298 



Dr. W. W. J. Nicol on 



t°. 



Mulder. 



Kopp. 





100 



425 



42-597 



Formula II. 



90 



431 



42-717 



M 



80 



43-7 



43-242 





70 



44-4 



44-840 





60 



453 



45-391 





50 



46-7 



46-958 





40 



48-8 



48-811 





30 



409 



41135 



Formula I. 



33 



Nicol. 



50*263 



Formula II. 



51-09 



30 



51-94 



50-921 





25 



5535 



52-064 





20 



5563 



53-260 



i) 



The lower half of the table compares the results I obtained 

 as described above, compared with the figures obtained from 

 Kopp's second formula extended below 33° C. ; and the con- 

 cordance here is, I venture to think, thoroughly satisfactory 

 when the difficulties attending such determinations are taken 

 into account. My results w T ill also be found to agree well 

 with those of Loewel*, who determined the solubility at 20°, 

 and 25°, and 30° of the anhydrous salt by heating an excess 

 of the decahydrate and water above 33°, and then allowing 

 the solution thus obtained to cool in contact with the separated 

 anhydrous salt* 



These experiments conclusively prove the truth of my con- 

 tention, that a so-called supersaturated solution differs in no 

 way whatever from an ordinary solution. The arguments 

 advanced in the previous paper on this subject were incom- 

 plete in one point. They left room for the objection that a 

 solution of sodium sulphate might, for all we know, have a 

 different constitution, after heating and cooling, from that 

 possessed by a similar solution that has not been heated. To 

 such a change of constitution has been ascribed the possibility 

 of the existence of supersaturated solutions; but now that 

 supersaturated solutions have been prepared from cold water 

 and cold dehydrated Na 2 S0 4 , and have been found pre- 

 cisely similar to those prepared with the aid of heat, this 

 theory falls to the ground, and there is no reason for regard- 

 ing them as anything but ordinary solutions of the anhydrous 

 salt. 



Why, then, do these solutions crystallize when brought in 

 contact with the air ? or why is it that they cannot be pre- 



* Ann. de Chim, et Phys. [3] xlix. 



