690 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
am mollification and pass through the acid solution unabsorbed, or, if absorbed, are 
not accurately determined by the titration or other means used to find the amount of 
nitrogen in the solution. 
c. Escape of nitrogen in the free state. 
II. Loss of ammonia through — 
a. Dissociation at high heat in the combustion tube, 
b. Oxidation by air present in the tube before, or introduced in aspirating to wash 
out ammonia after the combustion. 
c. Neutralization by acid products, e. g.,of sugar, where the latter is used in the 
combustion. 
d. Incomplete absorption by the acid solution. 
(5) Complete decomposition of the substance has, in our experience, been readily 
secured by pulverization fine enough for it to pass through a sieve of 1 mm. aper- 
ture ; thorough mixing with soda lime ; avoiding the shaking by which the particles 
gather at the top of the soda lime ; and heating to low redness. 
(6) With sufficient soda lime, not too dry, we have found no reason to fear the forma- 
tion of cyanides, nor have we been able to obtain any indication of the escape of free 
nitrogen when the operation is properly conducted, although it might, perhaps, occur 
by oxidation of ammonia if there were nitrates or nitrites present, or if aspiration 
with air were done while tube and contents are hot. Turning off the flame before 
aspirating has, in our experie nee, sufficed to avoid oxidation by air. At least, if 
ammonia has been oxidized, the quantity has been too small to be detected. 
(7) When sugar is used, acid products maybe formed in quantities large enough 
to impair the accuracy of the determinations. With ordinary animal and vegetable 
protein compounds, provided enough soda lime is employed, the use of hydrogen, or 
sugar, or other substances for supplying gases, either to expel air, or to yield nascent 
hydrogen to form ammonia with the nitrogen, or to dilute the ammonia and prevent 
dissociation, or to wash out the ammonia, appears to be unnecessary. The danger of 
loss by incomplete absorption of the ammonia by the acid solution appears to be 
very small indeed, even when the development of gases is very rapid, provided suf- 
ficient acid solution be used. 
The chief sources of loss appear to be from incomplete ammomfication and from 
dissociation of the ammonia formed. 
(8) The first of these two difficulties is a serious one. With protein compounds, the 
great trouble is evidently the formation of volatile decomposition products which do 
not readily yield their nitrogen to form ammonia with hydrogen. This is easy to 
under stand when we consider that protein compounds are prone to yield cleavage 
products such as leucine and its congeners, compounds allied to the alkaloids, amido 
compounds, etc. ; and that it is very difficult to get all the nitrogen of these latter 
into the form of ammonia with soda lime, evidently because of their proneness to 
form compounds that resist the ammonifying action. 
With alkaloids and allied compounds, leucine and other amido compounds, amines, 
and azo and nitro compounds, c omplete aminonification is not always effected even 
with the utmost care. Concerning peptones our experience does not enabl.e us to 
speak; but for the protein of ordinary animal and vegetable substances, including 
casein, proper precautions appear to insure complete ammonification of the nitrogen. 
The important condition appears to be sufficient contact with heated soda lime ( i . e., 
with water vapor at high temperature). 
This contact is best secured by (a) intimate mixture of substance with soda lime ; 
(&) close packing so as to avoid open space inside the tube; (c) providing a reasona- 
bly long anterior layer of soda lime; (jd) heating this latter to dull redness before 
bringing the heat to bear upon the substance, and keeping it hot until the combus- 
tion is done. In order to insure the maximum of surface for contact it is well to 
have the anterior layer consist of coarse particles of soda lime containing enough 
lime to prevent fusing together. It is possible that too long heating may result in 
expelling the water from the soda lime, so that there will not be enough in the latter 
part of the operation to insure complete ammonification. 
