. The Bell System technical journal . small dimensions are to bestudied. A number of methods have been developed and used by the Labora-tories Microchemical Group for the collection and study of centralofiice dusts. A device which deserves particular mention is theimpinger, an adaptation of which has been employed to remove dustsfrom the extremely localized area represented by a single relay contactpoint. The device is so constructed that the particles, after beingpicked up by suction, are projected at high velocity against a micro-scope slide, the surface of which is coated with an adhesive m
. The Bell System technical journal . small dimensions are to bestudied. A number of methods have been developed and used by the Labora-tories Microchemical Group for the collection and study of centralofiice dusts. A device which deserves particular mention is theimpinger, an adaptation of which has been employed to remove dustsfrom the extremely localized area represented by a single relay contactpoint. The device is so constructed that the particles, after beingpicked up by suction, are projected at high velocity against a micro-scope slide, the surface of which is coated with an adhesive slide is removed from the apparatus and the dust subjected tophysical and chemical treatment to determine its nature. In quantitative microanalysis, the analyst is faced with the added 496 BELL SYSTEM TECHNICAL JOURNAL problem of weighing a few milligrams of material with the same pre-cision as might be obtained with samples of the usual size. The Nernstquartz fiber balance, capable of weighing to a few ten-thousandths of a. Fig. 5—The micromanipulator finds use when it is necessary to operate on unusuallysmall particles or within areas bounded by the microscopic field. milligram, has proved very useful in certain types of work, where thetotal load does not exceed a few tenths of a gram. Its application tochemical analysis, however, is quite limited because of the difficultyof reducing the load to this extent. The quantitative extension of ANALYSIS IN COMMUNICATION RESEARCH 497 microtechnique consequently made little progress until a beam balancewas produced by W. Kuhlmann of Hamburg, which was capable ofweighing to a thousandth of a milligram with no appreciable changein sensitivity with loads up to 20 grams. With the perfection of this essential instrument quantitative micro-technique developed rapidly, and because of the economy of time andmaterial it is in many cases actually displacing older methods operatingon the usual scale. This is particularly true in orga
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