54 Report on the Memoirs presented to the 



it is of a vegeto- animal nature, cither from the smell which 

 it exhales when placed on hot coals, or hy the prussiale 

 of ammonia which upon distillation furnishes the acetate 

 of potash prepared with distilled vinegar: a product 

 which does not give the same salt prepared with radical 

 vinegar : w hence the author concludes that the radical prin- 

 ciple which colours the acetate of potash is no'hing but a 

 part of the ferment of common vinegar, carried into the 

 distillation and more or less altered bv this operation. 



Independently of this colouring principle, inherent in 

 the constitution of common vinegar, the author of the 

 memoir mentions another still more capable of making 

 the acetate of potash look brown: this is the empvreumatic 

 oil with which the vinegar is charged when the distillation 

 is carried too far. He further says, that this salt may also 

 be coloured by the oxides of iron and of manganese con- 

 tained in the alkali, or by the metallic utensils used in its 

 preparation : but this colour being merely accidental, we 

 may avoid it entirely by using a pure potash and vessels of 

 tin or porcelain. We must therefore adhere to the fer- 

 ment and the empyreumatic oil. The following directions 

 'are given for avoiding these two colouring principles: the 

 ferment may be separated from the acetate of potash the 

 more easily the less of it there is in the distilled vinegar, 

 and the latter will contain so much the less in its turn ; as 

 in common vinegar, the proportion of the ferment will be 

 smaller with respect to that of the arid, on account of the 

 quantity of ferment brought over in distillation being al- 

 ways more or less in proportion with that which exists in 

 common vinegar. It follows therefore that it is necessary, 

 above all, to employ common vinegar, which is at once the 

 most acid and the least charged with ferment; and this re- 

 quisite may be attained by choosing a clear vinegar, be-? 

 sides being very strong and completely fermented. After 

 the choice of the vinegar, the process of distillation may 

 also have some influence on the quantity of the ferment 

 contained in distilled vinegar: for, since this principle is less 

 volatile than the acetic acid, the less of it will pass over in 

 distillation, the more slowly this process is conducted; and 

 in this respect we may admit a slight ebullition as being 

 the fittest degree of heat. 



If the preceding rules have been well attended to, the 

 distilled vinegar will contain so small a quantity of fer- 

 ment that it will be capable of furnishing immediately an 

 acetate of potash almost entirely colourless ; but if, not- 

 withstanding every precaution, the whiteness of the salt 



still 



