The Determination of Organic Matter in Air. 241 



such as sulphuretted hydrogen, nitrous acid, sulphurous acid, &c. 

 (3.) That the organic matter in air is of various kinds, and that con- 

 sequently the permanganate will most probably be selective in its 

 action. Our knowledge on this point, however, is so defective that 

 no definite conclusion is possible in regard to it. (4.) There is no 

 satisfactory means of checking the results, the only method being to 

 make duplicate determinations of the same air. This test, such as it 

 is, the method stands extremely well, as will be seen from the results 

 given below, which are taken quite promiscuously from a large 

 number of examples : — 



Organic Matter. 



Vol. of O required to oxidise 

 the O.M. in 1,000,000 vols, 

 of air. 



1st 

 Determi- 

 nation. 



2nd 

 Determi- 

 nation. 



Mean. 



Outside air (Dundee) 



(Perth) 



Class room (Dundee) 

 (Perth) . . 



Small room 



9-0 

 12-0 

 10-0 

 8-6 

 2-0 



2-0 



2-4 

 4-8 



10- 5 



7*6 

 4-0 



11- 9 



12- 9 



17-2 

 20-0 



11-5 



10- 2 

 8-1 

 1-6 



1- 5 



2- 



4- 6 



8-8 



7-8 



5- 



11- 4 



13-0 



17-0 

 20-5 



8-95 

 11-85 



10- 1 



8- 35 

 1-8 



1- 75 



2- 2 

 4-7 



9- 65- 



7-7 



4-5 



11- 65 



12-95 



17-1 | 

 20-25 



Immediately after rain. 

 JS"o rain during day. 

 Heavy rain, with wind. 

 Eain shortly before. 

 Strong wind and rain. 

 Strong wind, rain at in- 

 tervals. 

 Storm shortly before. 

 Fine. 



Unoccupied, but just 



after dusting. 

 29 present for one hour. 

 31 



Unoccupied, but with 



two gas jets burning 



for 15 minutes. 

 With one person and one 



gas jet for 20 minutes. 

 Ditto after one hour and 



40 minutes. 

 Ditto on another occasion. 



(5.) The uncertainty that the permanganate exerts its full action in 

 a cold acid solution of such dilution as that recommended above. The 

 method, however, does not claim to give absolute, but only relative 

 results. 



In the general lack of better methods we trust that the modification 

 of the permanganate process we have described will be found of great 

 value, on account of its extreme simplicity and rapidity of execution, 



e 2 



