Economic Importance of Plants 259 



Petroleum or crude oil is a dark-brown or yellowish-green inflam- 

 mable liquid formed by the partial decay of organic ooze (foraminifera, 

 diatoms, algae, etc.) by bacterial action, thus liberating fats and waxes 

 to produce petroleum. 



Kerosene is an inflammable liquid obtained by the distillation and 

 purification of petroleum. It is used for heating, lighting, and cooking 

 purposes where gases are not available. 



Gasoline is a volatile and highly inflammable liquid obtained by the 

 distillation and purification of petroleum. Its principal use is for motor 

 fuel. 



Oils. — Oils are very generally present in the plant kingdom as either 

 volatile or fixed oils. Generally speaking, the volatile oils easily and 

 quickly vaporize at ordinary temperatures, while the fixed oils do not. 

 The fixed oils are chemical mixtures in various proportions of glycerides 

 (glycerine and an acid). Examples of the volatile oils are oil of winter- 

 green, oil of cloves, oil of peppermint, etc. Examples of fixed oils are 

 oil of almonds, peanut oil, olive oil, etc. 



Plant oils are used (1) in flavoring materials, (2) as foods, (3) as 

 medicines, (4) in industries in the manufacture of paints, printing inks, 

 soaps, perfumery, lubricants, illuminants, etc. 



Certain fixed oils are used to hold particles of coloring matter in sus- 

 pension in paints. The oil permits the even application of the paint and 

 its prompt hardening through the process of oxidation. Linseed oil, 

 which is pressed from the seeds of flax, is an excellent "drying" oil 

 whose properties may be improved by boiling (boiled linseed oil). For 

 fine paints, such oils as nut oil (from nuts of English walnut) and 

 poppy oil (from seeds of opium poppy) may be superior to linseed oils. 

 In certain printing inks the linseed oil is boiled until it is very thick. 

 Linseed oil is used extensively when united with resins to make varnish. 



Any fixed oil with its contained glyceride (glycerine plus an acid) 

 when combined with an alkali will form a soap. In this process the 

 glycerine is given off" as a by-product. A fixed oil plus potash or lye 

 forms a "soft" soap. A fixed oil plus soda forms a "hard" soap. 



As lubricants, only fixed oils which are nondrying can be used. The 

 oil must be thin enough to penetrate to all parts and at the ^ame time 

 have a consistency which will withstand high temperatures and friction. 

 Examples of such oils are crude oils, motor oils (refined crude oils), 

 castor oil (from castor bean), olive oil, cotton-seed oil, rape oil (from 

 certain varieties of turnip). 



