434 
THE GEOLOGIST. 
Moreover, I am convinced that this formation of sulphate of iron by the 
pyrites in contact with the atmosphere determines also the production 
of a certain quantity of carbonic acid gas at the expense of the organic 
elements of the lignite. So that, besides the iusecticidal properties 
recognised by M. Millot-Brute, and its efficacy as a remedy for grape 
disease, this black earth will furnish to plants the two principal ele- 
ments of their nutrition, namely, carbonic acid and ammonia. 
We will add, in conclusion of this subject, that the friable, pulverulent 
lignite impregnated with pyrites, of which we have been speaking, has 
been applied with success by Dr. Apelt, under the name of Schwefelhohl, to 
preserve timber, more particularly that employed in railway-construc- 
tions.'^'' 
About a year and a half ago, a precious stone, supposed to be a diamond, 
weighing nearly 25 ounces, or 819 carats, and which was valued 
at some millions of francs, was brought from the Brazils to Europe. 
It was cut in the form of the " Eegent ;" its height is 43 millimetres, its 
diameter being 53 millimetres. A miueralogical consultation has been 
held on this stone at Vienna, and M. Haidinger, who formed part of 
the commission, has just published the result of this inquiry ; — The 
pretended diamond turns out to be a topaz, having the double refrac- 
tion, the specific gravity, the hardness of ordinary topazes, and being 
"Worth simply (as a curiosity) from 225 to 250 francs, or about £10. 
It appears also that M. Elie de Beaumont was of this opinion when he 
first saw the new Brazilian stone, about eighteen months ago. The 
following are the characters- JVI. Haidinger assigns to it : — 
It is perfectly transparent, having the dimensions and weight 
mentioned above, and possessing a slight blue tint. Being a transparent 
substance the phenomenon of simple refraction would have immediately 
indicated a diamond or an artificial stone — double refraction would have 
led to the supposition that the stone was quartz, white beryl, or 
topaz. M. Haidinger assured himself that the Brazilian stone pos- 
sessed double refraction, and that its specific gravity was 3"57 (that of 
the topaz has been given by some authors 3-56) ; its hardness was also 
proved to be precisely that of the topaz, for the two minerals, when 
rubbed together, scratched one another. There exists, therefore, no 
doubt that this Brazilian stone is a fine topaz. 
The salts of the metal called Cerium, which up to the present time 
has only been discovered in a few of the rarer species of minerals, have 
lately been found by Messrs. Damour and H. Ste-Claire Deville, to 
constitute a good and, delicate tost for recognizing the presence of 
phosphoric and arsenic acids. It was observed that an acid solu- 
tion of any phosphate will produce a voluminous precipitate, of a white 
or yellowish colour, with acid solutions of either sulphate or nitrate 
of cerium. Arseniates act in the same way. 
This is rather important to mineralogists, as it procures them an easy 
method of recognizing the presence of cerium in minerals. For, if acid 
salts of cerium can be employed with advantage to detect phosphoric 
and arsenic acids, the latter, or their acid salts, may naturally be used 
~ Dr. Apelt's process has been doscribcd in our Paris contemporary Le Cosmos, 
t. iii. p. 141 H scq, where it Avas inserted on the dcuiaud of Baron Alex, voa 
Humboldt.— T. L. P. 
