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_.

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THE FILTRATION AND THE SECRETION THEORY.