﻿4 METHODS FOR THE DETERMINATION OF 



For the direct estimation of ammonia in air Uffelmann " employs 

 the following method : Twenty to thirty litres of air are aspirated 

 through 10 c. c. of dilate sulphuric acid ; this is then tested with 

 Nessler's reagent and the color produced compared with that of a 

 solution of ammonium chloride of known strength. He uses 0.8147 g. 

 NH4-C1 in 1 litre of water, which is equal to 0.100 g. NHg to the 

 litre. This solution is diluted with water (for the comparison) until 

 its color is similar to that produced by the sample of air. A yellow 

 color indicates 0.005 mg. NHg in 100 c. c. of water. 



A method which I employed in an earlier series of experiments ^ 

 consists in conducting measured volumes of air through a coil of glass 

 tubing laid in ice so as to condense the atmospheric moisture and dust. 

 The fluid collected in this manner is then subjected to distillation. The 

 chief difficulty in this method is the slowness with which the con- 

 densation of moisture takes place. It is only on days when the 

 atmosphere is nearly or completely saturated with moisture that an 

 appreciable amount of fluid is collected. On clear days the evapora- 

 tion of the moisture often exceeds the condensation, and in consequence 

 the fluid already collected may be lost through evaporation. 



A method employed by Grray,'® of l^ew Zealand, consists in collect- 

 ing the rain water as it falls and subjecting it to distillation. 



The methods of the second group also have a common object, the 

 determination of the amoimt of oxygen required to oxidize the organic 

 matter in a known volume of air. These methods differ, however, 

 very greatly as to the forms of apparatus employed by the different 

 experimenters. 



E. Angus Smith' used a flask of about 100 cu. in. (1175 c. c.) 

 capacity. The air is pumped out of the flask by means of a hand 

 bellows, so that the air of the place may pass in to take its place. The 

 flask is then closed with a rubber stopper perforated by two holes, the 

 one containing a glass tube through which a weak solution of perman- 

 ganate of potash is introduced from a small burette ; the other opening 

 allows the air that is displaced by the permanganate solution to escape. 

 A small quantity of the permanganate solution is used at first and 

 agitated with the sample of air. More of the permanganate solution is 

 added as fast as it is being decolorized, a permanent color indicating 

 that the " air contained no more material capable of decomposing 

 permanganate." The solution of permanganate which Smith used 

 was of such strength that 1 c. c. tested with proto salt of iron 

 equalled 0.00225 g. of metallic iron, or, 0.00032 g. of oxygen. Alka- 

 line salts seemed to him to be more sensitive than pure permanganate. 



A second method devised by Smith is as follows : Thirty cubic 

 centimetres of water containing a small amount of a weak solution of 



