112 



METHODS OF ANALYSIS. 



by comparison of the volume of nitric oxid with that evolved by a definite 

 volume (5 to 10 cc) of normal sodium nitrate solution. 



(b) PHENOL-SULPHONIC ACID METHOD." PROVISIONAL. 



Weigh 1 gram of the sample into a 100 cc flask, add from 20 to 30 cc of water, 

 and heat on the water bath for fifteen minutes, shaking occasionally. Add 3 cc 

 of a saturated solution of silver sulphate for each per cent of sodium chlorid 

 present, then add 10 cc of lead subacetate and 5 cc of alumina cream, shaking 

 after each addition. Make up to mark with water and filter through a folded 

 filter, returning the filtrate to the filter until it runs clear. Evaporate to dry- 

 ness 25 cc of the filtrate, add 1 cc of phenol-sulphonic acid,& mix thoroughly 

 with a glass rod, add 1 cc of water and 3 or 4 drops of concentrated sulphuric 

 acid, and heat on a steam bath for two or three minutes, being careful not to 

 raise the temperature sufficiently to char the material. Add about 25 cc of 

 water and an excess of ammonium hydroxid. Transfer to a 100 cc flask, add 1 

 or 2 cc of alumina cream if not perfectly clear, dilute to the mark with water, 

 and filter if necessary. 



Prepare a number of 50-cc Nessler tubes, preferably the long, narrow tubes, 

 placing in the first 1 cc of the standard nitrate solution, containing 0.01 nig of 

 nitrogen as potassium nitrate in each cubic centimeter, in the second 2 cc, and 

 so on to 10 cc, then 12 cc, 15 cc, 18 cc, and 20 cc. Compare with the standards 

 the solution prepared as directed above. If dilution is necessary to bring within 

 this range, calculate to original concentration, and note in the following table 

 the percentage of potassium nitrate in the original sample. 



Per cent potassium nitrate. 



12. Detection of Preservatives. Provisional. 



The chemical preservative-; oaimionly used with moat products are borax and 

 boric acid and sulphites. Salicylic and benzole acids are occasionally used. The 

 methods for the detection of these pivscrvaiivos are given under "XXVII. Food 



This method is a modification of the one ordinarily employed for determining potas- 

 sium nitrate in water. It was adapted to the examination of meat by Arthur Given. 



* Prepared by mixing !J7 cc of concentrated sulphuric acid, .'i cc of distilled water, and 

 6 grams of phenol. 



