This pulp contains practically all the constituents of the original wood, has little strength, inferior felting properties, and is not of permanent character. Its utility results largely from its cheapness. When made into paper with a suitable admixture of sulphite pulp, for strength’s sake, it proves to be admirably adapted for the fast-running newspaper presses, as ink dries upon it almost instantly. It is also used in the making of boxboards, cheap cardboards, pie plates, wall papers, etc. It should, however, be strictly excluded from all papers of more than ephemeral purposes, because of its lack of permanence. The appearance of a paper containing much ground wood is inferior, as the color is poor and small shives of wood may be discerned on the surface. An easy and reliable way to ascertain the presence of ground wood is to moisten the paper with a drop of strong nitric acid, which develops a dark-brown stain if ground wood is present. Another good test is phloroglucine, which turns ground wood to a bright carmine shade. The quantity of ground wood is roughly indicated by the intensity of the stain. BLEACHED GROUND WOOD A quality of pulp intermediate between chemically produced wood cellulose and ground wood is obtained by bleaching an especially finely ground quality of pulp wood. This product is excellent as a filler for medium grades of paper, as it is opaque--fine, and of fair color. Nevertheless, it is open to the same criticism as other ground wood as to permanence, though in a less degree. CHAPTER FIVE THE CONSTITUENTS OF PAPER--_Continued_ CHEMICAL WOOD-PULPS.--Chemical wood-pulps are obtained by a variety of processes, all of which have as their object the isolation of the pure cellulose fiber by the dissolution of non-cellulose components. The same principles are applied to the treatment of esparto straw or other plants. The character of the pulp depends not only upon the nature of the wood, but also upon the solvents used and the duration and severity of the cooking. The preparatory steps to any process by which chemical wood-pulp is made are identical with the preparation of trees for ground wood, only after the logs have been “barked,” they are reduced to chips by a mechanical “chipper.” The ordinary practice in America is to sort out any knotty or imperfect logs as they pass on a conveyor from the “barker,” and if the log it too faulty it is discarded. As it is desirable to have a uniform size of chips, the chips are passed through a screen for this purpose. The chips are stored in bins convenient to the digesters. The digesters are of two types, rotary and stationary. The rotary type is horizontal and the stationary is vertical.