J 8 15.] Elements of Organic Nature are combined. 177 



crystals in a small retort to a moderate heat. They at first gave out 

 water, and then sublimed, and left a blackish brown mass, in 

 which it was easy to recognise the presence of tannin ; so that these 

 crystals had been composed of gallic acid and tannin. The sub- 

 limed acid was colourless, had a bitter taste, and a smell somewhat 

 empyreumatic, owing no doubt to a portion of tannin having been 

 decomposed by the heat. 



The sublimed acid does not alter the colour of litmus. It dis- 

 solves readily in water, and the solution immediately blackens a 

 solution of iron; but it does not decompose the earthy carl)onates. 

 The alkaline carbonates are decomposed by it; and if the mixture 

 contains an excess of alkali, it speedily becomes brown. This 

 decomposition does not appear to take place if the air be excluded. 

 In consequence of the property which gallic acid has of being 

 decomposed by the influence of the bases with which it is combined, 

 it is difficult to obtain a gallate which is not somewhat altered. To 

 obtain a gallate of lead as pure as possible, I dissolved gallic acid in 

 a very small portion of water, and added carbonate of ammonia in 

 a solid form. I tiien put the mixture under the receiver of an air- 

 pump, along with sulphuric acid. When the ammonia ceased to 

 effervesce, I pumped out the air. The surplus of ammonia flew off 

 first, and then the water evaporated. The saline mass remaining 

 had a yellowish colour. I dissolved it in warm water, and poured 

 into the solution a boiling solution of nitrate of lead. The whole, 

 being put into a phial (wiiich was filled with it), was digested till 

 the gallate of lead assumed the form of grains, which readily 

 separated from the liquid. I decanted off the liquid, and filled the 

 phial with boiling water ; and this I repeated till the gallate was 

 sufficiently washed. I then threw it on a filter, and dried it at first 

 by pressure between folds of blotting-paper, and then in a vacuum. 

 The gallate of lead thus obtained formed a white crystalline 

 powder with a shade of grey. After being exposed to the air for 

 some days, it became brown ; but the analytical experiments were 

 made as soon as it became dry. 



200 of gallate of lead formed \'J'2'l of sulphate of lead, equi- 

 valent to 127 of oxide of lead. Hence it follows that the salt is 

 composed of 



Gallic acid 36-5 100 



Oxide of lead C3-5 173-07 



The analysis by combustion furnished only C3 per cent, of oxide 

 of lead. The oxygen contained in 173-U7 «* oxide of lead is 

 12-44. 



Gallate of lead is not easily decomposed by ammonia. The 

 alkali must be concentrated and hot. 1 obtained by that means a 

 subgallatc, which, being dried in the ten)peraturc of 230'^ in a 

 vacuum, where it deposited its water of combination, gave by 

 tombusiion 8'l-08 per cent, of oxide of lead. Hence it is com- 

 posed of 



Vol. V. N*' III. M 



