Noelting and Herzberg have also observed that the fastness to light, even of basic colors, e.g., magenta, methyl violet, malachite green, etc., is increased by a subsequent treatment of the dyed fabric with copper sulphate solution, although in many cases the color is much soiled thereby.

Still more recently, A. Scheurer records that by impregnating or padding certain dyed fabrics with an ammoniacal solution of copper sulphate, the colors gain considerably in fastness to light.  As the result of his experiments Scheurer concludes that this protective influence of copper on dyed colors is a general fact, apparently applicable to all colors; that it is not necessarily due to its action as a lake-forming substance, since intimate union between the coloring matter and the copper salt is not necessary.  He seems rather inclined to ascribe its efficacy to the light being deprived of its active rays during its passage through the oxide of copper.

Knowing, however, the strong reducing action of light in many cases, and with the absence of positive knowledge concerning the cause of the fading of colors, it seems to me that the beneficial influence of the copper may just as probably be due to its well known oxidizing power, which counteracts the reducing action of the light.

It is interesting to note, in connection with Scheurer’s view, that, many years ago, Gladstone and Wilson (1860) proposed to impregnate colored materials with some colorless fluorescent substance, e.g., sulphate of quinine, evidently with the idea of filtering off the active ultra-violet rays.  How far some such method as this might prove successful I cannot say, but since we cannot keep our dyed textile materials in a vacuum, as Chevreul did, nor is it desirable to impregnate them with mastic varnish for the purpose of excluding air and moisture, as Mr. Laurie proposes, in order to preserve the colors of oil paintings, it is perhaps well to bear in mind the principle here alluded to as a possible solution of the difficulty.

I have dwelt rather long on this important question of the action of light on dyed colors, but I have done so because I thought it would most interest you.  With the remaining portions of my subject I must be more brief.

(To be continued.)

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To introduce free fat acids from an oil, it must be decomposed.  This may be done by the use of lead oxide and water or by analogous processes.  To clarify an oil, expose to the sun in leaden trays.  Often washing with water will answer the purpose.

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COMPOSITION OF WHEAT GRAIN AND ITS PRODUCTS IN THE MILL.