26 PROXIMATE CONSTITUENTS OF PLANTS 



for the detection of cotton-seed oil in cheap olive oil, 

 margarine, etc. 



(d) Carbohydrates. 



When carbon is assimilated from the CO2 of the air by the 

 action of chlorophyll in conjunction with protoplasm (see p. 54), 

 it is elaborated into sugars, starches, and cellulose. There is still 

 some doubt as to which of these substances is the first product of 

 the assimilation. Brown and Morris (1893) concluded that cane 

 sugar was the primary substance, while according to the later 

 work of Campbell (191 2) it was concluded that dextrose and 

 Isevulose are the first carbohydrates to be found. 



As to the states in which the above carbohydrates exist in 

 plants, the sugars are in solution in the cell sap, the starch is in 

 the solid form of granules in the plant cells, while the cellulose 

 largely makes up the framework of the cells. 



15. Preparation and Qualitative Examination of 

 Cellulose. 



About 2 grams of finely ground straw or hay, or 

 other suitable material, are placed in a flask and boiled 

 for twenty minutes with a mixture of 200 c.c. water 

 and 2 c.c. concentrated sulphuric acid. Various mineral 

 constituents, together with alkaline bodies, etc., are 

 thereby removed. The acid liquid is poured off, the 

 residue thoroughly washed free from acid, and 200 c.c. 

 water containing 2- 5 g. caustic soda added. The mixture 

 is again boiled for twenty minutes, the alkaline liquid 

 poured off, and the residue carefully washed as before. 

 The alkali removes the acid constituents, phenols, etc., 

 that may be present. The fibrous product is fairly pure 

 cellulose, but is generally dirty grey in colour, in which 

 case it should be bleached by warming with 2C)0 c.c. of 

 a 50 per cent, solution of HCl and adding a few crystals 

 of potassium chlorate. The nascent chlorine evolved 

 bleaches the colouring matter, and the cellulose is then 

 well washed several times with boiling water. 



