Croll, whose assistant I was for ten of the busiest
and most important years of his eventful life; and having (with my son
Bruce) taken part in the experiments, I have been asked to describe
the process to the Institute.
The manufacture of sulphate of ammonia, as hitherto conducted, has
consisted either in bringing together sulphuric acid and ammoniacal
liquor or in distilling the liquor by external heat, or by the
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 11/4 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.
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