178 On the Definite Proportions in which the [March;, 



Acid 15-92 100 



Base 84-08 528 



100-00 



But 173-97 X 3 = 521-91. Hence in the subgallate the acid is 

 combined with thrice as much base as in the neutral gallate. 



One part of gallate of lead, equivalent to 0-36'5 of acid, pro- 

 duced by combustion 0-1568 water and 0*77 carbonic acid. These 

 quantities indicate 5-05 per cent, hydrogen and 57*37 carbon. 

 Hence the oxygen is 37*68. 



0-4 of melted gallic acid produced by combustion 0-1 7 water, 

 equivalent to 4-994 per cent, of hydrogen, and 0-833 carbonic acid, 

 equivalent to 56*64 carbon. The difference between these two 

 results is owing to the decomposition of the gallic acid, by means of 

 which the quantity of carbon is increased. This acid, then, is 

 composed of 



Hydrogen 5-00 



Carbon 56-64 



Oxygen 38-36 



100-00 



But 12*44 X 3 = 37*32, which approaches very nearly to the 

 result of the Brst experiment ; but if these 38-36 are three volumes, 

 we find that the carbon and hydrogen constitute each six volumes j 

 so that gallic acid is composed of6H + 6C + 30; which con- 

 stitutes per cent. 



Hydrogen 5*02 



Carbon 56-96 



Oxygen 38-02 



100-00 



From all tliis it follows, that if we take two volumes of carbon 

 from gallic acid, it becomes acetic acid ; if we farther take two 

 volumes of hydrogen, the remainder will be succinic acid. 



Theuard and Gay-Lussac, in their Recherches Phys. Chimiques, 

 ii. 321, have established three laws for vegetable combinations : — 

 1. That a substance is acid when its oxygen has to its hydrogen a 

 greater ratio than exists in water between these two bodies. 2. That 

 a substance is resinous, oily, or alcoholic, when its oxygen has to 

 its hydrogen a smaller ratio than in water. 3. That every vegetable 

 substance in which the oxygen bears to the hydrogen the same ratio 

 as in water is analogous to sugar, gum, starch, wood. The analysis 

 of acetic and gallic acids shows us what value ought to be attached 

 to the first and la^t of these laws. We shall find afterwards, by the 

 analysis of benzoic acid, that the second law is equally erroneous. 



Before proceeding further, it will be necessary to make some 

 observations on the substances which have been analyzed. They 



