492 BELL SYSTEM TECHNICAL JOURNAL 



nized and as little as 0.0001 mgm. of zinc has been observed on a 

 previously coppered cathode. The electrodes are formed by encasing 

 closely spaced platinum wires in glass which is subsequently cut and 

 polished through a perpendicular plane, thereby exposing cross- 

 sectional areas of the wires. The drop to be electrolyzed is placed on 

 the polished glass surface and the portion covering the platinum areas 

 observed under the microscope. 



A process rarely used in ordinary analysis but of great service in 

 microwork is that of sublimation. A few thousandths of a milligram 

 of a volatile crystalline solid may be separated in this way from a 



Fig. 3 — The electrolysis cell shown here, when used under the microscope, permits 

 one to observe the deposition of metals from tiny drops of solutions. Less than a 

 thousandth of a milligram of copper or zinc may be detected by its use. 



large bulk of inert material in a condition that permits immediate 

 treatment with reagents. In order to apply this process to dusts, 

 corrosion products and other frequently-encountered materials, an 

 improved microsublimation chamber has been designed by this 

 Laboratory. The apparatus is so arranged that both temperature 

 and pressure can be regulated. The vapor condenses on a water- 

 cooled microscope cover-glass and the recovery is practically quanti- 

 tative. As little as 0.002 mgm. of mercuric iodide was found to give 

 a deposit of definitely recognizable crystals. 



A phenomenon that has long been familiar, yet not applied to 

 analysis until its value in microwork was recentlv demonstrated, is 



