The variations would appear to be largely due to the difference in quality of the gall-nuts, treatment, and temperature of the atmosphere; perhaps, however, not so much to-day as it was ten or twenty years ago, when to make ink of this character boiling processes were employed. Most of them as already stated are now "cold" made. Inks of this class consist of a finely divided insoluble precipitate suspended in water by the use of gum and possessing a slight acidity. The requisites of a good black writing ink or black writing fluid require it to flow readily from the pen, to indicate in a short time a black color and to penetrate the paper to an appreciable degree, and more important than all the rest, to be of great durability. When kept in a closed vessel no sediment of any account should be precipitated, although such will be the case in open ink-wells, and this the quicker the more the air is permitted to get to it. If it is to be used for record or documentary purposes it must not be altogether obliterated if brought into contact with water or alcohol, and should depend for permanency on its chemical and not on its pigmentary qualities. The second class, called for distinction "chemical writing fluids," possesses the same essential ingredients to be found in class one, but much less in quantity and with some "added" colored substance which I shall term "loading," for its real purpose is to cheapen the cost of production and not altogether as some manufacturers state "simply to give them an agreeable color." Previous to the discovery of the soluble anilines, logwood, indigo, madder, orchil and other dyeing materials were used for a period of some eighty years and vanadium for some twenty years (very costly at that time), for this purpose, but since 1874, and with frequent changes as the newer aniline compounds were invented, these by-products of coal-tar, as well as logwood, etc., have been and are to-day employed for "loading," or as the manufacturer expresses, it "added color." The chemical writing fluids as now prepared, yield when first written a blue or green color with a tendency to change to black afterwards. They are not as permanent as those of the first class. Another black ink not durable, however, is "logwood;" its extract is combined with a little chromate of potassium and boiled together in water. It possesses its own "gum" and contains some tannin. In combination with alum and water, it forms a dark purple ink.