoholometer is at rest, the lower meniscus coincides with the percentage content of alcohol in the given liquid.

CLEANSING OF UTENSILS

GENERAL RULES OR INSTRUCTIONS

In making homoeopathic preparations, utmost cleanliness must be observed

1. Utensils should be thoroughly washed even when used for first time and should be again washed immediately after use.

2. Hydrochloric acid, nitric acid, aqua regia or a concentrated solution of potassium bichromate in concentrated sulphuric acid may be beneficial to remove dirt and other stains from glass vessels.

3. Ordinary cleaning can be done with soda and hot water.

4. To remove greasy and oily materials, methylated spirit, ether, chloroform or benzene can be used.

5. Vessels made up of metals should never be washed with acids.

PARTICULAR RULES OR INSTRUCTIONS

1. Mortar and pestle

After the completion of trituration of the medicinal substance, the mortar, pestle and spatula are to be several times scalded with boiling water, being after every scalding wiped quite dry and clean. If the further precaution is used of exposing mortar, pestle and spatula to a heat approaching red heat, this will dissipate every thought that any least rest of the medicine last triturated can cling to them.

Footnote to aphorism 270

Mortar, pestle and spatula must be cleaned well before they are used for another medicine. Washed first with warm water and dried, both mortar and pestle, as well as spatula are then put in a kettle of boiling water for half an hour. Precaution might be used to such an extent as to put the utensils on a coal fire exposed to a glowing heat.

Glass mortar and pestles - Firstly the glass mortar and pestle is washed with cold water, followed by its immersion in a solution of potassium dichromate for an hour. Rinse it in cold water with the help of hard brush, followed by hot boiling water. Dry it completely and process through alcohol, allowing it to evaporate by itself.

After mercurial preparations, the mortar and pestle should be washed with nitric acid to neutralize the residue.

2. Spatula

The horn spatula is first wiped with soft cloth. Then it is washed by running tap water. Then it is washed with alcohol and wiped with a clean cloth. Horn spatula should never be washed with hot water or touched with sodium carbonate.

3. Bottles

The bottles are kept in cold water for 6 - 7 hours, using hard brush. Then they are washed with moderate warm water and rubbed with soft brush. Then they are washed with purified water. Some amount of alcohol is poured to wash them properly. Then the bottles are exposed to sun for drying.

4. Corks

The corks are first rubbed under tap water and then with purified water in a sieve. Then they are kept for drying and then rinsed with dilute alcohol.

Afterwards they are dried thoroughly, exposing to sunrays.

5. Tincture press

The press is separated into its component parts. Then the parts are washed carefully with cold and hot water and then with purified water. They are then dried well, after each extraction.

6. Phials and glasses

They are washed several times with hot water, using brush. They are then rinsed with alcohol. They are then dried at moderate temperature.

7. Knife

It should always be wiped after washing and should be kept dry to avoid rusting.

8. Wooden instruments

Wooden instruments are washed under running tap water with hard brush. Then it is washed with warm water with soft brush. It is lastly washed with purified water and kept under sunlight for drying.

9. Pipette

The pipette must be clean and free from grease before use. For this purpose, the pipette is first washed with sodium carbonate solution and then with hydrochloric acid. It is then washed thoroughly with purified water and finally with alcohol or acetone, which not only removes the grease, but also helps in drying it quickly. The clean pipette is then rinsed once or twice with a little of the liquid that is intended to be measured. A little of the solution is sucked by the mouth into the pipette and the open end is closed by the forefinger. The pipette is now rotated in a horizontal position so that the entire internal surface is thoroughly washed. The liquid is then run out and discarded.

10. Burette

The burette must be cleaned and made grease-free before use. This is done in the same way as described for the cleansing of pipette. The clean burette is also rinsed with the liquid with which the burette is to be filled, in the same way as the rinsing of a pipette.

SELF ASSESSMENT

* Describe in detail, the instruments used for preparation of homoeopathic medicines

* Describe in detail, the instruments used for weighing and measurement

* Describe in detail, the instruments used for purpose of heating in the laboratory

* Describe in detail, the instruments used in standard laboratory procedures

* Mortar and Pestle

* Leather pad

* Percolator

* Presses

* Sieves

* Metrological instruments

* Analytical balance

* Measuring tile

* Spatula

* Liebig condenser

* Pycnometer

* Alcoholometer

* Cleansing of utensils

QUIZ

1. For triturating hard substances as Nux Vomica seeds,

(a) Agate mortar and pestle is used

(b) Porcelain mortar and pestle is used

(c) Iron mortar and pestle is used

(d) Glass mortar and pestle is used

2. Which apparatus should be always wiped after washing and kept dry to avoid rusting

(a) Porcelain mortar and pestle

(b) Chopping knife

(c) Glass beaker

(d) Leather pad

3. Which equipment is used to remove moisture completely from substances

(a) Desiccator

(b) Percolator

(c) Beaker

(d) Hydrometer

4. Measuring tile is used for

(a) Measurement of temperature

(b) Measurement of weight

(c) Measurement of volume

(d) Preparation of ointments

5. Which one of the following is used to remove dirt and other stains from glass vessels

(a) Silver nitrate

(b) Nitric acid

(c) Iodine

(d) Ammonium oxalate

ANSWERS: 1 (c); 2 (b); 3 (a); 4 (d); 5 (b).

0 Comments:

Post a Comment

PLEASE WRITE YOUR SYMPTOMS HERE TO GET SUGGESTION.