OF ARTS AND SCIENCES. 121 



ALUMINO-MOLYBDATES. 



Heinrich Struve,* in 1854, described a remarkable series of salts, 

 ■which he regarded simply as double molybdates of the sesquioxides 

 of aluminum, iron, manganese, chromium, and ammonia, potash, or 

 soda. These salts were embraced under two different types, particular 

 aluminic, ferric, and chromic salts, having respectively the formulas 



AI0O3 . 6 M0O3 + 3 (K,0 . M0O3) + 20 aq 

 FeA . 6 M0O3 + 3 (KoO . 2 M0O3) -|- 20 aq 

 CroOa . 6 M0O3 + 3 (NagO . 2 M0O3) -j- 21 aq. 



The manganic salt, on the other hand, was represented by 

 Mn.Os . 6 M0O3 + 5 (K2O . 2 M0O3) + 12 aq. 



Parmentier f has recently added a new term to this series, the type 

 being 



R.Oa . 10 M0O3 . 2 R',0 + X aq. 



The true character of these compounds could not be understood at 

 the time of their discovery. I find that in solutions of the salts de- 

 scribed by Struve, potassium or ammonium may be directly replaced 

 by other metals or by alkaloids, — a fact which was, however, noticed 

 by Struve himself. In addition, — and this is of more importance, — 

 I find that there are series which contain the sesquioxides named with 

 phosphoric and molybdic oxides, so that we have classes of ferro-phos- 

 pho-molybdates, etc. From my point of view, the compounds in ques- 

 tion may be classed under three types, of which the following will serve 

 as representatives : — 



Alumino-dodeka-molybdates, 



Ferrico-dodeka-molybdates, 

 Chromico-dodeka-molybdates, 

 Manganico-hekkaideka-molybdates, MuoO; 



Alumino-deka-molybdates, 



Ferrico-deka-molybdates, 



Chromico-deka-molybdates, 



All these classes of salts containing oxides corresponding to chlorides 

 of the type ^2^K ^"^^ very much less stable than compounds containing 



* Petersburg Acad. Bull., xii. 142. f Coniptea Kenilus, xcv. 839. 



