76 PROF. H. E. ROSCOE ON CERTAIN 



It is a common thing in Sulphuric-acid manufacture to 

 find the acid which has passed through the Gay-Lussac 

 tower of a deep red colour. This has been referred to the 

 presence of the lower oxides of nitrogen, their presence 

 being explained by the fact that the mixture of nitrate of 

 soda and sulphuric acid, used for the production of nitric 

 acid, has been heated to too high a temperature ; this may 

 be one good reason for it, but I think the arsenic must 

 also come in for a share of the blame. The arsenic is 

 expelled from the pyrites as arseniems acid, and, coming in 

 contact with the nitric-acid gas, is oxidized and converted 

 into arsenic acid, always causing, of course, a loss of nitric 

 acid, and in part a conversion of it into the lower oxides of 

 nitrogen. That such happens I have no doubt, as in the 

 deposit formed in the chamber I found clear and perfect 

 crystals of arsenic acid. 



But this seems like getting up a case of prosecution 

 against arsenic, and enumerating and multiplying the evils 

 manufacturers have to fight against. Whether greater 

 evils be found out or not, they have their work before them 

 in discovering methods of getting rid of their persistent 

 enemy. 



X. A Study of certain Tungsten Compounds. By Henry 

 E. Roscoe, B.A., Ph.D., F.R.S., Professor of Che- 

 mistry in Owens College, Manchester. 



Eead January 23rd, 1872. 



The formulae of the tungsten compounds, the atomic 

 weight of the metal, and even its elementary nature are 

 subjects upon which, for many years, serious doubts have 



