EXAMINATION OF AIR 65 



without any calculation. The method consists in subjecting 

 25 c.c. of air to exposure to caustic potash, which absorbs 

 the CO 2 , and the diminution in volume is measured under 

 the same conditions of temperature and pressure, and the 

 divisions on the graduated portion of the burette are each 

 TiTTfTToth part of the whole capacity of the burette, so that 

 the result is read off in parts per 10,000. 2KOH + CO 2 = 

 K.COa + H.0. 



Hesse's Modification of Pettenkofer' s Method is to collect 

 the sample in a flask, from 250 c.c. to 1000 c.c. capacity, 

 closed with a rubber stopper with two holes plugged with 

 glass rods. One of the plugs is removed, and a pipette 

 containing 10 c.c. of baryta is inserted in its place. The 

 other plug is loosened, and the baryta allowed to run into 

 the flask. The pipette is then removed and the plugs are 

 reinserted, and the flask shaken from time to time. After 

 half an hour a plug is withdrawn, a drop of phenol- 

 phthalein added, and the nozzle of a burette containing 

 standard oxalic one-tenth the strength of that used in 

 Pettenkofer's process is placed in the vacant hole, and the 

 baryta in the flask titrated. The other titration to ascer- 

 tain the oxalic equivalent of 10 c.c. of fresh baryta is 

 done as before. The advantage of the method is that 

 there is less exposure of the baryta to the air not in the 

 flask. Equations 



Ba(OH) 2 + CO 2 = BaCO 3 + H 2 O 

 Ba(OH) 2 + H 2 C 2 4 = BaC 2 4 -f 2 H 2 O. 



Pettenkofer's name is attached to another method in 

 which air is aspirated through a known bulk of baryta 

 water spread out lengthwise in a tube so that the air 

 bubbles through the baryta solution. 



Lunge and Zeckendorfs Method is to take a known 

 quantity of N/5oo Na 2 CO 3 in a glass bottle fitted with a 

 two-holed stopper and two glass tubes as in a wash-bottle. 

 An indiarubber bulb of a standard capacity with an inlet 

 and an outlet tube, both fitted with valves, has its outlet 

 tube attached to the glass tube leading to the bottom of 

 the bottle and under the surface of the solution of sodium 

 carbonate. The bulb is compressed slowly, and the air 

 expressed bubbles through the fluid in the bottle, and 



