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A System of Instruction in the Practical Use of the Blowpipe - Being A Graduated Course Of Analysis For The Use Of Students And All Those Engaged In The Examination Of Metallic Combinations by Anonymous
page 45 of 359 (12%)
18. _Silver Foil._--A small piece of silver foil is used for the
purpose of detecting sulphur and the sulphides of the metals, which
impart a dark stain to it. If no silver foil is at hand, strips of
filtering paper, impregnated with acetate of lead, will answer in many
cases.


19. _Nitroprusside of Sodium_ (Fe^{2}Cy^{5}, NO^{5}, 2Na).--This is a
very delicate test for sulphur, and was discovered by Dr. Playfair.
This test has lately been examined with considerable ability by Prof.
J.W. Bailey, of West Point. If any sulphate or sulphide is heated by
the blowpipe upon charcoal with the carbonate of soda, and the fused
mass is placed on a watch-glass, with a little water, and a small
piece of the nitroprusside of sodium is added, there will be produced
a splendid purple color. This color, or reaction, will be produced
from any substance containing sulphur, such as the parings of the
nails, hair, albumen, etc. In regard to these latter substances, the
carbonate of soda should be mixed with a little starch, which will
prevent the loss of any of the sulphur by oxidation. Coil a piece of
hair around a platinum wire, moisten it, and dip it into a mixture of
carbonate of soda, to which a little starch has been added, and then
heat it with the blowpipe, when the fused mass will give with the
nitroprusside of sodium the characteristic purple reaction, indicative
of the presence of sulphur. With the proper delicacy of manipulation,
a piece of hair, half an inch in length, will give distinct
indications of sulphur.

_Preparation._--The nitroprussides of sodium and potassium (for either
salt will give the above reactions), are prepared as follows: One atom
(422 grains) of pulverized ferrocyanide of potassium is mixed with
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