£$(52 CeNTRACTION OF WATER BY HEAT. 



Annotation. — W. N. 

 Sir Charles It does not feem to me that Sir Charles Blagden's explana, 



Bbgden's theory t j on d ow nec eflarily imply that the fluidity of the mafs taken 

 of expanfionor , , f t * ./ . ... ... 



water by heat as a whole, mould be lenfibly impaired when tried by the ap- 



does not fuppofe plication of a mechanical teft. It might be impaired in the 



that it fliould be r . _ ° . . V. ,. _ 



lefs fluid. fame manner as tne wafer is affe&ed by mixing fmall floating 



fragments of a folid along with it. When a faline folution 

 which would become folid by cold, fuch for example as the 

 fulphate of foda, is cooled below its point of congelation, the 

 cryftals will be differently formed according to circumftances. 

 Inflanee of cry- If the fluid be gently (haken or made to ofcillate, a mower of 

 ftal«Mtion dif- minute cryftals will gradually fall through the fluid ; and the 

 to circumftances. whole mafs will be a confiderable time before the cryftalliza* 

 tion isfinimed; but if, inftead of this method of agitation, 

 the glafs be fcratched by a quill underneath the fluid, in Sir 

 Charles Blagden's way, or if a fmall inftrument, having a 

 cryftal of the fait adhering to it, be dipped into the folution, 

 the cryftals will radiate with great rapidity from that centre of 

 perturbation, and in a few feconds the whole of the folution 

 Whence it is will become rigid. This common and very linking experi- 

 conjeftured that men t f chemical lecturers,, feems to me to indicate at leaf! a 

 water by cold pofiibilily that fmall cryftals of ice may be formed and float 

 may arifefrom diftinftly from each other in water, at 40 degrees and lower : 

 2 ^cVinthe and I think the metals afford us a number of inftances in which 

 £uid, a confiderable interval of temperature is found to be between 



the commencement of cryftallization and the folidiflcation of 

 the whole mafs. In pewterers folder the interval is not lefs 

 than 40 degrees. This hypothefis of fuch difleminated parti- 

 cles of ice, which feems to be nothing more than an expreflion 

 of Sir Charles Blagden's theory in different words, will explain 

 why the colder water mould be lighter ;— namely, becaufe it 

 muft contain more ice, and alfo why the expanfion ought not 

 to begin but at fome definite temperature. 

 Ameafureof Though it does not appear to me that the theory of Sir 

 the greater or Charles muft neceflarily imply a change in the mechanical re- 



fcadie fl s1sTer 0f *i ftance of water frora what ma y be called rl g idit y » yet there 

 defuable. are many other reafons why philofophers fliould be delirous of 



meafuring the variations of fluidity in bodies ; that is to fay, 

 the greater or lefs facility with which their parts are moved 

 Dr. Hope's trial amongft each other. The ingenious attempt of Dr. Hope to 

 may be modified tf CQl & m tfjj s f wm the refiftance made by a fluid to the perfo, 

 ******* ration. 



