112 Economy of Machinery and Manufactures, 



In converting cast into wrought iron, it is of importance, that the 

 mass of softened metal should receive the greatest possible number 

 of strokes before it cools; but as the momentum of the hammer, de- 

 rived merely from the space through which it falls, would consume 

 much time, the velocity is increased by throwing the hammer up 

 with a jerk, against a large beam, which acts as a powerful spring, 

 and drives it down with such force and rapidity as to make double 

 the number of blows in a given time. " The smaller tilt hammers 

 are made to rebound with such velocity, that from three to five hun- 

 dred strokes are made in a minute." 



There is also, in extending the time of the action of forces, a very 

 great advantage, e.g. the winding up of a clock, or watch, extends 

 the action of the original force for hours and days. Small machines 

 set in motion by springs, with a train of wheels, are employed in 

 magnetic and electric experiments, to produce a rotatory motion of 

 a metallic disk or other body, thus giving the experimenter the un- 

 impeded use of his hands. The domestic smoke jack is a familiar 

 illustration of this principle. A similar apparatus is sometimes ap- 

 plied to polish minerals, and in certain chemical processes, to agitate 

 a solution.* 



Machinery is also employed to save time in natural operations. 

 An accelerating process in tanning was long a desideratum. In the 

 old method, it required two years for the tanning principle to become 

 so thoroughly combined with the animal fibre, as to make firm and 

 durable leather. 



" The improved process consists in placing the hides with a solution of tan in close 

 vessels, and then exhausting the air. The consequence of this is to withdraw all 

 the air contained in the pores of the hides, and to employ the pressure of the at- 

 mosphere to aid capillary attraction in forcing the tan into the interior of the skins. 

 The effect of the additional force, thus brought into action, can be equal only to one 

 atmosphere, but a further improvement has been made. The vessel containing the 

 hides is, after exhaustion, filled up with a solution of tan : a small additional quan- 

 tity is then injected with a forcing pump. By these means, any degree of pressure 

 may be given, which the containing vessels are capable of supporting, and it has beeft 

 found, that the thickest hides may thus be tanned in six weeks or two months." 



In noticing the practical value of science to the arts, the beautiful 

 and improved process of bleaching with chloride of lime, although 

 more of a chemical than of a mechanical operation, can scarcely be 

 passed in silence. 



* Economy of Machinery, p. 28. 



