Wells, Wheeler and Pen field — Halides of Silver, etc. 155 



EXPLANATION OF PLATE. 

 Glottidia albida Hinds. 



Figure 1. — Nepionic shell ; Obolella stage. x36. 



Figure 2. — Nealogic stage; showing anterior growth producing Lingula-like 



form, x 16. 

 Figures. — Ephebolic stage, xf. 



Orbiculoidea minuta Hall. 



Figure 4. — Nepionic shell ; Paterina stage, x 36. 



Figure 5. — Nealogic stage ; first holoperipheral growth, x 16. 



Figure 6. — Ephebolic stage, x 10. 



Lej)twna rhomboidatis Wilck. 



Figure 7. — Nepionic stages, with short hinge, x 36. 

 Figure 8.— Early nealogic stage, with radiating strite. x 10. 

 Figure 9.— Ephebolic stage, x.-f-. 



Terebratulina septentrionalis Couth. 



Figure 10. — Nepionic stage, with open delthyrium. x 26. 



Figure 11. — Early nealogic stage, with radiating striae, x 16. (After Morse.) 



Figure 12. — Ephebolic stage, xf. (After Davidson.) 



Art. XX. — On some Double Halides of Silver and- the 

 Alkali-metals; by H. L. Wells and H. L. Wheeler. 

 With their Crystallography ; by S. L. Penfield. 



. During a systematic search for well crystallized salts of the 

 type M'Hl . AgHl,* which we were anxious to obtain on 

 account of their probable isomorphism with the alkaline 

 trihalides, three well defined compounds of another type, 

 2M / H1 . AgHl, were obtained. Our experience indicates that 

 these 2 : 1 salts are more easily prepared and crystallize better 

 than the 1 : 1 compounds. 



The bodies to be described are 2CsCl. AgCl, 2RbI . Agl and 

 2KI . Agl. Two of these are believed to be new salts ; the 

 other, 2KI . Agl has been described by Boullay.f We have 

 not obtained a complete series of these compounds, for good 

 crystals could not be made of the other members, and, under 

 the circumstances, no products were analyzed except such as 

 could be measured. 



The compounds are interesting from the fact that they do 

 not conform to Kemsen's law concerning the composition of 

 double halides,^; for, contrary to this, they contain a number of 

 alkali-metal atoms "which is greater than the number of halogen 

 atoms belonging to the silver. In his latest contribution to the 



* This Journal, III, xliii, 30 and 485. f Ann. Chim. Phys., II, xxiv, 377. 

 X Am. Chem. Jour, xi, 291. 



