246 DR HOPE ON THE MAXIMUM DENSITY OF SEA-WATER. 



possess its greatest density at a temperature of T or 8° above its freezing point, 

 as it ought to have, were the principle of Su* Charles Blagden sound. 



Experiment, No. 3. A solution of salt was made in the proportion of 1 part 

 of salt and 4.8 of water, which were the proportions employed by Su- Charles 

 Blagden in his solitary experiment, and introduced into a sunilar large thermo- 

 meter glass. The apparatus was immersed first in a mixture of snow and 

 water, and then in a frigorific mixture at temperature 8°. The fluid descended 

 in the tube uniformly and regularly till it reached the temperatm-e of the frigo- 

 rific mixture. It did not exhibit any interruption in its progress, or any retro- 

 cession. 



I then removed the apparatus from the mixture, and suspended it in the air, 

 the temperatm-e of which was nearly 45°, the fluid ascended slowly but steadily. 

 After a while I plunged it into water, and it continued to ascend without any halt 

 or retrocession. 



Eocperhnent, No. 4. In this case I made use of a more powerful frigorific mix- 

 ture, which brought the liquor more speedUy to its stationary point, but it de- 

 scended as in the preceding trial, without any inten-uption in its progress, or any 

 retrogression. I then withdi-ew the apparatus from the freezing mixture, and sus- 

 pended it in the air. The fluid immediately began to ascend, and continued to do 

 so steadUy. It was then immersed in water, wliich caused an acceleration of the 



ascent. 



From experiments Nos. 3. and 4, it appears that a solution of salt of the 

 strength employed by Blagden, contracted by cold, and expanded by heat, con- 

 formably to the common law, and exhibited no indication whatsoever of the pecu- 

 liar anomaly which exists in piu-e water. 



Experiment, No. 5. As the particular object of my research was to discover 

 whether sea- water observes the same relation in regard to the effects of heat and 

 cold as pm-e water does, I next employed an apparatus containing sea-water 

 taken from the Frith of Forth, a couple of miles to the westward of Leith. Its 

 specific gravity at temperature of 60° is 1.024. It contains 3.6 per cent, of saUne 

 matter. Its congealing point is 29°. 



According to the principle deduced from Blagden's experiment, did it pos- 

 sess the same peculiarity which fi-esh- water has, it ought to begin to expand at 

 temperature 36^°, and the expansion should go on increasing as its temperature 

 falls to the 29th degree, its freezing point ; and again, when heat is apphed to it 

 at that temperature, it ought to contract tiU it reach temperature 36|°, and then 

 begin to expand. The result of the experunent, however, was very different. 



The sea-water at the commencement was somewhat above 40°, and when the 



