Mr. B. Stewart on the Sjjecific Gravity of Mercury. 317 



Weighed in air. 

 Mercury from the cistern of the old Kew 1 grs. 



standard barometer, filling the bottle, V 13591*36 



weighed at 62° F J 



Mercury from the cistern of the new Kew 1 l s ^ Q 1 • f f 



standard barometer weighed at 62° F. J 



Mercury used in experiments with air- 1 13" en -of, 



thermometer weighed at 62° F J 



the mean of these will be 13591*66 grs. 



It was found that the specific-gravity bottle had an internal volume 

 equal very nearly to 4 cubic inches ; and assuming that a cubic inch 

 of air weighs 0'31 gr., then the air displaced by the liquid filling the 

 bottle would weigh 1*24 gr. 



In like manner the air displaced by the Kew standard weights 

 (sp. gr. 8*2) would have the volume of 6*6 cubic inches, and would 

 weigh 2*04 grs. 



From these premises we find that the real weight of the mercury in 

 vacuo would have been 13590*86 grs. 



Again, the amount of water which the same bottle held at 02° F. 

 weighed in air 1 000*53 grs. 



Here the air displaced by the bottle is, as before, 1*24 gr., while 

 that displaced by the weights is only 0*15 gr. 



From this we find that the real weight of water filling the bottle at 

 62° F. would be in vacuo 1001*62 grs. We have thus — 



grs. 



True weight of mercury filling the bottle at 62° F. = 13590*86 



True weight of the same volume of water at 62° F. = 1001*62 

 And hence the specific gravity of mercury at 62° F., as compared 

 with water at the same temperature, will be 13*569 nearly. 



Again, if we assume the correctness of Regnault's Table of the 

 absolute dilatation of mercury, and also that of Despretz's Table of the 

 absolute dilatation of water, we shall find that the weight at 32° F. of 

 a volume of mercury weighing 13590*86 grs. at 62° F. will be 



13590*86 xl"00298=13631-361 grs. 

 Also the volume at 4° C, or 39°*2 F., of a volume of water weigh- 

 ing at 62° F. 1001*62 grs., will be 



1001*62x 1*0011437 = 1002*766 grs. 



Hence the specific gravity of mercury, according to the French me- 

 thod of determining it, will be 



13631-361 _ 

 1002-766 - ldo94 - 

 A determination by Regnault gives 13*596. 



These two results agree very nearly with one another ; and this 

 agreement tends not only to verify the correctness of Regnault's de- 

 termination, but to show that Regnault's Table of the dilatation of 

 mercury, and Despretz's Table of the dilatation of water, agree toge- 

 ther — a remark that had been previously made by Dr. Matthiessen 

 in a paper which he recently presented to the Society. 



