An amorphous brownish organic deposit has been found on non‐arcing palladium contacts. It is shown that this material is produced when a number of metals, notably those of the palladium and platinum groups, are rubbed together in the presence of low concentrations of organic vapors. The deposit is given by a very wide variety of organic materials, and is thought first to involve chemisorption of the vapor on the metal, followed by frictional activation and polymerization of the chemisorbed layers to form the visible accumulation. The use of a gold alloy overlay on the palladium to minimize the troublesome effects of the polymer on contact performance is discussed.

Silver migration may be defined as a process by which silver, when in contact with insulating materials under electrical potential, is removed ionically from its initial location, and is redeposited as metal at some other location. This process requires adsorption of water on the insulation surface. Silver is unique in this respect in that it is easily oxidized and reduced and does not passivate. Other metals do not present a practical migration hazard. Presented herein are examples of actual experience wherein silver migration caused trouble, and an explanation of this phenomenon based upon chemical and physical considerations and related laboratory evidence. It is concluded that silver should be used with great caution under the conditions noted.

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THEterm sublimation describes the transition of a substance between its vapor and solid states without passage through the intermediate liquid state. If on raising the temperature of a solid substance the vapor pressure reaches 760 mm. before the fusion point is attained, the substance will sublime when heated in an open vessel under atmospheric pressure (iodine, ammonium chloride). Even if a substance has its triple point below 760 mm., it can be made to undergo true sublimation by heating in vacuo.Where sublimation is feasible, it is frequently a useful technique in analysis, particularly in microanalysis. In a suitable apparatus separations can be effected on microsamples, and it is often possible to produce sublimates that are readily identifiable under the microscope by their crystal form and habit. In synthetic work sublimation has been found useful in the purification of materials. In the authors' laboratory the apparatus to be described has also proved convenient for the separation, by simple distillation, of the volatile and condensable components of minute samplese. g., dust particles. In such cases the condensate takes the form of liquid droplets or amorphous or imperfectly crystalline masses, or a mixture of these.The essential requirement for sublimation is a chamber so divided that a temperature difference can be maintained between two surfaces, on the warmer of which is placed the material to be sublimed. This temperature difference, 9, will raise the pressure of the vapor in equilibrium with the solid by an amount Ap. The molecules leave the specimen surface, therefore, under a pressure p + Ap but are returned

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