THE VAPOR DENSITY OF STEAM' C. S. MARTIN,STATENORMALSCHOOL, BOWLINGGREEN,Omo, AND J. E. DAY AND W. I ,. EVANS, THE Omo STATE UNIVERSITY, COLUMBUS. Om0 For a number of years the Department of Chemistry of The Ohio State University has divided the students taking first-year chemistry into two major groups: A, those entering with one unit of high-school chemistry in the subject; B, those entering without such credit. During this period of time much attention has been given by those responsible for the instruction of these two groups of students to the matter of suitable laboratory work for those who have had the subject in high school. One of the proj-
e d s assigned to the advanced class is that of studying quantitatively the experimental basis for the language of chemistry. One of our exercises consists in the experimental determination of the exact formula for water. This project involves not only the quantitative determination of hydrogen and oxygen, but also an accurate determination of the vapor density of steam. The work below is the result of much study on the part of the authors in the two institutions from which this communication has been sent to THISJOURNAL. I n a previous paper two of us' described a method for the determination * Read before the Division of Chemical Education of the American Chemical Society at the St. Louis Meetinp. April 18, 1928. Evans, et al., THISJOURNAL, 1, 152F-3 (Sept., 1924).
of the vapor density of steam. The design and manipulation involved in the use of that apparatus presents certain inherent difficulties to the general chemistry student. With these points in mind we have several times rebuilt the apparatus retaining the original basic idea. The present apparatus is arranged in accordance with the figure. The flask is kept out of immediate contact with the clamp by the insertion of two or three thicknesses of asbestos paper. Failure to do this may result in the condensation of water vapor back of the clamp, which is attended by a subsequent high value for the molecular weight of the steam. All stoppers are preferably of the ~ b b e variety. r The connectors A , B, C, and D are of pure gum rubber tubing; E and F are of any common type of rubber tubing. It should be noted in particular that the lower end of the glass tube, H, is drawn out to a capillary, bent and sealed as shown. A light file scratch is then made on the under side of the tube a t the point indicated by the arrow. About 10 cc. of water are introduced into the flask and the train tested for air-tightness by opening the screw-clamp, I. The clamp is then closed and the U-tube with the connectors C and D is removed, plugged, and weighed a t a convenient time. The temperatnre is raised to between 135-140°C. and kept there. Any water condensing in the outer end of the outlet tube may be removed by means of a filter paper. When all of the water in the flask is evaporated, that condensed in the side-arm is also vaporized by means of a small flame. The siphon is started by opening the screw clamp, the weighed U-Tube re-inserted in the train and the temperature immediately recorded. The glass tube H is then forced downward against the nearest wall of the flask until the tip is broken. The accomplishment of the latter is easily determined by the resumation of air bubbles through the sulfuric acid wash bottle. Twenty to thirty minutes are required for the sweeping of the vapor into the U-tube if the siphon is operated a t the rate of two to three bubbles of air per second. The U-tube is disconnected, plugged, and reweighed, the gain representing the weight of the known volume of steam.
