214 
Book IV. 
Properties. 
Action ot 
water, 
Acibs, 
VEGETABLE SUBSTANCES. 
lian philosopher, to whom we are indebted for the first 
analysis of wheat flour *. 
Gluten, when thus obtained, is of a grey colour, ex 
ceedingly tenacious, ductile, and elastic, and may be ex 
tended to twenty times its original length. When very 
thin, it is of a whitish colour, and has a good deal of re 
semblance to animal tendon or membrane. In this state 
it adheres very tenaciously to other bodies, and has often 
been used to cement together broken pieces of porce 
lain. Its smell is peculiar. It has scarce any taste, and 
does not lose its tenacity in the mouth. When expo 
sed to the air it assumes a brown colour, and becomes 
as it were covered with a coat of oil. 
When exposed to the air, it gradually dries ; and, 
when completely dry, it is pretty hard, brittle, slightly 
transparent, of a dark brown colour, and has some re 
semblance to glue. It breaks like a piece of glass, and 
the edges of the fracture resemble in smoothness those 
of broken glass; that is to say, it breaks with a vitreous 
fracture. 
When exposed to the air, and kept moist, it soon 
putrefies; but when dry, it may be kept any length of 
time without alteration. When not entirely deprived 
of starch, instead of putrefying, it assumes the appear 
ance and taste of cheese †. 
It is insoluble in water; though it imbibes and re 
tains a certain quantity of it with great obstinacy. To 
this water it owes its elasticity and tenacity. When 
boiled in water it loses both these properties. 
All the acids dissolve it, even when very much dilu 
ted; alkalies precipitate it again, but it is deprived of its 
* Colicct. Academ. X. i. 
Rouelle.