CHEMICAL COMPOSITION OF FOOD-FISHES. 
689 
tail elsewhere,* a recapitulation of the results and conclusions will 
perhaps suffice here. For this purpose I quote from an article in the 
American Chemical Journal : f 
The experimental and other considerations presented in this and the previous arti- 
cles on the determination of nitrogen by soda lime may be conveniently summarized, 
after first recalling the probable reaction by which the nitrogen is changed to 
ammonia and the principal sources of error in the operation : 
(1) It seems decidedly probable that the change of nitrogen to ammonia is effected 
by union, at high temperature, with water vapor yielded by the soda lime (or slaked 
lime in case the latter is used). It is essential that the contact between nitrogenous 
distillation products and water vapor be sufficient and at not too high or too low 
temperature to insure conversion of all the nitrogen to ammonia, and that the 
ammonia be not dissociated or oxidized. The main objects, then, are to secure com- 
plete ammonification and to avoid dissociation and oxidation. 
(2) The chief difficulty in the way of complete ammonification of protein compounds 
appears to be the formation of gases which do not readily yield their nitrogen to be 
united with the hydrogen of the water vapor. With certain other classes of nitro- 
genous compounds, as leucine and its congeners, alkaloidep, amines, and amido and 
azo compounds, this difficulty is greater and sometimes apparently insuperable. 
The tendency of protein compounds to be decomposed by heat and other agencies 
into leucine, amines, etc., appears to explain the difficulty frequently found in getting 
all their nitrogen into the form of ammonia by heating with soda lime. The evident 
means to secure complete ammonification must be sufficient contact with soda lime 
at proper temperature. 
(3) The danger of dissociation of ammonia evidently increases with increase of tem- 
perature and time of exposure, and is probably diminished by presence of water 
vapor and other diluting gases. If this be so, the danger will be avoided by measur- 
ably rapid combustion at not too high heat, and by keeping the ammonia in contact 
with sufficient moisture from the soda lime until it leaves the heated tube. 
(4) Leaving out of account substances such as nitrates, nirro-compounds, etc., whose 
nitrogen is imperfectly converted into ammonia by soda lime, even in the presence of 
organic matter, and assuming palpable errors of manipulation to be avoided, such as 
(a) loose packing of asbestos plug, which would allow particles of soda lime to be swept 
into the acid bulb ; (&) heat at anterior end of the tube so low as to permit ammonia 
to be retained with moisture about the cork, or so high as to char the cork and give 
rise to acid or alkaline distillation products; (c) use of soda lime containing nitrates 
or nitrites, which may, according to circumstances, either furnish nitrogen to be 
transformed into ammonia or oxygen to burn the ammonia formed from the nitrogen 
of the substance ; ( d ) use of distilled water containing ammonia for rinsing the acid 
bulb ; ( e ) imperfectly cleaned or incorrectly calibrated burettes ; the principal sources 
of error above discussed involve loss of nitrogen, and maybe recapitulated thus: 
I. Loss from imperfect ammonification of the nitrogenous substance, due to — 
a. Incomplete decomposition of the substance, part of the nitrogen being (from 
coarseness of the particles of the substance, imperfect mixing with the soda lime, 
insufficient heat, or other cause) left behind in the charred residue. 
b. Change of nitrogen into compounds other than ammonia, either such as may 
remain in the tube, e. g.. cyanogen, or volatile distillatiou products which escape 
* Notes on the soda-lime method for determining nitrogen, W. O. Atwater and 
C. D. Woods, Am. Chem. Journal, vol. 9, p. 311. Note on the absorption of ammonia 
by acid solution in nitrogen determinations with soda lime, I. S. Haynes, loc. cit. y 
10, p. 111. On certain sources of loss in the determination of nitrogen by soda lime, 
W. O. Atwater and E. M. Ball, loc. cit., 9, p. 319. On sources of error in determina- 
tions of nitrogen by soda lime, and means for avoiding them, W. O. Atwater, loc. cit., 
10, pp. 197 and 262. 
t Am. Chem. Journal, vol. 10, p. 277, 
H, Mis 274 44 
