1408 FOODS AND FOOD ADULTERANTS. 



FIRST METHOD. 



The mixture of ash and precipitated silica is placed in a platinum 

 crucible and about 1 cc of concentrated sulphuric acid is added. 

 The crucible is covered with a watch glass (which is not coated with 

 wax or paraffin) to whose under side a drop of water is suspended, and 

 heated one hour at a temperature of 70 to 80. The silicon fluorid 

 formed is decomposed by this drop of water, leaving a gelatinous 

 deposit of silica. 



SECOND METHOD.* 



The mixture of ash and precipitated silica is placed, with the addi- 

 tion of 1 or 2 cc of concentrated sulphuric acid, in a short test tube 

 which is attached to a small U-tube containing a few drops of water. 

 The test tube is now placed in a beaker of water, which is kept hot on 

 the steam bath for a few minutes. If any fluorid be present the sili- 

 con fluorid generated will be decomposed by the water in the U-tube 

 and will form a gelatinous deposit on the walls of the tube. 



The filtrate is now tested as directed under boric acid. If both 

 hydrofluoric and boric acids be present, it is probable that they were 

 combined as borofluorid. 



DETECTION OF SALICYLIC ACID. 



This substance is not well adapted to the preservation of meat, but 

 nevertheless is sometimes added to meat products. For its detection, 

 50 grams of the sample are heated in about 50 cc of water, about 

 10 cc of a concentrated solution of glacial phosphoric acid added to 

 coagulate proteids, and the mixture strained through a cotton bag and 

 the filtrate extracted in a separatory funnel with about 50 cc of ether. 

 The ether is allowed to evaporate spontaneously and the residue is 

 taken up with 2 or 3 cc of water and tested with 1 or 2 drops of 

 one-half per cent solution of ferric chlorid. The presence of salicylic 

 acid is indicated by the formation of a characteristic purple color. 



DETECTION OF BENZOIC ACID. b 



Like the preceding, benzoic acid is not well adapted to the preserva- 

 tion of meat preparations, but is sometimes used for this purpose. 

 For its detection about 50 grams of meat are digested in hot water, 

 treated with glacial phosphoric acid, and strained as directed under 

 salicylic acid. It is found convenient to treat a somewhat larger 

 weight of meat and divide the filtrate into different portions for the 

 two determinations. The filtrate is transferred to a short-necked 



a Neviere and Hubert, Mon. sci., 1895 (4), 9, 324. 



b The methods given for the detection of benzoic acid can not be employed in the 

 presence of saccharin. 



