ANALYTICAL EDITION
January, 1946
79
c.,
Raoult's law. The total pressure maintained in the apparatus dioxide plus the vapor pressure Of the was 760 mm. Of solution a t 25" C. The solubilitv data are given as milliliters of carbon dioxide a t 760 mm. and25" C. dissGlved in 1 ml. of solution. From this is calculated the Bunsen coefficient, a, which is the milliliters of carbon dioxide, calculated to 760 mm. and 0 O C., dissolved in 1 ml. of solution ( 4 ) Although the precision of the results is 0.002, it can be consideEed that the accuracy of a is 0.005. The data are given in Table I.
acidified sodium sulfate solution below 16O this solution i l l continue to dissolve less gas than the acidified glycerol solution. Only a t temperatures below the cryohydric point would the acidified glycerol solution have advantages. The cryohydric temperature of saturated aqueous sodium sulfate solution is and of sodium chloride is -21. 0 aqueous solution of sodium chloride is recommended for use at temperatures to -20°C. ( - 4 ' F . ) .
c.
0
LITERATURE CITED
DISCUSSION
(1) Burgess and Wieeler, J . Chem. SOC.,97, 1923 (1910). (2) Kobe and Kenton, IND.Ero. CHEM.,ark^. ED.,10, 76-7 (1938). (3) Kobe and Williams, Ibid., 7, 37-8 (1935). (4) Markham and Kobe, Chem Reviews, 28, 519-88 (1941). THIRD paper in series; for NOS. 1 and 2 688 (a, s).
The Bunsen coefficient for an acidified 50% glycerol (0.423) is almost twice that found for the 20% sodium sulfate plus 5% sulfuric acid solution (0.247) previously recommended ( 2 , 3 ) . Although sodium sulfate decahydrate will crystallize from the
Electronic Timer JOHN KEENAN TAYLOR
AND
JOSEPH GILMAN REID, JR.
National Bureau of Standards, Washington,
R
E C E S T n-ork in the physical chemistry laboratory of this bureau involved the use of a solenoid-operated, enclosed glass pump. The electronic timing device described by Bechtold (1) appeared particularly well suited for controlling this solenoid because of its simplicity, ease of construction, and readily controlhblr, pulse rate. However, this timer proved unsatisfactory in operation since, under the conditions which obtained, the gas-filled triode (885) had an average service life of only about 12 hours. S o current-limiting element was included in the triode plate circuit. Thus, the charging surge supplied to capacitor C2 (Bechtold's designation) was, upon breakdown of the triode, in excess of the rated peak current for the tube. This overload caused the tube t o fail prematurely. Insertion of re-
r
1
D. C.
sistance to limit the peak current to the specified maximum (300 milliamperes) resulted in feeble actuation of the relay. Satisfactory operation required the use of a more sensitive relay, or of a tube having a higher peak current rating. I n the improved circuit given in Figure 1 the type 885 tube has been replaced by a type 2050 gas-filled tetrode and a currentlimiting resistor has been inserted. This resistor, &, has a value of about 170 ohms and limits the charging surge of C2 to less than the rated maximum (1 ampere) of the 2060 tube: Resistor R j has been added to limit grid current and rheostat R, to reduce arcing of the relay contacts on an inductive load, such as a direct current solenoid. The modified circuit has proved highly satisfactory as evidenced by over 200 hours of operation, including continuous periods of as long as 60 hours, with no evidence of tube failure. Its readily adjustable pulse rate, obtained by manipulaPI tion of potentiometer R1 and the adjustability of the range of rates depending upon the values of RI, RP,and CI, make it applicable to a wide variety of timing operations.
" ,
CI
ACKNOWLEDGMENT
0 1 6d
D t IN
TOLOAD
ll0V
Suggestions made by P. J. Franklin in connection with the design of this circuit are gratefully acknowledged.
AC
Figure 1.
Circuit for Electrcn:c Timer
CI, 3 paper condensers, 400 wv, P r f d . each; Cn,250 wv. electrolytic condenser, 8 r i d Ca paper condenser 450 wv 1 aM.1 Ri I-megohm potentiometer N o 6 taper1 Ra 50 000 D 1-watt carbon; R s R; lO,OOOD, 1 -wati carbon;'Rs 1 -megbhm 1 -watt carbon; Re 150 n'5-watt wire-koind; R;, 100 D, 9-amperc'rhoostat; T,6.3-volt 3-ampere dlament tran;former; R e , double-pole, double-throw relay, PO00 n coil; F, P.O-ampere furor S doublo-pole, single-throw toggle switch; 9050, RCA type PO50 gas-filled tetrode; PI, P, relay contact point;
LITERATURE CITED
(1) Bechtold, I. C., IND.ENG.
C H ~ MAXAL. ., ED.,14, 429 (1942).
