of Ammonia in Atmospheric Air. 55 



metre 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 

 6° with the horizon. 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 immersed. 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 imparted 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 potas- 

 sium sulphate does not interfere with the delicacy of Nessler' s reaction. 



If the experiment has been conducted with proper care, at least |- 

 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 some- 

 what in composition ; 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. 



In the immediate vicinity of towns some of the ammonia must also 

 be in the form of sulphate, sulphite, or ammonium chloride. 



;; " When the air to be examined is highly charged with ammonia, as that from 

 stables &c., a perfectly dry bottle of o 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 NIL estimated by the Nessler 

 solution as usual. 



