296 Dr. W. W. J. Nicol on 



some time the two bottles were taken out and shaken, so as to 

 break the bulbs and thus bring the dehydrated Na 2 S0 4 in 

 contact with the water. After a few seconds' shaking, the 

 salt was completely dissolved in bottle No. 2, which had been 

 heated ; but the salt in bottle No. 1 had caked into hard 

 masses, which dissolved only very slowly. In this case the 

 solid hydrate was formed ; while in the other, solution had 

 taken place without hydration. 



Another experiment with the same quantity of water, but a 

 larger amount (10 grms. of Na 2 S0 4 in both bottles), w r as 

 attended with a like result. 



A third experiment, with the same quantities of water and 

 salt as in the previous case, differed to some extent from it. 

 In both bottles solution was complete at once ; but the con- 

 tents of the bottle which had not been heated crystallized out 

 again in a few seconds. 



A fourth experiment gave results identical with the second 

 experiment. In each of these three last experiments the 

 solution in bottle No. 2 was distinctly supersaturated, crystal- 

 lizing on removing the stopper. 



I have made numerous other experiments similar to the 

 above, and have never failed in obtaining a supersaturated 

 solution in this way. I noted that when special care was 

 taken in cleaning the bottles and fresh distilled water was 

 employed, it was frequently the case that the solution behaved 

 as in experiment No. 3 above • but I shall return to this later. 



A saturated solution at 20° of the hydraied salt contains, 

 according to Mulder*. 19*5 parts of the anhydrous salt per 

 hundred parts of water. Thus, the supersaturated solutions I 

 prepared as above described contained more than twice as 

 much Na 2 S0 4 as a saturated solution prepared in the ordinary 

 way. It remained to be seen to what extent this supersatu- 

 ration may be pushed — in other words, to find the amount of 

 salt in a true saturated solution of Na 2 S0 4 . 



A bottle containing 25 cubic centim. of water and 15 grms. 

 of Na 2 S0 4 sealed up in a bulb was treated as above, and after 

 shaking was allowed to remain in the bath at 20° for several 

 hours. The stopper was then removed and some of the clear 

 solution was rapidly poured into a previously weighed platinum 

 dish, and in this way the percentage of salt was obtained. 

 Two trials gave : — 



(1) 35*87 per cent.,~l corresponding to 55*63 parts 



(2) 35*61 per cent., j per 100 parts of water. 



# Bijdragtn tot de geschiedenis van hot schcikundig gebonden Water 

 (Rotterdam, 18G4). 



