vi] THE FATS AND LIPASES 81 



Malvaceae: Cotton (Gossypium herbaceum) 24/o- 



Sterculiaceae : Cocoa (Theobroma Cacao) 54/ . 



Lecythidaceae : Brazil Nut (Bertholletia excelsa) 68 /o- 



Oleaceae: Olive (Olea europaea) 20-70%: Ash (Fraxinus excelsior) 

 27 o/ . 



Rubiaceae : Coffee (Coffea arabica) 12/ . 



Cucurbitaceae : Pumpkin (Cucurbita Pepo) 41 / . 



Compositae : Sunflower (Helianthus annuus) 38%. 



The conclusion must not be drawn from the above list that the 

 seeds of the plants mentioned have exclusively fats as reserve materials. 

 In many cases fat may be the chief reserve product, but in others it 

 may be accompanied by either starch or protein or both. 



Some of the best-known examples of fat-containing seeds which 

 yield " oils " of great importance in commerce, medicine, etc., are Ricinus 

 (castor oil), Brassica (colza oil), Gossypium (cotton-seed oil), Cocos 

 (coconut oil), Elaeis (palm oil), Olea (olive oil). 



In the plant the fats are present as globules in the cells of the fat- 

 containing tissues. 



Plant fats may vary from liquids, through soft solids, to wax-like 

 solids which generally have low melting-points. They float upon water 

 in which they are insoluble. They are soluble in ether, petrol ether, 

 benzene, chloroform, carbon tetrachloride, carbon bisulphide, etc. : some 

 are soluble in alcohol. With osmic acid fats give a black colour, and 

 they turn red with Alkanet pigment which they take into solution. 



Expt. 82. Tests for fats. Weigh out 50 gins, .of Linseed (Linum usitatissimum) 

 and grind in a coffee-mill. Put the linseed meal into a flask, cover with ether, cork 

 and allow the mixture to stand for 2-12 hrs. Filter off the ether into a flask, fit 

 with a condenser and distil off the ether over an electric heater. (If a heater is 

 not available, distil from a water-bath of boiling water after the flame has been 

 turned out.) When the bulk of the ether is distilled off, pour the residue into an 

 evaporating dish on a water-bath and drive off the rest of the ether. With the residue 

 make the following tests in test-tubes : 



(a) Try the solubilities of the oil in water, petrol ether, alcohol and chloroform. 

 It is insoluble in water and alcohol, but soluble in petrol ether and chloroform. 



(6) Add a little 1 % solution of osmic acid. A black colour is formed. (This re- 

 action is employed for the detection of fat in histological sections.) 



(c) Add to the oil a small piece of Alkanet (Anchusa officinalis) root, and warm 

 gently on a water-bath. The oil will be coloured red. Divide the oil into two portions 

 in test-tubes. To one add a little water, to the other alcohol. The coloured oil will 

 rise to the surface of the water in one case, and sink below the alcohol in the other. 

 The Alkanet pigment being insoluble in both water and alcohol, these liquids remain 

 uncoloured. 



Keep some of the linseed oil for Expt. 83. 

 o. 6 



