592
INDUSTRIAL AND ENGINEERING CHEMISTRY
A n Improved Timing Siphon
Vol. 16, No. 9
By controlling the rate of influx of water, the rate of draining with the siphon, and the placing of the electrodes, almost any length of cycle can be obtained.
WILLIAM R. McMlLLANl Carnegle Institute of Technology, Pittsburgh, Pa.
UTERATURE CITED
(1) Rudy
and Fugassi,
[email protected].,ANAL.ED., 12,.757 (1940).
C
YCLIC processes can best be controlled by the use of a clock motor or other similar device. However, a substitute for a mechanical timer is often needed. In this laboratory the common siphon proved unsatisfactory for such use because after the first delivery of water, the siphon tube remains full of bubbles. I n this case, the siphon vessel may never again fill up, the water siphoning out as fast as it runs in, or the siphon may operate when the vessel is only one-fourth or one-half full. This difficulty is overcome in the design given in Figure 1.
L
Simple Automatic Pump For Collecting Gases at Low Pressures 1.
E. PUDDINGTON
Divition of Chemistry, National Research Council, Ottawa, C n r d r
IN A
particular piece of work it was found desirable to maintain a reaction mixture a t low pressure and a t the same time to collect evolved gases. Since the reaction was being followed for extended periods, a manually controlled pump such as a 7-Toepler was inconvenient. The following simple design was found to be efficient and required virtually no attention during long periods of operation. The details of the desi n are shown in the 6 ure. It consists essentially of a mercury !iffusion pump in w h i z the compreaeed gas, instead of being removed by a mechanical pump in the usual way, is entrained by the condensed mercury, as in the ordinary S rengle pum carried down the capillary tube, A , and discgarged into tRk gaa holder, C. A second capillary, B, returns the mercury from the gas holder to the boiler. The height of the diffusion pump above the mercury boiler must be sufficiently great to keep the hydrostatic pressure of the mercury and entrained gas in A always greater than the mercury alone in B. In the present design, which operated successfully on systems where the pressure was aa hieh as 3 cm. of mercury, this height is about 40 cm. eds should be greater increased. In order that the collected gaa should not occupy too lar e a volume, the gas holder should %e located about 40 cm. below the level of the mercury in the boiler. Capillary tubing of 2-mm. diameter is satisfactory for the top half of A , while the use of I-mm. tubing in the bottom half greatly reduces the tendency for comp r d gas bubbles to move up the tube. A heath5 element of about t%watt capacity wrapped about the tube dehvering mercury vapor to the jets reduces bumping in the boiler and eliminates excessive refluxing of the mercury.
%%?g:fis
Figure 1
The central tube is 1.5 cm. in diameter and joins on to a 5-mm. tube. This large central tube completely breaks up the bubble string and gives cycles which are accurate to 2 or 3 % if the water temperature does not vary too greatly. The size of the outer vessel can be vaned to any size, while the central tube and the draining tube can be enlarged to any degree, provided the ratio of sizes is not made smaller and the draining tube does not become too large actually to function as a siphon. A conventional constant-head device furnished a constant flow of water to the vessel containing the siphon. The conductivity of the water can be used to work the control mechanism as follows: Two electrodes which are intermittently bathed by the water can be connected to a source of power and a suitable relay which in turn can actuate gumgs, valves, hts, etc. A satisfactory relay circuit is descri ed y Rudy a 3 F u g a s s i (1). Liquids other than water can be used with this device, with due regard for abnormal viscosity or for vapor pressure which might caw bubble formation due to the lower pressure a t the top of the siphon tube. In place of conductivity control, a photoelectric control may ala0 be used. Prment hddreu, Mine Safety Appliance4 Co., Pittabur~h,Pa.
This pump is particularIy useful for collecting gases at low pressures. Its limited capacity makes it rather slow a t higher pressures. The design described reduced the pressure in a 350-02. volume from 35 to less than 10-6 mm. in 3 hours. A lowering from 1 to 10-6 mm. was obtained in the same system in 15 minutes. I S E U ~ DM N.R.C.No. 1216.
