1393.] 



On the Densities of the Principal Gases. 



141 



The Water Contents of the Globe. 



The globe being packed in finely-divided ice, was filled with boiled 

 distilled water up to the level of the top of the channel through the 

 plug of the tap, that is, being itself at 0°, was filled with water also 

 at 0°. Thus charged the globe had now to be weighed ; but this was 

 a matter of some difficulty, owing to the very small capacity available 

 above the tap. At about 9° there would be a risk of overflow. Of 

 course the water could be retained by the addition of extra tubing, 

 but this was a complication that it was desired to avoid. In 

 February, 1882, during a frost, an opportunity was found to effect 

 the weighing in a cold cellar at a temperature ranging from 4° to 7°. 

 The weights required (on the same side of the balance as the globe 

 and its supports) amounted to 0'1822 gram. On the other side 

 were other weights whose values did not require to be known so long 

 as they remained unmoved during the whole series of operations. 

 Barometer (corrected) 758 - 9 mm. ; temperature 6'3°. 



A few days later the globe was discharged, dried, and replaced in 

 the balance with tap open. 1834-1701 grams had now to be associated 

 with it in order to obtain equilibrium. The difference, 



1834-170-0-182 = 1833-988, 



represents the weight of the water less that of the air displaced by it. 

 The difference of atmospheric conditions was sufficiently small to 

 allow the neglect of the variation in the buoyancy of the glass globe 

 and of the brass counterpoises. 



It remains to estimate the actual weight of the air displaced by the 

 water under the above mentioned atmospheric conditions. It appears 

 that, on this account, we are to add 2'314, thus obtaining 



183630 



as the weight of the water at 0° which fills the globe at 0°. 



A further small correction is required to take account of the fact 

 that the usual standard density is that of water at 4° and not at 0°. 

 According to Broch (Everett's ' C.Gr.S. System of Units '), the factor 

 required is 0'99988, so that we have 



1836-30 _ 

 0-99988 ~ 183(V52 



as the weight of water at 4° which would fill the globe at 0°. 



Air. 



Air drawn from outside (in the country) was passed through a 

 solution of potash. On leaving the regulating tap it traversed tubes 



