CALCIUM. ()7 



And for the atomic weight of strontium itself we have 

 two values, as follows : 



1. From mol. wt. of SrCl,, Sr = 87.384, rb .032 



2. From (4) " := 86.765, zb .244 



General me.in_.. " = 87.374, rfc .032 



If = 10, then Sr = 87.575. 



CALCIUM 



For determining the atomic weight of calcium we have 

 sets of experiments by Berzelius, Erdmann and Marchand, 

 and Dumas. Salvetat* also has published an estimation, 

 but without the details necessary to enable us to make use 

 of his results. I also find a referencef to some work of 

 ^larignac ; wliicli, however, seems to have been of but little 

 importance. The earlier Avork of Berzelius was very in- 

 exact as regards calcium, and it is not until we come down 

 to the year 1842 that we find any material of decided value. 



The most important factor in our present discussion is the 

 composition of calcium carbonate, as worked out by Dumas 

 and by Erdmann and Marchand. 



In 1842 DumasJ made three ignitions of Iceland spar, 

 and determined the percentages of carbon dioxide driven 

 off and of lime remaining. The impurities of the material 

 were also determined, the correction for them applied, and the 

 weighings reduced to a vacuum standard. The percentage 

 of lime came out as follows : 



56.12 

 56.04 . 

 56.06 



Mean, 56.073, zh .016 



* Compt. Rend., 17, 318. 1843. 

 f See Oudeman's monograpli, p. 51. 

 J Compt. Rend., 14, 537. 1842. 



