183^.} Seimtifie Moti6e9^MiH&alogy. Ui 



platina dish, they begin at first to melt, and afterwards, by i 

 slight explosion, accompanied by a flash of light, they decompose 

 themselves into oxygen gas, and the green protoxide of chrome. 

 The chromic acid which has been dissolved in the water does 

 not present this phenomenon. It fuses dming its decomposition, 

 but it does not give a flash of light. This difference does not 

 arise from its containing water, for it is perfectly free from it 

 when it is heated to a little above 100° centigrade. 



M. Unverdorben had already observed, that crystals of chro- 

 mic acid introduced into ammoniacal gas, are decomposed with 

 a flash of light. The ammonia is destroyed, and the acid 

 leaves the protoxide as a residue. It is necessary to make these 

 experiments quickly, as the crystallized acid is deliquescent. 



In distilling chromate of lead with chloride of sodium, we 

 obtain a gas similar to the preceding, and which contains chrome 

 combined with chlorine in such proportions that the water, by 

 its decomposition, gives rise to the formation of the hydrochloric 

 and chromic acids. The gas is red, and may be collected over 

 mercury, but it is very much charged with chlorine, when it is 

 prepared by means of the common concentrated sulphuric acid, 

 Whose water of combination destroys a certain quantity of sks. 

 -"(Edin. Jour, of Science.) 



Mineralogy. 

 3, Arseniate of Iron. 



(To the Editors of the Annals of Philosophy.} 

 GENTLEMEN, Glasgow, Jan. 9, l8?6. 



In the January number of the Annals, p. 23, there is inserted 

 a letter of Prof. Berzelius to M. A. Brogniart, in which that 

 excellent practical chemist gives the result of his analysis of two 

 varieties of arseniate of iron, and you express, in a note, some 

 doubt about the meaning to be affixed to Berzelius's statement. 

 The French expression which you transcribe is obviously non- 

 sense; owing probably to a typographical error in the periodical 

 work from which you copied it. Luckily you have given us 

 Berzelius's formulae, from which the constituents of the mine- 

 rals, according to his view of the subject, are sufficiently 

 obvious. Perhaps I may make the nature of these arseniates 

 obvious to the readers of your work by translating his formulae 

 into English. 



1. The Villa RicCa specimen is a compound salt composed of 



1 atom protarseniate of iron, 



2 atoms perarseniate of iron, 

 12 atoms water. 



2. The second species is the cube ore of mineralogists ; for 

 ! tteed htrdly ttite that the word wurfelerz is not the name <Jf a 



l2 



