pH Value of Blue-Print Sensitizing Solutions Effect of Addition of Ccrtain Salts PAULK. W I N T ANU ~ HAIWEYV. MoYEn, Ohio State University, Columbus, Ohio
D
IAM1LIOXIUM pliosphate is sonietinses added to blue-print semitizing solutions to prevent the formation of a trace of blue color in the wliite portions of the print. I t seemed of interest to determine whether the effect of the phosphate salt is due to a change in the hydrogen-ion activity or to the presence of the added salts. Schneider (e) has studied tlie effect of adding acids and bases to blue-print sensitizing solutions, but no measurements of hydrogen-ion activity seem to he reported. The pH value of sensitizing solutions is difficult to measure 1,y the usual methods. Colorimetric methods are impracticable hecause of the color of thesolutionsand the high concentration of salts. The hydrogen electrode and the quiuhydronc electrode give erratic results because of tlie praence of oxidizing substances. The glass electrode as described by ;LIacInnes and Dole ( 1 ) gave reasonable and reproducible ralues. EXPEEIMENTAL 1’HOCEDURE Potassium ferricyanide and ferric ainmonium citrate Each mlution, wlsen rrady for use, vas 0.2 molar with respect to each of these were used to prepare the sensitizing solutions.
~ H 6 . 1 5 6.91 0.m
i\lUiesii 0
5.111 8.10 5.87 5.84 5.81 0.40 0.60 0.05 0.10 0.20 ERect 01 diiirnrnoniurn phoaphete
rill 6.14 Mde/l. 0
pII 8.12
xoier/i.o
6.16 0.01
6.16 8.15 612 6.00 0.05 0.10 0 . ~ 0 0.40 Effect
