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.
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.
Sodium arsenate (-10--yl-a gr.) is somewhat less commonly prescribed, though all the compounds of this metal have great value in experienced hands.
Normal ferric arsenate, FeAs0 4.2H2O, constitutes the mineral scorodite; pharmacosiderite is the basic arsenate 2FeAsO4Fe(OK)3.5H2O.
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.
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.
The two most useful arsenical sprays are Paris green and arsenate of lead.
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.
The iodide of arsenic (dose k gr.) is one of the ingredients of Donovan's solution (see Mercury); and iron arsenate (dose -3gr.
Silver arsenate and antimoniate are also readily soluble, metallic silver slightly so, silver sulphide not at all.