of WATER by HEAT. 383 



The denfity of water, he thence inferred, is at its maximum 

 at 41 °, and decreafes with equal certainty whether the tempera- 

 ture is elevated or deprefled. 



M. DE Luc fays, indeed, that very nearly the fame alteration 

 in volume is occafioned in water of temperature 41 °, by a varia- 

 tion of any given number of degrees of temperature, whether 

 they be of increafe or of diminution ; and confequently that the 

 denfity of water at temperature 50°, and at temperature 32°, is 

 the fame. 



This philofopher did not conceive that the conftitution of wa- 

 ter, in relation to caloric, undergoes a change at the temperature 

 of 41°, fuch that fhort of this degree caloric fliould occafion 

 contradion, and beyond it expanfion. He imagined that heat 

 in all temperatures tends to produce two but quite oppofite ef- 

 fedls on this fluid, the one expanfion, the other contradlion. 



In low temperatures, the contradive efFeds furpafs the expan- 

 five, and contradion is the confequence : In temperatures be- 

 yond 41 °, the expanfive predominate, and the vifible expanfion is 

 the excefs of the expanfive operation over the contradive. 



In 1788, Sir Charles Blagden added the curious obferva- 

 tions, that water, which by flow and undifl;urbed refrigeration 

 permits its temperature to fall many degrees below its freezing 

 point, perfeveres in expanding gradually as the temperature de- 

 clines ; and that water having fome muriate of foda or fea-falt 

 diflblved in it, begins to expand about the fame number of de- 

 grees above its own term of congelation that the expanfion of 

 pure water precedes its freezing, that is, between eight and nine 

 degrees. More lately, {Philo-Jophical Tranfaclions, 1801), he, or 

 rather Mr Gilpin by his diredion endeavoured to afcertain, by 

 the balance and weighing bottle, the amount of this change of 

 denfity caufed by a few degrees of temperature. 



Every one mufl: be famiUar with the ufe which Count Rum- 

 ford has made of this peculiarity in the conftitution of water. 



Vol. v.— P. II. 3D in 



