Metallurgical Miracles

A patent for improved photographic technique was taken out in 1868 by a lady named Sarah A. L. Hardinge. In the 70 years which followed, she and her descendants took out 174 other patents. Mrs. Hardinge's smart son, Hal, for instance, invented a machine which pulverizes ore by feeding it into a whirling drum containing a lot of little steel balls. Many a fortune has been made with it. It became generally known last week that Mrs. Hardinge's smart grandson had added a smart refinement to his father's famed "ball process" of ore reduction.

Hal Hardinge's son, Harlowe, vice president and general manager of Hardinge Co. of York, Pa., studied his father's "ball mill" in operation. There was a certain rate of feeding in ore at which it performed most efficiently, and that rate could be estimated by sound. When the feed was too slow, the noisy clatter of the mill increased; when too fast, the sound was muffled. Workmen were trained to listen for these changes in sound and manipulate the ore flow accordingly. But Harlowe Hardinge noticed that the listeners' judgment was likely to vary as much as 20 decibels. They judged the sound differently when they were tired and when they were fresh, before lunch and after lunch.

Harlowe Hardinge therefore invented a sensitive "electric ear" to replace human hearing. A parabolic reflector picks up the sound from the mill, focuses it on a microphone. If the sound is at the most efficient level, the microphone current keeps a galvanometer balanced between two contacts. If it rises or falls as little as one-quarter of a decibel, the galvanometer makes contact on one side or the other, closing a circuit which starts or stops the flow of ore as the situation requires. More than 75 of these electric ears are already in use.

At a meeting in Manhattan of the American Institute of Mining & Metallurgical Engineers, big, bald Mr. Hardinge last week publicly described his invention for the first time. Other metallurgical miracles described at the meeting:

Sink-&-Float. If a handful of bird shot mixed with sawdust is thrown into a pail of water, the shot will sink, the sawdust float. Reason: the specific gravity of water is greater than wood's, less than lead's. The flotation method of separating ores from waste, using liquids of higher specific gravity than water, has been used for nearly a century. For over three decades E. I. du Pont de Nemours & Co. has been trying to devise an economical flotation method for separating impurities such as shale and slate from low-grade anthracite coal. For "parting liquids," they needed mixtures of controllable specific gravity up to three times that of water. Pentachlorethane and tetrabromethane filled this bill--after the Du Pont men worked out a way to use them over & over again cheaply.

Last week, Du Font's Willing Bayard Foulke announced his research crew's success. He calculated that the new "sink-&-float" technique could recover 285,000,000 tons of marketable anthracite from existing mounds of refuse. Since the method can also be applied to low-grade iron ore which it was not previously worthwhile to treat thus, iron and steel men estimated that it would increase the potential iron ore reserve in Minnesota's great Mesabi range by 3,250,000,000 tons, extend its useful life from 35 to 100 years.

Old Gold. Another new ore-processing technique, which may have a marked effect on the financial structure of the U. S., was announced by Dr. Thomas Garfield Chapman of the University of Arizona. Dr. Chapman has found a way to extract gold profitably from low-grade ores and old tailing dumps, already reworked once when the famed cyanide process was developed late in the 19th Century. The gold is dissolved with cyanide, then deposited in thin layers on activated charcoal. It is finally removed from the charcoal by flotation (see above).

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