PEOFESSOE B. C. BEODIE ON THE ATOMIC WEIGHT OF GEAPHITE. 
251 
The details of this process are as follows A portion of graphite is intimately mixed 
with three times its weight of chlorate of potash, and the mixture placed in a retort. A 
sufficient quantity of the strongest fuming nitric acid is added, to render the whole fluid. 
The retort is placed in a water-bath, and kept for three or four days at a temperature 
of 60° C. until yellow vapours cease to be evolved. The substance is then thrown into 
a large quantity of water, and washed by decantation nearly free from acid and salts. 
It is dried in a water-bath, and the oxidizing operation repeated with the same pro- 
portion of nitric acid and of chlorate of potash until no further change is observed : 
this is usually after the fourth time of oxidation. The substance is ultimately dried, 
first in vacuo ^ and then at 100° C. A modification of the process which may be advan- 
tageously adopted, consists in placing the substance with the oxidizing mixture in flasks 
exposed to sunhght. Under these circumstances the change takes place more rapidly, 
and without the application of heat. 
These crystals, when examined with the microscope, are perfectly transparent, and 
exhibit beautiful colours by the agency of polarized light. Professor Miller of Cam- 
bridge, who was good enough to examine them, has communicated to me the following 
observations : — “ The crystals, though not absolutely too small to be measured, are too 
thin and too imperfect to admit of measurement with the reflective goniometer. I have 
examined them under a microscope, for the purpose, if possible, of making out at least 
the system of crystallization to which they belong. Their system appears to be either 
the prismatic or the oblique, — most likely the former Sometimes the crystals appear 
broken, as in the annexed figure. The straight- 
ness of the fractured edges (in the direction 
EF) evidently indicated the existence of a 
cleavage in that direction. The crystals are so 
extremely thin in a direction perpendicular to 
the paper on which the above figure is traced, 
that it is impossible to obtain any reflexion, 
except from the faces parallel to the plane of the paper.” 
The crystals, on the apphcation of heat, are decomposed with ignition. Gases are 
evolved, and a black residue is left of a substance resembling in appearance finely 
divided carbon. 
I have not discovered any reagent by which these crystals may be dissolved, and they 
admit of no process of purification. The explosion which the crystals undergo on the 
application of heat render special methods of analysis necessary, and I have taken, with 
regard to the analysis, every precaution which suggested itself. Neither chlorine nor 
nitrogen could be detected. 
The substance was placed in a platinum boat in a porcelain tube and burnt in a 
* Measxirements of the crystals, by means of the microscopic goniometer, which have subsequently been 
made by Mr. A. H. Chuech, of Lincoln College, have determined with certainty that the crystals belong 
to the one or other of these systems. 
J3 C 
