Selenium in Commercial Sulphuric Acid. 317 



the acid, attributing the bad colour in the oils to a tank of 

 tlie other maker's vitriol, which by some inadvertence had 

 been allowed to pass into the relinery. Three days were 

 allowed to elapse, when, in place of the oil getting better in 

 colour, it grew worse. The supply of both these makers' 

 acid was then stopped, and an acid which we knew to be pure 

 used in the refinery. 



I told my friend Mr Hunter of our difficulties with the 

 oil, and of my opinion that there was something seriously 

 wrong with the acid, which had given the indigo and not the 

 iron reaction. He advised me to bring in a sample, and we 

 would examine it together. One of the results of this ex- 

 amination was, that it contained practically no nitric acid, 

 and yet it gave the sulphate of indigo reaction. The other 

 result was, that there was something foreign in the sul- 

 phuretted hydrogen precipitate, as it was reddened to a con- 

 siderable extent. A portion of this precipitate, with gentle 

 heating, almost completely dissolved in ammonium sulphide, 

 leaving a very slight black residue, which was at the time 

 thought, and afterwards proved to be, lead. Another portion 

 was boiled with ammonium carbonate, when the yellow 

 arsenic sulphide dissolved, and left a reddish brown residue, 

 which was reduced by the action of stannous chloride. This 

 strange residue was at once put down as the cause of our oil 

 going back in colour, but we had not at that time sufficient 

 leisure to go into the matter further. 



In the meantime our oil had come back to its original 

 colour, with the acid which we knew to be free from any 

 impurities, and this of course almost conclusively proved 

 that there was no fault in the process. But, in order to further 

 prove that it was the faulty acid which had done the damage, 

 it was again allowed into the refinery, when the same symptoms 

 were noticed. 



As this could not be allowed to go on, an official sample 

 of the acid was sent to Mr King and ]\Ir Hunter, wdien they 

 in a few days reported that the only thing that was peculiar 

 about the acid, was the presence of an element resembling 

 selenium, and which they thought was selenium. On further 

 examination the impurity was conclusively shown to be 



