412 Scientific Proceedings, Royal Dublin Society. 
take the point #. The height of # will evidently represent the 
difference of the heats evolved by the solution of amorphous silica 
and quartz in hydrofluoric acid or other suitable reagent. I have, 
therefore, undertaken some experimental measurements on the 
subject. The difficulty of the determination will be at once 
apparent; for, especially in the case of quartz, the reaction isso slow 
at ordinary temperatures that it is practically impossible to measure- 
any rise of temperature that may occur. There is also the additional 
inconvenience that one’s thermometer must be covered with wax to 
prevent its being attacked by the hydrofluoric acid. Mr. J. B. 
Mackintosh! found that only 1:56 per cent. of powdered quartz was 
acted upon by a 9 per cent. solution of hydrofluoric acid in an hour, 
while in the same time 77°28 per cent. of similarly powdered opal 
was dissolved by the same acid. This in itself looked promising 
for a final result, if only the difficulties of slowness could be 
overcome. I determined to make use of Lavoisier’s form of ice 
calorimeter. A leaden crucible was obtained (platinum was too 
expensive) to fit the inner chamber of the calorimeter. This being 
half filled with the aqueous hydrofluoric acid, and the calorimeter 
carefully packed with ice and allowed to stand until the temperature 
had fallen inside, the powdered silicate was then introduced into 
the crucible and the calorimeter rapidly closed. A weighed flask 
was then placed in position, and the whole allowed to stand for 
from two to five hours, according to the velocity of the reaction. 
This ice calorimeter is at best avery rough apparatus, and it seems 
impossible to prevent some external heat entering the inner 
chamber, which has, therefore, to be estimated and allowed for in 
the final result. Ihave unavoidably been engaged on other work, 
and my experiments in this direction are really only in their pre- 
liminary stage. I hope to be able to give a full account of my 
work when it is completed. I may, however, say that I have got 
distinct indications of the large latent heat (or pseudo-latent heat 
at 0°, as I may call it,) in the case of quartz. This “latent heat ’” 
of adularia is also distinctly measurable, but I cannot, up to the 
present, get any appreciable difference between the heat generated 
by fused and unfused augite. I admit that my method is a rough 
one, perhaps too rough to give very trustworthy numerical results; 
but I hope it may be capable of improvement. 
1 J. B. Mackintosh, ‘‘ The Action of Hydrofluoric Acid on Silica and Silicates,’” 
School of Mines Quarterly, vol. vii., p. 384, and Chem. News 44 (1886), 102. 
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