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XIII. Remarks on Jpec'ific Gravities taken at different Degrees of 

 Heat, and an eafy Method of reducing them to a common Stan- 

 dard. By Richard Kirwan, Efq, F. R. S. 



Read February 17, 1785. 



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THAT a comparative view of the weights of equal volumes 

 of water and all other fubftaiiccs is highly uleful on 

 many occafions, is too well known to require any proof; but 

 that a principal ule refaiting from this compariion, when pro- 

 perly made, is unattainable by a perulal of the common tables, 

 I fhall here endeavour to ihew, and at the fame time point 

 out a remedy for this defeft. 



One capital advantage derivable from a table of fpecific gra- 

 vities, is the knowledge of the abfolute weight of any lolid 

 meafure of the fubftances therein contained, or that of the folid 

 meafure of a given weight of thofe fubftances, a cubic foot of 

 water being luppofed to weigh 1000 ounces avoirdupois, and 

 confequently a cubic inch of water weighing 253,182 grains. 

 But the authors who havedifcovered this equation of weight and 

 meafure, and all thofe who have fince treated this fubjec^l, have 

 neglected to inform us of the temperature at which this agree- 

 ment takes place ; yet that it cannot take place in all tempera- 

 tures is evident from the experiments of Dr. Halley and 

 others, who have found, that from a few degrees above the 

 freezing to the boiling point, water is dilated about ^'-^ of its 

 bulk; and, confequently, if 1000 ounces at the freezing point 

 be equal to one cubic foot, they mud be equal at the boiling 



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