798

SODA.— Hydrochloric Acid Towers.

acid obtained in one of the largest works in Lancashire from actual trial. After allowing for 1‘6 per cent.HC1 left in sulphates, the average escape is 1-8 percent., and the average acid condensed is 96'6 percent.

A certain escape of gas always takes place incharging and discharging the furnaces, which hasbeen found by the writer to vary, according to thecare taken, from 04 to 0-72 per cent. It is verynecessary that all condensers should be providedwith a supply of water from at least two separatesoirees, so that in case of accident in the one case,the other can at once be applied.

The size of condensers must always bear a relativeproportion to the weight of salt used daily; and asa rule, it is better to have more condenser spacethan practice actually requires. The plan nearlyalways adopted in the decomposition of salt on the

large scale is to charge the “ pan ” or pot, which isa metal vessel about 9 feet diameter and 2 feet 6inches deep in centre, with about 9 cwts. to 10 cwts.of salt per hour, and with rather more than itsequivalent of sulphuric acid, which, if possible,should be run into the pan quite warm, and stand-ing about 130° to 140° Fahr. The charge remainsin the pot nearly an hour, during which time abouttwo-thirds of the hydrochloric acid passes off to the“ pan condenser.” The charge is then pushed for-ward into the furnace, which is kept at a red heat,and where the remainder of the gas (about one-third) is driven off to the “ drier condenser.” Thegases given off from the furnaces, and which passedaway to the flue at a high heat, were the chief diffi-culty to contend with, and were the cause of nearlyall the claims for damages made by farmers on themanufacturers in former years. This difficulty has

been almost entirely overcome by the adoption ofcooling flues or cooling shafts, by which means thegases are considerably reduced in heat before enter-ing the condensers, and a more perfect condensationis obtained. In some works the heat of the gasesas they leave the pan and drier are as under :—

Pan gas,. 175° Fahr.

Drier gas,. 1200° “

By the adoption of a proper system of cooling,the pan gas may be reduced to 120° Fahr. and thefurnace gas to under 200° Fahr. before they enterthe condensers. During the best condensation, evenwhen cold water is used, there is a certain amountof heat always generated in addition to the heat asit enters, and the escaping steam and gases at theexit pipe seldom stand much less than about one-half of the heat as it enters.

A new decomposing furnace, which is worked bymachinery instead of hand labour, has recentlybeen introduced by Jones and Walsii (see ante.).The escaping gases from this furnace are generallyabout one-half the degrees of heat as the ordinarydrying furnace, and the condensation is thereforemore easily accomplished, and is more perfect.The usual size of a condenser is about 50 to 70feet high by 6 to 7 feet square, but these pro-portions vary in different works. They are con-structed of stone flags, which are cemented andbolted together; and the condensers are packed witheither bricks or coke, through which the gas travels,and is met by a continuous stream of water, regulatedat the top of the condensers to suit the strengthof acid required and the proper condensation of thegases. In some cases fine spray is thrown in atthe foot of the condenser, or in a cistern, from a