VEGETABLE ALKALOIDS. 
§ 309-1 
251 
the precipitate is in the form of minute dots, but the majority of the 
precipitates are amorphous, and all are more or less coloured. 
Iodine dissolved in a solution of potassic iodide gives with alkaloids 
a reddish or red-brown precipitate, and this in perhaps a greater dilu¬ 
tion than almost any reagent. Since the testing solution may be also 
used for ascertaining the weight of the alkaloid, it is convenient to make 
it a decinormal one, that is, 12-7 grins. I and 60 grms. KI, dissolved in 
a litre of water. When added to an aqueous solution, the precipitates 
are amorphous, but if added to an alcoholic solution, certain alkaloids 
then form crystalline precipitates ; this, for example, is the case with 
berberine and narceine. The aqueous solution should be either neutral 
or feebly acid. The alkaloid may be recovered by the process detailed 
on page 255. A solution of bromine in potassic bromide solution also 
gives similar precipitates to the above, but it forms insoluble compounds 
with phenol, orcin, and other substances. 
Mercuric potassic iodide is prepared by decomposing mercuric 
chloride with potassic iodide in excess. The proportions are 13*546 
grms. of mercuric chloride and 49-8 of potassic iodide, and water 
sufficient to measure, when dissolved, 1 litre. The precipitates from 
this reagent are white and flocculent; many of them become, on 
standing, crystalline. 
Bismuthic potassic iodide in solution precipitates alkaloids, and the 
compounds formed are of great insolubility, but it also forms compounds 
with the various albuminoid bodies. 
Iodised parethoxyphenyl succinimide is another reagent which 
precipitates alkaloids, and is said to be even more sensitive than iodine 
in pot. iodide. 
Chloride of gold forms with the alkaloids compounds, many of which 
are crystalline, and most admit of utilisation for quantitative determina¬ 
tions. Chloride of gold does not precipitate amides or ammonium com¬ 
pounds, and on this account its value is great. The precipitates are 
yellow, and after a while are partly decomposed, when the colour is of a 
reddish-brown. 
Platinic chloride also forms precipitates with most of the alkaloids, 
but since it also precipitates ammonia and potassic salts, it is inferior to 
gold chloride in utility. 
§ 309. 1. Phosphomolybdic Acid as a Reagent for Alkaloids.— 
Preparation: Molybdate of ammonia is precipitated by phosphate of 
soda ; and the well-washed yellow precipitate is suspended in water and 
warmed with carbonate of soda, until it is entirely dissolved. This solu¬ 
tion is evaporated to dryness, and the ammonia fully expelled by heat¬ 
ing. If the molybdic acid is fairly reduced by this means, it is to be 
moistened by nitric acid, and the heating repeated. The now dry residue 
is warmed with water, nitric acid added to strong acid reaction, and the 
