Zz On preparing Lakes <ivttb the Tungjllc Ac'uJ. 



' It was not now neceflary to examine the liquor by re- 

 agints, for principles which no longer exifted in it, but to try 

 whether the colour adhering to the oxyd was fixed there in 

 fuch a manner as to promife any advantages to dyeing, or at 

 lead to painting. Water boiled a long time, and in fuc- 

 ceffion, on this oxyd rather darkened than weakened its co- 

 lour. This water made no impreffion upon turnfol paper. 

 Though limpid, it afliimed, by the addition of the muria- 

 tic acid, a fliade of a pale rofe red colour; and by the addi- 

 tion of pot-afli, a greenifli (hade ; but thefe colours totally 

 disappeared in a few minutes, and could not be made to re- 

 appear, by pouring over them frefli acid and frefli alkali. 

 What is more remarkable, the hydro-fulphure brought back 

 a flight tint of violet, which did not difappear. 



" A portion of the coloured oxyd of tungften was mixed 

 up with gvim water, and with a brufh daubed over a piece of 

 paper. The ftratum being drj-, a thin fcale of it was de- 

 tached, in order to be expofed to the rays of the fan, and at 

 the end of nine days the colour was neither changed nor 

 weakened. Another fcale was immerfed in the acetous acid; 

 and being immediately drawn out and dried, it was found to 

 have experienced no change. As little effeft was produced 

 upon it by the acetic acid. Lime water applied to it left no 

 feufible traces of its effccl. The cafe was the fame with 

 ammonia. A folution of foap only weakened the tint with- 

 out changing it. A folution of potafli made a red fpot, in 

 which the violet (hade was deftroyed. A folution of the car- 

 bonat of potafli produced an alteration ftill more fenfible, 

 the part which had been touched inclining rather to yellow 

 than to red. A folution of alum, even concentrated, efleft- 

 ed no change. A ilieet of paper, tinged with the colour of 

 this oxvd, being kept for twcntv-four hours in a clofe jar, at 

 the bottom of which was fome hydro-fulphure, no change 

 whatever was obferved. In the laft place, a (lieet of this pa- 

 per expofed to the vapour of the oxygenated muriatic acid, 

 ;il the iamc time as a like flicet of paper coloured by turnfol^. 



thd 



