and it is repeated until the accumulation of sulphur in the oxide is
so great (45 to 55 per cent.) that it can be profitably sold to the
vitriol maker. Hawkins discovered that by introducing about 3 per
cent. of air into the gas before passing it through the purifiers, the
oxygen of the air introduced set free the sulphur from the iron as
fast as it was absorbed. Thus the process of revivification could be
carried on in the purifiers themselves simultaneously with the
absorption of the sulphur impurities in the gas.

A great saving of labor was thus effected, and also an economy in the
use of the iron oxide, which in this way could be left in the
purifiers until charged with 75 per cent. of sulphur. Unfortunately it
was found that this introduction of air for the sake of its oxygen
meant also the introduction of much useless nitrogen, which materially
reduced the illuminating power of the gas. To restore this
illuminating power the gas had to be recarbureted, and this again
meant cost in labor and material. Now, Mr. Ogden has found by a series
of conclusive experiments made during a period of seventy-eight days
upon a quantity of about 4,000,000 cub. ft. of gas, that by
introducing 1 per cent. of oxygen into the gas instead of 3 per cent.
of air, not only is the revivification _in situ_ effected more
satisfactorily than with air, but at the same time the illuminating
power of the gas, so far from being decreased, is actually increased
by one candle unit.

[Illustration: THE PRODUCTION OF OXYGEN BY BRIN'S PROCESS.]

So satisfied is he with his results that he has recommended the
corporation to erect a plant for the production of oxygen at the
Blackburn gas works, by which he estimates that the saving to the town
on the year's make of gas will be something like L2,500. The practical
observations of Mr. Ogden are being followed up by a series of
exhaustive experiments by Mr. Valon, A.M. Inst. C.E., also a gas
engineer. The make of an entire works at Westgate is being treated by
him with oxygen. Mr. Valon has not yet published his report, as the
experiments are not quite complete; but we understand that his results
are even more satisfactory than those obtained at Blackburn.

In conclusion we may indicate a few other of the numerous possible
applications of cheap oxygen which might be realized in the near
future. The greatest illuminating effect from a given bulk of gas is
obtained by mixing it with the requisite propor