1 78 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



The presence of fatty acid in the precipitate is shown : 



(1) By dissolving a small portion in ether and adding the solution 

 to alcohol containing a dfop of phenolphthalein and a few drops of 

 dilute sodium hydroxide. The red colour disappears. 



(2) By dissolving another portion in dilute sodium hydroxide. A 

 soap lather is formed on shaking it up with warm water. 



The soap is salted out by adding sodium chloride and rises to the 

 surface. 



A precipitate of calcium soap is formed on adding calcium chloride. 



(3) On heating with acid potassium sulphate there is no smell of 

 acrolein, if the precipitate has been washed free from glycerol. 



The presence of glycerol in the filtrate is shown by neutralising it 

 and evaporating it to a syrup on the water-bath. The 



J syrup is mixed with alcohol which precipitates the 



sodium sulphate. The alcoholic solution is poured off 

 and evaporated, and the residue tested for glycerol by 

 heating it with acid potassium sulphate, when acrolein 

 is formed. 



Estimation of Fats, etc. 



In the estimation of fat, the tissue must first be 

 dried : this is effected by mixing a known weight of 

 the material with clean dry sand or other suitable ab- 

 sorbing medium and then heating for 1-2 hours in a 

 steam oven. In the case of milk, it is most convenient 

 to absorb a known weight (or volume) in clean fat-free 

 filter paper, which is made into a small roll, and to dry 

 this. The dried material is then placed in a paper 

 thimble of suitable size and this is extracted with ether 

 for 2-3 hours in a Soxhlet apparatus, which allows of 

 a continual extraction for that time without constant 

 attention. The Soxhlet apparatus (Fig. 37) consists 

 of (i) a small dry flask, the weight of which has been 

 accurately determined, (2) a special extracting tube 

 into which the thimble and material is placed, (3) a short 

 condenser. The extracting tube is composed of a wide 

 piece of glass tubing like a test tube fused at its closed 

 end to a narrower piece of glass tubing which is cut off 

 at an angle at its other extremity. Just below the join of these pieces 

 of tubing a glass side tube is fused into the narrower piece ; its other 

 end is fused into the wider piece at the upper end. At the base of the 

 wide tube, on the other side of the 'apparatus, one end of a narrow 



FIG. 37. 



