﻿12 METHODS FOE THE DETEEMINATION OF 



that without the utmost caution in the entire manipulation the experi- 

 mental error may exceed several times the amount of ammonia really 

 present. Aside from these difficulties there is also the difficulty of 

 securing absolute freedom of all ammonia in the retort, condenser, and 

 in the receivers, as well as the great difficulty generally experienced 

 in preparing distilled water sufficiently free from ammonia to make its 

 use safe for the purposes required in these methods. 



The pumice-stone also affords the most reliable results in the 

 methods depending upon the oxidation of the organic matter in the 

 air by means of permanganate solution. Since, however, the results 

 obtained in this manner are influenced by the presence of other redu- 

 cing bodies in the air, this cannot be looked upon as being an ideal 

 method. 



It is evident that the quantity of organic matter in the air varies 

 from hour to hour and from day to day. As to the source of this 

 organic matter, it may be stated that this will vary constantly with the 

 locality and the nature of its surroundings. The dust of the air is 

 undoubtedly a rich source of ammonia and is also an active reducing 

 agent upon permanganate. The relative proportion of the organic 

 matter in the air that is of a nitrogenous nature seems to be quite large, 

 yet it is evident from the results of analyses that a portion of the 

 organic matter is non-nitrogenous in character. It is probable that a 

 large proportion of the nitrogenous organic matter in the air exists in 

 the form of dust particles arising from vegetable and animal debris, 

 and that the proportion of gaseous, nitrogenous organic matters is much 

 smaller than is commonly supposed, at least in ordinary air ; and such 

 as do exist are presumably of the form of amines from putrefactive pro- 

 cesses. Such gaseous bodies could occur in large amounts only in the 

 vicinity of excessive quantities of putrefying materials, or of certain 

 manufacturing establishments, as, for instance, soap factories or bone- 

 boiling establishments. 



In the opinion of Grray,^^ " the organized nitrogen exists in the air 

 in the form of germs and minute organisms and possibly of minute 

 particles of disintegrated organic matter. The combined nitrogen con- 

 tained in rain is derived from three sources : the ammonia compounds 

 derived from the decay of animal and vegetable substances and from 

 the combustion of fuel ; the organic matter existing in the air ; and, 

 lastly, the nitric acid resulting either from the oxidation of ammonia, 

 and probably some of the organic matter, or, from the direct union of 

 atmospheric oxygen and nitrogen imder the influence of electrical dis- 

 charges taking place in the atmosphere." 



From the fact, therefore, that the greater portion of the organic mat- 

 ter in the air is in the form of dust particles, and that but a relatively 



