foMoy «4 
XV. 
THE CARBONIC ANHYDRIDE OF THE ATMOSPHERE. 
By PROFESSOR E. A. LETTS, D.Sc., Pa.D., ann R. F. 
BLAKE, F.1.C., F.C.S. 
(Prates XVI.-XVIII.) 
[Read, Part I., June 22, 1898; Part II., April, 1899; Received for Publication 
Jury 7, 1899. Published Marcu 9, 1900.] 
[COMMUNICATED BY DR. W. E. ADENEY, F.I.C., F.C.S. | 
PAIR YM Ie. 
Section [.—Intrropucrion AND Metruops oF DETERMINATION. 
Tue existence of carbonic anhydride in the air was first demon- 
strated by Dr. Black of Edinburgh, and probably between the 
dates 1752 and 1754.1. In his Lectures we find the following 
statement concerning lime water’ :— 
“‘When this fluid is exposed to the open air, the particles of 
lime which are at the surface gradually attract fixed air which 
is mixed with the atmosphere.... In framing this theory I was 
necessarily led to perceive a distinction between the atmospheric 
air or the greater part of it, and that sort of air with which the 
alkaline substances are disposed to unite. It was plain that the 
lime of lime water, for example, is not disposed to unite with 
the whole mass of atmospherical air that happens to be confined 
with it or with every part of it equally.... The only circum- 
stances in which lime water loses its qualities and throws up 
the lime to its upper surface are when we expose it to the 
open air or keep it in bottles that are left open. From this 
it was evident that the sort of air with which the lime is dis- 
posed to unite is a particular species which is mixed in a small 
1 Preface to “ Lectures on the Elements of Chemistry,” by Joseph Black, M.D. 
Edinburgh, 1803. By John Robison, p. xxiii. 
2 Lectures, vol. il., p. 74. ere 
K 
SCIEN. PROC. R.D.8., VOL. IX., PART II. 
