Letts & Braxe—The Carbonic Anhydride of the Atmosphere. 129 
due precautions being observed to prevent access of air during the 
operation. At first we thought this washing to be unnecessary, 
for owing to the greasy nature of the surface of the paraffin wax, 
only droplets of the absorbent remain behind. The extent of the 
error thus introduced is shown in Series 4, p. 183, compared with 
subsequent Series. 
The receiver now contained air free from carbonic anhy- 
dride, and it was next charged with a definite volume of that 
gas—the operation being performed with the apparatus figured 
on following page. 
By raising the reservoir HZ of the apparatus, and turning 
the stop-cock C, the measuring pipette H, and the tube A were 
completely filled with mercury (the cock J of the manometer 
tube being closed meanwhile). The receiver of purified air, clamped 
in an inverted position as shown, was next brought over K, and 
the latter attached to it by the rubber junction which with the 
short glass rod had served to plug the tube I. During the attach- 
ment and previous removal of the glass rod, the rubber tube was 
pinched between the finger and thumb to prevent entrance of the 
external air. H was next lowered so as to produce a vacuumi in 
H and F, the tap C turned so that A communicated with H, and 
a stream of carbonic anhydride flowed into the apparatus. The 
pinchcock G was now opened, and a stream of gas allowed to flow 
into J, which contained strong caustic potash solution, and indicated 
eventually by the complete absorption of the bubbles that all air 
had been displaced from A, and that the measuring pipette H was 
full of pure carbonic anhydride. The stop-cock C was then closed 
and FE raised, so that mercury flowed into H and F, and past G, 
which was closed. The stop-cock J of the manometer tube was: 
next opened, and the stop-cock CO and reservoir EZ so manipulated 
that a definite volume (usually 1 ¢.c.) of carbonic anhydride was 
enclosed in the measuring pipette at the existing atmospheric 
temperature and pressure—with due allowance for the capillary 
rise of mercury in its lower extremity. 
A note having been taken of this volume as well as of the 
barometric height, and temperature of the air (as indicated by a 
thermometer placed in the neighbourhood of I), the stop-cock J 
was closed, the reservoir E raised, and C turned, so that the 
measured volume of carbonic anhydride passed slowly into the 
