ENGINEERING ON THE FARM 



175 



It was manufactured in France and England as early as 

 1338. In 1858 Lamotte du Pont, of Wilmington, Delaware, 

 invented blasting powder (Fig. 155), which differs from gun- 

 powder in that Chile saltpeter (sodium nitrate) is used in 

 the place of India saltpeter (potassium nitrate). 



Gunpowder ingredients are ground to a powder separately, 

 then ground together with a little water until completely 



€&&&. 





After E. I. du Pont de Nemours & Co. 

 FiG. 155. Various sizes of Du Pont "A" blasting powder 



mixed. The material is then formed into cakes, after which 

 it is broken up into grains and dried. It is glazed by rub- 

 bing and sorted into sizes by sieves. The object of the glaz- 

 ing is to prevent the grains from absorbing moisture from 

 the air and to cause them to be free-running so they will 

 fit more closely together. 



Nitroglycerin. Nitroglycerin was first made in Paris in 

 1846 from glycerin treated with strong nitric and sulphuric 

 acids. The ordinary process of manufacture consists of 

 mixing five parts sulphuric acid, three parts nitric acid, and 

 one part glycerin in a lead vessel. The acids are placed in 

 the vessel and the glycerin added in a small stream, the 

 temperature being kept below 85 Fahrenheit by an air 

 blast. The nitroglycerin settles and the spent acid is 



