﻿14 



METHODS FOR THE DETERMINATION OF 



bodies become oxydized by the permanganate is sufficiently slow to 

 •escape detection by this process as ordinarily conducted. Finally, the 

 process of determination by boiling with acidulated solution of perman- 

 ;ganate of potash and titration with oxalic acid solution is a very deli- 

 ■cate one, requiring considerable care and experience to obtain concordant 

 results. 



Those methods in which the determination is made with cold per- 

 manganate solution, and where the amount of organic matter is 

 estimated colorimetrically, are open to several objections. The 

 permanganate acts quite slowly in cold solution and without any de- 

 gree of regularity. The estimation colorimetrically, as in the method 

 'of Carnelly and Mackie," is a most uncertain process because of the 

 difficulty of detecting slight variations in the tints of permanganate solu- 

 tions of the strength employed by them, or even of solutions of but 

 half that strength. It appeared to me that the operation was rendered 

 somewhat easier by using a permanganate solution of only one-half the 

 strength recommended by them. The same objections apply to those 

 methods in which cold solutions of permanganate are shaken with 

 successive portions of a sample of air until they are decolorized, as in E. 

 Angus Smith's " air- washing " ; and in methods already described in 

 which the permanganate is added slowly to a sample of air in a flask 

 as long as it is being decolorized. Under such conditions the perman- 

 ganate acts slowly and u.nsatisfactorily ; and there is great difficulty in 

 recognizing the exact point of neutralization since the end-reaction is 

 not sharply defined, and as yet there appears to be no way in which it 

 €an be made more definite. 



THE RESULTS OBTAINED IN AIR ANALYSES BY THE 

 DIFFERENT METHODS. 



Method I. 

 Absorbent material : twice distilled water. 

 Absorption apparatus : a Pettenkofer absorption tube. 



table I. 



:no. of 



Date, 



experi- 



1895 



ments. 





1 



20-VI 



2 



20- VI 



3 



21-VI 



4 



21-VI 



5 



22- VI 



« 



22- VI 



7 



24-VI 





Time 



Amount 





Source of the 



taken 



of air 





air aspirated. 



m aspi- 



aspi- 



Window. 





rating. 



rated. 





Room 



7 hours 



36.0 L. 



Closed 



Sewer pipe 



7 " 



73.6 " 







Room 



6i " 



33.0 " 



Closed 



Sewer pipe 



6i " 



109.0 " 





Room 



6 " 



26.0 " 



Closed 



Sewer pipe 



6 ^' 



84.9 " 





Room 



7i " 



122.0 " 



Closed 



Mgs. of NH3 in 1 cbm. of air. 



Free NH, 



69.444 

 47.554 



75.757 



27.523 



0.000 



0.000 



0.000 



mgs. 



Alb. NHs. 



458.333 mgs. 



33.967 " 



181.818 " 



22.935 " 



250.000 " 



88.339 " 



0.000 " 



