32 CHEMISTRY. 
lamp, PP, to a proper height, the communication between the two being 
through the tube, NN. A glass bottle is inverted over the cup, M, so as to 
permit a glass tube passing through the stopper, L, to dip somewhat into 
the spiritin M. As soon as the level of the spirit in the cup sinks, that in 
the bottle flows out, and in this way its level in the lamp, PP, remains the 
same. The substance is burned as formerly, and the only difference 
between this and the preceding method consists in the passage of a current 
of oxygen over the oxyde of copper. In this is involved the apparatus, I, 
placed next to the potash apparatus. It consists of an U-shaped tube filled 
with pieces of potassa. This, as well as the chloride of calcium tube, and 
the potash apparatus, is weighed, and its object is to take up a certain 
amount of water carried off by the dry oxygen in passing through the 
potash apparatus. T[*urthermore, since all this apparatus had been weighed 
before the experiment when partly filled with air, and since the space 
occupied by the air is partly filled by oxygen (one tenth heavier than air) 
after the combustion, this gas must be again replaced by air for the final 
weighing. This is done by means of the second gasometer, after the cock 
of the first has been closed. : 
Substances which, like most that belong to the animal kingdom, contain 
nitrogen in addition to the rest, require this new element to be determined. 
After its amount of carbon has been ascertained, a second mixture of the 
substance with oxyde of copper is brought into a combustion tube (pl. 31, 
fig. 34). Only a part of the substance introduced into the combustion tube 
is burned at first, the resulting gaseous products being used to expel the air 
occupying the tube. As soon as this has been driven out, the remainder of 
the substance is burned, and the gaseous mixture furnished by the body 
together with the oxyde of copper, is collected. This is done by means of 
the tube, a, which carries the mixture into a graduated cylinder, C, filled 
with mercury. The cylinder being filled about one third with the gas, and 
the amount measured by the graduation on the tube, a sufficient quantity 
of solution of potash is taken up in the pipette (fig. 35), ard thus introduced 
into the cylinder, C. The object of this is to remove the carbonic acid 
from the gaseous mixture, which consists of carbonic acid and nitrogen, after 
the condensation of the major portion of the watery vapor ; in this way we 
are enabled to ascertain the relation of volume between these two gases. 
By calculation we can extend this ratio to the relative amount by weight 
of the two gases, and as the carbon has already been determined by a 
preceding analysis, we shall have the data necessary to determine the 
quantity of nitrogen corresponding to the carbon already found. 
Another method of determining the nitrogen consists in directly burning 
a weighed amount of the substance to be investigated, and after procuring 
the entire amount of the contained nitrogen,to measure it. For this purpose 
we may use the apparatus shown in fig. 36. The combustion is conducted 
in the usual manner in the combustion tube ab, which is filled from @ to h 
with a mixture of the substance with oxyde of copper, and from b to ¢ with 
copper turnings. The solution of potassa is placed in the vessel f, which 
incloses the graduated tube g, also filled with the solution. As all the 
462 
