It is certain that many of the poisonous substances which in former times have been detected in beer, such as strychnine, hyoscyamine, picric acid, and picrotoxine, are not used at present. It is much more probable that such bitters as gentian and quassia may be met with, especially at times when hops are dear. These latter far exceed hops in bitterness, and do not exert deleterious effects upon health. Willow bark, or its active principle, salicine, has also been employed. The detection of some of the most apocryphal substitutes for hops is effected, according to Wiltstein,[80] by the following method: One litre of the beer is concentrated over the water-bath to a syrupy liquor, which is introduced into a rather capacious tared cylinder and weighed. The gum, dextrine, and mineral salts are first separated by adding to the syrup five times its weight of 95 per cent. alcohol, with which it is thoroughly mixed, and allowed to digest for twenty-four hours. The clear, supernatant solution is now drawn off, and the residue treated with a fresh quantity of alcohol, which is afterwards united with the solution first obtained, the whole being then evaporated until the alcohol is expelled. A small portion of the residue is dissolved in a little water, and tested for picric acid, as described later on. The remainder is repeatedly shaken with about six times its weight of pure benzol, which is subsequently removed by decantation, the operation being then repeated with fresh benzol, the two solutions added and evaporated to dryness at a very moderate temperature. The residue thus obtained is divided into three portions, which are placed in small porcelain dishes and tested as follows:-- To one portion a little nitric acid (sp. gr. 1·330) is added; if a red coloration ensues, _brucine_ is present; if a violet colour, _colchicine_. A second portion is treated with concentrated sulphuric acid; the production of a red colour indicates the presence of _colocynthine_. To a third portion, a few fragments of potassium dichromate and a little sulphuric acid are added; if a purple-violet coloration takes place, _strychnine_ is present. The portion of the syrup which has remained undissolved by benzol is first dried over the water-bath, and then agitated with pure amylic alcohol, by which treatment picrotoxine and aloes, if present, will go in solution, and impart a bitter taste to the liquid.