en the colcurmg iWatter of Pegetables. tay 
fower of the violet acquired in tin veffels a beautiful blue 
fhade, and the ufe of it was recommended in pharmacy for 
the preparation of fyrup of viclets. The original colour of 
fyrup whieh had been changed was upon this principle re- 
ftored by long digeftion in tin; but few philofophers paid 
any attention to enquire into the caufe of thefe phenomena, 
and my colleague Berthollet mentioned only as a probability 
in his Elements of Dyeing, that this effet refulted from a 
combination of the acid with the oxyd formed at the fur- 
face of the tin. Such was the ftate of our knowledge on this 
fubje&, when, {truck with the difference in the colour of twa 
preparations of the fame fruit, I undertook a continued exa- 
mination of the circumftances in which thefe changes took 
place. 
I fhall omit giving a detailed account of the comparative 
experiments to which I fucceflively fubjected almof all the 
acid coloured fruits, fuch as the cherry, the goofeberry, the 
plum, as well as the petals of flowers, turnfol, brafil wood, 
turmeric, &c. by treating them in veflels of elafs, porcelain, 
metal, and metallic mixtures, or by holding them in digef- 
tion, either on plates of metal perfectly clean, or on metallic 
oxyds. I fall confine myfelf at prefent to refults which may 
ferve to throw fome light on the theory of vegetable colours, 
or to furnith the means of applying them with advantage to 
procefies in the arts. 
My experiments proved that the red. colour of fruits evi- 
dently arifes from the re-ation of their peculiar acid on theiz 
colouring matter. Thai tin, im reviving or reftoring the co- 
loa? of violets, only refumes by its greater affinity the acid 
which made it turn red, That it is not only tin or its oxyd, 
as has hitherto been fuppofed, which exercifes this affinity ; 
_ but that lead, bifmuth, antimony and zine produce the fame 
effet; that it is fill more rapid and complete with iron; 
and that the contact of all thefe metals inclines to violet, 
very fenfibly, infufions which otherwife ‘vould be of a bright 
and itong red. That the grcen and acid part of fruits fod 
not 
