-1SOTE O S THE ROLE E’L-l17ED 1317THE CARBOSAITE IS P H 0TOG RAP HI C D E1-I3L0P11E XT B T J . HOTT-.IRD 3LITHETT-S .‘ISD
FLOYD E
BXRMEIEK
The statement is commonly made that the functioii of the cdrbonate in a photographic developer is t o open the pores of the qelatin 50 ‘is to provide readier access for the de\-eloper to the altered silver halide ?rains. S o record of any- nieaiurements on the rate of dil‘fusion of carbonate solutioni into qelatin havinq come under the obser7-ation of the n-riters it seemed to us to be hiqhly desirable to make such measurements rather thick gelatin solution containing a trace of phenolphthalein was cast in glass tubes of in. diameter and allom-ed to set The tubes were then cut off sharply so as to produce a square edge and the gelatin \vas cut square across with a sharp knife. The tubes so prepared were placed in solutions of sodium and potassium carbonates, care being taken to ensure their being immersed to the same depth. The carbonate diffused into the gelatin and produced a pink color having a very sharp boundary. The rise of the pink column in the tubes u a s accurately measured by a good cathetometer It was found that the rate of diffusion increased n-ith the concentration u p to a certain limit and then fell off again. This may be due to a hardening action of the carbonate on the gelatin It is curious, and significant, to note t h a t the solution having the greatest rate of diffusion is one having a concentration of carbonate which is the same as is customarily used in a normal dexTeloping solution. Judging from the form of the accompanying curves which give the behavior of the solutions investigated, it seems likely t h a t there is a certain strength of carbonate solution tvhich -4 paper read before thc Eighth International Congress of Applied Chemistry in S e w Tork, September, 1912.
Note
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Photographic Decelopmeiit
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would diffuse more rapidly than any other, and t h a t in all probability this would be the concentration most desirable in a developer. Lack of time has prevented our making further determinations along this line. I t seems likely that this optimum value for the concentration of the carbonate solution depends on the particular gelatin used, and possibly on the n-ater content of the solidified gelatin on the plate.
Fig.
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Fig.
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These measurements support the statement that the function of the carbonate is to open the pores of the gelatinthough this probably is not the whole story-and the accompanying curves shon- why the carbonate may vary n-ithin certain, yet rather 11-icle,limits. The data obtained in these measurements, and the cur\ e\ derived therefrom, appear belon- :
684
J . Howard JJathews and Flojid E . Barmeier
