TECHNIQUE OF ELECTROCHEMICAL MEASUREMENTS 457 



Dr. F. G. Cottrell; they have been described in detail by Schmidt 

 and Finger.* 



The hydrogen is generated by the electrolysis of 6 per cent (by 

 volume) sulphuric acid, in an apparatus which has previously been 

 described by Schmidt and Finger in the paper cited above. To 

 guard against the possibility of any oxygen, ozone or hydrogen 

 peroxide being carried over with the hydrogen from the generator, 

 the gas is passed through a heated glass tube which is loosely filled 

 with platinized asbestos and which has wrapped around it for a 

 distance of about 20 cm. a coil of fine resistance- wire, the internal 

 diameter of the tube being about 0.5 cm. The hydrogen is com- 

 pletely cooled before it reaches the electrodes, because, after leaving 

 the heater, it passes through a narrow glass tube, partly filled with 

 glass wool, about 70 cm. long, leading to the water-bath; since a 

 considerable portion of this tube is within the incubator which 

 holds the water-bath, the temperature of the hydrogen, when it 

 reaches the electrodes, may be considered as that of the incubator 

 itself. The coil of the heater attached to the hydrogen-generator 

 is heated by a portion of the same current (110- volt circuit) which 

 generates the hydrogen, the current being led into the generator 

 through 4 lamps in parallel, one of the lamps being connected in 

 series with the coil. In order to maintain the pressure of hydrogen 

 which is necessary to drive it through the electrodes, the oxygen 

 which comes off from the outer cylinder of the generator is carried 

 off by a tube which dips into a column of water, the depth of the 

 opening of the tube in the water being adjusted until the levels of 

 the fluid in the inner and outer cylinders of the generator are 

 approximately equal. 



The complete chain is arranged as follows: The syphon-tube of 

 the " half -element " containing the fluid into which the electrode 

 dips is immersed in a beaker filled with the same fluid. Thus the 

 " half -element " containing the solution of unknown hydrogen- or 

 hydroxyl-concentration is in fluid connection with a beaker which 

 contains the same solution and the " half-element " containing the 

 solution of known hydrogen- or hydroxyl-concentration is in fluid 

 connection with a beaker filled with that solution. The two 

 beakers are then connected by a U-tube filled with agar saturated 



* C. L. A. Schmidt and C. P. Finger, Journ. of Physical Chem., 12 (1908), 

 p. 406. For improvements in the original design, Cf. C. L. A. Schmidt, Univ. 

 of Calif. Publ. Pathol., 2 (1916), p. 157. 



