Determination of Carbon in Graphite. 353 
oxydation, was by dropping nitric acid into hot sulphuric acid sur- 
rounding the graphite and then boiling the liquid until all the ni- 
tric acid was decomposed. But he adds, it was only after a repe- 
tition of the process for the fourth time, that the last trace of graph- 
ite had disappeared and the acid remained perfectly clear. 
_ The method about to be described, compared with the preced- 
ing, is easy of execution, and if we may judge from our experi- 
“Inents, is capable of yielding uniform and accurate results. W 
trust, therefore, that it may be thought worthy of the attention 
of analytical chemists. As a means of comparing the purity of 
the different varieties of native graphite, we have found it entire- 
ly satisfactory. . As applied to the still more important purpose of 
determining the entire amount of carbon in the several kinds of 
cast iron and steel, our experiments have not yet been sufficient- 
ly numerous to enable us to pronounce confidently upon its ac- 
curacy, but we are not without hopes of making it available also 
for this object, as a substitute for the very troublesome procedure 
by organic analysis. 
The oxydizing agent employed in this process is a mixture of 
bichromate of potassa and sulphuric acid, which, when applied 
to the graphite, under the conditions about to be described, con- 
verts the carbon rapidly and completely into carbonic acid. ‘The 
gas being intercepted by a Liebig tube, gives, by the equivalent 
of carbon, the amount of this substance present in the graphite. 
he details of the method are as follows: 
l. Preliminary treatment of the Graphite-——As the native 
graphite not unfrequently contains adhering organic matter and a 
trace of earthy carbonate, both of which would add to the car- 
bonic acid evolved in the process, it is proper after reducing the 
mass to a coarse powder, to moisten it with dilute sulphuric acid, 
and expose it to a red heat for afew minutes. It must then be 
brought to a state of extremely minute division. ‘This great com- 
minution, which is indispensable to prompt and entire oxydation, 
can not be affected by grinding in the usual way, as the graphite 
thus treated, forms flakes or plates under the pestle. But the 
requisite subdivision is readily attained by grinding it ina Wedge- 
Wood mortar. with pure quartzose sand, or what is better with 
small fragments of granular quartz. ‘The material we use for this 
and other similar purposes, is a very pure white granular quartz, 
found in a thick vein in the neighborhood of the University. It 
readily yields under the pestle, and may be reduced in a few min- 
utes to an almost impalpable powder. Pumice stone we have 
found equally efficient, though somewhat more difficult to break 
d wn. Any trace of the graphite that may adhere to the mortar, 
48 completely washed out by trituration with a small additional 
portion of the siliceous matter. 
