Oct. 16, 1916 
Acidity and Adsorption in Soils 
141 
inum between determinations with a little diluted hydrochloric acid, 
afterward rinsing in many changes of distilled water. 
The electrode vessel must be closed to the air. A simple and easily 
constructed cell may be made from a wide-mouthed bottle of 75 to 100 
c. c. capacity. Through holes in the rubber stopper are fitted the 
hydrogen electrode, an agar connecting tube, a small exit tube, and a 
tube for saturating the solution with hydrogen when desired. A hole 
to admit the tip of a burette should also be provided for purposes of 
titration. The most convenient method of making the liquid connection 
is by means of bent glass tubes, filled with agar jelly prepared with a 
saturated solution of potassium chlorid. Only thoroughly washed agar 
should be used in making the jelly. In order to avoid contact potentials 
as far as possible connection with the calomel cell is made through a 
beaker, containing saturated potassium-chlorid solution. The con¬ 
struction of a normal calomel cell is described by Ostwald (22). In 
the present work N/10 potassium chlorid was used. 
An adequate supply of pure hydrogen is of primary importance, and 
this is most conveniently obtained from the decomposition of water by 
means of a direct electric current. Such a generator may easily be pre¬ 
pared by using a large bottle and an inner cylinder made from a wide 
glass tube as a means of separating the electrodes. The latter may be 
of nickel, or pure iron and a 25 per cent (by weight) potassium hydroxid 
solution is convenient as an electrolyte. In order to purify the hydrogen 
from small quantities of oxygen, it is passed through a long glass tube 
filled with platinized asbestos. This is heated by a fine nichrome wire 
wound around the outside of the tube'and connected through a lamp 
with a source of current. To provide a rapid stream of hydrogen re¬ 
quires the consumption of several amperes of current. 
E^ERIMKNTAIv procedure 
After placing the soil suspension in the bottle, hydrogen gas is per¬ 
mitted to flow through the electrode raised above the surface of the 
liquid for several minutes. The electrode is now lowered until the plat¬ 
inum gauze is partially submerged in the liquid and the exit tube closed. 
The bottle is now rotated back and forth for several minutes, as originally 
described by Hasselbach and Gammeltoft (16). The agar tube (at 
other times kept out of the liquid) is now lowered so that a connection 
is made with the calomel cell through the beaker of potassium chlorid. 
The rheostats are adjusted so that no deflection of the galvanometer 
needle is noted when momentary connection is made by tapping the 
key. The reading on the voltmeter is then recorded. The procedure 
is repeated until constant readings are obtained. This occurs in the 
case of acid s 6 i\s within a few minutes, but for soils approximately 
neutral a slightly longer time will be required. In the case of titrations 
