70 THE ATOMIC WEIGHTS. 



spar was carefully converted into calcium sulphate, and the 

 gain in weight noted. One hundred parts of spar gave of 

 sulphate : 



136.07 

 136.06 

 136.02 

 136.06 



Mean, 136.0525, zh .0071 



In 1843 the atomic weight of calcium was redetermined 

 by Berzelius,* who investigated the ratio between lime and 

 calcium sulphate. The calcium was first precipitated from 

 a pure solution of nitrate by means of ammonium car- 

 bonate, and the thoroughly washed precipitate was dried 

 and strongly ignited in order to obtain lime wholly free 

 from extraneous matter. This lime was then, with suitable 

 precautions, treated with sulphuric acid, and the resulting 

 sulphate was weighed. Correction was applied for the trace 

 of solid impurity contained in the acid, but not for the 

 weighing in air. The figures in the last column represent 

 the percentage of weight gained by the lime upon conversion 

 into sulphate : 



1.80425 yrm. CaO gained 2.56735 grm. 142.295 



2.50400 " 3-57050 " 142.592 



3.90000 " 5-55HO " 142.343 



3.04250 " 4.32650 " 142.202 



3.45900 " 4-93140 " 142.567 



Mean, 142.3998, ± .0518 



Last of all we have the ratio between calcium chloride 

 and silver, as determined by Dumas.f Pure calcium chlo- 

 ride was first ignited in a stream of dry hydrochloric acid, 

 and the solution of this salt was afterwards titrated with a 

 silver solution in the usual way. The CaCL, proportional 

 to 100 parts of Ag is given in a third column : 



* Journ. fiir Prakt. Chem., 31, 263. Ann. Cliem. Pharm., 46, 241. 



f Ann. Chim. Phys., (3,) 55, 129. 1S59. Ann. Chem. Pharm.. 113, 34. 



