64 PHYSIOLOGICAL, CHEMISTRY. 



tine holds an intermediate position in this respect, and oleine is the 

 most fluid. 



1. Stearine, C 57 H no 6 , 



So called from the readiness with which it assumes the solid form, is a 

 main ingredient of the more consistent fats. It liquefies at 66. 5 C., 

 and again solidifies when the temperature falls below this point. It 

 crystallizes, on cooling from a warm solution in oleine, in fine radiating 

 needles, which often follow a wavy or curvilinear direction. It is rather 

 less soluble in alcohol and ether than the other fatty substances. 



2. Palmitine, C 51 H 98 O 6 , 



Was first recognized as an ingredient of palm oil, a semi-solid fat 

 obtained from the seed of an African palm. It crystallizes, on cooling 

 from its concentrated alcoholic or ethereal solution, in the form of 

 slender needles. It liquefies at 60 C. It occurs abundantly in a 

 variety of animal and vegetable fats. 



3. Oleine, C 57 H 104 6 . 



As its name indicates, this is the representative ingredient of the oils, 

 or liquid fatty substances. When pure it is transparent and colorless. 

 It retains its fluidity at ordinary temperatures, and even below the 

 freezing point of water. It readily dissolves both stearine and palmi- 

 tine, its solvent power increasing with the elevation of the temperature. 



Physical and Chemical Changes of the Fatty Substances. There are 

 certain changes of condition produced in the fats by external influences 

 which are characteristic of these substances as a class. The first is 

 that by which an oily substance, when mingled with a watery liquid, 

 is reduced to the state of an emulsion ; that is, a mixture in which 

 the oil is broken up into minute particles and uniformly disseminated 

 through the watery liquid. This change will not take place when oil 

 is added to pure water, or to a watery solution of neutral or acid salts. 

 But if a trace of alkali or alkaline carbonate be present, the fatty sub- 

 stance is at once disseminated throughout the mass, and held in per- 

 manent suspension. In such a mixture there is no change in the chem- 

 ical characters of either the oil or the watery liquid, but only in their 

 physical condition ; the two being retained in contact with each other 

 in a state of minute subdivision. By evaporation the watery parts 

 may be separated and the oil left behind unaltered. An emulsion formed 

 in this way is whitish or white in color, and opalescent or opaque, 

 according to the proportion of oily matter present. The emulsion of oil 

 may also be accomplished by certain organic matters in watery solu- 

 tion, especially by the albumen of egg, or the albuminous ingredients of 

 the blood and secretions. It is under this form that oily matters exist, 

 when in considerable quantity, in the animal fluids, such as the milk, 

 the chyle, or the blood. 



Another change which may be produced in the fats is that of saponi- 

 fication. This is a chemical change in which the oily substance loses 



