K)6 ABSOLUTE ATOMIC WEIGHT. 



VIII. THE ATOMIC WEIGHT OF CALCIUM. 



The best determinations have been obtained by using 

 purest calcite, Iceland Spar, as substance. 



The first determinations, made by Dumas, give a mean 

 analytical excess of 55, which would correspond to the 

 atomic weight C = 40.055. 



The determinations by Erdmann and Marchand on spar 

 are very fine, giving a mean analytical excess of 28, corres- 

 ponding to Ca = 40.028. Their determinations on artificial 

 carbonate bring the mean excess almost to zero, and the 

 atomic weight almost to 40 exactly. 



On account of the high importance of these determina- 

 tions we reprint the weighings from our True Atomic 

 Weights, p. 184, which were copied from vol. 8 of the 

 Annales de Chimie et de Physique for 1843. 



In the work of Clarke, which at least ought to give the 

 data of observations in full, these data are horribly incom- 

 plete. Fortunately, the volume of the Annales was at the 

 Mercantile Library of St. Louis. 



Ca O : Ca Oa C = 56 : 100 = 0.56 ooo. Change 100 high. 

 Dumas, 1842. Dissociation of Iceland Spar: 



Due impuritv, 030 



Annales de Chimie et de Physique, III Series, T. S, p. 202. 

 This excess would correspond to Ca 40,023 to 40.093; 



mean 40.051. 



Erdmann and Marchand, 1842. Artificial Carbonate: 



Corresponding atomic weight Ca = 40.004. Same volume 

 of Annales, p. 14. 



