On the exceptionally hot days of an exceptionally hot summer, when all ink dries with exceptional rapidity, it is not difficult to write somewhat more thickly than usual, and thus maintain the wetness of the words until a page is completed ready for copying. In very moist weather when the finished document written with this ink would not dry rapidly, and therefore would he liable to become smeared, it is not impracticable to use a fine pointed pen or to hold your sheet before a fire or over a gas flame for a moment or two. Lastly, the extreme facility with which letters are copied with this ink and the great convenience attached to the advantage of possessing transcripts of letters, etc., are cheaply purchased at the price of a little care and practice in making one's up-strokes and down-strokes pretty much of a thickness.

But I am exaggerating difficulties. Processes, apparently practicable when described, often turn out hopelessly impracticable when applied. Conversely, processes apparently impracticable often admit of ready application. My description of the use of my ink must, I am sure, convey an impression of impracticability. As a matter of fact, however, I use the ink from year's end to year's end without any trouble whatever. The case of this ink is one of those in which unavoidable disadvantages are compensated by an amount of personal carefulness to which one easily becomes habituated. The disadvantages, of course, preclude the introduction of the ink into indiscriminate wholesale and retail .trade. The firm of manufacturers that, consulting me respecting copying ink, entertained my suggestion to use such an ink as this, went to the expense of provisionally patenting it, in the hope that before the period of provisional protection elapsed it would be improved sufficiently to render it an ordinary commercial article. They have long abandoned that hope. I, too, have now abandoned it sufficiently to induce me to publish the mode of making and using the ink, in order that at least others may enjoy its use to the extent to which I enjoy it myself. The ink is really invaluable to me.

To pharmacists, retail tradesmen, professional men, private persons and others who desire to keep copies of their letters and writings, but who do not write enough to render worth while the use of a copying-book and copying-press, or the employment of a junior clerk or office boy for press copying, or who may desire to keep a private copying-book, this ink will also prove invaluable. The ink can be made by chemists and druggists, who also might vend the article with no loss of dignity. For the sale of it would be accompanied by one of those little intelligent statements respecting mode of use and attendant conditions which come so naturally from the pharmacist.

I have only to add the process of preparation. The principle of the method consists in dissolving a moderately powerful hygroscopic substance in any ordinary ink. After experimenting on all such substances known to me, I give the preference to glycerine. Reduce, by evaporation, 10 volumes of ink to 6; then add 4 volumes of glycerine. Or manufacture some ink of nearly double strength, and add to any quantity of it nearly an equal quantity of glycerine. (Professor Attfield.)

Indelible Ink (16)

Triturate 1 3/4 grams aniline black with 60 drops strong hydrochloric acid and 42-43 grams strongest alcohol; then add to it a hot solution of 2 1/2 grams gum-arabic in 170 grams water. This ink attacks steel pens but little. It is not destroyed either by strong mineral acids or by strong lye. If the first alcoholic solution of aniline black be diluted with a solution of 2 1/2 grams shellac (instead of gum-arabic) in 170 grams water, an ink is produced which may be employed for writing on wood, brass, or leather, and which is remarkable for its deep black colour.

Invisible Ink (V)

Finest potato starch, 13.5 kilos., and powdered iodine 1 kilo., are mixed and then rubbed - through a sieve, then mixed with 4 litres water and 1 litre rectified spirit. The resulting black powder is allowed to stand for 14 days, then dried and exposed to the air. 1 he dry powder contains 10 per cent. of iodine. The iodide of starch becomes soluble when heated with stirring in an enamelled saucepan over a gentle fire. As soon as the powder is dry the operation is finished, it then emits a pungent smell. From time to time during the heating it must be ascertained whether the powder has become soluble, by heating some of it with water in an iron spoon. At a strong heat it yields a red solution with loss of iodine. In order to purify the powder and make it thoroughly soluble, of a violet tint in.cold water, a concentrated solution is made by heating, so that it shows 7-8°. This solution is allowed to deposit for several days, decanted and precipitated with rectified spirit. The precipitate is strained, and dried in the drying closet. If excess of spirit is used in the precipitation, a gummy matter is thrown down, the presence of which is superfluous. A certain firm claims to be the sole manufacturers of the ink.

They advertise that writing executed with it gradually fades away and cannot be restored by any chemical, and state that the time it takes to fade depends on the paper that is used; if written with a perfectly clean steel or quill pen on un-glazed paper the evanescence will be more rapid than when written on glazed paper. On some papers it will disappear in a day, whilst on other kinds it will take more than a week. I tried this ink on various sorts of paper, and found the writing quite visible after 6 weeks. It can easily be restored to a jet black by exposing the writing to the fumes of iodine. Perfection has not yet been obtained in the production of this useful ink; there appears to be some chemical either absent or not present in a sufficient quantity to induce a rapid evanescence.

(S. L.)

Harking Ink. (y) Blue. - Mix a sufficient quantity of ultramarine with barytes (sulphate of barium, blanc fix), and water to produce the desired tint. It may be rendered more permanent by adding some liquid glue (solution of glue in acetic acid) or some starch paste, prepared with the addition of a little wax. (Chem. and Drug.)