240 W. Gibbs and F. A. Genth 
oxyd formed during the combustion is surprising, and it is abso- 
lutely impossible to get rid of it by means of ignited metallic. 
copper, placed in front of the in orn tube. Will and Var- 
rentrapp'’s method with soda lime is inapplicable, because one 
equivalent of ammonia is always decomposed by the aque 
of oxygen set free in thé reduction of sesquioxyd to protox i 
of cobalt. Good results could not be obtained by boiling 
salts with caustic alkalies, collecting the ammonia in chlorhydrie 
acid, and determining it by bichlorid of platinum. Even after 
the reduction of the sesquioxyd of cobalt to protoxyd by means 
of sulphurous acid, this method was found unreliable. The j im- 
provements made by Simpson in the absolute determination of 
nitrogen by volume at last furnished us with a reliable process; 
and seer all the analyses in this, memoir were executed by his 
method. The improvement introduced by Simpson consists es- 
sentially in mixing oxyd of mercury vite the oxyd of copper 
nekared to effect the combustion. The vapor of metallic mer- 
cury completely decomposes the oxyds of nitrogen, and any eX: 
cess of free oxygen is absorbed by means of metallic coppen 
By. this method we have analyzed most of our compounds wi 
out special difficuly, though we have often found it necessary to 
employ me much. larger proportion of oxyd of mercury than is 
by Simpson. One class of ammonia-cobalt bases 
have, Rairaiven, been the source of frequent analytical failures, 
and of great loss of time and material. We refer to the salts of 
Xanthocobalt, a base containing deut-oxyd of nitrogen, and giv: 
ing off this gas ata gentle heat, eae that at which oxyd of 
m decompo Simpson’s method has not always been 
found accurate, since even when a very large amount of oxyd 
of mercury is employed there is frequently much nitric oxyd in 
the nitrogen collected for measurement. In many cases the sim- 
ple admixture of a large proportion of metallic copper with the 
oxyd, as recommended by Winkelblech, has been found to give 
most excellent results. It is proper also to state here that, m 
consequence of difficulties in obtaining proper apparatus with 
which European chemists do not have to contend, we aot in 
the majority of cases, measured the volume of nitrogen in t 
old way, using, however, very notoniale graduated tubes for 
collection, and co correcting with great care for temperature 
pressure. We have also found it advantageous to operate _ 
quantities of substance gpaeecrm to yield at least two 
cubic centimetres of this f reading 
gas, since way the error of rea 
acid.—This acid cannot be accurately determined in 
the phe. amenonie-enbals salts by direct precipitation with chlorid of 
. almost nt excess of is 
all cases, a great appare 
eg may amount to five per cent, even when the 
