A little gum-tragacanth is also added to obtain a proper consistence. It is absolutely necessary to use the chrome salt in the right proportion. An excess gives a disagreeable appearance to the writing; while, if too little is used, the black matter is not sufficiently soluble. The other chrome salts cannot be used in this preparation, as they would crystallise, and the writing would scale off as it dried. The nitrate of oxide of chrome is prepared by precipitating a hot solution of chrome alum with carbonate of soda. The precipitate is washed till the filtrate is free from sulphuric acid. The precipitate thus obtained is dissolved in pure nitric acid, so as to leave a little still undissolved. Hence the solution contains no free acid, which would give the ink a dirty-red colour. Oxalic acid and caustic alkalies do not attack the writing. Dilute nitric acid reddens, but does not obliterate the characters. This ink is manufactured into ink-pencils, which give a very black writing, capable of reproduction in the copying-press, and not fading on exposure to light. (f) 20 parts by weight extract of logwood are dissolved in 200 parts water, and the solution is clarified by subsidence and decantation. A yellowish-brown liquid is thus obtained.

In another vessel, 10 parts ammonia alum are dissolved in 20 parts boiling water; the two solutions are mixed, there being also added 1/5 part sulphuric acid, and finally 1 1/2 part sulphate of copper. The ink should be exposed to the air for a few days to give it a good colour, after which it should be stored in well-corked bottles, (g) 30 parts extract of logwood are dissolved in 250 parts of water; 8 parts crystallised carbonate of soda, and 30 parts glycerine (sp. gr.

1.25), are added; lastly, 1 part neutral chromate of potash and 8 parts gum-arabic, reduced to a powder and dissolved in water. This ink does not attack pens, does not turn mouldy, and is very black, (h) That which is called in trade "alizarine ink" has nothing in common with alizarine, either natural or artificial. The name was applied to an improved kind of ink over 30 years ago. It is a writing fluid in which the iron is maintained in a ferrous (protoxide) condition, and in perfect solution, which is accomplished by slightly acidulating the liquid with acetic or sometimes with sulphuric acid. The liquid has usually a rather pale greenish or bluish colour, and the writing is at first green, not black. Not long afterwards, however, the acid menstruum evaporates, leaving a very thin layer of the ferrous tannate, which gradually oxidises in the air, and turns to black ferric tannate. Contrary to what might be expected, steel pens are not usually much corroded by properly prepared alizarine inks; the first coating of oxide which is produced upon the pen generally adheres so firmly that further action is very much retarded.

The very pale tint of such a writing-fluid is frequently heightened by the addition of some indigo-solution, best in form of indigo-carmine. A good formula for making so-called alizarine ink is the following: - Powdered nutgalls,40 parts; solution of acetate of iron, 15; gum-arabic, 10; wood-vinegar, 10; indigo-carmine, 5; and water, 100 parts. Prepare the solution of acetate of iron by pouring a sufficient quantity of wood-vinegar upon scrap-iron contained in a cask, and allow it to act upon the iron for at least 8 days. Macerate the powdered nutgalls for 8 days with the 100 parts of water mixed with the 10 parts of wood-vinegar. Before mixing the strained liquid obtained from the nutgalls with the iron solution, it is necessary to ascertain whether the quantity of acetic acid present is sufficient to keep the ferrous acetate in solution. For this purpose 10 volumes of the liquid nutgall extract are mixed with one volume of the iron solution. If a clear mixture results, and of a dark-green colour in thin layers, the liquid contains enough acid; but if a black opaque liquid results, the acid is deficient.

In the latter case more wood-vinegar must be very gradually and cautiously added from a measured volume, until the liquid is clear and dark green, and the requisite amount of acid, determined by this experiment, must be added to the extract of nut-galls. The gum-arabic is next dissolved in the latter, the iron solution then added, and finally the indigo-carmine, or as much thereof as may be required to produce the desired tint. {New Remedies.) (i) Decoctions of logwood to which alum has been added give a reddish or violet colour, which darkens slowly, particularly with ink prepared from the wood and not the extract. Such inks prepared with alum alone are costly, because to obtain a sufficiently deep tint one is obliged to employ decoctions or solutions of the extract in a very concentrated condition. It is otherwise when a metallic salt is added along with the alum. Alum produces a reddish purple colour in decoctions of logwood, while metallic salts produce in the oxidised solution of the colouring matter a precipitate of a black or bluish-black colour. These inks are analogous to the so-called alizarine inks; the ink is coloured by the tint produced by the alum.

Under the influence of air there is produced between the metallic salts and the colouring matter a reaction which determines the formation of a bluish-black precipitate. To prevent as much as possible this action of the air upon the ink before it is applied to the paper, there is added, as in the case of alizarine inks, a trace of sulphuric acid, designed to dissolve the precipitate which may be produced. This acidity of the ink has several disadvantages; it attacks the pens used for writing with it unless they are either of gold, platinum, or gutta-percha. Sulphate of copper or sulphate of iron may be the metallic salts used in such inks; the former is preferable.

G. Miscellaneous

(ft) The juice or sap of the ink-plant (Coriaria thymifolia) of New Granada, to which is given the name of chcmchi, is at first of a reddish tint, but in a few hours becomes intensely black. It may be used without any preparation. The chanchi corrodes steel pens less than ordinary ink, and better resists the action of time and chemical agents. It is said that during the Spanish rule all public documents were required to be written with this ink; written otherwise, they were liable to damage by sea-water. (6) 20 gr. sugar is dissolved in 30 gr. water, and a few drops concentrated sulphuric acid are added; the mixture is heated, when the sugar is carbonised by the acid, (c) It is well known that aniline black, properly so called, is nearly insoluble in most chemical re-agents. It is applied to textile fabrics in a pounded state, or developed on the texture or paper by the reaction of a salt of copper on hydvechlorate of aniline. It thus furnishes an intense and indelible black. But a mixture of salt of copper and hydrochlorate of aniline is not long in the air without undergoing great changes. It soon turns to green and deposits insoluble aniline black. This prevents the use of this black for flowing ink.