GOO EXPERIMENT STATION RECORD. 



sum. It is 8.2 small calories in tLe formation of trilaurin from glycerin 

 and lauric acid and 4.3 small calories in the formation of trimyristin 

 from glycerin and myristic acid'. In the formation of ethers from the 

 unsaturated acids it is somewhat larger. In the formation of trierucin 

 from glycerin and erucasic acid it is 23.2 small calories. The mean 

 value of these three is 11.9 small calories and may be considered as a 

 constant in the formation of the mixed ethers of all the fatty acids. 

 The heat equivalent of 1 gram molecule would be as follows: 



Calories. 



1 molecnle of glycerin 397. 1 



1 molecnle of stearic acid 2, 711. 8 



1 molecule of oleic acid 2, 682. 



1 molecule of palmitic acid 2, 398. 4 



Heat of formation — 11. 9 



1 molecule of fat 8,177.4 



r. . n . 8,177.4x1,000 ci rn(\ n 1 -^c. 



or for 1 gm. fat, -i . ' = 9,50!) .small calories. 



800 



The calculated value, therefore, agrees with 9,600 small calories, the 

 value found by experiment. 



Butter fat. — The fat of butter differs from the fat of animal tissues in 

 this respect: it contains, in addition to the glycerids of the higher fatty 

 actds, those of fatty acids which contain fewer carbon atoms. Ihe 

 chemically homologous acids form also a regularly i)rogressing thermal 

 series.^ Therefore the glycerids of the acids which contain few carbon 

 atoms must have a smaller heat equivalent than those formed from 

 acids containing more carbon atoms. It was therefore probable that 

 butter fat would have a smaller heat equivalent than the fat of animal 

 tissue. Experiment has shown this to be the case. 



By the potassium chlorate method the heat equivalent of butter fat 

 ■was found to be 9,192 small calories per gram. The correct value, 

 determined by combustion in the bomb, is 9,231.3 small calories per 

 gram. These numbers nve to each other as 99.57:100. 



Vegetable fat. — It is not possible that the vegetable fats shoukl pos- 

 sess as regular composition and heat equivalents as the animal fats, 

 since the glycerids which they contain are derived from the most 

 various acids. Indeed, the same fats not infrequently show quite 

 noticeable variations in thermal value. Little investigation in this 

 field has been made, so it is impossible at present to say whether this 

 variation is due to the fact that the plant may really produce fats of 

 different composition under different conditions of growth, or whether 

 it is due to the imi)erfect methods followed by the investigators. 



We have investigated a large number of vegetable fats by the potas- 

 sium chlorate method. We have not yet thought it necessary to repeat 



'Jour, prali. Chem., 2d ser., 42, i>. 376. 



'^Ber. matb.-phys. Klasse kgl. siicbs. Ges. Wissenscli. Leipzig, 1893, p. 625; Jour, 

 prak. Chem., 2d ser., 49, p. 108. 



