40 THE ATOMIC WEIGHTS. 



Finall}^ there are seven determinations by Stas,* made Avitli his usual 

 accuracy and with ever}^ precaution against error. In the first, second, 

 and third, silver was heated in chlorine gas, and the syntliesis of silver 

 chloride tlnis effected directly. In the fourth and. fifth silver was dis- 

 solved in nitric acid, and the chloride thrown down by passing hydro- 

 chloric acid gas over the surface of the solution. Tiie whole was then 

 evaporated in the same vessel, and the chloride fused, first in an atmos- 

 ])here of hydrochloric acid, and then in a stream of air. The sixth syn- 

 thesis was similar to these, only the nitric solution ^vas precipitated by 

 hydrochloric acid in slight excess, and the chloride thrown down was 

 washed by repeated decantation. All the decanted liquids were after- 

 wards evaporated to dryness, and the trace of chloride thus recovered 

 was estimated in addition to the main mass. The latter was fused in an 

 atniosphere of HCl. The seventh experiment was like the sixth, only 

 ammonium chloride was used instead of hydrochloric acid. From 98.3 

 to 399.7 grammes of silver were used in each experiment, the operations 

 were performed chiefly in the dark, and all weighings were reduced to 

 vacuum. In every case the chloride obtained was beautifull}^ white. 

 The following are the results in chloride for 100 of silver: 



132.841 



132.S43 

 132.843 



132.849 

 132.846 

 132.848 

 122.8417 



Mean, 132.8445, dr .0008 



We ma}^ now combine the means of these seven series, representing in 

 all thirty-three experiments. One hundred parts of silver are equivalent 

 to chlorine, as follows : 



Berzelius 32-757, ± .0190 



Turner 32.832, ± .0038 



Penny 32.8363, i .0012 



Marignac 32.839, zh .0024 



Maumene 32.7364, dr .OO77 



Dumas 32.8755, =b .0044 



Stas 32.8445, dr . 0008 



General mean 32.84 1 8, ±z .0006 



Here, again, we have a fine example of the evident comy)ensation of 

 errors among different series of experiments. We have also another 

 tribute to the accuracy of Stas, since this general mean varies from the 

 mean of his results only within the limits of his own variations. 



*Aronstein"s translation, p. 171. 



