158 Wisconsin Academy of Sciences^ Arts^ and Letters. 



the University mactiine shop shows well the effect of cutting 

 through the outside of the iron. A piece of common five-eighths 

 square iron was cut on the four sides with a cold chisel, so that it 

 was well marked. A slight blow from the hammer caused it to 

 break, the ends showing crvstalization. A second piece was 

 marked on but one side, which on being broken, was crjstalized 

 about half through, the rest showing the fibre undisturbed, and 

 tearing out the iron for half an inch up the bar. It has been 

 claimed that the principal strength of iron is destroyed by cutting 

 through the " skin,'' yet, a piece of this same bar marked as in the 

 first instance, was placed in the lathe and the marks turned out, 

 after which it was bent to more than ninety degrees before break- 

 ing. 



It is estimated that about forty-four per cent, of the original 

 strength of the material has been destroyed by the time a boiler 

 is ready for riveting. The axiom that the " strength of any sfcruct- 

 iire must be estimated from the weakest point," is a good one. 

 By these various operations, six per cent, more will be of ques- 

 tionable value. Eepeat them at every joint in a boiler twelve to 

 twenty-four feet long, and who will tell where the weakest point 

 may be? Imagine if you can a boiler so constructed of any flexi- 

 ble material, it would contain more kinks and puckers and gath- 

 ers than a fashionable dress. New boilers are often submitted to 

 the hydraulic test, which consists of forcing in cold water to a cer- 

 tain pressure, and then assuming it safe to carry one-third or two- 

 thirds as much steam pressure. I believe it a questionable method 

 and an unsafe assumption. If there are blisters or imperfect 

 welds in the plates it may develop them. A careful inspection 

 would probably accomplish the same result. But in these tests 

 the boiler is subjected to strains under conditions which do not 

 occur in actual use. The water and iron are both cold, stay rods 

 and braces are loosened which do not again come tight of their 

 own accord. Further, most boiler iron, as demonstrated by the 

 experiments of the Franklin Institute Committee and Fairbairn, a 

 noted English mechanical engineer, has a greater tensile strength 

 with an elevation of temperature, some proving stronger at 600 ° 

 Fahrenheit, than at any lower point. Now it is quite certain that 



