486 Chemical Study of Food Fishes 
Methods of Analysis. 
Total Solids, Total Nitrogen, Fat, and Ash.—The methods used for the 
estimation of the quantity of total solids, fat, and ash, were those given 
in Bulletin No. 107 (revised) of the Bureau of Chemistry, United States 
Department of Agriculture. Total nitrogen was determined by the 
method of Kjeldahl and Gunning, using 0.1 N solutions of acid and alkali. 
Cold Water-Soluble Nitrogen.—The amount of nitrogenous compounds 
soluble in cold water was found by grinding 50 gm. of the sample, placing 
in a 12 ounce wide-necked bottle, adding 240 cc. of water, corking tightly, 
and shaking on a mechanical shaker. The bottles were removed from the 
shaker at the end of 15 minutes and the suspended matter was separated 
by centrifuging for 10 minutes. The opalescent supernatant fluid was 
poured through a plug of cotton in a funnel. Seven more extractions, 
each with 240 cc. of water, brought the final volume of the combined fil- 
trate to about 1,900 cc. This solution was transferred to a 2 liter flask 
and diluted to the mark with water. A second filtration through paper 
was made when required, though this was usually unnecessary, as the 
extract could be obtained in most cases free from suspended matter. Ali- 
quots of 50 cc. each were analyzed for nitrogen by the Kjeldahl-Gunning 
method. 
Coagulable Nitrogen.—Portions of 500 cc. of the neutral extract were 
evaporated to a little less than 250 cc. in 400 cc. beakers. The beakers 
were placed on wide asbestos gauzes to prevent scorching, and the height 
of the flame was so regulated that about 2 hours were required to reduce 
the volume of the solution one-half. The mixture was stirred occasionally 
to prevent clumps from sticking to the bottom of the beaker. After 
removing the flame, and while the solutions were still hot, they were al- 
ways treated with exactly 2 cc. of 20 per cent acetic acid solution to com- 
plete the precipitation of the coagulable protein. On.cooling, the mix- 
ture was transferred to a 250 cc. volumetric flask and diluted to the mark 
with water. The mixture was filtered and aliquots of 25 ec. each were 
analyzed for nitrogen. 
Hot Water-Soluble Nitrogen.—The flesh residue remaining from the cold 
water extraction was washed into a 400 cc. beaker with about 250 ce. of 
hot water. The mixture was boiled for 15 minutes, filtered hot through 
cotton, the residue again treated with hot water, and boiled for another 15 
minutes. The filtrate from the second extraction was added to that of the 
first and the combined filtrates were transferred to a 500 cc. volumetric 
flask, cooled, and diluted to the mark with water. This extract was fil- 
tered through fine filter paper and nitrogen was determined on 50 ce. 
aliquots of the filtrate. 
Ammonia Nitrogen.—For this determination a modification of the Steel- 
Gies! method was used. 10 gm. of NaCl were dissolved in 100 cc. of water 
1 Steel, M., and Gies, W. J., Some notes on the efficiency of the Folin 
method for the quantitative determination of urinary ammonia, J. Biol. 
