56 Dr. R. D, Thomson on Hair Salt, or [July 



becoming yellow by exposTire to the air, occurring in alum 

 slate, and found its chemical composition to be 



lOO-OOf 

 equivalent to 7 Al.S. + /S. + 31 Aq. 



2. The same chemist states that the hair salt from the 

 mercurial mines of Idria, (Halotrichum Scopolii), found in 

 alum slate, possesses a silvery white colour, and consists 

 essentially of sulphate of magnesia, united with a small 

 portion of sulphate of iron. According to a recent analysis 

 hair salt from Idria consists of 



Magnesia .... 16*389 - 1 atom. 

 Protoxide of iron . 0-226 - 

 Sulphuric acid . . 32-303 - 1 ,, , 

 Water 50-934 - 7 atoms. 



99-852f 

 which answers to MS. -f- 7 Aq. mixed with a little sulphate 

 of iron, agreeing exactly in composition with the right 

 prismatical crystals of the common Epsom salt. A similar 

 mineral from Calataynd, in Arragon, yielded, 



Magnesia .... 16*495 

 Sulphuric acid . . 31*899 

 Water 51*202 



99-596 



* Beitrage, iii. lOS, Chemische Untersuchung des federalauns von Freyen- 

 walde. 



t Beitrage, iii. 104. 



X Poggendorff, Annalen, xxxi. 144. 



