488 



Fig. 48. 



the places of the joints of the lower series are shown by dotted lines ; the 

 position of the rings of each series one above the other is shown in the sec- 

 tion fig. 49. The joints of the inner series of rings are so placed as to lie 



Fig. 49. 



between those of the outer series, to prevent the escape of steam which 

 would take place by one continued joint from top to bottom of the packing. 

 The segments into which the rings are divided are pressed outward by steel 

 springs in the form of the letter V, the springs which act upon the outer 

 series of segments abutting upon the inner series, and those which a-ct on the 

 inner series abutting upon the solid centre of the piston : these springs are 

 represented in fig. 48. 



An improved form was given to the metallic piston by Barton. Barton's 

 piston consists of a solid cylinder of cast-iron, represented at A in section in 

 fig. 50, and in plan in fig. 51. In the centre of this is a conical hole, in- 



Fig. 50. 



