Mr. J. E. Myers on a new Volumenometer. 197 



curv shall still be at the same level in both tubes is that the 



AC 

 volume-ratios ^ an ^ yi stall be equal. This principle forms 



the basis of action of the instrument. The vessel B contains 

 mercury, the quantity of which may be reduced by opening 

 the tap P, and allowing some to run out. In this way the 

 equality of volume-ratios may readily be obtained. The two 

 volumes A and B can be put in communication with each other 

 by means of the iron tube F, which is of small bore and is 

 provided with a tap, G. The main difficulty encountered in 

 using each of the instruments above described arises from the 

 necessity of hermetically closing the cavity of the instrument. 

 This difficulty we have successfully surmounted by providing 

 that the pressures on the under and upper surfaces of the cap 

 employed to close the instrument shall be approximately 

 equal. The device employed will be readily understood by 

 reference to figs. 1 and 2. C, D, and M are glass pipettes, 

 each of about 20 cub. centim. capacity. They differ from 

 ordinary pipettes in one particular, the upper attachments of 

 the bulbs consisting of glass tubes of capillary bore (1 millim. 

 diameter) . The top of the pipette C communicates with the 

 cavity of A. By means of the screw-cap E it will be seen 

 that the cavity of B is divided into two compartments, an 

 upper and a lower. The pipette D communicates with the 

 lower, and M with the upper compartment of the cavity of B. 

 It will be clear from this, that as pressure is applied to the 

 mercury in the reservoir it will force the mercury up the 

 pipettes, thus compressing the air both above and below the 

 screw-cap. An approximate balance of pressure is sufficient 

 to guard against leakage. 



The lower extremities of the pipettes are connected to an 

 ircm portion N, which is in communication with the reser- 

 voir 0, containing mercury, to which the arrangement for 

 applying pressure Q, is attached. 



At the places of juncture of the pipettes and the iron por- 

 tions, iron pieces whose diameter is equal to the diameter of 

 the pipettes are screwed in. The joints are made air-tight 

 by means of thick-walled indiarubber tubing carefully wired 

 down. The arrangement Q employed for applying, varying, 

 or removing pressure consists of a cylindrical tube closed at 

 both ends, connected with the water-main by means of a 

 narrow tube R, provided with a tap. The tube S serves to 

 effect communication with the reservoir 0, and the pressure 

 may be reduced at any time by opening the tap on the 

 tube U. The pipettes C and D with the connecting piece N 

 form a convenient differential manometer. 



