94 THE ATOMIC WEIGHTS. 



In the memoir by Richards now under consideration, his fourth upon 

 copper, the greater part of his attention is devoted to the sulphate, 

 Harape being followed closely in order to ascertain what sources of 

 error affected the work of the latter. Crystallized sulphate, CuSO^.SH^O 

 was purified with every precaution and made the basis of operations. 

 Three series of experiments were carried out, the water being determined 

 by loss of weight upon heating, and the copper being estimated electro- 

 lytically. In the first series the following data were found, the weights 

 being reduced to a vacuum, as in all of Richards' determinations : 



CiiSOi- 5 aq. CuSO^ at 250°. Cu. 



1 2.SS15 .7337- 



2 2.7152 .6911 



!i7 



Hence the subjoined percentages. 



Water at 2^0°. Cu in Cryst. Salt. Cu in CuSO^. 



1 25.462 



2 25.452 



3 35-955^ 25.454 39.745 



Mean, 25.456 



In the second series of anah'ses, which are stated with much detail, 

 several refinements were introduced, in order to estimate also the sul- 

 phuric acid. These will be considered later. The results, given below, 

 are numbered consecutively with the former series. 



CuSOy 5 aq. 



4 . . 3.06006 



5 2.S1840 



6 7.50490 



Hence percentages as follows : 



Water, 260°. Water, j6o°. Cuiii Cryst. Salt. Cuin CuSO^,26o°. Ditto, 360!^ 



4 35-959 36.068 25.452 39-744 39-S'i 



5 35-964 25.454 39-750 



6 35-957 36-065 25.446 39.733 39-799 



Mean, 35.960 36.067 25.450 39-742 39-So5 



Hampe worked with a sulphate dried at 250°, but these data show that 

 a little water is retained at that temperature, and consequently that his 

 results must have been too low. The third of Richards' series resembles 

 the second, but extra precautions were taken to avoid conceivable errors. 



CiiSO^.jaq. CuSO^ at 260°. CuSO^ at j/o°. Cu. 



7 ' • 2.88307 .733S0 



8 3-62913 2.32373 .92344 



9 5-81352 3.71680 1.47926 



