180 COPIES OF WRITTEN PAPER BY PRESSURE. 



Solutions ap- Mechanical means having failed, it was necessary to en- 



pli.cd t0 the , crease the power by the assistance of chemistry. 



writing, or the ...... 



copying paper With this intent, I soaked either the old writing or the co- 

 pying paper in various solutions, and passed them through 

 the press. Old writing is rendered blacker by being soaked 



Infusion of for some hours in infusion of "alls, but it has no power to bring 

 galls. , & ' x s 



it on to the copying paper. 



Green vitriol. Solution of sulphat of iron produced no effect. 

 p . With triple prussiate of potash a faint copy was sometimes 



fish, obtained; often it had no effect : a few drops of sulphuric 



acid added to it increased its power, but the whole was ren- 

 dered green. 



Hidrosulphuret of ammonia has more powerful action on 

 writing than any thing I have yet tried. When this liquid is 



,„, poured on faded or almost any kind of writing, it changes it 



ITidrosulphu- . . . 



ret of ammo- io an intense black colour. By the aid of this preparation, 



^ ia - I have been enabled sometimes to procure tolerably good 



copies, but could not obtain a constant effect, though I often 

 varied the progress. 



But the action of hidrosulphuret of ammonia is incom- 

 plete, the black it gives to writing is not permanent, and on 

 some writing it has no effect. 



As this substance appeared more likely to succeed than any 

 other, I was induced to examine it more particularly, but the 

 result has convinced me its power is inadequate to the 

 purpose. 



The reason it gives a black colour to writing is this : almost 

 allinks contain an excess of sulphate of iron; the ammonia 

 combines with the acid, and the sulphuretted hidrogen with 

 the iron, forming the black colour; and because different 

 inks contain different proportions of sulphate ofiron, they will 

 not be equally affected by the hidrosulphuret of ammonia. 



Hidrosulphu- The hidrosulphuret ofiron is decomposed by the carbonic 



ret of iron de- ac i<] f t h e atmosphere. 



composed by 



The following experiments will prove these positions'. Write 

 on paper with ; 

 No. 1. A solution of tan. 

 No. 2. A solution of green sulphate ofiron. 



No. 



the air. 



