46 



quantity and combination of the water they contain, being more 

 properly arseniates of hydrate of copper. 



This first species is not to be put on the same footing with the 

 others ; since, by admitting a due proportion of water, it would, by 

 calculation, be reduced to a lower class than that which it really 

 occupies. 



Lastly, the proportion of acid in each of the species except No. 2. 

 is here assigned. And as to this last- mentioned species, it is observed, 

 that it is to be considered as a particular variety, consisting of a much 

 greater proportion of oxide, with a less quantity of water, combined 

 with nearly the same proportion of arsenic acid. 



After having carefully examined the natural arseniates, Mr. Che- 

 nevix paid some attention to a few artificial ones, being precipitates 

 from nitrate of copper, by an arseniate of ammonia. And here he 

 found very different proportions of the ingredients, the arsenic acid 

 in one species being no less than 40 per cent. Hence we gather, 

 that only two simple ingredients, combined in four different pro- 

 portions, produce no less than eleven different species or com- 

 binations, which are now determined both by external and chemical 

 characters. 



Speaking next of the arseniates of iron, Mr. Chenevix observes, 

 that they have but lately been distinguished from those of copper. 

 One species, in fact, contains a sufficient proportion of this last metal 

 to merit the name of cupreous arseniate of iron. This proportion was 

 27'5 of iron to 22'5 of copper, both in the oxide state ; the arsenic 

 acid amounting to 33'5, whilst 12 of water and 3 of silica made up 

 within 1| the 100 parts on which the experiment was tried. The 

 proportions of what is properly called the arseniate of iron were 

 45 oxide of iron, 9 oxide of copper, 31 arsenic acid, 10 water, and 

 4 silica. Upon this ore are often seen certain crystals of a cubic 

 form and of a deep brownish red, which, according to Count de 

 Bournon, are in a state of decomposition. These were found to con- 

 tain but little acid or water, probably owing to their decomposition. 



Artificial arseniates of iron, produced by the decomposition of green 

 and red sulphate of iron by arseniate of ammonia, were next examined. 

 The ingredients of the green arseniate were found to be, 43 oxide of 

 iron, 38 arsenic acid, and 19 water ; and of the red arseniate, 36'5 

 oxide of iron, 41 '5 arsenic acid, and 20 water. 



Observing in the course of these experiments a great variety of 

 appearances assumed by the combinations of iron with salts, the 

 oxygen, and other ingredients, the author enters into a curious in- 

 quiry on this subject ; from which he deduces, in particular, the great 

 variety of colours exhibited by that metal in divers stones or fossils, 

 in which that variety, he infers, is derived from the different degrees 

 of oxygenation of the iron. 



In a third section the author enters into an analysis of a red 

 octaedral copper ore found in Cornwall, of which he had occasion to 

 examine several specimens in the preceding investigation. After 

 describing several fruitless attempts, chiefly by means of acids, to 



