ATOMIC WEIGHTS 



129 



The experiments of Dean ' on silver cyanide, may be conveniently sum- 

 marized here, althongii they involve nitrogen as well as carbon. Dean's 

 object was to determine the atomic weight of nitrogen, the values for 

 silver and carbon being supposedly known. The cyanide was dissolved 

 in nitric acid, or, in the last experiment in sulphuric acid, and its con- 

 tent of silver was determined by titration Avith a standard solution of 

 potassium bromide. The silver equivalent of the latter compound was 

 previously fixed by titration against a definite solution of silver. The 

 weights obtained, corrected to a vacuum, are subjoined, together with a 

 column giving the percentages of silver : 



Mean, 80.567, ± .0010 



Still another pair of ratios, involving bromine, were measured by 

 Scott.' Tetra?thylammonium bromide, purified with great care, was 

 titrated with silver solutions of known strength. The results obtained, 

 with vacuum weights, were as follows : 



Mean, 194.870, ± .0045 



A single experiment with the corresponding tetramethyl compound 

 was also made. 8.64585 grammes of (CH3)^]SrBr are equivalent to 

 6.05348 of silver. Eatio, 142.824, ±.0123, when the probable error is 

 assumed equal to that of one experiment in the ethyl series. From these 

 figures Scott deduces a value for the atomic weight of carbon mucli 

 higher than that given by the direct : C ratio. 



iJourn. Chem. Soc, 77, 117. 1900. 

 ='Journ. Chem. Soc, 95, 1200. 1909. 



