rarely attain a higher temperature than a little above 90°. To control the temperature when substances must be heated above 100°, glycerin baths, oil baths and solution baths are employed. <Callout type="tip" title="Tip">Glycerin baths can help maintain precise temperatures for sensitive compounds.</Callout> Exsiccation is a term used to express the heating of chemical compounds for the purpose of expelling water of crystallization. Sulphate of iron, alum, sodium carbonate, sodium phosphate, magnesium sulphate and various other salts containing large quantities of water of crystallization may be dried so as to expel all water or a portion of it. <Callout type="warning" title="Warning">Be cautious when heating compounds that contain water of crystallization; improper drying can lead to chemical instability.</Callout> Calcination is the process of converting metallic carbonates and other metallic salts into metallic oxides by heat. Strong heat is usually required for this purpose, and the by-products formed are volatile. When a carbonate is calcined, the by-products are CO2 and water, or C02 alone, according to the composition of the carbonate decomposed. Nitrates and sulphates can also be calcined. The word calcination is derived from the Latin calx, which means lime, because lime is produced by strongly heating limestone or calcium carbonate in kilns. <Callout type="important" title="Important">Calcination requires strong heat to convert carbonates into oxides; ensure proper ventilation and safety equipment.</Callout> Dry distillation, or 'destructive distillation,' is a term employed to express the decomposition of organic substances by strong heat, resulting in the formation of new products, some of which are volatile and others fixed. For example, when oak billets are heated strongly in closed iron cylinders provided with an outlet for the volatile products, the oak wood undergoes decomposition, and, among the volatile products which distill over, acetic acid is one of the most valuable, and the residue in the cylinder is a tarry mass of mixed composition. <Callout type="risk" title="Risk">Inadequate ventilation during dry distillation can lead to toxic fumes; ensure proper safety measures are in place.</Callout> Sublimation is the distillation of solids; in other words, volatile solids are vaporized, and the vapor conducted into condensing vessels in which they reassume a solid form. The product is called a sublimate, and is generally of crystalline character. Sublimation is employed as a method of separation of volatile substances from fixed substances for purposes of purification. <Callout type="beginner" title="Beginner">Sublimation can be used to purify volatile compounds by separating them from non-volatile impurities.</Callout> The coarse mechanical division of drugs is an important pharmaceutical operation. For the preparation of mixed teas, drugs are required to be very coarsely comminuted. If they are flexible, they may be cut with sharp-edged tools so as to produce pieces free from dust or powder, but if they are hard so that they cannot be cut, they are comminuted by crushing, in which case more or less powder is unavoidably produced. The crushing of plant drugs is best accomplished in an iron mortar with an iron pestle, but smaller pieces of drugs can be crushed also in hand-mills of iron. <Callout type="gear" title="Gear">An iron mortar and pestle are essential tools for comminuting drugs.</Callout> An iron mortar used for crushing and powdering drugs must be very large in proportion to the amount of drug operated upon in order to do effective work. It should be solid, heavy, and placed upon a solid block, which, if possible, should rest upon the ground instead of upon the floor. The crushing of drugs in a mortar by means of blows with the pestle is technically called contusion. <Callout type="tip" title="Tip">A larger mortar allows for more effective drug comminution.</Callout> The iron mill used by druggists for making coarse powders of drugs is similar to the mill used by grocers for grinding coffee, but there is an essential difference in the construction and position of the grinding plates, so that the hand drug-mills are not identical with coffee mills and spice mills. There are several makes of hand drug-mills, and the best forms are those which have the grinding plates in a nearly horizontal instead of vertical position. These hand-mills are provided with set-screws which enable the operator to move the grinding plates nearer to each other or farther apart at will, to make coarser or finer powder, as may be desired. It is usually necessary to pass a drug through the hand-mill more than once, if a com- paratively fine powder is required ; in other words, the drug is first crushed, then passed through the mill to make a coarse powder, then the mill is set finer and the coarse powder passed through the mill again, this operation being repeated until the required fineness is attained. But very fine powder cannot be made with the hand drug-mill. A coarse powder can, however, be easily enough made very fine by contusion in the iron mortar. <Callout type="risk" title="Risk">Using a hand drug-mill for extremely fine powders may result in uneven particle sizes.</Callout> Trituration is the grinding produced in the mortar by a rotary motion of the pestle accompanied by pressure. When trituration is performed, the pestle is grasped firmly by the whole hand in order to apply sufficient force to crush the parti- cles of substance triturated. Comparatively brittle substances can be powdered by tritu- ration, but in order to do effective work the trituration mortar should be large in proportion to the quantity of substance triturated, for if too deep a layer of powder is operated upon at one time, the operation is necessarily slower. Trituration is also employed for mixing powders, but if the ingredients of the mixture are already sufficiently fine, no pressure is required 'n mixing them. The spatula is usually necessary, in ac- complishing trituration, to scrape the substances from the end of the pes- tie and the bottom and sides of the mortar, in order to do rapid and effective work. Trituration mortars are generally made of porcelain or of Wedgewood ware. <Callout type="important" title="Important">Trituration requires a large mortar for efficient grinding.</Callout> Levigation is the trituration of substances in a fine state of division, either upon a slab with the muller or in a mortar with the pestle, with the addition of some liquid to PHARMACEUTICAL OPERATIONS 271 the solid substance to aid in its further division. Water, alcohol and oil are all used for such purposes. Sometimes the levigation has for its object not only the production of a very fine powder, but also the removal of impurities with the aid of the liquid added. For example, calomel is levigated by trituration with water in order to wash out from it the corrosive sublimate which may be con- tained in sublimed calomel and which is soluble in water. When purification of calomel is effected by levigation, several successive portions of water must, of course, be used until all of the corrosive sublimate has been finally removed. 463 While the pharmacopoeias always prescribe a method of expressing the fineness of powders, they do not all of them prescribe a given degree of fineness for each individual drug. In the American pharmacopoeia, for instance, there is no information given as to how fine powdered digitalis should be when ordered by the physician, although the powder to be used of digitalis for the preparation of the tincture, the fluid extract or the extract is specifically prescribed. Very full directions are given in some pharma- copoeias, stating how fine the powder should be of any important drug prescribed by a physician to be used in powder form or in pill-masses, and to fail to give such directions would seem to be a serious omission. 464 By 'dusted powders' is meant powders so fine that when made in a mill constructed expressly for the purpose, they rise in the mill-box like dust, which settles upon shelves along the walls of the mill-box or on the floor of that box away from the circle in which the millstones run like wheels. 465 Colored substances become lighter when reduced to fine powder, and the color grows lighter as the powder gets finer. 466 The solution of soluble substances may be effected in many different ways, but most quickly by reducing the substance to a more or less fine powder, except in cases where the fine powder would be- come agglutinated by the action of the solvent. A solution mortar is a deep mortar provided with a lip. A salt or other substance to be dissolved in water may be put in the solution mortar and there crushed, after which one portion after another of solvent is added and poured off as solution results, until all of the solvent to be used has been employed and the solid substance liquefied. 467 Circulatory displacement consists in placing a soluble substance on a strainer at the top of a vessel containing the solvent, just below the surface of the liquid; the solution formed, being denser than the solvent itself, then runs down to the bottom of the vessel so that fresh portions of solvent come in contact with the solid matter, and the solution is thus more rapidly effected. This method is a very useful one, and if a strainer of the right kind is employed the solution obtained by circulatory displacement may be rendered so clear as not to require further clarification. 468 Extraction methods by which soluble substances contained in plant drugs are extracted and separated from the insoluble substances are of great importance. The solvents employed are called 'menstrua,' and the most common menstrua are alcohol and water and mixtures of these. The extraction methods are maceration, digestion, infusion, decoction and percolation. 469 Maceration consists in placing the comminuted drugs in the menstruum and permitting them to remain in contact with each other a sufficient length of time at the ordinary room temperature, after which the solution obtained is separated from the undissolved residue, which is called the 'marc.' But maceration may be varied so as to be rendered more effective, by using several successive portions of menstruum upon the undivided amount of drug to be exhausted of its soluble matter. If, for instance, a pound of drug be mixed with enough diluted alcohol to produce a thick mixture, and this mixture be allowed to stand a day or two, after which the solution formed is expressed by means of a hydraulic press or other effective pharmaceutical press, the press-cake can then be disintegrated again and mixed with another portion of fresh menstruum to produce a thick mixture as before, allowing this new portion of menstruum to extract as much of the remaining soluble matter as it may, after which this second solution is separated by expression as before. These successive macerations with new portions of PHARMACEUTICAL OPERATIONS 275 menstruum may be repeated until absolutely no more soluble matter remains in the drug. If at the same time the several macerates or solutions obtained by maceration be kept separate from one another, these several macerates may be employed over again as menstrua upon a fresh portion of drug, the drug being macerated first with the first macerate from the preceding portion of drug and then with a second and third and fourth macerate, and finally with a fresh portion of previously unused menstruum, until this second portion of drug has also been completely exhausted, the object being to use each portion of menstruum over and over again as long as it still retains any solvent power, in order to effect the extraction of all the soluble matter with the smallest possible amount of menstruum, so as to obtain as concentrated a solution as may be made. [This is also the object of percolation and re-percolation, as will be seen later on.] A very common form of maceration when employed in the preparation of tinctures is to use two-thirds of the whole amount of menstruum upon the whole amount of drug in the first period of maceration, and then, after separating the solution formed, to use the remaining third of the menstruum to finish the exhaustion of the drug. 470 Digestion differs from maceration in one particular only, namely, the temperature. While maceration is per- formed at any ordinary room temperature, or, in other words, without the application of artificial heat, digestion is performed at any temperature above that of the work- room, or, in other words, with the application of more or less heat. The temperature of digestion may be any degree of heat from 25° 0. up to nearly 90° 0. The effectiveness of digestion as compared with maceration is great, and the employment of even a comparatively moderate degree of heat generally increases the solvent power of the menstruum so greatly that digestion ought to be employed more largely than it is, for it accomplishes in great part the same object as is gained by percolation and re-percolation, namely, the exhaustion of the drug with a minimum amount of menstruum. 471 Infusion is a process consisting of putting boiling water upon a plant drug and letting the hot water exert its solvent action upon the drug without taking any measures to maintain the temperature, but allowing that to gradually fall even to the temperature of the atmosphere of the room, after which the solution formed is separated from the marc by straining and expression. But the process of infusion is at the present time most frequently performed by means of a water bath or 'digestorium,' and when this is the case, the temperature is maintained at such a high degree that che result is very different from that obtained by the old method of infusion. The products or preparations made by the process of infusion are generally called infusions. 472 Decoction is a process of extraction consisting of boiling a drug in the menstruum for a given length of time. This process is rarely applicable except when water is the menstruum and the drug contains no substance of value liable to be injuriously affected by the high temperature. The products made by decoction are called 'decoctions,' and decoctions are rarely made of potent drugs. 473 Percolation is an effective method of extraction which is extremely useful when concentrated liquid extracts are to be made or when it is desired to exhaust the drug with a minimum amount of menstruum. These objects are gained in the process of percolation by using the same quantity of solvent over and over again on successive portions of drug, until the solvent is so charged with soluble matter or so nearly saturated that it is no longer capable of doing PHARMACEUTICAL OPERATIONS 277 effective work. This can be accomplished in various ways. The simplest form of percolation consists in moistening the drug in the form of powder with a sufficient amount of menstruum to dampen it, after which the dampened powder is allowed to lie long enough thoroughly to absorb the menstruum, so that each particle of powder may be soft- ened and permeated by the solvent as far as it can be. The dampened drag is then packed more or less firmly in a tall cylindrical tube called a perco- lator, the form of which is indicated by the illustration on this page. If the drug is uniformly and not too firmly packed in the percolator by means of the plunger or packer, the descent of the menstruum, afterwards poured upon the drug, will be very regular. A sufficient quantity of men- struum is poured upon the drug in the percolator completely to saturate the packed drug from top to bottom, leaving a layer of menstruum above the surface of the drug, after the packed mass has been filled and satu- rated. The apparatus is closed so that no liquid can pass out from it. In the percolator described in the pharma- copoeia and figured in the text, a rubber tube is attached to the lower end of the percolator, and when this tube is raised and tied to the side of the percolator so that the end of the tube is above the level of the liquid, the atmospheric pressure will prevent any portion of liquid from passing out. The apparatus is left in this condition a greater OLDBERG'S PERCOLATOR 278 A CORRESPONDENCE COURSE IN PHARMACY
Key Takeaways
- Understanding the process of calcination is crucial for converting carbonates into oxides.
- Sublimation can be used to purify volatile compounds by separating them from non-volatile impurities.
- Percolation is an effective method for making concentrated liquid extracts with minimal solvent usage.
Practical Tips
- Use a solution mortar when dissolving substances in water, as it helps maintain the integrity of the substance during dissolution.
- Employ circulatory displacement to achieve clearer solutions by allowing fresh solvent to continuously interact with the solid matter.
- Utilize maceration and digestion techniques for extracting soluble compounds from plant drugs, ensuring thorough extraction.
Warnings & Risks
- Be cautious when handling substances that contain water of crystallization; improper drying can lead to chemical instability.
- Ensure proper ventilation during dry distillation to avoid toxic fumes.
- Use appropriate equipment and follow safety guidelines for percolation to prevent contamination or loss of solvent.
Modern Application
While the techniques described in this chapter are rooted in historical practices, they still hold relevance in modern survival preparedness. Understanding these methods can be crucial for creating effective medicines from natural resources, purifying substances, and ensuring the stability of chemical compounds. The principles of controlled heating, precise dissolution, and efficient extraction remain fundamental to both traditional pharmacy and contemporary survival medicine.
Frequently Asked Questions
Q: What is the difference between maceration and digestion in pharmaceutical operations?
Maceration involves placing comminuted drugs in a menstruum at room temperature for an extended period. Digestion, on the other hand, uses heat to increase the solvent's effectiveness, allowing for more efficient extraction of soluble compounds from plant drugs.
Q: How can one ensure the purity of calomel when preparing it?
Calomel is purified by trituration with water. This process washes out any corrosive sublimate that may be present, as it is soluble in water. Multiple successive portions of water are used until all corrosive sublimate has been removed.
Q: What equipment is necessary for effective drug comminution?
An iron mortar and pestle or a hand drug-mill are essential tools for comminuting drugs. These tools allow for precise control over the fineness of the powder produced, which is crucial for pharmaceutical operations.