12 Blake — Some Isomorphoiis IVijole Thiocyanates. 



Art. II. — A Comparatwe Study of Some Isoinorphous 

 Triple Thiocyanates / by J. C. Blake. 



Four triple thiocyanates, recently prepared by Wells and 

 others,"^ have been studied crystallographically. These salts 

 have compositions represented by the following formulas : 



Cs3Ag,Ba(SCN), 

 Cs3Cu,Ba(SCN), 

 Cs3Ag,Sr(SCN), 

 Cs3Cu,Sr(SCN), 



The crystals are well suited for optical investigation, and are 

 especially interesting because the sphenoidal group of the 

 tetrahedral system, to which they belong, has few representa- 

 tives, either natural or artificial, and because the salts are iso- 

 morphous and hence offer a new field for the comparative 

 study of the physical and chemical properties involved. Unfor- 

 tunately the number of salts belonging to the series which 

 have been prepared is as yet too small to throw much light on 

 the relative variations which change of composition induces, or 

 to lend much weight to the conclusions reached. 



The following forms have been observed : 



c (001) 

 a (100) 



m (110) 

 p (111) 



q (201) 



The general habit of the crystals is indicated by the illustra- 



tions, figures 2 and 3 showing the sphenoid j9 (111). 



* Am. Chem. Jour., xxviii, 245. 



The 



