INDUSTRIAL AND ENGINEERING CHEMISTRY
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pressure a t both points of pressure connection. The walls of the reservoir should be reasonably straight and its diameter reasonably large only to minimize the small errors due to evaporation, wet)tirigof gage walls, and oscillation of the meniscus during adjustment. In Operation, the meniscus is simply adjusted t o the hairline with atmospheric pressure a t both ends of the gage, a micrometer head reading taken, the pressure or pressure differential condition that is to be measured established by turning suitable cocks, the meniscus readjusted to the hairline, and the micrometer head again read. The simple difference between the two readings, in marked divisions,
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gives the pressure or the differential directly in 0.001 inch of gage fluid column. Since the instrument is so sensitive, it is often necessary to protect the pressure connections from drafts, to check on temperature variations, and to read the zero adjustment of the meniscus frequently whenever a long series of observations is being made. Being a t once elementary in theory, simple in operation, inexpensive in construction, rapid in adjustment, precise, direct-reading, and rugged, the American Gas Association Testing Laboratories' micromanometer should find wide use in many industrial fields. RECEIVED January 7 , 1936
Device for Determining Rate of Siphoning in Metal Extraction Systems R. S. ASBURY, Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, Pa.
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THE course of investigations on the solvent extraction of bituminous coal in a steel Soxhlet apparatus a t elevated temperatures and pressures, an indicating system has been developed for determining the frequency of siphoning. Extraction in such an apparatus requires intermittent siphoning and, since this could not be observed, an indicator within the extractor was necessary. The indicating system is simple and inexpensive and could be adapted to any apparatus in which knowledge of frequency of transfer of liquid from one part to another was required, and in which visual observation was impossible or inadvisable. The apparatus developed has been in satisfactory operation for over 8 months,
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FIGURE1. APPARATUS Upper left high-pressure closure Upper rigdt, essential parts
Lower left, front view Lower right, side view
using as solvents aniline and tetralin a t temperatures to 400" C., and a t pressures to 25 atmospheres. As shown in Figure I, the system consists essentially of a metal siphon tube, A, from the siphon cup above (not shown); a bucket arrangement, B; insulators, C; an insulated lead to the exterior, D; and an indicating system, E. All metal parts of the indicator proper except the main steel frame are made of nickel. The siphon tube, A, extends down into a grounded metal frame, F , which holds the buckets, B, loosely between two pivot bearings, G. A second metal framework, H , insulated from the first and held rigidly by small radio-type stand-off electrical insulators, C, serves as contact between the buckets and the wire lead to the exterior. This frame, H , also limits the downward motion of the buckets, which are counterbalanced by an attached weight, K. The insulated lead to the exterior, D, consists of a glass-insulated copper wire, M , to which is soldered a copper washer, 0,compressed between two Bakelite washers, N , within the steel body of the closure as shown. The high-pressure closure is approximately 17.5 em. (7 inches) above the extractor, but only a t the higher temperatures is it necessary to cool the portion containing the Bakelite disks to prevent their decomposition.
Liquid overflowing through the siphon tube causes one of the buckets to fill, descend, and spill its contents. This movement of the bucket past the siphon tube, A , prevents more liquid from entering and raises the other bucket of the unit to a position where it now receives the overflow and in turn fills and descends. The downward motions of the buckets are stopped by the frame, H . The buckets continue this oscillation as long as liquid flows from the siphon tube. Each time contact of one of the buckets with H is made within the extractor, the electrical circuit through the dry cell, resistance, milliammeter, and steel wall of the extractor is completed and the pointer of the meter moves to its upper limit; when this contact is broken the pointer returns t o zero position. By counting the swings of the pointer the frequency of siphoning can be determined, and knowing the approximate volume of each bucket, the amount of liquid being transferred can be estimated. In the system used in this laboratory the external resistance in the indicating circuit, E , is so adjusted that current from one dry cell causes the meter to register one milliampere when contact is made within the bomb. With this small amount of current flowing through the circuit, the deterioration of the nickel contacts used is negligible. In certain cases, it has proved desirable to use platinum contacts. RECEIVED December 23, 1935
