A pinch of the powder so
obtained is taken up on the point of a penknife, and transferred into
a test tube. Two or more of these should be provided, about six inches
long. They may be obtained in the apparatus shop for a trifle. Some
hydrochloric, or, as it is generally called, muriatic acid, is poured
upon it to the depth of about three quarters of an inch; the tube is
then placed in some boiling water heated over a lamp in a tinned or
other vessel, and allowed to boil for from ten to fifteen minutes;
the tube is then removed and its contents allowed to cool, and then
examined. If the powder has all disappeared, we term the mineral
"soluble;" if more or less is dissolved, "partly soluble;" if none,
"insoluble;" and if the contents of the tube are of a solid transparent
mass like jelly, "gelatinous;" while if transparent gelatinous flakes
are left, it is so termed. As this method of distinguishment is always
applicable, it is very important, and its detail and result should be
carefully noticed. Care should be taken that only a small portion of
the mineral is used, and also but little acid; the action should be
observed, and is frequently a characteristic, in the case with calcspar,
which effervesces while dissolving. The acid used is hydrochloric at
first, and then, if the mineral cannot he recognized, the same treatment
may be repeated using nitric acid. Both of these acids should be at hand
and two ounces are generally sufficient.
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