without pro- 

 cess. 



Further trial. 



Did not svtc- 

 -cced. 



More oxide 

 decomposed 

 the acid. 



Proust found 

 the same, 



Sfirtholilf's ex- 



perimentv 

 repeated. 



tUSTORY OF THE GAELIC ACtD. 



alkaline base, I washed it well with boiling, water, and then 

 boiled it for some time in a fresh quantity of water. I then 

 treated it with gallic acid, and evaporated to the consi tence of 

 thick honey. I then added distilled water: and. the liquor, 

 after being filtered, was colourless, limpid, without taste, and 

 without smell. On evaporating to dryness nothing remained. 



This difference from the result obtained by Mr. Berthollet 

 led me to suspect, that I had fallcD into some error. T there- 

 fore repeated the experiment with all the attention possible. 



I dissolved 6l grammes of gallic acid, confusedly crystallized 

 and very brown in 500 grammes of boiling water. Part of this 

 solution 1 set by as a standard of comparison : the rest I boiled 

 with 6*1 grammes of oxide of tin well washed, and still wet. 

 When about "half the liquor was wasted, I made it up to its 

 original weight with fresh water, compared it with the standard, 

 and found it had lost a great deal of its colour. The difference 

 of acidity was scarcely perceptible. It still precipitated glue : 

 but the precipitate was yellow and floculcnt, while that of the 

 solution not purified was brown, heavy, mote copious, and even 

 united in a mass. It appears, that the acid was not yet decom- 

 posed : but I could not obtain crystals equally white and pure 

 with those afforded by sublimation, as Mr. Berthollet did. 



Desirous of knowing whether a fresh quantity of oxide of tin 

 would deprive the acid of tannin entirely, I added to the liquor 

 30 grammes of oxide of tin, and evaporated till about 100 

 grammes of liquor only remained. It passed through the filter 

 clear and colourless, and precipitated neither sulphat of iron 

 nor glue. I could not obtain any gallic acid by evaporation. 



This experiment proves, that it is very difficult to free gallic 

 acid completely from tannin ; and that by repeating the action 

 of oxide of tin the acid is decomposed. Thus no doubt Mr- 

 Proust proceeded ; for this chemist observed,, in his memoir 

 printed in the Annates dc C/timie, vol. 42., that the oxide of tin 

 he employed to purify the gallic acid afforded him as a product 

 only a colourless insipid liquor, without taste, and not having 

 the s lightest effect on solutions of iron or tincture of litmus. 



As to the means proposed by Mr. Bartholdi, I do not 

 imagine they can be employed. Yet, as the author neglected 

 to examine the products of-his operations, I thought it necessary 



t* 



