By GEORGE CRAIG.
For wellnigh two years I have been estimating sulphur in iron and steel
by a modification of the evolution process, which consists in passing
the evolved gases through an ammoniacal solution of peroxide of
hydrogen, which oxidizes the sulphureted hydrogen to sulphuric acid,
which latter is estimated as usual. The _modus operandi_ is as follows:
[Illustration]
100 grains of the iron or steel are placed in the 10 oz. flask, a, along
with ½ oz. water; 1½ oz. hydrochloric acid are added from the stoppered
funnel, b, in such quantities at a time as to produce a moderate
evolution of gas through the nitrogen bulb, c, which contains 1/8 oz.
(20 vols.) peroxide of hydrogen and ½ oz. ammonia. The tube, d, is to
condense the bulk of the hydrochloric acid which distills over during
the operation. When all the acid has been added and the evolution of gas
becomes sluggish, heat is applied and the liquid boiled till all action
ceases. Air is blown through the aparatus for a few minutes and the
contents of c and d washed into a small beaker and acidified with
hydrochloric acid, boiled, barium chloride added, and the barium
sulphate filtered off after standing a short time. A blank experiment
must be done with each new lot of peroxide of hydrogen obtained, which
always gives under 0.1 barium sulphate with me.
The whole operation is finished within two hours, the usual oxidation
process occupying nearly two days; and the results obtained are
invariably slightly higher than by the oxidation processes.
Until lately I have always added excess of chlorate of potash to the
residue left in a, evaporated it nearly to dryness, diluted, filtered,
and added chloride of barium to the diluted filtrate, but only once
have I obtained a trace of precipitate after standing 48 hours, and the
pig-iron in that case contained 8 per cent. of silicon, so that all
the sulphur is evolved during the process. It has been objected to the
evolution process that when the iron contains copper all the sulphur is
not evolved, but theoretically it ought to be evolved whether copper is
present or not; and to test the point I fused 3 lb. of ordinary Scotch
pig-iron with some copper for half an hour in a Fletcher's gas furnace.
No copper could be detected in the iron by mere observation with a
microscope, but it gave on analysis 0.225 per cent. of copper, and on
estimating the sulphur in it by the above process and by oxidation with
chlorate of potash and hydrochloric acid, using 100 grains in each case,
and performing blank experiments, I found:
By peroxide of hydrogen process 0.0357 per cent.
By oxidation (KClO_{3} and HCl) process, 0.0302 "
so that even in highly cupriferous pig-iron all the sulphur is evolved
on treatment with strong hydrochloric acid.--_Chem. News_.
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