«*6 A new Sympathetic Ink. 



ceeded with him, I refolvecl to make fome experiments to 

 afcertain the point. My firft object was to procure pure 

 cobalt ; but as I was unwilling to facrifice pure pieces of 

 any considerable fize, I made choice of one which was visi- 

 bly mixed with bifmuth, iron and quartz. I endeavoured 

 to feparate the bifmuth as much as poffible', and alfo the 

 arfenic if it fhould contain any, by bringing it {lowly to a 

 red heat; and I fucceeded pretty well, as the bifmuth flowed 

 from it in abundance; and the arfenic, the quantity of which 

 was fmall, was volatilifed : many globules of bifmuth ft ill 

 adhered to it. By bringing it repeatedly to a red heat, and 

 then quenching it in water, it was reduced to fuch a ftate as 

 to be eafily pulverifed. Having poured nitrous acid upon 

 the powder, I obtained by digeftion a beautiful rofe red fo- 

 lution; the filiceous earth was feparated in the form of a 

 white (lime, and by diluting it with water there was de- 

 posited a white powder, which was oxyd of bifmuth. The 

 folution being filtered, I added to it a folution of potafh, and 

 obtained a precipitate inclining more to a yellow than to a 

 red colour. I again poured over it a little of the nitrous 

 acid, by which a part of the oxyd was re-diffolved of a red 

 colour: the remaining part, which had a dark brown colour, 

 was oxyd of iron. From the folution, by the addition of 

 potafh, a precipitate was formed, which was now reddifh. 

 Having by this procefs obtained it pure; that I might now 

 prepare from it the wifhed for red ink, I diffolved the wafhen 

 pure oxyd of cobalt in different acids. That diffolved in the 

 nitrous acid with a mixture of nitre, gave a green ink like 

 the common : that diffolved in the fulphurous acid, with- 

 out the addition of falts, gave a reddifh ink, which remained 

 after it was expofed to heat, and would not again dilappear, 

 even when a folution of nitre was applied ; and that dif- 

 folved in the muriatic acid gave a green ink, darker and 

 more beautiful than the common. By diffolving it, how- 

 ever, in the acetous acid, and adding a little nitre, I obtained 

 what I had in view; for it gave, on the aoolication of heat, 



an 



