. The Bell System technical journal . f the discolored areas under the micro-scope, and allowed to act for a few seconds, after which it was removed,transferred to a capsule and the excess acid evaporated. The residuewas re-dissolved in a small drop of water and drawn up into a secondcapillary tube containing a few mm. of No. 32 copper wire. Bothends were sealed and the tube heated in boiling water for a few^minutes, after which one end was opened and the liquid withdrawn bymeans of a finer capillary. The open end was then drawn out to avery fine tube of microscopic bore. The closed end was he
. The Bell System technical journal . f the discolored areas under the micro-scope, and allowed to act for a few seconds, after which it was removed,transferred to a capsule and the excess acid evaporated. The residuewas re-dissolved in a small drop of water and drawn up into a secondcapillary tube containing a few mm. of No. 32 copper wire. Bothends were sealed and the tube heated in boiling water for a few^minutes, after which one end was opened and the liquid withdrawn bymeans of a finer capillary. The open end was then drawn out to avery fine tube of microscopic bore. The closed end was heated by amicroflame, gently at first to drive out moisture, then strongly untilthe glass had completely fused about the copper wire. Heating in 494 BELL SYSTEM TECHNICAL JOURNAL this manner was continued almost to the constricted portion. Whenthe capillary, after cooling, was examined under the microscopeminute globules of condensed mercury were plainly \isible. In thisprocess, the mercury is displaced from solution by the copper and. Fig. 4—With this electrolytic cell as little as a milligram of various heavy metalsmay be precisely determined. ANALYSIS IN COMMUNICATION RESEARCH 495 deposits on the wire from which it is sul)st(iiuntl\- (Hstillcd. As Httleas mgm. can he readily detected in this \va>. A considerable part of the microanalysts task is the physical isola-tion and recovery of the material on which his analytical operationsare to be performed. His problems very often recjuire examinationsof minute particles or aggreiiates of foreign substances which havebecome attached to or embedded in the surface of a material. Hemay also be required to isolate and study the structural units whichcompose a given formation. For , a deposit occurs on thesurface of a metal as a result of corrosion. This deposit is not of ahomogeneous nature but is built up in successive layers, each of whichdiffers in composition. To obtain a satisfactory picture of the mech-anism of
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