210 THE ATOMIC WEIGHTS. 



By Van der Plaats* three methods of determination were ado])ted, 

 and all weights were reduced to vacuum standards. First, silver was 

 precipitated from a solution of the sulphate by means of phosphorus. 

 The latter had been twice distilled in a current of nitrogen. The silver, 

 before weighing, was heated to redness. The phosphorus equivalent to 

 100 parts of silver is given in the third column. 



.9096 grm. P gave 15.8865 Ag. 5.7256 



.5832 " 10.1622 " 5-7389 



Mean, 5.7322, ± .0045 



The second method consisted in the analysis of silver phosi)hate ; but 

 the process is not given. Van der Plaats states that it is difficult to be 

 sure of the purity of this salt. 



6.6300 grm. AggPO^ gave 5.1250 Ag. 77.300 per cent. 



12.7170 " 9-8335 " 77.326 " 



Mean, 77.313, ± .0088 



In the third set of determinations, yellow phosphorus was oxidized by 

 oxygen at reduced pressure, and the resulting P.^Oj was weighed. 



10.8230 grm. P gave 24.7925 PjOg. Ratio, 2 29072 



7.7624 " 17.7915 " " 2.29201 



As these figures fall within the range of Schrotter's, the}' maybe aver- 

 aged in with his series, the entire set of twelve determinations giving 

 a mean of 2.28955, ± .00032. 



From the following ratios an equal number of values for P may now 

 be computed : 



(i.) 2P : PjOj : : i.o : 2.28955, ± .00032 

 (2.) 3Ag : PCI3 : : 100 : 42-4553, ± .0036 

 (3.) 5^5 : P : : 100 : 5.7322, ± .0045 

 (4.) AggPO^ : 3Ag : : 100 : 77.313, ± .0088 



Starting with = 15.879, ± .0003, Ag = 107.108, ± .0031, and CI = 

 35.179, ± .0048, we have— 



From ( I ) P = 30. 784, zb .0077 



From (2) " zz= 30.S82, ± .0189 



From (3) " ;=r 30.698, ± .0241 



From (4) " = 30.774, ± .0382 



General mean P = 30.789, zh .0067 



If = 16, P = 31.024. 



The higliest of these figures is that from ratio number two, represent- 

 ing the work of Dumas. This is })0ssibly due to the presence of oxy- 

 chloride, in traces, in the trichloride taken. Such an impurity, if present, 

 would tend to raise the apparent atomic weight of phosphorus. 



*Compt. Rend., 100, 52. 1885. 



