( 242 ) 



XV. Inqtiiry whether Sea- Water has its Maximum Density a few Degrees above 

 its Freezing Point, as Pure Water has. By Thomas Charles Hope, M. D., 

 V. P. R. S. E., F. R. S., Professor of Chemistry in the University of Edin- 

 burgh. 



Bead 2d April 1838. 



Sir Charles Blagden concludes a memoir in the Philosophical Transactions 

 of London, vol. Ixxviii., for the year 1788, " On the Effect of various substances 

 in lowering the Point of Congelation in Water," with the account of an experi- 

 ment to determine the effect of salt upon the expansion of water by cold. 



From that experhnent, he imagined that he had reason to conclude, as far as 

 one experiment goes, that the combination of a salt with water has no other effect 

 upon its quaUty of expanding by cold, than to depress the point at which that 

 quality begins to be sensible, just as much as it depresses the point of congelation. 



The scientific world appear to have admitted this general deduction of Blag- 

 den, and, trusting to the result of a single experiment, extended it so far as to 

 lay it down as a general law, that, as pure water has its maximum of density at 

 7^° above its freezing point, so every saline solution has a maximum of density 

 at a temperature above its point of congelation, and that this temperatm'e will be 

 exactly 7^° distant from the freezing point of the solution. 



The water of the ocean holding in solution saline matter of different kinds, 

 was believed to obey the same law to which the solutions artificially made were 

 supposed to be subject ; and as the congealing point of sea- water was alleged to 

 be, at an average, about 29°, it was consequently imagined that it had its maxi- 

 mum density at nearly 36^°. 



As sea-water collected in different latitudes, at different depths and at dif- 

 ferent distances from shore, contains different quantities of saline matter, its 

 point of congelation must be liable to variation, and with it the temperature of 

 its supposed maximum of density. 



Every one conversant with the writings of Count Rumford, will remember 

 how much use he makes of the strange anomaly in the constitution of water to 

 account for several interesting aqueous phenomena of Natm-e ; and several writers 

 on oceanic occurrences have availed themselves of the belief that the same ano- 

 maly exists in sea-water, and employed it to explain several hydrographic facts 

 of curiosity and interest, and, in particulai-, some remarkable currents in the 

 ocean. 



