42 MILK ANALYSIS 



acid will have been converted into salicylic acid by the process 

 and the latter may be detected by dilute solution of fenic chlorid 

 or ammonio-ferric sulfate. 



Salicylic acid. This is usually detected by extraction with 

 an immiscible solvent. 25 to 50 c.c. of the sample are rendered 

 feebly acid with a few drops of sulfuric acid and shaken vigor- 

 ously with about an equal bulk of a mixture of equal parts of 

 ether and petroleum spirit, the liquids are allowed to separate, 

 as much as possible of the solvent is drawn off, filtered, and 

 evaporated at a gentle heat. When salicylic acid has been 

 added as a preservative, distinct needle-like crystals will be 

 usually seen. A few drops of water should be added and then 

 a drop of very dilute ferric chlorid solution. The reaction of 

 salicylic acid is distinct. When a crystalline deposit cannot be 

 obtained, a larger quantity of the sample may be concentrated 

 at a gentle heat and extracted as above. 



Some analysts prefer chloroform as the extracting liquid. 

 In this case the shaking should be done in a stoppered sepa- 

 rator, that the solvent may be readily drawn. A solution of 

 ammonio-ferric alum is in some respects preferable to ferric 

 chlorid as a testing agent. If 50 c.c. of the sample properly 

 extracted does not give a visible deposit of the acid, it is not 

 likely that it has been added as a preservati^'c. 



Saccharin. A suitable amount of the sample (50 or 100 

 c.c.) is acidilied with dilute (25 per cent.) sulfuric acid and 

 extracted with a mixture of equal parts of petroleum spirit 

 boiling below 60° and ether. The solvent is evaporated at a 

 gentle heat. The presence of saccharin in the residue may be 

 detected by the taste. 2 c.c. of a saturated solution of sodium 

 hydroxid are added and the dish heated until the residue dries 

 and then to 2io°-2i5°, and maintained thus for half an hour. 

 The saccharin is converted into salicylic acid, which may be 

 detected in the residue by acidulating it with sulfuric acid and 

 applying the ferric chlorid test. If salicylic acid be pi-esent 



