But when the object of the
testing is merely careful comparison of the sample in question with an
original sample or previous deliveries, the case is much simplified,
and comes within the scope of the general chemist or the laboratory
attached to works. A few years ago I recommended carefully conducted
dyeing trials on woolen cloth mordanted with bichromate of potash as
the best and simplest mode adapted to such cases, and my subsequent
experience enables me to confirm that observation to the fullest
extent. Most of these extracts contain the coloring matter in two
states, the developed and the undeveloped, and an oxidizing mordant
such as bichromate of potash causes the latter as well as the former
to enter completely into combination with a metallic base; whereas
many of the other mordants, such as alumina or tin compounds, merely
take up the developed portion of the coloring matter together with
such small and variable proportions of the undeveloped as might
undergo oxidation during the process of dyeing. I would therefore
suggest dyeing trials with alumina, tin, iron, etc., only as
subsidiary tests indicating the suitability of an extract for certain
special purposes, while recommending the trial with bichromate of
potash as the one giving the best information respecting the actual
strength of the extract in relation to the raw material from which it
was obtained, and as giving a fair idea of the money value of the
sample.
Pages:
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86