Lerts & Braxe—The Carbonic Anhydride of the Atmosphere. 119 
Blochmann, his store bottle for the baryta water and measuring 
pipette, form a closed system into which only purified air can 
enter. His absorbing vessel (7-12 litres capacity) is fitted with a 
hollow glass stopper carrying two stop-cocks. He, however, 
measures the baryta water into thin-walled pipettes (previously 
filled with purified air) which are then sealed. One of these tubes. 
is placed in the absorbing vessel previous to filling it with the air 
to be examined. Air is then aspirated for a sufficient time, the 
stop-cocks closed, the baryta tube broken, and after shaking, the 
vessel is left for 24 hours. An aliquot portion of the clear fluid is 
then titrated with standard oxalic acid and phenol-phthalein as 
indicator, all due precautions being observed to avoid access of air 
containing carbonic anhydride during the process. 
Secrion I].—Tue Avuruors’ ExPERIMENTS ON PETTENKOFER’S. 
PROCESS AS MODIFIED BY THEM. 
The experimental work we are about to describe originated in 
a set of determinations we had to make of carbonic anhydride in 
the air of a weaving shed in a linen factory at Belfast. For these 
determinations we employed a somewhat rough modification of 
Pettenkofer’s process, in which the vessels serving for the collec- 
tion of the air samples, the absorption of the carbonic anhydride, 
as well as for the subsequent titrations, were ordinary Winchester 
quart bottles of greenish-white glass. For the titration itself we 
used dilute hydrochloric acid, with phenol-phthalein as indicator. 
Although no considerable degree of accuracy was necessary for 
the purpose we had in view in making the determinations, we were- 
struck with the discrepancies in the results obtained with duplicate 
samples of air; and following the matter up we were gradually led 
into an inquiry regarding Pettenkofer’s process, the extent of 
accuracy and delicacy of which it is capable, and the most suitable 
method of performing it and overcoming incidental errors. 
We use the term “ Pettenkofer’s process”’ in a somewhat wide 
sense. The essence of the method we understand to be the 
enclosure of a relatively small volume of air in a glass vessel: tho. 
absorption of the carbonic anhydride by an alkaline fluid: andthe 
subsequent titration of the excess of the latter with standard acid 
and a colour indicator. 
As we have already said, the inception of the method was. 
