Zinc Sulphate ZnSO

The circumstances are similar, but simpler, with a hydrated salt. Frowein, e. g. (p. 57), found that zinc sulphate (ZnSO. 7H2O) at 18° has a maximum pressure of 8 4o6 mm., in accordance with the fact that a higher external pressure produces the reverse reaction ... 

Zinc sulphate (ZnSO 7 H2O) Calcium chloride (CaCl2 6 H2O) Molybdenum trioxide (M0O3)... 

Evaluation.—5 gms. sodium sulphide are dissolved in water up to 250 c.cs. and carefully neutralised with dilute acetic acid in presence of phenolphthalein until the latter is colourless. A N solution of crystallised zinc sulphate (57-514 gms. ZnSO TB O per litre) is run in from a burette until all the soluble sodium sulphide is converted into zinc sulphide. A cone, solution of cadmium sulphate is spotted on thick blotting-paper, and a drop of the liquid being analysed is placed near it. A yellow stain will be produced as long as any soluble sulphide remains. The zinc sulphate is added until no yellow colour is given. 

ZnSO, 6H2O + H2O = ZnSO. 7H2O is associated with the current, since the removal of zinc sulphate from the solution in B, so long as saturation lasts, results in the dissolving, and therefore disappearance, of ZnSO. 6H2 0 while the taking up of zinc sulphate by the solution in a necessarily makes ZnSO. 7H2O separate out. 

Fit up the apparatus as shown in Fig. 75, p. 224, replacing the cell W, by the cell Cu solution of CUSO4 Cu or the cell Zn solution of ZnSO Zn connected in series with the standard cell Wj. By means of the two-way key, the point of balance on the bridge wire is determined, with the cell W, alone in the circuit, and then for the cell Wx tr ether with one of the above cdls. If the two copper (or zinc) electrodes are uniform, the point of balance should be the same in the two cases, the cells Cu solution of CuSO Cu and ZnJ solution of ZnSOx Zn should exhibit no e.m.f. If, however, an e.m.f. of more than i millivolt should be found (for method of calculation, see p. 226), then the two copper (or zinc) electrodes should be placed in a solution of copper sulphate (or zinc sulphate) and short-circuited for several hours or a... 

Two glass vessels A and B (Fig. 59), each provided with a pair of electrodes, are to be used the upper electrode is a piece of metallic zinc, the lower mercury, covered with a layer of mercurous sulphate. The vessel A contains moist ZnSO. 7H2O the other, b, contains moist Zn SO. 6H20. Although the two hydrates in the moist state are both stable only at 39°, yet with certain precautions, like those to be attended to in working with supersaturated solutions—especially the closure (with shellac) of the two vessels at the top—it is possible, to work with both salts at temperatures other than 39°. To prepare the hexahydrate in Bit is then only necessary to warm that vessel... 

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