ATOMIC WEIGHTS 117 



Penny ' dissolved silver in nitric acid in a flask, evaporated to dryness 

 without transfer, and weighed. One hundred parts of silver thus gave 



of nitrate: 



157.430 

 157.437 

 157.458 

 157.440 

 157.430 

 157.455 



Mean, 157.4417, ± .0033 



Marignac's ^ results were as follows. In the third column they are 

 reduced to the common standard of 100 parts of silver: 



68.987 grm. Ag gave 108.008 grm. AgNO.. 157.433 



57.844 " 91.047 " 157.401 



66.436 " 104.592 " 157.433 



70.340 " 110.718 " 157.404 



200.000 " 314.894 " 157.447 



Mean, 1574236, ± .0061 



Corrected for weighing in air this becomes 157.449. 



Stas," employing from 77 to 405 grammes of silver in each experiment, 

 made two different series of determinations at two different times. The 

 silver was dissolved with all the usual precautions against loss and 

 against impurity, and the resulting nitrate was weighed, first after long 

 drying without fusion, j^^st below its melting point; and again, fused. 

 Between the fused and the unfused salt there was in every case a slight 

 difference in weight, the latter giving a maximum and the former a 

 minimum value. 



In Stas' first series there are eight experiments; but the seventh he 

 himself rejects as inexact. The values obtained for the nitrate from 100 

 parts of silver are given below in two columns, representing the two con- 

 ditions in which the salt was weighed. The general mean given at the 

 end I have deduced from the means of the two columns considered 

 separately : 



1 Phil. Trans., 1839. 



^ Oeuvres Completes, 1, 88. From the sum of the weights, corrected to a vacuum, Marignac 

 computes the ratio 1 : 157.455. 

 ' Oeuvres Completes, 1, 346, 724. 



