August 15, 1943
523
ANALYTICAL EDITION
use of more exact temperature control or of temperature coefficient corrections. The reproducibility of the method was determined by repeated standardizations with varying “brass” concentrations using different galvanometer sensitivities, with and without compensation for the residual current of the copper wave. The diffusion current ratio was found t o be reproducible to within +0.5 per cent average deviation from the mean if the galvanometer has a linear response and if the temperature is constant within 1’. The maximum probable error is about 1 per cent of the ratio. This represents a n error of about +0.3 per cent copper in 70-30 brass, and can be safely said to represent the maximum error of the method using carefully controlled conditions and the accurate method of calculation. The error introduced by using the rapid empirical method of correcting the copper percentages is very small. In 28 determinations the maximum difference between values obtained b y this method and the accurate method of calculation was 0.3 per cent copper and the average difference was 0.1 per cent copper. The maximum probable error of the routine method of analysis in which the temperature is controlled only to *2’ C.,
one standardization is used for all quantities of brass from 5 t o 25 mg. per 5 ml. of solution, and the rapid empirical method of calculation is used, can be found from the above discussion t o be about *I per cent copper. The average error will be considerably less than this value.
Summary
A polarographic method is described for the determination of copper and zinc in brass plate on iron or steel, which is capable of determining the copper percentage to within *1 per cent in routine analysis and within 0.5 per cent under carefully controlled conditions. The total time for a single analysis is approximately 20 minutes, and since the attention of the operator is required for less than 10 minutes, about six analyses can be made per hour. Literature Cited (1) Hohn, H., 2. Elektrochern., 43, 127 (1937). (2) Kolthoff, I. M., IND.ENQ.CHEM.,ANAL.ED.,14, 195 (1942). (3) Kolthoff, I. M.,and Lingane, J. J., “Polarography”, p. 339, New York, Interscience Publishers, 1941. (4) Ibid., pp. 482, 487.
Water Thermoregulator WM. E. BOYD, Inspection Board of the U n i t e d K i n g d o m a n d Canada, Nobel, Ontario, Canada
A
N IXEXPENSIVE, easily portable thermoregulator, capable of maintaining a variation of *0.5’ C. in bath temperature, is quickly constructed from a branched-tube regulator using a mercury valve. No electricity is used, power being obtained directly from the feed water.
B
I
C
FIGURE1
As shown in Figure 1, the bath was used a t 20” C., with warm water entering A to keep it up to temperature. Above 20’ C. an external heater is to be preferred, with cold water entering a t A controlling the excess quantity of heat supplied. The regulator consists of two parts: the pendulum group and the valve group. The pendulum group consists of a tube, C, of 7-mm. bore, about 45 cm. (18 inches) long, suspended by a piece of rubber tubing, B firmly clamped a t its upper end. The amount of ming allowed the pendulum is regulated by the slotted guide plate, E. A tube, F , holding a t least 10 ml. of water, is held on an arm a t right angles to the vertical tube, C , but free to move vertically up and down it. A weight, G, counterbalances the weight of F . The valve group consists of a toluene-mercury regulator, P, with a branched tube serving as a valve. -4vessel holding at least 75 ml. of toluene is recommended. The adjusting device consists of a large-diameter knurled setscrew entering a 7-mm. glass side arm. The vertical tube and side arm are made of 3mm. bore tubing. N is a constant-level device, while R is a bleeder emitting water to the drain a t approximately 30 ml. per minute. The action is as follows: A small amount of water enters the valve group a t M , flowing into the constant-level tube, N . Any exceys is led to waste. Water flows down tube 0 into the vertical arm of the regulator and up the inclined arm through tube Q to fill vessel F . The weight of F is now great enough t o force tube C over and deliver water into the bath. As the temperature rises the mercury assumes the shape as shown in the diagram and seals off tube &, preventing water from reaching F. Bleeder R, though operating rontinuously, is now able to empty F in a few seconds and allows tube C to swing back over the baffle. When the temperature drops the mercury falls, allowing the water to reenter &, and the cycle is repeated. No cutting off of the mercury column takes place when the water leaves by way of the inclined tube. A small head, h, of water is to be preferred. Good results were obtained when a head of 15 to 20 cm. (6 t o 8 inches) was used. A temperature variation of *0.5” C. was easily maintained in 6-day runs.
