186 Analysis of the Chinese Varnish. [May, 



of the nitric acid, a marked smell of bitter almonds is perceived, although 

 on saturation with potash, no trace of prussic acid is found. 



Many chemists have inclined to believe in the identity of the two acids, and 

 have attributed the slight differences observable to the presence of foreign matter. 

 Nevertheless in seeking some method of discrimination, I have observed two 

 circumstances in which the benzoic and succinic acids behave in dissimilar ways. 

 1. With the salts of copper, a very neutral solution of benzoate of ammonia gives 

 a pale blue ashy precipitate, while the succinate furnishes an abundant curdled 

 deposit of a fine green ; neither of the acids alone precipitating copper. 2. With 

 the salts of cobalt, the succinate of ammonia hardly disturbs the liquid, and it is 

 only after a day that a rose coloured deposit is perceived, while the benzoate throws 

 down a copious flocculent precipitate of a pale rose colour. 



By employing these two tests, I ascertained that the acid extracted from the 

 varnish acted like the benzoic. I should add that, when I treated with nitric acid 

 the residue left by the evaporation of the water in which the varnish had been 

 boiled, I obtained, besides the unaltered benzoic acid, a small quantity of oxalic 

 acid, which I attribute to the presence of the little gum which had rendered the 

 alcoholic solution opalescent, but which was in too small a proportion to be 

 separated. 



If the varnish is distilled in a retort with water, there passes into the receiver 

 an essential oil, white, transparent, swimming on the water, of a strong scent, 

 similar to that of the varnish itself, of a very acrid taste, disagreeable and per- 

 sistent, having all the properties of other essential oils, without any apparent 

 peculiarity. 



Boiled with dilute sulphuric acid, the pungent odour of the varnish disap- 

 pears, and an iridescent white pellicule forms on the surface of the liquid, giving 

 to the vessel and liquid, by reflection, a fine blood red or purple colour ; but on 

 removal from the fire, the liquid is seen to be colourless. The pellicule maybe 

 skimmed off in scales : it is dry, insipid, soluble in turpentine, which it colours 

 yellow ; insoluble in caustic potash ; it becomes brown in alcohol and ether, by 

 degrees losing this colour and imparting a milky tinge on solution : on the 

 addition of a few drops of water, the alcohol becomes sensibly acid ; heated 

 j>er se the purple matter softens, melts, loses colour, turns black, and reddens 

 litmus strongly ; heated in boiling distilled water, it is also discoloured without 

 imparting any tint to the water, which becomes strongly acid ; and the residue 

 dissolves entirely in alcohol with the aid of a gentle heat. Water renders this 

 solution milky, and this residue appears to be nothing but resin little altered 

 The solution shewed indications of acid, which, saturated with potash, dried and 

 strongly heated, gave out an odour of sulphurous acid, one of the charac- 

 teristic marks of hyposulphuric acid ; the residue was merely sulphate of potash. 

 The purple matter therefore appears to be a compound of resin and sulphuric 

 acid modified in its composition, and to be nothing therefore but another form 

 'of artificial tannin. This led me to imagine, that the artificial tannin produced 

 by the action of sulphuric acid on resin should give analogous results : and in 

 fact, sulphuric acid diluted with twice its weight of water having been mixed 

 with cclophony (resin) in powder, the liquid took a brown colour, and by the 

 gentle heat of the sun disengaged sulphurous acid : the filtered solution evapo- 

 rated and washed, presented all the characters of tannin. The excess of sulphu- 

 ric acid having been separated by barytes, the liquid was evaporated, and the 



