How to Oxidize Silver.--For this purpose a pint of sulphide of
potassium, made by intimately mixing and heating together 2 parts
of thoroughly dried potash and 1 part of sulphur powder, is used.
Dissolve 2 to 3 drachms of this compound in 1-3/4 pints of water, and
bring the liquid to a temperature of from 155 degrees to 175 degrees
Fah., when it is ready for use. Silver objects, previously freed from
dust and grease with soda lye and thorough rinsing in water, plunged
into this bath are instantly covered with an iridescent film of silver
sulphide, which in a few seconds more becomes blue black. The objects
are then removed, rinsed off in plenty of fresh water, scratch
brushed, and if necessary polished.
Useful Household Recipes.--To purify water in glass vessels and
aquariums, it is recommended to add to every 100 grammes of water four
drops of a solution of one gramme of salicylic acid in 300 grammes of
water. The _Norsk Fiskeritidende_, published at Bergen, Norway, says
that thereby the water may be kept fresh for three months without
being renewed. A cement recommended as something which can hardly
be picked to pieces is made as follows:--Mix equal parts of lime
and brown sugar with water, and be sure the lime is thoroughly
air-slacked. This mortar is equal to Portland cement, and is of
extraordinary strength. For a few weeks' preservation of organic
objects in their original form, dimensions and color, Professor
Grawitz recommends a mixture composed of two and a half ounces of
chloride of sodium, two and three-quarters drachms of saltpetre, and
one pint of water, to which is to be added three per cent.
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