66 PRELIMINAKY COLD STORAGE STUDIES. 



Fat Determinations. 



The study of the fat consisted in the determination of the iodin 

 number, the saponification number, the acid value, ester value, the 

 Hehner number, and the index of refraction. 



The fat of the fowl, prepared as previously described (page 63), was 

 heated for 2 days in the thimble of a Soxhlet extractor, with a petro- 

 leum ether having a boiling point of between 40° and 60° C. If any 

 solid particles separated after the extraction the solution of the fat 

 was filtered through paper, and the ether was then distilled off. Dry- 

 ing the fat, with the small amount of adhering tissue, before extract- 

 ing, was not practiced. The quantity of tissue was very small, 

 because the mechanical separation was carefully made, and it was 

 deemed better to risk the mixture of a certain amount of nitrogenous 

 extractives with the fat than to subject it to the splitting produced by 

 the action of air and heat. It is proposed to make a study of these 

 two procedures to determine their relative accuracy. It was found 

 exceedingly difficult to remove the last traces of petroleum ether 

 without altering, to a greater or less extent, the composition of the fat 

 itself. The result was accomplished best by allowing the fat, freed as 

 far as possible from petroleum ether by means of distillation, to stand 

 in a vacuum desiccator over calcium chlorid freshly ignited and acid 

 free. It was found that sulphuric acid, in a vacuum desiccator, very 

 materially altered the value of the fat, probably owing to the absorp- 

 tion of a certain amount of sulphuric acid vapor. 



Though it is generally agreed among bacteriologists that pure dry 

 fat is not a culture medium for bacteria, the precaution was never- 

 theless taken to preserve the samples of fat, even for the short interval 

 between the distillation of the petroleum ether and their further anal- 

 ysis, in sterile flasks, plugged with sterile cotton, and the transfer of 

 the material when necessary was made with sterile pipettes. Because 

 of the action of light and air on pure fat the analysis of the samples 

 was conducted with all possible haste. 



The iodin number was determined according to the official Hanus 

 method." For the saponification number the official method was 

 also followed, and the Hehner number was determined as officially 

 recommended. a The acids, however, were dried at 100° C. until a 

 gain in weight occurred, when the minimum weight was taken as 

 expressing the quantity of acid. 



For the acid value 4 or 5 grams of the fat were weighed in a 250 cc 

 Erlenmeyer flask; 100 cc of a 15 per cent sodium chlorid solution 

 were added, and the flask was immersed in hot water until the fat 

 was liquefied. The free acid was then titrated with tenth-normal 

 sodium hydroxid, using phenolphthalein as an indicator. Vigorous 



«II. S. Dept. Agr., Bureau of Chemistry, Bulletin 107, pp. 136-139. 



