74 
PKOFESSOR W. RAMSAY AXD DR. M. M7 TRAVERS 
was read at a kiiowji temperature and pressure in the tube c, which had previously 
been graduated and calibrated. The capillary tube d, which was a piece of even- 
bore thermometer tubing, was sui’roimded with a suitalde cooling agent, so that the 
gas was near its boiling-point under normal pressure. By altering the level of h, 
Fig. 6 
and reading the difference in level of h and c, the actual pressure ot the gas was 
measured. A })ortion licpiehed in d ; its volume was read, and also the volume of gas 
remaining in c, after a ])ortion had been licpiehed. As the density of the gas was 
known, it was easy to calculate the weight of the })ortion I'emaining in c, and conse- 
(piently of the portion licpiefied in d. 
The volume of one division of the tul)e c was e(puvalent to gramme ot 
mercury ; that of the capillary d, to 0’00UG78 gramme. The volume in grammes 
of mercury from the 1 ugliest mark on c to the end of the capillary was found by 
determining the cliange in volume of the gas in c, conseipient on known changes of 
pressure ; and as a mean of five concordant determinations, it vras found to he equal 
to the volume of ()'55 gramme i of mercury. 
