( 916 ) 
E By means of such a cock (A, fig. 2) and 
ur Pome the glass cock B the Cailletet tube is in 
carbonic acid connection with the calibrated space D, 
A C which according as the mercury reservoir 
HW is raised or lowered, is closed by mer- 
cury or is brought in connection with the 
tube PF, which leads with a T-joint to the 
airpump and the carbonic acid reservoir. 
We now start with exhausting the whole 
space, then close 4 and introduce a quan- 
E tity of carbonic acid into D, which is 
measured by the difference in pressure in 
D and F, and the temperature of the 
waterbath, in which D is found (omitted 
in the figure). Now the Cailletet tube is 
Fig. 2. cooled by means of liquid air) and the 
cock B opened, which causes all the carbonic acid to be distilled 
over, and the whole conduit C, with the cock A and the steel and 
glass capillary to be filled with mercury in. consequence of the dimi- 
nished pressure. To prevent the mercury from filling the whole 
Cailletet tube, the glass capillary?) has also been cooled with 
liquid air, so that the mercury congeals in it, and does not fall. 
Now A is closed and the carbonic acid thawed. To prevent the 
mercury from no longer adhering to the steel and the glass capillary 
and from falling in consequence, it is kept frozen in the glass capillary 
till the carbonic acid is thawed, and a sufficient pressure in the tube 
is ensured. As it is very easy’ to enclose a desired quantity of car- 
bonie acid by regulating the pressure in the measuring vessel D, 
we can in this way easily obtain every required concentration with 
great accuracy. Moreover this arrangement has the advantage that 
we can inerease or decrease the quantity of carbonic acid without 
being obliged to take the apparatus to pieces. To admit more carbonic 
acid we have only to open A very slowly so that the compressed 
gas drives the mercury before it almost to the cock B; then A is 
closed again. We then measure the required quantity in J, join the 
two quantities of carbonic acid, which are still separated by the 
mereury above B, to each other, and lead all the carbonic acid into 
1) With a view to these repeated great refrigerations the Cailletet tube has 
been made of borosilicate glass (Schott 59 III); bursting of these tubes hardly 
ever occurs. 
2) Not before all the carbonie acid has passed, to prevent the capillary from 
being stopped. 
