1891.] PUBLIC DOCUMENT — No. 33. 67 



Method for determining Volatile and Non-volatile Fatty Acids 



(first). 

 Directly after receiving the sample of cream from the 

 Cooley cream-setting apparatus, the solids and fat were 

 determined as usual. The cream was churned by vigorous 

 shaking in a bottle, and was washed several times with cold 

 water. The butter was then 'dissolved in ether, filtered 

 from the curd, and the ether evaporated. About 2.5 grams 

 of fat were placed in a weighed Erlenmeyer flask, the exact 

 weight taken, and the fat saponified by 1 gram of potassium 

 hydrate dissolved in 50 cubic centimetres of 70 per cent, 

 alcohol. Heat is necessary for complete saponification. 

 The alcohol is next driven off by continued heating in a 

 boiling-water bath. The resulting soap is dissolved in 50 

 cubic centimetres of water, and decomposed by means of 20 

 cubic centimetres of dilute sulphuric acid (1 part of strong 

 acid to 10 of water) ; 50 cubic centimetres are then distilled 

 off, using a condenser for that purpose, the distillate passing 

 through a filter. The distillate is titrated with one-tenth- 

 normal sodium hydrate solution (4 grams of pure sodium 

 hydrate per litre of water) , 50 cubic centimetres of water 

 are added to the contents of the flask, and an equal quantity 

 distilled off, which is titrated as before. This treatment is 

 continued until .1 cubic centimetre or less of the soda 

 solution is required for neutralization. Phenolphthalein is 

 used as an indicator. The volatile fatty acids are calcu- 

 lated from the gum of the cubic centimetres of soda solution 

 required to neutralize all the distillates, calculating the acid 

 as butyric. After cooling, the liquid remaining in the flask 

 is poured off from the solidified non-volatile fatty acids 

 through the same filter used in filtering the distillates. The 

 solid fatty acids are washed repeatedly with hot w r ater, until 

 all traces of sulphuric acid are removed. The condenser 

 is then washed out with hot alcohol, and the filter exhausted 

 with the same solvent, the washings being collected iu the 

 flask. The alcohol is then driven off, the flask and contents 

 dried at 100° C, and weighed, and the percent, of non- 

 volatile fatty acids calculated. The above method is that of 

 R. W. Moore, as modified by "Waller, and described in the 

 " Journal of the American Chemical Society," No. 9, 1889, 

 by R. W. Moore. 



