1 26 
water merely are separated from the alcohol by the 
sulphuric acid, and that ether differs from alcohol 
in containing a larger proportion of carbon and 
hydrogene. Like alcohol it possesses intoxicating 
powers. 
A number of the changes taking place in the 
vegetable principles depend upon the separation of 
oxygene and hydrogene as water from the com- 
pound ; but there is one of very great importance, 
in which a new combination of the elements of 
water is the principal operation. This is in the 
manufacture of bread. When any kind of flour, 
which consists principally of starch, is made into a 
paste with water, and immediately and gradually 
heated to about 440°, it increases in weight, and is 
found entirely altered in its properties ; it has lost 
its solubility in water, and its power of being con- 
verted into sugar. In this state it is unleavened 
bread. 
When the flour of corn or the starch of potatoes, 
mixed with boiled potatoes, is made into a paste 
with water, kept warm, and suffered to remain 30 
or 40 hours, it ferments, carbonic acid gas is dis- 
engaged from it, and it becomes filled with globules 
of elastic fluid. In this state it is raised dough, 
and affords by baking, leavened bread ; but this 
bread is sour and disagreeable to the taste ; and 
leavened bread for use is made by mixing a little 
dough, that has fermented, with new dough, and 
kneading them together, or by kneading the bread 
with a small quantity of yeast. 
In the formation of wheaten bread more than £ 
of the elements of water combine with the flour ; 
