24 
THE A IK OF OUR HOUSES. 
BY FRANK T. SHUTT, M.A., F.I.S., F.C.S., IS! VICE-PRESIDENT. 
Delivered December 15th, 1S92. 
I have selected this subject, chiefly, for two reasons. First : 
although it is one of great importance, and has a vital interest for 
every one of us, widespread ignorance prevails regarding the grave 
danger to health from continuously breathing impure and vitiated air. 
Secondly : because it will form a fitting sequel to the lectures on Water 
and Food which I delivered on former occasions before this Club. 
In pursuance of the course I adopted in those addresses, I propose 
to discuss the subject from the hygienic, as well as from the chemical, 
standpoint. My endeavour will be to point out the composition of 
pure, normal air ; the nature, sources, and amounts of impurities in 
vitiated air ; and the effects of these impurities upon the system. 
THE ATMOSPHERE. 
The atmosphere that surrounds our earth is composed, chiefly, of two 
elements Oxygen and Nitrogen. These ^ases exist in the air, not as 
a chemical compound of the two, but in the free and uncombined con- 
dition. This can be easily and abundantly proved. I shall content 
myself, however, with telling you of a few of the reasons why 
air must be considered as a mechanical mixture of its con- 
stituents, and not a compound. The ratio, or proportion of the oxygen 
to the nitrogen in the air does not correspond tc the ratio existing 
between these elements in any of the oxides of nitrogen, which 
are true chemical compounds. Neither the relative nor absolute 
amounts of the oxygen and nitrogen remain always the same and 
constant ; and it is a sine qua non that the ratio between the constituents 
of a chemical compound should be invariable. Again, water dissolves 
from air both oxygen and nitrogen, but owing to the greater solubility 
of the former and the laws of gas absorption, the proportion between 
them in the dissolved air is not that existing between them in the 
atmosphere. For instance : 
