312 BUTTER. 



50 grammes of butter should be placed in a stoppered cylinder, 

 50 c.c. of chloroform added, and the mixture gently warmed 

 till perfect mixture takes place. A quantity of water, which 

 will, with that present in the butter, make up 50 grammes, is 

 added, and, after shaking, the cylinder is put aside to allow 

 the aqueous portion to separate. Each cubic centimetre of the 

 solution will contain the preservative in 1 gramme of butter. 



For the estimation of boric acid Thompson's method is con- 

 venient (p. 85). As butter is practically free from phosphates, 

 the process for their removal may be omitted, and the titration 

 performed on an aliquot portion of the solution which has been 

 made alkaline, evaporated to dryness, and ignited ; the ash is 

 extracted with hot water, and titrated first with acid till neutral 

 to methyl-orange, and then with alkali in the presence of glycerol, 

 till neutral to phenolphthalein, the result will be the total boric 

 acid, free and combined. 



It is, of course, obvious that any of the other methods for the 

 estimation of boric acid (pp. 86 to 88) may be used in place of 

 Thompson's method. 



The author and Harrison have devised a rapid method for the 



estimation of boric acid in butter ; 25 grammes of butter are 



weighed into a beaker, and just melted in the water-oven, 



25 c.c. of water are added, and the contents of the 



beaker well mixed by stirring ; the aqueous portion is allowed 



to settle ; the contents are again mixed, and allowed to settle. 



20 c.c. of the lower layer are withdrawn, and the boric acid 



estimated therein by the method of Miller and the author. The 



100 + W 

 weight of boric acid multiplied by ;r-r (W = percentage 



of water) will give the percentage of boric acid ; the factor 

 5 "65 may be used without great error. 



The fat may be filtered, and used for the examination of its 

 composition. 



The boric preservative is usually expressed as boric acid, 

 H3BO3. 



The Preservatives Committee has recommended : — 



(D) That the only preservative permitted to be used in butter 

 and margarine be boric acid or mixtures of boric acid and borax, 

 to be used in proportions not exceeding 0"5 per cent, expressed 

 as boric acid. 



An estimation of the total sulphurous acid may be made by 

 distilling a portion of the liquid with dilute hydrochloric acid, 

 passing the gas evolved into decinormal iodine solution, and 

 titrating with sodium thiosulphate ; 254 parts of iodine convert 

 64 parts of SO2 into sulphuric acid. The gas evolved may also 

 be passed into bromine water, and the sulphuric acid formed 



