APPLICATION OF CHAINS. 127 



common puUies with semicircular grooves, are not in the and hs^ 



lea.st calculated to prevent. Ilcnce the alternate links of c^t^each odie?, 



the chain, in coiling round a barrel, or working over when bearing 



pullies, form obtuse angles in assuming the spiral form, on a barrel. 



bearing upon the lower parts of their circumferences, and 



forming as it were two levers, which wrench open and 



crush each other in proportion to the weight suspended, 



as well as prevent the freedom of motion in the links 



themselves, and thereby load the chain with additional 



friction. 



A still greater obstruction to the uniformity of its mo- its colls will 



tion, is the tendency which the chain has to make a double ^^^^ upon each 



other 3.n.ci icric 

 coil as it approaches the middle of the barrel and crosses when'theysHdc 



its centre, and that of the pullies at right angles, by means off; 

 of which the chain is frequently broken by the sudden 

 j«rk caused by the upper coil slipping off the under- 

 most. 



It is to these causes that all the accidents that occur to gnd thus' 



workmen and machinery from the failure of chains may they will break 

 be attributed (bad iron excepted), and which form the 

 sole objection to their becoming a general substitute for 

 ropes. 



As a preventive to these evils, I have grooves cast in The Inventor 

 iron pullies, of sufficient dimensions to receive the lower prevents this 

 circumferences of the links of the chain, which work ^^^ pulUef • *^ 

 vertically ; those which v/ork horizontally and form the 

 gudgeon part of the chain (if we may be allowed the 

 expression), bearing npon each side of the grooves. 



,The barrels are also of cast iron, with spiral grooves _.^|iich ad- 

 of the same dimensions, at such distance from each other mit the half of 

 as to admit the chain to bed without the danger of a ^^^^ alternate 

 double coil; hy these means the links are retained at 

 right angles with each other, the only position for free, 

 and uniform motion. 



The links of the chains are made as short as possible, 

 for the purpose of increasing their flexibility, and' they are 

 reefed perfectly free from twist, in the pullies, and on the 

 barrels for the same reason. 



When applied in blocks, the grooves in the pullies — — aBd pro- 

 prevent the different falls of the chain from coming 4uce many ad- 

 in contact, and render plates between them (as in the ^*" *^^'* 

 2 



