1870.] 



Estimation of Ammonia in Atmospheric Air. 



287 



in length and 12 millims. bore. These are connected air-tight by means of 

 a smaller glass tube, and inclined at an angle of 5° or G° with the hori- 

 zon. Into each of the larger tubes are introduced 100 cub. centims. of 

 a mixture of perfectly pure water and two drops of dilute sulphuric acid 

 (sp. gr. 1*18). Through this acidulated water a measured quantity of the 

 air under examination is slowly drawn, in small bubbles, by means of an 

 aspirator. 



No porous substance must be used to filter the air, for reasons to be 

 stated hereafter. The air is conducted into the absorption liquid through 

 a small piece of quill tubing drawn out to a small aperture at the end im- 

 mersed. This tube must be kept quite dry throughout the experiment. 

 Great care must be taken to cleanse perfectly every part of the apparatus 

 with water free from ammonia, and the caoutchouc plugs, or corks, used 

 must be boiled for a short time in a dilute solution of caustic soda. 



The stream of air is so regulated as to allow about 1 litre to pass through 

 the apparatus in an hour. 



By directing the point of the delivery-tube laterally, each bubble has im- 

 parted to it on rising an oscillatory movement which facilitates complete 

 absorption of the ammonia. 



When from 10 to 20 litres of air have passed, the liquid is emptied from 

 the tubes into upright glass cylinders, an excess of a perfectly pure solution of 

 potash added, and then 3 cub. centims. of a Nessler solution. The standard 

 of comparison is made in the ordinary way, only using acidulated in place of 

 pure water, and neutralizing with potash after adding the standard solution 

 of ammonium salt. Beyond somewhat retarding the point of maximum 

 coloration, a little potassium sulphate does not interfere with the delicacy 

 of Nessler' s reaction. 



If the experiment has been conducted with proper care, at least 4 of the 

 total ammonia ought to be found in the first tube. Four or five litres of air 

 are generally quite sufficient to give a decided reaction, but it is better to 

 use not less than 10 litres, as before mentioned*. 



Very many experiments have been made by this method, both on air 

 from the town of Burton-on-Trent, and that of the adjoining country. 

 The air from the town, as might be expected, varies somewhat in composi- 

 tion ; much more so than that taken from the open country, as may be 

 seen from the following Tables, in which are given some of the numerous 

 results obtained. 



The ammonia is calculated in every case as carbonate ((NH 4 ) 2 C0 3 ); 

 for although nitric acid is sometimes found in air, yet its presence must 

 be looked upon as accidental. 



* When the air to be examined is highly charged with ammonia, as that from stables 

 &c, a perfectly dry bottle of 3 or 4 litres capacity should be carefully filled with a pair 

 of bellows, 100 cub. centims. of acidulated water introduced, and, after closing securely, 

 the whole well agitated at intervals for three or four hours. The liquid is then poured 

 out, and the NH 3 estimated by the Messier solution as usual. 



