M E C H 
Pour parts of filler with one of tin - - lbs. 41,000 
Six parts of copper with one of tin - - . 41,000 
Five parts of Japan copper with one of Banca tin 57,000 
Six parts of Chili copper with one of Malacca tin 60,000 
Six parts of Swedifh copper with one of Malacca tin 64,000 
Brafs confifts of copper and zinc in an unknown 
proportion; its ftrength is - 51,000 
Three parts of block tin with one part of lead 10,200 
Eight parts of block tin with one part of zinc 10,000 
Four parts of Malacca tin with one part of regu- 
lus of antimony ----- 12,000 
Eight parts of lead with one of zinc - - 4>5oo 
Four parts of tin with one of lead and one of zinc 13,000 
Thefe numbers are of confiderable life in the arts. The 
mixtures of copper and tin are particularly intCrefting in 
the fabric of great guns. We fee that, by mixing copper 
whofe greatelt ftrength does not exceed 37,000, with tin 
which does not exceed 6000, we produce a metal whofe 
tenacity is almoft double, st the fame time that it is harder 
and more eafily wrought. It is, however, more fufible, 
which is a great inconvenience. We alfo fee that a very 
fmall addition of zinc almolt doubles the tenacity of tin, 
and increafes the tenacity of lead five times ; and a fmall 
addition of lead doubles the tenacity of tin. Thefe are 
economical mixtures, This is very valuable informa¬ 
tion to plumbers for augmenting the ftrength of water- 
pipes. By having iecourfe to thefe tables, the engineer 
can proportion the thicknefs of his pipes (of whatever 
metal) to the preflures to which they are expofed. 
Mr. Banks, an ingenious lecturer on natural philofo- 
phy, has at various times made many experiments on the 
real and comparative ftrengths of oak, deal, and iron. He 
found that the worlt or weakeft piece of dry heart of oak, 
1 inch fquare, and 1 foot long, bore 66olbs. though it was 
much bent; and 2 pounds more broke it. The (trongeft 
piece he tried of the fame dimenfions, broke with 974lbs. 
The w'oift piece of deal bore 46olbs. but broke with 4 
more. The beft piece bore 6901ns. but broke with a little 
more. And with refpeft to caji iron, he concludes that a 
bar of the weakeft kind, an inch fquare and a foot long, 
would break with about 2i9olbs. The following are fome 
of the experiments he mentions. They were tried at Ket- 
ley, in March 1795. The different bars were all call at 
one time out of the fame air-furnace, and the iron was 
very loft, fo as to cut or file eaiily. 
Exp. 1. Two bars of iron, one inch fquare, and ex- 
sdlly three feet long, were placed upon a Horizontal bar 
fo as to meet in a cap at the top, from which was fuf- 
pended a fcale ; thefe bars made each an angle of 45° with 
the bafe-plate, and of confequence formed an angle of 
90 0 at the top : from this cap was fufpended a weight of 
feven tons, which was left for fixteen hours, when the 
bars were a little bent, and but very little. 
Exp. 2. Two more bars of the fame length and 
thicknefs were placed in a fimilar manner, making an 
angle of 22! with the bafe-plate ; thefe bore four tons 
upon the fcale: a little more weight broke one of them, 
which was obferved to be fomewhat crocked when firft 
put up. In this cafe the preffure would be as the fines 
of the angles of elevation, viz. as 3826 to 7071 ; and, as 
3826 : 4 tons :: 7071 : 7'6 tons; that is, if the fecond 
bars broke with four tons, the firft ought to have taken 
7 6 tons to break them ; and it is likely that would, if 
tried, have been the cafe. 
Exp. 3. Another bar was placed horizontally upon two 
fupporters, exactly three feet diltant; it bore 6cwf. 3 qrs. 
but broke when a little more was added. 
Exp. 4. The fame experiment repeated with the fame 
refult. 
Exp. 5. The bearings were 2 feet 6 inches apart, the 
bar bore 9Civt. and broke. Three more experiments were 
tried the next day with the prifms 3 feet diftant; the aver¬ 
age refult was 6cwt. 2 qrs. 7-5 lbs. nearly as in Exp. 3. 
The following experiments were tried at Cokbrook- 
dale, on curved bars or ribs of caft iron, April 1795. 
A N I C S. 659 
Exp. 6. Rib 29 feet 6 inches fpan, and ti inches high 
in the centre; it fupported 99cwt. 1 qr. i4lbs. it funk 
in the middle 3|, and rofe again £ when the weight was 
removed. The fame rib was afterwards tried without 
abutments, and broke with J5cwt. oqrs. 14lbs. 
Exp. 7. Rib 29 feet 3 inches in fpan, a fegment of a 
circle, 3 feet high in the centre; it fupported iaocwt. 
iqr. 14 lbs. and funk in the middle. The fame rib 
was afterwards tried without abutments, and broke with 
64Civt. i qr. i4lbs. 
The thicknefs of thefe ribs unluckily is not fpecified ; 
but the experiments prove that each rib exerted little 
more than half the ftrength when the abutments were 
removed. 
Mr. Banks made fome experiments on the ftrength of 
caft iron, at Meffrs. Aydon and Elwell’s foundry, Wake¬ 
field. The iron came from their furnace at Shelf, near 
Bradford, and was calt from the air-furnace; the bars one 
inch fquare, and the props exactly a yard diftant. One 
yard in length weighs exactly 9 lbs. or one was about half 
an ounce lefs, and another a very little more: they all 
bent about an inch before they broke. 
1. The firft bar broke with - - 963 lbs. 
a. Bar broke with - 658^5. 
3. Bar broke with - - - - 994 .1 l>s. 
4. Bar made from the cupola, broke with 864 lbs. 
5. Bar equally thick in the middle, butb 
the ends formed into a parabola, and > 874lbs. 
weighed 6 lbs. 30Z. broke with - -j 
This gentleman made many other experiments. He 
concludes from the whole, that caft iron is from 35 to 41- 
times ftronger than oak of the fame dimenfions, and from 
5 to 6£ times ftronger than deal. Mr. Banks has pub- 
lillied the refults of his various experiments, including 
particularly thofe on the ftrength of beams to work cy¬ 
linders, and of iron (hafts or axles for mills, in a ufeful 
little treatife “ On the Power of Machines, &c.” 
PRACTICAL MECHANICS-, or, The CONSTRUCTION 
of MACHINERY. 
The practical application of mechanics to theconftruc- 
tion of machinery, is a fubject of the utmoft importance 
to the welfare o( our country, depending fo materially as 
it does upon commerce, which is derived chiefly from' 
our manufactures; and thefe owe the pre-eminence they 
have over other nations to the general introduction of 
machinery, which has taken place within thefe forty 
years, to abridge manual labour in every department, and 
in every trifling operation. It is to this fource we mult 
look for the increafe of property of every defcription, as 
the introduction of every machine is a real creation of all 
tl;e work it will perform, without the addition of farther 
increafe of human labour. An idea is very generally en¬ 
tertained, that machinery is prejudicial to the intereft of 
mankind, as far as it tends to diminifh the value of that 
labour by which the lower clalfes of fociety can alone 
purchafe the means of fnbfiftence : this idea is, however, 
founded ou error, as applied to any fuppofed injury fo- 
ciety in general can fuftain ; though individuals whofe la¬ 
bours are fuperfeded by machines will (after inconveni¬ 
ence for a time, yet it is only for a time, and fo long as 
till they, or others more intelligent, (hall difcover a new 
channel for the exertion of their induftry. As machines 
tend to increafe the quantities of thofe luxuries and ne- 
celfaries of life which mankind are fo anxious to obtain, 
it only requires that an equitable diviiion of thefe benefits 
lhould be made, to obviate every objection, and really 
improve the condition of all dalles. A retrofpeCf of the 
laft forty years (hows the truth of this oblervation ; for, 
though fo many machines have been employed in all 
trades and manufactures as probably to do more work 
than the whole population could do previous to that pe¬ 
riod, yet the value of human labour has, notwithstanding, 
increaied in the fame proportion as other articles have ad¬ 
vanced in price. And the editor of the Edinburgh Re¬ 
view. 
