those on Painting (1633) by Vincenzo Carducci, are
celebrated. In Italian, collections of dialogues, on the model of Plato,
have been composed by Torquato Tasso (1586), by Galileo (1632), by
Galiani (1770), by Leopardi (1825), and by a host of lesser writers. In
our own day, the French have returned to the original application of
dialogue, and the inventions of "Gyp," of Henri Lavedan and of others,
in which a mundane anecdote is wittily and maliciously told in
conversation, would probably present a close analogy to the lost mimes
of the early Sicilian poets, if we could meet with them. This kind of
dialogue has been employed in English, and with conspicuous cleverness
by Mr Anstey Guthrie, but it does not seem so easily appreciated by
English as by French readers. (E.G.)

DIALYSIS (from the Gr. [Greek: dia], through, [Greek: luein], to
loosen), in chemistry, a process invented by Thomas Graham for
separating colloidal and crystalline substances. He found that solutions
could be divided into two classes according to their action upon a
porous diaphragm such as parchment. If a solution, say of salt, be
placed in a drum provided with a parchment bottom, termed a "dialyser,"
and the drum and its contents placed in a larger vessel of water, the
salt will pass through the membrane. If the salt solution be replaced by
one of glue, gelatin or gum, it will be found that the membrane is
impermeable to these solutes. To the first class Graham gave the name
"crystalloids," and to the second "colloids." This method is
particularly effective in the preparation of silicic acid. By adding
hydrochloric acid to a dilute solution of an alkaline silicate, no
precipitate will fall and the solution will contain hydrochloric acid,
an alkaline chloride, and silicic acid. If the solution be transferred
to a dialyser, the hydrochloric acid and alkaline chloride will pass
through the parchment, while the silicic acid will be retained.

DIAMAGNETISM. Substances which, like iron, are attracted by the pole of
an ordinary magnet are commonly spoken of as magnetic, all others being
regarded as non-magnetic. It was noticed by A. C. Becquerel in 1827 that
a number of so-called non-magnetic bodies, such as wood and gum lac,
were influenced by a very powerful magnet, and he appears to have formed
the opinion that the influence was of the same nature as that exerted
upon iron, though much feebler, and that all matter was more or less
magnetic. Farada