An Apparatus for Semimicro Evaporations SHIRLEY GADDIS. Eureka College, Eureka, Illinois
AN INTERESTING apparatus for micro-evaporations has been described by L. T. Kurtz.' Since the technic offers a number of advantages, it seems desirable to adapt it to the semimicro scale of working. Since steam and electricity are usually not available in the freshman laboratory the following modiications of the Kurtz method are suggested in adapting it to the semimicro scale: A 5-ml. tapered test tube containing 3 ml. of the test solution is slipped into the neck of a 25-ml. Erlenmeyer flask which has in it 15 ml. of water. The dimensions of the flask and the tube are such that the tube is supported upright yet there is space left for the escape of steam. The water in the flask is boiled for 8 minutes. Then air from an atomizer bulb is blown through a glass jet over the surface of the test solution. 1Kmn.
Id.Eng. C h . , Anol. Ed..
14, 191 (1942).
I t is not necessary to preheat the air. Most of the evaporation seems to be brought about by the spreading of a thin film of the test solution over the walls of the hot tube. For that reason the glass jet should be adjusted so that a swirling motion is imparted to the surface of the liquid. Six minutes of air blowing is enough time to evaporate 3 ml. of the test solution to dryness. In using this method for the first time one might be led to believe that some of the test ions are lost by spattering as well as by entrainment in the vapor. That this danger is more apparent than real can be proved by using two 3-ml. portions of some test ions of Groups I1 or 111. Evaporate one portion to dryness by the method described. To the residue add 3 ml. of water and then add sulfide ions to both tubes. Centrifuge. The amounts of precipitate will be seen to be the same.
