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:
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 and HCl) process,||0.0302 per cent.|