628 abstracts: inorganic chemistry 



2 per cent between the two forms, but none of these forms showed 

 any' variation in specific heat near the inversion temperature. In 

 quartz, below the a-/3 inversion at 575°, the heat absorption is greater 

 than can be accounted for even by the abnormal expansion. If such 

 absorption, unusual change of volume, and change of crystal properties 

 are each or all together the sign of a change of state, then quartz under- 

 goes a gradual change of state over an interval of 400° below what is 

 commonly called its a-^ inversion. Quartz and probably other forms 

 of silica exhibit what appear to be two kinds of inversion, due to dif- 

 ferent mechanisms. Some of these facts militate against certain hypothe- 

 ses which make polymorphism the resultant of polymeric or isomeric 

 changes in the solid. W. P. W. 



INORGANIC CHEMISTRY.— r/j^ hydrated ferric oxides. Hugen 

 PosNjAK and H. E. Merwin. Amer. Journ. Sci. 47: 311-348. 

 May, 1 919. 



Microscopic and chemical studies show that no series of hydrates 

 of ferric oxide exists among the natural minerals. The only existing 

 hydrate is ferric oxide monohydrate. This substance occurs in nature 

 in two polymorphic forms — goethite and lepidocrocite — and in an 

 "amorphous" condition — limonite. The two crystallized forms are 

 contrasted as follows: 



Goethite. — Orthorhombic, a : b : c = 0.91 : i : 0.602; density (grams 

 per cc.) 4.28 ±0.01; a = 2.26, /3 = 2.394, 7 = 2.400; streak, dull 

 orange-yellow; pleochroism faint. When crystallized in dense aggre- 

 gates of thin blades and fibers inclosing much adsorbed and capillary 

 water, it has commonly been called limonite; however, sufficient proof 

 is now given to show that such crystallized material is really goethite. 



Lepidocrocite. — Orthorhombic, a : b : c = 0.43 : i : 0.64; density, 

 4.09 ± 0.04; a = 1.94, /3 = 2.20, 7 = 2.51; streak, dull orange; pleo- 

 chroism very strong. 



The name limonite is retained for material which appears to be 

 essentially isotropic ferric oxide monohydrate with adsorbed and capil- 

 lary water. However, this substance should not be considered a dis- 

 tinct form of ferric oxide monohydrate, as the real nature of such 

 "amorphous" substances is still uncertain. 



The fibrous mineral turgite is variable in composition, and considerable 

 evidence is given that it probably represents solid solutions of goethite 

 with hematite, together with inclosed and adsorbed water. 



The genetic conditions of the hydrated ferric oxides and the stability 

 relation of the two monohydrates are unknown. 



