Fig. 8.
Sufficient information is now available to warrant the formulation of the following law: “That every substance has its own rate of colour development for regularly increasing intensities, which, when once established, becomes a constant for identifying similar substances in future.” This is the meaning of specific colour, and when a series of measurements at regularly increasing densities of a given substance have been made, the specific colour rate of that substance is established. This can be charted in curves and used as a basis for estimating quantities, properties, changes of condition, differences in value, detecting adulteration, etc.
Applications.—The author has permission to use the names of several gentlemen who have used the tintometrical scales for various purposes.
Sir Arthur H. Church, F.R.S., has employed the tintometrical standards for the purpose of registering the colours of certain wild flowers.
Sir Boverton Redwood has used the scales and system for petroleum investigations. At his instance the specific colour rate of petroleum was established, and the several composing colours plotted in curves, as in [Fig. 8], where the ordinates represent the scale of units irrespective of colour, and the abscissæ the scale of strata thicknesses.
The measurements were made at two-inch intervals, and the four perpendicular lines are at the colour points selected for valuing the four distinguishing marks, technically known as “Water White,” “Superfine,” “Prime,” and “Standard.” Intermediate qualities find their position in the scale of curves according to their measured colour values.
This method of standardizing commercial values has also been adopted by the International Tanners’ Association, the Inter-States Cotton Seed Oil Association, and other oil industries. Also for scale, solid fats, and such substances as can be easily melted and measured by transmitted light.
Varying Effects of Different Lights. Pathological Applications.—The law of specific colour development was made use of by Dr. George Oliver in determining the degrees of hæmoglobin in the blood. The method is fully explained in his Croonian Lecture before the Royal College of Physicians of London, July 11, 1896.