398 Expanfae Power of Froft. [Book VII. 



filled up with water and expofed to a fevere froft 

 which prevailed, in that country. The expanfion of 

 the ice forced out the plug, and the water, which im- 

 mediately followed, was frozen into an irregular rnafs 

 or column of ice. The inftances, however, already 

 mentioned, are far lefs ftriking than one defcribcd by 

 Mufchenbroeck, in which a ball of iron, an inch thick, 

 was burft afunder in the courfe of twelve hours by the 

 expanfive power of froft. That philofopher having 

 calculated the force exerted by the freezing of water 

 in a fimilar cafe, found it equal to a force capable of 

 raifing a weight of twenty- feven thoufand feven hun- 

 dred and twenty pounds. That the expanfive power 

 of freezing water, however, has certain limits, appears 

 from the following experiment, made by the Floren- 

 tine academicians. A brafs globe filled with water, 

 and clofed at its orifice by a well-fitted fcrew, was im- 

 merfed in freezing water, but did not burft j they then 

 pared bfF fuch a quantity of the metal as lefc the fides 

 of the globe unable to refift the expanfion of the water; 

 the force which was required to burft the globe in this 

 ftate was computed at twenty-feven thoufand pounds. 

 When fuch is the expanfive power exerted by water in 

 palling to the ftate of ice, we cannot be furprized that 

 veffels, which are left filled with water in frolty wea- 

 ther, ihould be burft by its freezing, and that the fame 

 thing fhould happen to water-pipes expofed to the 

 aclion of froft. The pavement is fometimes loofened 

 from the fame caufe, and in countries where very fe- 

 vere colds prevail, the fap of trees congeals, and their 

 trunks are burft afunder with a noife like that of can- 

 non. Froft fertilizes the ground, by loofening the co*- 

 hefion of the 'particles of earth. 



As ice is never perfectly clear or tranfparent, and as 

 we find fmall cavities in it, fome have thought that the 



air 



