﻿10 METHODS FOR THE DETERMINATION OF 



when the permanganate solntion is diluted with 125 c. c. of twice dis- 

 tilled water. Another glass cylinder of similar size contains 25 c. c. 

 of fresh permanganate solution diluted with 125 c. c. of water. The 

 tints of the solutions in these cylinders are compared after about ten 

 minutes, and the tint of the solution in the first cylinder is deepened 

 so as to compare with that in the second cylinder by the addition of a 

 few drops of the i-qVo" solution of permanganate from a burette. The 

 amount of permanganate solution required for this purpose indicates 

 the bleaching effected on one-half of the permanganate solution in the 

 flask by the organic matter in the air which it contained. Since 1 c. c. 

 of the TTToir permanganate solution is equal to 0,008 mg. of oxygen, it 

 is easy to calculate the number of milligrammes of oxygen required 

 for the entire sample of air used. The results obtained in this method 

 are given in Table YII. 



B. Carnelley and Mackie's method modified. This method dif- 

 fers from the foregoing in that the permanganate solution is run 

 into the flask from a burette until no further bleaching effect is noted. 

 The flask contains 50 c. c. of pure distilled water, and the bleaching 

 effected is shown by the tint of the water after it has been agitated 

 with the sample of air for several minutes. The permanganate solu- 

 tion is added until a very faint rose tint is perceptible in the water 

 and remains permanent for five minutes. The permanganate solution 

 used in this method is -g-oVo" strength ; Ice. equals 0.004 mg. of oxy- 

 gen. The number of cubic centimetres of the permanganate solution 

 required to produce the faint rose tint in the 50 c. c. of water will 

 indicate the amount of organic matter in the sample of air used. The 

 results obtained by this method are given in Table YIII. 



Method Y. 



A. In this method the ammonia in the air is estimated directly, by 

 aspirating the air through a y^ solution of sulphuric acid (100 c. c.) 

 which is contained in a Pettenkofer absorption tube and afterward 

 titrating the acid with a y-g- solution of ammonium hydroxid, 1 c. c. 

 of the ammonium hydroxid solution being equal to 1.7 mg. of NHg. 

 The results obtained with this method are given in Table IX ; the 

 apparatus employed is shown in Fig. 1. 



B. By aspirating the air through 100 c. c. of pure distilled water 

 contained in a Pettenkofer absorption tube and nesslerizing ; the 

 depth of the color produced being compared with standard ammonium 

 chloride solution. The results obtained with this method are given 

 in Table X. 



C. Uffelmann's method, by aspirating the air through 10 c. c. of 

 diluted sulphuric acid and titrating with Nessler's reagent. 



