ADULTERATION. 175 



by an increase in the chlorides above O'lO per cent. ; an estimation 



of sodium should also be made, as milk does not contain more 



than 0'05 per cent. ; carbonate or bicarbonate of soda is also 



detected by the increased alkalinity of the soluble ash ; this 



does not exceed in genuine milk an amount equal to 0"025 per 



cent. NajCO.j ; an amount appreciably exceeding this is due to 



addition of alkali. The alkalinity of the ash should be estimated 



N 

 by titrating with -j-r acid, using phenolphthalein as indicator ; 



1 c.c. of the acid is with this indicator equal to 0"0106 gramme 

 of NaX'O,, 



Other mineral additions, such as boric acid, borax, fluorides, 

 etc., may be added as preservatives, and not to mask the addition 

 of water ; the methods of detecting these will be given later. 



It has been alleged that salts of ammonia have been added 

 to raise the total nitrogen. These would be detected by rendering 

 alkaline with magnesium carbonate, distilling the milk, and 

 testing the distillate with Nessler's reagent (an alkaline solution 

 of mercuric chloride in potassium iodide). 



Calculation of Pat Abstracted. — The detection of adultera- 

 tion by removal of cream can only be effected with certainty by 

 the estimation of fat ; if this falls below 3() per cent., a pre- 

 sumption is raised that cream has been abstracted. From the 

 table on p. 159 it is seen that the mean percentafje of fat varies 

 at different times of the year ; a limit of 3 "25 per cent, could be 

 used from October to January with as much justification as a 

 limit of 'VO for the other months. 



The percentage of cream abstracted is calculated by the 



formula 



F 

 Cioain abstracted = 100 — .j- X 100, 



where F = percentage of fat. 



This formula gives a minimum percentage of fat abstracted. 

 The figure thus calculated is almost always seriously below the 

 truth ; the probable amount can be calculated by subititutiug 

 3'74 for 3, or, better still, the monthly average figure given in 

 Table XXX. on p. 159 for the month in which the analysis is made. 



If " appeal to the cow " has been made, or if the mean com- 

 position of the milk was approximately or exactly known, the 

 figure representing the actual composition should be substituted 

 for 3. 



The colour of the fat is of some aid in judging the amount of 

 cream abstracted ; if it is very yellow, the milk is very likely 

 yielded by Jersey cows, and a high figure — e.'j., 4 — may be 

 substituted for 3. 



