On preparing Lakes "iVith the Tungjlic Acid: %t 



*rhefe candles, befides burning longer than the commoa 

 bnes, have alfo this advantage, that they do not flare, and 

 Uiat they are lefs prejudicial to the eyes of thofe vi'ho are ac- 

 cuftomed to read or write at night. It is however to be ob- 

 ferved, that a pair of fliarp fciffars muft be employed for 

 fnuffing them, and that in performing that operation care 

 muft be taken not to break or derange the wick. 



XIII. Experiments on the Colouring Matter of Vegetable 

 Juices with the Tungjlic Acid. Bj Cit. Guvton. 



I 



N the fecond volume of the Philofophical Magazine, page 

 126, we laid before our readers a paper by the fame author 

 on the colouring matter of vegetables, and the a6lion exercifed 

 on it by metallic fubftances and their oxyds ; with a new pro- 

 ccfs for obtaining lakes of more intenfe and fixed colours. 

 The prefent may be conddered as connefted with that paper, 

 being, in fact, a detail of the experiments with tungften, on 

 which the conclufions there given were eftahliihed. 



" Having fubje6led to experiment an oxyd hitherto little 

 known, T mean the tungftic oxyd, I foon difcovered that it 

 is one of the moft valuable fubftances for receiving and fixlno" 

 Vegetable colours. I digcfted the juice of the red plum 

 with the white oxyd of tungften, procured from wolfram, 

 tliat is to fay, in the ftate in which it is confidered as an 

 acid. The liquor loft a great deal of its colour, and the me- 

 tallic oxyd became of a very dark red violet, I decanted the 

 li(|U()r, and boiled it on a new portion of the tungften. It 

 aftunied the fame colour, and the liquor ftill retained a faint 

 iliade of red. The liquor being filtered and diluted with wa- 

 ter, to defend it from the action of the fire, was treated a 

 third time with frefli oxyd. It then remained colourlefs, 

 and the oxyd of tunrfftcn was found coloured as much as the 

 firft. 



' From Annales dc CliimL-, No. LXXXIX. 



^''JL, IV. G " It 



