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varieties of pumpkin, appearing as a thin whitish coating, 
commonly called the “‘bloom.” In the same way they 
occur upon the surface of many leaves. The term glaucous 
is applied in descriptive botany to such surfaces. In a 
few cases, wax exudes in such quantity as to be collectable 
in commercial quantity. This is usually done by placing 
the wax covered tissue in hot water, when the wax is 
melted and may be skimmed off of the surface of the water. 
A good illustration of this wax is that found upon the surface 
of the bayberries, illustrated in our collection. 
Fixed Otls or Fats. Case 53.—Fat is a very abundant 
plant product, occurring more abundantly in ripe seeds 
than in other parts. Fats also often occur abundantly 
in the pericarps of fruits, especially those of the palm 
family. The best method of extracting oils is by a simple 
process of pressure, in the cold state. Such an oil, if the 
pressure be moderate, is likely to be quite pure. Pressure 
with heat is often employed, the yield of oil thus being 
increased. In many cases, oils are obtained by boiling 
the product in water, from the surface of which the extracted 
fat may be skimmed. In many cases, this method is 
liable to cause deterioration of the fat by its partial de- 
composition. Many oils, as those of coconut, cotton-seed, 
and olives, yield important food products. Many others, 
as linseed oil, are largely employed in paints, others in 
soap-making or for lubricating purposes. In other cases, 
as castor and croton oils, they are highly medicinal. 
There are vast numbers of oil-yielding products in tropical 
countries which are not collected, the annual wastage of 
such products running into enormous values. 
Soap and Soap Substitutes. Case 54.—One of the most 
important uses of the fixed oils is for soap-making, and of 
the volatile oils, that of perfuming such soap. The manu- 
facture of soap consists essentially in boiling the oil or 
fat with an alkali by which process the acid of the fat is 
caused to combine with the alkali, this product constituting 
soap. ‘The glycerin of the fat is set free as a by-product. 
