c. of which contains 0.001 gram of the metal.
The standard bottles should be refilled once every three or four months,
since their colorimetric value becomes slowly less on keeping. The
following determinations of a set which had been in use for three months
will illustrate this. The figures indicate milligrams of copper in 100
c.c.: the first row gives the nominal and the second row the actual
colorimetric value of the standards. The difference between the two
shows the deterioration.
1 2 3 4 6 8 10 12 14
1 2 3 3.7 5.5 7.5 9 11 13
The amount of copper in the assay is got by increasing that found
colorimetrically by one-half and adding to that found on the platinum
cylinder. The percentage is calculated in the usual way. The following
examples will illustrate this, as well as the method of recording the
work in the laboratory book:--
---------------------------------------------
Cylinder I. + Cu 9.5410
Cylinder I. 9.5170
------
0.0240
By colour 100 c.c. = 0.0015}
0.0007} 0.0022
------ ------
0.0022 0.0262
IX. Sample. Took 5 grams.
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