286 TOWERS AND TANKS FOR WATER-WORKS. 



defect is a common one, and it is very serious, both because 

 it reduces the shearing-area of the rivet, and because it 

 greatly increases the difficulty of making the rivets fill the 

 holes perfectly. A shop that turns out work of this kind is 

 particularly censurable, not only because the work itself is 

 poor and weak, but also because the defect is not easy to dis- 

 cover, after the rivets are in place, and the owner of the boiler 

 is therefore likely to be deceived by a fair external appear- 

 ance, and to carry more pressure than the boiler can safely 

 withstand. The inspector also found that the heads were 

 not driven evenly over the holes, the centres of the heads 

 often lying well towards the side of the rivet. This defect, 

 although not so dangerous as the unfairness of the holes, 

 would not be tolerated in a good shop having any pretense 

 of turning out first-class work. It is very easily detected, 

 even by one who has had little experience in inspecting; 

 and there is no excuse for it whatever. . , . The only thing 

 that could be done in the way of improvement would be to' 

 cut out all the rivets, ream out the holes until they should be 

 true, and rivet them up again with larger rivets." 



There are many reasons for the belief that a machine- 

 driven rivet makes a much more satisfactory job than 

 where a rivet is driven by hand, for the metal cooling rapidly, 

 the greatest power and certainty is required to forge the head 

 before the rivet material is too cold to work. Various types 

 of power riveting-machines are now built whose motor force 

 is either air, steam, water or electricity, affording a constant 

 pressure throughout the stroke of about 80 pounds. 



From comparative tests with both power- and hnnd- 

 driven rivets, in Kent's " Mechanical Engineer's Handbook/' 

 is recorded the slip of plates pulled apart. In this it is shown 

 that machine-driven rivets of equal diameter held twice as 

 much as hand-driven rivets. 



At the Gas Exhibition, held in New York about 



