Aluminium ammonium ferrocyanide

Aluminium ammonium ferrocyanide, Al(NH4)Fe(CN)6.4H20, is formed as a jelly on mixing equivalent solutions of aluminium chloride and ammonium ferrocyanide.6 The salt is difficult to isolate, but is obtained as a precipitate by centrifugating at 3000 revolutions per minute. The precipitate is washed with acetone and ether and dried in vacuo. It resembles the potassium salt in appearance, being dark green and transparent m lumps, but a light bluish green when powdered. At 100° C. it becomes anhydrous and assumes a deep blue colour. 

Aluminium ferrocyanide, Al4[Fe(CN)6]3.17H20, is formed when solutions of alum and potassium ferrocyanide are mixed in the cold,5 the alum being (presumably) in excess6 otherwise the double aluminium ammonium salt is produced. 

There are several salts that behave in this way at atmospheric temperatures, the more important being ammonium acetate potassium bromate, carbonate, cyanide, ferricyanide, ferrocyanide, iodate, and permanganate disodium hydrogen phosphate and sodium borate and carbonate.4 In the case of potassium chlorate the points L and S appear to be practically coincident, whilst for the majority of salts the point S lies somewhere to the left of L, namely at S —that is to say, saturation occurs before the limiting concentration is reached. Generally speaking, at the ordinary temperature, concentrated solutions of salts are less corrosive than distilled water—that is, the point S lies below the level of A, exceptions being 5 ammonium sulphate, aluminium... 

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