Draw a rectangle, placing the per cent of fat in the cream at the upper left-hand corner, and the per cent of fat of the milk at the lower left-hand corner. Place the desired per cent of fat in the center. The difference between the numbers in the center and at the lower left-hand corner should be written at the upper right-hand corner, and the difference between the numbers in the center and at the upper left-hand corner should be written at the lower right-hand corner. These right-hand numbers represent the proportions of the substances represented at the corresponding left-hand corners, which must be mixed to produce a milk testing the desired amount of fat.

Thus : To raise the fat test of a 3.8 per cent milk to 4 per cent by the use of cream testing 25 per cent, by completing the figure as explained, it will be seen that for every 21 pounds of 3.8 per cent milk there should be used .2 of 1 pound of 25 per cent cream.

Butter moisture-test (Cornell test).

The apparatus used in the Cornell moisture-test is an alcohol lamp, stand, asbestos sheet, hot-pan lifter, aluminum cup for holding the sample, and a special moisture scale. The scale is especially adapted for moisture work, but may be used as a cream scale in operating the Babcock test.

The scale has a tare weight for balancing the cup and a large and small weight for weighing the sample and obtaining the percentage of moisture. The beam has two rows of figures, which give readings with the larger weight. The lower row gives readings in grams and the upper row in percentages. The smaller weight gives readings in grams when the weight is moved from 1 forward. Each notch represents .02 gram, the total value of the small scale being .2 gram. When the small weight is moved from 0 backward, each notch represents a loss of .1 per cent of moisture when 20.2 grams of butter are used. The small weight is intended to be used only in moisture work. In using the scale for Babcock work, the small weight is not used, but is left at rest on the figure 1. Then when the scales are balanced, the small weight is negligible. Care must be taken not to let any draft of air, as from an open window, strike the scales when in use, as they are so sensitive that a very slight current of air would throw them out of balance. The scales will give readings in percentages only when 20.2 grams of butter have been weighed, or, in other words, when the large weight is on 20 (of the gram scale) and the small weight is on zero.

The cup used is of cast aluminum, and is durable and perfectly smooth. The absence of creases or crevices allows it to be cleaned and dried thoroughly.

Taking the sample. — It is necessary that a representative sample be taken for a moisture-test. If the butter is sold in tubs, the sample should be taken from the tub with a butter-trier, after the butter has been packed. It is best to take three drawings — one from near the edge, one from the middle, and one half-way between the edge and the middle. Some butter-makers test the butter as soon as it is worked. This is a mistake, since considerable moisture is lost in the process of printing and packing.

Operation of the test. - After the cup is thoroughly cleaned and dried, it is placed on the scales and balanced by means of the tare weight on the round bar attached to the beam of the scales. The large weight should rest on the zero mark (of the gram scale) and the small weight on 1 while the cup is being balanced. The cup should not be balanced until it is about the same temperature as that of the room. After the cup is balanced, the larger weight is moved to the 20 mark (of the gram scale) and the small weight to the zero mark. Butter from the prepared sample is then added to the cup until the scales are accurately balanced. The alcohol lamp is then placed under the iron stand and the asbestos sheet placed on the stand. The lamp is lighted and the cup placed on the asbestos sheet. It is well to light the lamp at least two or three minutes before placing the cup on the asbestos in order to heat the asbestos and save time. The heat of the flame may be increased or diminished by raising or lowering the wick. The cup should always be handled with the hot pan lifter, as by so doing it will be kept clean and errors in weight due to dirt on the cup will be avoided.