Complete Text (Part 28)

accomplished by ordinary maceration ? 34. Can all drugs be subjected to percolation ? If not, what drugs cannot be so treated ? 35. Name the several means commonly employed for rendering liquid preparations clear. 36. Make one plain filter and one plaited filter and return both with your recitation paper. 37. By what means can the passage of fine particles of powder through paper filters be prevented in certain cases ? 38. For what purposes is evaporation employed in pharmaceutical processes ? How is it rendered most effective ? 39. What are the practical uses made of distillation in pharmacy ? 40. What kind of a still is best for distilling volatile liquids ? PHARMACEUTICAL OPERATIONS 289 41. What is the difference between the Liebig condenser and the Mitscherlich condenser ? 42. Describe the worm-condenser. 43. Can a still be so made that a separate condenser is not necessary ? If so, how ? 44. By what several means can solids be made to assume a crystalline form ? 45. What is meant by granulation ? 46. What is the technical term used to designate the liquid from which crystals are deposited ? 47. Define precipitation. 48. What are the practical uses of crystallization ? 49. What are the practical uses of precipitation ? 50. What is meant by the term supernatant liquid ? 51. How long should a precipitate be washed before it is dried? 52. How is the washing of a precipitate effected ? 53. What is the difference between physical precipitation and chemical precipitation ? 54. By what means can precipitations be rendered heavy instead of light, or fine instead of coarse ? 55. Draw a figure showing the construction of a Liebig condenser. 56. Make an outline drawing showing the construction of a Mitscherlich condenser. 57. What would you call the kind of chemical reaction by which precipitation is produced ? 58. What are the usual means adopted to produce large crystals of water-soluble salts ? 59. By what means can very small crystals of water-soluble salts be secured ? 60. How would you produce crystals of insoluble volatile substances ? 61. Give three examples of physical precipitation. 290 A CORRESPONDENCE COURSE IN PHARMACY 62. Give ten examples of chemical precipitation. 63. What is contained in the liquid in which a precip- itate is produced by chemical reaction, and how can the sub- stance contained in that liquid be recovered from it, if desired ? LESSON NINETEEN XXVIII The Chemical Constituents of Plant Drugs 483. The substances contained in plant drugs may be classified into groups, as follows: 1, water; 2, cellulose in its various forms, the principal of which is woody fiber; 3, starch in its many forms; 4, pectinous substances; 5, vegetable mucilage; 6, sugars; 7, albuminoids; 8, fixed oils and fats; 9, organic acids ; 10, tannin; 11, bitters, called in Latin amara; 12, volatile oils; 13, resins; 14, glucosides; 15, alkaloids. 484. Water is contained in all plants. Some fresh plants contain over 90 per cent., others much smaller amounts. Plant drugs must be dried in order to preserve them. The condition in which they are ordinarily employed is that called "air-dry." An air-dried drug contains no more moisture than it necessarily must contain as usually kept, exposed as it is to the ordinary atmosphere. If dried beyond that point, it absorbs moisture again ; if it contains more than that amount of moisture, it is liable to be damaged by mold or fermentation. Fresh drugs are also used for making pharmaceutical preparations, but whenever this is done, the amount of moisture contained in the undried drug must be considered in connection with the method of preparation adopted. 485. Cellulose, starch, pectin, mucilage and sugar are all so-called carbohydrates. By the term carbohydrate is 291 '-202 A CORRESPONDENCE COURSE IN PHARMACY meant an organic substance having the formula or com- position C6H10O5, or a multiple of that formula. Some carbohydrates differ from this formula, but only by two hydrogen atoms and one oxygen atom, added or deducted. The carbohydrates have no medicinal action of great importance, but some drugs containing starch, and others containing mucilage, are employed for the purpose of pre- paring demulcent or mucilaginous liquids, to serve as vehicles for more potent remedies, or to protect local mucous surfaces. 486. Cellulose, which exists in plant drugs chiefly as woody fiber, is entirely insoluble in all ordinary solvents, such as water, alcohol, glycerin, etc. Therefore, cellulose con- stitutes a large proportion of the undissolved residue obtained when extracts are made of plant organs. 487. The various classes of constituents of plant drugs are contained in the cells and the intercellular spaces in the tissues. These cavities are bounded by the cell walls, made of the insoluble cellulose. Hence, the cellulose offers more or less obstruction to the extraction of soluble substances contained in the drugs. This fact renders it necessary to grind or powder the plant drugs sufficiently to break down the obstruction. 488. Water has the power to pass through vegetable membranes, even when the pores in those membranes are extremely minute. This power of liquids to pass through vegetable membranes is called osmosis. Its passage out- ward is called exosmosis. The current inward is called en- dosmosis. We make use of this property of water in our pharmaceutical operations, as will be explained in the next paragraph. 489. Certain substances soluble in water may pass through vegetable membranes in a state of solution, and this phenomenon is called dialysis. Other substances soluble in water cannot pass through vegetable membranes, or do THE CHEMICAL CONSTITUENTS OF PLANT DEUGS 293 it so slowly as to be practically undialyzable. We are there- fore able to separate dialyzable substances from the undia- lyzable substances, even in drugs so coarsely powdered that only a small proportion of the cells and intercellular cavities are broken into. Therefore, whenever the valuable con- stituents of a drug are best dissolved in water, it is not necessary to powder the drug finely. Even a piece of whole drug will give up a good deal of its dialyzable constituents when put in water. For instance, a piece of gentian placed in water will very quickly make all of that water bitter. 490. Alcohol passes through plant membranes so extremely slowly that we cannot take any advantage of its slight power to do so. We consider it practically unable to penetrate plant membranes. Whenever, therefore, the valuable constituents of a plant drug are such as require alcohol for their solution and extraction, it is necessary that the drug shall be powdered finely so that the alcohol may come in actual contact with the substances to be dis- solved, for the alcohol will only wash off what is on the surface of the particles of powder, and will extract nothing from the interior of cellular structures. 491. Starch in its normal condition is entirely insoluble in alcohol and in water, but the starch 'in plant drugs is often altered starch. It has been changed under the influence of heat, moisture and the action of various substances contained with the starch in the drug, in such a way that it is not insoluble. Altered or partially altered starch is sometimes soluble in water to such an extent that when extracted from the drug by a very diluted alcohol, it may form a consider- able deposit on the bottom of the bottle upon standing for some time; for the altered starch, although soluble in water and very diluted alcohol, reverts to its normal insoluble condition when long in contact with alcohol. Hence, when sarsaparilla or licorice root is extracted by percolation with 291 A CORRESPONDENCE COURSE IN" PHARMACY a very diluted alcohol, the liquid extract, although perfectly clear or free from solid particles, will, in the course of a few weeks, deposit a large layer of white or nearly white starch. Starch is altered by water having a temperature above 60° C. , so that the starch granules burst and a mucilage results. From this starch -mucilage the starch cannot be recovered in its normal condition. Yet the starch held in the mucilage is not, strictly speaking, dissolved; it is simply held in suspension, distributed through the liquid uniformly. To make starch-mucilage, it is customary to employ one part of starch to one hundred parts of water ; but to make a starch- paste, one part of starch is necessary with ten parts of water. 492. To illustrate how the constituents of drugs guide us in making pharmaceutical preparations, I may mention that some drugs containing a large amount of starch in addition to their more important constituents may be treated in different ways, according to whether or not we desire the product to contain the starch. The pharmacopoeias contain an infusion of calumba and also a decoction of calumba. The infusion is made with hot water, but the temperature is not maintained and hence the starch is not extracted and rendered mucilaginous. But the decoction is made by boiling the drug in water, and that preparation accordingly is thick and demulcent, because it contains the starch. Barley, rice, oats and wheat consist largely of starch, and decoctions are made of them. Whenever a decoction of starch or a starchy drug is made, it is intended that so much drug shall be used that the preparation will be sufficiently thick. Other preparations are scarcely ever made from starchy substances. 493. Pectin and pectinous substances are water-soluble. They resemble mucilage in many respects, but have the characteristic property of forming jellies. Apples, currants and other fruits form jellies because they contain pectin. THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 295 Some other fruits, like cherries, do not form jelly because they contain an insufficient amount of pectin. The forma- tion of the jelly requires the presence of a sufficient amount of pectin, and the formation of the jelly is aided by the addi- tion of much sugar. Some drugs contain pectin. As an example, we may mention kino, which contains so much pectin that a tincture of kino made with diluted alcohol sometimes changes to a solid jelly in the bottle. Pectin is insoluble in alcohol, and is therefore not contained in pharmaceutical preparations made with strong alcohol. 494. Mucilage is contained in nearly all plants. It may be normal or physiological mucilage, formed in the natural growth and life of a plant, or it may be pathological mucilage, formed by the breaking down of plant tissues, caused by injury. We see physiological mucilage in many leaves and in the inner bark of plants. We also find it covering the seed-coat of flaxseed, quince-seed and some other seeds. Pathological mucilage occurs in masses on the trunks and branches of certain trees and shrubs, when the bark has been perforated by insects. Apple tree gum, peach tree gum, cherry tree gum and gums upon other trees of the same natural order are familiar. These solid gums are formed by the evaporation of the plant-juice exuding through the wound made in the bark of the tree by an insect. 495. There are two classes of gums — the arabin gums and the bassorin gums. The arabin gums are completely soluble in water; the bassorin gums simply absorb water and swell in it to form translucent jellies, but do not dissolve. Gum arabic is a typical example of the arabin gums. Tragacanth is a typical example of the bassorin gums. A piece of gum arabic put in water dissolves completely, forming a mucilage, but a piece of tragacanth put in a large amount of water 296 A CORRESPONDENCE COURSE IN PHARMACY simply swells and softens until it has taken up all the water it is capable of absorbing, and then forms a gelatinous mass, the outlines of which can be readily seen in the water, and this gelatinous mass remains distinct from the water about it. If the mixture is stirred actively, the jelly is, of course, disintegrated, but it does not dissolve, and if the mixture is thoroughly shaken in a bottle and then allowed to stand at rest, the gelatinous tragacanth separates again. 496. The word "gum" is so much misused that it perhaps ought to be discarded from technical nomenclature. Tech- nically, gum is dry mucilage. It is either perfectly soluble in water or forms a mucilage with water, even if it is not really soluble. Hence, no substance insoluble in water, or nearly so, can be a gum. Nevertheless, many resins which are entirely insoluble in water are called gums, as, for instance, shellac, benzoin, copal, mastic, etc. Gums are entirely insoluble in alcohol. For this reason, when alcohol is added to a water-solution of any gum, the gum separates from the solution, or is precipitated. Aloes, kino and catechu are extract-like drugs soluble in diluted alcohol. They are therefore not gums, although frequently called so. There are, in fact, only two kinds of gums in the pharma- copoeia, namely, acacia and tragacanth. When a gum or dry mucilage is heated, it becomes drier and harder instead of fusing, and when the temperature is sufficiently high, the gum is charred but does not ignite so as to burn with a flame. Compare this behavior of the gums with the properties of resins. Dried mucilage or gum undergoes no change when kept with ordinary care, but moist gum or a solution or mucilage undergoes fermentation when exposed to the air, and muci- lage ferments so readily that it can be kept unaltered only a few days. Acacia and tragacanth are employed pharmaceutically in THE CHEMICAL CONSTITUEKTS OF PLANT DRUGS 297 making pill-masses and other masses cohesive, and also in making emulsions. The pharmacopoeias contain mucilages made of sassafras pith, slippery elm bark, flaxseed, quince-seed and other plant drugs containing mucilage of the arabin type. When bassorin gum is heated twenty-four hours in water, it is rendered soluble. The mucilage of acacia of the pharmacopoeia is made by dissolving one part of whole acacia in two parts of water. 497. Sugars of various kinds are contained in many plants and plant drags. All sugars are water-soluble. They are also soluble, though less freely, in alcohol. A weak sugar-solution made with water undergoes fer- mentation when exposed to the air, forming alcohol. Hence, a small amount of sugar present in an aqueous liquid preparation invites fermentation, but when so much sugar is added to a watery solution that the solution acquires great density, it acts as a preservative, because it excludes air. Air is soluble in water, but is not sol able in a dense water-solution of other substances. Sugar is used to a great extent to sweeten certain pharma- ceutical preparations. Medicated syrups are both sweetened and preserved by sugar. Fresh plant substances and animal substances placed in a large amount of sugar are in a measure preserved, especially plant tissues, because the sugar takes up the water, and water is essential to the changes that cause organic matter to decompose. Sugar is also used in pharmacy and in medicine as a diluent. One class of dilutions ordered by the pharmacopoeia is called triturations. These preparations are composed of one part of some active medicinal agent mixed with nine parts of milk sugar. 498. The principal sugars of interest to pharmacists are 298 A CORRESPONDENCE COURSE IN PHARMACY cane sugar and milk sugar. Cane sugar, or ordinary white sugar, is extensively used. Milk sugar, which is much less readily soluble, is employed as a diluent mainly for insoluble substances. Starch-sugar, or glucose, is employed in the form of a solution, called glucose syrup. Other saccharine substances used in pharmacy and medicine are honey and manna. 499. When sugar ferments, it forms alcohol, as has already been mentioned, but the process of fermentation ceases as soon as 14 per cent of alcohol is contained in the liquid. Accordingly, when wine is made from grape juice, the prod- uct cannot naturally contain more than 14 per cent of alcohol. Any wine containing a larger percentage of alcohol has been fortified by the addition of alcohol after the process of fermentation. Alcohol acts as a preservative. For this reason, many liquid pharmaceutical preparations are made with alcohol. The principal preparations of this kind are the tinctures and the fluid extracts, but other liquid pharmaceutical prepara- tions are also preserved by the addition of smaller quantities of alcohol. From what has already been said, it is evident that any liquid containing fermentable matter must have at least 14 per cent of alcohol in it in order to be proof against fermentation. Usually 15 per cent or more is added for this purpose. 500. Albuminoids, or vegetable albumins, are contained in many plants and drugs. Vegetable albumin is much like animal albumin, and the most familiar and striking type of animal albumin is the white of egg. It is a colorless, water- soluble substance, insoluble in alcohol, and coagulated by heat. When an egg is boiled or heated to a temperature above 60° C, the white of the egg becomes a solid, white, insoluble substance, which cannot again be changed back to its original THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 299 soluble condition, and we say that it is coagulated. Alcohol has a similar effect upon the white of egg. Albumin, when exposed to the air in the presence of moisture, putrefies; that is, it undergoes decomposition, resulting in the formation of ill-smelling sulphur compounds, because all albumin contains sulphur, together with carbon, hydrogen, oxygen and nitrogen. The fact that albumin so easily undergoes decomposition renders it desirable that most pharmaceutical preparations shall not contain it. Moreover, if the albumin is present in any considerable quantity, it dilutes the preparation unnecessarily. There- fore, in making aqueous extracts of plant drugs, the watery liquid containing the soluble matters is brought to the boil- ing point, or at least to a temperature above 60° C, in order to coagulate the albumin, when