ORGANIC SUBSTANCES.] 



CHEMISTRY. 



329 



in forming bases, they combine with a small quantity of 

 oxygen. We pass now briefly to enumerate these bases. 



The combination of potassium with oxygen is potash ; 

 soda is composed of sodium and oxygen, just as common 

 salt is composed of sodium and chlorine : soda is often 

 elicited from common salt by the introduction of oxygen, 

 which expels the chlorine. Potassa and soda are called 

 alkalies in a stricter sense ; they readily dissolve in water. 

 Calcium with oxygen constitutes lime ; and magnesia, a 

 substance very similar to lime, is formed from oxygen 

 and magnesium. Magnesia is the base of the well- 

 known medicine, carbonate of magnesia. For th.3 future 

 we shall include lime and magnesia under the common 

 name of earths ; they differ from alkalies principally in 

 being much less soluble in water, and in having a 

 slighter affinity for acids. 



Iron combined with a higher proportion of oxygen than 

 that which with calcium forms lime, is called oxide of 

 iron, which, in combination with water, produces iron- 

 rust. It differs from the earths and alkalies in being 

 insoluble in water. 



All the above-named bases appear in aliment, only in 

 union with acids, forming salts. The most important 

 a-;i<ls are constituted of those elements which we have 

 called intermediate between inorganic and organic sub- 

 stances. 



mr forms, with a large proportion of oxygen, 



io acid, generally known by the name of oil of 



* Phosphorus, combined with still more of oxygen 



than ilphuric acid contains, is called phosphoric acid, 



which constitutes with lime the solid material of bones, t 



: may be added carbonic acid, which produces the 



sparkling bubbles of champagne, and is a compound of 



carbon with a smaller proportion of oxygen than is found 



K. sulphuric acid. 



The alkalies, potash, and soda appear in our food, com- 

 pounded with the three above-mentioned acids. They 

 i'urm neutral salts with sulphuric acid, sometimes acid 

 salts with carbonic acid, and always basic salts with phos- 

 phoric acid. Of these three classes, the last-mentioned 

 enter by far the most largely into the composition of our 

 food. 



Amongst the earthy salts, those formed with phos- 

 phoric acid again prevail. These are always basic, and 

 can only be dissolved with difficulty in pure water, but 

 become easily soluble if a little acid be added. 



The sulphate of magnesia, known to everybody as 

 Epsom salts, is soluble in water ; but sulphate of Line or 

 gypsum can only be dissolved with great difficulty. 



iy, the oxide of iron enters into our food in com- 

 binatinn with phosphoric acid ; and the salt thus formed, 

 though insoluble in water, is dissolved by acids with 

 tolerable case. 



The inorganic principles of nutriment are therefore 

 as follows : Compounds of chlorine and alkali salts, 

 both soluble in water; earthy salts and phosphates 

 of iron, which dissolve in water with difficulty, or 

 not at all. 



5. The organic alimentary substances without nitrogen 

 are in part compounds of carbon, hydrogen, and oxygen, 

 which are capable of being transformed into fat, and we 

 therefore call them constituents of fat. In part they con- 

 sist of different kinds of fat itself, all of which are com- 

 pounded of the same three elements. 



In most constituents of fat, these elements are com- 

 bined in the same relative proportions ; and two of them, 

 hydrogen and oxygen, in the same as that in which they 

 are found in water. 



All fatty substances contain the same proportion of 

 oxygen, and proportions of carbon and hydrogen mutually 

 equal, though varying in different kinds of fat. In com- 

 parison with hydrogen, fat itself contains much less 

 oxygen than water or the constituents of fat. 



The most important constituents of fat are starch, gum, 

 and sugar. We shall often include these under the name 

 of starchy substances. Starch is only soluble in boiling- 

 water, but the other two easily in cold. 



Of the fatty substances we must here mention oleine, 



Sec ante, p. 308. t Ante, p. 314. Ante, p. 320. 



VOL. J. 



mnraarine, and stearine.^ Oleine is the chief component 

 of all oils, and denotes their characteristic part, which 

 slowly coagulates by cold. Besides oleine, oils contain a 

 fat which hardens more readily, and may be obtained in 

 crystals, glittering like mother-of-pearl. On this account, 

 and not because it is actually found in mother-of-pearl, 

 it is called mother-of-pearl fat, or margarine. Stearine 

 is the firmest of all fats. It is the principal solid sub- 

 stance in the fat of mutton and beef, where it is com- 

 bined with margarine and oleine. Stearine caudles con- 

 tain stearine and margarine. || 



While most constituents of fat are identically com- 

 posed, sugar only containing more hydrogen and oxygen 

 than the others, there is in oleine, with the same quan- 

 tity of oxygen, more carbon and hydrogen than in 

 stearine, and in stearine more than in margarine 



The above-named fatty substances are not soluble in 

 water, and cannot as such be united with other sub- 

 stances in soluble combinations. As though saturated 

 in themselves that is to say, without any inclination to 

 combine with other substances, and, so to speak, stand- 

 ing impartially between acids and bases we may call 

 them neutral fats, just as the salts in which acids and 

 bases are in equilibrium are termed neutral salts. By 

 the admixture of alkalies, neutral fats are separated 

 into two substances, one of which is called the sweet 

 principle of oil, or glycerine, a substance compounded of 

 carbon, hydrogen, and oxygen ; the other, and by far 

 the greater part, is a fatty acid, which combines with 

 the alkalies to form a soap. Thus oleine yields oleic 

 acid ; stearine, stearic acid ; and margarine, margaric 

 acid. As glycerine, which has been separated from 

 neutral fats by potash or soda, is of the same composi- 

 tion, from whatever fat it is extracted it follows that the 

 remaining acids retain the- same proportion of carbon 

 and hydrogen, as the primitive neutral fats ; that is to 

 say, oleic acid contains more carbon and hydrogen than 

 stearic acid, and stearic acid more than margaric acid. 



The compounds of fatty acids with potash are called 

 potash-soaps ; and those of soda and fatty acids, soda- 

 soaps. Soaps, therefore, may be regarded as analogous 

 to salts, the acids being an organic substance destitute 

 of nitrogen, the basis an inorganic body. 



6. Another group of organic alimentary principles are 

 those containing nitrogen, which are compounded of a 

 greater number of elements than fat and its constituents 

 contain. Of these constituents of food, we have only to 

 mention the albuminous substances. All albuminous 

 aliments contain nitrogen, carbon, hydrogen, oxygen, 

 and sulphur, and most of them phosphorus also. The 

 white of a hen's egg gave its name to these substances, 

 which have been properly united into one group. The 

 proportions of nitrogen, carbon, hydrogen, and oxygen, 

 of which they chiefly consist, show a most surprising, if 

 not complete agreement ; recent chemical investigations 

 having proved, that, with respect to the four latter ele- 

 ments, their composition is almost identical. Before this, 

 however, the great similarity of their properties had led 

 to their being comprised under one general name. Four 

 of them, the caseine of milk, the principle of the yolk of 

 eggs, the gluten of grain, and the globuline in the crys- 

 talline lens, as well as in the globules which float in the 

 blood, are distinguished by not containing any phos- 

 phorus. The quantity of sulphur is different in these 

 several instances, just as that of phosphorus is in those 

 which contain this element. In the following list the 

 albuminous subtances are given in order, according to the 

 quantity of sulphur they contain ; those which possess 

 the higher proportion being placed first : The albumen 

 at eggs, the albumen of blood, fibrino and globuliue of 

 blood both of which contain an equal quantity of sul- 

 phur ; the principle of the yolk of eggs, gluten, caseine, 

 soluble vegetable albumen, coagulated vegetable albu- 

 men, and legumine. The largest proportion of phos- 

 phorus exists in legumine ; the albumen of eggs stands 

 nuxt, which, however, contains scarcely a quarter of tins 

 phosphorus of the former ; and last of all, iibrine and 

 albumen of blood. The amount of phosphorus in 

 I See ante, p. Si. || Ante, p. K. 



