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81 isoMOErinsM. 280. An exception, rather apparent than real, to the laws stated in (274), is presented by some isomorphous substances which arc found to crystallize together in all proportions. A mixed solution of sulphate of oxide of copper (cui) and sulphate of oxide of zinc (zu§), yields crystals having the form of sulphate of protoxide of iron (tesit 7 ), in which the oxides of copper and zinc occur in variable proportions. The oxygen of the sulphuric acid is three times, and that of the water con tained m the crystals seven times as great as the oxygen con tained in the oxides of copper and zinc together. The consti tution ot such a crystal is represented by the symbol (cu.zn)sH 7 , w ich may be regarded as an abbreviation of the more correct represen ation (cuSH 7 ),(z n sii 7 ). This mixture is described ver ally by saying, that a portion of the oxide of copper is replaced by oxide of zinc. A crystal of the mixed sulphate of oxide of copper and sulphate 0 oxide ot zinc with seven equivalents of water, placed alternately m a saturated solution of sulphate of protoxide of iron, with which 1 is isomorphous, and of the sulphates of oxide of copper and zinc, was found to be enlarged by alternate green and blue ayers, the former being pure sulphate of protoxide of iron, lesu, and the latter the mixed sulphates of oxides of coimer and zmc (cu,zn)sii ? . Perhaps the crystals formed in the mixed solution of sul phates of oxides of copper and zinc may, in like manner, consist o a mechanical mixture of portions of pure Cusi't 7 and znsft 7 , ut too minute to be distinguished from each other. On is hypothesis, however, we must assume that the presence o the sulphate of oxide of zinc influences the sulphate of oxide of copper so as to make it combine with seven equivalents o water instead of five, the proportion with which it uuites under ordinary circumstances. ulphate of oxide of copper crystallizes also, in all propor- 10ns, with sulphates of magnesia, sulphate of oxide of nickel, u p ia e of oxide of cohalt, sulphate of protoxide of iron, in the 0 le hatter salt, and, like it, with seven equivalents of _ j r ' , , a * so potash and alumina alum, ks + ais + n*‘, and f 1 ' 1 , chrome alum, ks + -6r s + n 2 ‘, and chloride of potassium crystallize together. minerals 1 " 0118 ° t] ' er exani P les are presented by crystallized a mpfhiI!. 116 f 0nst ' tut ' on °h a mineral is sometimes disguised by of which iT!. mix ^ re impurity, derived from the solution out of actimr eitbJ 8 a ' i . * len 11 s °l vent can he found capablo both the irm 1 " "'moral or the impurity, but not upon SphiiL3v“^ y f“ ay b «. d ^d ai such. Thus, o y ntains a mechanical mixture of iron, which