62 REPORT—1850. 
quantity may be advantageously increased. As filtration is indispensable to the con- 
ducting of this process, considerable fear was entertained lest fermentation might 
supervene. This fear, however, practice has demonstrated to be groundless, inasmuch 
as we possess in sulphurous acid an agent most antagonistic to fermentation. Another 
speculative fear was, lest danger might arise from the lead employed : this fear, too, 
practice demonstrates to be entirely without foundation, for not only is the sulphate 
of lead most easily removed, but even were it to remain, no injury could supervene, 
inasmuch as this agent is as harmless as chalk. 
On the Tetramorphism of Carbon. By Henry Ciirron Sorsy. 
The object of this paper was to show that the great difference between the various 
states of carbon is produced by its existence in different crystalline forms and volumes. 
First, we have diamond, crystallized in the regular system, its primary form being 
the regular octahedron, and having a specific gravity of 3521; and graphite, erystal- 
lized in regular hexagonal prisms, with a specific gravity of 2-177 when in fine powder, 
due allowance being made for the ashes. But besides these, the author had found, 
by the microscopical examination of the fine powders of coke, anthracite and charcoal, 
that there are two other modifications which have not hitherto been distinguished. 
Coke is crystallized in the regular system, its primary form being a cube, and its den- 
sity quite different from diamond, viz. 1°891; and its properties varying so much in 
other respects, that it is obviously a totally different modification of carbon. The 
specific gravity of coke and that of graphite are however related to one anotherin the 
ratio which mathematical calculation shows they ought to be, if they are supposed to 
consist of spherical atoms of precisely the same size, arranged in the different man- 
ners indicated by their respective crystalline forms. ‘Their relations to heat and elec- 
tricity also agree with that supposition, 
Anthracite and charcoal have a form and volume differing from any of the others, 
being crystallized in the square prismatic system, the axes being to one another as 
5, 5 and 3, and the specific gravity being 1°773, or one-half that of diamond; whereas 
its specific heat is double. Anthracite, lamp-black and charcoal belong to this form; 
and when their specific gravities are determined with proper precautions, they agree 
very closely, that of anthracite being 1-760, lamp-black 1°774, and charcoal 1-784. 
The properties of this form are different in important particulars from those of any 
of the others, the most marked between it and coke being, that it is very much softer 
and a much worse conductor of electricity. By exposure to a low red heat, no change 
is produced in it; but when heated to a bright red or white heat, its change in pro- 
perties shows that it is converted, as far as regards its ultimate atoms, into the coke 
form, but not in its crystalline structure or specific gravity, and it is therefore 
pseudomorphous. 
On a direct Method of separating Arsenious from Arsenic Acid, and on its ap- 
plication to the estimation of Nitric Acid. By Jamus Stein, of Glasgow. 
Chemists have not as yet been supplied with a method for the direct separation of 
arsenious from arsenic acid. In the course of an investigation on the salts of arsenious 
acid, with which he was lately engaged in Prof. Liebig’s laboratory, the author ob- 
served a fact which led him to a solution of this problem. He found, that, on adding 
arsenite of ammonia to a solution of sulphate of magnesia, no precipitate was formed 
in the presence of free ammonia or chloride of ammonium, provided these bodies were 
present in sufficient quantity; and further, that a previously-formed precipitate was 
redissolved by these reagents. Now Prof. H. Rose has given us a very exact method 
of estimating arsenic acid by precipitation as ammonio-arseniate of magnesia, similar 
to the process usually employed for the determination of phosphoric acid. M. Stein 
accordingly found that arsenic acid might be precipitated from a fluid containing arse- 
nious acid, while the latter remained in solution and was easily filtered off. He did 
not think it necessary to make any quantitative separation of these acids, as he con- 
sidered that if the arsenious acid were thoroughly washed out, the completeness of 
the separation would be apparent from Prof. Rose’s paper. The evidence, however, 
that it was so, he has also indirectly supplied in testing the following process for the 
estimation of nitric acid, to which he soon perceived the above might be applied. 
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