PHARMACOSIDERITE, a mineral species consisting of hydrated basic ferric arsenate, 2FeAs04 Fe(OH)3.5H20.
The two most useful arsenical sprays are Paris green and arsenate of lead.
Of arsenate of soda in water and mixing the two well together, and adding the whole to 16 gallons of soft water; to this is added a small quantity of coarse treacle.
(() An infusible white residue may be obtained,which may denote barium, strontium, calcium, magnesium, aluminium or zinc. The first three give characteristic flame colorations (see below); the last three, when moistened with cobalt nitrate and re-ignited, give coloured masses; aluminium (or silica) gives a brilliant blue; zinc gives a green; whilst magnesium phosphates or arsenate (and to a less degree the phosphates of the alkaline earths) give a violet mass.
Mitscherlich, in the case of the acid phosphate and acid arsenate of potassium, KH 2 P(As)04, who adopted the term isomorphism, and regarded phosphorus and arsenic as isomorphously related elements.
Of other lead minerals we may mention the basic sulphate lanarkite, PbO PbSO 4; leadhillite, PbSO 4.3PbCO 3; the basic chlorides matlockite, PbO PbC12j and mendipite, PbC1 2.2PbO; the chloro-phosphate pyromorphite, PbC12.3Pb3(P04)2, the chloro-arsenate mimetesite, PbC12.3Pb3(As04)2; the molybdate wulfenite, PbMoO 4; the chromate crocoite or crocoisite, PbCrO 4; the tungstate stolzite, PbW04.
Tin is removed mainly as a powdery mixture of stannate of lead and lead oxide, arsenic and antimony as a slagged mixture of arsenate and antimonate of lead and lead oxide.
I a the basic tellurate montanite, Bi 2 (OH) 4 TeO 4; the silicates eulytite and agricolite, B14(S104) 3; and the uranyl arsenate walpurgite, Bi(U02)3(OH)24(As04)4.
The mineral brushite, CaHPO 4.2H 2 0, which is isomorphous with the acid arsenate pharmacolite, CaHAs04.2H20, is an acid phosphate, and assumes monoclinic forms. The normal salt may be obtained artificially, as a white gelatinous precipitate which shrinks greatly on drying, by mixing solutions of sodium hydrogen phosphate, ammonia, and calcium chloride.
Copper arsenate is similar to cupric phosphate, and the resemblance is to be observed in the naturally occurring copper arsenates, which are generally isomorphous with the corresponding phosphates.
Olivenite corresponds to libethenite; clinoclase, euchroite, cornwallite and tyrolite are basic arsenates; zeunerite corresponds to torbernite; chalcophyllite (tamarite or " copper-mica ") is a basic copper aluminium sulphato-arsenate, and bayldonite is a similar compound containing lead instead of aluminium.
Silver arsenate and antimoniate are also readily soluble, metallic silver slightly so, silver sulphide not at all.
It permits coarser crushing of the ore, the cost of plant is lower, the power required is nominal, the cost of chemicals is lower than that of quicksilver, less water is necessary, and the extraction is often higher, as silver arsenate and antimoniate are readily soluble, while they are not decomposed in amalgamation.