30 BOTANY 
To show the test, make a little thin starch paste. 
A single drop of iodine added to this will give a blue 
colour. In testing substances for starch, the best. 
results are obtained by scraping the material very fine, 
boiling in a test tube with water, cooling by letting the 
tap run on the tube, and then adding the drop of 
iodine. The cooling is very important, for, when the 
material is above a certain temperature, the blue 
colour will not appear. Various substances, such as 
potato, parsnip, and seeds may be tested in this way. 
Fehling’s Solution is a substance used to test for 
grape sugar, which is present in various parts of 
plants. 
The following rough and ready method of pre- 
paring the Solution will serve all practical purposes :— 
Add tartaric acid to bluestone (copper sulphate) 
dissolved in water, till the colour is slightly green, and 
then add caustic soda till the solution is dark blue. 
To show the test, crush a piece of apple or banana, 
cover with water, add a drop of Fehling’s Solution 
and boil in a test tube; a yellow or orange red sediment 
is formed, showing the presence of grape sugar. The 
earbon of the sugar has taken away from the copper 
in the solution some of the oxygen that was united 
with it, and thus caused the change in colour from blue 
to yellow. In other words the higher oxide of copper 
has been reduced by the carbon of the sugar to a lower 
oxide, which, being insoluble, has been thrown down 
as a precipitate. 
Carbohydrates are solid substances that consist of 
carbon combined with the elements of water or, since 
water is a compound of oxygen and hydrogen, carbo- 
hydrates may be said to be formed from carbon, 
_ oxygen, and hydrogen, the oxygen and hydrogen 
being in the same ‘proportion as they are found in 
water. The most important carbohydrates are sugar, 
starch, and cellulose. 
