sulphur is contained in wool, fur, and hair,
and not in silk nor in vegetable fibres. First, I will heat strongly
some cotton with a little soda-lime in a tube, and hold a piece of
moistened red litmus paper over the mouth of the tube. If nitrogen is
present it will take up hydrogen in the decomposition ensuing, and
escape as ammonia, which will turn the red litmus paper blue. With the
cotton, however, no ammonia escapes, no turning of the piece of red
litmus paper blue is observed, and so no nitrogen can be present in the
cotton fibre. Secondly, I will similarly treat some silk. Ammonia
escapes, turns the red litmus paper blue, possesses the smell like
hartshorn, and produces, with hydrochloric acid on the stopper of a
bottle, dense white fumes of sal-ammoniac (ammonium chloride). Hence
silk contains nitrogen. Thirdly, I will heat some fur with soda-lime.
Ammonia escapes, giving all the reactions described under silk. Hence
fur, wool, etc., contain nitrogen. As regards proofs of all three of
these classes of fibres containing carbon, hydrogen, and oxygen, the
char they all leave behind on heating in a closed vessel is the carbon
itself present. For the hydrogen and oxygen, a perfectly dry sample of
any of these fabrics is taken, of course in quantity, and heated
strongly in a closed vessel furnished with a condensing worm like a
still. You will find all give you water as a condensate--the vegetable
fibre, acid water; the animal fibres, alkaline water from the ammonia.
The presence of water proves both hydrogen and oxygen, since water is a
compound of these elements. If you put a piece of potassium in contact
with the water, the latter will at once decompose, the potassium
absorbing the oxygen, and setting free the hydrogen as gas, which you
could collect and ignite with a match, when you would find it would
burn. That hydrogen was the hydrogen forming part of your cotton, silk,
or wool, as the case might be. We must now attack the question of
sulphur. First, we prepare a little alkaline lead solution (sodium
plumbate) by adding caustic soda to a solution of lead acetate or sugar
of lead, until the white precipitate first formed is just dissolved.
That is one of our reagents; the other is a solution of a red-coloured
salt called nitroprusside of sodium, made by the action of nitric acid
on sodium ferrocyanide (yellow prussiate). The first-named is very
sensitive to sulphur, and turns black directly. To show this, we take