In case Hoppe-Seyler's method is used, the stains, separated as directed above, are macerated with a little _cold_ water (warm water would coagulate the albumen present, and consequently prevent solution taking place): the stains become soft, striae and brown or reddish clouds are observed, especially when the dried blood is fresh, and, at the same time, the objects upon which the stains were deposited are decolorized. Upon allowing the fluid obtained in this way to spontaneously evaporate on a watch-glass, a reddish brown or brownish residue is left, from which the crystals of haemin are prepared in the following manner: An almost imperceptible amount of common salt is added to the residue, then, six to eight drops of concentrated acetic acid, and the mass thoroughly mixed by stirring with a small glass rod. The mixture is at first heated over a small gas flame, then evaporated to dryness by the heat of a water-bath. If the stains were produced by blood, a microscopic examination of the residue will reveal the presence of haemin crystals. This method presents an objection: if the stained objects have been washed with warm water previously to the examination, the albumen will be coagulated, and the blood rendered insoluble; in this case, cold water will fail to dissolve anything, and the residue will not produce crystals when treated with acetic acid. In order to remedy this difficulty Brücke operates directly upon the stained woven or ligneous fibre, or the matter removed from the stone or iron: The materials are boiled in a test-tube with glacial acetic acid, the fluid decanted or filtered, a trace of common salt added, and the liquid then evaporated on a watch-glass at a temperature between 40 and 80°. If the stains really originated from blood, haemin crystals will now be easily perceptible upon examining the residue obtained under the microscope. The stained fabric, the matter removed from the stone or iron, or the residue left by the solution with which the stains have been treated, is placed on the glass, a trace of chloride of sodium added, and the whole covered with a thin glass plate. A drop of acetic acid is then placed at the edge of the plates--between which it is soon introduced by capillary attraction--and the mixture allowed to rest in the cold for a few moments. The mass is next brought into solution by slightly heating, and is then evaporated by holding the plate at a considerable distance above a gas burner. The fluid is examined from time to time under the microscope: when it is sufficiently concentrated, crystals, presenting the appearance represented in Figs. 21 or 22, will be observed. These are especially well-defined, if an insoluble substance is also present between the plates--which prevents their adhering. The fluid collects by capillary attraction at the points of contact of the plates as a more or less colored layer, in which the crystals are deposited.