A New Apparatus for Microsublimation

Abstract

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

Review of Organic Microchemistry

“…A more elaborate apparatus for quantitative work with traces of material, designed by Clarke and Hermance (67), offers advantages. It is electrically heated and thermostatically controlled, and sublimation takes place under a vacuum.…”