abstracts: mineralogical chemistry 9 



2CaO.Al2O3.SiO2 compositions. Type V is dependent on the nature and 

 location of point 13 and is to be regarded as tentative. 



If solid solutions are formed they are very limited in extent and are 

 not sufficient to affect the optical properties of either silicate, the lime 

 or the aluminate. This fact serves to give greater defmiteness to the 

 problem and an unexpectedly clear field for studies of the cement- 

 forming quality of ciinkers of nearly related composition but different 

 chemical constitution. It therefore seems inevitable that such studies 

 will lead to more reliable standards in cement practice. 



The diagram indicates that the constitution of slag cement will be 

 seriously affected by relatively small differences of composition in the 

 neighborhood of the line joining the compounds calcium orthosilicate 

 and 2CaO.AbO3.SiO2. It is, however, unwise to draw positive conclu- 

 sions about the character of this portion of the diagram until it has been 

 more carefully r studied. 



Incidentally, it has been observed that Fe 2 3 appears not to form solid 

 solutions with CaO, 2CaO.Si0 2 , or 3CaO.Al 2 3 . It does appear to 

 react in some waj r with 5Ca0.3Al 2 3 , but the nature of this reaction has 

 not yet been studied. Attention should also be called in passing to 

 the important fact that Fe 2 O s dissociates at about 1400° with the for- 

 mation of Fe 3 4 . 



Finally, too great importance can not be given to the constant use 

 of the microscope in cement study and practice. It is not improbable 

 that microscopic examination will eventually provide much of the infor- 

 mation desired about the constitution of test samples, with the advantage 

 over chemical methods of giving immediate results. 



It remains to determine the isotherms of the diagram and to deter- 

 mine whether or not the five typical "clinkers" possess any differences 

 in properties when hydrated to form cement. The work on the iso- 

 therms is well under way. E. S. S. and G. A. R. 



MINERALOGICAL CHEMISTRY.— The mineral sulphides of iron. 

 E. T. Allen, J. L. Crenshaw, and John Johnston; with Crystal - 

 lographic Study by E. S. Larsen. Am. J. Sci. (In press.) 

 . The formation of iron disulphide was accomplished (1) by the action of 

 hydrogen sulphide on ferric salts, or the action of sulphur and hydrogen 

 sulphide on ferrous salts; (2) by the addition of sulphur from solution to 

 amorphous ferrous sulphide or pyrrhotite; (3) by the action of soluble 

 poly sulphides on ferrous salts; (4) by the action of soluble thiosulphates 

 on ferrous salts according to the equation 4M2S2O3 + Fex 2 = 3M 2 S0 4 



