McDonnell and Smith — Lead-Chlor Arsenate. 139 



Art. XVII. — The Preparation and Properties of Lead- 

 Chlor Arsenate, Artificial Mimetite / by 0. C. McDonnell 

 and C. M. Smith. 



The mineral mimetite, the composition of which as first 

 shown by Woliler in 1825 is 3Pb 3 (As0 4 ),.PbCl 2 or Pb 4 (PbCl) 

 (AsO,) 3 , was made artificially, first by Lechartier,* and also by 

 Michel, f by fusing together lead arsenate and lead chloride. 

 Weinschenk;}: accomplished the same by heating a mixture of 

 water, ammonium chloride, lead chloride and ammonium arsen- 

 ate at a high temperature in a sealed tube. Its preparation in 

 the wet way at ordinary temperature has never been recorded, 

 although it was observed by H. Rose§ that when a solution 

 containing arsenates and chlorides is precipitated with lead 

 nitrate or acetate, " lead chloride is also precipitated with the 

 lead arsenate and forms a double compound with the latter 

 which cannot be decomposed by washing with a large volume 

 of water." The nature of this compound was not further 

 studied by him and has apparently been overlooked by later 

 investigators. 



During an investigation of the arsenates of lead, while 

 endeavoring to pi'oduce crystallized dilead arsenate (PbH As0 4 ), 

 various media were tried as solvents. It was found that a 

 boiling 40 per cent solution of ammonium chloride dissolved 

 dilead arsenate to the extent of about \ per cent of the ammo- 

 nium chloride present. When such a solution was poured into 

 a large volume of cold water a gelatinous precipitate was pro- 

 duced, which on analysis was found to contain 74/54: per cent 

 PbO and 23 - 00 per cent As a 5 , leaving 2 - 46 per cent unac- 

 counted for. Qualitative tests revealed the presence of chlor- 

 ine, and another sample of the material prepared in the same 

 way, and washed free from soluble chlorides, was analyzed with 

 the following results: 



Theory for raitnetite 

 Found Pb 4 (PbCl)(As0 4 ) 3 



Lead oxide, PbO 74-64$ 74-97$ 



Arsenic pentoxide, As 2 O ft 22-81 23-18 



Chlorine, CI 2-72 2-38 



100-17 100-S3 



O, equivalent to CI 61 0-53 



99-5G 100-00 



*Comptes Rendus. lxv, 172, 1867. 



tBull. Soc. Min. de Prance, x, 133, 1887. 



% Zeitschr. Kryst. Min., xvii, 489, 1890. 



§ Ausfiihrlickes Handbuck der Analytiscken Cheinie, II, 406, 1851. 



Am. Jour. Sci. — Fourth Series, Vol. XLII, No. 248. — August, 1916. 

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