188 THE ATOMIC WEIGHTS. 



If we reject the first three values, retaining only those due to the ex- 

 periments of Crookes and Lej)ierre, we have— 



Tl =^ 202.605, ± -O'oj 



If = 16, this becomes 204.149. This mean exceeds Crookes' deter- 

 mination only by 0.01, and may be regarded as fairly satisfactory. 

 Crookes' ratio evidentlv outweighs all the others. 



SILICON. 



Although Berzelius * attempted to ascertain the atomic weight of 

 silicon, first l)y converting pure Si into SiO^, and later from the analysis 

 of BaSiF'g, his results were not satisfactory. We need consider only the 

 work of Pelouze, Schiel, Dumas, and Thorpe and Young. • 



Pelouze,t experimenting upon silicon tetrachloride, emploj'ed his 



usual method of titration with a solution containing a known weight of 



silver. One hundred parts of Ag gave the following equivalencies of 



SiCl, : 



39-4325 

 39-4570 



Mean, 39.4447, zh .0083 



Essentially the same method was adopted by Dumas. J Pure SiCli 

 was "weighed in a sealed glass bulb, then decomposed by water, and 

 titrated. The results for 100 Ag are given in the third column : 



2.899 grni- SiCl^ = 7.3558 grm. Ag. 39.41 1 



1.242 " 3.154 " 39-379 



3.221 " 8. 1875 " 39.340 



Mean, 39.377, zt .014 



Dumas' and Pelouze's series combine as follows : 



Pelouze 39.4447, i .0083 



Dumas. 39-377, ±.014 



General mean 39.4265, =b .0071 



Schiel, § also studying the chloride of silicon, decomposed it by am- 

 monia. After warming and long standing it was filtered, and in the 



*I.,ehrbuch, 5 Aufl., 3, 1200. 

 t Conipt. Rend., 20, 1047. 1845. 

 J Ann. Chem. Pharm., 113, 31. i860. 

 § Ann. Chem. Pharm., 120,94. 



