-~ Alexandei P. Marion, Quetm.
Electrolysis Microapparatus. College, Fluching, N. Y.
u alternating-direct current transformerless electrolytic ap-
A-paratus is useful in separations on a micro scale requiring currents of less than 0.2 ampere. Rectification of the alternating current is accomplished by a miniature selenium rectifier stack available a t reasonable cost a t local radio supply distributors. On direct current the series combination of R1 and R? can be used to limit the current to the required amount. N C
ungrounded side, a shock hazard is present. The neon lamp, which should be of the 0.25-watt type with a current-limiting resistor incorporated in the base, will eliminate this hazard if the plug connection to the power line is such that this lamp glows when the other side is connected to a good electrical ground. -4s a further precaution the electrodes should be inserted with the apparatus disconnected completely from the power lines or a doublepole single-throw on-off switch should be used to break both legs of the input.
h
Automatic Washing Apparatus for Precipitates. Alois Langer, Research Laboratories, Westinghouse Electric Corporation, East Pittsburgh, Pa. preparation of precipitates for quantitative analysis of I-their element,s in order to establish the composition, it is somey THE
times necessary to wash them very thoroughly to remove traces of foreign material. Especially with some of the voluminous precipitates of metals with organic reagents, the washing procedure is rather slow. To perform such an operation without any attention, even though several liters of washing liquid might be used, an apparatus was designed as shown schematically in Figure 1. The filtering follows the cycle prescribed for washing analytical precipitates-draining the liquid as far as possible before the next liquid is added and then filling the filter entirely each time.
1 ~
.4. 0-300 milliammeter, d.c. CI. 0.01-mfd., 6 0 0 - ~ 0 l t ,paper Cz. 2000-mfd., 6-volt, electrolytic JVe. Neon l a m p , 0.25-watt, with resistor R I . 300-ohm, 25-watt Rz. 15,000-ohm, 0.2-amp. Re. Relay, normally closed Sw. Double-pole double-throw switch V . 0-6 voltmeter, d . c .
As the output from the rectifier is half-wave, some filtering action is necessary to smooth out the fluctuations. The 2000-mfd. condenser, C?, serves satisfactorily and when checked on an oscilloscope showed a very slight ripple under full load and no ripple whatsoever under a light load. The regulation of the unit is improved by bleeding some of the available current through the coil of the relay, which must be normally closed. Because it serves as a protective device in case the potential across it exceeds 6 volts, it must have a coil resistance of approximately’1200 ohms and be activated by a direct current of 5 milliamperes. Other lox-current 6-volt relays would be expected to function satisfactorily, but the lower the coil resistanre the less current is available for the electrolysis. The relay may be replaced by a suitable resistor, but the full resistance of R? must then be placed in the circuit before the electrodes ale removed from the solution; othernise the output voltage ill soar and both the voltmeter and the filter condenser will be ruined. K i t h the relay in the circuit, however, these components are protected; the relay also sounds as a m r n ing buzzer in such a case. The rectifier element is a miniature, five-plate, selenium stack similar t o S o . 404D2795 of the Federal Telephone and Radio rorporation. The polarity of the electrodes can be reversed by the double-pole double-throw sivitch, Sw. R1is a current-limiting resistor used as a safeguard against burning out the apparatus, should a low resistance be placed across the electrodes with RS near zero setting. The variable resistance, Rz, is a tubular resistor capable of passing 0.2 ampere and is used in this laboratory model in order to obtain anv saecified volbage a t any current from a few milliamperes t o t6e maximum rating. Forroutine analyses where the resistances of the solutions being electrolyzed fall within a restricted range. a rheostat of smaller ohmage could be used and the series resistlance, R1, increased accordingly. Caution. One side of the alternating current line is brought directly to an electrode terminal. Should this happen to be the
The precipitate rests on a filt’er paper, the size of which is chosen accordiiig to the amount of the precipitate. The filter paper has to be laid firmly to the walls of funnel F , so that no air is sucked in between the glass and the filter paper during the washing. The washing liquid is stored in bottle B, and the disposed solution drops into flask C. As B and C form a closed system-; by connecting them through tubing A as indicated, the amount of air displaced in C by the washing fluid will displace the same amount of liquid in B , which will flow through tubing D onto the precipitate, thus making the washing contiiiuous. In order to make the procedure intermittent, a siphoning device is introduced between B and F . Siphon arm S is movable in funnel E by sliding in rubber tube T , thus making the amount, of liquid to be dispensed at one time variable according to the filter size. The liquid flow through holes onto cone H , whereby the liquid is dispersed evenly i over the whole preIP cipitate. In order to i elimhatedust. and exi cessive evaporation I of the liquid, the unit ; is shielded by a transA : parent cover, P . I Khen once adjusted, the TTashing proceeds as long as t,here is liquid present in B. Only large fluctuabiens in room temperature disturb somewhat the smooth operation of the device.
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Figure 1.
650
Apparatus
