70 
PROFESSOR W. RAMSAY vVXD DR. M. M7 TRAVERS 
ture, the argon was solid. The temperatures were measured by the resistance of a 
platinimi coil, immersed in the liquid. 
For the remaining experiments, the pressure-apparatus was used. The tube was 
first surroinided by liquid nitric oxide, boiling at 123T° abs. under atmospheric 
pressure ; the temperature was measured simultaneously by help of the platinum- 
resistance thermometer ; the l;)oiliug-point of the nitric oxide, a large quantity of 
which had been prepared and purified Ijy fractional distillation, was previously 
measured l)y the hydrogen thei'iiiometer. The next temperature was that of 
ethylene, boiling under reduced pressure; readings were obtained at 136'8° and at 
temperatures up to 149° al)s. As with nitric oxide, a large cpiantity of ethylene 
was prepared, and purified by fractional distillation. The temperatures were here 
determined with a hydrogen thermometer. Owing to the length of tube immersed 
in the ethylene, we did not succeed in reading directly the critical temperature, for 
the mercury froze in the capillary tube. But on using an air-bath (a vacuum-jacket, 
previously cooled with liquid air), containing the experimental tube, together with 
the hydrogen thermometer, all being cooled externally by surrounding the inner 
vacuum-tube with liquid air, the critical change was twice observed, at 155'5° and 
1557° abs. The critical pressure was afterwards determined graphically from the 
vapour-pressure curve plotted liy means of the straight line indicating ratios. 
Krypton .—Two olrservations were made at the temperature of liquid air ; at 
these tempei'atures the krypton was solid. The next oljservation was at the tem¬ 
perature of boiling metliane (1127° abs.), determined as the mean of five experi¬ 
ments with tlie platinum-resistance thermometer. The boiling-point of nitric oxide 
(125T°) gave the next readiiig ; a further observation was made at the boiling- 
point of ethylene under atmospheric pressure (170’9°); this temperature had 
pi-eviously been determined by the hydi'ogen thermometer. Lastly, a series of 
observations was made, using pure dry ether, contained in a vacuum-vessel of half 
a litre capacity; the rise of temperature of the ether was very slow, owing to its 
considerable mass, and to the slow transmission of lieat through tlie walls of the 
vessel ; and close to the tube were placed the bulb of the h 3 nlrogen thermometer 
and a mechanical stirrer, so that the temperature was iiearl}" uniform throughout. 
To hasten the rise of tenq^erature, small (piantities of ether were introduced from 
time to time, and two observations were taken at two consecutive temperatTires, 
close together, before adding a fresh dose of wan'in ether, so as to raise the tempera¬ 
ture for the next set of oljservations. The critical temj^erature and pressure were 
also observed. 
AT a 0 a.—Observations were made, as before, at the temperature of liquid air, but 
the va})Our-])ressure was hardl}^ appreciable. When the temperature of liquid air 
is alluded to, it must be understood tliat the thermometer was alwaa^s used to 
determine the actual tempenatiire ; and that as the tenqierature rose owing to the 
evapo]'ation of nitrogen, fi'esh observations were made. An attempt vas also made 
