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II. — On a Method of Testing the Strength of Steam Boilers. 

 By J. P. Joule, LL.D., F.R.S., §-c. 



Kead November 29th, 1859. 



In the course of my experiments ou steam^ I had to 

 employ pressures which I did not consider absolutely 

 safe unless the boiler was previously tested. The means I 

 adopted, being simple, inexpensive and efficacious, may, I 

 think, be recommended for general adoption. My plan 

 is as follows : — The boiler is to be first entirely filled with 

 water, care being taken to close all passages leading there- 

 from. A brisk fire must then be made under it, and, after 

 the water has become moderately heated, say to 90° Eahr., 

 the safety valve must be loaded to the pressure up to 

 which the boiler is intended to be tried. Bourdon's cir- 

 cular gauge, or other pressure indicator, is then to be 

 constantly observed ; and if the pressure arising from the 

 expansion of the water goes ou increasing continuously, 

 without sudden decrease or stoppage, until the testing 

 pressure is attained, it may be inferred that the boiler 

 has sustained it without having suffered strain. 



In testing my own boiler, the pressure ran up from zero 

 to sixty-two pounds on the inch in five minutes. It rose 

 more rapidly at the commencement than towards the ter- 

 mination of the trial, owing to leakage, which was con- 

 siderable, and of course increased with the pressure. But 

 as there was no sudden alteration or discontinuity in the 



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