December 2, 1921] 



SCIENCE 



557 



The method of preparing the solution was shown 

 to influence the slope of the curves. 



The action of dilute c7iloride solutions upon sil- 

 ver chloride: Geo. Shannon Forbes and H. Isa- 

 EELLE Cole. 



The potentials at the jun^itions of chloride solu- 

 tion: D. A. MacInnes and Y. L. Yeh. E.m.f. 

 measurements were made on cells of the type: 



Ag/AgCl + MCI L M'Cl = AgCl/Ag 

 (in which M and M' are the alkali metals and 

 hydrogen) using a flowing junction similar to 

 that developed by Lamb and Larson. With widely 

 varying rates of flow the potentials were con- 

 stant to + 0.02 mv. for indefinite periods. With 

 equal concentrations on both sides of the junction 

 and assuming the chloride ion activity to be the 

 same in all the solutions the measured e.m.f. is 

 that of the liquid junction only. The results may 

 be expressed by a simple additive rela,tion in the 

 few cases in which the formula of Lewis and 

 Sargent does not hold. 



Electrometrio titration of ortho-phosphoric acid: 

 E. T. Oakes and Henet M. Salisbury. New 

 curves for ortho-phosphoric acid titrated with 

 sodium hydroxide and sodium carbonate are 

 shown. These curves are plotted to show observed 

 e.m.f. values as well as Ph values. Condenser 

 method, and saturated calomel cell are used for 

 measuring e.m.f. Teohnio of titrations, method 

 of calculating results and sources of error are 

 discussed briefly. Curves obtained by titrating 

 phosphoric acid with sodium hydroxide, and so- 

 dium hydroxide with phosphoric acid are not 

 mirror images. The second end point of phos- 

 phoric acid required more than twice as much 

 alkali as the first. Curves obtained by titrating 

 phosphoric acid with sodium carbonate, and so- 

 dium carbonate with phosphoric acid are vastly 

 different. Equations conforming to these curves 

 differ from those commonly accepted. 



Oxidation-reduction potentials of certain indo- 

 phenols and thiamine dyes: Barnett Cohen and 

 W. Mansfield Clare. A series of indophenols 

 consisting of the condensation products of para- 

 amino phenol with phenol, o-cresol, m-cresol, o- 

 chlorophenol, guaiaeol, thymol and earvacrol were 

 synthesized. The potentials of mixtures of each 

 of these with its reduction product were measured 

 with a gold electrode at different Ph values. It 

 is shown that the same general relations hold that 

 were found by Clark in the study of methylene 

 blue and indigo sulfonate, the potentials being a 

 function of both the ratio of oxidation product 



to reduction product and of the hydrogen-ion 

 concentration. The effect of substitutions in 

 changing the characteristic potentials is noted. 

 Previous work with methylene blue has been ex- 

 tended to other thiaziues. Characteristic con- 

 stants for thionine, gentianine, toluidine blue o, 

 thiocarmine E, methylene green G' and new methyl- 

 ene blue N have been established. 



Oxidation-reduction potentials of sulfonated in- 

 digos: M. X. Sullivan and W. Mansmeld Clark. 

 A trisulfonate and tetrasulfonate were found to 

 have identical characteristic potentials when each 

 was in definite ratio to its respective reduction 

 product. These potentials are distinctly more posi- 

 tive than those of mono- and disulfonates. The 

 potentials of the mono- and disulfonates are ap- 

 proximately the same but more refined measure- 

 ments will have to be made to distinguish them. 



A series of oxidation-reduction indicators: W. 

 Mansfield Clark and H. F. Zoller. It is shown 

 that certain dyes are as susceptible to precise elec- 

 trode study as are certain inorganic oxidation-re- 

 duction combinations. The great importance of 

 hydrogen-ion concentration is emphasized. The 

 potentials for each dye can be reduced to a char- 

 acteristic value from which there may be calcu- 

 lated the hypothetical hydrogen pressures in equi- 

 librium with the oxidation-reduction products. 

 These values are used in the form log (1/H,) to 

 which is given the symbol rH. Plotting the equi- 

 libria on the rH scale gives a picture of oxida- 

 tion reduction indicators comparable with that 

 of the acid base indicators plotted on the Ph 

 scale. The following oxidation-reduction indicators 

 were shown plotted on the rH scale: guaiaeol in- 

 dophenol, o-cresol indophenol, o-chloro indophenol, 

 methylene green, thionine, methylene blue, indigo 

 tetrasulfonate, new methylene blue, indigo disul- 

 fonate, neutral red and safranine. These consti- 

 tute a series from rH 21.7, at the more oxidative 

 end to rH 2.8 at the more reductive end of the 

 scale. 



Selenium galvanometric colorimeter: Alexan- 

 der LowY and Oswald Blackwood. 



A submerged floating equilibrium bob that ad- 

 justs its weight to the density of the liquid m 

 which it is placed: C. W. Foulk. This is a 

 modification of the Eiehards floating equilibrium 

 bob so that it can be used for the determination 

 of the density of liquids over a considerable range. 

 Preliminary experiments show that measurements 

 of density can be made with it with an accuracy 



