j<j Analyfis of the Spinel Ruhr. 



colour, as well as by a paffage of Klaproth, in which ho fays, 

 that magnefia extracted from that precious ftone, being dif- 

 fo'.ved in the fulphuric acid, had given to it a green colour. 

 The rubies of different colours preferved in collections, fuch as 

 the fapphire-blue in the poffeffion of the Hon. Mr. Greville, 

 the green belonging to Mr. Hawkins, and the white in the 

 collection of Mr. Macie of London, authorifed me to fufpeel: 

 that iron is not the colouring principle of that ftone. 



Thefe different confiderations induced me to make a new 

 analyfis of the fpinel ruby : and the refult of this labour 

 will prove, that my doubts were not without foundation, 

 and that it not only does not contain a fingle particle of the 

 oxydof iron, but that there is evennofiliceous earth in it, as 

 announced by Klaproth. The rubies employed for this ana- 

 lyfis were cryftallifed, tranfparent, and free from any foreign 

 mixture. 



Exp. I. A hundred parts of this ftone being expofed to a 

 violent heat, loft nothing of their weight, but their tint was 

 weakened and changed to a rofe colour, 



II. A hundred parts of the fame ftone reduced to a fine 

 powder, and ftrongly heated in a charcoal crucible, were ag- 

 glutinated into one mafs of a grecnifh grey colour. 



III. A hundred parts of the fmall fragments of rubies re* 

 duced to an impalpable powder in a mortar of filex, were in- 

 creafed fiye parts. 



IV. I heated for anhour, inafilvercrucihle, ioopartsofa ru- 

 by thus pulverifed, with 300 partsof cauftiepotafh : themixture 

 was not fufed ; on the contrary it was reduced to a pulverulent 

 mafs of a green colour, of which fome particles were merely 

 agglutinated. I mixed this with diftilled water, in which it 

 was all fo nearly diffolved that there remained of it only fome 

 particles which weighed fcarcely three parts. I poured upon 

 the folution, which remained ftill mixed with the undilTolved 

 matter above-mentioned, fume diluted muriatic acid. The 

 firft portions of this acid made the folution affume the ap- 

 pearance of a mafs as thick as ibup-(!;ouillie), which was re- 



diuolved. 



