AN AUTOMATIC ALARM FOR USE IN GAS ABSORPTION
In carrying out reactions in which a gas is passed into a reaction chamber and absorbed, one of two systems is usually used. Either the gas is contained in a gasometer and the reaction conducted in a closed system or an excess of gas is run into the reaction chamber and the surplus discharged. In many cases neither of these systems is satisfactory. A gasometer is a bulky piece of apparatus and requires close attention during filling. Moreover, the gas from a gasometer is contaminated with vapors of the
GAS IN
confining liquid used and these vapors are sometimes very difficult to remove. When an excess of gas is used a considerable amount of the gas is lost. If volatile substances are produced by the reaction these are also carried out by the gas stream and the yield thereby diminished. The apparatus to be described was designed to provide the advantages of the closed absorption system without the disadvantages attending the use of a gasometer. The construction of the device is apparent from the accompanying diagram. It consists of a heavy rubber toy balloon slipped over a rubber stopper. Two glass bends and a U-tube of the design shown, are in528
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AN AUTOMATIC ALARM
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serted through the stopper. One of the glass bends is fitted with a short length of rubber tubing and a pinch cock. The U-tube is partly filled with mercury and two insulated copper wires inserted through the open end. One of the wires is pushed a centimeter or so beneath the surface of the mercury and fastened in position. The other wire is adjustable. These wires are connected to a dry cell and bell as indicated. The apparatus may be assembled in a number of ways. For ease of portability, the bell, U-tube, etc., are fastened to the dry cell by means of adhesive tape. To use the apparatus, it is connected to the outlet of the reaction vessel and the adjustable contact set for the upper limit of pressure at which the reaction is to he run. After sweeping the air out of the system through A with a stream of the gas being used, A is closed and the balloon partly inflated. The gas flow is then adjusted as nearly as possible to the rate of absorption. From this point on, the apparatus requires hut little attention. By merely glancing at the balloon from time to time one can tell approximately how the absorption is progressing and can modify the gas flow as indicated. If the balloon is increasing in size the flow of gas should he diminished and vice versa. The apparatus may be left without shuttmg off the gas supply, for if the pressure increases above the predetermined value the mercury manometer closes the bell circuit and sounds an alarm. When this happens the pressure can he released by opening A and cutting down the gas flow. Should the warning he ignored the excess gas bubbles through the mercury, which automatically regulates the pressure. By sealing a wire into the U-tube at B,the bell may be made to sound when the pressure in the apparatus drops below a certain level. By the use of this extra contact the pressure may be kept within definite limits. A greater sensitiveness to pressure changes may be obtained by constructing the U-tube of glass tubing of small diameter and dispensing with the widened open side. Such a tube possesses the disadvantage, however, of being easily emptied of mercury in case of a sudden rise in pressure. This difficulty may be overcome by using two U-tubes, one of narrow construction for the hell circuit and the other, of the design shown in the 'diagram, to act as a relief valve. The alarm device can also be used in a number of places where a safety bottle is usually inserted. Thus in the preparation of ethylene dibromide by the bromination of ethylene the device may be connected by means of a T-tube to the ethylene line and will give an alarm should any part of the apparatus become clogged. This apparatus has been successfully used in several acetylene reactions. In the synthesis of acetals from alcohols and acetylene, where traces of water vapor from the gasometers commonly used prove disastrous, the device has been of great value.
