86 THE ATOMIC WEIGHTS. 



Dumas and Pelouze's series combine as follows : 



Pelouze 39.4447, zt .0083 



Dumas 39-377> ±.014 



General mean 39.4265, ± .0071 



Hence SiCl, = 169.810, ± .034. 



Schiel,* also studying the chloride of silicon, decomposed 

 it by ammonia. After warming and long standing it was 

 filtered, and in the filtrate the chlorine was estimated as 

 AgCl. One hundred parts of AgCl correspond to the quan- 

 tities of SiCl^ given in the last column : 



.6738 grm. SiCl^ gave 2.277 g™i- ^gCl. 29.592 



1.3092 " 4.418 " 29.633 



Mean, 29.6125, zb .013S 



Hence SiCl, = 169.437, ± .080, and Si = 27.957. 

 Combining the values for SiCl^ we have this result : 



Pelouze and Dumas SiCI^ ^ 169.810, ^ .034 



Schiel " = 169.437, ±z .080 



General mean ♦' = 169.675, zb .031 



Hence Si = 28.195, ± .066; or, if = 16, Si = 28.260. 



It will be observed that all of these determinations rest 

 upon the composition of SiCl4, a compound for which it 

 would not be easy to guarantee absolute purity. All the 

 errors likely to occur in the determination of the atomic 

 weight would be plus errors, so that the value deduced 

 above is almost certainly too high. 



*Ann. Chem. Pharm., 120, 94. 



