It is graduated usually from 25° to 36°, corresponding to specific gravities 1.029 to 1.038. It is graduated to degrees and half degrees. Sometimes a thermometer is combined with the instrument. The specific gravity rises as the temperature is lowered and decreases with increase of temperature, so that it is important to make the test at the figure at which the lactometer was graduated, which is usually 60° F. Failing this, an allowance has to be made for higher or lower temperatures. The milk to be tested is well mixed, and placed in a deep vessel, and the lactometer placed in it, holding it at first at an angle. It stands upright and remains deeper or higher according to the specific gravity. The reading is taken on the stem at the level of the milk. As the latter is drawn up a little round the stem, about a half degree should be added on to get the true figure. Thus, if the apparent reading is 31, the true reading may be taken as 31.5. This is the average figure for good milk, corresponding to a specific gravity of 1.0315; anything above this is all to the good. Lower readings mean inferior quality, the latter being proportionate to the lowness of the readings. The tests are most conveniently made in a glass cylinder (Fig. 7), which may be purchased with the lactometer. As there are many inaccurate instruments in the market, it is necessary to go to a reputable maker, because an unreliable lactometer is worse than useless. The following table gives, in a condensed form, the allowances to be made when the temperature is above or below the standard (60° F.): ────────────┬────────────────────────────────────────────────────────── Temperature.│ Reading of Lactometer. ────────────┼─────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬──── Degs. F. │ │ │ │ │ │ │ │ │ │ │ │ 40 │ 23.5│24.5│25.5│26.4│27.3│28.2│29.1│30.0│31.0│31.9│32.8│33.7 45 │ 23.8│24.8│25.9│26.8│27.8│28.6│29.3│30.4│31.3│32.3│33.2│34.2 50 │ 24.1│25.1│26.1│27.0│28.0│29.0│29.9│30.9│31.8│32.8│33.7│34.7 55 │ 24.5│25.5│26.5│27.5│28.5│29.5│30.4│31.4│32.4│33.4│34.3│35.3 ────────────┼─────┼────┼────┼────┼────┼────┼────┼────┼────┼────┼────┼──── 60 │ 25.0│26.0│27.0│28.0│29.0│30.0│31.0│32.0│33.0│34.0│35.0│36.0 ────────────┼─────┼────┼────┼────┼────┼────┼────┼────┼────┼────┼────┼──── 65 │ 25.5│26.6│27.6│28.7│29.6│30.7│31.7│32.8│33.8│34.8│35.8│ ... 70 │ 26.1│27.2│28.2│29.3│30.2│31.3│32.4│33.4│34.5│35.5│36.5│ ... 75 │ 26.8│27.8│28.8│29.9│30.8│32.1│33.1│34.2│35.2│36.3│ ...│ ... 80 │ 27.4│28.4│29.5│30.7│31.6│32.8│33.9│35.9 36.1│ ...│ ...│ ... ────────────┴─────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────