introduction of steam, and bringing it into contact with the acid in
the form of gases and vapor of water. In either case a large volume of
noxious gases is given off, the chief of which, being sulphureted
hydrogen, has to be fixed by another method, in order to comply with
acts of Parliament for the prevention of nuisances.

By the processes hitherto used, we sometimes get only 1¼ tons of salts
to every ton of acid used; while in the more perfect forms of
apparatus, we may get 1-1/3 tons of salts. By Mr. Croll's process,
however, we get an increased yield of salts on the acid used, as
follows: The experiments were made with sulphuric acid of the specific
gravity of 1838, or nearly concentrated oil of vitriol; and the
quantity used was 8 ounces in each experiment. The ammoniacal liquor
was of uniform strength throughout all the experiments, being kept in
a corked jar; and the solution of sulphate of ammonia was passed
through filter paper before being crystallized. Thus we obtained a
white salt. In each experiment the solution of sulphate was divided
into four equal parts by weight, and one part filtered and
crystallized to dryness over a spirit lamp; the weight in each
experiment being as nearly as possible the same, or 3¼ oz. of salt to
2 oz. of acid--being in the proportion of 26 oz. of sulphate to 1 lb.
of acid, or 32½ cwt. of salts to 20 cwt. of acid.

The results surprised me; and being uniform over a number of
experiments, pleased me. Still, I preserved the character of a critic
and said: "I should like to treat 8 oz. of acid in the ordinary
way--saturating it with ammoniacal liquor, and then crystallizing it."
"Oh!" Mr. Croll said, "we know what that will produce." I replied:
"Yes; but I would like to do it with the precise acid and liquor we
have been using, so that we may have the experiment on all fours with