Letts & Braxe—The Carbonic Anhydride of the Atmosphere. 117 
that interval a small narrow bottle was filled with the turbid 
absorbent, the barium carbonate allowed to subside, and an 
aliquot part of the clear liquid titrated with oxalic acid solution 
—1 cc. = 1 mg. CO,. 
Pettenkofer pointed out that traces of caustic alkalies interfere 
with the delicacy of the titration, and recommended the addition 
of barium chloride to the baryta water, by which means barium 
hydrate and a corresponding quantity of alkaline chloride are 
formed, he says, and the delicacy of the reaction no longer 
interfered with. 
Since the introduction of Pettenkofer’s process many modifi- 
cations have been proposed and employed. 
Angus Smith! in his work on air employed a confectioner’s 
glass jar, instead of a flask, as absorbing vessel : the broad mouth 
of which permitted the hand to enter, so as to readily clean and 
dry the vessel; and instead of blowing air into it he operated in 
the reverse manner, that is to say by extracting by means of 
a flexible bellow’s pump, thus causing the air of the locality 
to enter in its place. 
Schulze,’ whose investigations on the amount of atmospheric 
carbonic anhydride extended over a considerable period, and are 
among the more important which have been made, modified the 
method of titration and introduction of the absorbent, so as to 
avoid access of breath or the air of the laboratory during the 
process. This he accomplished by binding a sheet of thin india- 
rubber over the mouth of the (4 litre) flask immediately after 
filling it with the air to be examined. This sheet was then pierced 
by the nozzle of the pipette delivering the baryta water and a 
second one bound on. After a suitable time for absorption, the 
latter was removed, and after the introduction through the 
pierced rubber sheet of a few drops of alcoholic turmeric solution, 
and about 26 ¢.c. of boiling water to wash down the baryta water 
adhering to the sides of the vessel—the nozzle of the burette was 
passed through the perforation, and the titration with (oxalic) 
acid proceeded with. Schulze controlled his results by parallel 
determinations with other methods. 
1 ¢¢ Air and Rain,”’ p. 450. 
2 « Landw. Vers. Stat.,”” 9 [1867], p- 217; 14 [1871], p. 366. 
