10 Mr. B. Stewart on the Specific Gravity of Mercury. [Feb. 1, 



February 1, 1866. 

 Lieut.-General SABINE^ President, in tlie Chair. 

 The following communications were read : — 



1. "On the Specific Gravity of Mercury." By Balfour Stewart, 

 M.A., LL.D., F.R.S., Superintendent of the Kew Observatory. 

 Received January 25, 1866. 



Some time since, in connexion with a research on the fusing-point of 

 mercury, several observations were made at Kew of the specific gravity of 

 this fluid. 



A specific-gravity bottle was used for this purpose and it was washed, 

 in the first place with sulphuric acid, secondly with distilled water, and 

 thirdly with alcohol ; when this was done it was found to contain mercury 

 without any air-specks or any diminution of that metaUic lustre which pure 

 mercury exhibits when in contact with a vessel of clean glass. Three dif- 

 ferent specimens of pure mercury were used and were separately weighed 

 in the specific-gravity bottle at 62° Fahr. The following results were 

 obtained : — 



Weighed in air. 



Mercury from the cistern of the old Kew 1 grs. 

 standard barometer, filling the bottle, >- 13591*36 

 weighed at 62° F j 



Mercury from the cistern of the new Kew 1 13591*66 

 standard barometer weighed at 62° F. J 



Mercury used in experiments with air- 1 1359 1*96 

 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 m vacuo 

 would have been 13590*86 grs. 



Again, the amount of water which the same bottle held at 62° F. weighed 

 in air 1000-53 grs. 



Here the air displaced by the bottle is, as before, 1*24 grs., 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- — 



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

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



