1832.] Analysis of the Chinese Varnish. 185 



its consistence is viscous, like thick turpentine. It orms, when spread, a brilliant 

 even surface, drying easily, and assuming a fine polish. It fixes well the colors 

 usually mixed with it, as minium, cinnabar, lamp-black ; and forms good 

 colored varnishes, which do not scale off when dry. To mark its difference from 

 turpentine, varnish, and balsam of copahu, whose physical and chemical properties 

 are otherwise so analogous, I ground up with the latter some of the same colors, 

 but found that the varnishes thus made would not dry ; and after three months' 

 exposure to the air, they still yielded to the finger, so as to be totally useless. 



Poured into a vessel of distilled water, the varnish spreads upon its surface, 

 in the form of a yellowish film, which by degrees absorbs water in its pores, and 

 becomes white and completely transparent ; so that it may be said to be hydro- 

 phanous, like some particular minerals. Turpentine has not the same property, 

 but the balsam of copahu has it in some degree : on straining the varnish 

 it becomes opake, and soon grows yellow from the evaporation of the water 

 it had taken up : the water acquires a slightly bitter taste. The varnish 

 dissolves gently, in cold, and more rapidly in hot alcohol ; water precipitates 

 from it an abundant white resin. It is also soluble in ether and in cold spirits 

 of turpentine. 



Digested in boiling water, the varnish whitens and resembles curdled 

 milk ; its own peculiar odour is disengaged, and after long boiling, there 

 remains a white resin, solid, brittle when cold, softening and melting in hot 

 water, soluble in alcohol, in all proportions — whence water precipitates it in a 

 white powder — soluble in turpentine, caustic potash, &c. Heated in a tube gradu- 

 ally raised, the resin gives out much water which it had dissolved : this water is 

 strongly acid, and contains benzoic acid, as will be presently noticed. The resin 

 deprived thus of the water it had absorbed, remains transparent and yellowish : 

 when cold it is hard and brittle, softens and melts at the fire, and under a gradu- 

 ated heat gives out by sublimation white silky flexible crystalline needles of 

 benzoic acid. Soon after a very acid water is disengaged, (acetic acid,) the resin 

 blackens, and decomposition commences. 



On examination of the water in which the varnish was boiled, we find that it 

 reddens litmus, and has a slightly sour taste. Evaporated, it leaves a light residue 

 soluble in alcohol, whence it is precipitable partly by water. This acid saturated 

 with ammonia, acts with re-agents like the benzoic ; it must have existed in the 

 varnish in a free state to be thus separated by simple boiling ; gum benjamin also 

 and balsam of Mecca, when boiled in water, impart a marked acidity and of the 

 same nature. To assure myself, that the acids so dissolved was positively the ben- 

 zoic, (for I remembered that the Italian chemists had proved the existence of succinic 

 acid in turpentines, and this might therefore be the case with the varnish) : — I 

 first sought to recognise the differences between the two, and was surprised. 

 to find, that it was almost impossible to distinguish them. In fact they both melt 

 and volatilize, leaving a carbonaceous residue; both sublime in white, flexible, silky 

 needles; the remarkable property enjoyed by the succinates of precipitating 

 iron of a yellow brown, and forming a soluble salt with manganese, which proves 

 so useful in analysis, belongs also to the benzoates. They precipitate in the 

 same manner the salts of lead, silver, tin, and neither of them affect antimonial 

 solutions. These two only, of all the vegetable acids, dissolve without decom- 

 position in nitric acid, and are recovered unaltered on evaporation. Sometimes, it 

 is true, a few red vapours arise, and when benzoic acid is so treated, on evaporation 



B B 



