Securites against Fire, &c. 991 
plosions of boilers in steam engines, seems a third ground for the con- 
jecture, that these gentlemen have not in their examinations on such 
occasions, invariably comprehended all the principles which have 
had a_ bearing on the subject.* 
* Tt is only in anote that I am entitled to speak of the tenacity of metals, as having 
some concern in the case of machinery, where heat is employed; there being noth- 
ing in my letter to call for the mention of it; but a note may be admitted in this place 
to shew that both tenacity and expansion in metals may, on these occasions, have 
a singular operation. The case will become more striking where two metals are em- 
ployed; for the metals may differ from each other on these points, as also be opera- 
ted upon in different proportions as to these points at different rates of temperature. 
Of all metallic substances mercury has the least tenacity and most expansion; but 
both iron and copper have peculiarities worth noticing in these respects; particular- 
ly where both metals are employed together in the same machinery. 
What I have to state on this subject will be founded chiefly on different data col- 
lected from the able report made on the explosion which occurred to the boilers of 
the steam boat New England, at Essex in Connecticut, on Nov. 9, 1833; to which 
report are affixed the names of three truly scientific gentlemen in the vicinity; 
namely, Benjamin Silliman, W. C. Redfield and Denison Olmsted; and those also 
of an expert artist, Daniel Copeland and an experienced navigator by steam John F. 
Lawson. 
1. Datum. Mr. Smeaton gives the expansion of iron as 151 ten thousandth parts 
of an inch at 180 degrees of Fahrenheits thermometer; and that of copper as 204 
ten thousandth parts of an inch at the'same temperature; and Mr. Smeaton says, 
that his results sufficiently agreed with what others had ascertained at the same pe- 
riod. See Hutton’s Mathematical Dictionary, article expansion; and the Phil. 
Trans. Vol. xlviiii—The report above mentioned says (p. 20), that the experiments 
of Guyton Morveau, shew, that the tenacity of iron compared with copper is nearly 
as 540 to 302; or more than 80 per cent in favor of iron.—2. Datum. Copper is 
weakened by the action of heat at about 250°; anda copper boiler will bear a great- 
er pressure when cold, than when heated. An iron boiler if heated not beyond 480°, 
will bear a greater pressure, than when cold, (p. 14.)—3. Datum. Melted copper 
at a white heat, will pass through a high column of water, and remain for some time 
ignited at the bottom of the vessel. According to the statement of Mr. Adam Hall, 
ten pounds of copper heated to such a degree of redness as to be merely visible in 
the dark, will convert a pound of water into steam; making more than 27 cubic feet. 
at the common atmospheric pressure. It follows therefore, that copper flues as they 
have, on the whole, an extensive surface and great density, may produce an uncon- 
trollable quantity of steam, even at a heat far below redness. (See, says the report 
p. 17, the valuable experiments of Prof. Walter Johnson, in the American Journal of 
Science.)—4. Datum. There were a few square feet of iron plate in the chim- 
nies [that is to each chimney, there being two boilers to the engine ;] to which 
[plates] the steam had access on one side; and there can be no doubt that these flues 
frequently became red hot. (p. 17 and aslo p. 5.)—5. Datum. The position of the 
safety valve on the steam pipe was 20 or more feet from the boilers. * * * The 
diameter of the steam pipes which led from the boilers was about 10 inches. (p. 8.) 
—6. Datum. The copper varied in thickness in different parts. (p. 6.)—7. Datum. 
A heavy fall or crash, or a sudden cracking, preceded the first explosion, which 
was(by all but one person who heard it,) thought unusual. (See 9, 10, and 203 
Vou. XXVI.—No. 2. 38 
