420 Mr. Wart’s Method of preparing 
acids and alkalies, which the following fact feems to alls in 
queftion. 
I have obferved, that a mixture of phlositicasat nitrous 
acid with an alkali will appear to be acid, by the teft of lit- 
mus, when other tefts, fuch as the infufion of the petals of 
the fearlet rofe, of the blue iris, of violets, and of other 
flowers, will fhew the fame liquor to be alkaline, by turning 
green fo very evidently as to leave no doubt. 
At the time I made this difcovery, the fcarlet rofes and 
feveral other flowers, whofe petals change their colour by acids 
and alkalies, were in flower. JI {tained paper with their juices, 
and found that it was not affected by the phlogifticated nitrous: 
acid, except in fo far as it acted the part of a neutralizing acid ; 
but I found alfo, that paper, {tained in this manner, was by no 
means fo eafily affeted by acids of any kind as litmus was, 
and that in a fhort time it loft much of that degree of fenfibi- 
lity it poffefled. Having occafion in winter to repeat fome ex- 
periments, in which the phlogifticated nitrovs acid was con- 
cerned, I found my ftained paper almoft ufelefs. I was, there-- 
fore, obliged to fearch for fome fubftitute among the few vege-’ 
tables which then exifted in a growing ftate; of thefe I found 
the red cabbage (braffica rubra) to furnith the beft teft, and in’ 
its frefh ftate to have more fenfibility both to acids and alkalies’ 
than litmus, and to afford a more decifive teft, from its being 
naturally blue, turning green with alkalies, and red with acids ; 
to which is joined the advantage of its not being affected by 
phlogifticated nitrous acid any farther than it acts as a real acid. 
To extract the colouring matter, take thofe leaves of the cab’ 
bage, which are frefheft, and have moft colour; cut out the 
larger ftems, and mince the thin parts of the leaves very {mall ; 
then digeft them in water, about the heat of 120 degrees, for 
a few 
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4 
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J 
