24 VINEGAR, CIDER, AND FRUIT-WINES. 



many seeds, and generally ap|>ears in the putrefaction of sub- 

 stances rich in nitrogen, such as albumen, glue, etc. It appears 

 also in the so-called lactic fermentation, the lactic acid formed by 

 the specific ferment of this species of fermentation being by 

 further processes of fermentation decomposed into butyric and 

 acetic acids. 



Acetic acid, belonging to those bodies which may be considered 

 as quite far advanced products of oxidation of higher compound 

 combinations, its occurrence in living organisms is not remarkable. 

 It is found in many fluids of animal origin, for instance, in meat- 

 juice, milk, sweat, and urine. It also occurs constantly in the 

 fresh fruit of the tamarind. What processes take place in its 

 formation in these cases are not known, though it is very likely 

 directly formed from certain varieties of sugar. Just as little do 

 we know about the origin of the acetic acid found in the mineral 

 water of Briickenau. 1 



There is quite a large series of chemical processes in which 

 certain quantities of acetic acid are always formed. Sugar, starch, 

 woody fibre, and, in general, all compounds known as carbohy- 

 drates, when fused with caustic alkalies, always yield certain 

 quantities of acetic acid, as also by themselves when subjected 

 to destructive distillation. 



Among the processes by which acetic acid is produced in a 

 purely chemical manner, /. r., without the cooperation of organ- 

 isms, the most interesting is that by which itvS formation is effected 

 by the action of very finely divided platinum (the so-called plati- 

 num black) upon alcohol. Platinum black is easily prepared by 

 boiling a solution of platinic chloride with an addition of an 

 excess of sodium carbonate and a quantity of sugar until the 

 precipitate, formed after a little time, becomes perfectly black and 

 the supernatant liquor colorless. The black powder is collected 

 on a filter, washed and dried by gentle heat. From its minute 

 state of division this substance condenses within it several hun- 

 dred times its volume of oxygen ; consequently, when the vapor 

 of alcohol comes in contact with it, a supply of oxygen in a 

 concentrated state is presented to it, and the platinum, without 



1 Free acetic acid is also claimed to occur in the water of a river of Brazil. 



