10 
Avhere a change of color must be depended on for ascertaining the 
end of the reaction, the titration of colored liquids, which is not an 
infrequent occurrence in alkaloidal assaying, presents no little diffi- 
culty; and while phenolphthalein has in such cases the advantage 
over most other indicators in that the end reaction is not indicated 
simply by a change from one color to another, but from colorless to 
deep pink, still it must be conceded that the end reaction under 
such circumstances, even with phenolphthalein as the indicator, 
can not be obtained in all cases with as much precision as when a 
colorless liquid is titrated. If, however, we convert the estimation 
of the alkaloids into a simple chlorine determination, we can hi 
many cases add to the solution containing the chlorine and acidified 
with nitric acid, a measured excess of a standard silver solution, 
filter, and determine the excess of silver in the filtrate; and if the 
latter happens to be too highly colored so as to obscure the action of 
the ferric indicator, it (or an aliquot portion) can be evaporated to 
dryness on the water bath and the organic matter, to which the 
color is usually due, gotten rid of by ignition, thus leaving the whole 
of the silver in condition to be taken up with nitric acid and titrated 
with standard thiocyanate in the usual wai^. In order to determine 
whether such a volumetric method would be practicable, the following 
experiments were carried out. 
GENERAL MODE OF PROCEDURE. 
It is evident that the practicability of such a method hinges 
almost entirely on whether or not the temperature employed for 
getting rid of the excess of the volatile acid, as well as the length 
of time such temperature is allowed to act, will always insure the 
complete removal of the free acid but leave the portion which has 
become fixed in a stable condition, and therefore also in constant 
proportion to the amount of alkaloid present. Hence in taking up 
any alkaloid it was first determined whether the combmation of 
alkaloid and acid resulting from the evaporation to dixmess of a 
given amount of the alkaloid dissolved in an excess of the volatile 
acid would remain stable, at the temperature chosen, for a time 
sufficiently long as to permit of its being considered stable at that 
temperature for thn purpose m view. The temperature chosen was 
that of the boiling water bath (90-95 C.), since this is the most con- 
venient and almost universally accessible,, as well as requiring little 
or no attention in maintaining it at a reasonably constant temper- 
ature. Having found that such stability exists with the amount 
taken, quantities of the alkaloid varying between certain limits, 
which might conveniently be used in actual practice, were then 
similarly treated, keeping both the temperature and time constant. 
The general mode of procedure was as follows : 
