a straight wire, and spin it round without shaking it, then he will
see the ring break off, and either return if the rotation is quickly
stopped, or else break up into three or four perfect little balls. The
disc should be wetted with oil before being dipped into the mixture of
spirit and water.

_A Good Mixture for Soap-Bubbles._

Common yellow soap is far better than most of the fancy soaps, which
generally contain a little soap and a lot of rubbish. Castille soap is
very good, and this may be obtained from any chemist.

Bubbles blown with soap and water alone do not last long enough for many
of the experiments described, though they may sometimes be made to
succeed. Plateau added glycerine, which greatly improves the lasting
quality. The glycerine should be pure; common glycerine is not good, but
Price's answers perfectly. The water should be pure distilled water, but
if this is not available, clean rain-water will do. Do not choose the
first that runs from a roof after a spell of dry weather, but wait till
it has rained for some time, the water that then runs off is very good,
especially if the roof is blue slate or glass. If fresh rain-water is
not to be had, the softest water should be employed that can be
obtained. Instead of Castille soap, Plateau found that a pure soap
prepared from olive-oil is still better. This is called oleate of soda.
It should be obtained freshly prepared from a manufacturing chemist.
Old, dry stuff that has been kept a long time is not so good. I have
always used a modification of Plateau's formula, which Professors
Reinold and Rucker found to answer so well. They used less glycerine
than Plateau. It is best made as follows. Fill a clean stoppered bottle
three-quarters full of water. Add one-fortieth part of its weight of
oleate of soda, which will probably float on the water. Leave it for a
day, when the oleate of soda will be dissolved. Nearly fill up the
bottle with Price's glycerine and shake well, or pour it into another
clean bottle and back again several times. Leave the bottle, stoppered
of course, for about a week in a dark place. Then with a syphon, that
is, a bent glass tube which will reach to the bottom inside and still
further outside, draw off the clear liquid from the scum which will have
collected at the top. Add one or two drops of strong liquid ammonia to
every pint of the liquid. Then carefully keep it in a stoppered bottle
in a dark place. Do not get out this st