186 TURQUOIS STONE. 



lange of our stOHes, by concluding that they have less tena- 

 city. 



Aquaregia likewise acts differently upon these two kinds 

 of stone. It totally dissolves ours, and it reduces those of 

 Persia into a kind of paste, more whitish than the turqiiois 

 was, but which is not, nevertheless, deprived of all its blue co- 

 lour. 

 Tm^Boises -^'^ general, this kind of stone has a singular defect ; namely, 



lose u*ieir co- that, without the assistance of any other agent than that of time. 



lour, and their 

 Talae bydmc. 



their colour changes : insensibly their blue assumes a shade of 

 green, they become greenish, and at last green ; whereas the 

 colour of other precious stones is unchangeable. When the 

 turquoises have become green, they are no longer of any value; 

 the convention of society has placed them in no estimation 

 whatever with that colour. 



Chemical Examination. 

 Characters of Physical characters. Specific gravity, 3.127. — Colour, light 

 theuaquois. gfeen and blue ; surface, smooth or polished; hardness, such 

 as slightly to scratch glass ; difficult to be pounded ; powder, 

 greenish grey; fracture, polished. 

 Hab"* d '1th Chemical characters. Before the blow-pipe, it loses its 

 the blow-pipe, colour, and becomes of a greyish white, but does not melt. 



Heated in a crucible of platina, it acquires the same colour, 



but becomes friable, and is easily reduced to powder. In this 



experiment it loses 6 per cent, of its weight. 



Soluble inn" T\^'& nitric and muriatic acids totally dissolve the turquois, 



neraJ acids. The solution, in the latter aciJ, is yellow ; and that in the 



nitric, is colourless. 

 Kiiiic solution. The nitric solution presented the following phaenomenon : — 

 I. with lime-water, a white flaky precipitate — 2. by ammonia 

 in excess, a precipitate of the same colour, but more abun- 

 dant: the supernatant fluid did not acquire any bluish tinge 

 — 3. carbonate of ammonia likewise gave a precipitate — 

 4. with the oxalate of ammonia, the precipitate was very light 

 and very divided — 5. precipitate of pot-ash gave a deep blue 

 precipitate. 



These preliminary experiments already afford an approxi- 

 mation to a knowledge oF the ctmstituent parts of the turquois ; 

 they are not sufficient to lead to a regular classification. I 

 therefore chose out of a certain quantity of turquoises, those 



which 



