COLLECTING SAMPLES OF RAIN WATER 479 



for about 20 minutes, moving it back and forth without taking the 

 bottom of it out of the dish. When there is no longer any evolu- 

 tion of gas, water is added through a slowly, until the heavy potas- 

 sium ferrocyanid solution is almost completely driven out of the 

 eudiometer. The opening of the tube at e is then closed with the 

 thumb, the apparatus is taken out of the dish, shaken for some 

 time in a vertical direction and again placed in the dish. Water 

 of any required temperature is now allowed to flow through the 

 jacket gh, until the temperature is constant, when the volume 

 of nitric oxid is read. The whole experiment can be performed 

 in less than an hour. Operating in this way, at the end there 

 is in the eudiometer a liquid which is not very different from 

 water and one whose coefficient of solubility for nitric oxid 

 is practically the same as that of water. The gas volume read is 

 to be corrected for temperature, pressure, tension of the aqueous 

 vapor, height of the water column in the eudiometer, and, after 

 the end of the calculation, five per cent, of the volume of water 

 remaining in the eudiometer is to be added to the volume of gas 

 obtained. This is to compensate for the volume of the gas 

 absorbed by the water. The method gives good quantitative re- 

 sults. 



410. General Observations. The determination of nitrous acid 

 in itself is of little interest in fertilizer examinations. It exists 

 in fertilizers only in negligible quantities. Its determination is of 

 greater importance in sanitary water analysis than in fertilizer 

 control. It is of some importance, however, in connection with 

 the occurrence of nitric acid, and this fact warrants the space 

 which has been given to its discussion. 



411. Method of Collecting Samples of Rain Water for Analysis. 

 In pot and field experiments with fertilizers the study of 

 the drainage waters is of supreme importance. For this reason 

 the methods for determining nitrous and nitric acids have been 

 given in detail. The collection of the drainage waters is an 

 important factor of this study. Warington collects rain water in 

 a large leaden gauge having an area of o.ooi of an acre. 95 Of 

 the daily collection of rain, dew and snow water, an aliquot 



95 Journal of the Chemical Society, 1889, 55 :537- 



