On rendering Writing indejlriiFt'ible hy Tire. 177 

 10 vifible, in a clear white colour on a dark ground, that they 

 could be read with as much eafe as characters written with 

 the beft ink on white paper. 



I mall now examine whether diffblved nitrite of zinc^ 

 . which produces fo beautiful a fympathetic ink, can be com- 

 bined with common ink, without the latter being fo changed 

 in its colour as to be rendered unfit for ufe as before. I 

 made this mixture, and found that the ink became fome- 

 what pale by the nitrite of zinc, on account perhaps of the 

 nitrous acid, which probably leflened the combination of the 

 acid of galls with the iron : but I could write with it very 

 well on paper prepared by my liquor of flint; for the colour 

 of common ink mixed with nitrite of zinc, which appeared 

 on common paper to be fomewhat weakened, became fo 

 dark on prepared paper, that words written with it appeared 

 more confpicuous than thofc written with common ink. 

 The white colour of which the chara&ers appeared, on the 

 charred paper, was not changed by the mixture of ink, as I 

 was fully convinced by repeated experiments. 



One part of my curiofity was ftill not gratified, as I wifhed 

 to know of what colour the diflblved metals would appear 

 on paper impregnated with different falts. For thatpurpofe 

 I made the following experiments : 



I wrote on paper, which had been impregnated with acetite 

 of barytes, with a folution of gold, nitrite of filver, copper 3 

 bifmuth, tin, lead, antimony and zinc. The characters 

 written with a folution of gold appeared on the charred 

 paper of a beautiful poppy red, and thofe with a folution of 

 copper of a dark yellow. Thofe written with a folution of 

 antimony, zinc, bifmuth, tin and lead, could not be feen. 



I wrote alfo with folutions of the above metals on paper 

 which had been foaked in muriate of lime. The characters 

 written with folutions of gold and filver appeared on the 

 paper like thofe written on paper foaked in acetite of barytes. 

 Thofe written with folutions of lead and bifmuth appeared 

 white; and thofe written with a folution of copper appeared 

 Vol. I. N red. 



