GEOPHYSICAL LABORATORY. 155 



(5) The results of qualitative experiments indicate that enrichment pro- 

 ceeds faster in the presence of cuprous sulphate than in the presence of cupric 

 sulphate. 



(6) The influence of sulphuric acid on the enrichment reactions has been 

 studied. The enrichment of chalcopyrite and pyrite in our experiments has 

 been retarded by an increase in the concentration of sulphuric acid. The 

 explanation for this is found in the fact that hydrolysis of the ferric sulphate, 

 formed as we have stated above (paragraph 4), is either hindered or prevented, 

 and thus the influence of the cuprous sulphate formed from cupric sulphate 

 by the reducing action of ferrous sulphate is held back. The result is that 

 the formation of cuprous sulphate is limited, and since the rate of reaction of 

 cuprous sulphate on the sulphide is much faster than that of cupric sulphate, 

 enrichment itself is retarded. The enrichment of galena, sphalerite, pyrrho- 

 tite, and bornite is accelerated by sulphuric acid, for the "solubility" of these 

 sulphides is thus materially increased. Chalcopyrite is one of the products at 

 higher temperatures between bornite and 2 per cent sulphuric acid alone. 



(7) The influence of ferrous sulphate on the enrichment reactions has also 

 been studied to some extent. The first effect is to increase the rate by increas- 

 ing the quantity of cuprous sulphate in solution, and cuprous sulphate is more 

 rapid than cupric in its action on the sulphides. However, the effect is soon 

 lost unless the ferric iron formed is removed from the solution. 



It may be stated here that a reversal of the principal enrichment reactions, 

 such for example as 



5FeS2+ 14CuS04+ I2H2O = 7Cu2S-f5FeS03+ I2H2SO4 



has not been reproduced experimentally. The attempt to introduce iron into 

 bornite by allowing the sulphide to react with ferrous sulphate alone has not 

 met with success. 



(24) Preliminary report on the system, lime: ferric oxide. R. B. Sosman and H. E. Merwin. 



J. Wash. Acad. Sci., 6, 532-537 (1916). 



The melting-point diagram of this system was worked out by means of 

 thermal curves and optical examinations on mixtures of Fe203 and CaO, 

 heated in platinum crucibles in air. Near the Fe203 side of the diagram too 

 much ferrous iron is formed by dissociation at temperatures above 1250° to 

 permit of the determination of the melting temperatures except under pres- 

 sures of oxygen greater than atmospheric. Two compounds are formed 

 between CaO and Fe203, namely, 2CaO.Fe203 and CaO.Fe203. Both appear 

 to be dissociated at their melting-points. The compound 2CaO.Fe203 dis- 

 sociates with partial fusion at 1436°, and the compound CaO.Fe203 likewise 

 at 1216°. There is a eutectic at 1203° between CaO.Fe203 and Fe203. Optical 

 properties were measured by m.eans of a new imm^ersion medium, consisting 

 of an amorphous mixture of selenium and arsenic selenide. 



(25) The chemistry of portland cement. G. A. Rankin. Address dehvered at the Tv/elfth 



Annual Convention of the American Concrete Institute, Chicago, Feb. 14-17 

 (1916). (Pubhshed by the Institute.) 



A presentation of the chemical problem which confronts the portland- 

 cement manufacturer, considered in the light of recent studies of lime, 

 alumina, and silica. See "The ternary system CaO-Al203-Si02," Rankin 

 and Wright, Am. J. Sci. (4), 39, 1-79, 1915, reviewed in Year Book 13, page 155, 

 (1914) and "The constituents of portland-cement clinker," J. Ind. Eng. 

 Chem., 7, 466, 1915, reviewed in Year Book 14, page 165 (1915). 



