28 DR. R. ANGUS SMITH ON THE 



and shows us that those places contaimng impurities, and 

 which are in or near all our houses, are also subjected to a 

 diminution of oxygen. The diminution is not entirely 

 made up by carbonic acid, and must be made up by other 

 substances. This diminution is very sensible when it 

 comes to 2075, or even in some places 20*85, being equal 

 to a removal of 0'2 to o*i of oxygen; so that it indicates 

 more clearly in some cases than the carbonic-acid test 

 does. These cases are probably such as allow for the 

 absorption of oxygen into the soil or elsewhere. We do 

 not require to seek deadly places for air with diminished 

 oxygen ; the air of every house is subjected to this diminu- 

 tion, which must of necessity be an indication of the amount 

 of impurity existing in the air, although giving no clue to 

 the quality of that impurity, which may be more or less 

 innocent or noxious. 



It is well known that oxygen over putrid substances is 

 absorbed, whilst carbonic acid and other gases take its 

 place. This reasoning does not touch the question. What 

 is the effect of a loss of oxygen when no impurities take its 

 place ? — a condition little known. I wish particularly to 

 say that it is probable that the objection to the air which 

 has a little less oxygen than the normal amount may not 

 arise from this fact itself. The loss of oxygen may only 

 be an indication of the presence of a pernicious body. 



Carbonic Acid of the Atmosphere. 



Horace de Saussure first paid minute attention to the 

 carbonic acid of the atmosphere, and showed its presence 

 on the mountains of Switzerland as well as on the plains. 

 He used lime-water. His results were published in his 

 ^Voyages dans les Alpes* in 1796. His son Theodore in 

 1828 published a resume of a much fuller inquiry, and in 

 1830 the complete account. He used a vessel of 34 litres 

 in volume, and washed the air with baryta- water, collecting 



