122 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



be recognized by the development of acrolein when boiled with glacial 

 phosphoric acid. Under the influence of certain ferments fats split up 

 into glycerin and a &tty acid by combining with the elements of water, 

 thus : 



C 3 H 5 (OC 16 H 31 0) 3 +3H 2 0:=C 3 H 5 (OH) 3 +3(C 16 H 31 0,OH). 

 Tripalmitin. Water. Glycerin. Palmitic Acid. 



The composition of the four principal fats is represented in the 

 following formulae : 



Glycerin, C 3 H 5 (OH) 3 . 



Palmitin, C 3 H 5 (OC 16 H 31 O) 3 . Palmitic Acid, C 16 H 31 O,OH. 

 Stearin, C 3 H 5 (OC 18 H 35 O) 3 . Stearic Acid, C 18 H 35 O,OH. 



Olein, C 3 H 5 (OC 18 H 33 0) 3 . Oleic Acid, C I8 H 33 O,OH. 



Butyrin, C 3 H 5 (OC 4 H 7 O) 3 . Butyric Acid, C 4 H 8 O 2 . 



Stearin. Stearin is the chief constituent of the more solid fats. 

 Its melting point varies between 53 and 66 C. It is insoluble in cold 

 alcohol and in ether, but is soluble in both when boiled. It never occurs 

 in the vegetable fats. It crystallizes from boiling alcoholic solutions in 

 brilliant quadrangular plates. 



Palmitin. This fat is the chief component of the animal fats, but 

 also is largely found in fats of vegetable origin. It is more soluble in 

 cold and hot ether and alcohol than is stearin. Its melting point is 

 45 C. It crystallizes in fine needles. 



Olein. When pure, olein is a colorless oil which is fluid at the 

 ordinary temperature and solidifies at C. When exposed to the air 

 it absorbs oxygen and becomes yellow. It dissolves all other fats, 

 especially at 30 C. It is soluble in cold absolute alcohol and ether. 

 It is more abundant in vegetable than in animal fats. 



Butyrin. Butyrin is found in butter. It is a pungent liquid ; and 

 when it decomposes, butyric acid, to which the odor and taste of rancid 

 butter are due, is set free. 



Spermaceti is found in the cranial sinuses of whales, and is a deriva- 

 tive of cetyl alcohol (C 16 H 33 )O. This is a solid body which melts at 

 50 C., and when saponified yields in addition stearic, myristic, and 

 lauric acids. 



Bees-wax is also a form of animal fat, which is likewise capable of 

 saponification, the radical here being cetyl alcohol. Waxes possess 

 many points in common with the fats, but are not acted on by the 

 digestive juices. 



Margarin. Formerly this name was given to a substance which was 

 supposed to be a special fat, but which is now known to be a mixture of 

 stearin and palmitin. It occurs in the form of needle-like crystals which 

 are often found in the interior of fat-cells, and which were supposed to 

 be a glycerin ether of a hypothetical acid, margaric acid. 



