On rendering Writing IndejlruSlille by Fire. Tj£ 



gold; nitrite of filvcr, copper, tin, lead, bifrrruth, cobalt, 

 antimony, and manganefe. None of the characters written 

 with the above folutions could be read by the naked eye, 

 except that written with nitrite of copper, which appeared" 

 of a beautiful green colour. I burnt all thefe leaves in a- 

 name, and the refults were as follows : 



The characters made with folutions of gold and filver 

 were not vifible on the charred paper, on account of the 

 dark tint which they affumed in the fire. The cafe was the 

 fame with thofe characters made by folutions of cobalt, an- 

 timony, and lead. 



I have found that dmolved nitrite of cobalt may be em- 

 ployed with great advantage for making fympathetic ink, not 

 inferior to the celebrated ink prepared from the fame metal' 

 diffolved in the nitro-muriatic acid, or aqua-rcgia ; which, 

 as is well known, becomes vifible of a beautiful green colour 

 by heat, and difappears in the cold. Characters written with 

 diffolved nitrite of cobalt became vifible, of a beautiful violet 

 colour, on paper prepared as above. I held the leaf of paper, 

 on which I had written with the before-mentioned fblution, 

 a few feconds over the fire ; and when I took back the leaf I 

 could read the characters, before invifible, as they now ap- 

 peared of a violet colour; but the colour gradually difagi- 

 peared, and the writing again became invifible. When I 

 held the paper fo near the fire that it was a little finged, the 

 characters appeared white, and difappeared again in the cold. 



Characters made with nitrite of antimony were not vifible, 

 becaufe they were as black as the charred paper. But when 

 the paper was held to the light they could be read a little, 

 becaufe the oxydated metal made the characters exceedingly 

 opaque, and therefore eafily to be diftinguifhed from the reft 

 of the paper, which was more or lefs tranfparent. 



Characters made with diffolved nitrite of tin gave the 

 fame refult as the preceding. Thofe alfo made with a fo-« 

 lution of bifmuih were fcarcely vifible after being in the fire; 

 and when the fire was brifk it deftroyed the charred papery 



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