Tear up small about 100 grammes of paper, and boil it in alcohol, in a flask or a reflux condenser. This must be done before the stripping with water, so as to extract the size which would otherwise protect the dye from the water. Of course the alcohol treatment is omitted with unsized paper. The paper is now boiled with from three to five lots of water, taking each time only just enough to cover the paper. This is done in the same flask after pouring off any alcohol that may have been used, and also with the reflux condenser. The watery extract is mixed with the alcohol extract (if any). Three cases may occur:--(1) The dye is entirely stripped, or very nearly so. (2) The dye is partly stripped, what remains on the fibres showing the same colour as at first or not. (3) The dye is not stripped. To make sure of this the solution is filtered, as the presence in it of minute fragments of fibre deceive the eye as to the stripping action. In the first two cases the mixed solutions are evaporated down to one half on the water bath, filtered, evaporated further, and then precipitated by saturating it with common salt. The dye is thrown out at once, or after a time. It may precipitate slowly without any salt. The precipitated dye is filtered off and dried. To see whether it is a single dye or a mixture, make a not too dark solution of a little of it in water, and hang up a strip of filter paper so that it is partly immersed in the solution. If the latter contains more than one dye they will usually be absorbed to different heights, so that the strip will show bands of different colours crossing it. If it is found that there is only one dye, dissolve some of it in as little water as possible, and mix it with "tannin-reagent," which is made by dissolving equal weights of tannin and sodium acetate in ten times the weight of either of water. If there is a precipitate there is a basic dye, if not, an acid dye. In the former case mix the strong solution of the dye with concentrated hydrochloric acid and zinc dust, and boil till the colour is destroyed. Then neutralise exactly with caustic soda, filter, and put a drop of the filtrate on to white filter paper. If the original colour soon reappears on drying, we draw the following conclusions:-- (_a_) The colour is red; the dye is an oxazine, thiazine, azine, or acridine dye, _e.g._, safranine. (_b_) It is orange or yellow; the dye is as in (_a_), _e.g._, phosphine. (_c_) It is green; the dye is as in (_a_), _e.g._, azine green. (_d_) It is blue; the dye is as in (_a_), _e.g._, Nile blue, new blue, fast blue, or methylene blue. (_e_) It is violet; the dye is as in (_a_), _e.g._, mauveine. If the original colour does not reappear on drying, but does so if padded with a 1 per cent. solution of chromic acid, we draw the following conclusions:--