en by Jouglet; but many
modifications have been tried in the laboratory of the Sydney
University by Mr. Pollock, starting from the imperfect note in the
Central Zeitung, which led to no real success.

It was found that it is perfectly easy to obtain brilliant films of
platinum by the following process, provided that the presence of a few
pin-holes does not matter.

The platinum salt employed is what is bought under the name of
platinic chloride; it is, however, probably a mixture of this salt
and hydro-chloro-platinic acid, and has all the appearance of having
been obtained by evaporating a solution of platinum in aqua regia to
dryness on the water bath. A solution of this salt in distilled water
is prepared; the strength does not seem to matter very much, but
perhaps one of salt to ninety-nine water may be regarded as a standard
proportion. To this solution is added a few drops of ordinary gum
water (i.e. a solution of dextrin). The exact quantity does not
matter, but perhaps about 2 per cent may be mentioned as giving good
results.

The glass is painted over with this solution and dried slowly on the
water bath. When the glass is dry, and covered with a uniform hard
film of gum and platinum salt free from bubble holes, it is heated to
redness in a muffle furnace. The necessary and sufficient temperature
is reached as soon as the glass is just sensibly red-hot.

The mirrors obtained in this way are very brilliant on the free
platinum surface. If the gum be omitted, the platinum will have a mat
surface; and if too much gum be used, the platinum will get spotty by
bubbles bursting. There does not appear to be any advantage in using
lead.

It is quite essential that the film be dry and hard before the glass
is fired.

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