534 
COLONEL P. YOEKE’S EESEAECHES ON SILICA. 
With regard to the arguments in favour of the first-mentioned formula, derived from 
a consideration of the boiling-point of chlorides and bromides, I should mention that 
M. Kopp, since the publication of a notice by Mr. Duppa communicated to the Eoyal 
Society by Dr. Hofmann, has appended to a translation of this note some remarks of his 
own*, in which he states that the law he had suggested cannot now, in its primitive 
generality, be regarded as true. 
From what has preceded it may be observed, that the only instance in which the 
formula of silicic acid has been sought for by a direct method, as for example, in which 
its equivalent has been determined by the quantity of some other acid displaced, is in 
the experiments of Rose. These experiments, however, which are introduced inciden- 
tally in a memoir on titanic acid, have not generally attracted the attention of authors of 
chemical systems, but as it appeared to me that the method deserved preference over 
the others which have been used, or any that I could devise, I resolved to repeat the 
experiments, entertaining the notion that if the results were confirmed, this ought to 
establish the formula which they had suggested to Rose. 
I imagined that with the means I meant to apply, what I had in view would prove an 
easy matter ; in this I was deceived ; but though I am still unable to give a definite 
answer to the question which I had proposed to myself, I have obtained some results 
which I venture to think have interest, and which, under the uncertainty I am in of the 
time it may take before I can complete these researches, I desire to offer to the Society 
in their present state. 
Experiments on the quantity of Carbonic Add expelled from excess of 
Alkaline Carbonates by fusion with Silica. 
The silicic acid used was obtained by the ignition of perfectly transparent and colom-- 
less rock-crystal, and subsequent reduction of this to powder. The carbonate of potash 
was produced by the ignition and subsequent fusion of crystallized bicarbonate of pot- 
ash. The carbonate of soda was mostly obtained by a similar treatment of the pimest 
bicarbonate I could procure, though a few experiments were made uith some cai'bonate 
obtained by the purification of the crystallized carbonate, by Gay-Lussac’s method. 
In my earlier experiments I adopted methods varying a little from one another, of 
adding the silicic acid to the alkaline carbonate, whilst in a state of fusion, in a platinum 
crucible ; after some experience I found that it was in all respects a better plan to add 
the alkali to the silica. The latter was placed in a counterpoised platinum crucible, 
and weighed ; the fused alkaline carbonate in fragments was then weighed in a comiter- 
poised closed glass tube, then gradually added to the silica heated in the crucible, and the 
tube again weighed, by which the quantity of alkaline carbonate was determined. The 
heating was performed by a gas-flame, through which a stream of air was forced by 
means of a table bellows. The crucible was heated for some time after all efiervescence 
had ceased, and the materials used appeared in a quiet state of fusion. The crucible 
* Ann. de Chim. &c. 3 ser. xlvii. 66. 
