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TEMPERATURE CORRECTIONS FOR THE LACTOMETER [Vol. XIX, Part I,
from the table for the correction of lactometer readings. Over 400 readings were
thus experimentally obtained from samples taken at random including cow and
buffalo milks and covering the entire range of fat percentages of the table prepared.
The summary of the results of this verification showed that 17.0 per cent of the
results agreed with corrections found in the prepared table, 22.0 per cent differed
by ±0.1; 19.5 per cent differed by ±0.2; 15.0 per cent by ±0.3; 7.0 per cent
by ±0.4 ; 9.0 per cent by ±0.5; and only 10.5 per cent exceeded a difference of
±0.5. On the whole, 90.0 per cent of the samples tested agreed within an error
of ±0.5. Since Richmond's Table extends only up to 80°F. and since he has not
mentioned the fat percentage of the milk, the correction factors obtained by Table
II can not be strictly compared with Richmond's. However, for milk with 3 per
cent fat, the correction factor obtained by our table was found to be much higher
than that obtained by Richmond's Table.
Since ordinary lactometers are graduated only in whole numbers indicating
only the third place decimal of the specific gravity (0.001), an error of one degree
in the lactometer reading may be permitted without much serious inaccuracy in
the specific gravity. If such an error is permissible, all the values taken for verifying
the new table agree with the Correction Table worked out. Sixty-five readings
obtained from the milk of two Ayrshire cows and 150 readings from the milk of
half-breed cows were also found to agree with the new table prepared and now
recommended as a result of this investigation.
HOW TO USE THE NEW TABLE (ZAL-KRISHNAN TABLE) FOR THE CORRECTION OF
LACTOMETER READING
To obtain the correct lactometer reading at 60°F. of any milk sample at any
temperature between 50ºF. and 110ºF., the milk need not be heated or cooled.
If the sample is to be examined directly after milking, sufficient time (at least 2
hours) should be allowed, or proper precautions taken to see that the Recknagel
phenomenon has ceased. The sample should then be stirred well and the fat
percentage of a representative sample determined. The milk should then be poured
into a suitable container (preferably a glass container), which should permit free
floating of the Gerber's thermolacto-densimeter, without touching either the bottom
or the sides. Usually one quarter of a pound of milk will suffice for this purpose,
if a cylindrical vessel of suitable diameter is available. The lactometer should then
be immersed to the full length of the graduated scale and set free so that it freely
moves up and down. When it comes to rest the reading should be noted without
any error due to parallax. Simultaneously with the noting of the lactometer reading,
the temperature of the sample should also be noted with a good Fahrenheit thermo-
meter. The correction factor should then be read out from the table against the
observed temperature and fat percentage, and added or subtracted from the
observed reading according to the observed temperature being above or below 60°F.
In applying the correction factors the fat percentage may be corrected to the nearest
whole number and the correction factor read out from the respective column.