50 i Mr. A. Liversidge on Supersaturated Saline Solutions. [June £0, 



phate, they were proved to be inactive, having been changed to the inactive 

 anhydrous salt. 



But such dried normal crystals were active to a solution of sodic sulphate, 

 even after three days' exposure to the sulphuric acid*. It seems as if the 

 normal crystals become covered with a coating of effloresced anhydrous 

 salt which acts as a protection to the underneath portions, in the same 

 way as oxide of lead does to metallic lead ; hence it takes a long time to 

 convert a crystal of the normal salt into the anhydrous by simple exposure 

 to dry air, although it is an exceedingly short operation to perform at tem- 

 peratures superior to 34° C. 



Yet another form of this experiment was tried again and again, and always 

 with the same result. 



A glass tube bent into the form of an elongated letter S was suspended 

 by a plug of cotton-wool in the neck of a flask containing a supersaturated 

 solution ; the solution was boiled, and the tube was also boiled in it, so as 

 to get all nuclear particles adhering to it thoroughly destroyed. 



The solution was then allowed to cool, with the tube still in it ; the tube 

 was then raised out of the solution and a dirty wire passed down it ; crys- 

 tallization was, of course, set up in the portion of supersaturated solution 

 contained within the tube ; the crystals gradually grew down the tube, then 

 through the first bend, travelled up the upright portion, then travelled 

 round the second bend, and finally down the third and last straight portion. 

 Now, on lowering the extreme tip of the crystals formed at the end of the 

 tube into the solution, crystallization was immediately set up from it as a 

 centre, and thence throughout the mass. 



By this arrangement access of extraneous nuclei was entirely prevented. 

 The upper end of the tube was plugged with cotton-wool until the dirty 

 wire was passed down. 



That the normal crystals thus formed did not act by any transient mo- 

 lecular movements, which recently formed crystals might be supposed to 

 have, is proved doubtless by the fact that such crystals were found to act 

 just as readily even -when they had been kept over the solution for 2^, 5, 10, 

 24, and 48 hours, and then lowered into the solution, and when any mo- 

 lecular agitation may with fairness be supposed to have ceased. 



* At a future day I hope to have the results of more experiments upon this point. 



