AN EASILY CONSTRUCTED MANOMETER ALBERT I. CASTRO and ALDEN E. BLOOD' San Jose State College, Sari Jose, California
THE need for a simple, inexpensive manometer for The use of a drop of glycerin as a lubricant for this opuse in the first-year organic chemistry laboratory that can be readily constructed by an unskilled worker prompted us to develop the manometer described below and shown in the accompanying diagram. This manometer can be used for rough measurements in the pressure range of 1 to 110 mm. of mercury, and by suitable obvious modification the range could be extended. It will be recognized that the general design is itself a replica of a t y p e of manometer already widely used. However, the method of construction of our instrument is such that the mercury column can be prepared free of a gas bubble more readily than is the case with some other models. Furthermore, its fabrication from readily available and inexpensive supplies is an added feature. The inner tube of the manometer is prepared from a 26-cm. length of clean 6-mm. o. d. Pyrex glass tubing. The tube is provided with a seal 4 cm. from one end and the near end is fire-polished. The inner tube is then shrunken and drawn so that an opening of about 0.5 mm. occurs 12.5 cm. from the seal. A piece of No. 24 B & S gage copper wire is a suitable gage for the opening. The open end of the tube nearest the constriction is then flared to provide a wider opening. The tube is held in the vertical position with the flared end up and clean mercury is added until the tube is filled to 1 to 2 em. above the constriction. The filling is aided by tapping the tube on the desk top. The mercury is then heated carefully in the tuhe until free of any gases, and finally boiled. The tube is maintained in a vertical position and allowed to cool to room temperature. Starting at the end of the tuhe nearest the seal, a No. 1 one-hole rubber stopper is worked onto the tube to the Proper position as shown in the diagram. 1
Present addreas: Stanford Universitv. Stanford. California.
eration is recommended. The tube is cut a t the proper point in the constriction by making a file mark and breaking carefully while the tube is held in a vertical position. It is then carefully turned over and inserted into the test tube which should contain 3 ml. of mercury. It is important that the mercury fill the tip of the inner tube after the tube isbroken a t the constriction. If this does not occur, the tube can be warmed
until the mercury expands sufficiently to accompyish this and the tube is then immediately inverted into the mercury contained in the test tube as already described, ~t is also imperative, of course, that no mercury fall from the tube while it is being inverted and set in position in the test tube, A convenient scale, which is not shown in the diagram, is provided by cementing a 15-mm.-wide strip of cross-section paper along the outside of the test tube. It is helpful if the scale is numbered every 10 mm.
