Anahfu of the Spinel Ruhy. 45 



X. 1 united the five parts of Ex. VI. and the two parts of 

 Ex. IX ; boiled them five or fix times fucceffively in a por- 

 celain vefiel with concentrated nitric acid, evaporating each 

 time to drynefs. The matter at firft affumed a beautiful dark 

 green colour, and at the end of each operation it boiled and 

 was puffed up like alum. At laft, when the greater part of 

 the acid was evaporated, and the matter began to dry, it af- 

 fumed an orange yellow colour. After treating the matter 

 in this manner, I mixed with it a little pure cauftic potafh ; 

 and when the mixture was well formed and reduced to a 

 kind of pafte, I diluted it with diftilled water, in which al- 

 moft the whole of the matter was diflblved. Nothing re- 

 mained but a little grey matter which weighed about i-£ 

 parts, and which I found to be filiceous earth. The alka- 

 line folution had a weak golden yellow colour ; and as it con- 

 tained an excefs of alkali, I added, in order that it might be 

 faturated, a few drops of nitric acid. By this addition there 

 was produced a {light white precipitate, which weighed at 

 mod one part, and which appeared to me to be aluminc. 

 The liquor had then a reddifh colour. 



XI. As I fufpecled, from all the phenomena which had 

 appeared during the courfe of this analyfis, that the colour- 

 ing matter of the ruby was chrome, I mixed the liquor of 

 the preceding experiment, firft, with nitrat of lead, and I 

 immediately obtained a precipitate of a beautiful orange- 

 yellow colour ; fecond, with nitrat of mercury, and there 

 was produced a depofit of a cinnabar red colour; and, third, 

 with the nitrat of filver, which gave a precipitate of a crim- 

 fon red colour. I was convinced by thefe phenomena that 

 the ruby, like the emerald of Peru, contains a certain quan- 

 tity of chrome, to which it is indebted for its colour. But it 

 feems difficult at firft to reconcile the colour of the emerald 

 with that of the ruby, by referring them to the fame fub- 

 ftance ; for nothing feems more remote from green than 

 red. If we however recollect that this metal is lufceptible 



of 



