164 APPLIED SCIENCE 



includes magnesium chloride, calcium chloride, glycerin, and 

 common salt. 



192. Mercerizing. Cotton may be made to resemble 

 silk, so far as the luster is concerned, through the application 

 of a solution of caustic soda under tension. This process 

 is called mercerization. The effect of the caustic soda is 

 to cause the cotton fibers to become smooth and cylindrical 

 in form so that they reflect the light and appear " shiny" 

 with a strong luster. It is a physical and not a chemical 

 change. 



193. Gassing. The luster of mercerized cotton may 

 be increased by passing the material rapidly over a platinum 

 plate heated to a very high temperature. The effect is to 

 take off the loose fibers. This operation is called gassing. 



194. Spontaneous Combustion. Spontaneous combus- 

 tion is an expression used to explain the setting on fire of a 

 substance without the employment of any external agent, 

 such as a lighted match, a flame, or a spark. To illustrate: 

 There are times when a pile of coal will burst into flame 

 without the application of a flame or spark. The reason 

 for this is quite different from the reason for the burning of 

 coal in a stove or under a boiler. The first burning is caused 

 by spontaneous combustion, and the second by the ordinary 

 combustion of coal. In both cases, however, the fires follow 

 definite laws. 



All combustion is a chemical action attended with the 

 liberation of heat and is the result of the combination of oxy- 

 gen with the combustible material. Ordinary combustion 

 or burning is merely the result of a substance being heated, 



