142 CARNEGIE INSTITUTION OF WASHINGTON. 



form of the dissociation-pressure curve of this system, and the relation of 

 adsorbed oxygen to Fe203. The physical problems are of special interest 

 because of the variety of magnetic properties exhibited by iron and its oxides; 

 the nature of magnetic inversions and of polymorphism in general, and the 

 bearing of the properties of the magnetic form of Fe203 on this problem are 

 discussed. It appears that the magnetic properties of iron and its compounds 

 are intimately connected with the spacing and arrangement of the iron atoms 

 and that the inversions may occur within the atom itself. The origin of mag- 

 matic and pneumatolytic ores is one of the geological problems now attracting 

 attention ; magnetic studies are expected to throw light on this question. The 

 genesis of the sedimentary iron ores is a problem in colloid chemistry, com- 

 plicated by the question of the activities of the so-called iron bacteria. 



(6) A method for the determination of dissociation pressures of sulphides, and its applica- 



tion to covellite (CuS) and pyrite (FeS2). E. T. Allen and Robert H. Lombard. 

 Am. J. Sci. (4), 43, 175-195 (1917). 



A new method has been devised for the determination of dissociation pres- 

 sures at comparatively high temperatures in cases where mercury gages can 

 not be used. It is intended especially for sulphides. It depends in principle 

 upon balancing the dissociation pressure of the sulphide by the vapor pressure 

 of sulphur at a known temperature; the pressure is not directly measured. 

 The method applies to other compounds than sulphides provided there is a 

 single volatile dissociation product which does not attack glass (or quartz 

 glass) and which condenses at accessible temperatures. The method can not 

 be used above 1100° to 1200°. By it the dissociation pressure curves of covel- 

 lite (CuS) and pyrite (FeS2) have been determined from about 1 mm. to 

 500 mm. 



The method's chief advantage is that the equilibrium is approached from 

 both directions and the experimenter is therefore not liable to be deceived by 

 false equilibria; it has the disadvantage of being slow and is inaccurate at 

 pressures much above an atmosphere. It was devised for the investigation of 

 complex sulphide systems where the dissociation pressure is a factor in stability 

 that can not be neglected. There seems to be no reason why it should not find 

 a broader application to other systems of similar characteristics. 



The method also supplies a convenient means for the synthesis of sulphides 

 the dissociation of which causes difficultj^ 



(7) The electrometric titration of zinc with ferrocyanide. F. Russell von Bichowsky. 



J. Wash. Acad. Sci., 7, 141-143 (1917). 



In the course of the titration of a zinc salt with a ferrocyanide solution, 

 the electromotive force of a polarized platinum electrode placed in the mixture, 

 instead of decreasing with the addition of the reducing agent, at first increases, 

 reaching a maximum usually just before the end-point. The conditions 

 governing the position of this maximum have been studied and on this basis a 

 theory is proposed to account for this effect and the similar effect noted by 

 Forbes and Bartlett for the titration of ferrous iron with chromic acid. It is 

 further proposed that the change of electromotive force of the platinum elec- 

 trode be used as an end-point in the titration of zinc. 



(8) The electrometric titration of zinc. F. Russell von Bichowsky. J. Ind. Eng. Chem., 



9, 668-671 (1917). 



This is a more extended account of the practical applications of the research 

 outlined in the above abstract. The electrometric method for the analysis of 

 zinc ores has the advantage that less care and time are required in the prepara- 

 tion of the solution for titration, the titration is quicker, and the end-point 



