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.
The specific gravity for any lot of potatoes shall be the average of at least 3 corrected readings on separate tests from the composite sample. Specific gravity may also be determined, if requested, in accordance with size classifications or weighted value in proportion to size and/or grade separations in the lot.
(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.[3]
The pulp temperature of the potatoes and the temperature of water shall be recorded immediately before testing and the specific gravity reading corrected using Table I.
Table I - Correction Factors for Specific Gravity of Potatoes4
[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 |
When requested to convert the weight in water of 5000 gram samples used in the weight in air versus weight in water method of specific gravity determinations, the conversion to total solids shall be based on Table II.
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 |
Whenever the recorded water weight for an individual reading falls between two sets of numbers as indicated in Table II, the next higher reading shall be used.