OP ARTS AND SCIENCES. 



267 



filtration caused no further formation of precipitate is a satisfactory 

 {)roof that no cuprous salt remained iu sokitiou, even if it had been 

 formed in the first place. 



The outcome of all these more or less indirect experiments points 

 to the conclusion that cupric sulphate retains about 0.12 per cent of 

 its water of crystallization, even when heated to 400° C. This last 

 trace of water is given olf only at a temperature at which the cupric 

 sulphate itself begins to decompose. It must be admitted that the 

 evidence upon the point is not absolutely certain, but there is no doubt 

 of its great probability. Upon such a matter as this it is dilhcult to 

 see how more definite results could have been procured. 



Total Percentage Composition of CuSOi . 5 H2O. 



Per Cent. 



Water lost at 360° — 400° = 36.067 



" " between 400° and redness = 0.042 



Copper, average = 25.449 



SO4 = 38.436 



Total = 99.994 



If the amounts of copper and sulphuric acid supposed to be lost 

 during the electrolysis are added, the total becomes 100.004. 



Either of these total results is now accurate within the limits of 

 error of ordinary analysis. But it will be seen that the total percent- 

 age of crystal water indicated by the analyses is much too large as 

 compared with the sulphuric acid, which is our only certain standard 

 of reference. This excess of water must have been occluded in the 

 original crystals, which were not very finely powdered. Accordingly 

 two specimens of the purest cupric sulphate were much more finely pul- 

 verized, and their loss of weight at 400° was then found to be 36.057 

 (average of Experiments 21 and 23) instead of 36.067 per cent. Mr. 

 H. M. Richards kindly measured many diameters in the two powders, 

 and found that the particles of the coarser powder approximated one 

 tenth of a millimeter, while those of the finer were less than one 

 hundredth. Since more than half an hour's continuous powdering, at 

 the very slow rate adopted to prevent warmth from friction, had been 

 necessary to reduce a small amount of material to the finer state, it 

 was concluded to abandon the attempt at obtaining cupric sulphate 

 free from occluded water. 



It must be remembered that the salt had been very slowly crystal- 

 lized by the evaporation of the solution, and of course had had every 



