30G Mr. Crum on the Acetates of Alumina. 



alumina is precipitated. The properties of the alumina are at the same 

 time materially changed. 



A solution of binacetate of alumina, diluted so as to contain not more 

 than 1 part of alumina in 200 of water, was placed in a close vessel which 

 was immersed to the neck in boiling water, and kept in that state day 

 and night for ten days. It had then nearly lost the astringent taste of 

 alum, and acquired the taste of acetic acid. The liquid was now placed 

 in a wide and shallow vessel, where it was kept at a uniform depth of a 

 quarter of an inch ; and on heat being applied to make it boil briskly 

 over the whole surface, the acetic acid was driven off in about an hour 

 and a-half, so as to be no longer sensible to litmus paper. The liquid in 

 this operation should not contain more than 1 part of alumina in 400 of 

 water, and the loss from evaporation is supplied by continual additions 

 of water. 



The solution thus obtained is nearly as transparent and limpid as 

 before the loss of its acid. By longer boiling, and particularly by concen- 

 tration, it becomes more and more gummy ; a quality of which it is 

 partially deprived by acetic acid. It is altogether tasteless. 



When one grain of sulphuric acid (SO3) in 1000 grains of water, is 

 mixed with 8000 grains of the solution, containing 20 grains of alumina, 

 the whole is converted into a solid transparent jelly. By pressure in a 

 bag the liquid part of this jelly is readily separated from the solid; whose 

 volume in the compressed state, is not more than g\j or J,y of the volume 

 of the jelly. On examination it was found that the solid part of the 

 coagulum contained almost the whole of the sulphuric acid which had 

 produced it — about one equivalent of sulphuric acid to fifteen of alumina. 



One atom of citric acid (tribasic) coagulates as powerfully as three 

 atoms of sulj)huric acid ; and tartaric acid (bibasic) as much as two. 

 Two atoms of oxalic acid are required to produce the same effect as one 

 of sulphuric acid. Of muriatic and nitric acids not less than 300 

 equivalents must be employed to produce an effect equal to that of one 

 equivalent of sulphuric acid. 



Of the other acids which have been tried, the chromic, molybdic, 

 racemic, suberic, salicylic, benzoic, gallic, lactic, cinnamic, butyric, valer- 

 ianic, carbazotic, camphoric, uric, meconic, comenic and hemipinic acids 

 all coagulate the solution ; but their exact power has not been ascertained. 



The acetic, formic, boracic, arsenious, aud cyanuric acids do not 

 coagulate, at least when moderately concentrated ; and, of the opium 

 acids, for a supply of which I am indebted to Professor Anderson, the 

 pyromeconic and opianic aci<is also do not coagulate. 



One grain of potash in lUOO grains of water coagulates 9000 grains of 

 the solution — a proportion which gives about 1 equivalent of potash to 

 20 of alumina. The mixture has a slight alkaline reaction. Soda, 

 ammonia, and lime have an equally powerful effect. The coagulum they 

 produce is partially re-dissolved when the alkali is saturated by acetic or 

 by muriatic acid. The salts which arc thus formed render the solution 

 somewhat oily. 



