Manchester Memoirs, Vol. I. (1906), No. VI. 9 



tion of 0'2 gramme cadmium sulphate, a mirror equivalent 

 to 4 c.c. was obtained. 



I dissolved 0'5 gramme of nickel in 100 grammes of 

 pure zinc, and tried this alone ; it gave no mirror. I then 

 added 4 c.c. of standard As^Og solution, and it gave a 

 mirror equal to that obtained when pure zinc is employed 

 in the manner previously recommended by me.* On 

 repeating this with the addition of 0'2 gramme of cadmium 

 sulphate a mirror of about the same size was obtained. 

 Even I c.c. of the standard solution (which is equivalent 

 to 0'000,ooo,7i4 gramme of AS4O6) gave the full mirror. 

 Thus the zinc nickel alloy was quite as sensitive as pure 

 zinc, although it dissolved much more readily in the 

 sulphuric acid, and the addition of 0'2 gramme of cad- 

 mium sulphate made no difference in the size of the 

 mirrors obtained. 



We then made alloys of zinc with 0*5 gramme of 

 cobalt, iron (in the form of wire), and copper respectively, 

 and of these iron shewed the most marked retention of 

 arsenic, for from 20 c.c. of standard arsenic solution a 

 mirror equivalent to about 3 c.c. was obtained, whereas 

 cobalt and copper gave mirrors corresponding with about 

 20 c.c. in each case. 



The addition of 0'2 gramme of cadmium sulphate 

 increased the sensitivity of the iron alloy, a mirror equi- 

 valent to about 10 c.c. being obtained from 20 c.c. of the 

 standard arsenic solution. 



It seems to me that the action of cadmium sulphate 

 in rendering zinc and other metals more sensitive in the 

 determination of arsenic in the Marsh-Berzelius apparatus 

 must be further studied. 



I have pleasure in stating that I am indebted to the 

 care and ability which has been shewn by my assistant, 

 Mr. Edwin Hopkinson, M.Sc. (Vict.), in carrying out these 

 experiments. 



* British Food Journal, vol. 4, nos. 44 and 45. 



