The Chemistry of Hat Manufacturing | Page 9

F.). Soap
and carbonate of ammonium have the least injurious action. Every
washer or scourer of wool, when he uses soaps, should first ascertain if
they are free from excess of alkali, i.e. that they contain no free alkali;

and when he uses soda ash (sodium carbonate), that it contains no
caustic alkali. Lime, in water or otherwise, acts injuriously, rendering
the fibre brittle.
_Reactions and tests proving chemical differences and illustrating
modes of discriminating and separating vegetable fibres, silk and wool,
fur, etc._--You will remember I stated that the vegetable fibre differs
chemically from those of silk, and silk from wool, fur, and hair, in that
with the first we have as constituents only carbon, hydrogen, and
oxygen; in silk we have carbon, hydrogen, oxygen, and nitrogen; whilst
in wool, fur, and hair we have carbon, hydrogen, oxygen, nitrogen, and
sulphur. I have already shown you that if we can liberate by any means
ammonia from a substance, we have practically proved the presence of
nitrogen in that substance, for ammonia is a nitrogen compound. As
regards sulphur and its compounds, that ill-smelling gas, sulphuretted
hydrogen, which occurs in rotten eggs, in organic effluvia from
cesspools and the like, and which in the case of bad eggs, and to some
extent with good eggs, turns the silver spoons black, and in the case of
white lead paints turns these brown or black, I can show you some still
more convincing proofs that 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 a quantity of
flowers of sulphur, dissolve in caustic soda, and add to the lead solution.
It turns black at once, because the sulphur unites with the lead to form
black sulphide of lead. The nitroprusside, however, gives a beautiful
crimson-purple coloration. Now on taking a little cotton and heating
with the caustic alkaline lead solution, if sulphur were present in that
cotton, the fibre would turn black or brown, for the lead would at once
absorb such sulphur, and form in the fibre soaked with it, black
sulphide of lead. No such coloration is formed, so cotton does not
contain sulphur. Secondly, we must test silk. Silk contains nitrogen,
like wool, but does it contain sulphur? The answer furnished by our
tests is--no! since the fibre is not coloured brown or black on heating