j t Analyjis of the Spinel Ruby. 



VIII. Thefe io' parts were diffolved by the fulphuric 

 acid. The folution had a greeniih colour. This folution 

 mixed with the faturated carbonat of potafh, precipitated a 

 greeniih matter, which, when waflied and dried, weighed 

 two parts. A fmall portion of this precipitate melted with 

 borax communicated to it a beautiful emerald green colour*. 

 This matter, which I placed apart, I fhall fpeak of hereafter. 



IX. As I had diflblved in the fulphuric acid 10*5 of mat- 

 ter, and as the carbonat of potafh precipitated only 2, there 

 muft have remained 8*5 in the folution. Sufpe&ing there- 

 fore that the matter was retained there by an excefs of the 

 carbonic acid, I boiled the liquor for fome minutes, and I 

 obtained a white granulated precipitate, weighing 16 parts, 

 which by calcination were reduced to 8. This matter, com- 

 bined with the fulphuric acid, gave a fait cryftallifed in te- 

 traedral prifms, terminated by pyramids with four faces, the 

 tafte of which was firft fweet, and afterwards bitter ; which 

 was not precipitated by the faturated carbonat of potafh j 

 was only partly To by ammonia ; and, in a word, which 

 prefented all the characters of fulphat of magnefia. 

 The ruby therefore, according to this experiment, fhould 

 contain 8 parts of magnefia in iooj but as \ part was want- 

 ing in that fubjecled to experiment, we may eftimate the 

 quantity at 8*5. 



*In heating the colouring matter of the ruby with borax over charcoal, 

 and flopping the operation before the effervefcence had ceafed, I have 

 twice obtained a vitreous globule of a red colour, perfectly fimilar to that 

 of the ruby ; but in heating again this red globule, the effervefcence was 

 renewed, and the globule became of an emerald green colour. In vain 

 did 1 afterwards try to make the red colour re-appear, whether I applied 

 the exterior or the interior flame of the blow-pipe. It is even very diffi- 

 cult to obtain, in the firft inftance, the vitreous globule of a red colour. It 

 is neceffary for that purpofe that the colouring matter mould not touch 

 the charcoal; that it fhould not be added till the borax is melted; and that 

 it fhould be heated with the exterior flame. Though I often attempted 

 to produce this phenomenon, I never fyeceeded but twice. 



X, I 



