294. The estimation of solids in milk: Part I. Determination of solids-not-fat by various methods of hydrometry

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Abstract
1. Estimations of solids-not-fat by evaporation and by hydrometry were made in two laboratories on samples of the same raw and pasteurized milks.2. General agreement was found between the results by stated evaporation techniques and those by Richmond's formula (S.N.F. = 0·25G + 0·2F + 0·14) when the latter was applied to milks which had been stored cold (i.e. Recknagel contraction complete as required by Richmond).3. General agreement at a lower level of S.N.F. (0·2% approx.) was found between Richmond's formula and the density formula (S.N.F. = 0·25D + 0·21F + 0·66) when both were applied to milks heated as required by B.S.S. no. 734 (1937) (i.e. Recknagel effect absent).4. Adoption of the B.S.S. technique and formula placed a very much greater proportion of samples, below the presumptive legal standard of 8·5% S.N.F.5. The need is indicated for the standardization of evaporation technique before attempting a permanent revision of the density formula.6. Seasonal variations between ‘calculated’ and ‘found’ results have been observed.