CONTRACTION OF WATER BY HEAT. JS9 



VIII. 



Experiments and Ohfervatiom upon the Contraclion of Water by 

 Heat at low Temperatures. % Thomas Charles Hope, 

 M. D. F. R. S. Ed. Profejfor of Chemifiry in the Univerfity 

 of Edinburgh . From the Edinburgh Philofophica I Tranfa&ions, 

 for 1804. 



JL O the general law, that bodies are expanded by heat, and Expanfion of 

 contracted by cold, water at the point of congelation, and &* # e „ ea y r c £ e * 

 for fome degrees of temperature above it, it feems to afford a freezing point. 

 very lingular and curious exception. 



The circumftances of this remarkable anomaly have been for 

 fome time believed to be the following : 



When heat is applied to water ice cold, or at a temperature General or ufual 

 not far diftant, it caufes a diminution in the bulk of the fluid. %£***** 

 The water contracts, and continues to contract, with the aug- Ice-cold water 

 mentation of temperature, till it reaches the 40lh or 4lft de- cont ; aft f h Y ™' 



t> • m crea » e of temp. 



gree. Between this point and the 42d or 43d, it (utters to about 4a , 

 fcarcely any perceptible change ; but when heated beyond the and then ex " 

 laft-mentioned degree, it begins to expand, and increafes in ' 

 volume with every fubfequent rife of temperature. 



During the abftraction of caloric, the peculiarity in the con- and fuffers the 

 ftitution of water equally appears. Warm water, as it cools, "verfe change 

 ftirinks, as other bodies do, till it arrives at the temperature of 

 43° or 42°. It then fuffers a lofs of two degrees without any 

 alteration of denfity. But when farther cooled, it begins to di- 

 late, and continues to dilate, as the temperature falls, till con- 

 gelation actually commences, whether this occurs as foon as the 

 water reaches the 32°, or after it has defcended any number of 

 degrees below it. 



Suppofing this peculiarity of water to be eftabliflied, it muft This fdppofed 

 appeal, indeed, a very odd circumftance, that heat fhould pro- P ecull4rlt y has 

 duce contraction in this fluid, while it caufes expanfion in other 

 bodies *; and no lefs ftrange, that within one range of tempera- 



* Is this mode of change peculiar to water ? — I do not know of 

 any experiments with other fluids, except that mentioned on page 

 343. Perhaps it may be common to all, or at leaft to all thofe 

 which expand by congelation. Decifive trials of this point are thd 

 more defirable, becaufe fome of Count Rumford's general induc*» 

 tions require or fuppofe that feawater mould not be thus affected.:— -N. 



Z 2 ture 



