Mr. F. Guthrie on Salt Solutions and Attached Water. 1 7 



§ 30. The above are arranged according to the molecular 

 ratio, NaCl having the least number of molecules of water. At 

 once an important law declares itself : those cryohydrates 

 which have the lowest solidifying temperatures have the fewest 

 molecules of water. This law hoids true with all which have 

 been examined, with the exception of the bichromate of potas- 

 sium, which, if placed according to its temperature of solidifi- 

 cation, would be above the sulphate of sodium. Is this due to 

 its abnormal composition ? Such questions suggest themselves 

 by the score on contemplating this Table VIII. 



§ 31. I have found the solidify ing-points, and have hermeti- 

 cally sealed specimens, of the cryohydrates of a few other salts, 

 and am collecting more previous to analyzing them. I give their 

 solidifying-points in the order of the degree of cold ; and it will 

 be of great interest to see whether their molecular ratios fall in 

 accord with the above rule. 



Solidifying temperature 

 Salt. of cryohydrate. 



KI -230 



KBr -130 



KC1 ' -11-4 



Na 2 C0 3 . ... - 20 



BaN0 3 .... - 0-8 



H 2 C 2 4 ... - 0-5 



Perhaps the most promising direction of inquiry for the 

 establishment of such a uniformity of result as may be used for 

 the prediction of untried experiments will consist in a careful 

 study of the nine salts between K, Na, and NH 4 on the one 

 hand, and CI, Br, and I on the other. 



Some Experiments with Sea-ivater. 



§ 32. Freezing sea-water. — The sea-water with which the fol- 

 lowing experiments were performed was procured from Dover. 

 After filtration, it was found to have at 760 millims. the boiling- 

 point 100 o, 6, while the temperature of its vapour was 100° '2. This 

 sea-water began to freeze at —2° C. On evaporation on a water- 

 bath and keeping at 100° C. for two hours, the percentage of solid 

 residue was 6*5786. A large beaker of this sea-water was cooled 

 to 0° C. A tin vessel was supported inside the beaker so that its 

 bottom just touched the surface of the water ; and a freezing- 

 mixture was placed in the tin vessel. When about t Jq of the 

 whole had solidified, the solid was removed and divided into 

 two parts : one was allowed to melt, and its percentage of solid 

 matter was determined as above ; the other was broken up and 

 frequently pressed between linen and flannel in a screw press, 

 being allowed to melt as little as possible. The percentage of 



Phil. Mag. S. 4. Vol. 49. No. 322. Jan. 1875. C 



