118 Scientific Proceedings, Royal Dublin Society. 
Blochmann! was the first to suggest phenol - phthalein 
as indicator in Pettenkofer’s process, and to that author we 
are also indebted for suggesting modifications in the latter, 
whereby several of its sources of error are avoided. In his very - 
complete and valuable paper on the amount of carbonic anhy- 
‘dride in the air’? the apparatus is fully described and figured. 
Here we can only indicate its essential features. 
(1.) The bottle holding the stock of baryta water is perma- 
nently attached to a measuring pipette, and is so arranged that on 
withdrawing a portion of the fluid, its place is taken by air freed 
from carbonic anhydride. The titre of the solution is thus 
preserved. 
(2.) The absorbing vessel is a clear glass bottle of a capacity 
of 5-6 litres closed by a glass stopper pierced with two holes, into 
which two glass tubes are ground. Both of these latter terminate 
externally in glass stopeocks, while within the bottle one reaches 
nearly to its bottom, the other barely passing through the stopper. 
To ensure air-tight junctions the space (purposely left) above the 
stopper in the neck of the bottle is filled with mercury, on to 
which a layer of paraffin wax is afterwards poured. ‘These two 
tubes are employed for the ingress and egress of the air to be 
examined, and subsequently of the absorbing fluid also—the 
bottle being inverted for the removal of the latter. 
(3). The titration of an aliquot portion of the absorbent (pre- 
viously freed from barium carbonate by filtration through an 
asbestos plug) is performed within a burette of peculiar construc- 
tion, so arranged that while its lower portion receives and measures 
off a charge of the fluid to be titrated, its upper part contains the 
standard acid (sulphuric), and communication between the two is 
established by a three-way cock. All contact with external air 
during the removal of fluid from the absorbing vessel and during 
the titration of the latter is avoided. 
Lebedinzefi? more recently has taken up the subject, but as far 
as we can judge from the abstract of his work he has not introduced 
any important modifications into Pettenkofer’s process. Following 
1 «Ber. d. deutsch. chem. Ges.,’’ 17 [1884], p. 1017. 
» “Tiebig’s Annalen,’’ 237 [1887], p. 39. 
3 “ Zeitschr. f. anal. Chem.,”’ 30 [1891], p. 267. 
