GLYCEROL AS SENSITIZER’ BY CHARLES W. BENNETT
Three years ago von Hiib12 published some work onlthe bleach-out process. He added glycerol and found a marked increase of sensitiveness to light with methylene blue, phenosafranine, and scarlet. When a gelatine film containing I O grams gelatine and 3 cc glycerol was stained with methylene blue, the color bleached completely in an hour’s exposure to sunlight. With a film containing no glycerol, no change was observed in the same time. From his experiments von Hub1 concludes that the light-sensitiveness of methylene blue is increased five hundred to a thousand fold by the addition of glycerol. No explanation is offered for this rather remarkable result. WursterS states that it is a well-known fact that glycerol makes oxygen active; but he gives no reference and we have not yet been able to find any authority for this statement. This is not of any great importance, however, because further consideration made it seem probable that the bleaching was not due to oxidation. Methylene blue can bleach by reduction or by oxidation. When the bleaching is done by reduction, the color comes back when the reduced dye is exposed t o air. Now von Hub1 found that the blue color reappeared when the prints were kept in the dark. This made it seem probable that sunlight caused glycerol to react with oxygen forming glyceric aldehyde --especially as it has already been noticed in Manila4 that sunlight converts methyl alcohol to some extent into formaldehyde. To test this point various concentrations of glycerol were placed in glass flasks and were exposed to a powerful arc lamp. Distinct evidence of the presence of an aldehyde was A paper read before the Eighth International Congress of Applied Chemistry in New York, September, 1912. Phot. Mittheilungen, 46, 253 (1909). * Ber. chem. Ges. Berlin, 19, 3211 (1886). Freer: Philippine Jour. Sci., 5B, 8 (1910).
Glycerol as Sensitizer
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obtained by means of the fuchsine test. Glycerol, which had been acted on by light was found to bleach methylene blue, safranine, and Biebrich scarlet appreciably a t 50" in the dark. I n presence of sunlight the dye would react more rapidly. It was also shown that solutions of acetaldehyde bleach these three dyes in the dark, although slowly. It was also found by von Hub1 that an addition of arsenates and glycerol increased the sensitiveness of methylene blue. Since arsenates as such could only increase the light-sensitiveness of methylene blue by acting as an oxidizing agent, it is clear that there is an error of some sort here. Since no details are given, it is impossible to say whether von Hub1 really used sodium arsenite instead of arsenate, or whether the react'on takes place faster in two stages, the aldehyde from the glycerol reducing the arsenate to arsenite, and the arsenite reducing the methylene blue. Whichever explanation one adopts, the arsenite is the important substance theoretically. It is interesting to note that I,immerl found a sensitizing effect due to what he calls arsenic trioxide, in the absence of glycerol. It seems probable that he was using sodium arsenite though he does not say so. The general results of this paper are: I . When glycerol and air are exposed to a bright light, an aldehyde is formed, presumably glyceric aldehyde. 2. Methylene blue, safranine, and Biebrich scarlet are bleached in the dark by acetaldehyde or by a solution of glycerol which has been exposed to light, the reaction taking place faster a t higher temperatures. 3 . The sensitizing action of glycerol on certain dyes, as discovered by von Hiibl, is due to the formation of the aldehyde. 4. Dyes, which are not bleached by reduction, will not be sensitized in this way. 5 . The alleged sensitizing action of arsenates in presence of glycerol is really due to arsenites. I
Cornell University
Zeit. angew. Chem., 1909,1715.
