A COMBINED PNEUMATIC TROUGH, STEAM-,AND WATER-BATH
There are certain obvious objections to providing permanently installed steam- and water-baths in sufficient number to meet the varying and occasional needs of elementary chemistry students. Make-shift conversions of sinks into pneumatic troughs present objectionable difficulties. There is therefore a need for simple, inexpensive apparatus to be usedfor evaporations and collection of gases. To supply an elementary student with individual pneumatic troughs and steam- and water-baths is unnecessarily expensive, and these bulky pieces of apparatus are inconvenient to store in lockers. If it is arranged to have a common supply of such apparatus used by several sections in turn, parts of the apparatus are frequently lost or rendered inoperative due to misuse. Since it is seldom, if ever, necessary to use any two of the three previously mentioned pieces of apparatus a t the same time, we have designed a combination outfit which serves equally well for all of the purposes just discussed. The combined waterbath, steam-bath, and pneumatic trough is illustrated in the accompanying figure. As made in this laboratory, the device consists of a spun, . . sheet-co~oer vessel. BhTH ARRAnGFO FOR USE AS PNEUMTLZ TROUGH 20.5 cm. in diameter and 8 cm. deep. Near the middle of the vessel a copper shelf extends over slightly more than one-half of the nosssectional area and is fastened by rivets or hard solder. An opening near the front edge of this shelf allows for the delivery of gases. The simple brass stopcock is attached by means of a brass nut, and the upper tubing connection is attached with hard solder. For use as a pneumatic trough, the stopcock is closed and the vessel filled with water to the level of the upper connection which leads through rubber tubing to a waste water outlet. The shelf provided in the apparatus will support four 250-cc. bottles, which can be collected separately and allowed to remain on the shelf after filling. For use as a water-bath, a standard set of 20.5-cm. concentric copper rings is placed on the vessel, the stopcock is closed, and water added to some convenient level. The bath has sufficient water capacity to provide steam for a laboratory period of the usual length, but it
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is possible to attach a water supply to the lower tube and run a connection from the upper tube to a drain and thus have a somewhat inefficient but, nevertheless, effective constant level bath. When functioning as a portable steam-bath, the apparatus is connected to a steam cock through the upper inlet and through the stopcock condensed water is drawn away to a drain. The tubing used for connecting the bath, when it is used with steam, is tubing which has been returned by students after one year's use. While copper has been found to be most satisfactory as the material for the construction of this piece of apparatus, cheaper baths can be prepared by the use of lead-coated iron.
