(IOO) 



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 Oils 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. 



