The problem of decomposing chloride of magnesium is one which has attracted the attention of technical chemists for many years. The solution of this problem would be of great importance to the alkali trade, and, consequently, to nearly every industry. The late Mr. Weldon made many experiments on this subject, but without any particular success. Of late a furnace has been patented in Germany, by A. Vogt, which is worked on a principle similar to that applied to salt cake furnaces; but with this difference, that in place of the pot it has a revolving drum, and instead of the roaster a furnace with a number of shelves. The heating gases are furnished by a producer, and pass from below upward over the shelves, S, then through the channel, C, into the drum, D, which contains the concentrated chloride of magnesium. When the latter has solidified, but before being to any extent decomposed, it is removed from the drum and placed on the top shelf of the furnace. It is then gradually removed one shelf lower as the decomposition increases, until it arrives at the bottom shelf, where it is completely decomposed in the state of magnesia, which is emptied through, E. The drum, D, after being emptied, is again filled with concentrated solution of chloride of magnesium.
The hydrochloric acid leaves through F and G. If, instead of hydrochloric acid, chlorine is to be evolved, it is necessary to heat the furnace by means of hot air, as otherwise the carbonic acid in the gases from the generator would prevent the formation of bleaching powder. The air is heated in two regenerating chambers, which are placed below the furnace. - Industries.