PLYMOUTH ROCK 



4715 



PNEUMATIC TIRES 



anteed the rights and privileges of English citi- 

 zens. 



In 1607 the company made an unsuccessful 

 attempt to plant a colony in Maine, near the 

 mouth of the Kennebec River; it has to its 

 credit no permanent settlement. A new com- 

 pany was formed in 1620 known as the Council 

 for New England, but this organization relin- 

 quished its powers to the king in 1635. The 

 colony established at Plymouth in 1620 was an 

 independent venture, and had no connection 

 with the original Plymouth Company. B.M.W. 



See, in this connection, PLYMOUTH COLONY; 

 PILGRIMS : also titles there suggested. 



PLYMOUTH ROCK, a huge granite boulder 

 on the edge of the water at Plymouth Harbor, 

 Massachusetts. When the Mayflower reached 

 America on December 21, 1620, the Pilgrims 

 disembarked on this rock. In 1774, when it was 

 raised to be consecrated to liberty, it split into 

 two pieces, an incident which was regarded as 

 an omen of the separation of the colonies from 

 England. On July 4, 1834, part of the rock was 

 removed to Pilgrim Hall. The other half, cov- 

 ered with a granite canopy and surrounded by 

 an iron fence, may still be seen in the harbor. 

 See illustration, in article PLYMOUTH, MASS. 



PNEUMATICS, numat'iks, that branch of 

 physics which treats of the properties of gases, 

 it her at rest or in motion. It includes the 

 study of the atmosphere. How useful and im- 

 portant such a study is becomes evident when 

 we consider that we are living at the bottom 

 of an atmospheric ocean, just as fish are living 



beneath the surface of a water ocean. As a re- 

 sult of the knowledge acquired about the prop- 

 erties of gases and the laws governing them 

 there have been constructed numerous tools 

 and machines used in modern industry, all of 

 which are based on the laws of pressure and 

 elasticity of the air. The operations of various 

 Isof pumps are also based on the same prin- 

 ciples. See AJR PUMP; PUMP; PNEUMATIC 

 TOOLS. 



PNEUMATIC, numat'ik, TIRES. The 

 pneumatic tire .became prominent in 1889, when 

 it was first applied to the bicycle, although a 

 pneumatic tire was patented in England in 

 1843, and in the United States in 1847. Its 

 name is derived from the fact that it is filled 

 li compressed air. Pneumatic tires are now 

 used on automobiles, bicycles and motorcycles, 

 etch of which is described in these volumes un- 



Manufacture. A pneumatic tire consists of 

 two parts: an inner tube of thin rubber which 



is air-tight, and an outer tube or case consist- 

 ing of several layers of strong fabric into which 

 rubber has been pressed, with an outer cover- 

 ing of harder rubber. The rubber reaches the 

 tire manufactories ready for use. For its prepa- 

 ration, see RUBBER AND RUBBER MANUFACTURE. 



The Inner Tube. The sheets of rubber for 

 the inner tube are cut into strips of the length 

 and width necessary to make tubes of the re- 

 quired size. The long edges of these strips are 

 beveled, so that they will form a smooth, strong 

 seam. The strip is then drawn over a mandrel 

 and the edges are nicely fitted together and 

 held in place by wrapping the mandrel with 

 thin pieces of wet cloth, upon which strips of 

 wet duck are wound spirally. The whole is 

 then heated until the edges are cemented to- 

 gether. After cooling, the tube is removed 

 from the mandrel by being turned inside out. 

 An air valve is then inserted and the ends of 

 the tube are cemented together. With this last 

 process the tube is ready for use. 



The Outer Tube. The outer tube or case 

 needs to be strong enough to sustain the weight 

 of the vehicle for which it is made. The outer 

 case of a bicycle tire is light; that of a motor- 

 cycle tire is much heavier and stronger, and 

 still stronger casings for automobile tires vary 

 in weight and strength according to the weight 

 of the automobile for which they are made. 

 This case is the most important part of the tire. 

 Only the best material can be permitted to en- 

 ter into its construction, and it should be made 

 with extreme care. A strong cotton fabric is 

 the most desirable for making casings. Rub- 

 ber is pressed into this cloth by passing it with 

 a sheet of rubber between steel rollers that press 

 the two sheets together. The resulting fabric, 

 known as friction by the workmen, is cut 

 into strips of the proper size by machinery. 

 The strips are placed between layers of cotton 

 cloth to keep them from sticking together and 

 are allowed to cure. 



In the actual building of tires, the hand proc- 

 ess is regarded with most favor, although ma- 

 dunes may be used. The builder mounts the 

 core on which the tire is to be shaped, on a 

 building stand. The first ply of fabric is then 

 stretched on the core and is spliced, rolled 

 down with a hand roller and trimmed at tin 

 base with a knife. Other plies are treated in 

 the same manner, and then a layer of rubber 

 compound about one-sixteenth of an inch thick 

 is applied. The tread, or outer center surface, 

 is then folded over the whole. This is made by 

 laying up narrow strips of rubber in different 



