338 ACCOUNT AND DESCRIPTION 



grains were magnesia. These crystals of sulphat of magnesia, 

 had a very slight tinge of green, a circumstance which was 

 doubtless connected with the dark appearance of the magnesia, 

 when first heated. It shall be resumed presently. It should 

 be observed, that in some of the experiments with sulphuric 

 acid, on the supposed magnesia, a white matter, in small quan- 

 tity, remained undissolved at the bottom of the vessel. It 

 could hardly be silex, and preliminary experiments led me to 

 conclude that no lime was present. Was it accidental, or was 

 there a small portion of alumine? This white matter, when 

 heated with sulphuric acid, and sulphat of potash, didjnot af- 

 ford crystals of alum, on evaporation. I have not. yet had lei- 

 sure, fully to decide this point, but, intend to resume it. The 

 stone has a very slight argillaceous smell, when breathed upon. 



8. The remaining solution still retained its greenish colour. 

 Previous trials had decided that neither copper nor iron was pre- 

 sent in the solution. Nickel was therefore sought for, and the 

 observation of Howard and Vauquelin, in their analyses of the 

 stone of Benares, led me to expect it in triple combination with 

 the ammoniacal metal and muriat, which had been formed in 

 the liquor by a previous step of the process. — According to the 

 experience of Howard, I found the hydro-sulphuret and the 

 prussiat of ammonia, the only agents among those which I tri- 

 ed, that would precipitate the nickel. The prussiat of ammo- 

 nia gave a white precipitate, inclining to purple; the hidro- 

 sulphuret of ammonia, a voluminous black precipitate. The 

 hidro-sulphurct was used, and the precipitate was separated by 

 the filter. The filter being dried, it was with great difficulty 

 that about three fourths of a grain were collected. The portion 

 adhering to the filter, was estimated at about a grain. That 

 which had been collected was ignited, in a platinum crucible, 

 and became green. It was, without doubt, the oxid of nickel, 

 and, with every allowance for loss and other circumstances, 

 the whole cannot be estimated at more than 1,5 grain. In this 

 estimate is included a portion of nickel, adhering to the 

 magnesia, when it was precipitated, which caused it to turn 

 black, when first heated, gave the sulphat of magnesia for- 

 med from it, a slightly greenish tinge, and whose existence 



