The Use of the Slide Rule in Calculating Hydrogen-Ion Concentration and pH Values M. C. SANZ,University of Southern California, Los Angeles, Calif. 7.8 X 10-4must be expressed as 0.78 X Then pH = 3 +. 0.78 is set on the CI scale and read directly on the L scale as 0.108. Then pH = 3.108. Again, given (H+) = 3.339 x 10-6, find pH. Expressing the value of (H+)as 0.3339 X 10-q H 5.477. 0 477 is read on the L scale under 78 on &e scale. The procedure for finding (€I+), given pH, is the reverse. Given pH = 6.3, find (€I+). (H+) = 0.5 X 10-8. The 5 is read on the CI scale above 3 on the L scale.
FIGURE 1
R ~ C E I V EJanuary D 24, 1933.
T
HE method now in use for the calcula-
tion of pH values by means of the slide rule is to set the number desired on the D scale and find the logarithm on the L scale, which involves the following calculations: Given (H+) = 7.8 X find pH. pH = l/log (H+) = 4log 7.8 = 40.892 = 3.108 By the method here proposed the required value may be read directly.
FIGURE2
Improved U-Type Mercury Thermoregulator J. B. RAMSEY,University of California a t Los Angeles, Los Angeles, Calif.
M
UCH work on automatic temperature controls has been hydrogen. Finally the hydrogen is introduced until the done to minimize the control current through thk mercury stands about 1 em. below the wire in the capillary thermoregulator in order to diminish the rate of corrosion when the stopcock of the regulator is closed. The chamber at the metal-mercury contact. This would have been un- is then connected with the air via the three-way stopcock necessary if an inert gas had been maintained at the contact. and immediately sealed off. To set the regulator for conSeveral investigators have stressed the difficulty of providing and maintaining an inert atmosphere. A modification of trol a t a desired temperature, a the method described by elark (g), which has been adapted it is allowed to attain this temp e r a t u r e with the stopcock to the ordinary U-type mercury regulator, has proved so simple and satisfactory that its description may be of value open. Then, with the circuit b r e a k e r connected at A and to others. The regulator (Figure 1) is completely assembled ‘from D (via mercury), slight suction Pyrex glass with a tungsten wire (5) sealed in place a t C. or pressure i s applied a t E This wire extends about 1 cm. into the capillary which is until the mercury barely conapproximately 1 mm. in diameter. The side arm, B, of tacts the tungsten wire, when the contact chamber is bent as shown and drawn down for the stopcock is closed. To sealing off. Clean dry mercury is then added a t E until change the setting to another it reaches somewhat above the stopcock, which is about temperature merely r e q u i r e s FIGURE1 level with the contact point in the capillary. Dry hydrogen opening the stopcock and refrom a source of conveniently small pressure (Kipp generator peating the above procedure. It is thus not necessary to or gasometer) is admitted to the contact chamber by means move the regulator in order to change the setting. To eliminate the necessity of opening and refilling with of a three-way stopcock, which permits connecting the contact chamber alternately with the hydrogen source and hydrogen when too little has been left in the contact chamber the air. By applying suction at E when connected with the to permit bfeaking contact by gentle suction at E (a difficulty hydrogen source and releasing when opened to the air, the often encountered), the side arm is bent down as shown at chamber may be thoroughly washed out and filled with B. This permits trapping some of the mercury away from
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