1424 FOODS AND FOOD ADULTEKANTS. 



with from 70 to 100 cc of water and extract with from 50 to 60 cc 

 of ether. In case the two liquids do not separate, a few cubic centi- 

 meters of alcohol m&y be added. Separate the water solution and 

 wash the ether with water containing few drops of sodium hydroxid. 

 Again extract the soap solution and washings with ether and evaporate 

 the combined extracts to dryness. In most cases it is advisable to add 

 a little alcoholic potassium hydroxid to the residue and heat in order 

 to saponify any traces of fats left unsaponified and extract again with 

 ether. Transfer to a weighed dish and dry as quickly as possible in 

 water oven. 



Many of the hydrocarbon oils are volatile at 100, so that the dry- 

 ing should not be carried any further than necesary. With resin oil, 

 paraffin wax, and the denser mineral oils there is little danger of loss 

 at 100. 



On account of the solubilit}^ of soap in ether and'petroleum ether it 

 is well to wash with warm water containing a little phenolphthalein. 

 If it shows alkaline reaction there is soap present. 



DETERMINATION OF MELTING POINTS OF FATS. 



WILEY'S METHOD." 

 PREPARATION OF REAGENTS. 



(a) A piece of ice floating in distilled water that has been recently 

 boiled. 



(V) A mixture of alcohol and water of the same specific gravity as 

 the fat to be examined. This is prepared by boiling distilled water 

 and 95 per cent alcohol for ten minutes to remove the gases which they 

 may hold in solution. While still hot, the water is poured into the 

 test tube described below until it is nearly half full. The test tube 

 is nearly filled with the hot alcohol, which is carefully poured down the 

 side of the inclined tube to avoid too much mixing. If the alcohol is 

 not added until the water has cooled, the mixture will contain so many 

 air bubbles as to be unfit for use. These bubbles will gather on the 

 disk of fat as the temperature rises and finally force it to the top. 



APPARATUS. 



The apparatus for determining the melting point consists of an 

 accurate thermometer reading easily tenths of a degree; a cathetom- 

 eter for reading the thermometer (but this may be done with an eye- 

 glass if held steadily and properly adjusted); a thermometer; a tall 

 beaker 35 cm high and 10 cm in diameter; a test tube 30 cm long 

 and 3.5 cm in diameter; a stand for supporting the apparatus; some 

 method of stirring the water in the beaker (for example, a blowing 



a U. S. Dept. Agr., Div. Chem. Bui. 46, revised, p. 52. 



