188 THE ATOMIC WEIGHTS. 



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

 periments of Crookes and Lepierre, we have 



Tl = 202.605, .0103 



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

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

 Crookes' ratio evidently outweighs all the others. 



SILICON. 



Although Berzelius * attempted to ascertain the atomic weight of 

 silicon, first by converting pure Si into Si0 2 , and later from the analysis 

 of BaSiF 6 , his results were not satisfactory. We need consider only the 

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



Pelouze,f experimenting upon silicon tetrachloride, employed 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 4 : 



39-4325 

 39.4570 



Mean, 39.4447, .0083 



Essentially the same method was adopted by Dumas. J Pure SiCl 4 

 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 grm. SiCl 4 = 7.3558 grm. Ag. 39.41 1 



1.242 " 3.154 " 39-379 



3.221 8.1875 " 39.340 



Mean, 39.377, db .014 



Dumas' and Pelouze's series combine as follows : 



Pelouze 39.4447, dr .0083 



Dumas 39.377, .014 



General mean 39.4265, =fc .0071 



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

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



* Lehrbuch, 5 Aufl., 3, 1200. 

 f Compt. Rend., 20, 1047. 1845. 

 I Ann. Cheni. Pharm., 113, 31. 1860. 

 Ann. Chem. Pharm., 120,94. 



