88 PUBLIC HEALTH CHEMISTRY 



acids, refractive index, iodine absorption, and foreign 

 oils. Butter may also be examined for starch, annatto, or 

 other colourings, benzoic and salicylic acids, and with the 

 polariscope. 



Water. Weigh 2 grin, of butter into a weighed 

 capsule, and dry in the water-oven to constant weight. 

 The drying may be expedited by adding 1*5 c.c. of absolute 

 alcohol after melting the butter in the water-oven. The 

 amount of water should not exceed 16 per cent (" Butter 

 Regulations," 1902). The same standard now applies to 

 margarine (" Butter and Margarine Act," 1907). 



Salt. The residue, after burning off the fat and curd 

 from the dried butter, may for all practical purposes be 

 taken as salt. Or, melt 2 grm. of butter in some hot 

 water, make up the bulk to 200 c.c. with hot water, and put 

 into a separating funnel. Allow fat to separate to top, 

 take 20 c.c. of the clear liquid, titrate with standard silver 

 nitrate solution, and calculate result in terms of NaCl. It 

 rarely exceeds 10 per cent. Often high in Irish butter. 



Curd or Casein. Varies from 0-3 to 4 per cent. It is 

 usually calculated by difference. 



Fat. The amount of fat may be estimated in a Soxhlet 

 apparatus ; using a prepared thimble made of filter-paper ; 

 or by washing the dried solids with ether. For the other 

 processes the fat is separated by rilling a Nessler glass with 

 butter, and melting on the water-bath. The fat gradually 

 rises to the top, and the water and curd sink, so that three 

 layers are noted ; fat, curd, and water. The fat is now 

 filtered through a dry filter-paper placed in a funnel sur- 

 rounded with hot water. Care is taken not to pour any 

 of the wet curd or water on to the paper. The water-free 

 fat is then used for the various processes. 



I. Reichert-W ollny Process for the estimation of the 

 volatile fatty acids. 



Five grms. of the liquid fat are introduced into a 300 c.c. 

 boiling-flask ; 2 c.c. of 50 per cent NaOH solution (free from 

 CO 2 ), and 10 c.c. of 92 per cent alcohol, are added. The 

 mixture is heated for fifteen minutes (under a reflux con- 

 denser) on the water-bath kept at ioo C. The fats are 

 thus saponified. Remove the condenser, and continue the 



