CHAPTER XII.

The Physiological Light Unit 45

APPENDIX I. Colour Education 59

APPENDIX II. The Possibilities of a Standard Light and Colour Unit 69

APPENDIX III. Dr. Dudley Corbett’s Radiometer 83

Index 89

ERRATA.

Plate I. Newton’s Theory. The Indigo line is erroneously placed between the Violet and the Red; it should be between the Blue and the Violet.

Page 40.--_Fifth line from the bottom, for_ Fraunhoper _read_ Fraunhofer.

_To face p. vi., Lovibond, Light and Colour Theories._] [P.R. 1317

LIST OF PLATES

TO FACE PAGE

Plate I. Six Colour Theories 4

" II. Circles Illustrating Absorption of White Light 11

" III. Diagram Illustrating Analysis of White Light 13

" IV. First System of Charting Colour 31

" V. Second System of Charting Colour 33

" VI. Six Tintometrical Colour Charts 39

" VII. Two Circles 40

" VIII. Absorption Curves of Dyes 76

" IX. Fading Curves of Dyes 78

" X. Comparison Curves of Healthy and Diseased Blood 80

" XI. Specific Colour Curves of Healthy and Diseased Human Blood 82

PURPOSE

The purpose of this work is to demonstrate that colour is a determinable property of matter, and to make generally known methods of colour analysis and synthesis which have proved of great practical value in establishing standards of purity in some industries.

The purpose is also to show that the methods are thoroughly scientific in theory and practice, and that the results are not likely to be changed by further discoveries. Also that out of the work done a new law has been developed, which the writer calls the Law of Specific Colour Development, meaning that every substance has its own rate of colour development for regularly increasing thicknesses.

THE THEORY.

Of the six colours in white light--red, orange, yellow, green, blue and violet; Red, Yellow and Blue are regarded as dominants, because they visually hold the associated colours orange, green and violet in subjection.

An equivalent unit of pure red, pure yellow and pure blue is adopted, and incorporated into glass. The unit is multiplied to obtain greater intensities, and divided to obtain lesser intensities.

The coloured glasses are called absorbents. The red absorbent transmits violet, red and orange, but the red ray alone is visible as colour, until the other absorbents are superimposed, and the character of the group of rays changed. In the same way yellow transmits orange and green, and blue transmits green and violet, whilst the yellow and blue alone are visible as colour. Orange, green and violet are here called subordinates, which may be developed as follows:--

Or. = R. + Y. Gr. = Y. + B. Vi. = B. + R.

Twenty-five years’ experience in the application of the theory and the method to the requirements of practical work, have given no reason for change. Following will be found a list of awards from International Juries and Scientific Societies, also a list of industries in which the writer’s method is giving entire satisfaction.

Awards by International Juries.

St. Louis 1 Silver Medal. 2 Bronze Medals.

Brussels 1 Gold Medal. 3 Silver Medals.

Turin Diploma of Honour. 1 Gold Medal. 1 Silver Medal.

Awards by Scientific Societies.

Sanitary Institute of Great Britain-- _Bronze_ Medal for Colourometrical Water Analysis.

Royal Sanitary Institute-- _Bronze_ Medal for Measuring Smoke Densities.

International Congress on School Hygiene-- _Bronze_ Medal for Colour Educator.

Royal Sanitary Institute-- _Silver_ Medal for Colour Educator.

Smoke Abatement Society, Sheffield-- _Diploma_ for System of Colour Measurement.

Royal Sanitary Institute-- _Bronze_ Medal for Quantitative Estimation of Colour Blindness.

Franco-British Exhibition-- _Gold_ Medal for Colour Educator.

International Medical Congress-- _Bronze_ Medal for Tintometer as Medical requisite.

Royal Sanitary Institute-- _Silver_ Medal for recent developments.

Royal Sanitary Institute-- _Silver_ Medal Corbett’s Radiometer.

Formal Adoption of Tintometer Standards by--

The Petroleum Industry. The Massachusetts Board of Health. The International Association of Leather Trades Chemists. The Inter-states Cotton Seed Oil Association. The Bureau of Engraving and Printing, China.

In general use by the following Industries--

Brewing and Malting. Tanning. Wine and Spirit Merchants. Dyeing and Printing. Paint, Oil and Varnish Merchants. Millers. Water Works Chemists. Ceramic Works. For estimating per cent. of Carbon in Steel. For estimating per cent. of Ammonia. For estimating Colours for Anthropological Classifications. For estimating Smoke Densities. For estimating Haemoglobin in the Blood. For estimating Colour of Whale Oil, etc., etc.

THE METHOD.

The colour composition of any object may be measured by superimposing units of different colours until the colour of the object is matched. A convenient apparatus is furnished for this purpose. The composition of the colour is learned by merely reading the markings on the glasses.

It is of course necessary that in the isolation of colour rays, some unit for measuring the intensity of both light and colour be established. As will be explained later, all such units are necessarily arbitrary. In this method the unit has been established by taking the smallest amount of colour easily perceptible to the ordinary vision. This unit or “one” is divided into tenths in the darker shades, and hundredths in the lighter scale. One one-hundredth is the smallest amount of colour measurable by a normal trained vision.

When equivalent units in the three colours are superimposed, their equivalent value (not their aggregate value) represents so much white light absorbed. For instance, 2 R. + 2 Y. + 2 B. absorbs two units of white light.

When the absorptive power of the colour standards is less than the intensity of the light, associated white light remains.

JOSEPH W. LOVIBOND.

The Colour Laboratories, Salisbury.

_December, 1914._

Light and Colour Theories