7. _Animal charcoal_, previously purified by hydrochloric acid and thorough washing with water, when digested with neutral or alkaline solutions of alkaloids, not too dilute, absorbs them from the liquid. The charcoal, washed twice or thrice with small quantities of water, is dried at a moderate temperature, and boiled with strong alcohol, which extracts the alkaloid. This process has been used for separating picrotoxin from beer, but has the inconvenience that the alkaloid is liable to gradual oxidation within the pores of the charcoal, and that the separation is never complete. It is this property that has caused charcoal to be recommended as an antidote in poisoning. 8. All alkaloids form with _platinic chloride_ double salts of more or less sparing solubility. These precipitates, washed, dried and weighed, and then burnt, leave metallic platinum, the amount of which yields a clue to the composition of the base. But aconitine and narcotine are only thrown down from concentrated solutions, and a few are not precipitated at all. Hence this test is of only occasional value in toxicological work. The same may be said of _auric chloride_. 9. _Tannin_ or tannic acid, a moderately strong solution in water, throws down most alkaloids. Coffee and tea, and other tannin-containing infusions, have, therefore, been used as antidotes with dubious success. As a test it is not distinctive. 10. _Phospho-antimonic acid_ (Schultze), prepared by mixing antimony pentachloride with ordinary sodium phosphate and decanting the clear liquid, gives whitish amorphous precipitates with alkaloids. 11. _Silico-tungstic acid_ is prepared by boiling commercial tungstate of soda with fresh gelatinous silica. Filter and allow to crystallize. This gives precipitates with very dilute solutions of alkaloids, but it is also precipitated by ammonium chloride (Godefroy, Arch. d. Pharm., Nov. 1879). Zaubenheimer recommends it as a most delicate test: the precipitate may be decomposed by soda or potash, and the base extracted by ether-chloroform. 12. Auric chloride, palladious chloride, and mercuric chloride have been proposed, but are not of much use. Potassium chromate and sulphocyanide, and sodium nitroprusside give somewhat insoluble precipitates, generally crystalline and of characteristic appearance under the microscope. These tests should be strong, and must be used in small quantity.