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sable in order to keep the nitrogenous and gummy substances dissolved 

 and to insure uniform drying when used. 



Urushiol: — Crude lac contains 60-80% of urushiol, the most impor- 

 tant ingredient of lac. Freshly collected crude lac is translucent, but it 

 turns to a dark brown viscous liquid when exposed to the air. Urushiol is 

 soluble in common organic solvents and it readily hardens with lac juice 

 when exposed to the air owing to the nitrogenous matter contained in it. 

 Pure urushiol, however, does not readily harden; yet it does so when 

 heated at a temperature of 100''-150°C. Once dried, it is no more liable 

 to be attacked by ordinary solvents such as ether, alcohol, benzine or even 

 by acids and alkalies. 



Nitrogenous Substance : — The nitrogenous substance contained in crude 

 lac is only 2-3% but it gives an important drying property to urushiol; 

 the substance is insoluble in ether or alcohol, but it is soluble in water 

 to a certain extent. When heated above 60°C. the nitrogenous substance 

 renders urushiol hard to dry. 



Gummy Substance: — The gummy substance contained in crude lac 

 ranges between 7-20% or sometimes over 30%, rendering the lac viscous 

 and often hindering the work of lacquering. The gummy substance which 

 left on the coated surface after hardening of lac absorbs the moisture and 

 thereby renders the surface weak, so a large content of this substance in 

 the liquid is undesirable. 



Since the knife or spatula used in tapping are daubed with the oil 

 for easy working crude lac commonly contains a small quantity of perilla 

 oil but it is not an ingredient of lac itself. 



The lacquer used in varnishing is further mixed with a certain quantity 

 of the same oil, because pure lac is expensive and it produces a rather 

 rough and less lustrous effect; moreover, it is not easy to put on pure 

 lac. For containing the crude lac, wooden tubs or bent wood cases are 

 commonly used. When kept for a long time, the water and gummy 

 substance generally settled to the bottom while the urushiol always floats 

 as a thin liquid of brownish black color. Thus, the upper part of the 

 crude lac in a tub is therefore generally far superior than the lower part. 

 For this reason, in taking the sample for analysis, the tub must be care- 

 fully stirred from the bottom, otherwise a considerable error will occur 

 in estimating the value. 



