351 



prevent distillation of li([uid into tlio bulb. After tlio weighing the 

 weight of the empty bulb was determined a second time as a test. 



Subsequently deterniinations at room temperatui-e were made at 

 pressures of '/a ^^^^^ V4 ^^tm. The pressure was in this case read on 

 the mercury-gauge. 



It appeared necessary to determine the contraction of the bulb 

 by the diminution of the internal pressure. For this purpose the 

 weight of air contained in the bulb at a pressure of Vn of an atm. 

 was measured. 



Finally two weighings were made with butane-vapour at 0° and 

 at V» •'^'id -/s of an atm. 



Measurements ^). 



Empty bulb. The tarra-bulb -\- 8 grammes made equilibrium with 

 the empty bulb -\- .84036 grms. A later weighing gave .84033, a 

 third .84036. The mean of these is .84035. This weight is in 

 error by an amount n:\ owing to the change of the external volume 

 by exhaustion. 



Bnlb inith dri/ air. At 18°.58 and 76.738 cms. the weight of the 

 air was found to be .47370 gruis ; a second weighing gave 

 .47735 grms. at 16°.88 and 76.805 cms. For the weight at 0° and 

 76 cms. they give .5009 grms and .5014 grms. the mean of which 

 is .5012 grms. This figure has to be increased by the amount x 

 mentioned above. 



Bulb löitli dry air at loioer internal pre.'^snre. At a pressure of 

 26.816 cms and a temperature of 16°. 71 the air weighed .16596 

 grms. The weight of the air contained in the bulb at 0° and 76 cms 

 would have been .49899 grms. It is easily proved, that the error 

 of this figure owing to the change of external volume is approximately 

 equal to x. The ditference between .5010 and .49899 is therefore 

 independent of .r and represents the diminution of weight due to 

 the diminution of internal volume at the lower pressure : as the 

 diminution may be taken proportional to the change of pressure, it 

 follows that the diminution of weight for 1 atmosphere would be 

 .00333 grms. The external change of volume being approximately 

 equal to the internal change, this latter weight is equal to the 

 correction x. The weight at 0° and 1 atm. is thus .5012 -|- .0033 = 

 .5045 grms. From this weight the volume is found by dividing by 

 the normal density of air. The measured weights of butane have 



1) Tlie calculations as given liere differ slightly from those in the Dutcii ediliun 

 owing to a correction which had been overlooked. 



