Mr. A. Liversidge on Supersaturated Saline Solutions. 73 



capsule of sulphuric acid was placed under the bell. The crust of 

 crystals was by this means dried, and became effloresced to a greater 

 or less extent. Now, on lowering them into a supersaturated solu- 

 tion of alum or of magnesic sulphate 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 sul- 

 phate, 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 under- 

 neath 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 temperatures 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 con- 

 taining a supersaturated solution ; the so- 

 lution was boiled, and the tube was also 

 boiled in it, so as to get all nuclear parti- 

 cles 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 ; crystallization was, of 

 course, set up in the portion of supersa- 

 turated 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 lower- 

 ing 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 pre- 

 vented. 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 

 molecular movements, which recently formed crystals might be sup- 

 posed 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 molecular agitation may with fairness be sup- 

 posed to have ceased. 



point, 



At a future day I hope to have the results of more experiments 



upon 



thi 



