140 



KECOKDS OF THE AUSTRALIAN MUSEUM. 



sulphide, arsenic was precipitated by addition of hydrocliloric 

 acid, oxidised by strong nitric acid and estimated as magnesium 

 pyro-arsenate, which weighed -1550 gram, yielding 1 7-95 "/„ arsenic 

 pentoxide. Phosphorus was estimated as before in the filtrate 

 from the sulphides of lead and arsenic. The result was 

 -0248 gram magnesium pyro-phosphate, equivalent to 2-47 "/„ 

 phosphorus pentoxide. 



Antimony if present would be left on the solution of sulphide 

 of arsenic in nitric acid but its presence was not proved. 



Thus we arrive at the conclusion that petterdite is really 

 mimetite containing an appreciable amount of phosphoric, 

 isomorphously replacing arsenic acid ; chemically it would be 

 classed with the variety campylite, and it is noteworthy that 

 Twelvetrees mentions campylite as sometimes associated with 

 petterdite,** while Petterd in another place alludes to campylite 

 as occurring in pale, almost white crystals at the Britannia Mine." 



The result of analyses is tabulated below ; III is the mean 

 of analyses I and II, under IV is given for comparison Rammels- 

 berg's analysis of campylite from Cumberland, England,^" while 

 V is the theoretical composition for 2 (3 Pbg P., Og. Pb CI.) + 7 

 (3 Pb:, As, Oh. Pb CI,). 



The angular measurements obtained from petterdite may 

 now be compared with the angles given by Goldschmidt for 

 mimetite. 



•* Twelvetrees — Loc, cit. 



9 Petterd— Proc. Roy. Soc. Tas., 1902 (19u3), p. 20. 

 10 Rammelsberg — Pogg. Ann., xci., 185-i, p. 316. 



