On the Contraction of If'ater bj Heati 1 dl 



fn low temperatures, the contractive etfects surpass the 

 expansive, and contraction is the consequence : \n tempe- 

 ratures beyond 41% the expansive predominate, and the vi- 

 sible expansion is the excess of the expansive operation over 

 the contractive. 



In 178S sir Charles Blagden added the curious observa- 

 tions, that water, which by slow and undisturbed refrig'era- 

 tion permits its temperature to fall many deurecs below its 

 freezing point, perseveres in expanding gradually as the 

 temperature declines ; and that water, having some muriate 

 of soda, or sea salt, dissolved in it, begins to expand about 

 the same number of degrees above its own term of congela- 

 tion that the expansion of pure water precedes its freezing, 

 tha.t is, between eight and nine degrees. More lately (Phi- 

 losophical Transactions I SOI), he, or rather Mr. Gilpin by 

 his direction, endeavoured to ascertain, by the balance and 

 weighing-bottle, the amount of this change of density caused 

 by a few degrees of temperature. 



Every one nmst be familiar with the use Vv'hich count 

 Rumford has made of this peculiarity in the constitution of 

 water, in explaining many curious appearances that pre- 

 sented themselves in his experiments upon the conducting 

 power of fluids, and in accounting for certain remarkable 

 natural occurrences. The count, with his usual ingenuity, 

 has endeavoured to point out the important purposes which 

 this peculiarity serves in the oeconomy of nature, and to 

 assign the final cause of so remarkable an exception from a 

 general law. 



In recording the observations and opinions that have been 

 published concerning this point, I might now, in order, 

 notice those of Mr. Dalton, of Manchester, related in the 

 fifth volume of the Manchester Memoirs, which tended to 

 confirm and enlarge our knowledge of it. But as Mr. Daltou 

 himself has called in fjuestion the iiccuracv of the conclu- 

 sions which had been drawn from his experiments, and from 

 those of preceding observers, I shall only remark, that they 

 are of the same nature, and ncaily to the same purport, zt> 

 those of M. de Luc. 



It was in consequence of a conmnmication with which 

 Mr. Dalton favoured me, three months ago, that my at- 

 tention was directed to this subject. He informed mc, that 

 after a long train of experiments he was led to believe that 

 he, and his predecessors in the same field of investigation, 

 had fallen into a mistake with regard to the contraction of 

 water by heat, and its expansion by cold, in consequence 

 of overlooking or underrating the effect vvhich tlic change 



in 



