78 CINCHONA BARKS. 
becomes clear and slightly yellow. This liquid is poured off," and 
the resinous substance is washed by heating it on a water-bath 
with distilled water ; after washing it is heated on a water-bath 
until all the water has evaporated. It is then soft and tenacious at 
the temperature of the water-bath, but becomes hard and brittle 
after cooling. One part of this substance is now heated on a water- 
bath with six parts of alcohol of ninety-two or ninety-four per cent., 
and is thus dissolved, and the solution allowed to cool. On cooling, 
a part of the dissolved substance becomes separated. The clear, 
dark-colored solution is evaporated on a water bath and the residue 
dissolved in five parts of cold alcohol. This second solution leaves 
a small portion of insoluble substance. The clear solution obtained 
by the separation of this insoluble matter, either by decantation or 
filtration, constitutes the reagent employed for the qualitative and 
quantitative estimation of crystalizadble quinine. 
2. EstimaTIon oF QuintnE.—To determine the quantity of qui- 
nine contained in the mixed alkaloids obtained from a cinchona 
bark, one part (one gram) of these alkaloids is dissolved in twenty 
parts of alcohol, of ninety-two or ninety-five per cent., containing 
1.5 percent. of H,SO,, and this solution is diluted with fifty parts 
of pure alcohol. From this solution the quinine is separated at the 
ordinary temperature, by adding carefully, by means of a pipette, 
the above-mentioned solution of iodosulphate of chinoidine as long 
as a dark brown-red precipitate of iodosulphate of quinine (era- 
pathite) is formed. As soon as all the quinine has been precipitated, 
and a slight excess of the reagent has been added, the liquid 
acquires an intense yellow color. The beaker containing the liquid 
with the precipitate is now covered by a watch-glass, and heated 
until the liquid begins to boil and all the precipitate is dissolved. 
The beaker is then left to itself, and, in cooling, the herapathite is 
separated in the well-known beautiful crystals. After twelve hours’ 
rest, the beaker is weighed, to ascertain the amount of liquid, which 
is necessary in order to be able to apply later the necessary cor- 
rection, the herapathite being very slightly soluble in cold alcohol. 
The clear liquid is poured off, as far as possible, on a filter, leaving 
most of the crystals in the beaker, which is now weighed again, to 
ascertain the amount of liquid, and the weight noted. The few 
crystals on the filter are now washed down into the beaker, and as 
much alcohol added as is necessary to redissolve all the crystals at 
the boiling point. The object of this redissolving is to be absolutely 
rae prevent the use of an excess of iodine, the amount of the latter is intentionally 
made insufficient to precipitate all the chinoidine in the form of iodosulphate. Therefore 
the liquid still contains chinoidine, which can be obtained in a very pure state if a little 
sulphurous acid is added before precipitating the alkaloid by sodium hydrate. _ 
