178 On rendering Writing indijlru&ible by Fire. 



red. Thofe written with folutions of tin, antimony and 

 zinc, were not legible. Paper impregnated with fulphite of 

 potafh was totally deft roved in the flame, as above remarked. 

 I thought it neceffary therefore to make experiments with 

 other fulphites; becaufe I had before obferved thatfuch falts, 

 by means of inflammable bodies, are converted into fulphu- 

 reous bodies. 



I wrote alfo with the common diflblved metals, on paper 

 which had been impregnated with muriate of foda. The 

 characters written with a folution of gold could fcarcely be 

 diftinguifhed of a dark red colour j but thofe written with 

 all the other diflblved metals were not legible. 



I wrote with the fame folutions on paper which had been 

 foaked in a folution of muriate of ammoniac, but none of 

 the characters were vifible on the paper when reduced to coal. 



I wrote, in the laft place, with the fame fubftances on 

 paper which had been foaked in a folution of nitrite of lime, 

 and, when reduced to coal, I could read the characters writ- 

 ten with a folution of gold of a beautiful rofe red ; and 

 thofe written with a folution of filver of a yellow colour \ 

 but the charred paper was white. The other characters 

 were not legible, except thofe written with nitrite of bif- 

 muth, which had aflumed a blackifli colour. 



The other pieces of paper foaked in folutions of different 

 falts gave no refult worthy of notice. 



The above obferved effects and before-mentioned chemi- 

 cal preparations were the means of leading me to feveral 

 pleafant experiments. I wifbed, for example, to bring it 

 about that the burnt paper fhould be converted into a white 

 indeftrudtible coal, on which the characters might be legible 

 of different colours, and accompliflied my object in the fol- 

 lowing manner : — I rubbed fome gum arabic mixed with pure 

 raagnefia by means of a hair brufh, over the paper foaked in 

 liquor of flint. When the paper was dry, I wrote on it fe- 

 veral lines, fome with a folution of gold, and others with a 

 folution of antimony in aqua-regia.. The characters made 



with 



