MECHANICAL CHEMISTS GUYBARTLEM,GENERAL ELECTRIC COMPANY, SCHENECTADY, NEWYORK
The routine chemist-with his test tubes, retorts, delicate balances, and array of bottles covered with hieroglyphics-is being replaced in many manufacturing plants by different automatic devices for conducting analyses For instance, in one manufacturing plant there is an automatic electric signal which says, "Don't use that batch of copper. There's a little bit of iron in it somewhere; and, if you use it, it will spoil the brass." Whereupon the operator removes the 40-pound brick of scrap copper from the traveling tahle and consigns it t o the pile of material which is destined for use in less particular work. In another place there is a device which rings a warning gong. To the workmen the gong says, "There must be a leak somewhere in the mercury system, and you'd better check up on it. There's a slight trace of mercury vapor in the atmosphere-just about one part in a millionbut it's dangerous." Whereupon the men see to it that plenty of fresh air is admitted to the room, and that the leak is found and repaired. As still another example of the automatic chemist there is the x-ray diffraction apparatus which identifies different substances according to the pattern made on a photographic film when a capillary tube filled with the powdered substance is exposed to x-rays.' Finding a Speck of Iron In salvaging scrap metal such as copper, it is often necessary to determine whether there is iron in the scrap in such amounts that it would be spoiled for certain uses when melted down. The chemist could quickly determine the amount of iron after the scrap pieces had been melted down, but the analyses are needed previous to the melting. Bits of iron might be removed with a magnet, but such a procedure would mean that the scrap would need to he spread out loosely within the field of the magnet. The scrap is received as bits of tangled copper wire, compressed into bricks weighing about 40 pounds each. The Federated Metals Corporation of St. Louis received a contract to supply high-grade copper for use in making cartridge brass, and in order to use the bricks of scrap copper i t was necessary to make sure that the iron content was very low. Apparatus which detects iron in such quantities as 0.05 per cent in the 40-pound bricks was thereupon developed in the General Engineering Laboratory of the General Electric Company. The apparatus consists of a tahle on which is mounted a hollow test coil, Reference was made to oue of the nurnuuus applicalions of x-ray dillraclion apparatus in "Millionths of an Inch," THISJOURNAL, 4,822-30 (July, 1927).
a platform on which the brick of scrap to be tested is placed, and a sensitive galvanometer relay which works in conjunction with a second relay to operate a signal system. A 40-volt storage battery supplies voltage for the test coil, relays, and signal system. The complete apparatus is shown in Fig. 1, with a brick of compressed copper wire resting on the platform, ready to be tested. The details of the double-screw arrangement which moves the platform carrying the brick back and forth through the test coil a t a rate of one foot per second are shown in Fig. 2. This double-screw arrangement, driven by a small induction motor, makes i t unnecessary to reverse the
motor each time the direction of travel of the platform is reversed. The platform travels back and forth automatically after the motor is started. On the panel, the rear view of which is shown in Fig. 3, are mounted a relay, signal buzzer and light, and an ammeter and triple-pole switch. The galvanometer is mounted separately so that it will be free from vibration. The wiring diagram of the device is shown in Fig. 4. The bricks to be tested are placed, one a t a time, on the platform when it is in front of the control panel. One operator, standing in front of the panel, can both place the bricks on the table and remove them; or a second operator, a t the opposite end of the table, may remove the bricks after the test. Each brick must pass through the coil three times. After each trip through the coil the brick is turned a t right angles
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to its previous position, so that all three dimensions of the brick are passed through the coil parallel with the axis of the coil. This is done so as to detect iron which may extend mostly in one direction with reference to the dimensions of the brick, since the impurity is most easily detected when passed through the coil in the direction of the longest dimension of the bit of iron. The test coil consists of a primary and a secondary winding, with an air core. The primary is excited by a storage battery, giving a constant excitation a t all times. Upon the passage of a piece of iron, such as might --exist in one of the copper bricks, through the core, the ffux threading the coil builds up to a higher value, and drops again to its previous value after the iron h a s passed beyond the core. When the brick of scrap copper i s moved through the coil with a constant velocity, the variation of the flux is dependent upon t h e a m o u n t of iron present in the brick and on zv 4, the direction in which the iron passes through the coil with reference to its longest dimension. This variation of the flux induces an electromotive force in the secondarv of the coil. If enough iron is Fm. ~.-CONNECT~ON DIAGRAM(SCHEMATIC) (i, e,, above a certain IRONDETECTOR percentaxe), an electromotive . force of sufficient value will be produced in the secondary coil; and the galvanometer relay will be deflected and the contacts closed. This in turn completes the circuit to the secondary relay and the signal system. After the brick has been passed through the coil three times it is removed, and another brick is placed on the platform. If a signal does not occur during the test, the brick is free from iron within the limits of 0.05 per cent, the value for which the apparatus is adjusted. The apparatus will easily test 50 bricks per hour.
Detecting Traces of Mercury As small a proportion as one part of mercury in 20,000,000 parts of the atmosphere can be measured accurately by the mercury detector (Fig. 5)
which has been developed in the Research Laboratory of the General Electric Company; and one in 8,000,000 parts can be determined quickly as well as accurately. Mercury poisoning is accumulative; it seems to make little if any difference whether the vapor is inhaled as relatively large amounts in a short period of time, or as slight amounts over a period of months. Because of the increased industrial use of mercury in heating operations in various chemical processes and in the newly developed mercury turbine,
FIG.5.-MEncun~ DETECTOR FOR DETERMINING TEE AMOUNTOF IN THE ATMOSPHERE
THE
ELEMENT
it has become important to have a method whereby leaks in apparatus and traces of mercury vapor in the atmosphere can be detected quickly. Previous methods for determining the amount of mercury vapor in the atmosphere were tedious processes that required considerable time and the services of an expert chemist, and even then the results were usually far from accurate, especially when considering tiny amounts of the substance. The new method gives quick results, does not require the services of a trained chemist, and is accurate. The principle on which the new method is based is a reaction between a solid substance, selenium sulfide, and the mercury vapor, with a
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J O ~ N OP AL CHEMICAL EDUCATION
JANUARY, 1928
colored substance, easily observable with the eye, as the product of the reaction. Yellow selenium sulfide is applied as a coating on paper. The paper is blackened on exposure to air containing mercury vapor, the degree of blackening depending on the concentration of the mercury, the time
FIG. G.-AuTOMATIC
M E n c u n ~UI%TZcTOn w r T M CLOCKMOVEMENT
FEEDING THB
RECORDING
TAPE
of exposure, and various other factors which can be definitely controlled. There seems to be practically no lower limit to the concentration that can be detected by this method. For continuous and automatic registration of the mercury vapor, there has been devised a system in which a continuous strip of the coated paper is drawn slowly over an opening through which the air flows, a small clock motor moving the strip of paper a t a uniform rate (Fig. 6). Within a short time after the exposure, the colored strip of paper can be compared
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with a standard scale in which the diierent shades from yellow to black have been calibrated in terms of mercury concentration. If an incandescent lamp is placed in front of the strip of paper and a photoelectric cell behind it, the amount of light reaching the cell will depend on the amount of blackening of the paper. The light can regulate the readings of an ammeter, so that the concentration of the mercury vapor can be determined either by observing the color of the paper or by reading an ammeter. I t is also possible to so arrange the photoelectric cel' circuit that a warning gong will be sounded if the mercury concentration becomes dangerously high.
