DEGREES OF TABLE I. CORRECTIONS FOR SPECIFIC GRAVITY OF MILK FOR VARIATIONS IN TEMPERATURE TEMPERATURE OF MILK 132 51° F. 52° F. 53° F. 54° F. 55° F. 56° F. 570° F. 58° F. 59° F. 60° F. 61° F. 62° F. 63° F. 64° F. 65° F. 66° F. 67° F. 68° F. 69° F. 70° F. 25 26 26 29.1 26.2 26.2 26.3 26.4 26.5 26.6 26.7 26.8 26.9 27.1 27.2 27.3 27.4 27.5 27:6 27.7 27.8 27.9 28.1 28.2 28.3 28.4 28.5 28.6 28.7 28.8 28.9 29.9 Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. Lact. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. deg. 24.2 24.3 24.4 24.5 24.6 24.6 24.7 24.8 24.9 25.1 25.2 25.3 25.4 25.5 25.6 25.7 25.2 25.2 25.3 25.4 25.5 25.6 25.7 25.8 25.9 26.1 26.2 26.3 26.5 26.6 26.7 26.8 27.1 27.3 27.4 27.5 28.1 28.3 28.4 28.5 28.6 29.1 29.3 29.4 29.5 29.6 25.9 26.0 26.1 29.8 29.9 30.1 30.2 30.3 30.0 31.0 29.1 29.2 29.3 29.4 29.6 29.7 29.8 30.1 30.2 30.3 30.4 30.5 30.6 30.8 31.1 31.2 31.3 31.4 31.5 31.6 31.7 31.9 31.9 32.0 32.1 32.3 32.4 32.5 32.6 32.7 32.9 32.9 33.0 33.1 33.2 33.3 33.5 30.9 33.6 33.7 33.9 34 33.8 33.9 34.0 34.2 34.3 34.5 34.6 34.7 34.9 30 30.9 31.1 31.2 31.3 31.4 31.5 31.7 31.8 31.9 32.0 32.2 32.4 35 then corrected, if the temperature is above or below 60° F. For example, the lactometer settles in milk, which is at a temperature of 65° F., to the point marked 29. Adding to the reading for correction .I for each degree above 60° F., which in this case is .5, the reading becomes 29.5. This means that the specific gravity is 1.0295. If the temperature of the milk were 55° F., the correction is subtracted and the reading becomes 28.5, equal to specific gravity 1.0285. THE NEW YORK BOARD OF HEALTH LACTOMETER Description. This lactometer has been in common use among milk-inspectors in the eastern and middle states. Its scale is quite different from that of the Quevenne lactometer, since it is divided into 120 equal parts. Beginning at the top of the instrument, the zero point on the scale is the point to which the lactometer sinks in water; and the point is marked 100 to which it settles in milk of specific gravity 1,029 at 60° F. (Quevenne reading, 29), the lowest limit supposed to belong to normal milk. The distance between the zero and 100 points is divided into 100 equal parts and the scale is then prolonged beyond the 100 mark for 20 divisions to 120. The instrument is used in the same way as the Quevenne lactom- LACTOMETER eter in testing milk, FIG. 49 CYLINDER FOR Comparison of the two lactometer scales. In comparing the scales of the Quevenne and Board of Health lactometers, the following points will make clear their relations: (1) The zero point on both instruments indicates the specific gravity of water, that is, 1.000. (2) On the B. of H. lactometer, the 100 divisions or degrees from 0 to 100 correspond to 29 divisions on the Quevenne. Therefore one degree on the B. of H. lactometer Corresponds to .29 degree on the Quevenne. To convert the B. of H. lactometer reading into that of the Quevenne, multiply the reading of the former by .29. The relation of the specific gravity scale of a hydrometer to the scales of the Quevenne and B. of H. lactometer is shown in Fig. 50. TABLE II.-DEGREES ON QUEVENNE LACTOMETER CORRESPONDING TO DEGREES ON NEW YORK BOARD OF HEALTH LACTOMETER Corrections for temperature.-In using the B. of H. lactometer, correction is made for temperatures above or below 60° F. For each degree of temperature of milk above 60° F., add .3 to the lactometer reading, and for each degree below 60° F. subtract .3 from the reading. PRECAUTIONS IN TESTING SPECIFIC GRAVITY OF MILK 1. Milk should, for best results, not be examined until I to 2 hours or more after milking, since the specific gravity of milk is lower for a while after being drawn than it is later, due chiefly to the presence of gases. 2. The sample of milk must be completely mixed. 3. The lactometer must be kept clean. 4. In milk which has been preserved by potassium bichromate, the specific gravity is about one degree higher than in the normal milk, in case the usual amount of bichromate has been added. (See p. 30). VALUE OF LACTOMETER IN DETECTING ADULTERATED MILK The value of the lactometer in detecting adulterated, especially watered, milk was formerly overestimated. Taken alone, the results given by the lactometer may be thoroughly unreliable and misleading. It has come to be quite generally recognized that the proper use of the lactometer in milk inspection is largely to indicate whether a sample is suspicious and to furnish a guide as to whether it is necessary to take a sample for further detailed investigation by chemical anal |