their results based upon work under different conditions.

The electrolytic method of copper assaying given under _Copper_ is a
modification of Luckow's; it was introduced by us into the offices of
the Rio Tinto Copper Company, and has been in use for many years with
success. This modification is now employed in copper-works in Spain,
Germany, and England, and is used in place of the dry assay for the
commercial valuation of copper ores.

We have adhered to the gram and the "c.c." as the units of weight and
volume. Those who prefer working with grains and grain-measures can use
the figures given, multiplied by ten. For example:--When 1 gram is
mentioned, 10 grains should be used, and 10 grain-measures take the
place of 1 "c.c." It is not advisable to mix the two systems, as by
using gram weights and grain-measures.

We have intentionally to a large extent omitted to mention the names of
those who have originated or modified the various processes. The
practice of naming a process after its discoverer has developed of late
years, and is becoming objectionable. It is a graceful thing to name a
gas-burner after Bunsen, or a condenser after Liebig; but when the
practice has developed so far that one is directed to "Finkenerise" a
residue, or to use the "Reichert-Meissl-Wollny" process, it is time to
stop.

We are indebted to the standard works of Allen, Crookes, Fresenius,
Lunge, Michell, Percy, and Sutton, and wish to express our sense of
special indebtedness to Mr. Richard Smith, of the Royal School of Mines.
One or two of the illustrations are taken from Mr. Sexton's excellent
little book on _Qualitative Analysis_. Our obligation to some others is