7 CFR 51.3417 – Optional test for specific gravity
Tests to determine specific gravity shall be made in accordance with the procedures set forth in this section.
(a) The potatoes used for such determinations shall be:
(1) Taken at random from a composite sample drawn from containers representative of the lot.
(2) A comparable sample from a bulk load or storage bin.
(3) From a portion of the divided sample initially drawn or submitted for determination of grade or contract compliance.
(4) Representative of the lot with respect to size and quality.
(b) Specific gravity shall be determined by either;
(1) Calculation from the weights of the sample in air and in water made with USDA approved equipment. The reading obtained from each test shall be corrected for temperature variations using Table I.
(2) A hydrometer specifically designed for determining the specific gravity of potatoes.
Table I—Correction Factors for Specific Gravity of Potatoes 4
[Corrected to zero at 50 °F potato temperature and 50 °F water temperature]
Water temperature (degrees Fahrenheit) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|
38° | 40° | 45° | 50° | 55° | 60° | 65° | 70° | 75° | 80° | |
Potato temperature: | ||||||||||
38° | ?0.0021 | ?0.0020 | ?0.0018 | ?0.0018 | ?0.0020 | ?0.0023 | ?0.0029 | ?0.0038 | ?0.0047 | ?0.0056 |
40° | ?.0017 | ?.0016 | ?.0014 | ?.0014 | ?.0016 | ?.0019 | ?.0025 | ?.0034 | ?.0043 | ?.0052 |
45° | ?.0009 | ?.0008 | ?.0008 | ?.0006 | ?.0008 | ?.0011 | ?.0017 | ?.0026 | ?.0035 | ?.0044 |
50° | ?.0003 | ?.0002 | 0000 | 0000 | ?.0002 | ?.0005 | ?.0011 | ?.0020 | ?.0029 | ?.0038 |
55° | +.0001 | +.0002 | +.0004 | +.0004 | +.0002 | ?.0001 | ?.0007 | ?.0016 | ?.0025 | ?.0034 |
60° | +.0004 | +.0005 | +.0007 | +.0007 | +.0005 | +.0002 | ?.0004 | ?.0013 | ?.0022 | ?.0031 |
65° | +.0005 | +.0006 | +.0008 | +.0008 | +.0006 | +.0003 | ?.0003 | ?.0012 | ?.0021 | ?.0030 |
70° | +.0006 | +.0007 | +.0009 | +.0009 | +.0007 | +.0004 | ?.0002 | ?.0011 | ?.0020 | ?.0029 |
75° | +.0007 | +.0008 | +.0010 | +.0010 | +.0008 | +.0005 | ?.0001 | ?.0010 | ?.0019 | ?.0028 |
80° | +.0008 | +.0009 | +.0011 | +.0011 | +.0009 | +.0006 | 0000 | ?.0009 | ?.0018 | ?.0027 |
85° | +.0009 | +.0010 | +.0012 | +.0012 | +.0010 | +.0007 | +.0001 | ?.0008 | ?.0017 | ?.0026 |
90° | +.0010 | +.0011 | +.0013 | +.0013 | +.0011 | +.0008 | +.0002 | ?.0007 | ?.0016 | ?.0025 |
95° | +.0011 | +.0012 | +.0014 | +.0014 | +.0012 | +.0009 | +.0003 | ?.0006 | ?.0015 | ?.0024 |
100° | +.0012 | +.0013 | +.0015 | +.0015 | +.0013 | +.0010 | +.0004 | ?.0005 | ?.0014 | ?.0023 |
4 To apply correction factor, change actual specific gravity reading by adding or subtracting the appropriate factor according to the plus or minus sign.
Table II—Specific Gravity Conversion Chart for 5,000 Grams of Potatoes
Water weight | Specific gravity | Total solids |
---|---|---|
300 | 1.0638 | 17.2 |
310 | 1.0661 | 17.7 |
320 | 1.0684 | 18.2 |
322 | 1.0688 | 18.3 |
324 | 1.0693 | 18.4 |
326 | 1.0697 | 18.5 |
328 | 1.0702 | 18.6 |
330 | 1.0707 | 18.7 |
332 | 1.0711 | 18.8 |
334 | 1.0716 | 18.9 |
336 | 1.0720 | 19.0 |
338 | 1.0725 | 19.1 |
340 | 1.0730 | 19.2 |
342 | 1.0734 | 19.3 |
344 | 1.0739 | 19.4 |
346 | 1.0743 | 19.5 |
348 | 1.0748 | 19.6 |
350 | 1.0753 | 19.7 |
352 | 1.0757 | 19.8 |
354 | 1.0762 | 19.9 |
356 | 1.0766 | 20.0 |
358 | 1.0771 | 20.1 |
360 | 1.0776 | 20.2 |
362 | 1.0780 | 20.3 |
364 | 1.0785 | 20.4 |
366 | 1.0790 | 20.5 |
368 | 1.0794 | 20.6 |
370 | 1.0799 | 20.7 |
372 | 1.0804 | 20.8 |
374 | 1.0808 | 20.9 |
376 | 1.0813 | 21.0 |
378 | 1.0818 | 21.1 |
380 | 1.0822 | 21.2 |
382 | 1.0827 | 21.3 |
384 | 1.0832 | 21.4 |
386 | 1.0836 | 21.5 |
388 | 1.0841 | 21.6 |
390 | 1.0846 | 21.7 |
392 | 1.0851 | 21.8 |
394 | 1.0855 | 21.9 |
396 | 1.0860 | 22.0 |
398 | 1.0865 | 22.1 |
400 | 1.0870 | 22.2 |
402 | 1.0874 | 22.3 |
404 | 1.0879 | 22.4 |
406 | 1.0884 | 22.5 |
408 | 1.0888 | 22.6 |
410 | 1.0893 | 22.7 |
412 | 1.0898 | 22.8 |
414 | 1.0903 | 22.9 |
416 | 1.0908 | 23.0 |
418 | 1.0912 | 23.1 |
420 | 1.0917 | 23.2 |
422 | 1.0922 | 23.4 |
424 | 1.0926 | 23.5 |
426 | 1.0931 | 23.6 |
428 | 1.0936 | 23.7 |
430 | 1.0941 | 23.8 |
432 | 1.0946 | 23.9 |
440 | 1.0965 | 24.4 |
450 | 1.0989 | 24.9 |
460 | 1.1013 | 25.4 |
470 | 1.1040 | 26.0 |