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. 5. Scheibler has proposed _Phosphotungstic acid_ as a precipitant. Sodium tungstate is digested with half its weight of phosphoric acid, sp. gr. 1·13: on standing, phosphotungstic acid crystallizes. Its solution is said to give a distinct precipitate with 1/200000 of a grain of strychnia and 1/100000 of quina, and with similar amounts of other alkaloids. From this precipitate the alkaloid is obtained by treating with sufficient milk of lime and shaking with ether-chloroform, &c., as before. He recommends the previous removal of impurities by lead acetate and sulphuretted hydrogen as already described (p. 7) (Fresenius, Zeitschr. f. anal. Chemie, 12, 315). 6. _Picric acid_, a saturated aqueous solution, gives precipitates in _neutral_ solutions of morphia and atropia. In solutions acidified with sulphuric acid it gives the following:—morphia, and pseudomorphia, no precipitate; aconitia, a precipitate only in concentrated solutions; other alkaloids of opium, a thick precipitate.[7]