7 he Determination of Organic Matter in Air. 245 





Perth (outskirts). 





Wo. of 



cases. 



Lowest. 



Highest. 



Mean. 



Organic matter (0 required perl 



1,000,000 vols, of air) J 



Carbonic acid (per 10,000 vols. 1 



5 

 3 



11 



2-9 



4-5 

 3-5 



31 

 3-1 



(3.) A relation of organic matter to carbonic acid in outside air 

 shows, so far as the tabulated results go, a high carbonic acid accom- 

 panied by a high organic matter, and vice versa. This, however, is by 

 no means invariably the case, and is in fact only evident on comparing 

 the averages of a large number of cases. To show this all the deter- 

 minations which have been made in outside air were divided into 

 four groups, according to the quantity of organic matter present, and 

 the averages of the corresponding carbonic acid found, as in the fol- 

 lowing table : — 



Yols. of O required to 

 oxidise the organic matter 

 in 1,000,000 vols, of air. 



Average carbonic acid in 

 10,000 vols, of air. 



No. of deter- 



Lowest. 



Highest. 



Average. 



minations. 



to 2-5 | 



2-5 to 4-5 

 4-5 to 7-0 

 7-0 to 15-8 



too small to 

 estimate. 



1- 8 



2- 



3- 7 



| 5-6 



4'9 

 5-4 

 4-9 



2- 8 



3- 



32 

 3 7 



20 



20 

 20 

 20 



(4.) The organic matter in outside air has a far wider range of 

 variations than carbonic acid. For whereas the carbonic acid seldom 

 passes beyond the limits of 2 to 6 vols, per 10,000, the organic 

 matter varies from a quantity too small to estimate to as much as 

 will require for oxidation about 16 vols, of oxygen per 1,000,000 

 vols, of air. 



It is also subject to more rapid fluctuation in its value than 

 carbonic acid. 



(5.) The combustion of gas does not appreciably increase the 

 amount of organic matter in air. This was proved by burning gas in 

 a small practically air-tight room (which had previously been well 

 ventilated, and the carbonic acid and organic matter determined), 



