A LECTURE-TABLE DEMONSTRATION OF BOILING-POINT ELEVATION JACOB
CORNOG AND HOMER HALL,UNIYBRSINOF IOWA, IOWA CITY,IOWA
The apparatus shown in the figure uses some very old and familiar ideas to accomplish a particular purpose, viz., a simple and positive demonstration of boiling-point elevation visible to all students in a lecture room
of fair size. The apparatus shown was easily made from a Victor Meyer apparatus. The inner tube of the Victor Meyer apparatus was cut just above the bulb and connected, by a capillary tube, to the manometer a t the right. To operate, the water in the outer jacket is caused to boil for several minutes. Then the meniscus in the manometer is adjusted to a suitable height by means of the cock inserted in the rubber stopper in the bottle. Finally, after the meniscus remains stationary for several minutes, its position is marked, then by adding about 100 cc. of syrupy orthophosphoric acid to the boiling water through the reflux condenser, the boiling point of the water is elevated and the meniscus is raised about one foot. A second 100 cc. portion of acid causes a second foot of rise and similarly with a third addition. With colored water in the manometer this rise is visible for some distance. Tight joints and absence of moisture in the inner system are essential. We found that rubber stoppers in bottles usually form tight joints more readily than rubber stoppers in flasks. A quite satisfactory application of this same idea may be had by substituting for the Victor Meyer apparatus a rubber-stoppered test tube submerged in a beaker of boiling water and connected by a rubber tube to the manometer. Of course, the elevation of the meniscus is not so great.
