THE GEOLOGIS'T* 



Moreover, I am convinced that this formation of sulphate of iron hy 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 insecticidal 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 hj Dr. Apelt, under the name of SchwefelkoJd, 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 Erazils to Europe. 

 It was cut in the form of the " Eegent;" its height is 43 millimetres, its 

 diameter being 53 millimetres. A mineralogical 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 Eeaumont was of this opinion when he 

 first saw the new Brazilian stone, about eighteen months ago. The 

 following are the characters AT. 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 test 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, wath 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. Eor, 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 



y Dr. Apelt's process lias been described in our Paris contemporary Le Cosmos, 

 t. iii. p. 141 d. S('(7. \\liere it was inserted on the demand of Baron Ales, tou 

 Humboldt.— T. L. P. 



