Lerts & Buake—The Carbonic Anhydride of the Atmosphere. 115 
volume of air. But 125 grains of the lime water used require 
70 grain measures of carbonic acid to saturate it.”’ 
Later, Dalton appears to have employed a different method 
based on the same principle as Pettenkofer’s, viz. absorption of the 
carbonic anhydride by a solution of an alkaline earth, and sub- 
sequent titration of the latter by a standard acid. 
Hadfield,’ a pupil of Dalton’s who continued the latter’s re- 
searches on atmospheric carbonic anhydride, gives the following 
particulars of the process :— 
“Mr. Dalton considers a globe one-fifth the size’ sufficiently 
ample, and uses lime water of a well-known strength instead of 
barytic, taking care to have more than enough to engage the acid 
gas; after the agitation and absorption the residue of lime water 
is poured out, and its reduced value is then ascertained, as it was 
before, by means of some test acid of known strength. ‘Thus data 
are gained for the calculation of the carbonic acid engaged to the 
lime.” 
“In my investigations of this subject I have adopted 
Mr. Dalton’s mode, and from December, 1828 to 1830, the ex- 
periments have been made in a glass bottle of a balloon shape of 
the capacity of 471 cubic inches (about 732 litres), fitted with a 
brass cap and stop-cock for the purpose. ‘The experiments of the 
present year (1830) have been made in a larger bottle of the 
eapacity of 498 cubic inches (about 81 litres). The method of 
filling the latter bottle with air was a little different from that 
of the former, for instead of filling the bottle with rain- 
water, as was the case with the first bottle to get the air in, 
the end of a bellows pipe was introduced into the latter and 
the air blown in.” 
Another of Dalton’s pupils,? H. H. Watson, also worked on the 
same subject, and according to Blochmann, both he and Hadfield 
employed the same method of procedure, viz. after absorbing the 
earbonic anhydride with excess of lime water, they filtered and 
washed the precipitated chalk and titrated the excess of lime water 
1 Tbid., 6 [1842], p. 10. 
* This refers to De Saussure’s absorbing vessel, which Hadfield says had a capacity _ 
-of one cubic foot or more. 
§ “Journ. f. prakt. Chem.,’’ 6 [1835], p. 75; “‘ Brit. Assoc. Reports,’’ 3 [1834], 
p- 583. Communicated by Dalton. 
