312 Mr. Crum on the Acetates of Alumina. 



aluminous solution more rapidly, and the new acetate then precipitates 

 as a granular powder. At the boiling temperature the liquid is thus 

 deprived, in about half an hour, of the whole of its alumina, which goes 

 down with two-thirds of the acetic acid ; leaving one-third in the liquid. 



4. The red acetates of iron treated in a similar manner do not pro- 

 duce corresponding isomeric binacetates. By heating the binacetate of 

 the sesquioxide there is a total separation of acid and base. The facility 

 with which the binacetate is decomposed, even in the cold, furnished the 

 means of freeing the solution of binacetate of alumina of traces of iroa 

 which could not otherwise be separated from it. 



5. The soluble binacetate of alumina is decomposed by" heat, and 

 affords a new and remarkable product. When a dilute solution of that 

 salt is exposed to heat for several days, the whole acetic acid appears 

 to become free, and the alumina to pass into an allotropic condition, in 

 which, although it remains in solution, it ceases to be capable of acting 

 as a mordant, or entering into any other definite combination. When 

 the acetic acid is expelled by boiling, the alumina, in its altered state, 

 remains alone dissolved in pure water. It is more soluble, however, in 

 acetic acid. The allotropic hydrate of alumina retains two equivalents of 

 water when dried at the heat of boiling water. Its solution is coagulated, 

 more or less powerfully by the mineral, and most of the vegetable acids 

 and their salts ; by the alkalies, and by decoctions of dyewoods. The 

 coagulum which is formed by the various acids, is not re-dissolved when 

 they are added in excess. The solid part of the coagulum yields, 

 however, to the continued action of oil of vitriol, especially if assisted by 

 heat, and the result is the ordinary sulphate of alumina. Boiling potash 

 also dissolves it, and changes it into the ordinary terhydrate. Its coagulum 

 with dyewoods has the colour of the infusion, but is translucent and entirely 

 different from the dense opaque lakes which ordinary alumina forms 

 with the same colouring matters. 



6. The insoluble binacetate of alumina, when digested in a large 

 quantity of water, is gradually changed into the soluble binacetate ; of 

 which a part, however, becomes decomposed during the process into 

 acetic acid, and the allotropic bihydrate of alumina. 



7. The precipitate which is formed on the application of heat to a 

 mixed solution of acetate of alumina and sulphate of potash, andTwhich 

 is soluble in cold acetic acid, is a bibasic sulphate of alumina. 



The Society, on the recommendation of the Council, agreed to meet 

 next Wednesday night for the purpose of overtaking arrears of business. 



Ma>/ 4, 1853. — 27ie President in the Chair. 

 The concluding meeting of the session was held this evening. 



