56 Report on the Memoirs presented to the 



wards s:uv that this substance was very slightly of a co- 

 louring nature by itself: he observed that the acetate of 

 potash well saturated, is found a> a consequence of its eva- 

 poration with an excess of alkali ; and it is this excess of 

 alkali which reacts on the foreign principle contained in 

 the distilled vinegar, and colours it. In order to show 

 more clearly this reaction of the potash, he divided into 

 two equal portions a solution of acetate of potash : he eva- 

 porated both at the same degree of heat, maintaining con- 

 stantly in the one an excess of acid, and in the other an 

 excess of alkali : the salt produced by the liquor with ex- 

 cess of acid was much less coloured than that furnished by 

 the liquor with an excess of alkali *. After having ascer- 

 tained the origin of the colouring principle and the cause 

 which develops it, the author next endeavoured to destroy 

 it; and charcoal in his opinion is the fittest agent: with, 

 this view he filters the distilled vinegar through charcoal, 

 he then saturates it with carbonate of potash, leaving in it 

 an excess of acid, which he takes care to keep constantly 

 in the liquor during its evaporation. The result is an ace- 

 tate equally white with that obtained by means of fusion. 



This process, although very simple, did not appear to 

 him to be practicable, because the acetate of potash is 

 mixed with a certain quantity of acetate of lime, to which 

 the lime contained in the charcoal has given rise; and this 

 salt, by altering the purity of the acetate of potash, retards 

 its desiccation. It would, indeed, be very easy to separate 

 it by adding a slight excess of carbonate of potash, in order 

 to precipitate the lime j and we should afterwards put in an 

 excess of acid : but it is easier to saturate the acid first. 

 The following is the process as described in the memoir: 



Pour into distilled vinegar a solution of carbonate of 

 potash, until no mere carbouic acid is extricated: after- 

 wards evaporate the liquor, taking care always to Keep an 

 excess of acid in it : when it is reduced to three-fourths, 

 allow it to cool, in order to separate from it the sulphate 

 of potash and some impurities; decant it in order to heat 

 it, and pour it when hot on a charcoal filter f. 



* We have reason to believe, from our own experiments, that the potash 

 st'll reacts, but much less on the colouring principle, even when the liquor 

 contains an excess of acid •, since by operating in this manner we always 

 obtain an acetate cf potash which is more or less coloured, whilst the same 

 vinegar is capable of furnishing acetate of lime, magnesia, and aluminc, 

 wh»ch are very white. Soda did not appear to us to act so strongly as 

 potash on this principle. — Kmte ty the ConuutHet. 



f The acetate of lime when dried is less deliquescent than the acetate of 

 potash, and yet it is much more difficult: to produce the desiccation of it. — 

 ■Note hj the Juihor. If 



