tarts and ob- oxide is also at 28 in 100. In this oxide, whose fragiticfiti 



tuIamUtscxw- ^''^ oqualiv vitreous with those of the artiricial, the condensa- 



poimd*k flon is so great, that when heated witli sulphur, it yields but 



slovvfy to disoxidation ; the process must be repeated two or 



fhree times, during which it emits sulphureous gas, and is at 



last changed into mosaic gold. 



White crystals ought, undoubtedly, to be replaced among 

 ores of tin, from which they have been separated for want of 

 firoper examination. It is true that tungstein has been fre- 

 quently taken for the white oxide ; but this last, though tare, 

 tloes not less positively exist. Among a collection of minerals 

 sent me from the mines of Monteray, in Gallicia, were three 

 %hite crystals, opaque, and quite disfigured by rolling about, 

 which I at first took to be tungstein ; but finding that, after 

 remaining in muriatic acid for a twelvemonth, they still re- 

 raained unchanged, I examined them again, and found they 

 were pure oxide ; these are the same which I changed into mo- 

 saic gold by sulphur. The grey and brown crystals also change 

 into this substance, but with more diflficulty ; their mosaic gold 

 is contaminated with sulphuret of iron ; it may be discovered 

 by muriatic acid ; it also retains some sand and small frag- 

 naents of undecomposcd crystals. 



A phenomenon not less interesting to the sight than the judg- 

 ment may be observed in the solution of indigo in potash, pre- 

 pared by the medium of the oxide at ihe minimum. Put indigo, 

 oxide, and liquid potash into a bottle, and stop the mouth quite 

 close ; let it be well shaken from time to time ; and when the 

 indigo has entirely disappeared and the liquor become of an 

 orange-yellow colour, proceed to the following experiment: 



Pour cold water into one glass ; boiling water into a second; 

 and hydro- sulphurated water into a third : then pour a few 

 drops of the indigo solution into each ; the water in the first, 

 glass will imjiicdiately become blue; that in the second, a, 

 beautiful orange-yellow ; and that in tlie third, will be similar 

 to the second. In all this we may perceive the influence of 

 the atmospheric oxigen. The indigo being disoxidated in the 

 solution instantly attracts the oxigen commonly suspended by 

 cold water, and resumes its primitive colour ; whilst the boil- 

 ing water, being deprived of its atmospheric aiy, fails to pro- 

 duces ft similar phenomenon. In the hydro-sulphurated water, 



n«» 



