ATOMIC WEIGHTS 291 



Dumas ' oxidized pure tin by nitric acid in a iiaslc of glass. The re- 

 sulting SnOo was strongly ignited, first in the flask and afterwards in 

 platinum. His weighings, reduced to the foregoing standard, give for 

 dioxide from 100 parts of tin the amounts stated in the third column: 



12.443 grm. Sn gave 15.820 grm. SnO,. 127.14 



15.97C " 20.301 " 127.07 



Mean, 127.105, ± .024 



Hence Sn= 118.06. 



In an investigation later than that previously cited, Vlaanderen' 

 found that when tin was oxidized in glass or porcelain vessels, and the 

 resulting oxide ignited in them, traces of nitric acid were retained. 

 When, on the other hand, the oxide was strongly heated in platinum, 

 the latter was perceptibly attacked, so much so as to render the results 

 uncertain. He therefore, in order to fix the atomic weight of tin, reduced 

 the oxide by heating it in a porcelain boat in a stream of hydrogen. Two 

 experiments gave Sn = 118.08, and Sn = 118.24. These become, if re- 

 duced to the above common standard, 



127.100 

 127.0f;4 



Mean, 127.0S2, ± .012 



Hence Sn = 118.lC). 



Van der Plaats ' prepared pure stannic oxide from Banca tin, and 

 upon the material obtained made two series of experiments : one by re- 

 duction and one by oxidation. The results, with vacuum weights, are 

 as follows, the ratio lietween Sn and SnO^ aj^pearing in the tliird column : 



Oxidation Series. 



9.6756 grm. tin gave 12.2967 SnO„. 127.091 

 12.7356 " 16.1885 " 127.114 



23.4211 " 29.7667 " 127.093 



Reduction Series. 



5.5015 grm. SnO, gave 4.3280 tin. 127.114 



4.9760 " 3.9145 " 127.117 



3.8225 " 3.0078 " 127.086 



2.9935 " 2.3553 " 127.096 



Mean of both series as one, 127.102, ± .0033 

 Hence Sn = 118.0T. 



The reductions were effected in a porcelain crucible. 

 Bongartz and Classen' purified tin by electrolysis, and oxidized the 

 electrolytic metal by means of nitric acid. The oxide found was dried 



1 Ann. Chem. Phaiin., 113, 26. 



= Jahresbeiicht, 1808, 183. 



^Compt. Rend., 100. r^2. 1885. 



■•Bericlite Deiitsrli. cIumii. Gesell., 21. 2!)on. 18SS. 



