BOBIO ACID AND BOEAX. 23 



varieties it was thought best to subject all samples to the same method 

 of drying. The water determinations were all made by Mr. W. L. 

 Dubois. 



DETERMINATION OF FAT. 



The residue from the determination of water was transferred to an 

 extraction tube and the lead bottle cap which contained it was cut into 

 small pieces and also introduced into the tube. The tube was then 

 placed in position in a continuous-ether-extraction apparatus, mercury- 

 sealed, and the residue extracted with anhydrous sulphuric ether for 

 thirty-six hours. The fat determinations were made by Messrs. War- 

 ner, Given, Burd, and Jones. 



DETERMINATION OF NITROGEN. 



Nitrogen was determined by the Gunning method, as described in 

 Bulletin 46 of this Bureau. Owing to the large volume of work it 

 was found impossible to take into consideration the nature of the 

 nitrogenous compounds. The total content of nitrogen only was 

 determined. The nitrogen determinations were made by Messrs. 

 T. C. Trescot and L. S. Munson, with the assistance of Mr. H. W. 

 Hough ton. 



DETERMINATION OF PHOSPHORIC ACID. 



The samples were moistened with water, treated with magnesium 

 nitrate, dried, and ignited, and a solution was prepared as directed 

 on page 12 of Bulletin 46 of the Bureau of Chemistry. In this solu- 

 tion the phosphoric acid was determined by the volumetric method 

 of the Association of Official Agricultural Chemists given on page 13 of 

 the bulletin above mentioned. This method consists in dissolving the 

 yellow precipitate in a definite amount of potassium hydroxid, and 

 titrating with a standard solution of nitric acid. The phosphoric acid 

 determinations were made by Mr. L. M. Tolman. 



DETERMINATION OF HEAT OF COMBUSTION. 



Almost all of the samples were burned in the bomb calorimeter. 

 In some cases of foods having a very high water content, such as 

 canned fruits and soups, the heat of combustion was calculated, using 

 the factors 5900 for protein, 9300 for fat, and 4200 for carbohydrates. 

 The heat of combustion determinations were all made by Mr. E. M. 

 Chace. * 



ANALYSIS OF URINE. 



The urine was collected and preserved in bottles of about 1 pint 

 capacity. It was kept in a cool place and returned to the laboratory 

 each morning. The entire volume for each man for twenty-four hours 

 was then mixed, measured, and subjected to analysis. With theexcep- 



