26. _Fallacy of Infusion of Litmus as a Test_, _by_ M. Magnus.—When pure water is heated for a sufficient time with infusion of litmus, reddened by an acid, it restores the blue colour. It is supposed that the heat gradually causes the free sulphuric acid, which had occasioned the reddening, to combine with the excess of alkali contained in the infusion, and thus to cause the restoration of the blue colour. Hence this preparation cannot be used to test the [p215] presence of ammonia in a solution, as water alone produces the effect anticipated from the alkali. The earthy salts contained in ordinary water also produce this effect.—_Jour. de Pharmacie_. 27. _Tests for the Natural Colouring Matter of Wine_.—M. A. Chevalier states,—i. That potash may be employed as a re-agent, to ascertain the natural colour of wines, which it changes from red to a bottle green, or brownish green—ii. That the change of colour produced by this substance upon wine is different for wine of different ages—iii. That no precipitation of the colouring matter takes place, the latter remaining dissolved by the potash—iv. That the acetate of lead should not be employed as a test of the colour of wines, because it is capable of producing various colours with wines of a natural colour only—v. That the same is the case with lime-water, with muriate of tin mixed with ammonia, and with subacetate of lead—vi. That ammonia may be employed for this purpose, the changes of colour which it produces not perceptibly varying—vii. That the same is the case with a solution of alum to which a certain quantity of potash has been added, and which may, therefore, be used for the purpose.—_Annales de l’Industrie_. 28. _Test of the Presence of Opium_.—Dr. Hare says he can detect opium in solution, when the quantity is not more than that given, by adding ten drops of laudanum to half a gallon of water. The following is the process:—a few drops of solution of acetate of lead is to be added to the solution containing the drug; after some time an observable quantity of meconiate of lead will fall down: from six to twelve hours may sometimes be required, and the precipitation is best effected in a conical glass vessel, for then, by gentle stirring now and then to liberate that which adheres to the side, the insoluble salt may be collected together at the bottom. About thirty drops of sulphuric acid are then to be poured on to the meconiate by means of a glass tube, after which as much of a solution of red sulphate of iron is to be added in the same manner. The sulphuric acid will liberate the meconic acid, and thus enable it to produce with the iron the appropriate colour, which demonstrates the presence of that acid, and consequently of opium.—_Silliman’s Journal_, xii. 290.