L. TECHNOLOGY. 495 



the machine, the letters are freed from the bur caused by the 

 pressure of the stamp by means of a quickly rotating disc of 

 steel, and are then converted into steel by cementation, mak- 

 ing them of sufficient hardness not to require any further 

 change. Letters thus produced are said to be sharper and 

 more perfect than those of ordinary type-metal. One ma- 

 chine, driven with one-horse power, will, it is asserted, manu- 

 facture thirty-five thousand letters in twelve hours, the price 

 of which is much less than that of the ordinary kind. The 

 question still remains to be solved, however, whether these 

 letters, in printing, will not cut through the paper, and be in- 

 juriously liable to rust. 6 C, September 22, 379. 



writing-ink. 



We have already presented to our readers numerous re- 

 ceipts for the manufacture of writing-ink, and we find still 

 another among our exchanges, which, like all the rest, profess- 

 es to be better than any thing else. How far this may be. 

 true can only be determined, of course, by proper experiment. 

 This ink is prepared by digesting, for twenty-four hours, at a 

 gentle heat, three thousand seven hundred and fifty grains of 

 powdered nut-galls in a pint of alcohol of eighty-two per cent., 

 and in another vessel one thousand three hundred and fifty 

 grains of sulphate of iron, and the same quantity of gum ara- 

 bic, with three pints of pure water. These two liquids, pass- 

 ed through a flannel strainer, are then to be mixed, and al- 

 lowed to settle for eight days, and again strained. It is 

 claimed that the ink thus obtained does not form any deposit, 

 nor does it mould, and that it is more permanent than any 

 other. It is said to become very black, and to maintain its 

 intensity of color indefinitely. 2 .2?, January 22, 98. 



REMOVAL OP INK BLOTCHES EE03I WETTING. 



When jnk blotches have been formed over writing which 

 it is desired to decipher, we are advised to brush off the spot 

 carefully with a weak solution of oxalic acid by means of a 

 camel's-hair pencil. In this way layer after layer of the su- 

 perincumbent ink will be removed, and finally the writing. it- 

 self will, in most cases, come to view. This is especially pos- 

 sible where s,ome considerable interval has elapsed between 

 the two applications of ink. As soon as the letters are vis- 



