72 On the Strength of Cylindrical Steam Boilers. 



, ,• , ^ TT 30X1000 



an inch thick? Here 5 =-2-— 05— = 60,000. Hence we see that 



the metal must be capable of sustaining sixty thousand pounds to the 

 inch bar, or in that proportion, for any other size. This formula en- 

 ables us to determine whether among the metals of known tenacity 

 any one can be found to fulfil the conditions under the thickness as- 

 signed. 



12. On the basis of the foregoing formulas, the following table of 

 diameters, thicknesses of iron, and strairfs to the inch of metal, in both 

 directions, has been formed. It is obvious that the actual tenacity of 

 the metal employed in a given case must be of the greatest impor- 

 tance to the result. The extensive series of experiments recently 

 undertaken by the Institute to determine this question, in reference 

 to different kinds and varieties of boiler plate, and with regard to the 

 various circumstances of its manufacture and application, will here- 

 after furnish us with important data to aid in applying the formulas 

 to each separate case. I shall for the present assume the tenacity 

 of an inch square bar of rolled iron at 55000 lbs. in the direction of 

 the length of the sheet. Supposing the pressure generally employed 

 in cylindrical high pressure boilers to be 150 lbs. to the square inch, 

 agreeably to the practice in this city, the table is calculated upon the 

 principle that the boiler ought to have five times as great a strength 

 as it is ordinarily required to exert. The calculation is upon a con- 

 tinuous sheet of metal, without seams in any direction. The thick- 

 nesses are given in ten-thousandths of an inch ; but in practice -the 

 last figure may be omitted without material error. 



