MODIFIED RAMSEY-YOUNG APPARATUS FOR MEASURING VAPOR PRESSURES OF LIQUIDS WALTER H. DUMKE Colorado School of Mines, Golden, Colorado
INRECENT years several modifications of the original Ramsey-Young vapor-pressure apparatus have been devised. The apparatus illustrated is another modification and is used by our students in the physical chemistry laboratory with excellent results. A very brief description of the apparatus is given. A 500-ml. flask is provided with a ground-glass 35/20 ball joint C, a side arm which supports a ground-glass standard-taper 10/30 thermometer, -lO°C t o llO°C, D. An inner-sealed glass tube extends from the reservoir B to almost the thermometer bulb which is covered with a wick. A piece of cellophane sponge or glass wool serves well as a hygrometer wick. The vapors from the flask travel up a side arm and condense in the reservoir B with the aid of a cold-water condenser A . The system is evacuated through outlet G by means of a water aspirator or a Hy-Vac pump. This outlet is connected through a large bottle F which in turn connects with an open manometer I. An adjustable meter stick H slides in a grooved channel. All ground-glass joints are provided with clamps to permit pressure readings from a range of 100 mm. to 800 mm. The entire apparatus is mounted on a portable wooden stand. I n brief, the apparatus is operated in the following manner. The system is evacuated to about 200 mm. pressure, and the water bath E is heated to a temperature which will assure that all excess liquid leaves the 500-ml. flask. The flame under the water bath is lowered, the system is further evacuated to about 100 mm., and liquid from the reservoir is slowly allowed to drop on the thermometer wick. When the rate of evaporation becomes equal to the rate of condensation, temperature and pressure readings are made. The pressure within the system is now adjusted to about 200 mm. and again readings are taken. In order to maintain good workable equilibrium conditions, the water bath is kept a t a temperature of from 15 to 20 degrees higher than that recorded on the thermometer with the wick. Many advantages in this design become apparent; however, several should be mentioned. The pressure above the liquid in the reservoir is always equal to the inside system pressure, which permits a uniform flow of drops. A cold-water condenser adds to the con-
venience of vapor condensation. An adjustable meter stick aids in more accurate pressure readings. The apparatus is leakproof and is mounted on a movable stand which practically eliminates all breakage. Liquids can be added to the reservoir by removal of the 500-ml. flask and application of a slight vacuum.
Our departmeut of physical chemistry has six of these setups which are used by approximately 200 students in any one semester. Each student works independently, which means that each apparatus is used a t least 30 times during any semester. Very little breakage was encountered during the five years of student use. On the average, the student found the apparatus easy to manipulate and succeeded in obtaining excellent data.
