ATOMIC WEIGHTS 249 



MEECUEY. 



In dealing with the atomic weight of mercury we may reject the early 

 detenninations by Sefstrora ' and a large part of the work done by Tur- 

 ner." The latter chemist, in addition to the data which will be cited 

 below, gives figures to represent the percentage composition of both the 

 chlorides of mercury; but these results are neither trustworthy nor in 

 proper shape to be used. 



First in order we may consider the percentage composition of mercuric 

 oxide, as established by Turner and by Erdmann and Marchand. In 

 both investigations the oxide was decomposed by heat, and the mercury 

 was accurately weighed. Gold leaf served to collect the last traces of 

 mercurial vapor. 



Turner gives four estimations. Two represent oxide obtained by the 

 ignition of the nitrate, and two are from commercial oxide. In the first 

 two the oxide still contained traces of nitrate, but hardly in weighable 

 proportions. A comparison of the figures from this source with the others 

 is sufficiently conclusive on this point. The third column represents the 

 percentage of mercury in HgO : 



144.805 grains Hg = 11.54 grains O. 92.619 per cent. 



125.980 " 10.08 " 92.592 



173.561 " 13.82 " 92.625 



114.294 " 9.101 " 92.620 



iVEean, 92.614, ± .0050 



Hence Hg = 200.626. 



In the experiments of Erdmann and Marchand ' every precaution was 

 taken to ensure accuracy. Their weighings, reduced to a vacuum standard, 

 give the subjoined percentages : 



82.0079 grm. HgO gave 75.9347 grm. Hg. 92.594 per cent. 



51.0320 " 47.2538 " 92.597 



84.4996 " 78.2501 " 92.604 



44.6283 " 41.3285 " 92.606 



118.4066 " 109.6408 " 92.597 



Mean, 92.5996, ±: .0015 



Hence Hg = 200.205. 



Hardin's determination of the same ratio, being different in character, 

 will be considered later. 



1 Sefstrom. Berz. Lehrb., 5th ed., 3, 1215. Work dune in 1S12. 



2 Phil. Trans., 1S33, 531-535. 

 3Joum. prakt. Chcm., 31, 395. 1844. 



