36 DR. R. ANGUS SMITH ON THE 



meter. The results were comparative, but I do not find 

 that they were quantitative. These precipitates change so 

 much that they cannot be used for comparison after a few 

 hours. 



Pettenkofer lately took up the subject, using lime (now, 

 I believe, baryta) to remove the carbonic acid from the 

 air, and oxalic acid to test the solution. The bottles in 

 which the experiments were made were dried with great 

 care, and the solution of oxalic acid made very delicate. 

 One cubic centimetre of this solution was made equal to a 

 milligramme of hme, but it may also be made equal to a cubic 

 centimetre of carbonic acid. The strength, however, must 

 vary with the air. If the air is very bad, a stronger solu- 

 tion may be used. Indeed this is rather a difficulty in the 

 process, as you cannot use one solution for all conditions, 

 on account of its extreme delicacy. The carbonic acid 

 saturates part of the lime, and the amount remaining is 

 tested with oxalic acid to see how much is still uncombined. 

 The point of neutralization is found by putting a drop of 

 the liquid on a piece of turmeric paper. 



The plan is very beautiful and complete. In principle 

 it is exactly that of Hadfield^s ; but oxalic acid is used, and 

 the experiment made more delicately. 



He gives 0*5 per mille or '05 per cent., as the amount 

 in the air generally at Munich. This is above the number 

 of Saussure, and both are above the numbers found here. 

 Munich is 1690 feet, Geneva 1154 feet above the sea. In 

 the Handworterbuch der Chemie, under " Ventilation,^' 

 Pettenkofer gives a summary of the amount of carbonic 

 acid in dwelling-houses, as follows : — 



In a dwelling-house, during the day, 0*054. 



After a while it increased to 0*065, o"o6i, 0*064, 0*068, 

 0*074, and 0*087. Mean o*o68. 



In a bed-room at night, with closed windows, 0*230. 



Partly open, 0*082, 



