c. of it are filtered off
through a dry filter for the colorimetric determination. Since only
two-thirds of the solution are taken for this, the quantity of copper
found must be increased by one-half to get the quantity actually
present.
[Illustration: FIG. 55.]
The ~colorimetric determination~ may be made in the manner described
under that head, but where a number of assays are being carried out it
is more convenient to have a series of standard phials containing known
amounts of copper in ammoniacal solution. By comparing the measured
volume of the assay solution with these, the amount of copper present is
determined at a glance. These standard bottles, however, can only be
economically used where a large number of assays are being made daily.
A convenient plan is to get a quantity of white glass four-ounce phials,
like that in fig. 55, and to label them so that they shall contain 100
c.c. when filled up to the bottom of the labels. The labels should be
rendered permanent by coating with wax, and be marked with numbers
indicating the milligrams of copper present. The bottles are stopped
with new clean corks, and contain, in addition to the specified quantity
of copper, 6 c.c. of nitric acid and 10 c.c. of strong ammonia, with
sufficient water to make up the bulk to 100 c.c. The copper is best
added by running in the requisite amount of a standard solution of
copper, each c.
Pages:
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362