^8880 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 475 



lacquer is due. With plumbic acetate it yields a gray, flocculent pre- 

 cipitate. 



Although the drying, or rather the hardening, properties of lacquer 

 are doubtless clue to the oxidation of urusliic acid, the product extracted 

 by alcohol, as described above, possesses no drying qualities. This fact 

 was first observed by Professor Rein, in 1874:. More recently Korschelt 

 and Yoshida have investigated the process of lacquer hardening, and 

 have found that a peculiar albuminoid of lacquer effects the drying by 

 a diastatic or fermentive action. It is rather surprising that some one 

 has not ascribed the result to a new species of bacterium, but this is 

 doubtless due to the fact that the microscopists and bacteriologists have 

 not yet got to work on lacquer. The fact seems to be that the lacquer 

 hardens only when the albuminous substance is present. If heated 

 above 60° C, or above the temperature at which albumen coagulates, 

 the lacquer will not dry. 



The authors mentioned regard the drying as a process of oxidation 

 "brought about in some way by the albuminoid, C u Hj 8 3 +0=Ci 4 H 18 

 3 . Professor Rein, however, maintains that the process of hardening 

 is not so simple, for the reason that moisture is essential to the drying 

 of lacquer. The drying takes place only within a narrow range of tem- 

 perature — between 20° and 27° is the most favorable; Korschelt and 

 Yoshida have shown that no water is taken up by the acid in drying. 



The strongest evidence of the importance of the albuminoid to the 

 hardening process is found in the fact that while the urushic acid will 

 not dry by itself, it immediately hardens if a portion of the unboiled 

 gum and albumen that does not dissolve in alcohol be added to it, 

 and the rapidity of hardening depends upon the proportion added. It 

 is notable that the albuminoid does not lose its peculiar property of 

 effecting this oxidation by treatment with alcohol. This nitrogenous 

 constituent obtained from the aqueous solution has not been satisfac- 

 torily studied. It seems to contain less hydrogen than albumen. 



Besides urushic acid and the albuminoid raw lacquer contains a gum 

 resembling gum Arabic, which doubtless imparts some useful proper- 

 ties to the lacquer, and a volatile acid, to which Professor Rein ascribes 

 the poisonous effects of lacquer. 



The proportion of urushic acid varies from 85 to GO per cent, in dif- 

 ferent samples; of gum, from 3 to per cent.; nitrogenous substance, 

 2 to 3 per cent.; water, 9 to 33 per cent. 



Oxy urushic acid, the product of the oxidation of urushic acid, as 

 already explained, may be obtained by treating urushic acid with chromic 

 acid. The mixture becomes first pasty, then solid, and of a brown color. 

 The product was analyzed and gave the formula C u n 13 O,. It is in- 

 souble in every solvent tried: caustic alkalies, hot or cold, boiliug hydro- 

 chloric and sulphuric acids have no effect. Boiling nitric acid converts 

 it into a yellow mass, which gradually dissolves. 



The investigations of Korschelt and Yoshida included the study of 



