74 On the Strength of Cylindrical Steam Boilers. 
table at p. 27 of his “Young Steam Engineer’ s Guide,” he has given 
calculations for seventeen different diameters of boilers, with the 
power which, at each diameter, the steam would exert ‘to break 
every ring of one inch wide in any one place,” and “ the thickness 
_ of the sheets of good iron necessary to hold the power.” His table 
is formed on the supposition that sheet iron will bear 64,000 Ibs. to 
the square inch, and would consequently lead to considerable excesses 
‘if strictly applied in practice. To six of the diameters he has an- 
nexed the “ power exerted on the heads to burst them out, in pounds 
weight.”? These he has calculated in the usual manner, by multi- 
plying the area by the pressure per inch. Opposite to three of the 
numbers just mentioned, he has added “ the strength of the boiler to 
hold the head on; in pounds weight.” These he has calculated on 
the supposition that the metal had equal tenacity in all directions. 
On this supposition, and on the principles above developed, each of 
those three numbers shouid have been exactly double of that against 
which it stands in the preceding column. Neither of the three is so, 
precisely; but the first and third come as near it as could be expect- 
ed, considering that the thickness is expressed only in hundredths of 
an inch, a the second is too small by more than a million of 
pounds. These errors would not, I apprehend, have occurred had 
the author adverted to the general principle above developed, in re- 
gard to strength required of the metal in the two directions. 
The following extract-from the table just alluded to, will illustrate 
_ the precatise remarks: a column of corrected results has been added. 
Thickness of} - : 
F er to break the plate of \be fa to be ss 
Diameter « . wets ring of [iron sustain-| Power ex- | Strength to |tuted for those} 
: ra boiler | 1 inch, press- | ing 64,000 lerted on the ; hole on the jof col. 5, “agree- 
inches. |. ure being | Ibs. to the heads. heads eer to the fore: 
1500 Ibs. {square inc | oin 
42 31,000 48 2, 077,500 4,052,400 4, 155,000 
“36 |. 27,000 42 _|1,525,500 2,087,440] 3,051,000 |. 
20 15,000 23 | 471,000 918,777] 942,000 
* The very eel use, in this country, of strong cast iron heads, 
fastened to the wrought iron cylinders by broad flanches extending 
some inches within the latter, there riveted and subsequently further 
secured by a strong wrought iron hoop, driven on when hot and 
shrunk by cooling,—appears to obviate the necessity of examining 
the question in regard to the best form and monty thickness of 
