BLACK WRITING-INK. Ordinary black writing ink is a compound obtained by the action of ferrous sulphate on an infusion of nutgalls or any similar compound containing tannin. and is essentially a ferroso-fcrric gallate. Typical of this kind of ink is the one consisting of the fol lowing ingredients; nutgalls. 12 pounds; ferrous sulphate. 5 pounds; gum Senegal. 5 pounds; and 12 gallons of water. Tt is prepared by carefully selecting nutgalls, preferably the variety from Aleppo, as that contains a larger proportion of gallic and tannic acids than other varieties, which are then crushed and treated with distilled water for several days, after which the clear liquid is carefully drawn off and to it is added a clear mucilage. made by previously dissolving the gum in hot water and filtering. Finally, dissolve separately the ferrous sulphate and mix with the foregoing solutions. Slone authorities recommend instead of a solution of ferrous sul phate that clean iron filings be added to a por tion of nutgalls and gum and the liquid agitated until it becomes deep black in color. In either case the color is due to the oxidation of the iron salt and its combination with the gallic acid in the solution. In the manufacture of commercial inks. nutgalls are frequently sub stituted by oak bark. and sumach. It has been determined that the proportion of three parts of the galls to part of the ferrous sul phate yields a satisfactory ink, but in ;actual practice more ferrous sulphate is usually added.
The use of the foregoing ingredients has been conceded to result in the production of a writing fluid which is jet !clack at the time of use, flows freely in the pen, and is practically permanent. In order to obtain a deeper black. logwood and indigo extracts are sometimes added. Runge in 1S40 described a chrome ink which he made by adding one part of potassium eliminate to one thousand parts of a solution of logwood. made by exhausting one pound of logwood with fi quarts of boiling water. The potassium chro mate is added gradually when the solution is voided, the mixture being constantly stirred (lur ing the addition. This ink is cheap, permanent on paper, and unaffected by exposure to water or acids. The use of ammonium vanadate, with an infusion of nutgalls, has been reeommended as producing an exceedingly black writing-fluid, but the expense of the vanadium salt has pre vented its common use. Certain aniline blacks. especially nigrosin, owing to their fluidity. and the fact that they form no sediment, have been extensively used in fountain pens.