92 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



(k) DETECTION OF FLUOBORATES AND FLUOSILICATES. 



Make about 200 cc of wine alkaline with limew T ater, evaporate to dryness, and 

 incinerate. Extract the crude ash first obtained with water, to which sufficient 

 acetic acid has been added to decompose carbonates, filter, burn the insoluble por- 

 tion, extract with dilute acetic acid, and again filter. The insoluble portion now 

 contains calcium silicate and fluorid, while the filtrate will contain all the boric acid 

 present. 



(1) First method.* 



Incinerate the filter containing the insoluble portion, mix with a little precipitated 

 silica, and place, with the addition 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 from 30 to 40 minutes. If any fluorid be present the silicon fluorid gener- 

 ated 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. If, 

 however, silicon fluorid be detected and not boric acid, the operation is repeated 

 without the introduction of the silica, in which case the formation of the silicon 

 skeleton is conclusive of the presence of fluosilicate. b 



(2) Second method. 



Incinerate the filter containing the insoluble portion in a platinum crucible, mix 

 with a little precipitated silica, and add 1 cc of concentrated sulphuric acid. Cover 

 the crucible with a watch glass to whose underside a drop of water is suspended, and 

 heat an hour at the temperature of 70 or 80 C. The silicon fluorid which is formed 

 is decomposed by the water, leaving a gelatinous deposit of silica. Test the filtrate 

 for boric acid as described above. 



(B) BEER. 

 1. PREPARATION OF SAMPLE. 



Transfer the contents of bottle or bottles into a large flask and shake vigorously to 

 hasten the escape of carbon dioxid. The beer may then be poured into a second 

 receptacle from under the foam. 



2. DETERMINATION OF SPECIFIC GRAVITY. 



Follow the directions given for the determination of specific gravity in wine 

 (p. 82). 



3. DETERMINATION OF ALCOHOL. 



Follow the directions given for the determination of alcohol in wine (p 82). 

 4. DETERMINATION OF EXTRACT. 



Ascertain the extract content corresponding to the specific gravity of the dealco- 

 holized beer according to Table III. 

 For this purpose employ the formula: 



sp=g+(l a) 



'Neviere and Hubert, Mon. Sci., 1895 [/>], 9, :W4. 



b It mast be remembered that in an ash that contains an appreciable amount of silica, sulphuric 

 acid will liberate silicon fluorid rather than hydrofluoric acid. The presence of a fluosilicate is 

 indicated, therefore, and not of a fluorid. 



