46 



SCIENCE 



[N. S. Vol. XXXI. So. 785 



of the violence to whicli it has laeen sub- 

 jected by heating it very highly. Simi- 

 larly, while we recognize that carbon, 

 hydrogen and oxygen are contained in 

 cane sugar, we do not argue that the latter 

 consists of water and carbon, though these 

 products may among others be obtained 

 by heating sugar. Likewise we are loath 

 to conclude that proteins contain amino 

 acids, simply because these result as cleav- 

 age products when the proteins are sub- 

 jected to certain rather drastic treatment. 

 Turning now, for example, to a com- 

 pound like blue vitriol whose composition 

 we are wont toi express by the formula 

 CUSO4.5H2O, to indicate that it consists of 

 copper sulphate plus water, we find that 

 the water may be driven off by heat prop- 

 erly applied and that the dehydrated 

 copper sulphate remains behind. On heat- 

 ing the copper sulphate further it is de- 

 composed into copper oxide and sulphur 

 trioxide. If it were intended to express 

 these changes by means of a formula, 

 surely the old dualistic formula CuO-SOg. 

 5H2O would best indicate what has been 

 observed. But here again we have de- 

 parted from the idea that copper sulphate 

 contains copper oxide and sulphur trioxide 

 because upon electrolysis of an aqueous 

 solution of copper sulphate, metallic cop- 

 per, sulphuric acid and oxygen are ob- 

 tained; while upon adding zinc or iron to 

 a copper sulphate solution metallic copper 

 is thrown out, and the sulphate of the more 

 basic metal results. So far as the water 

 content of blue vitriol crystals is con- 

 cerned, we only know its relative amount 

 and that it can be driven off by heat, 

 higher temperatures being required to se- 

 cure complete dehydration, while rela- 

 tively lower temperatures will sufSce to 

 remove a large portion of the water. As 

 to how this so-called water of crystalliza- 

 tion is held, whether it is united with the 



copper sulphate simply as water mole- 

 cules adhering to the copper sulphate 

 molecule, or whether, like the oxygen and 

 hydrogen content of the cane-sugar mole- 

 cules, the oxygen and hydrogen in blue 

 vitriol are united with the sulphur and cop- 

 per in some more complicated way, is an 

 open question. So far as the facts known 

 are concerned, they are expressed by the 

 formula CuSO^.SHaO, just as at one time 

 the formula CaO.COo expressed what was 

 known about calcium carbonate. To me 

 it would seem very probable that the 

 hydrogen and oxygen content in blue 

 vitriol is not present as water molecules 

 clinging to the copper sulphate molecule, 

 but some subtle experimental method, as 

 yet quite unknown, is required to elucidate 

 this matter, and until such a method is 

 found we shall continue to write our for- 

 mula for blue vitriol as we are wont to do. 

 It is perhaps well in this connection to 

 allude to the well-known fact that many 

 salts containing water of crystallization 

 can not be dehydrated by heating them, 

 for when this is attempted not only water, 

 but other ingredients as well, are driven 

 off, in other words further deep-seated de- 

 composition occurs. 



If crystals of blue vitriol be placed in 

 water, a blue liquid is formed as a result 

 of the action of the crystals and water on 

 each other. This liquid we call a solution. 

 The amount of water and blue vitriol used 

 in its preparation may be varied arbitra- 

 rily within certain limits. For reasons al- 

 ready stated, this blue liquid contains no 

 water that is not in combination with the 

 salt present, and also no salt that is un- 

 combined with the water. The fact is that 

 this blue liquid is found to be perfectly 

 homogeneous by all tests that we are able 

 to apply. If we add more water to it, this 

 additional water also combines with all of 

 the salt present and the liquid is again 



