THKliMAL PROPERTIES OF CARBONIC ACID AT LOW TKMPKKATURES. 



it was not possible to keep the temperature of the liquid CO, aljsolutely constant 

 dm -ing an observation. Slight variations of temperature account for the irregularities 

 of the observations below 30 C. ; above that temperature the " infra-cooler" was 

 not used. The results of the tests with the original and with the new apparatus are 

 summarised in Table V., and both are plotted in fig. 9, p. 76. The two sets of results 

 are in good agreement, considering tin- smnllness of the quantities being measured. 



Scries V. The apparatus used for measuring the elasticity and dilatation of 

 liijiiid C() a is shown in figs. 10 and 17 : 



a is a capillary glass tube, the lower end of which is closed and the upper end 

 thickened and blown into a thistle funnel. A centimetre scale was etched along its 

 whole length, and it was carefully calibrated by measuring the 

 variation in the length of a thread of mercury in different 

 positions. 



It is a gunmetal socket, shown in detail in fig. 17, turned to 

 hold the glass tube, the joint being made by a thin rubber 

 sleeve. The top of the socket is closed by a screw plug. 



c is a fine copper pipe, J-inch bore, 12 feet long, connecting 

 the socket to the regulating valves, pressure gauge, and, through 

 a drying flask, to the CO., flask. This pipe is sufficiently 

 flexible to allow the glass tube to be moved about as required 

 while under pressure. 



The glass tul>e was charged as follows : The tube was laid 

 in a nearly horizontal position and a small quantity .of mercury 

 poured into the thistle funnel, where it lay without obstructing 

 the entrance to the tube. The plug was then inserted in the 

 gunmetal head. The air was removed by means of an air pump, 

 successive charges of CO 3 gas being admitted and exhausted. 

 The lower half of the glass tube was then surrounded with ice, 

 and COj, gas was admitted up to a pressure slightly above the 

 saturation pressure at C. The gas then condensed in the 

 glass tube, and the meniscus could be seen travelling up the tube. The rate of 

 condensation could be regulated with ease by modifying the pressure. When 

 sufficient liquid was condensed, the tube was raised into a vertical position so that 

 the mercury in the funnel flowed into it, on to the top of the liquid CO^. The tube, 

 kept vertical, was then lowered into the calorimeter, the temperature of which had 

 been adjusted to a few degrees below C. The amount of liquid used and the 

 length of the mercury column were chosen so that the whole of the liquid CO., was 

 below the level of the bath in the calorimeter, and therefore at a uniform tempera- 

 ture, and the top of the mercury showed above the lid of the calorimeter, so that 

 its position could be observed with a cathetometer. 



17 



