Lerts & Bhake—The Carbonic Anhydride of the Atmosphere. 127 
We eventually discarded filtration, which did not yield satis- 
factory results,' and employed a simpler form of vacuous vessel. 
We also titrated the whole of the absorbent, and not an aliquot 
part, and rinsed out the receiver with water free from uncombined 
carbonic anhydride. The construction of the apparatus shown in 
fig. 4 needs no special description, and the way in which it is 
used will be apparent from what has been 
said regarding the first vessel. 
After it has been exhausted and the 
stopcock closed, the tube B is attached by 
its rubber junction to the tube II of the 
inverted receiver clamped to a retort-stand. 
A soda-lime tube having been attached to 
the tube I, the absorbent is withdrawn 
by cautiously opening the stopcock, care 
being taken that no air follows it before 
the stopcock is closed. 
AsouT 
2000. c. CAPACITY To rinse out the receiver and collect the 
rinsings in the titrating vessel the manipu- 
lation is as follows:—The titrating vessel 
is first removed and the glass rod plug 
substituted for it. The receiver is then 
WHE. 4h 
No. 2 Titrating vessel. : 
unclamped and placed upright on a table. 
The nozzle of a measuring pipette filled with water free from car- 
bonie anhydride is now inserted in place of the glass rod plug 
attached to IL and the stopcock attached to this pipette 
opened, when water flows into the receiver. When sufficient has 
been added the pipette is removed and the glass rod plug attached. 
The receiver is then rolled round so that all parts of its inner 
surface are well washed, when it is once more inverted and the 
when ordinary distilled water is used either for washing out the receiving vessels or in 
preparing the standard acid is therefore considerable. 
The only reliable method for avoiding this source of error is to neutralize the dis- 
tilled water with dilute baryta. Redistillation of water, even from an alkaline 
solution, does not give at any period of the distillation a distillate free from carbonic 
anhydride, owing to absorption of that gas from the atmosphere. Mr. W. Caldwell 
has, at our suggestion, investignted the amount thus absorbed, and, on an average, has 
found 0°5 to 0°6 c.c. of the gas at N.T.P. per litre of water. 
1 Possibly the asbestos absorbed baryta. That filter-paper does so has been proved 
by both Miiller and Reiset. 
