34 Gas Analysis. IV 
same as with the usual form of instrument.? Attention may however 
be called to one or two points which are often overlooked. 
Red rubber should not be used on the connections where alkali may 
touch it, as 1t gives off sulfur which may finally appear as hydrogen sul- 
fide in the burette. 
To make the rubber connections tight (in case of leakage) it is conven- 
ient to wrap them with elastic bands. Loop the band around the rubber 
tube, pull tight, and wrap the free end around the tube several times. 
Pass a small curved forceps under the wrapping, catch the end of the 
rubber band over the points of the forceps, and twist the end under the 
wrapping by withdrawing the forceps. This is a much better method of 
making joints tight than wrapping them with wire. 
The walls of the burette should always be moistened with a fraction of a. 
drop of 1 per cent sulfuric acid, and 2 or 3 cc. of this fluid should be placed 
in the control tube. 
The analyst must remember that accuracy in the use of the instrument 
does not depend upon an extreme effort to read the burette as finely as 
possible, but rather upon making sure that the absorptions are complete. 
It is essential therefore frequently after an analysis is supposedly com- 
plete to pass the gas over again into the absorbent and make another 
reading to be sure that no change occurs. 
A check on calibration, tightness of joints, and efficiency of absorbents 
which should be used daily is to make an analysis of atmospheric air. If 
the apparatus is properly graduated and in good order the sum of the 
oxygen and CQ, in uncontaminated atmospheric air should be found 
20.96 per cent, with an allowable error of + 0.03 per cent. 
The method of graduation used by most American glass blowers is far 
too rough and inaccurate for the precision requisite for this instrument. 
Thus in some burettes of this type made in America I have found the 
errors of graduation ten or even twenty times as great as are allowable 
(giving an analysis of ordinary air at 21.20 per cent oxygen or worse). 
The absolute error of the instrument was only 0.1 cc. and this is not greater 
than is quite common and is allowable for common purposes in an ordinary 
titration burette. For the calibration of the gas burette the glass blower 
must not use water but mercury. The standard burette ‘against which 
he calibrates must be of at least as fine bore as that of the tube of the 
burette to be calibrated. The standard burette must have been cali- 
brated with weighed amounts of mercury and no mark on the burette 
purchased should have an error greater than 0.005 ce. ° 
The purchaser of a burette should test it before assembling by invert- 
ing the burette, connecting it with a reservoir of mercury, filling to the 
7, 8, 9, and 10 cc. marks, respectively, pouring this mercury into a small 
tarred beaker, and weighing. 1 cc. of mercury at room temperature 
(18°C.) weighs 13.55 gm. An allowance of 0.004 cc. may be made for the 
reversal of the convexity of the meniscus in the inverted burette. 
Haldane, J. 8., Methods of Air Analysis, London, 1912. 
