Determination of Total Solids in Normal and Watered Milks by Lactometric Methods1,2

Abstract

Summary Several lactometric procedures were checked as regards their accuracy for the determination of total solids in normal and watered milk. Babcock formula II yielded satisfactory results for normal milk, if the sample was warmed to 15.5° C. and read; Richmond's formula (III) yielded the best results among the formulae checked if the milks were heated to 45° C, held 2min., cooled to 15.5° C. and read. The Babcock and Richmond formulae yielded high values for watered milk by either of the methods indicated in the preceding paragraph, with the exception of Babcock formula II, which checked well at the 5 per cent water addition. The deviations of the results by these formulae from these by the Mojonnier method increased sharply as the percentage water added to the milk increased. When the samples were heated to 45° C, held 2min., cooled to 30° C. and read at that temperature, the results by the Herrington formula check the Mojonnier results more closely than those calculated in accordance with Sharp and Hart, Rueda or Livak. Although the differences between the total values by the lactometric and Mojonnier methods increased as the percentage added water increased, this increase was fairly small. When a constant, 0.15, was subtracted from the results calculated by the Herrington formula, the values obtained checked those by the Mojonnier method closely. This modified formula (VIII) was satisfactory for the determination of total solids in normal milks or in milks containing up to 15 per cent added water, for the milk received at the College Dairy.