224 M. Lechartier on Artificial Mimetisite. 



spectively the general formula 



3(P0 5 3R0)C1R and (P0 5 3KO)Cm. 



In nature the arseniates accompany the phosphates, with which 

 they are closely allied in composition and in crystalline form ; 

 pyromorphite, for instance, is accompanied, as Wohler found, 

 by a chlorarseniate of lead, to which he gave the name mimetisite, 

 from its resemblance to chlorophosphate of lead. Lechartier* has 

 succeeded in preparing a group of minerals isomorphous with 

 the apatite and Wagnerite group, but containing arsenic instead 

 of phosphoric acid. This was done.by fusing the arseniates with 

 excess of chloride of the same base; the arseniates dissolve,, 

 forming chlorarseniates, which crystallize in the fused mass when 

 it begins to solidify. As in the case of apatite and Wagnerite, 

 fluorine can either wholly or partially replace chlorine without 

 an alteration in the general form. 



The following minerals have been prepared : — 



Arsenical Apatites. 



f3(As0 5 3CaO)(CaCl) 



Arsenical lime apatite . < 0/A A r n ^ /CaCh 

 1 ^3(As0 5 3CaO)(^ CaP j. 



Arsenical lead apatite . . 3(As0 5 3PbO) (PbCl). 

 „ strontia apatite . 3(As0 5 3SrO) (SrCl). 

 „ baryta apatite . . 3(As0 5 3BaO)(BaCl). 



Arsenical Wagnerites. 



Arsenical lime Wagnerite. (AsO 5 3 CaO) (CaCl) . 



r(As0 5 3MgO)MgCl. 

 „ magnesia Wagnerite. | (AsQ5 3 Mg0) gIgCl^ 



„ manganese Wagnerite. (As0 5 3MnO) MnCl. 



Premy has described f a general method of obtaining, in the 

 state of crystals, many substances which are usually amor- 

 phous. It consists in allowing the precipitations and decompo- 

 sitions to take place very slowly. Various modifications were 

 used. In one series of experiments the substances were dissolved 

 in solutions of different densities containing gum, sugar, gela- 

 tine, &c, and these separated by porous substances, or by un- 

 sized paper, which were only gradually penetrated by the liquids, 

 and thus caused slow decompositions. In other cases endos- 

 mose was had recourse to, and the solutions separated by mem- 



* Comptes Rendus, July 22, 1867. 



t Comptes Rendus, vol. lxiii. p. 714. Zeitschift filr Chemie,Dec. 1866. 



