1878.] 



On Supersaturated Saline Solutions. 



121 



Theory. Experiment. 



Agl .. .. 53-89 

 Cal, .. .. 33-72 

 H 2 .. 12-40 



This salt is completely dissociated by water, a few drops even being* 

 sufficient to separate the whole of the iodide of silver. This reaction 

 enabled me to analyse the salt with facility. 



It was only necessary to add water to a known weight of the salt 

 and filter. The iodide of silver may then be determined on the filter, 

 and the calcium in the filtrate in the usual way by means of oxalate of 

 ammonia. The water I had to determine by difference, as the heat 

 necessary to expel the water drove off at the same time some iodine 

 from the iodide of calcium. A known weight of the salt, dried in 

 vacuo over sulphuric acid, did not lose weight when afterwards heated 

 for some time at 100° Cent. It partially fuses at the temperature of 

 boiling water. 



Iodide of calcium forms several interesting double salts, which I am 

 at present engaged in examining. 



III. " Further Note on Supersaturated Saline Solutions." By 

 Charles Tomlinson, F.R.S. Received January 7, 1878. 



In the paper which was read on the 20th of December last, I stated 

 that during some years past I had often recognised the existence of 

 a force in the atmosphere, which seemed to exert a powerful influence 

 on nuclei, in determining the sudden solidification of supersaturated 

 saline solutions. I had attempted to identify this force with evapora- 

 tion, with desiccation, with crystallisation, with electricity, and with 

 surface tension, and performed many experiments with this view, but 

 without success. I therefore determined to make daily observations on 

 the action of oils, &c, on these solutions, taking the typical one of 

 sodic sulphate of a uniform strength (2 salt to 1 water), and to record 

 the results from day to day, with especial reference to the state of the 

 atmosphere. These observations have now extended over three or four 

 months with this general result, that with a southerly or westerly wind, 

 the action of oils is to throw down the seven-atom salt at temperatures 

 above that at which it is naturally formed. The salt comes down on 

 shaking the solution in the flask. In dull and damp weather it falls in 

 a powdery form ; in fine weather in crystals of the modified salt, and 

 the powder previously formed in dull weather grows into well- shaped 

 crystals. Covered flasks with oil in contact with the solutions, have 

 thus been kept for days and weeks together, and although repeatedly 



