j go On T efts for det effing 



diflblved nitrite of antimony, black; and thole with a folia- 

 tion of gold, of a gold colour. Thofe made with the kit 

 folution appeared feveral times of the colour of black vel- 

 vet. When you write on the above-mentioned paper with 

 iron diflblved in diluted nitrous acid, the characters will 

 appear of an orange yellow colour, if the paper be often 

 heated without reducing it to coal. 



P. S. T am now employed in endeavouring to difcover a 

 method of rendering paper prepared with liquor of flint 

 flronocr, fo that when burnt it may not be fo friable, in 

 order that when feveral fhects of paper are burnt upon each 

 other thev mav he caiilv leparated, and the whole writing on 

 them be read. As foon as I have derived any refults from 

 my experiments, I ill ill 1 not fail to communicate them. 



XIII. On Teft Liquors for d< tetting Acids and Alkalis in Ch- 

 mical Mixtures. Extracledfrom Mr. Watt's Paper on thai 

 Suhje&tin thi Fhtfofbphical Tranla&ionsyor 1798, Part J. 



Mr. 



WATT of Birmingham, to whom the philofophical 

 world is fo much indebted for various difeoveries and im- 

 provements, has turned his attention to this fubject, and has 

 favoured the world with the refult of his inveftigation. He 

 ohferves, that the great degree' of fenfihility of an infufion of 

 litmus (fvrup of violets having been for fome time out or 

 ufe as a teft, as it has been found not to be furliciently ac- 

 curate), the blue colour of which is changed into red by the 

 prefence of a very minute quantity of any acid, would leave 

 very little neeeffity to fearch for any other, were there rcafon 

 to believe that it is always a tclt of the exacl point of fatu- 

 ration of acids and alkalis, which the following fafit fecms 

 to call in queition : "A mixture of phlogifticated ni- 

 trous acid with an alkali will appear to be acid by the teft 

 of litmus, when other tefls, fuch as the infufion of the pe- 

 tals of the fcarlet rofe, of the blue iris, of violets, and of 

 - other 



