INDUSTKIAI, A N D ENGINEERING CHEMISTRY
324
Discussion In Series A the time of boiling was varied while the other factors were kept constant. The results indicate that the transposition is reasonably complete after 5 minutes, and that further boiling increases the transposition but slightly. Series B was run in order to discover the optimum volume of sodium chloride. The results of this series are plotted in Figure 1. The curve is seen to level off a t about 60 ml. Accordingly, a volume of 60 ml. was chosen as the standard in this work. Series C shows the effect of using varying amounts of silver thiocyanate. Up to a certain point all of the silver thiocyanate is transposed but, after this point has been reached, the per cent of transposition drops, while the amount transposed remains practically constant. We must conclude, therefore, that the sodium chloride solution becomes saturated with respect to CSS-. Therefore, the larger the quantity of silver thiocyanate, the larger must be the volume of chloride solution required to transpose it. The foregoing conclusion is in harmony with the mass action law. The amount of silver thiocyanate transposed is governed by the solubility products of silver chloride and silver thiocyanate taken simultaneously :
x c4K-x
c4y+
cci-
SL
cc\s-
=
&IS2
x
CCI
From the solubility products of silver thiocyanate and silver chloride, calculated from their solubilities ( 2 ) , the number of milligrams of CSS- in 60 ml. was obtained. The values are: 36 mg. a t 25" C. and 245 mg. a t 100" C. The experimental value is 94 mg. of CSS-, the temperature being well above room temperature but certainly falling below 100" C. during the process of filtering off the silver chloride and untransposed silver thiocyanate.
Summary The most satisfactory conditions for the transposition of silver thiocyanate by M sodium chloride are: For every 100 mg. of thiocyanate as silver thiocyanate, 60 ml. of M sodium
I
20
ML FIGURE
61
= =
CCNS-
ov0
1
40 OF
M
60
80
1
too
SODIUM CHLORIDE
1, P E R CENT TR.4SXdISSION PLOTTED MILLILITERS OF ' iA XaC1
AGAINST
rhloride solution are required, and the mixture, must tie boiled for a t least 5 minutes. Under the above conditions a transposition of about 95 per cent of the thiocyanate is obtained.
Acknowledgment The authors wish to thank L. ,J. Curtman for suggesting this topic for investigation, as well as for his raluable advice throughout the work. Literature Cited 11) Curtman and Harris, J . A7n. Chem. Soc., 38, 2622 (1916).
(2) Seidell, "Solubilities," 2nd ed.. New P o r k , D. Van Yostrand C o . , 1919. RECEIVEDJanuary 15, 1938.
Automatic Cooling Device for Thyratron-Controlled Thermostats ALFRED B. GARRETT, The Ohio State University, Columbus, Ohio
P
F
T
GGR
.
200 000 ohms 50,600 ohms Thermoregulator F. Fan H . Heater Tube FG57 RI
R1:
T.
HE thyratron control unit, which is often used to replace the relay control unit for thermostats, is adaptable for automatic cooling as well as heating by the principle employed in a relay circuit described in an earlier paper ( 1 ) . The terminals of the fan circuit are connected in the heater csircuit in such a manner that the fan and heater form a parallel circuit with the thyratron and heater. When the current is flowing through the tube the fan is shunted out of the circuit because of the high resistance of the fan motor. When no current is flowing through the tube the current will flow through the fan-heater circuit, causing the fan to run and giving only a very small dissipation of energy from the heater. Figure 1 shows the conventional thyratron circuit with this adaptation.
Literature Cited (1) Garrett, A. B., IND. EVG.CHEX.,25, 355 (1933).
l//dKI
FIGURE 1. DIAGRAM OF THYRATRON CIRCUIT
RECEIVEDApril 29, 1038
