134 
ever observed on the flower. Camphor is used 
to preserve the collections of naturalists. The 
woods that contain aromatic oils are remarked 
for their indestructibility ; and for their exemp- 
tion from the attacks of insects: this is parti- 
cularly the case with the cedar, rose-wood, and 
cypress. The gates of Constantinople, which 
were made of this last wood, stood entire from 
the time of Constantine, their founder, to that 
of Pope Eugene IV., a period of 1100 years. 
The petals of many flowers afford saccharine 
and mucilaginous matter. The white lily yields 
mucilage abundantly ; and the orange lily a mix- 
ture of mucilage and sugar ; the petals of the 
convolvulus afford sugar, mucilage, and albumi- 
nous matter. 
The chemical nature of the colouring matters 
of flowers has not as yet been subject to any very 
accurate observation. These colouring matters, 
in general, are very transient, particularly the 
blues and reds; alkalies change the colours of 
most flowers to green, and acids to red. An imi- 
tation of the colouring matter may be made by di- 
gesting solutions of gall-nuts with chalk : a green 
fluid is obtained, which becomes red by the action 
of an acid ; and has its green colour restored by 
means of alkalies. 
The yellow colouring matters of flowers are the 
most permanent; the carthamus contains a red 
and a yellow colouring matter ; the yellow colour^ 
ing matter is easily dissolved by water, and from 
the red, rouge is prepared by a process which is 
kept secret. 
The same substances as exist in the solid parts 
