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500 CRABTREE, EATON, AND MUEHLER \j. s. M. P. E.
image. Conversion of the silver image to silver sulfide by sulfide toning in the usual manner, or to silver selenide or telluride, will also insure maximum permanency, although such treatments change the color of the image.
OCCASIONAL EFFECTS WHEN USING THE PEROXIDE-AMMONIA TREATMENTS
HE-1 AND HE-2
(1) A slight change in tone: This tone change is not as great as that produced by ferrotyping and, therefore, is considered to be negligible for glossy papers. When it is desired to prevent the slight tone change on professional papers, 15 grains of potassium bromide should be added to each quart (1 gram per liter) of the Kodak HE-1 bath.
(2) A slight yellowing of the whites (undetectable on buff papers) : To minimize this effect, the prints should be bathed in either a 1per cent acetic acid solution or a 1 per cent sodium sulfite solution for about 2 minutes immediately after treatment in HE-1 or HE-2 and prior to the final wash.
(3) If the prints feel too slippery after the eliminator, they should be immersed for 1 minute in a 1-per cent solution of acetic acid and then washed for 3 or 4 minutes.
(4) A slight tendency for treated prints to stick to a hot belt dryer. To prevent this, the prints should be bathed, prior to drying, for 3 to 5 minutes in a 50-per cent denatured alcohol solution. A 2-per cent potassium alum solution is effective but requires a rinse of several minutes in water after the treatment.
(5) An occasional tendency for treated glossy prints to ride the squeegee roll of the ferrotype dryer (especially prints which have been accidentally fed into the machine emulsion side up), or to stick to the chromium drum itself. To overcome these difficulties, the prints should be bathed for 2 minutes in a 50-per cent denatured alcohol solution just prior to ferrotyping.
(6) While cleanliness of the drum surface is essential for the satisfactory ferrotyping of all prints, it is especially important as a sticking preventative in the case of peroxide-ammonia treated prints. Excessive drum temperatures should also be avoided.
RELATION BETWEEN THE THEORETICAL AND PRACTICAL QUANTITIES OF HYPO REQUIRED TO PRODUCE FADING
It is of interest to study the relationship between the theoretical quantity of sodium thiosulfate required to convert any given silver