um 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_.

* * * * *

THE FILTRATION AND THE SECRETION THEORY.

At a recent meeting of the Physiological Society, Dr. J. Munk reported on
experiments instituted by him in the course of the last two years with a
view of arriving at an experimental decision between the two theories of
the secretion of urine--the filtration theory of Ludwig and the secretion
theory of Heidenhain. According to the first theory, the blood pressure
prescribed the measure for the urine secretion; according to the second
theory, the urine got secreted from the secretory epithelial cells of the
kidneys, and the quantity of the matter secreted was dependent on the rate
of movement of the circulation of the blood. The speaker had instituted his
experiments on excided but living kidneys, through which he conducted
defibrinized blood of the same a