d 



i.ih aldii'iir. 



-3ff 



8.TO 



ill 

 J 



Measuring the Water of Crijstallizaiion of Salts, 20l^ 



r^Oti repeating Dr. Dalton's experi^ '^^^'^^ J^"^ j'Pti"'*?^*" -^^^^ 

 Agents with this apparatus, there ap- '-^ i?yr.a br 

 peared to be considerable discrepancy '"^ .^. -'' 

 in the results; indeed they were so much *^^ ^* " ^'"* 

 at variance, that I was induced to sus- 

 pect at once that the law, which his in- 

 genuity had suggesteil, would not bear 

 the test of practical application ; for iiouciiujino :> 

 according to his results, "if the salt 

 was anhydrous it would all go into the 

 bottle, exactly filling it to a grain, 

 showing that the salt enters into the 

 pores or interstices of the water. If 

 the salt contained water, the quantity 

 of water was measured in all cases 

 whatever by the narrow tube, showing 

 that the solid matter had in reality en- 

 tered into the pores of the water. Thus 

 if the sulphate of magnesia be made 

 anhydrous and then dissolved, the so- 

 lution of the sulphate would exactly 

 fill the bottle as the water did before ;'' 

 or in other words, when a salt, whether 

 hydrous or anhydrous, is dissolved in 

 water, the acid and base of that salt will 

 occasion in all cases whatever a con- 

 densation exactly equal to the bulk of 

 that acid and base." 



Dr. Dalton here recommends that the sulphate of magnesia 

 be made anhydrous and then dissolved ; and with this salt, as 

 well as with the carbonate of soda, our experiments, both on' 

 the hydrous salts and when made anhydrous, very nearly 

 agreed, though in the experiments on several of the other salts 

 tried in the same manner the results varied. 



But Dr. Dalton seems to have overlooked the fact, that the 

 law in order to be correct must apply, not only to the hydrous 

 salts made anhydrous, but to the naturally anhydrous salts, as * 

 sulphate of potash, nitrate of potash, &c. ; and in no part of his' 

 paper can I find that he has tried any of this variety. ' " 



In ascertaining whether the really anhydrous salts dissolved I 

 in water without increasing the bulk, I was almost as much 

 surprised with the results of my experiments as Dr. Dalton 

 was with his; for I found that when a salt, whether 4iydrous 

 or anhydrous, dissolved in water, there was sometimes a con- ' 

 densation and sometimes an expansion of the whole volume 

 of the salt and water, according to the nature of the salt used. 



Phil, Mag. S. 3. Vol. 27. No. 179. Sept, 1845. P 



