icularly downward from
a nozzle made of lead pipe through an aperture 1/8 in. in diameter.
Under these circumstances the absorption of the steam is nearly
perfect, and takes place without any splashing. The temperature rises
with the increasing dilution, and may be regulated by the less
experienced by manipulating the cooling tank. An actual boiling is not
desired, because it protracts unnecessarily the operation by the less
perfect condensation of the steam. No separation of silver sulphate
occurs during this operation (and, consequently, there is no clotting
of the steam nozzle), the large amount of free acid, combined with the
increase of temperature, compensating for the diminution of the
solubility of the sulphate by the dilution. The most important point
in this procedure is to know when to stop the admission of steam. To
determine this, the operator takes a drop or two of the solution upon
a cold iron plate by means of a glass rod and observes whether after
cooling the sample congeals partly or wholly into a white mass of
silver bisulphate, or whether the silver separates as a monosulphate
in detached yellow crystals, leaving a mother liquor behind. As soon
as the latter point has been reached, steam is shut off and the
solution is allowed to crystallize, cold water being admitted into the
outer pan. The operator may now be certain that the liquid will no
longer congeal into a soft mass of silver bisulphate, which on contact
with water will disintegrate into powder, obstinately retaining a
large amount of free acid; but the silver will separate as a
monosulphate in hard and large yellow crystals retaining no acid and
preserving their physical characteristics when thrown into water.
After cooling to, say, 80 deg. F., the silver sulphate will have coated
the pan C about 1 in. thick. There will also be found a deposit of
copper sulphate when the mother acid, after having been used over and
over again, has been sufficiently saturated therewith. Lead sulphate
separates in a cloud, which, however, will hardly settle at this
stage.

The whole operation just described, which constitutes the most
essential feature of the author's improvement upon his old process
described in Dr. Percy's work, is a short one, as the acid requires by
no means great dilution. The steam has merely to furnish enough water
to dilute the free acid present to, say, 62 deg. B. Areometrical
determination is, of course, not possible, on account of