I ND U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
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also showed pitting; some were so pitted that their cross sections were reduced 50 per cent in size. The corrosion of the brass screws and galvanized nails was slight except under the most severe conditions where it mas noticeable but not excessive. There was no marked difference between the fastenings removed from the painted and unpainted halves of the pieces. The sodium dichromate had an erratic effect; it seemed to have reduced corrosion slightly in the fastenings on the fence but not in those in the relative humidity rooms. The loss in weight of the wire nails is shown in Figure 2. Each point represents the average of the losses shown by six nails from one piece. I n the 30 and 65 per cent relative humidity rooms there was no loss in weight within the error of gram-of nails in the pieces that were weighing-*O.Ol seasoned after treatment. When the wire nails mere driven into wet treated pieces there was no loss after the first 4 months. Pieces of this size require about 6 weeks to dry from a water-logged state to a condition in equilibrium with air a t 65 per cent relative humidity. The wire nails in the fence showed a greater loss than those in the 65 per cent room but considerably less than those in the 90 per cent room. The wire nails in the wood treated with 1.51 pounds of zinc chloride per cubic foot, seasoned after treatment, and kept on the fence, showed less corrosion than did the wire nails in an untreated piece kept in the 90 per cent
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room, which again shows the dominating effect of a high humidity. The mean annual relative humidity for the area in which the fence is located, as given by the weather reports, is 74 per cent, while for the winter months it is 82 per cent. The moisture content of the pieces kept on the fence was, of course, affected periodically by rain and snow. The rate of loss in weight in the dried pieces placed in the 90 per cent room tended to approach that of the undried pieces after the first 4 months. The wire nails from the piece treated with the mixture of zinc chloride and sodium dichromate and kept in the 90 per cent room showed the highest average loss-namely, 0.28 gram. These nails had originally weighed 1.59 grams; thus the loss represented 17.6 per cent of the original weight. The loss in weight of the brass screws in nearly all pieces kept in the 30 and 65 per cent rooms and on the fence was within the error of weighing. As to the pieces kept in the 90 per cent room, the screws from the untreated wood showed no loss in weight. Those from the treated wood showed a maximum loss of 0.10 gram from an original weight of 2.55 grams.
ACKNOWLEDGMEXT The tests reported here were started in cooperation with the Grasselli Chemical Company. RBCEIVBD September 28, 1934.
Pump for Delivering Liquids a t Low Constant Rates HANS TROPSCH AND w.J. MATTOX, Universal oil Products Company, Riverside, 111.
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HE pump shown diagrammatically in Figure 1 has been f o u n d v a l u a b l e in this laboratory for delivering gasolines a t constant rates from 100 to 400 ml. per hour and should prove useful for other purposes where an accurate, constant flow is desired. The construction is simple and consists of a s m a l l c o n s t a n t speed motor which, t h r o u g h a reduction gear, operates a 1-inch (2.5-cm.) copper bellows. The rate is regulated by the length of the stroke which is in turn varied by means of an adjustable stop, or stroke regulator. /N The valves consist of 0.25-inch (0.635-cm.) stainless-steel b a 11s seating on groundglass seats. Ten-mm. Pyrex glass tubing was constricted t o the shape shown in Figure 1 and then ground with a Pyrex glass r o d s h a p e d similarly to the constricted tubing. Va 1v e s constructed in this way show no tendency to leak after months of use with extremely corrosive samples of gasoline.
D/5CHARGE
S%A/NLE55 BALL VAL
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rate to vary slightly and is removed by filling with water and boiling. Filling the bellows with water also makes it unnecessary to clean the bellows when changing samples. The flow through the pump is necessarily in pulses but a steady flow is obtained after passing the liquid through the device shown in Figure 2: The liquid enters at A , rises in B, and issues dropwise from capillary C into coil D, the capillary being of such size that all the liquid does not drain from B before the next stroke of the pump. The same capillary is s u i t a b l e for a wide range of feed rates, since at higher rates the increased height of the liquid in B causes an increased pressure at C and a corresponding increased flow through C. E serves to equalize the pressure over the liquid. Fluctuations in flow at F are not noticeable.
u !F
A i r in t h e bellows causes t h e
FIGURE 1. PUMPFOR DELIVERING FlGURE2. FLOW EQUALIZER LIQTJIDSAT Low, CONSTANTRATES
The pump is capable of delivering a t atmospheric pressure any volume up to 500 ml. per hour a t a very constant rate. For periods of 12 hours a t a rate of 200 ml. per hour the deviation was *2 ml. per hour. The B a r b e r - C o l e m a n shaded pole motor mounted on a gear box for reducing the speed to 1.5 r. p. m. was purchased from the MerkIe-Korff Gear Company, Chicago, for less than 5 dollars. The authors wish to acknowledge the considerable assistance obtained in the dev e l o p m e n t of t h i s p u m p from Hugh Rodman and Harry Munn of the mechanical department. RECEIVED September 28, 1934.
