160 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



In this series the determinations of sulphuric acid gave essentially the 

 same results for all three samples of sulphate, although one was not 

 dehydrated, and the others were heated to 260° and 370°, respectively. 

 Hence the loss of weight in deliydration at either temperature represents 

 water only, and does not involve partial decomposition of the sulphate. 

 Between 360° and 400° copper sulphate is at essentially constant weight, 

 but further experiments indicated that even at 400° it retained traces of 

 water, and possibly as much as .042 per cent. The last trace is not ex- 

 pelled until the salt itself begins to decompose. 



Eichards also effected two syntheses of the si;lphate directly from the 

 metal by dissolving the latter in nitric acid, then evaporating to dryness 

 with sulphuric acid, and heating to constant weight at 400°. 



.67720 grm. Cu gave 1.7021 grm. CuSO*. 39.786 per cent Cu. 



1.00613 " 2.5292 " 39.781 



If we include these percentages in a series with the data from analyses 

 4, 6 and 9, which gave percentages of 39.811, 39.799 and 39.799, respec- 

 tively, of copper in sulphate dried at 360° and upwards, the mean becomes 



CuSO^rCu: : 100: 39.795, ± .0036 



Hence Cu = 63.499. 



Since even this result is presumalily too low, the other figures from 

 sulphate dried at 350° must be rejected. Since Hampe's work on the 

 sulphate is affected by the same sources of error, and apparently to a 

 still greater extent, it need not be considered farther. As for Richards' 

 nine determinations of Cu in CuSO^.SHsO, we may take them as one 

 series giving a mean percentage of 25.451, ±.0011, and Cu = 63.55. This 

 salt seems to retain occluded water, for the percentage of copper in it 

 leads to a value for the atomic weight which is inconsistent with the best 

 evidence, as will be seen later. 



In the second and third series of Eichards' experiments upon copi)er 

 sulphate, the sulphuric acid was estimated by a method which gave 

 valuable results. After the copper had been electrolytically precipitated, 

 the acid which was set free Avas nearly neutralized by a weighed amount 

 of pure sodium carbonate, and the slight excess remaining was deter- 

 mined by titration. Thus the weight of sodium carbonate equivalent to 

 the copper was ascertained. The resulting solution of sodium sulphate 

 was then evaporated to dryness, and a new ratio, connecting that salt 

 with copper, was also determined. The cross ratio NaoCOg : N'aoS04 has 

 already been utilized in a previous chapter. The results, ignoring the 

 weights of hydrated copper sulphate, are as follows, with the experiments 

 numbered as before : 



