ISOMORPHISM, ISOSTENISM AND COVALENCE 



249 



TABLE III 

 Nitrates and' Carbonates, Type ii (a). Trigonal Scalenohedral 



a 



NaNOs I 



CaCOs I 



MgCOs 1 



MnCOs I 



KNUa I 



0.8297 

 0.8543 

 0.S095 

 0.8259 

 0.8259 



Stable above 128° 



At high temperatures RbNOa, SrCOs and BaCOs also give trigonal crystals. 



All these substances show strong negative double refraction and similar cleavage. 



TABLE IV 

 Nitrates and Carbonates, Type ii (b). Orthorhombic Bipyramidal 



KNO3 0.5910 I 0.7011 



SrCOa 0.6090 I 0.7237 



CaCOa 0.6228 I 0.7204 



BaCOj 0.5949 I 0.7413 



Negative double refraction. 



TABLE V 



Perchlorates and Sulfates, Type 14 (a). Permanganates and Chromates, 

 Type 20. Orthorhombic Bipyramidal 



a. 



S:ci04 0.7817 



SrS04 •. • : • • o . 7790 



RbMnOi 0.83H 



BaCr04 0.8231 



RbClOi 0.7966 



BaS04 0.8152 



KMn04 0.7972 



SrCr04 o. 9496 



CSCIO4 0.8173 



CsMn04 o. 8683 



CaS04 0.8932 



NH4CIO4 0.7932 



Groth gives no data for the Types 15 (a), i5(&), 17 and 18 of Table II. 



The results given in these tables afford the strongest kind of evidence 

 for the octet theory of valence and prove that crystal form depends on the 

 covalence of the atoms forming the substance rather than upon the valences 

 given by the ordinary theory. 



In every one of the cases where isomorphism is predicted by the octet 



