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How to Determine Approximate Specific Gravities of Alloys

 

1.           Find the reciprocal of the specific gravity of each metal in the alloy. This is done by dividing 1 by the specific gravity. For example, the specific gravity of silver is 10.49 and the reciprocal is 1 divided by 10.49 or .094966.

 

2.           Multiply each reciprocal by the number of parts per thousand of that metal to be used.

 

3.           Add the results of the multiplications together.

 

4.           Divide 1,000 by this total‑the answer is the specific gravity of the alloy.

 

Example

Find the specific gravity of 14K yellow gold having

 

583 parts gold, 104 parts silver and 313 parts copper.

 

First figure the reciprocals of the specific gravities.

 

Fine Gold ‑ 1 divided by 19.32=.051759

Fine Silver ‑ 1 divided by 10.49=.094966

Fine Copper ‑ 1 divided by 8.96=.111617

 

Then multiply­

 

Fine Gold    ‑583 parts by weight X.051759=30.182

Fine Silver   ‑104 parts by weight X .094966= 9.876

Fine Copper ‑313 parts by weight X.111617=34.956

 

Totals          1000                                        75.014

 

1000 divided by 75.014=13.33, the specific gravity of the alloy.

 

*The specific gravity for any one karat will naturally vary for each composition.

Reducing the formulas down to simple functions to find the percentages of tin and antimony in 2-metal alloys.

To simplify matters a little more, reduce the equations for determing the percentages of tin or antimony in an alloy with a known specific gravity down to these two functions.

TIN - Let TSG = the specific gravity of a tin/lead alloy

or

ANTIMONY - Let ASG = the specific gravity of an antimony/lead alloy

Then:

2076.803 / TSG - 183.059 = the percentage of tin in the alloy

or

1636.416 / ASG - 144.241 = the percentage of antimony in the alloy

 

TABLE 4

 

Specific Gravity, Melting Point, and Weight of Various Metals and Alloys

 

Melting Point

 

Weight

 

 

 

Specific

in Tr. Ozs.

Metal

°F

°C

Gravity

per Cu. In.

Aluminum

1220

660

2.70

1.423

Antimony

1167

630

6.62

3.488

Beryllium

2340

1282

1.82

.959

Bismuth

520

271

9.80

5.163

Cadmium

610

321

8.65

4.557

Carbon

-

-

2.22

1.170

Chromium

3430

1888

7.19

3.788

Cobalt

2723

1495

8.90

8.90

Copper

1981

1083

8.96

4.719

Gold

1945

1063

19.32

10.180

18 K green

1810

988

15.90

8.375

18 K yellow

1700

927

15.58

8.211

18 K white

1730

943

14.64

7.712

18 K red

1655

902

15.18

7.998

14 K green

1765

963

14.20

7.482

14 K yellow

1615

879

13.07

6.885

14 K white

1825

996

12.61

6.642

14 K red

1715

935

13.26

6.986

10 K green

1580

860

11.03

5.810

10 K yellow

1665

907

11.57

6.096

10 K white

1975

1079

11.07

5.832

10 K red

1760

960-

11.59

6.106

Iridium

4449

2454

22.50

11.849

Iron (pure)

2802

1539

7.87

4.145

Lead

621

328

11.34

5.973

Magnesium

1202

650

1.74

.917

Manganese

2273

1245

7.43

3.914

Molybdenum

4760

2625

10.20

5.347

Nickel

2651

1455

8.90

4.691

Osmium

4892

2700

22.50

11.854

Palladium

2831

1555

12.00

6.322

Phosphorus

111

44

1.82

.959

Platinum

3224

1773

21.45

11.301

15% Iridio Plat.

3310

1821

21.59

11.373

10% Iridio Plat.

3250

1788

21.54

11.349

5% Iridio Plat.

3235

1779

21.50

11.325

Rhodium

3571

1967

12.44

6.553

Ruthenium

4500

2500

12.20

6.428

Silicon

2605

1430

2.33

1.247

Silver

1761

961

10.49

5.525

Sterling

1640

893

10.36

5.457

Coin

1615

879

10.31

5.430

Tin

450

232

7.30

3.846

Zinc

787

419

7.13

3.758