VICTOR MEYER APPARATUS EUGENE W. BLANK 241 N. Ninth Street, Allentown, Pennsylvania
R
ECENTLY the writer described a modified Victor Meyer apparatus for the determination of molecular weights.' Subsequent practice with this apparatus has led to several changes in design and technic tending to produce more uniform and concordant results. The apparatus, as now used, is illustrated by the accompanying figure. The inner tube ( A ) is immersed BLANK,J. CHEM.EDUC.,8, 546 (Mar., 1931).
in the vapor of a boiling liquid undergoing distillation from the flask (B). A small quantity of sand or a tuft of glass wool is placed on the bottom of the air chamber ( A ) to break the fall of the sample tube. The sample is introduced by means of a glass cock (C) which does away with the former use of a rubber stopper. The sample is sealed in a glass capillary tube of a diameter which allows it to pass through the bore of the stopcock plug. The capillary is prevented
filled and sealed tube is shown in position in the diagram. The capillary is suspended in the bore of the stopcock (C) by means of the bead of-fused glass. When the temperature of the apparatus has become constant (observed by closing the tube above (C) by means of a stopper if the capillary has been previously inserted in the bore of stopcock) the plug of the stopcock is turned, thereby breaking the capillary and allowing i t to fall to the bottom of the tube. The sample vaporizes and a volume of air equal to the volume of the vapor flows into (D) where i t quickly assumes the temperature of the water (water a t room temperature). The position of the leveling cylinder is now adjusted and the volume of the displaced air measured. Since the air is measured over water the pressure to which i t is subjected is that of the atmosphere diminished by the vapor pressure of water a t the temperature of the room. Calculation of the molecular weight involves application of the perfect gas relation P V = NRT. The following heating liquids may be utilized: water (100°) ; toluene (111') ; xylene (140') ; aniline (183") ; ethyl benzoate (213'); amyl benzoate (262'); anaphthylamine (300'); and diphenylamine (310°). A liquid with a boiling point 15O to 25'C. above that of the sample is used as the heating medium. In the event of using a very high-boiling-point material the water-cooled condenser may be replaced by an air-cooled tube. In case the compound under test tends to decompose upon vaporization a t atmospheric pressure, the initial pressure in ( A ) may be lowered by evacuation. A glass L pointing downward is attached to the apparatus a t point (E). The glass L is connected by pressure tubing to a reservoir of mercury and the apparatus evacuated through cock (C) until the mercury has risen to a fixed mark on the glass L. The sample is suspended in the bore of (C) before evacuation of the apparatus. When the mercury level is constant the sample is released by turning the stopcock (C) and the mercury brought up to the mark on the glass L by raising the mercury reservoir. The change of height of the mercury reservoir is an indication of the pressure change within the apparatus. The volume of the apparatus is previously determined by filling with water to the mark on the glass L. The advantages of this apparatus include low cost due to the use of regular laboratory stock, ready replacement of broken parts, elimination of the necessity for glassblowing skill, and saving of space. Very small LASSAR-COHN, "Organic laboratory methods." translated quantities of sample are required for a determination by R. E. Osspen, The Williams and Wilkins Co., Baltimore, and concordant results are readily and rapidly obtained. 1928, p. 304.
from falling into the vaporization chamber, until the plug is turned, by a globule of glass fused on the end. Turning the plug breaks the capillary and aUows i t to fall to the bottom of the vaporization bulb. The volume of air displaced by the vaporized sample is collected and measured in a graduated pipet (D) immersed in a cylinder of water. The procedure in a determination of vapor density consists in opening the stopcock (C), heating the liquid in (B) until distillation has proceeded for 3 to 5 minutes and then, by closing (C), determining if there is a change in the water level in the pipet. No change of the water level in the pipet is an indication that the temperature is constant. The water level is brought to the zero of the calibrated pipet. A sample of the material under test r n h f0.0200 to 0.0250 g.) is weighed into a capillary a n d sealed. Solids may be formed i n t o small rods.% Melting-point tubes of a .diameter that allowsof their passing ~eadilythrough the bore of the stop.cock (C) are drawn from 0.5 cm. diam.eter tubing and cut into 7-cm. lengths. A dry, 'clean tube is weighed on the micro-balance and a sample of appropriate weight added by means of a micro-pipet. The tube is carefully heated 1 to 1.5 cm. from the open end and traces of :sample adhering to the walls of the capillary distilled toward the main body of sample. Liquid from the heated portion of the tube to the open end is distilled into the atmosphere. The tube is constricted by drawing out and a tiny bead of glass formed a t the heated portion by doubling the hot tube back on itself. Re-weigh to obtain the weight of sample. A
Almost universal lip-service is accorded the pro osition that elementary chemical instruction should reflect the vitality of the science itself. Human inertia and perversity%eingwhat the are, however, the acceptance of this proposition too seldom leads to appropriate action. We are, therefore, particular6 &d to announce for the October number of the Grst instalment of a paper bl C. W. Stillwell, entitled "Chapters in Crystal Chemistry for College Freshmen." Aside from the fact that t e subject matter should be of great value to both college and high-school teachers, we are of the opinion that this contribution constitutes an excellent example of a truly sound method for making chemical instruction not only vital but interesting.
