Letts & Buaxe—The Carbonic Anhydride of the Atmosphere. 109 
method which was subsequently employed by Lewy? (1843-1850), 
De Luna’ (1860), Frankland* (1861), and Macagno,‘ in spite of 
the fact that De Saussure, Thorpe, and others had pointed out that 
it was not capable of giving sufficiently accurate results with the 
minute quantities of carbonic anhydride present in air. 
Thenard’ appears to have been the first to devise a method 
giving fairly reliable and approximately accurate figures. This 
consisted in weighing the barium carbonate produced on allowing 
a known volume of air to remain in contact with baryta water, 
and because air contains so small a proportion of carbonic anhy- 
dride, he insisted that the volume of air thus treated must be con- 
siderable—the actual amount which he employed being no less 
than from 237-300 litres. 
Théodore De Saussure’ in his classic researches on atmospheric 
carbonic anhydride which extended over a period of more than 
twenty years made use ofa somewhat similar method, of which the 
following are the essential particulars :— 
A glass balloon of 35-45 litres capacity was employed, to the 
neck of which a copper ferrule was cemented provided with a 
stopcock. ‘The balloon having been properly cleaned and dried, 
was exhausted by an air-pump, and the air to be examined slowly 
admitted. One hundred grms. of dilute baryta water (1 per 
cent.) previously saturated with barium carbonate, were next 
poured in through a long funnel, the balloon closed, and either 
agitated for an hour or left to itself during seven or eight 
days with occasional shaking. It was then again well shaken 
to distribute the barium carbonate throughout the liquid, and 
the mixture poured through a funnel into a stoppered bottle. 
The balloon was next rinsed out several times with water 
(saturated with barium carbonate) and the barium carbonate 
itself thoroughly washed by decantation. After this it was 
1 Lewy, “Journ. f. prakt. Chem.,’’ 30 [18432], p. 207. 
2 De Luna, ‘‘ Estudios quimicos sobra el aire atmosferico.”” Madrid. 1860. 
3 Frankland, ‘‘ Chem. Soc. Journ.,” 13 [1860], p. 22. 
4 Macagno, ‘‘ Chem. Centralblatt,”’ 11 [1880], p. 226. 
5 Thenard, ‘‘ Traité de Chimie,”’ 5th ed., vol. i. [1813], p. 303. 
6 De Saussure, ‘“‘ Bibliothéque Univers. Sciences et Arts,”’ 1 [1816], p. 124; also, 
«¢ Annales de Chimie et de Phys.,”” 2 [1816; title-page date, 1830], p. 199; 3 [1816; 
title-page date, 1830], p. 170; 38 [1828], p. 411; 44 [1830], p. 5. 
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