36 Gas Analysis. IV 
In Fig. 3 is shown a similar modification of the Haldane ana- 
lyzer for the CO. content of atmospheric air. The bulb of the 
burette for this apparatus should have a capacity of 30 ce., and 
the tube of the burette should be graduated up to 100 parts 
(0.003 cc. each) of absorbable gas (CO2) in 10,000 of air. This 
instrument is quite as accurate and much simpler and cheaper 
than the Pettersson-Palmquist analyzer. 
In Fig. 4 is shown an apparatus which has been found useful 
for teaching purposes in this laboratory (one instrument to each 
six or eight students). For beginners it is a very much easier 
apparatus to use than the form shown in Fig. 1. Acidulated 
water (1 per cent sulfuric acid) is used in the burette instead of 
mercury. Common glass 6 ounce bottles are used to hold the 
absorbents, sodium hydroxide, and potassium pyrogallate. A 
layer of paraffin oil is placed on top of the absorbents to protect 
them from the air. The bottles stand on a shelf which also— 
supports the water jacket of the burette. 
The apparatus is used in the same manner as that described in 
the first paper of this series except that the addition of a control 
tube renders it possible to compensate for temperature changes 
in the course of an analysis. The use of the control tube is as 
follows. <A strip of mm. paper is pasted on the leveling bottle. 
The top of the control tube is opened. The leveling bottle is 
lifted a few inches and the fluid allowed to rise part way up the 
control tube, the top of which is then closed. The leveling bottle 
is held so that the fluid is at the same level in the bottle and 
in the tube and a loop of wire (X) is placed at this height on the 
tube. Before each measurement of gas volume in the burette the 
leveling bottle is moved up or down the control tube, and by 
means of the mm. paper strip note is made of the height above or 
below the meniscus in the control tube at which the bottle must 
be held to bring the gas in the control tube to its original volume 
(at X). The leveling bottle is then held at the same height 
above or below the meniscus in the burette. In this way the 
gas in the burette can always be brought to the correct volume 
per molecule. 
This instrument is adequate to all scientific and clinical in- 
vestigations except those involving the most extreme accuracy. 
The elimination of mercury renders it very much easier to use. 
