This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
(Their English names terminating in ine, their Latin names terminating in ina.) Compounds of carbon, hydrogen and nitrogen, and usually containing also oxygen, either existing in the plant as proximate principles, or being derived from other alkaloids, having basic properties, and forming salts, usually crystallizable, with acids, without displacing any of the hydrogen of the latter. The chief characters are as follows :
(a) solid, mostly crystalline and colorless, non-volatile, or (b) liquid and volatile.
(2) They turn red litmus paper blue.
(3) They are soluble in alcohol, chloroform, benzin, benzol, and often in ether. They are insoluble in water, but not so their salts, while the latter are insoluble in chloroform, ether, benzin and benzol.
(4) They are usually precipitated from saline solutions by alkalies.
(5) One or more of the following will precipitate them : tannic, phospho-molybdic or picric acid, potassio-mercuric iodide or auric chloride.
(6) Their solutions are usually intensely bitter.
(Their English names terminating in in, their Latin names terminating in inum.) Bodies which, heated with a diluted mineral acid and water, or by the action of a ferment, split up into glucose and some other substances (alcohols, aldehydes, phenols). Examples in U. S. P.: Salicinum, Picrotoxinum.
Amaroids or Bitter Principles (their names ending in in and inum as above) are of such varied nature that they do not admit of any chemical diagnosis. The term includes all distinctly bitter extractives of definite chemical composition other than alkaloids and glucosides.
Glucosides and Amaroids are not the only principles whose names end in in.
Fixed Oils are ethers of the higher fatty acids which at ordinary temperatures remain liquid. The usual fatty acids entering into the composition of fixed oils are oleic, palmitic, and stearic.
Example: Olive oil consists of a mixture of a combination of oleic acid (C18H34O2) with glyceryl (C3H5) and palmitic acid (C16H32O2) with glyceryl. That is to say, ordinary olive oil is a mixture of two oils having the formulae C3H5 (C18H33O2)3 and C3H5 (C16H31O2)3 respectively. When acted upon by caustic alkalies or metallic oxides they form soaps (oleates, palmitates, or stearates of metals) and glycerin. This process is called saponification, e.g.., C3H5 (C18H33O2)3+3NaOH=3NaC18H33O2 +C3H5(OH)3.
Fixed oils are obtained by expression or by boiling with water and skimming off the melted oil, from the fruits or seeds of plants, or from animal tissues. When pure they are usually colorless or pale yellow; they float on water and cause a greasy mark on paper. They are called fixed because they cannot be distilled without decomposition. They are soluble in ether, chloroform, turpentine and volatile oils. Those in U. S. P. are Oleum Amygdalae Expressum, Lini, Morrhuae, Olivae, Ricini, and Tiglii.
Fats are fixed oils which are solid at ordinary temperatures ; if extracted by expression, sufficient heat to melt them must be used.
Waxes are chiefly composed of fatty acids combined with monohydric alcohols homologous with methyl alcohol.
Volatile or Essential Oils only resemble fixed oils in being soluble in the same media. They do not leave a greasy mark on paper. They are mostly inflammable, and mostly lighter than water. They are highly aromatic, and sufficiently soluble in water to impart their odor and taste to it. Most are prepared by distillation - that is, by passing a current of steam through the substance from which they are extracted, the steam is condensed, and the oil either floats to the top or sinks to the bottom of the water. A few, as oil of lemon, are obtained by expression. Their composition varies greatly, and they are of four classes :
(a) Terpenes, which consist of carbon and hydrogen; e.g., Oil of turpentine.
(3) Oxygenated, containing oxygen; e.g., Oil of eucalyptus.
(d) Nitrogenated, containing hydrocyanic acid; e.g., Oil of bitter almond.
They may contain aldehydes, phenol derivatives, ethers or ethereal salts, alcohols or ketones, generally associated with terpenes of varying composition.
Elaeoptens, their names ending in ene, are liquid hydrocarbons isomeric with terpene (C10H16).
Stearoptens, their names usually ending in ol, are oxidized hydrocarbons, usually solid and crystalline.
Resins are of very indefinite composition. They are among the products of oxidation of volatile oils, being usually oxidized terpenes. They are solid, most uncrystallizable, fusible, not volatile, combustible, insoluble in water, mostly soluble in alkalies and volatile oils, and also in one or more of the following: alcohol, ether, chloroform, and fixed oils. Since they are insoluble in water, but not in alcohol, they may be prepared by extraction with alcohol and precipitation with water. This is the reason for the precipitate which falls when water is added to a resinous tincture. Those which combine with alkalies form resin soaps. Hence the alkali in Tinctura Guaiaci Ammoniata, and `Tinctura Valerianae Ammoniata. When occurring naturally, there are usually two or more resins mixed.
Oleoresins are natural solutions of resins in volatile oils.
Those in the U. S. P. are Oleoresina Aspidii, Capsici, Cubebae, Lupulini, Piperis, and Zingiberis.
Balsam, is a term used in several different ways. As to the U. S. P. articles, they are liquid or soft products containing resin, an odorous principle, and benzoic, or cinnamic acids, or both.
Resins containing benzoic or cinnamic acids are sometimes called solid balsams.
Gums, are exudations from plants, having an insipid taste, insoluble in ether and alcohol, in water either dissolving to form a mucilage or swelling to form an adhesive jelly. They consist of one or more of the following:
(a) Arabin or soluble gums, e.g., Acacia.
(b) Bassorin or partially soluble gums, e.g., Tragacantha.
(b) Cerasin or insoluble gum.
Solutions of gum are precipitated by alcohol.
Gum-resins are exudations from plants consisting of a mixture of one or more gums and one or more resins. When they are rubbed with water the gum dissolves and the resin remains mechanically suspended in the solution, forming an emulsion. The U. S. P. gum-resins are Ammoniacum, Asafoetida, Cambogia, Myrrha, and Scammonium.