76 PUBLIC HEALTH CHEMISTRY 



two parts of water. The bottle is placed in the machine, 

 and balanced with a similar one filled with sulphuric (i in 2), 

 and the machine rotated for at least two minutes. On 

 stopping, the fat will be seen to have separated out as a 

 layer on the top, and the percentage is read off, each gradua- 

 tion representing o-i per cent of fat by weight. The 

 reading is from the extreme top of the fat column to 

 extreme bottom. 



There is also a Gerber process similar in principle. 



Maceration Process. Is used at Somerset House in the 

 Government Laboratory, and is specially suited to the 

 analysis of sour milks. It consists in neutralizing the 

 acidity with N /io strontia, evaporating to the consistency 

 of soft cheese, repeatedly washing with ether, which is run 

 through a filter-paper of known weight, weighing the fat- 

 free solids plus the filter-paper washed free of fat, and thus 

 the solids-non-fat are obtained, an allowance being made 

 for the strontia added. This figure deducted from the 

 total solids obtained from another portion of the sample 

 gives the amount of fat. (Several corrections are made in 

 calculating the solids for alcohol, for volatile acid, and for 

 ammonia.) 



Calculation Method by Hehner and Richmond's Formula. 

 F = 0-859 X T 0-2186 x G, where F represents the 

 percentage of fat, T the percentage of total solids, and G 

 the last two figures of the specific gravity (including any 

 decimal). For skim milks, where G -r- T exceeds 2-5, the 

 following modified formula is used : F = 0-859 X T - 

 0-2186 x G 0-05 (G -T- T 2-5). A third formula gives 

 T where G and F are known. T = 0-25 X G + 1-2 X 

 F -|- 0-14. 



Solids-not-Fat Are obtained by subtraction of the 

 fat from the percentage of total solids. Should not be less 

 than 8-5 per cent. 



Calculation of Amounts of Adulteration (by Skim- 

 ming and Added Water). A milk may be skimmed 

 of fat, or have water added, or be treated in both ways. 

 The Board of Agriculture has fixed the standard for fat in 

 milk at not less than 3 per cent, for solids-not-fat not less 

 than 8-5 per cent, and for total solids not less than 11-5 

 per cent (3 + 8-5). Most pure milk samples give total 



