eee TSS el yey ‘ 
TRANSACTIONS OF THE SECTIONS. 61 
To succeed in this experiment, it is necessary first to reduce the small chips of 
diamond used in the process to a. very fine powder. This is done by crushing them 
in a steel mortar, and then grinding the coarse powder that results with repeated 
portions of pure siliceous sand in a mortar of agate. By patient manipulation we 
have in this way succeeded in bringing the diamond to very minute division. 
_A single grain weight of the gem will suffice for several experiments. In our re- 
peated trials we have never used more than half a grain, and we have obtained clear 
evidence of oxidation, by the evolved carbonic acid, with even one-tenth of a grain. 
In operating with half a grain, we employ a retort of about 15 inches capacity fitted 
up as in our apparatus for the oxidation of graphite. - The Liebig tubes and U-tubes 
of that arrangement are replaced by tubes or small bottles charged with perfectly clear 
lime-water, and connected by bent tubes and perforated corks, so as to be air-tight at 
all the junctures. The drying tube of chloride of calcium is omitted, and in its place 
a slender tube connected with the beak of the retort carries the gas through a short 
test-tube containing a small quantity of water. This is adopted as a precaution in 
the event of sulphuric acid vapour escaping uncondensed. 
As the process is slow we find it necessary to use a large amount of the oxidating 
materials. In our experiments with half a grain the retort is charged with 4 cubic 
inches of sulphuric acid and 500 grains of bichromate of potassa. 
It is important to remark that these materials, of themselves, when heated to the 
temperature at which oxygen is evolved, never fail to yield a small amount of car- 
bonic acid. This result, due no doubt to the presence, in the bichromate, of a trace 
of carbonate or some carbonaceous matter, we have found it impossible entirely to 
prevent by re-crystallization cr the addition of acid to the salt, or even by continued 
ignition. But we avoid all chance of error from this cause, by first heating the acid 
alone in the retort to about 350°, then adding the bichromate by degrees, and 
stirring the mixture so as to effect a complete separation of the chromic acid. A 
very brisk reaction takes place, much oxygenis disengaged, and with it any carbonic 
acid which these materials themselves are capable of evolving. 
By using successive tubes of lime-water to test the evolved gas, and occasionally 
applying a lamp to the retort, we readily ascertained when the oxygen ceases to be 
mingled with carbonic acid; and as soon as we are assured of this we add the 
powdered diamond, and begin the main experiment, 
_The evolution of carbonic acid is soon evinced by the growing milkiness of the 
lime-water, and this continues slowly to augment as long as there is free chromic acid 
in the retort. 
Operating in this way with half a grain of diamond-powder and the proportions of 
sulphuric acid and bichromate above stated, we have in a first process obtained 
about six-tenths of a grain of carbonate of line, about one-seventh of that due to the 
weight of diamond considered as pure carbon, showing that about one-seventh of the 
gem had been consumed in the process. By washing out the contents of the retort 
with distilled water, and carefully collecting the powder suffered to subside in a 
covered glass jar, we have found that in a second similar process it yielded an amount 
of carbonic acid nearly as great as at first; and in like manner, in a third trial, we 
have found it still capable of giving milkiness to the lime-water. 
In order to complete the oxidation at a single trial, it would be necessary to have 
the diamond still more finely comminuted, or to use a much larger amount of the 
oxidating agent than in the experiments here cited. The chief point of interest in 
the subject however is the fact which we believe has now for the first time been shown, 
that diamond-is capable of being owidated in the liquid way, and at a comparatively 
moderate temperature, ranging between 350 and 450 degrees. 
On the Absorption of Carbonie Acid by Sulphurie Acid. 
By Professors R. E. and W.B. Rocers. 
—— 
‘Notice of Pseudomorphous Crystals from Voleanic Districts of India. 
By J. Tennant, F.G.S. 
