(j8 the atomic weights. 



About this same time Erdmann and Marchand* began 

 their researches upon the same subject. Two ignitions of 

 spar, containing .04 per cent, of impurity, gave respectively 

 56.09 and 50.18 per cent, of residue; but these results are 

 not exact enough for us to consider further. Four other ■ 

 results obtained with artificial calcium carbonate are more 

 noteworthy. The carbonate was precipitated from a solu- 

 tion of pure calcium chloride by ammonium carbonate, was 

 washed thoroughly with hot water, and dried at a tempera- 

 ture of 180°. With this preparation the following residues 

 of lime were obtained : 



56.03 

 55-98 

 56.00 



55-99 



Mean, 56.00, rb .007 



It was subsequently shown by Berzelius that calcium car- 

 bonate prepared by this method retains traces of water even 

 at 200°, and that minute quantities of chloride are also held 

 by it. These sources of error are, however, in opposite di- 

 rections, since one would tend to diminish and the other to 

 increase the weight of residue. 



In the same jDaper there are also two direct estimations of 

 carbonic acid in pure Iceland spar, which correspond to the 

 following percentages of lime : 



56.00 

 56.02 



Mean, 56.01, rfc .007 



In a still later paperf the same investigators give another 

 series of results based upon the ignition of Iceland spar. 

 The impurities were carefully estimated, and the percentages 

 of lime are suitablv corrected : 



* Journ. fur Prakt. Chem., 26, 472. 1842. 

 t Journ. fiir Prakt. Chem., 31, 269. 1844. 



