NOSHIR N. DASTUR, D. R. KASHYAP AND ZAL R. KOTHAVALLA 51
DISCUSSION
Refractive indices. Looking at the figure for
cow ghee samples given in Table I it will be
seen that the refractive indices show a variation
from 41.0 to 45.2. The corresponding ranges
for buffalo, mixed and yellow ghee are 39.0 to
45.0, 40.3 to 46.2 and 41.4 to 43.4 respectively.
These data therefore indicate that figures for
refractive index range very widely from 39.0 to
45.2. The majority of samples, however, fall
within a narrow range of 41 to 45. Even this
range of variation is quite considerable to make
this value of any use in checking adulteration
in ghee. Figures for yellow ghee fall within
the range for cow and buffalo.
Colour fringes for ghee.—Figures
in the
various tables show that genuine ghee shows
either orange, red, pink or violet colour. To a
certain extent this colour of the fringes is corre-
lated with the figures for refractive indices.
Thus fats having a refractive index of about 40
to 41 show orange or red colour. As the figure
increases the colour changes to pink and further
to violet. A large majority of samples show
pink colour. Like all other chemical tests,
therefore, the colour fringes also do not give a
constant indications.
The Effect of temperature on the colour
fringes.—The index of refraction of a fact and
the colour of the fringe are closely interrelated
and this is proved by the fact that if the re-
fractive index is changed, e.g., by raising or
lowering the temperature, there is a parallel
change in the colour observed. In the Table
V are given a typical series of results establish-
ing this fact. The colour of the fringe changes
from violet to orange as the refractive index
shifts from 49.7 to 36.6.
TABLE V
Effect of temperature on the refractive index and
colour fringes of ghee
Temperature °C
Colour of
the
fringes.
Refractive index
25°
Violet
40.7
30°
Pink
46.8
35°
Red
(+)
43.8
40°
Red
(++)
41.6
45°
Orange
37.6
50°
Orange
36.6
The data show that the colour of the fringe
cannot be taken as a constant characteristic of
ghee or any other fat, and is determined by its
refractive index.
Colour fringe of vanaspati.—In
the course
of the present studies, almost all the different
brands of vanaspati, as well as edible oils, were
examined to see how their colour fringes varied.
It would be rather out of place to give the de-
tailed results here, but the net result of this
study was that it was found that most of the
samples gave a blue band.
Their refractive
index generally was higher than the range nor-
mally found for ghee. Vanaspati made from
coconut oil gave a very low value for the re-
fractive index and the colour of the fringe was
red. By suitable blending of two vanaspaties
or vanaspati with coconut oil, etc., it was
quite possible to prepare a mixture having re-
fractive index and colour fringe similar to that
found for ghee. This is illustrated by some
examples given in Table VI.
For obvious
reasons it has not been possible to disclose the
names of vanaspaties used in these experi-
ments.
TABLE VI
Refractive indices and colour fringes of mixture
of different fats
Description of the mixture
I. Mixture of vanaspati brands A & B :
Brand
„
„ „
„
„ „
„
„
A
B
A
„
„
„
„
„ „
5% + Brand B
10% + „
„
20% + „
„
25% +
„
„
30% + „
„
40% + „
„
50% + „
„
95%
90%
80%
75%
70%
60%
50%
Refrac-
tive
index
at
40° C.
34.6
50.5
49.6
48.8
47.0
46.0
45.5
43.5
41.6
Colour of the
fringe
Yellow/red
Inky blue
Inky blue
Inky blue
Violet.
Violet
Violet
Pink
Red
II. Mixtures of vanaspati brands A & C
Brand
„
„
„
„
„
„
„
„
C
A
„
„
„
„
„
„
„
65% + Brand C
60%+ „
59%+ „
58%+ „
57%+ „
56%+ „
55%+ „
50%+ „
„
„
„
„
„
„
„
35%
40%
41%
42%
43%
44%
45%
50%
51.6
45.6
45.0
44.6
44.4
44.1
44.0
43.4
43.0
Inky blue
Violet
Violet
Violet
Pinkish violet
Pinkish violet
Pinkish violet
Pink
Pink
III. Mixture of coconut oil and ground-
nut oil.
Coconut oil
Groundnut oil
Coconut
oil
„
„
„
„
60% +
55% +
50% +
45% +
40% +
Groundnut
oil
40%
„ 45%
„ 50%
„ 55%
„ 60%
35.5
55.6
47.3
46.3
44.7
44.0
42.8
Yellow/red
Light blue/inky
blue
Inky blue
Inky blue
Violet
Pinkish violet
Pink
IV. Mixture of Coconut oil and Pig Depot fat
Pig Depot fat
Coconut
oil
„
„
„
„
60% +Pig Depot
fat
55%+
„
50%+
„
45%+
„
40%+
„
40%
45%
50%
55%
60%
54.0
46.6
45.3
45.0
43.2
41.8
Light blue/inky
blue
Inky blue
Violet
Violet
Pinkish violet
Pink