In the search for morphia the filtered fluid above referred to is also to be treated with sulphuretted hydrogen, to secure the precipitation of all acetate of lead, &c., which is next to be carefully separated from it by further filtration. The fluid now passing through, containing the acetate of morphia, is next to be concentrated by evaporation over a water bath, and carefully neutralized by bicarbonate of potass, if it be desired to obtain the pure alkaloid; but this is not necessary, as the acetate responds to all reagents. The acetate may be dissolved out of the mass in dilute alcohol (it is not soluble in ether), again filtered, the filtrate being finally evaporated to dryness and tested. MORPHIA.—The best tests for this alkaloid, in substance or in solution (substance is preferable) are: 1. Nitric acid, which strikes an orange red color, varying in intensity with the strength of the acid and the concentration of the morphia solution. Ruddy fumes are also developed. 2. Neutral perchloride of iron, strikes a rich blue color with morphia when added in small quantity; if added in excess, the yellow of the test, combining with the blue, may produce a green. This blue is destroyed by acids and by heat. Nitric acid not only destroys the blue produced by this test, but replaces it with the orange-red color; so that the nitric acid test may be applied to the same portion of morphia after the iron test, but not _vice versâ_. 3. Iodic acid. This acid becomes decomposed, owing to the reducing action of morphia, setting free the iodine. The latter is detected by its brown color, and the blue which it strikes with starch. The iodic acid should be previously tested to ascertain its purity, as it occasionally contains free iodine. 4. Bichromate of potassium gives a green with morphia, passing to a dingy brown. MECONIC ACID.—This is obtained from solutions of opium, in the form of little scaly crystals of a reddish tint, which are decomposed by heat and partly sublimed. In solution it may be detected by its acquiring a blood-red color on the addition of the perchloride of iron. A similar color is produced by sulphocyanide of potassium, as found in the saliva; but the color of the meconate is not discharged by chloride of gold; the sulphocyanide is. NARCOTINE dissolves in sulphuric acid with a yellow color, converted into a carmine red by the addition of a trace of nitric acid. CHAPTER XXIII. ANÆSTHETICS. NEUROTICS ACTING ON THE BRAIN AND PRODUCING INSENSIBILITY. CHLOROFORM—CHLORAL—BICHLORIDE OF METHYLENE—ETHER—AMYLENE—NITROUS OXIDE. The anæsthetics which have hitherto been employed in the practice of medicine are chloroform, sulphuric ether (or a mixture of these), bichloride of methylene and nitrous oxide, and amylene. Any of these agents may cause death when introduced into the system by inhalation.