1871.] Mr. C. Tomlinson on Supersaturated Saline Solutions. 41 



and west, but the angle for the east is less ; whilst for the horizontal-force 

 lines both the angle and the distance are somewhat in excess in the east, 

 though the difference is diminishing. 



VI. " On the Behaviour of Supersaturated Saline Solutions when ex- 

 posed to the Open Air," By Charles Tomlinson, F.R.S. 

 Received July 26, 1871. 



It is a remarkable proof of the difference between the air of a room and 

 that of a field or garden in the country, that supersaturated saline solu- 

 tions, which crystallize the moment they are uncovered in a room, may 

 be kept uncovered in an open space during many hours without crys- 

 tallizing. 



During the last three years I have made many experiments to confirm 

 this conclusion in the little garden at the back of my house at Iiighgate. 

 I have no doubt that in a more open space further in the country the results 

 would have been more perfect ; but still I venture to think they are suffi- 

 ciently striking to merit a place in the ' Proceedings.' The following were 

 conducted during the spring of the present year. 



A solution of two parts of sodic sulphate and one part of water was 

 boiled and filtered into 3- and 4-ounce flasks, of which the opening of the 

 short cylindrical neck is just three-quarters of an inch. The filtered solu- 

 tions were reboiled and the flasks covered with watch-glasses. One flask 

 was placed on a stool in the middle of a gravel- walk and the watch-glass 

 removed. I now proceed to quote from my note-book some results in the 

 order of time, and then to summarize them. 



18/1, March 17. Put out flask containing cold solution at 12.30 p.m. ; 

 temp. 56° Fahr. ; clouds, and afterwards sun, 60° and upwards. At 2.50, 

 therm. 50°. At 4.30 found the solution solid, and upon it a speck of soot 

 which had evidently acted as a nucleus. 



At 5.30 put out flask ; temp. 43°, with slight wind ; 6.30, 41°; 7.30, 

 42°, with a good deposit of the seven-atom salt. At 9, temp. 40°, and 

 deposit much increased. At 1 1, solution solid, and the seven-atom deposit 

 chalky white. 



March 18. 2.15, put out flask and uncovered it under clear skv. At 

 4, temp. 57°, fine crop of crystals, evidently due to evaporation, which was 

 so powerful that a round patch immediately below the opening of the neck 

 was white and pulverulent from the formation of anhydrous salt. In this 

 case the crystallization took place, as in the case of a saturated solution, in 

 an open dish, only much more quickly, on account of the much larger 

 quantity of salt in the supersaturated solution. There was no formation 

 of the seven-watered salt*. 



* With reference to some of the cases of crystallization given in my paper " On Su- 

 persaturated Saline Solutions, Part II." (Phil. Trans. 1871, p. 51), Professor Stokes 



