1877.] 



Supersaturated Saline Solutions. 



525 



Grenfell, some eighteen months ago, joining in the opposition, having 

 told me of his experiments, I asked him to prepare a paper on the subject. 

 In this *, as also in a second paper, he is at variance with all his pre- 

 decessors. In his second paper he gives a summary of the three prin- 

 cipal theories that have been propounded, and goes into minute experi- 

 mental detail in support of his own objections to them and of his own 

 views. His theory rests on absorption, which, it will be seen above, is 

 not so novel as he supposes it to be. 



There is one point upon which all observers, down to the time of Prof. 

 Grenfell, are agreed, namely, that if a supersaturated solution, say of 

 Glauber's salt, boiling in a flask, be tied over with bladder and left until 

 cold, it will, if the bladder be pierced, immediately become solid. Indeed 

 this has long been a common lecture-table experiment ; and I thought it 

 a step in advance when I showed that if this experiment be made in the 

 open air of the country, the solution remains liquid. I also exposed 

 solutions to the air of my garden with various residts, as I have already 

 had the honour of describing to the Society f. But Prof. Grenfell goes 

 far beyond any thing that I, or previous observers, have done ; he exposes 

 these solutions to the air of rooms, places them on various surfaces, 

 handles them, makes mud pies with them +, and yet they do not crystal- 

 lize. It is probable that his minute method of dealing with drops may 

 alter the conditions ; but certainly in the air of my house and garden I 

 cannot expose my flasks as he does his drops without producing sudden 

 solidification. 



I will give two or three out of a multitude of similar results. Last 

 summer I made a strong solution of sodium sulphate and filtered it into 

 two long-necked globular flasks, which were reboiled and tied over with 

 bladder. They were left during three weeks and remained unchanged. 

 The bladder over one flask was then pierced and the solution immediately 

 crystallized. I took the other flask into the fields and uncovered it ; it 

 remained liquid during a long walk, although the wind blew into the neck 

 with such force as to produce a musical note. When the still uncovered 

 flask was brought into the house the solution soon crystallized. I 

 have repeated this experiment with this and other salts with similar 

 results, and it furnishes an argument against the Gernez and Yiollette 

 theory. 



A strong solution of alum was tied over just after being boiled. It 

 was repeatedly shaken during several days. While resting on the 

 mantleshelf of my study the bladder was pierced, when immediately 

 some amorphous powder at the bottom of the solution began to assume 



* Proc. Roy. Soc. xxv. p. 124. 

 t Proc. Eoy. Soc. xx. p. 41. 



\ In April last, during an interval between heavy showers which had thoroughly 

 washed the mould of ray garden, I poured upon it a solution of Glauber's salt (2 to 1) 

 and it crystallized immediately. 



