60 



Dr H. D. Thomson on Hair Salt, or 



[July 



means a steady compound, as I have never obtained the 

 same quantity of alumina, and have found that of the 

 acid to vary considerably. That the latter is often in excess 

 is evident, from the salt tasting sour in many instances, 

 while at other times it is nearly tasteless. Mr. Phillips 

 informs us that he found the proportion of alumina less, 

 in a second trial which he made, than in his first analysis, 

 although the difference was not so considerable as to in- 

 duce him to repeat his experiments. 



The specimens which I examined were from Campsie, 

 and consisted of silky, albestus-like threads, mixed with 

 pieces of shale and sulphate of iron, which were carefully 

 excluded before dissolving the salt. 



It is very soluble in water, and often possesses a styptic 

 taste, from the presence of minute portions of sulphate of 

 iron ; 5 grs. introduced into a platinum crucible, and exposed 

 to the heat of a spirit lamp, lost, without altering in colour, 

 2-13 grs. By an additional heat, which rendered the salt 

 reddish, 0-03 disappeared. If we suppose that all the water 

 was expelled in the first experiment, without decomposing 

 the compound in any degree, we obtain a per centage of 

 42*6 ; by the second we have 43*6. 



The following table contains the result of three analyses 

 of hair salt from Campsie : 



In these experiments the composition is, 

 First. 

 Sulphuric acid . . 6' 5 

 Protoxide of iron . . 4-4 

 Alumina . . . . 1*1 



Water 39-8 



To represent the composition by these analyses, we have 

 the formulae respectively : — 



