DR HOPE ON THE MAXIMUM DENSITY OF SEA-WATER. 251 



Experiment, No. 8. — The preceding experiment was repeated and afforded 

 the same result. Again, as recorded in my memoir so often referred to, when the 

 jar was Med with water of 39^^ and the basin was charged with a mixture of 

 salt and snow, the thermometer at the top was cooled in the course of two hours 

 6^°, while that at the bottom did not fall half a degree ; thus indicating, that 

 water at 39^° expands as it cools below that point. 



Experiment, No. 9. — I filled the jar with the sea- water of temperature 40^ 

 and the basin with a frigorific mixture. The lower thermometer immediately 

 began to show the approach of a cold descending current, and in the course of 

 one hour and ten minutes fell to 30.° The temperature of the upper thermometer 

 was in no measure reduced, the temperature of ambient air being 44°. 



From this experiment, it appears that sea- water during cooling contracts, 

 and becomes more dense as it approaches its congealing point. 



The concurring testimony of this second series of experiments, and of the 

 preceding, shews that the same anomaly which exists in pure water does not exist 

 in sea- water. Hence the conclusions and general law deduced fi-om the solitary 

 experiment of Sir Charles Blagden must be corrected, and all the reasonings 

 founded upon them respecting peculiar currents in the ocean and other oceanic 

 phenomena, must fall to the ground. 



As the subject of inquiry in the preceding memoir relates to the law obser- 

 ved by sea- water, in the changes of volume occasioned by heat and cold for some 

 degrees above its freezing point, I have not thought it necessary to call the at- 

 tention of the Society to the same circumstances at temperatures below the freez- 

 ing point. Every body knows, that though the temperature of water while 

 congealing is invariably 32°, yet it permits its temperature to fall many degrees 

 without freezing, provided it be kept free from every kind of disturbance and be 

 cooled very gradually ; that this is also the case with saline solutions, sulphuric, 

 and nitric acid, &c. and that the temperature of each fluid, when it begins to congeal, 

 instantly rises to the proper freezing point of that fluid. Marcet in his memoir 

 above quoted concludes, upon the authority of four concurrent experiments, " that 

 if a vessel fiUed with sea- water of the specific gravity of about 1.027, and of any 

 temperature above the freezing point, be gradually and slowly cooled, the water 

 contracts in bulk ; and that this contraction continues to proceed, though in a 

 diminishing ratio, till the temperature has reached 22°. At this point the water 

 appears to expand a little, and continues to do so till its temperature is reduced 

 to between 19° and 18°, at which point the fluid" (congeals and) " suddenly expands 

 to a very considerable degree, shooting up with great rapidity, and forcing itself 

 out at the open end of the tube." 



M. Despretz of Paris, in his second memoir on the Maximum of Density of 

 Liquids, as we learn from an extract contained in the Comptes Rendus for March 



