50 DR, R. ANGUS SMITH ON THE 



the air to become deteriorated even to a very minute extent,, 

 and that a figure in the third decimal place is not to be 

 despised ; but they teach us more — namely, that in some 

 places, such as high mountains, a slight increase of carbonic 

 acid, such as is found in the third, or even to the length of 

 2 in the second place, is rather a proof that the oxygen of 

 the air has done its work Avell and purified the atmosphere, 

 and that this increase is probably owing to pure carbonic 

 acid. It would be well to have those experiments of 

 Schlagintweit confirmed, where 0*07 and O'og are found 

 on high mountains. To conclude, we all avoid an atmo- 

 sphere containing O'l of carbonic acid in crowded rooms; 

 and the universal belief of civilized men is that it is not 

 only odious but unwholesome. When men speak of good 

 ventilation in dwelling-houses, they mean, without knowing 

 it, air with less than 0*07 of carbonic acid. We must not 

 conclude that, because the quantity of carbonic acid is 

 small, the efi'ect is small ; the conclusion is rather that 

 minute changes in the amount of this acid are of the highest 

 importance. 



Carbonic Acid in Scotland. 



Ha^dng written so far, it was desired to throw more light 

 on the subject by obtaining specimens from purely rural 

 and hilly districts ; and for this purpose Scotland was pre- 

 ferred. The uniformity in the numbers is something re- 

 markable. There is no difference in the second decimal 

 place, even in one instance, until we enter a town. I must 

 therefore consider "0336 per cent, as the amount of car- 

 bonic acid in the pure winds of the north of this island. 

 Any amount above that is a deviation from purity. If 

 we have any regard to the third place of decimals, we find 

 there nothing to indicate a deterioration; and we can 

 scarcely hope to rely on the fourth place. Still the results 

 in the fourth place are not to be rejected : we find them 



