THE CONDENSATION OF COAL GAS 437
same direction as the gas. In the general way this procedure-—when slow travel is assured—would seem to be quite effective in the .removal of naphtbålene. In coiijunction with.the Steel foul main, steelis alsobeing employed to alarge extent in the constriiction of condensers. The horizontal condenser shown in the sketch is constructed in spiral form, and differs from the most simple type in that it rests upon its own stanchions. A common type of vertical air condenser complete with gas and tar outlets is shown in Fig. 267. The annular atmospheric condenser (Fig. 268) has in the past assumed a good deal of importance, and is probably the most satisfactory example of these types, in. that the intensity of cooling is to some extent under control. As can be seen from the sketch, the gas passage in the tall vertical
cylinders is annular in form, hence both an inside and outside surface are exposed to the cooling efEect of the air. The diagonal side pipes convey the warm gas to the upper ends of each annular cylinder, and in. this way a comparatively strong draught is caused to ascend the inner air tube. Butterfly valves or dampers are fitted to the top of each vertical air pipe, so that the amount of cooling can be regu-lated in accordance with requirements. These valves are usually operated by means of a hånd chain reaching to the ground. Occasionally this type of condenser is found with the diagonal pipes omitted, the cylinders being connected by short horisontal branches, in which case the gas travels up and down the cylinders alternately.