114 Scientific Proceedings, Royal Dublin Society. 
mixture was then passed through one of their absorbing tubes, and 
the amount of absorbed carbonic anhydride eventually determined. 
The result was 59°5 c.c. found as against 60°39 c.c. taken, or 
98:5 per cent. 
As a further check on the method, blank experiments were made 
with each series of the prepared absorbing tubes, one tube being 
taken from the beginning of the series, one from the middle, and 
one from the end, in order to determine any carbonic anhydride 
which their contents might contain. The average quantity thus 
found (amounting to about 1-1:2 ¢.c.) was deducted from the result 
of a determination. According to Mintz and Aubin it is to be 
traced to barium carbonate dissolved in the potash solution.1 The 
great advantage of their method, in addition to its accuracy, is 
that the collection of samples does not require any special skill. 
The tubes can be preserved for an indefinite time before and after 
absorption, they can be readily transported, and eventually 
examined by a skilled experimenter. Hence, at the suggestion of 
Dumas, the method was employed by the expedition sent out to 
Central and South America by the French Academy of Sciences 
to observe the transit of Venus in 1882.” 
Pettenkofer’s process, from its simplicity, rapidity, and 
readiness with which it can be performed, is in one way still the 
standard method for determining atmospheric carbonic anhydride. 
But as Angus Smith’ says, “as with most other inventions its 
early and later years have not been spent in the same place. 
Dalton,”* he continues, ‘used a bottle filled with 102,400 grains 
(nearly 7 litres) of rain water,” and says that ‘if it be emptied in 
the open air and 125 grains of strong lime water poured in, and 
the mouth then closed, by sufficient time and agitation, the whole 
of the lime water is just saturated by the acid gas it finds in that 
* This was specially prepared by dissolving 10 kilos. of caustic potash (‘‘ potasse é 
la chaux’’) in 14 kilos. water, adding 2 kilos. of barium hydrate, decanting the clear 
fluid, and further adding 200 germs. of barium hydrate. 
? A method similar in principle to that of Miintz and Aubin was also employed by 
Lévy and Allaire at the meteorological observatory at Montsouris, at the suggestion of 
Marié-Dayy, for daily determinations of atmospheric carbonic anhydride (‘*‘ Compt. 
Rend.,” 90 [1880], p. 32). 
3 « Air and Rain,” [1872], p. 448. 
4 «Mem. Lit. and Phil. Soc. Manchester,”’ [2], 1 [1805], p. 244. Paper read 
1802. 
