68 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On Isomorphism. — In an elaborate paper, Retgers lias 

 given the results of his later investigations upon isomorphism. 

 In an earlier paper he had pointed out the indefinite capability of 

 admixture of two crystalline isomorphous substances, and shown 

 that the best experimental proof of isomorphism was the con- 

 tinuous variation in the physical properties of these mixed crys- 

 tals. The physical property selected for the present research 

 was color. The substances made use of were potassium, per- 

 chlorate KC10 4 which is colorless, and potassium permanganate 

 KMn0 4 which is- dark purple-red ; or potassium sulphate K 2 S0 4 

 and potassium manganate K„Mu0 4 , the latter being green. The 

 two salts to be examined was dissolved in water and a drop of 

 each of the warm solutions were placed on a microscopic slide ; 

 these drops being allowed to touch or being connected with each 

 other by a narrow channel of liquid so that slow diffusion might 

 go on between them. If the salts are really isomorphous, like 

 those above mentioned, crystals are obtained having all depths 

 of color. Moreover a crystal may have its ends of different 

 depths of color, with all intermediate shades between. But if 

 the salts experimented on are not isomorphotis, no such gradation 

 of color is observed in the crystals. Adopting the axiom that if a 

 substance B is isomorphous with a substance A and also with a 

 substance C, the substances A and C are isomorphous with each 

 other, the author finds the perchlorates of ammonium, potassium, 

 rubidium and caesium to be isomorphous with potassium perman- 

 ganate and with each other, LiC10 4 . (H 2 0) 3 and LiMn0 4 . (H 2 0) s 

 form mixed crystals. AgC10 4 crystals were colored by an un- 

 stable rhombic modification of AgMn0 4 ; the mixed crystals 

 being highly pleochroic, changing from blue-green to ruby-red 

 on rotating the nicol prism. Mixed crystals containing manga- 

 nate retain their blue-screen color for weeks. K 2 S0 4 , (NH 4 ) 2 S0 4 , 

 Rb 2 S0 4 , Cs 2 S0 4 , T1 2 S0 4 , K o Se0 4 , Rb 2 Se0 4 , Cs 2 Se0 4 , Tl s Se0 4 , 

 KCr0 4 , RKCr0 4 , Cs CrO " K Mn0 4 , Rb o Mn0 4 and Cs Q Mn0 4 



2 4 7 2 4' 2 4?2 4 ' 2 i 2 4 



are all isomorphous forming rhombic (pseudo hexagonal) prisms 

 and pyramids. (NH 4 ) 2 Se0 4 crystallizes in monoclinic plates. 

 (NH 4 ) 2 Cr0 4 and Tl 2 Cr0 4 are only slightly soluble ; the former 

 being probably isodimorphous with K 2 Cr0 4 . The sulphates and 

 selenates of sodium and silver are isomorphous, crystallizing in 

 rhombic pyramids strongly double-refracting. The chromates of 

 sodium and silver and the manganate of sodium are isomorphous, 

 probably ; as are the sulphate, chromate and selenate of lithium, 

 when anhydrous. KLiS0 4 and KLiSe0 4 are not isomorphous 

 but morphotropic. K s W0 4 and K 2 Mn0 4 are isomorphous with 

 K 2 Mn0 4 . The author points out that between sulphates and sele- 



