22 
Carbon Assimilation. 
If an alcoholic solution of sulphur is poured into a large volume of 
distilled water, a sulphur sol is produced. 
Experiment 17. To show the difference between a true and a 
colloidal solution of chlorophyll. 
Evaporate 10 c.c. of the acetone extract to complete dryness 
and test its solubility in ether, petrol ether and benzene. Now add 
these solvents to some of the colloidal solution prepared in the last 
experiment, and note that the chlorophyll does not dissolve in any 
of these solvents. If, however, some salt solution, e.g., a little 
magnesium sulphate be added, the chlorophyll is precipitated from 
its colloidal state and is now soluble in ether and other solvents. 
Experiment 18. To show that chlorophyll in the plant is 
probably in the colloidal condition. 
Some nettle powder is carefully dried, e.g., by keeping it at 
30 ft C. to 40 n C. in an oven, and then further drying in a vacuum 
desiccater over sulphuric acid. Small quantities of this dry powder 
are put in test-tubes and different pure water-free substances such 
as acetone, ether, benzene and absolute alcohol are added. Note 
that these solvents are not coloured by the chlorophyll. It can be 
demonstrated that the extracted pigment’is easily soluble in any of 
these substances. 
Repeat the experiment with nettle powder moistened with a 
few drops of water, and note that the solvents are immediately 
coloured. 
Experiment 19. Eure solvents are able to extract chlorophyll 
from fresh leaves. 
Crush 10 grams of fresh leaves of nettle, horse-chestnut or 
elder in a mortar with some clean sand, and put the crushed 
material on a filter paper in a Buchner funnel. Add 20 c.c. pure 
acetone and suck it through by means of a water pump. Repeat 
this several times. The pure solvent is here able to extract the 
pigment. 
It can also be observed that the leaf substance after 
extraction is brown, owing to the action of oxydases on the leaf. 
If therefore, the leaves are dipped first in boiling water, these 
oxydases are destroyed, and the leaf substance after extraction 
remains colourless. 
Experiment 20. Treatment of fresh leaves with boiling water 
changes the condition of the chlorophyll. 
Dry a quantity of leaves which have been put in boiling water 
and examine their solubility as in Experiment 18. Note that the 
chlorophyll in this powder is soluble in pure solvents. 
