§ 3 2 3 *] estimation of' the alkaloids. 267 
The final reaction is found by filtering, from time to time, a drop 011 
to a glass plate, resting on a blackened surface, and adding the test 
until no precipitate appears. The results are only accurate when the 
strength of the solution of the alkaloid is about 1 : 200, and when the 
solutions are pure ; so that it is absolutely necessary first to ascertain 
approximately the amount present, and then to dilute or concentrate, 
as the case may be, until the proportion mentioned is obtained. 
Similarly, the iodine solution described on p. 251 may be used volu- 
metrically by precipitating the alkaloid by the solution, filtering, and 
then ascertaining by means of thiosulphate solution the amount of free 
iodine in the filtrate ; if the iodine solution is standardised by approxi¬ 
mately equal weights of the particular alkaloid under investigation, the 
process is capable of giving fair results, although more adapted for 
technical use than for forensic cases, as the precipitates, both with iodine 
and Mayer’s reagent, have not always a definite composition, being in¬ 
fluenced by solubility, concentration, and the presence of other bodies. 
It is useful for quantitative purposes to combine an alkaloid with gold 
or platinum, by treating the solution with the chlorides of either of those 
metals—the rule as to selection being to give that metal the preference 
which yields the most insoluble and the most crystallisable compound. 
The following table gives the percentage of gold or platinum left on 
ignition of the double salt:— 
Gold. 
Platinum. 
Atropine .... 
31-57 
Aconitine .... 
20-0 
, , 
Amanitine 
44-23 
. # 
Berberine .... 
29-16 
18-11 
Brucine .... 
# # 
16-52 
Cinchonine 
, # 
27-36 
Cinchonidine 
, # 
27-87 
Codeine .... 
# # 
19-11 
Coniine .... 
29-38 
Curarine .... 
32-65 
Delphinine 
26-7 
• • 
Delphinoidine . 
29-0 
15-8 
Emetine .... 
29-7 
Hyoscyamine . 
34-6 
• . 
Morphine .... 
• . 
19-52 
Muscarine.... 
43-01 
. • 
Narcotine .... 
15-7 
15-9 
Narceine .... 
14-52 
Nicotine .... 
# , 
34-25 
Papaverine 
• • 
17-82 
Pilocarpine 
35-5 
23-6 to 25-2 
Piperine .... 
• • 
12-7 
Quinine .... 
40-0 
26-26 
Strychnine 
29-15 
18-16 
Thebaine .... 
18-71 
Theine .... 
37-02 
24-58 
Theobromine 
25-55 
Veratrine .... 
21-01 
• • 
