All the other vegetable principles differ from the 

 vegetable acids in containing more hydrogene and car- 

 bon, "or less oxygene ; many of them therefore are 

 easily converted into vegetable acids by a mere sub- 

 traction of some proportions of hydrogene. The ve- 

 getable acids, for the most part, are convertible into 

 each other by easy processes. The oxalic contains 

 most oxygene ; the acetic the least : and this last sub- 

 stance is easily formed by the distillation of other ve- 

 getable substances, or by the action of the atmosphere 

 on such of them as are soluble in water ; probably 

 by the mere combination of oxygene with hydrogene 

 and carbon, or in some cases by the subtraction of a 

 portion of hydrogene. 



Alcohol, or spirits of wine, has been often men- 

 tioned in the course of these Lectures. This sub- 

 stance was not described amongst the vegetable princi- 

 ples, because it has never been found ready formed in 

 the organs of plants. It is procured by a change in 

 the principles of saccharine matter, in a process called 

 vinous fermentation. 



The expressed juice of the grape contains sugar, 

 mucilage, gluten, and some saline matter, principally 

 composed of tartaric acid : when this juice, or must, 

 as it is commonly called, is exposed to the tempera- 

 ture of about 70, the fermentation begins ; it be- 

 comes thick and turbid ; its temperature increases, and 

 carbonic acid gas is disengaged in abundance. In a 

 few days the fermentation ceases ; the solid matter 

 that rendered the juice turbid falls to the bottom, and 

 it clears ; the sweet taste of the fluid is in great mea- 

 sure destroyed, and it is become spirituous. 



