44 Mr. C. Tomlinson on Supersaturated Saline Solutions. [Nov. 23, 



March 20, 1871- Magnesic sulphate four parts, water two and a half parts; 

 hoiled and filtered into three small flasks, and at 7.10 p.m. exposed two of 

 them in the garden ; placed the third (covered) in the room on the window- 

 ledge in contact with the giass pane. At 8.10, temp. 40°, no change : 9.15, 

 temp. 40°, with much dew ; one solution solid, the other unchanged : 

 10, temp. 39°, the flask very wet with dew; no change. 21st, 8 a.m., 

 temp. 35°, wet fog, no change ; brought the flask indoors and uncovered 

 the one in window ; they became solid in less than half an hour. Two of 

 the flasks were reboiled and united, so that the globe of the flask was 

 quite filled. Put this into the garden at 4 p.m., temp. 55°. At 6, temp. 

 43i°; at 8, temp. 39j°; at 10.30, temp. 35°, with clear sky. 22nd, at 8 a.m., 

 temp. 31°, no change; at 10 the contents of flask were found in a solid 

 state with a speck of soot on the surface. 



Potash-alum three parts, water two parts ; boiled and filtered into three 

 flasks. When cold, put one flask in the garden and took off watch-glass. 

 Time 5.30, temp. 46°. At 6, temp. 43^°, and the sky very clear. At 

 6.35, no change ; temp. 40-^° ; removed the watch-glass from the flask in- 

 doors, and the solution crystallized immediately. At 8 the solution in the 

 garden crystallized, apparently from evaporation ; temp. 39|°. 



The results obtained by exposure to the open air of highly supersaturated 

 solutions of sodic acetate are not in harmony with the above, on account of 

 the tendency of such solutions, when left to repose, to arrange themselves 

 into layers of different density ; so that while the lower part of the solu- 

 tion becomes more supersaturated, the upper part becomes less so. By 

 keeping such a solution during some weeks in a long test-tube plugged with 

 cotton-wool, the upper part of the solution is scarcely more than saturated, 

 so that it may be touched with an unclean wire without crystallizing, and 

 the wire may be passed about one-third down the tube before the solution 

 becomes sensitive to the action of a solid nucleus. But when once the 

 crystallization is started, the whole contents of the tube become solid, and 

 the tube may be inverted without the escape of any liquid. 



For these garden experiments a solution of four parts sodic acetate 

 to one part of water was boiled and filtered into two small flasks, which 

 had been previously washed with spirits of wine, rinsed with water, and 

 then with a little acetic acid. 



March 18. At 8 p.m. the flasks were exposed in the garden ; at 11.15 

 the temp, was 35°. On the 19th, at 8.30 a.m., after being left out all 

 night, both the solutions were liquid, but very viscous. At 10.50 the 

 flasks were brought into a room and placed on the mantle-shelf, where they 

 remained all that day as well as the next. On the 21st they were still 

 liquid ; one of them was touched with the end of a wooden penholder, and 

 it at once became solid ; the other flask was left uncovered on the shelf 

 until the 24th before it became solid. On the 21st the solution that was 

 touched with the nucleus was reboiled with the addition of half an ounce 



