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.
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