66 PUBLIC HEALTH CHEMISTRY 



the latter is then shaken. The manoeuvre is repeated 

 until the fluid (which had been coloured pink by the addi- 

 tion of phenolphthalein) becomes colourless from the 

 Na 2 CO 3 absorbing CO 2 and forming NaHCO 3 . The 

 number of compressions of the bulb required are counted, 

 and by reference to a table the proportion of carbonic 

 acid gas present in the air tested is obtained. The method 

 is very tedious if the air is pure, as forty-eight compres- 

 sions are required to detect 3 parts per 10,000. 



Scurfield's Apparatus. Mr is aspirated through weak 

 baryta solution, 3 parts per 10,000, coloured red by 

 addition of phenolphthalein. 



Ozone. 



1. Houzeaus paper. A piece of neutral or faintly 

 reddened litmus paper soaked for a quarter of its length 

 in neutral KI solution and dried (keep in dark). When 

 exposed to ozone the KI is decomposed and K 2 O formed, 

 which turns the litmus blue at soaked part only. Cl and 

 Br would not do this. N 2 O 3 would turn rest red. NH 3 

 use control. 



2. Schbnbeins paper. KI and starch paper turned blue. 

 Cl, Br, N 2 O 3 , H 2 O 2 all give same result. 



3. KI and phenolphthalein papers turned red. H 2 O 2 

 gives same result. Cl, Br, and N 2 O 3 give a brown. 



4. Arnold-M entzel paper. Chromic acid paper is negative. 

 Hydroxyl gives a blue. 



5. Engler and Wild's manganous chloride paper. Ozone 

 turns it brown. Hydroxyl has no action, but ammonia 

 also gives a brown. 



Oxidizable and Organic Matter. This is best 

 determined by washing the air (by shaking with distilled 

 water or slowly aspirating through the same) and examin- 

 ing the washings, as in water analysis, for total nitrogen- 

 free, saline and albuminoid ammonias, nitrous and nitric 

 acids, and oxygen absorption. 



Carnelly's process is sometimes used, but is not very 

 reliable. A millinormal solution of permanganate is acidu- 

 lated with sulphuric acid, and 50 c.c. are added to an air 

 jar containing the sample, and exposed with occasional 

 shakings to its influence for about half an hour. There- 



