EXAMINATION OF AIR 67 



after 25 c.c. are removed and compared with the same 

 quantity of fresh solution, and the number of c.c. of 

 same required to be added to bring its colour up to that of 

 control is noted. From this number the amount of oxygen 

 absorbed can be calculated and the result expressed in 

 parts per million. 



Noxious Emanations. Under this heading is con- 

 sidered the search for foreign gases and vapours in the 

 air, such as fumes of hydrochloric, nitric and nitrous, 

 carbonic, and sulphurous acids, sulphuretted hydrogen, 

 chlorine, ammonia, carbon monoxide, ammonium sulphide, 

 carbon bisulphide, carburetted hydrogen, roburite, nitro- 

 benzol. 



Scheme for detection. Take sample in jar. 



1. Remove cap or stopper, smell, and replace stopper. 

 Chlorine, HC1, S0 2 , ammonia, ammonium sulphide, 

 sulphuretted hydrogen and carbon bisulphide, all have 

 characteristic odours. Carbonic, nitrous, and nitric acids 

 have not. 



2. Take a piece of red and a piece of blue litmus paper ; 

 moisten in some neutral distilled water, attach to a piece 

 of stick, and hang down into jar free of sides. After waiting 

 a minute, note change of colour. 



3. If reaction acid or alkaline, pour rapidly into jar 

 10 c.c. of ammonia-free distilled water, replace stopper, 

 and shake vigorously. Remove half of this water, and 

 test for dissolved gas. 



A. If the reaction was acid, then it is likely to be 

 carbonic, hydrochloric, sulphurous, nitric, or 

 nitrous acid. Add to water removed from jar a 

 few drops of silver nitrate solution. 



White precipitate denotes either : 



a. Carbonic acid : precipitate very slight, 

 acidity also very faint, baryta water added 

 to jar becomes turbid after shaking, and 

 turbidity is increased by adding ammonia. 



b. Hydrochloric acid : precipitate marked, 

 acidity ditto, precipitate insoluble in nitric 

 acid, soluble in ammonia, and also in KCN. 



