CHAPTER XII.

CLASSIFICATION OF NATURAL PRODUCTS USED IN
PHARMACY.

PLANTS, either spontaneously or after due subjection to various processes, yield certain vegetable substances which are extensively employed in pharmacy, and which, owing to their different behavior as to composition, solubility, etc., have been divided into distinct classes, thus: gums, resins, oleoresins, gum-resins, balsams, fats, essential oils, etc. Unfortunately the names which from long usage have been applied to some drugs are not in all cases indicative of their true nature; hence a knowledge of the characteristics of each class of plant products is essential to guard against errors in nomenclature, which are of daily occurrence in commercial transactions; for instance, the names balsam of fir and balsam copaiba are applied to substances belonging to the class of oleoresins, and not containing any of the principles which characterize the balsams; gum guaiac and gum mastiche are pure resins; gum benzoin belongs to the class of balsams, and gum opium is an inspissated juice of complex composition.

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True gums are amorphous exudations wholly soluble in cold water, which are not affected by iodine, but are precipitated by alcohol and solution of lead subacetate, the latter being a most delicate reagent for the presence of gums. Neutral or normal lead acetate is readily miscible with solutions of the true gums, of which acacia may taken as a type. A class of substances formerly called gums are now more appropriately known as mucilages, because they differ in several respects from the true gums; they are not completely soluble in water (cold or hot), but absorb the same, and in some instances swell to a gelatinoid mass. Mucilages are frequently mixed with starch, which is easily detected by the blue color produced upon addition of iodine solution. Tragacanth and the gummy constituents of flaxseed, elm bark, quince seed, etc., belong to the class of mucilages.

Resins are secretory products, in some instances the result of oxidation of volatile oils, and are widely diffused in the vegetable kingdom; they are wholly insoluble in water, except in the presence of caustic alkalies, but are readily soluble in alcohol, ether, and chloroform, and frequently in fixed and volatile oils. Resins are mostly solid and brittle at ordinary temperatures, generally amorphous, readily fusible and inflammable, become negatively electric by friction, decompose before volatilizing, and are precipitated from their solutions by water and acids. Pine resin, mastiche, jalap resin,

and guaiac resin, are examples of this valuable class of plant products.

Oleoresins occupy a position intermediate between resins proper and volatile oils, and partake of the properties of both classes; their existence confirms the view held as to the formation of some resins in plants, and their consistence varies with the relative proportions of resin and volatile oil. Like the resins proper, oleoresins are insoluble in water, but soluble in alcohol and ether; they possess a marked odor, due to the volatile oil present, which latter can be separated by distillation, leaving the resin as a solid residue. White turpentine is an example of solid oleoresins, and copaiba of liquid oleoresins.

Gum-resins exist in plants in the form of an adhesive milky juice composed of variable mixtures of resin and gum suspended in water; they are obtained as exudations, by wounding the stem or root of the plant and allowing the juice to dry spontaneously. The proportion of gum and resin varies considerably, not only for different gumresins, but also for different samples of the same gum-resin, and those lots are most valuable which contain the largest amount of resin. The activity of the drug resides wholly in the resin, and this fact is taken into consideration in the official formulas for the tinctures of asafetida and myrrh. A peculiarity of all gum-resins is that when properly triturated with water they yield milk-like mixtures termed emulsions, which fact is due to the suspension of very finely divided resin in the solution of gum; these milk-like mixtures cannot be obtained if the commercial finely powdered gum-resins be triturated with water, but require the use of the natural product in coarse powder. As prominent gum-resins may be mentioned asafetida, myrrh, scammony, and ammoniac.

Balsams are either resinous or oleoresinous secretions containing benzoic or cinnamic acid, or both; it is the presence of these acids which distinguishes the balsams from ordinary resins and oleoresins. Balsams are soluble in alcohol, ether, or chloroform, but insoluble in water, although the balsamic principles can be extracted by sublimation or by treatment with hot water. Benzoin and balsam of tolu are examples of resinous balsams, whilst storax and balsam of Peru belong to the oleoresinous variety.

Fats and Fixed Oils.

The fats used in pharmacy are derived from the vegetable as well as the animal kingdom, and are divided into fats proper and fatty oils, the latter being known in pharmacy more particularly as fixed oils; when strictly pure they are, as a rule, colorless, odorless, and tasteless. True fats are strictly chemical compounds of glycerin and fatty acids, and are known as olein, palmitin, and stearin, the former being liquid, while the two latter are solid. In fatty oils, olein predominates; while in solid fats, palmitin and stearin are present in greater proportions. Fixed oils, as a rule, are liquid at ordinary

temperature, while fats proper are of a soft consistence and mostly yield liquid fats when subjected to a gradually increased pressure; those of a firmer consistence are usually termed tallows or suets, and such as are brittle at common temperatures are known as waxes, but these are not true fats. The origin of fixed oils in plants is supposed to be the starch, while in animal fats they are more probably derived from albuminous matter. Fats are lighter than water, and insoluble in that liquid; sparingly soluble in cold alcohol, with one or two exceptions; but, as a rule, freely soluble in ether, chloroform, petroleum benzin, carbon disulphide, benzene, etc.; a hot alcoholic solution of fats, in most instances, will deposit them in a crystalline condition upon cooling. All fats, whether liquid or solid, appear greasy to the touch, and when dropped upon paper produce a stain which cannot be dissipated by heat; they have boiling-points varying from 260° to 300° C. (500° to 572° F.), and frequently, when thus heated, undergo decomposition and give off acrid irritating vapors. Fixed oils usually have a specific gravity of from 0.900 to 0.930 at 15° C. (59° F.), though occasionally it runs as high as 0.970, as in the case of castor oil; many oils do not congeal until the temperature has fallen considerably below 0° C. (32° F.), while others deposit solid matter at 10° C. (50° F.). Like water, fixed oils expand upon congealing, and have been known to burst the vessels containing them. Fats are not inflammable, but will burn more or less readily by the aid of a wick. Nearly all vegetable and animal fats consist of a mixture of two or more fats, and when exposed to the air become oxidized, many of them gradually assuming a disagreeable odor, due to the liberation of odorous fatty acids; this condition is known as rancidity, and may be avoided by keeping the fats as free from moisture as possible, in air-tight containers stored in a dry, cool, and dark place. Rancid fats may be improved and, to a certain extent, restored, by washing them with warm water, or by treating them with magnesia or other weak alkali, and afterward washing them well. During the oxidation of fats by exposure to air, heat is always developed, and certain fabrics, such as woollen and cotton rags, which are known to be poor conductors of heat, are liable to spontaneous ignition if saturated with fats and exposed to the air for some time. Fixed oils may be conveniently divided into drying and non-drying oils; the former upon exposure to air gradually thicken, and if in thin layers, form varnish-like masses, whereas the non-drying oils remain fluid and become rancid.

Although fats are found in various parts of plants, those intended for use are collected exclusively from the fruit and seed, and are obtained either by expression or by extraction with some suitable solvent; the former process yields somewhat lower results, but is preferred because less troublesome and productive in many cases of a superior article. In Fig. 195 is shown an hydraulic press extensively used for the expression of mustard, cotton seed, and linseed oils. The crushed material, after being heated somewhat, is placed in sacks

or press-cloths between the series of plates, and pressure applied from below, the oil being collected in the large box or trough, and from there delivered into the receiving vessel. The residue from certain seed expressions is used, under the name of oil-cake, as food for cattle and hogs or for fertilizing purposes. Cold expression

yields a finer oil than when heat is employed, although slight warming is generally resorted to so as to render the oil more fluid in the seed and thus insure a better flow. Expressed oils are always more or less contaminated with impurities, such as mucilaginous and albuminous matter, which are removed by allowing the oil to settle in large tanks and drawing off the clear liquid. Frequently filtration is employed for improving the quality of the oil, felt or flannel bags

being best adapted for this purpose. When purification of fixed oils becomes necessary they are treated either with sulphuric acid, caustic alkalies, zinc chloride, tannin, or alkali carbonates, and subsequently washed with hot water, after which they are carefully decanted.

The extraction of fixed oils is conducted in specially constructed extractors, frequently so arranged that the solvent is made to act upon successive portions of crushed seed, the saturated solution of fat being then transferred to a suitable distillatory apparatus, where the solvent is recovered, to be again used for subsequent operations. The solvents usually employed are petroleum benzin of low boilingpoint and carbon disulphide; the oil is obtained in larger quantity than by expression, and is free from many impurities often found in expressed oils.

Fixed oils are frequently subjected to a bleaching process, which consists in treating the oil with solution of hydrogen dioxide, potassium permanganate, potassium dichromate, chlorine, or sulphurous acid; of these methods, the hydrogen dioxide process is preferable, as it is least liable to injure the oil, while the use of other bleaching agents necessitates repeated washing of the oil with water and even weak alkali solutions to remove acid oxidation products.

The adulteration of fixed oils is effected by mixing the finer and more valuable oils with inferior and cheaper varieties, and as the crude methods of former years are no longer practised, a better knowledge of the chemical behavior of fats and fixed oils is necessary at the present day. Caustic and carbonated alkalies are practically without effect upon fats and fixed oils in the cold unless free acids, due to rancidity, be present; a more or less uniform mixture results, but no chemical change is produced. If boiled together with solutions of alkali hydroxide or carbonate, all fats and fixed oils used in pharmacy, with the exception of lanolin, wax, and spermaceti, readily undergo saponification and form water-soluble compounds; the amount of caustic soda or potassa necessary to saponify one gramme of fat varies for each fat and fixed oil, and expressed in milligrammes is known as Koettstorfer's saponification factor, by means of which the purity of fixed oils may be tested. Since fatty compounds are capable of uniting with iodine, a method for the detection of admixtures in fixed oils has been proposed by Huebl, the quantity of iodine combining with a given weight of the oil being different in each case; the number of grammes of iodine absorbed by 100 grammes of any fixed oil expresses the iodine addition factor of that oil. (These two methods are more fully explained under the head of Pharmaceutical Chemistry.)

Drying oils may be distinguished from non-drying oils by their behavior with sulphuric and nitrous acids. If 50 Gm. of a fixed oil be mixed with 10 Cc. of concentrated sulphuric acid, heat will he developed varying in intensity for different oils, the drying oils always showing the greatest rise in temperature; thus, while olive oil increases 42° C. in temperature, castor oil 47° C., and oil of