On tendering Writing indejlruclihle by Fire. 173 



without advantage, by way of fomentation, to gouty and pa-* 

 ralytic limbs, and for thofe afflicted with rheumatic com- 

 plaints. 



XII. Chemical Experiments re [peeling different Methods of 

 rendering "Paper and the Writing on it indejlruclihle by 

 Fire. By Mr. L. Brugnatelli. From Crell's Che- 

 mical Annalsybr 1797. 



Various Methods of rendering Writing indejlruclihle. 



[Concluded from Page 92.] 



Wi 



HEN I had difcovered the means by liquor of flint 

 to render paper fo much lefs combuftible, and alfo in parti- 

 cular to prevent its being converted into allies, I refolved to 

 examine how common ink would ftand on paper prepared 

 in that manner. I imagined that ink, on account of the 

 oxydated metal contained in its mixture, would not be fo' 

 ealily deftroyed by the fire ; for, though it is not naturally 

 black when freed from the acid of galls, it muft however be 

 fomewhat vifible as foon as the fubftance on which it h 

 put is rendered indeftructible. And this I actually found 

 to be the cafe, after writing a few lines with good common 

 ink upon a leaf of paper which had been carefully prepared 

 with liquor of flint, and putting it into the fire till it was 

 burnt to a coal. I examined the writing with attention, and 

 found that feveral words which I had written upon it could 

 be read, though the paper was reduced to a coal. All the- 

 Words could not indeed be diftin<miflied with the fame clear- 



o 



nefs, and therefore they could not be all properly read. 

 Some of them had a red ochrey colour, and thefe were the 

 cleared ; others were blackifh, and fome were of fo dark a 

 tint that they were almoft entirely blended with the colour 

 of the charred paper : the laft were totally illegible. Thefe 

 phenomena are perfectly agreeable to the nature of oxydated 



iron* 



