42 
ON QUINOIDINE. 
coloured mother-liquor remaining after the crystallization 
of the disulphate of quinine. In the evaporation of this 
liquor, similar changes no doubt take place to those which 
occur in the preparation of extracts ; and the quinoidine 
which is precipitated by the addition of an alkali, will be 
subject to variations, according to the greater or less degree 
of heat, and of atmospheric action to which the liquor has 
been exposed. Again, if, instead of adding an alkali to 
precipitate the quinoidine, the liquor be simply evaporated 
to dryness, the product, will, of course, be very different; 
it will now be more or less soluble in water, in consequence 
of the presence of the acid. Some specimens of quinoidine 
are said to have been obtained in this way. 
Thus quinoidine is liable to variations in quality and in 
composition, arising from two distinct causes. 
In examining specimens of quinoidine, with the view of 
estimating their qualities, the following method may be 
adopted : 
The specimen should be dried by the heat of a water- 
bath, until it ceases to sustain any further loss of weight. 
(a) A weighed quantity of it is to be dissolved in distilled 
water acidulated with sulphuric acid, and ammonia added 
to the solution as long as any precipitate is formed. This 
precipitate is to be collected on a filter, washed, dried by 
the heat of a water-bath, and then weighed. The two 
weighings should correspond, if the specimen be good. 
(b) A portion of the dried specimen is to be treated with 
rectified spirit, in which it should be perfectly soluble. 
Those specimens, the solutions of which have the lightest 
colour, are most free from smell, and in taste approach to 
a pure bitter, may in these respects be considered the best. 
(c) A weighed quantity of the dried specimen is to be 
treated with ether as long as anything is dissolved by this 
menstruum, the solution being promoted by trituration in 
a mortar; the ethereal solution is to be submitted to spon- 
taneous evaporation in a large porcelain dish, and the in- 
