TEST METHOD: SPECIFIC GRAVITY

Revised 4 August 2011 (temperature correction for stronger brines added)

RISK ASSESSMENT

Assess Safety, Health, Quality and Environmental aspects of each specific step.

OVERVIEW

The specific gravity of brines are measured to determine the relative concentration of salt, because the relationship between conductivity and dissolved salts is not constant, it varies with differing concentrations and different ions.

TASK SAFETY REQUIREMENTS

Safety boots are mandatory

SPECIFIC JOB STEPS

RISK ASSESSMENT

RISK CONTROL

Equipment required:

  • Measuring cylinder,
  • hydrometer, thermometer,
  • temperature correction chart
   

  To determine brine specific gravity:

  • Fill a measuring cylinder with brine sample to the point of overflowing
  • Float a hydrometer in brine sample
  • Read and record density level on shaft of hydrometer to level of water
  • Insert thermometer in brine sample
  • Read and record temperature of sample
  • Add or subtract degrees of density according to the temperature of the sample (see Temperature Correction, below).

The hydrometer either sinks to the bottom, or floats too high for a reading to be made.

You are using an incorrect hydrometer. Select one with a differing range.

Record reading in laboratory daybook

   

Temperature Correction

All hydrometer readings must be corrected from the temperature they were read at, to the temperature the hydrometer was designed for. Most hydrometers are set to 15.6 oC (60oF). Some saltfields have hydrometers calibrated to 20oC. Check any hydrometer prior to use!

Temperature correction of specific gravity also varies depending on the specific gravity itself. Make sure you use the appropriate section below. Most saltfield hydrometers have ranges that match the different corrections below, but you may find hydrometers with narrower ranges.

1. For brines between SG 1.000 and SG 1.100

The difference each degree of temperature makes to the SG is not constant, however very approximate corrections are:

This is sufficiently accurate for temperatures between 0oC and 40oC, but should not be used outside this temperature range. A more accurate formula is:

Correction (to add on to raw hydrometer reading) = Raw SG + (0.00000359 x temp2 + 0.00006971 x temp - 0.00151687) 

Alternatively, if you have brine in this range of SG you may like to try this online calculator

 

2. For brines between SG 1.100 and SG 1.200

The difference each degree of temperature makes to the SG is not constant, however very approximate corrections are:

This is sufficiently accurate for temperatures between 0oC and 40oC, but should not be used outside this temperature range. A more accurate formula is:

Correction (to add on to raw hydrometer reading) = Raw SG + (0.000012 x temp2 + 0.000016 x temp - 0.00288)

 

3. For brines above SG 1.200

The difference each degree of temperature makes to the SG is not constant, however very approximate corrections are:

This is sufficiently accurate for temperatures between 0oC and 40oC, but should not be used outside this temperature range. A more accurate formula is:

Correction (to add on to raw hydrometer reading) = Raw SG + (0.000009 x temp2 +0.000235 x temp - 0.005475)

 

Converting from SG to Total Dissolved Solids

If you wish to convert uncorrected SG directly to total dissolved solids (TDS g/L), use the chart below for SG’s up to 1.050. Outside this range, please refer to specialist texts, or report as a temperature corrected SG only. The SG is provided down the left column. The temperature is provided along the top row. The intersection provides the TDS in g/L.

 

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

21.0

22.0

23.0

24.0

25.0

26.0

27.0

28.0

29.0

30.0

31.0

32.0

33.0

                                                           

0.996

                                                     

0.0

0.0

0.997

                                           

0.0

0.2

0.4

0.6

0.8

1.1

1.3

0.998

                                     

0.0

0.2

0.5

0.7

1.0

1.2

1.5

1.8

2.1

2.6

0.999

                               

0.0

0.2

0.4

0.6

0.9

1.2

1.5

1.9

2.3

2.7

3.1

3.5

3.9

                                                           

1.000

       

0.0

0.2

0.3

0.3

0.3

0.3

0.4

0.4

0.4

0.5

0.6

0.8

1.1

1.4

1.6

1.9

2.1

2.5

2.9

3.2

3.6

4.0

4.4

4.8

5.1

1.001

0.2

0.2

0.2

0.2

0.5

0.5

0.6

0.6

0.7

0.8

1.0

1.2

1.5

1.6

1.9

2.1

2.4

2.5

2.8

3.1

3.4

3.8

4.2

4.5

4.9

5.1

5.5

5.9

6.4

1.002

1.5

1.5

1.6

1.6

1.6

1.8

1.9

2.0

2.1

2.3

2.4

2.5

2.8

2.9

3.2

3.4

3.7

4.0

4.2

4.6

4.9

5.1

5.5

5.9

6.3

6.6

7.0

7.5

7.9

1.003

2.8

2.8

2.8

2.9

2.9

3.1

3.2

3.3

3.4

3.6

3.7

3.8

4.1

4.2

4.5

4.8

5.0

5.3

5.5

5.9

6.2

6.6

6.8

7.2

7.6

8.0

8.4

8.8

9.2

1.004

4.1

4.1

4.1

4.2

4.2

4.4

4.5

4.6

4.8

4.9

5.0

5.1

5.4

5.5

5.8

6.1

6.3

6.6

7.0

7.2

7.5

7.9

8.3

8.5

8.9

9.3

9.7

10.1

10.5

                                                           

1.005

5.3

5.4

5.4

5.4

5.5

5.5

5.7

5.8

5.9

6.2

6.3

6.6

6.7

7.0

7.1

7.4

7.6

7.9

8.3

8.5

8.9

9.2

9.6

10.0

10.2

10.6

11.1

11.5

11.9

1.006

6.6

6.6

6.7

6.7

6.8

6.8

7.0

7.1

7.2

7.5

7.6

7.9

8.0

8.3

8.5

8.8

9.1

9.3

9.6

9.8

10.2

10.5

10.9

11.3

11.6

12.0

12.4

12.8

13.2

1.007

7.9

7.9

7.9

8.0

8.1

8.1

8.3

8.4

8.5

8.8

8.9

9.2

9.3

9.6

9.8

10.1

10.4

10.6

10.9

11.3

11.5

11.9

12.2

12.6

13.0

13.4

13.8

14.2

14.6

1.008

9.2

9.2

9.2

9.3

9.3

9.4

9.6

9.7

9.8

10.0

10.2

10.5

10.6

10.9

11.1

11.4

11.7

11.9

12.2

12.6

12.8

13.2

13.6

13.9

14.3

14.7

15.1

15.5

15.9

1.009

10.4

10.5

10.5

10.6

10.6

10.7

10.9

11.0

11.1

11.3

11.5

11.8

11.9

12.2

12.4

12.7

13.0

13.2

13.6

13.9

14.1

14.5

14.9

15.3

15.7

16.1

16.5

16.9

17.3

                                                           

1.010

11.7

11.7

11.8

11.8

11.9

12.0

12.2

12.3

12.4

12.6

12.8

13.1

13.2

13.5

13.7

14.0

14.3

14.5

14.9

15.2

15.6

15.8

16.2

16.6

17.0

17.4

17.8

18.2

18.7

1.011

13.0

13.0

13.1

13.1

13.2

13.4

13.5

13.6

13.7

13.9

14.1

14.4

14.5

14.8

15.0

15.3

15.6

16.0

16.2

16.5

16.9

17.3

17.5

17.9

18.3

18.8

19.2

19.6

20.0

1.012

14.1

14.3

14.3

14.4

14.5

14.7

14.8

14.9

15.0

15.2

15.4

15.7

15.8

16.1

16.3

16.6

17.0

17.3

17.5

17.9

18.2

18.6

19.0

19.3

19.6

20.1

20.5

20.9

21.4

1.013

15.4

15.4

15.6

15.7

15.8

15.8

16.0

16.2

16.3

16.5

16.7

17.0

17.1

17.4

17.7

17.9

18.3

18.6

18.8

19.2

19.5

19.9

20.3

20.6

21.0

21.4

21.9

22.3

22.7

1.014

16.7

16.7

16.9

17.0

17.0

17.1

17.3

17.5

17.7

17.8

18.0

18.3

18.6

18.7

19.0

19.3

19.6

19.9

20.1

20.5

20.9

21.2

21.6

22.0

22.3

22.7

23.2

23.6

24.0

                                                           

1.015

17.9

18.0

18.0

18.2

18.3

18.4

18.6

18.8

19.0

19.1

19.3

19.6

19.9

20.0

20.4

20.6

20.9

21.2

21.6

21.8

22.2

22.5

22.9

23.3

23.6

24.0

24.6

25.0

25.3

1.016

19.2

19.3

19.3

19.5

19.6

19.7

19.9

20.1

20.3

20.4

20.6

20.9

21.2

21.3

21.7

22.0

22.2

22.5

22.9

23.3

23.5

23.9

24.3

24.7

25.1

25.5

25.9

26.3

26.8

1.017

20.5

20.5

20.6

20.8

20.9

21.0

21.2

21.3

21.6

21.7

22.0

22.2

22.5

22.7

23.0

23.3

23.5

23.8

24.2

24.6

24.8

25.2

25.6

26.0

26.4

26.9

27.3

27.7

28.1

1.018

21.7

21.8

22.0

22.1

22.2

22.3

22.5

22.6

22.9

23.0

23.3

23.5

23.8

24.0

24.3

24.6

24.8

25.2

25.5

25.9

26.1

26.5

26.9

27.3

27.7

28.3

28.7

29.0

29.4

1.019

23.0

23.1

23.3

23.4

23.5

23.6

23.8

23.9

24.2

24.3

24.6

24.8

25.1

25.3

25.6

25.9

26.1

26.5

26.8

27.2

27.6

27.8

28.2

28.6

29.0

29.5

30.0

30.4

30.8

                                                           

1.020

24.3

24.3

24.4

24.6

24.7

24.8

25.1

25.2

25.5

25.6

25.9

26.1

26.4

26.6

26.9

27.2

27.4

27.8

28.2

28.5

28.9

29.2

29.6

30.0

30.4

30.9

31.2

31.6

32.1

1.021

25.6

25.6

25.7

25.9

26.0

26.1

26.4

26.5

26.8

26.9

27.2

27.4

27.7

27.9

28.2

28.5

28.9

29.1

29.5

29.8

30.2

30.6

30.9

31.3

31.7

32.2

32.5

33.0

33.4

1.022

26.8

26.9

27.0

27.2

27.3

27.4

27.7

27.8

28.1

28.2

28.5

28.7

29.0

29.2

29.5

29.8

30.2

30.4

30.8

31.2

31.5

31.9

32.2

32.6

33.0

33.5

33.9

34.3

34.8

1.023

28.1

28.2

28.3

28.5

28.6

28.7

28.9

29.1

29.4

29.5

29.8

30.0

30.3

30.6

30.8

31.2

31.5

31.7

32.1

32.5

32.8

33.2

33.5

33.9

34.4

34.9

35.2

35.6

36.2

1.024

29.4

29.5

29.5

29.8

29.9

30.0

30.2

30.4

30.6

30.8

31.1

31.3

31.6

31.9

32.1

32.5

32.8

33.2

33.4

33.8

34.2

34.5

35.0

35.4

35.7

36.2

36.5

37.1

37.5

                                                           

1.025

30.6

30.7

30.8

30.9

31.1

31.3

31.5

31.7

31.9

32.1

32.4

32.6

32.9

33.2

33.4

33.8

34.1

34.5

34.7

35.1

35.5

35.9

36.3

36.7

37.1

37.5

37.8

38.4

38.8

1.026

31.9

32.0

32.1

32.2

32.4

32.6

32.8

33.0

33.2

33.4

33.7

33.9

34.2

34.5

34.7

35.1

35.4

35.8

36.0

36.4

36.8

37.2

37.6

38.0

38.4

38.8

39.3

39.7

40.2

1.027

33.2

33.3

33.4

33.5

33.7

33.9

34.1

34.3

34.5

34.7

35.0

35.2

35.5

35.8

36.2

36.4

36.7

37.1

37.5

37.7

38.1

38.5

38.9

39.3

39.8

40.2

40.6

41.0

41.5

1.028

34.5

34.5

34.7

34.8

35.0

35.1

35.4

35.6

35.8

36.0

36.3

36.5

36.8

37.1

37.5

37.7

38.1

38.4

38.8

39.1

39.4

39.9

40.2

40.7

41.1

41.5

41.9

42.5

42.9

1.029

35.6

35.8

35.9

36.2

36.3

36.4

36.7

36.8

37.1

37.3

37.6

37.8

38.1

38.4

38.8

39.0

39.4

39.7

40.1

40.5

40.8

41.2

41.6

42.0

42.4

42.8

43.3

43.8

44.2

                                                           

1.030

36.9

37.1

37.2

37.3

37.6

37.7

38.0

38.1

38.4

38.6

38.9

39.1

39.4

39.7

40.1

40.3

40.7

41.0

41.4

41.7

42.1

42.6

42.9

43.3

43.8

44.2

44.6

45.1

45.6

1.031

38.2

38.4

38.5

38.6

38.9

39.0

39.3

39.4

39.7

39.9

40.2

40.5

40.7

41.0

41.4

41.8

42.0

42.3

42.7

43.1

43.4

43.9

44.3

44.7

45.1

45.5

45.9

46.5

46.9

1.032

39.5

39.6

39.8

39.9

40.1

40.3

40.6

40.7

41.0

41.2

41.5

41.7

42.0

42.4

42.7

43.0

43.3

43.7

44.1

44.4

44.8

45.2

45.6

46.0

46.5

46.8

47.3

47.8

48.3

1.033

40.8

40.9

41.0

41.2

41.4

41.6

41.9

42.0

42.3

42.5

42.8

43.0

43.3

43.7

44.1

44.3

44.7

45.0

45.4

45.7

46.2

46.6

46.9

47.3

47.8

48.2

48.6

49.2

49.6

1.034

42.0

42.2

42.3

42.4

42.7

42.9

43.2

43.3

43.6

43.8

44.1

44.3

44.6

45.0

45.4

45.6

46.0

46.3

46.7

47.0

47.5

47.9

48.3

48.7

49.2

49.5

50.0

50.5

51.0

                                                           

1.035

43.3

43.4

43.6

43.8

44.0

44.1

44.4

44.6

44.9

45.1

45.4

45.7

46.0

46.3

46.7

47.0

47.3

47.6

48.0

48.4

48.8

49.2

49.6

50.0

50.5

50.9

51.3

51.9

52.3

1.036

44.5

44.7

44.8

45.0

45.3

45.4

45.7

45.9

46.2

46.4

46.7

47.0

47.3

47.6

48.0

48.3

48.6

49.0

49.4

49.7

50.1

50.6

50.9

51.4

51.8

52.3

52.7

53.2

53.7

1.037

45.8

46.0

46.1

46.3

46.6

46.7

47.0

47.2

47.5

47.7

48.1

48.3

48.6

48.9

49.4

49.6

49.9

50.3

50.7

51.0

51.5

51.9

52.3

52.7

53.2

53.6

54.0

54.6

55.0

1.038

47.1

47.2

47.4

47.6

47.8

48.0

48.3

48.5

48.8

49.0

49.4

49.6

49.9

50.2

50.7

50.9

51.3

51.6

52.0

52.3

52.8

53.2

53.6

54.0

54.5

54.9

55.4

55.9

56.4

1.039

48.3

48.5

48.7

48.9

49.1

49.3

49.6

49.8

50.1

50.3

50.7

50.9

51.2

51.6

52.0

52.2

52.6

52.9

53.3

53.7

54.1

54.6

54.9

55.4

55.9

56.3

56.7

57.2

57.7

                                                           

1.040

49.6

49.8

49.9

50.1

50.4

50.5

50.9

51.1

51.4

51.6

52.0

52.2

52.5

52.9

53.3

53.5

53.9

54.3

54.7

55.0

55.5

55.9

56.3

56.7

57.2

57.6

58.0

58.6

59.0

1.041

50.9

51.0

51.2

51.4

51.7

51.8

52.2

52.3

52.7

52.9

53.3

53.5

53.8

54.2

54.7

54.9

55.2

55.6

56.0

56.3

56.8

57.2

57.6

58.0

58.5

59.0

59.4

59.9

60.4

1.042

52.1

52.3

52.5

52.7

53.0

53.1

53.5

53.6

54.0

54.2

54.6

54.8

55.1

55.5

56.0

56.2

56.5

56.9

57.3

57.6

58.1

58.6

58.9

59.4

59.9

60.3

60.7

61.3

61.7

1.043

53.4

53.6

53.8

54.0

54.2

54.4

54.7

54.9

55.3

55.5

55.9

56.1

56.4

56.8

57.3

57.5

57.8

58.2

58.6

59.0

59.4

59.9

60.3

60.7

61.2

61.6

62.1

62.6

63.1

1.044

54.7

54.9

55.0

55.3

55.5

55.7

56.0

56.2

56.6

56.8

57.2

57.4

57.7

58.1

58.6

58.8

59.2

59.5

60.0

60.3

60.8

61.2

61.6

62.1

62.6

63.0

63.4

64.0

64.4

                                                           

1.045

55.9

56.1

56.3

56.5

56.8

57.0

57.3

57.5

57.9

58.1

58.5

58.7

59.1

59.4

60.0

60.1

60.5

60.9

61.3

61.6

62.1

62.6

62.9

63.4

63.9

64.3

64.8

65.3

65.8

1.046

57.2

57.4

57.6

57.8

58.1

58.2

58.6

58.8

59.2

59.4

59.8

60.0

60.4

60.7

61.3

61.4

61.8

62.2

62.6

62.9

63.4

63.9

64.3

64.7

65.2

65.7

66.1

66.7

67.1

1.047

58.5

58.7

58.8

59.1

59.4

59.5

59.9

60.1

60.5

60.7

61.1

61.3

61.7

62.1

62.6

62.8

63.1

63.5

63.9

64.3

64.8

65.2

65.6

66.1

66.6

67.0

67.4

68.0

68.5

1.048

59.7

59.9

60.1

60.4

60.7

60.8

61.2

61.4

61.8

62.0

62.4

62.6

63.0

63.4

63.9

64.1

64.4

64.8

65.3

65.6

66.1

66.6

66.9

67.4

67.9

68.3

68.8

69.4

69.8

1.049

61.0

61.2

61.4

61.6

61.9

62.1

62.5

62.7

63.1

63.3

63.7

63.9

64.3

64.7

65.3

65.4

65.8

66.2

66.6

66.9

67.4

67.9

68.3

68.7

69.3

69.7

70.1

70.7

71.2

                                                           

1.050

62.2

62.5

62.7

62.9

63.2

63.4

63.8

64.0

64.4

64.6

65.0

65.2

65.6

66.0

66.6

66.7

67.1

67.5

67.9

68.2

68.8

69.2

69.6

70.1

70.6

71.0

71.5

72.1

72.5

 

 

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