CHEMICAL HISTOIIY OF VINEGAR. 105 



municate with the air, alcohol can be converted into Vinegar, 

 only in vessels exposing the liquors containing it to the free 

 action of the atmbsphere." It was also mentioned that while 

 the vinous fermentation appears never to take place in nature, 

 ready-formed alcohol being never found in plants, the acetous 

 fermentation does, acetic acid, or the pure principle of vine- 

 gar, existing, ready-formed, in the sap of many plants, either 

 uncombined, or united into a salt with the earth lime, or the al- 

 kali potash. Vinegar being the first acid substance which had 

 formed a subject of the Course, the opportunity was here taken 

 to explain the nature of the class of bodies termed Acids by 

 chemists, and to exhibit the characteristic properties, of their 

 sour taste, conversion of vegetable blue colours to red, and 

 union with bases into salts ; the last-mentioned property being 

 illustrated by reference to the action of vinegar upon carbonate 

 of lime, which was experimentally shown, and also by the 

 anecdotes, of the solution of a costly pearl, in Vinegar, by the 

 celebrated Cleopatra, Queen of Egypt, (pearls being composed, 

 chiefly, of carbonate of lime,) and the use of Vinegar, by Han- 

 nibal, in facilitating the passage of his army over the calcareous 

 rocks of the Alps, it being supposed that he might have em- 

 ployed it, to partially dissolve and soften a particular mass 

 of limestone, which might impede his progress through some 

 narrow pass. The nature of Acetic acid was next described 

 and shown by experiments, and the salts which it forms, called 

 acetates, such as acetate of lead, or sugar of lead, acetate of 

 copper, commonly called verdigris, &c., exhibited. The 

 modification of acetic acid obtained from Ants, and termed 

 Formic acid, was also noticed, and its use as vinegar by the 

 Laplanders mentioned. In describing the composition of 

 vinegar, its production from wood, by heat, (in the form of 

 what is called pyroligneous acid) was alluded-to ; and both 

 wood and pure vinegar (or acetic acid) being regarded as com- 

 pounds of carbon and water, the facility with which vinegar 

 is produced from wood, by this means, was illustrated by 

 showing how closely these substances approach to each other 

 in the proportions of their elements; 100 parts of pure wood 

 or lignin, consisting of 50 carbon and 50 water, and 100 parts 

 of pure vinegar, or acetic acid, of 4? 7 carbon and 53 water. 

 But in order to explain in some measure, at the same time, 

 how bodies so widely different in their obvious nature and 

 properties, can be so nearly identical in chemical compo- 

 sition, pure wood was regarded, provisionally, as a combina- 

 tion of 3 atoms carbon 18 and 2 atoms water 18, = 36, while 

 pure vinegar was stated to be (as deduced by Dr. Turner from 

 Dr. Front's analysis) a combination of 4 atoms carbon 24 and 



