THE strength or cohesion of the alloys, is in general greatly superior to that of any of the metals of which they are composed. For example, on comparing some of the numbers of the table, on pages 288 and 289, it will be seen that the relative weights, which tear asunder a bar one inch square of the several substances, stand as follows; all the numbers being selected from Muschenbrok's valuable investigations, so that it may be presumed, the same metals, and also the same means of trial, were used in every case.

Alloys.

Cast Metals.

10 Copper,

1 Tin,

32,093

lb.

Barbary Copper,

22,570

lb.

English Block Tin,

6,650

8 -

1 -

36,088

,,

Japan -

20,272

,,

Do. -

5,322

6 -

1 -

44,071

,,

Bam Tin,

3,679

4 -

1 -

35,739

,,

Malacca -

3,211

2 -

1 -

1,017

,,

1 -

1 -

725

,,

The inspection of these numbers is highly conclusive, and it shows that the engineer agrees with theory and experiment, in selecting the proportion 6 to 1 as the strongest alloy; and that the philosopher, in choosing the most reflective mixture, employs the weakest but one; its strength being only one-third to one-sixth that of the tin, or one-twentieth that of the copper, which latter constitutes two-thirds its amount.

It is much to be regretted that the valuable labours of Muschenbrok have not been followed up by other experiments upon the alloys in more general use. One curious circumstance will be observed however, in those which are given, namely, that in the following alloys, which are the strongest of their respective groups, the tin is always four times the quantity of the other metal; and they all confirm the circumstance, of the alloys having mostly a greater degree of cohesion than the stronger of their component metals.

Alloys.

Cast Metals.

4

English Tin,

1

Lead,

10,607

lb. .

Lead,

885

lb.

4

Banca Tin,

1

Antimony,

13,480

" .

Antimony,

1,060

"

4

- -

1

Bismuth,

16,692

"

Zinc,

2,689

"

4

English Tin,

1

GoslarZinc

10,258

" .

Bismuth,

3,008

"

4

- -

1

Antimony,

11,323

" .

Tin,

3,211 to 6,650

"

Fig. 137.

Section III Strength Or Cohesion Of Alloys 10076

Fig. 137 represents a very ingenious instrument, denominated an alloy-balance, by its inventor Mr. Roberts, of the present firm of Roberts, Fothergill and Dobinson, of Manchester. It is intended for weighing those metals the proportions of which are stated decimally, its principle, which is so simple as hardly to require explanation, depends upon the law that weights in equilibrium are inversely as their distances from the point of support.

For weighing out any precise number of pounds or ounces, in the common way, the arms of the ordinary scale-beam are made as nearly equal as possible; so that the weights, and the articles to be weighed, may be made to change places, in proof of the equality of the instrument. But to weigh out an alloy, say of 17 parts tin and 83 copper, unless the quantities were either 17 and 83 lb. or ounces, would require a little calculation.

* This, in truth, is an exception; it barely equals in strength the alloys with 8 and 2 parts of tin to 1 of zinc, but is superior to that of equal parts: it corroborates the great increase of strength in alloys generally.

This is obviated, if the point of suspension a, of the alloy. balance, which is hung from any fixed support b, is adjusted until the arms are respectively as 17 to 83; and for this purpose the half of the beam is divided into fifty equal parts number from the one end; and, prior to use, it only remains to adjust the weight, w, so as to place the empty balance in equilibrium. A quantity of copper, rudely estimated, having been suspended from the short arm of the balance, the proportionate quantity of the tin will be denoted with critical accuracy, when, by its gradual addition, the beam is exactly restored to the horizontal line; should the alloy consist of three or more parts, the process of weighing is somewhat more complex.

The annexed table was calculated by the author, for converting the proportions of alloys stated decimally, into avoirdupois weight. It applies with equal facility to alloys containing two or many components, so as to bring them readily within the power of ordinary scales.