<7"4 ® n rendering Writing indejlrucl'ible by The. 



iron, which, as is well known, afiumes the above-mentioned 

 tints, according as it contains more or lefs oxygene or carbon. 

 On account of the oxydated iron, as I could not employ 

 common ink for my propofed object, I fought among the 

 oxydated metals for one that was capable of finking the eye 

 on a black ground, and which at the fame time would com- 

 bine with common ink *. 



To common ink I added a portion of oxydated bifmuth, 

 which, according to its own nature, is exceedingly white, 

 and which on a black ground would produce vilible charac- 

 ters that mull then be legible. I prepared the mixture, and 

 obtained a fomewhat thick ink, which did not flow readily, 

 and with which I could write a few lines, but not without 

 difficulty, faper written upon with this ink I burnt in a • 

 wood fire, and examined it as foon as it was reduced to' 

 eoal. I however found that the words were not more ic-ijible 

 than thofe written with common ink ; for the oxydated bif- 

 muth communicated its oxygene to the inflammable parts of 

 the mixture, and the whole was revived into s fj etallic 

 regulus : feveral fmall grains of regulus of bifmuth could 

 therefore be diftinguifhed in it with the naked eye. I n ixed 

 common ink with feveral other oxydated metals, and with' 

 feveral kinds of earths ; but the ink by thefc was fo much 

 changed in its colour and confiftence, that I thought it un- 

 necetfary to pay any farther attention to it. I had recourfe, 

 therefore, to diflblved metals, becaufe ink by thefe is not 

 changed in its confiftence, as by oxydated metals, and parti- 

 cularly earthy bodies. 



But before I made any mixture with common ink, I wiflied 

 to try what colour characters made with ditTblved metals 

 only would afTiime, on paper prepared as- before, when re- 

 duced to coal. 



I wrote, therefore, oh different leaves of paper, which had 

 been foaked in liquor of flint, with a common folutbn of 



* For common ink any other black dye may be fubftitutcd. 



&^9 



