DETECTION OF FLUOKIDS AND SlLlCO-FLUOKIDS. 1407 

 QUANTITATIVE DETERMINATION OF BORIC ACID. 



In the absence of iron, Thompson's method* gives satisfactory 

 results. This method, however, is not applicable to canned meats, 

 since it is usually found that more or less iron has been taken up from 

 the can. Mr. Munson attempted to separate the iron by precipita- 

 tion with ammonium hydroxid, ammonium sulphid, and ammonium 

 acetate, but in all cases some boric acid was carried down with the 

 precipitates. A modification of Gooch's method b was finally adopted. 



About 50 grams of the meat under examination are incinerated 

 (complete combustion is not essential), transferred to a short-necked 

 flask and acidified with hydrochloric acid. The flask is connected with 

 a condenser and four or five 20 cc portions of methyl alcohol are 

 added and distilled over a calcium chlorid bath into sodium hydroxid. 

 The distillate is evaporated to dryness (to expel the methyl alcohol), 

 care being taken that it is distinctly alkaline, the residue dissolved in 

 from 15 to 20 cc of water acidified with hydrochloric acid, heated 

 just to the boiling point to expel carbon dioxid, and titrated by 

 Thompson's d method. 



The mineral acid is exactly neutralized to methyl orange with sodium 

 hydroxid (which leaves only the boric acid in the free state), 2 vol- 

 umes of glycerol and a little phenolphthalein added, and the boric acid 

 titrated with decinormal sodium hydroxid. Each cubic centimeter of 

 decinormal alkali employed is equivalent to 0.0062 grams of H 3 BO 3 . 



DETECTION OF FLUORIDS AND SILICO-FLUORIDS. 



The insoluble residue which results from the extraction of the 

 ignited sample used in the detection of boric acid will contain the cal- 

 cium salt of any fluorids and silico-fluorids present in the original 

 sample. It was found impossible to detect fluorids by warming with 

 sulphuric acid in a dish covered with a watch glass coated with wax 

 through which a character had been marked. This is probably owing 

 to the presence of silica in the ash of all meat products. It therefore 

 seems necessary to employ a method suitable for the detection of 

 silico-fluorids, and no method is suggested for distinguishing whether 

 the preservative emplo} r ed is a simple fluorid or a silico-fluorid. 



The insoluble residue referred to under boric acid (p. 1406) should 

 be ignited, the resulting ash mixed with precipitated silica, and the 

 presence of fluorin determined by one of the following methods, of 

 which the first has been found to give the most satisfactory results in 

 this laboratory. 



a Jour. Soc. Chem. Ind., 1893, 12, 432. 



b Amer. Acad. Arts and Sci., 1886-87, p. 167; abs. Ztschr. anal. Chem., 1887, 26, 

 364. 



c The residue in the distilling flask should be tested with turmeric paper, and the 

 distillation repeated as long as any boric acid remains. 



d Jour. Soc. Chern. Ind., 1893, 12, 432. 



