210 THE ATOMIC WEIGHTS. 



By Van der Plaats* three methods of determination were adopted, 

 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. 5-7 2 56 



.5832 " 10.1622 " 5.7389 



Mean, 5.7322, .0045 



The second method consisted in the analysis of silver phosphate ; 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. Ag 3 PO 4 gave 5.1250 Ag. 77.3 P er 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 2 5 was weighed. 



10.8230 grm. P gave 24.7925 P 2 O 5 . Ratio, 2 29072 



7.7624 I7-79 J 5 " " 2.29201 



As these figures fall within the range of Schrotter's, they 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 : P 2 O 3 : : l.o : 2.28955, .00032 

 (2.) 3Ag : PC1 3 : : 100 : 42-4553, -0036 

 (30 5 A S : p : : I0 : 5-7322, .0045 

 (4.) Ag 3 PO 4 : 3Ag : : 100 : 77.313, .0088 



Starting with = 15.879, .0003, Ag = 107.108, .0031, and Cl = 

 35.179, .0048, we have 



From (i) P = 30.784, =fc .0077 



From (2) " = 30.882, .0189 



From (3) " 30.698, =b .0241 



From (4) " = 30.774, .0382 



General mean P = 30.789, .0067 



If = 16, P = 31.024. 



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

 ing the work of Dumas. This is possibly 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. 



