Mr. C. Tomlinson on Supersaturated Saline Solutions. 389 



the solution crystallized on the addition of olive-oil, the first imme- 

 diately, and the other two after being shaken. 



Experiment 3. Sodic sulphate — 3 salt, 1 water. This solution 

 crystallized under the action of the oils of bergamot, almonds, colza, 

 rape, and sesame. 



Experiment 4. Sodic sulphate — 3 salt, 1| water, in six flasks, 

 all of which crystallized under the action of sesame oil. 



Experiment 5. Potash-alum — 8 salt, 3 water. The solution 

 crystallized suddenly, as with a flash, on being shaken up with 

 oil of olives. This is the more remarkable, as the usual action of 

 a nucleus is to produce a solitary octahedron, which grows rapidly 

 until the solution becomes solid. This last effect was produced by 

 a less violent shaking of the solution in contact with oil of lavender. 



Experiment 6. Ammonia-alum — 8 salt, 7 water. On shaking 

 the solution with olive-oil it suddenly became solid, and of an opaque 

 chalky white. 



This selection from a large number of experiments may be suffi- 

 cient to answer my present purpose — namely, to show that some 

 supersaturated saline solutions really do crystallize under the action 

 of other nuclei than a salt of the same kind as that of the solution 

 operated on. 



My experiments were performed in the open air, at temperatures 

 between 30° and 50° F. At comparatively low temperatures the 

 shaking of the flask containiug the solution sometimes produced a 

 copious liberation of anhydrous salt, which rapidly combines with 

 water and forms the 7-atom hydrate * ; but on allowing the flask 

 to rest for some time, it generally happens that the solution becomes 

 solid, and the 7-atom salt opaque white. 



I may perhaps be allowed to state that my experiments, con- 

 ducted as they were in the open air, were delayed by the rainy 

 weather of last year. There is, however, this advantage in wet 

 weather, that the saline particles said to exist in the air are washed 

 down and brought into solution, in which condition they are not 

 nuclear, as I have already shown in the case of sodic sulphate, alum, 



* The view adopted by me that the supersaturated solution of sodic sulphate 

 contains the anhydrous salt in solution, and that this is first thrown down on 

 lowering the temperature, agitating, &c, has been objected to, on the ground 

 that, according to Lowel, it is the 7-atom hydrate that is really in solution and 

 is deposited on cooling. There are numerous proofs that it is the anhydrous 

 salt which is really in solution ; these I have collected in two papers, contained 

 in the 'Chemical News' of 3rd and 10th December 1869. That the 7-atom 

 hydrate is built up on the anhydrous salt may, I think, be shown by an expe- 

 riment. Two flasks containing a solidified solution of sodic sulphate of the same 

 strength are heated over a spirit-lamp ; one of the flasks is constantly turned 

 round on the ring of the retort- stand until the whole of the salt has entered 

 into solution ; it is then boiled, closed, and set aside. The other flask, during 

 the heating, is allowed to remain at rest over the flame for a short time, so 

 as to liberate a portion of the anhydrous salt. This flask is also boiled, although 

 the operation is interrupted by violent bumpings. It is closed and placed by 

 the side of the other flask, under the same conditions. When both flasks are 

 cooled down to the temperature of the air (say about 50°), the flask containing 

 the anhydrous salt will contain a crop of the 7-atom hydrate, built upon the 

 anhydrous deposit. The other haskwill have no crystalline deposit at all. 



