Aconitine or aconitia melts at 183° to 184° C.
Pseudaconitine melts at 104° to 105° C., and easily decomposes, giving off water.
Commercial aconitine usually melts below 100° C., and gives an amorphous sublimate above 150° C.
The reactions of the other alkaloids will be found in Blyth’s Practical Chemistry.
In order to avoid repetition, the mode of preparing the general reagents for alkaloids will be given here.
1. Mayers Reagent, potassio-iodide of mercury, already described (p. 7; Liebig’s Annalen, 133, 286), gives white precipitates with almost all alkaloids. The latter can be recovered from the precipitate by treating it with a solution of zinc chloride mixed with caustic soda. (Mayer.)
2. Potassium tri-iodide, a solution of iodine in potassium iodide, gives a brown or reddish precipitate.[6]
3. Sonnenschein’s test, Phosphomolybdic acid, is prepared as follows. To a warm solution of molybdate of ammonia acidified with nitric acid, phosphate of soda is added as long as any yellow precipitate is obtained. The precipitate is washed with water containing a little nitric acid, and heated with sodium carbonate solution till dissolved. Evaporate to dryness, heat to expel ammonia, add a little nitric acid and heat again. One part of the residue is then dissolved in a mixture of one part of nitric acid of 1·4 sp. gr., and nine parts of water. With this reagent strychnia gives a pale, other alkaloids a bright yellow flocculent precipitate, in very dilute solutions. The precipitates are soluble in ammonia, with the production of a greenish blue colour in the cases of aconitia and morphia. From the alkaline liquid the alkaloid can be dissolved out by at once shaking with ether-chloroform or hot amylic alcohol as already described. Instead of using ammonia, the precipitate may be agitated with barium carbonate, which has less tendency to decompose the base on its liberation.
4. A solution of bismuth iodide in iodide of potassium is recommended by Dragendorff (Zeitschr. f. Chimie, 1866, 478). 80 grammes of commercial bismuth subnitrate are dissolved in 200 cubic centimetres of nitric acid of sp. gr. 1·18: 272 grammes of potassium iodide dissolved in a little water are added, the potassium nitrate allowed to crystallize out, and the whole diluted to one litre. This solution precipitates most alkaloids. The precipitate can be treated with sodium carbonate and the liberated alkaloid extracted by ether-chloroform, &c. For the equivalents, see Maugini, Gazz. Chim. Ital. 12, 155.