228 The Effects of Oxyds 
» nothold the colouring principle, difpofed to become red witht 
acids; and that the coloured part conceals the portion of the 
acid neceflary for maintaining the ftate of re-aétion, which 
determines its fhade. That if this colouring principle is mo- 
dified in fome vegetables fo as to refift more or lefs acid or 
alkaline re-agents, as brafil wood in regard to acids, and 
turnfol in regard. to alkalis, it may be brought back to that 
condition ; which feems to indicate that, if not effentially, at 
js at Jeaft originally of the fame nature. That all metallic 
oxyds are not equally proper to feize and fix vegetable co- 
lours; that fome of them feem to attack the aires with 
the ereateft eafe, while others retain them only in a very 
weak manner. In the laft place, that the new metal called 
tung {ten carried to the utmoft degree of oxydation, and which 
has not yet been tried in that refpect, has a decided advan- 
tage above all the other metallic oxyds; that it is capable 
of forming lakes valuable for paimting, which ftand, with- 
out alteration, tefts by lime water, the acetic acid or radical 
vinegar, fulphurifed hydrogen gas, and even to a certain 
degree oxygenated muriatic acid gas, that enemy of colours, 
which fuddenly burns them, and which, according to the 
expteffion of Berthollet, performs in a few moments what is 
effected in a long time bythe combined aétion of air and 
light. This affertion will excite Icfs furprife, when it is 
known that this is the onlyonce of all the metallic oxyds which 
withftands the folvent power of the three mineral acids. 
The oxyd of tungften charges itfelf cafily with the colours 
of all vegetables.. Hitherto I have found only one exception 
in the petals of the wc ago, from Which I could not extrac 
the beautiful purple red, though I was unable to difcoyver 
the caufe of my failure. 
_* Tn general the lakes formed with this oxyd become darker 
inftead of lighter when diluted, and it is therefore neceflary 
to foften the fhade. I haye remarked that they acquired 
alfo more intenfity, when I made the oxyd aflume a blue 
colour, by boiling i itin vinegar, C, yon Mens, one of my 
colleagues, 
