14 MODERN SCIENCE READER 



cover is a pipe, through which the gas passes into a reser- 

 voir below. From this it is forced directly into the engine, 

 and ignited by an electric spark. This causes it to explode, 

 and the force of the explosion drives the engines and the 

 other machinery. 



One of the most important discoveries which has been 

 made in connection with what we have called waste products 

 is the value of sawdust. Usually sawmills produce such 

 large quantities of the material, that it cannot be burned 

 to advantage. It is then thrown away, so to speak, some- 

 times being piled in great heaps and left to slowly consume. 

 A very good quality of alcohol, however, can be distilled 

 from ordinary sawdust by an inexpensive process, in such 

 quantities that two gallons of the liquid can be obtained 

 from 220 pounds of dust. The sawdust from birch and 

 some other species of forest trees will also yield a palatable 

 sugar after it has been treated with certain chemicals. In 

 America and in some parts of Europe an enormous quantity 

 of the dust is sold, being vended about in wagons and in 

 sacks carried on the backs of the venders. It is bought to 

 sprinkle on the floors of cafes, butcher shops, and other 

 places where it will prevent dirt from sticking to the floors. 

 In recent years so many dolls and other "stuffed" toys 

 have been made, that the sawdust is used very extensively 

 for this purpose also. It is a fact that there are five hun- 

 dred sawdust merchants in the city of New York alone, and 

 that they sell what is generally called waste to the value of 

 400,000 pounds in a single year. 



Since the slaughter of cattle, sheep, and other animals on 

 a large scale was begun at the abattoirs in America, France, 

 and other countries, the valuable articles and compounds 

 which have been made from dead animals is really amazing. 

 In some of the American abattoirs the carcass of a single 

 beef may enter into no less than four hundred different 

 articles, ranging from the beefsteak for the family table 

 to the buttons sewed on the family clothing. Parts of the 

 animals formerly discarded go into medicines, oils, soaps, 



