ad a considerable quantity of the mixture,
which may then be placed in a well-covered jar, and kept damp by the
addition of a little water.

Pottery thus made does not require to be glazed, but, of course, a
glaze can be obtained by any of the methods described in works on
pottery manufacture. The following glaze has been recommended to me
by a very competent potter:-

Litharge

7 parts by weight

Ground flint

2 parts by weight

Cornish stone or felspar

1 parts by weight

These ingredients are to be ground up till they will pass the finest
sieve--say 180 threads to the inch. They are then mixed with water
till they form a paste of the consistency of cream. They must, of
course, be mixed together perfectly. The ware to be glazed is dipped
into the cream after the first firing; it is then dried as before and
refired. The glaze will melt at a bright red heat, but it will crack
if not fired harder; the harder it is fired the less likely is it to
crack.

If colouring matters are added they must be ground in a mill free from
iron till they are so fine that a thick blanket filter will not filter
them when suspended in water. This remark applies particularly to
oxide of cobalt.

APPENDIX

PLATINISING GLASS

IN the Philosophical Magazine for July 1888 (vol. xxvi. p. 1) there
is a paper by Professor Kundt translated from the Sitzungsberichte of
the Prussian Academy. This paper deals with the indices of refraction
of metals. Thin prisms were obtained by depositing metals
electrolytically on glass surfaces coated with platinum. The
preparation of these surfaces is troublesome. Kundt recounts that no
less than two thousand trials were made before success was attained.
A detailed account of the preparation of these surfaces is not given
by Kundt, but one is promised--a promise unfortunately unfulfilled so
far as I am able to discover. A hunt through the literature led to
the discovery of the following references: Central Zeitung fuer Optik
und Mechanik, p. 142 (1888); Dingler's Polytechnik Journal, Vol.
cxcv. p. 464; Comptes Rendus, vol. lxx. (1870).

The original communication is a paper by Jouglet in the Comptes
Rendus, of which the other references are abstracts. The account in
Dingier is a literal translation of the original paper, and the note
in the Central Zeitung is abbreviated sufficiently to be of no value.
The details are briefly as follows:-

One hundred grams of platinum are di