CYNIPS QUERCUS FOLII. 



posed of the sesquisulphate is converted into the protosul- 

 phate, owing to the tannic acid attracting the oxygen. The 

 precipitate is a compound of gelatine 54 -j~ tannic acid 46 = 

 100, and is known under the name of Tanno- Gelatine. It 

 affords a pretty accurate test of the quantity of tannic acid 

 contained in any astringent vegetable infusion or decoction. 

 If an excess of the solution of gelatine, however, be added to 

 the vegetable infusion, the precipitate is re-dissolved. Lime- 

 water and barytic water precipitate tannic acid from its solu- 

 tion, the precipitate being a compound of the earth and the 

 acid ; but when the earth is separated by an acid, the freed 

 tannic acid again acts upon gelatine. It also precipitates all 

 the salts of quinia, morphia, strychnia, and the other alkaloids 

 from their solutions. From the analysis of Berzelius, the 

 constituents of tannic acid appear to be: hydrogen 4,186, 

 carbon 51,160, oxygen 44,654, in 100,000 parts ; but accord- 

 ing to Liebig it consists of 51.17 carbon + 44.09 oxygen + 

 4.12 hydrogen, or 18 eq. of carbon + 12 oxygen + 8 hydro- 

 gen, equiv. = 216.16. (C 18 Hja O 5 .) 



Braconnot has discovered in galls a new acid, which he has 

 called Ellagic, a word derived from reversing the word Galte, 

 in French, and adding ic, a singular and whimsical inno- 

 vation in nomenclature. This acid possesses peculiar proper- 

 ties, is insipid, inodorous, white, with a slight tinge of red ; 

 and is insoluble in boiling water, on which account it is read- 

 ily separated from gallic acid in the process of obtaining it 

 When ellagic acid is mixed with nitric acid and gently heat- 

 ed, the mixture acquires a red hue, and ultimately becomes 

 blood-red ; it is owing to the presence of this acid, therefore, 

 that nitric acid, added to the infusion of galls and of oak- 

 bark, produces a blood-red color. In the infusion of galls, 

 the application of heat causes the partial decomposition of 

 the nitric acid, nitrous fumes are emitted, and both the gallic 

 and the ellagic acids are converted into oxalic acid. 



In preparing galls for medicinal purposes, it is of impor- 

 tance to obtain the astringent matter as free from the other 

 ingredients with which it is combined as possible. The galls 

 should therefore be simply infused in distilled water of a tem- 

 perature not exceeding 180 ; this takes up little more than 

 the tannic acid, but when the galls are boiled, the starch is 

 partly converted into a tannate, which precipitates as the 

 decoction cools. The infusion in cold water is a very delicate 



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