of Edinburgh, Session 1884-85. 
185 
molecules of sugar (C 6 H 12 0 6 ), the molecular ratio which the product 
of inversion hears to cupric oxide will he exactly two-thirds of that 
of dextrose to cupric oxide, and consequently its cupric oxide 
reducing power or K will be 75. This, however, requires further 
confirmation. But whatever may he the nature of the sugar which 
is produced from this gum, its physical properties are identical with 
those of gum arabic. It is present in urushi juice in the form of an 
acid salt (probably of arabic acid), in combination chiefly with 
potash, lime, alumina and magnesia; and the point of difference 
which is of interest is the presence of an alumina salt, which has 
not hitherto been observed in other gums. A mixture of the gum 
and urushic acid with water in the proportion in which they exist 
in the juice does not undergo any change even when exposed to the 
conditions most favourable for the drying of the lacquer. More- 
over, part of the gum can be extracted in an unchanged state from 
the perfectly hardened lacquer, and since it exists in the original 
juice in the form of aqueous solution, it probably serves to keep 
the constituents of the juice in a state of uniform distribution 
and intimate emulsion. It may also act as a binding material, 
and assist the adhering power of the lacquer when laid on any 
surface. 
III. The Nitrogenous Matter and its action upon Urushic Acid . — 
That portion of the juice which remains insoluble in alcohol and 
boiling water consists essentially of a nitrogenous matter, the action 
of which upon urushic acid is the cause of the hardening of the 
lacquer. It forms from 2 to 8 per cent, of the original juice. The 
juice which contains most of it dries most quickly, but gives a varnish 
of inferior lustre. The substance, separated from the gum by the 
usual method of boiling water, has no action upon urushic acid, but 
the residue (after the separation of urushic acid) or its extract with 
cold water, shows its peculiar diastatic activity in an unimpaired 
degree. When such a solution is boiled, the albuminoid matter 
coagulates in the form of a white precipitate. 
The substance, first dried on a water-bath, and then over sulphuric 
acid, gave on analysis, the following numbers : — 
