322 Messrs. Haldane and Pembrey on an Improved Method 



At the end of the experiment pair No. 1 had absorbed 

 0*4371 gram of carbonic acid from 688 litres of air. We 

 concluded that 500 litres of air might be safely passed 

 through an absorption-apparatus. Other experiments con- 

 firmed this conclusion. 



The mean error of the method for carbonic acid was 

 estimated in the same way as with the method for moisture 

 (p. 311). 



Total C0 2 absorbed by tubes No. 1 . . 0*6464 

 Sum of variations of tubes No. 2 . . + 0*0007 



The mean error was thus about 0*1 per cent. 



The method is thus exceedingly accurate, in this respect 

 far exceeding, as will be shown below, the other methods 

 in common use. 



For free air about 20 litres or more, according to the 

 accuracy aimed at, will be required for an analysis. For 

 vitiated air, such as that of schools, 3 to 6 litres will suffice. 



The result of a pair of simultaneous experiments made out 

 of doors may be quoted here. 18 litres of air were aspirated 

 in each case. 



No. 1. 



Sulphuric acid pair 

 Soda-lime pair 



+ 0-0820 

 + 0-0109 



No. 2. 



Sulphuric acid pair .... +0*0819 

 Soda-lime pair .....+ 0*0109 



The methods just described have now been in use in this 

 laboratory for nearly a year. They have also been used for 

 some months in experiments out of doors at the Radcliffe 

 Observatory here, and in the country in Scotland. So far as 

 our own experience of them goes they have successfully 

 stood the test of every-day use. 



We may now review shortly the literature bearing on the 

 determination of carbonic acid in air, and record some experi- 

 ments which we made with a view to testing the two methods 

 at present in common use in this country. 



The first attempt at a quantitative analysis of the carbonic 

 acid in free air seems to have been made by A. von Hum- 

 boldt *. His numerous results were, curiously enough, 

 entirely illusory, since he concluded that about 100 vols, per 

 10,000 of air were usually present. In 1802 Dalton f, who 



* Gilbert's Annalen, iii. p. 79 (1800). 

 t Manchester Lit. Phil. Soc. Mem. 1802. 



