On the Contraction of Water ly Heat. 171 



move every doubt respecting the matter of fact, it remains 

 a very difficult problem for those who are fond of philoso- 

 phical investigation, to explain how heat shall occasion ia 

 the. same fluid, without producing any alteration of me- 

 chanical form or chemical condition-, at otie time contrac- 

 tion and at another expansion, and to reconcile the con- 

 tractive eflcct to the conceived notions of the mechanism 

 of the operations of this energetic agent. 



When heat causes expansion, it is imagined to act by 

 inducing a repulsion among the particles of bodies, which, 

 opposing and overpowering the cohesive attraction, causes 

 tile particles to recede. 



In what manner, then, the addition of heat can occa- 

 sion, or allow, the particles of water to approach each 

 other, and how the subtraction of it can make them retire 

 to a greater distance, 1 confess I can in no measure com- 

 prehend. 



An explanation, abundantly plausible at first view, very 

 readily suggests itself to every one Vv'ho is aware of the great 

 and forcible expansion which happens to this fluid at the 

 moment of its congelation. It is stated by sir Charles 

 Blagden, in the paper already quoted. 



The remarkable dilatation which water experiences at the 

 instant of being converted into ice, is very generally ascribed, 

 and I presume very properly, to a new arrangement which 

 the particles assume, determined probably by their polarity; 

 by which one side of the particle A is attractive of one side 

 of B, while it is repulsive of another. 



Now, if this polarity operates with so much energy as 

 to impart almost irresistible expansive force at temperature 

 S'i", it is reasonable to suppose that it may begin to exert 

 its intiuence, though in a far inferior degree, at tempera- 

 tures somewhat more elevated. The expansion, therefore, 

 that takes place, during the falling of temperature Irom 

 40", may be imputed to the particles beginning or aflccting 

 to assume that new arrangement which their polarity assigns 

 them, in which arrangement these particles occupy more 

 space than before. 



Again, when heat causes wattr of 32" to contrart, upon 

 the same principle it may be conceived to operate by 

 counteracting the small portion of the disposition to pola- 

 rity that survives tlie liquefaction. 



I am afraid that we caimot rest satisfied with this ex- 

 flanation. We must not be deceived by the plausibility 

 of it. 



The state of perfect fluidity depends upon the circum- 

 stance. 



