6Ca(PO₃)₂ + 2CaH₂P₂O₇ = 8Ca(PO₃)₂ + 2H₂O. Provided the drying is made at once at 210° the sum of the changes produced as indicated above, can be represented by the following formula: 8[CaH₄(PO₄)₂·H₂O] = 8Ca(PO₃)₂ + 24H₂O. COMPLETE ANALYSIS OF MINERAL PHOSPHATES. =19. Constituents to be Determined.=—The most important point in the analysis of mineral phosphates is to determine their content of phosphoric acid. Of equal scientific interest, however, and often of great commercial importance is the determination of the percentage of other acids and bases present. The analyst is often called on, in the examination of these bodies, to make known the content of water both free and combined, of organic and volatile matter, of carbon dioxid, sulfur, chlorin, fluorin, silica, iron, alumina, calcium, manganese, magnesia, and the alkalies. The estimation of some of these bodies presents problems of considerable difficulty, and it would be vain to suppose that the best possible methods are now known. Especially is this the case with the processes which relate to the estimation of the fluorin, silica, iron, alumina, and lime. The phosphoric acid, however, which is the chief constituent from a commercial point of view, it is believed, can now be determined with a high degree of precision. Often the estimation of some of the less important constituents is of great interest in determining the origin of the deposits, especially in the case of fluorin. While the merchant is content with knowing the percentage of phosphoric acid and the manufacturer asks in addition only some knowledge of the quantity of iron, alumina, and lime the analyst in most cases is only content with a complete knowledge of the constitution of the sample at his disposal.