152 MR. T. E. THORPE ON THE AMOUNT OF CARBONIC ACID 



the residual lime-water was neutralized by sulphuric acid 

 of a certain strength ; and from the amount of that acid re- 

 quired before and after absorption, the proportion of car- 

 bonic acid in the air was easily calculated. 



A few experiments made in a similar manner by Colonel 

 Emmet (Phil. Mag. xi. 1837) at Bermuda, about the end 

 of September and beginning of October 1836, gave as a 

 mean i'25 vol. of carbonic acid in 10,000 vols, of air — a 

 result considered, however, by Dalton, from whom the com- 

 munication was received, to be only approximative, since 

 the lime-water had not remained for a sufficient length of 

 time in contact with the air. Emmet observed qualitatively, 

 by means of lime-water, the invariable presence of carbonic 

 acid in the atmosphere above the sea during the voyage 

 out from England to Bermuda ; but the quantity apparently 

 fluctuated, the film of carbonate forming sometimes more 

 rapidly than at others. 



These old observations are, however, scarcely to be 

 trusted as regards quantity, owing to the inaccurate nature 

 of the methods employed. We now have to notice more 

 recent and reliable determinations. 



It appears from the experiments of Morren (Ann. de 

 Chimie et de Phys. xxxiii. 12, 1844), made near St. Malo, on 

 the French coast of the Channel, on the nature of the gases 

 which sea- water holds in solution at different periods of 

 the day and during the various seasons of the year, that 

 the alteration in the composition of these dissolved gases 

 may possibly cause a sensible alteration in the composition 

 of the atmosphere immediately above the sea. The air 

 contained in sea- water consists of variable quantities of free 

 carbonic acid, oxygen, and nitrogen, — the changes in the 

 relative proportion of these gases depending (i) upon 

 alteration of temperature, affecting the relative amounts of 

 the dissolved gases in accordance with the laws of gaseous 

 9,bsorption, and (2) upon the variations in intensity of 



