WINE. 89 



100 cc. The deep blue color formed in the presence of nitrates appears RO quickly 

 that it is not obscured, even in sweet wine, by the blackening produced by the 

 action of sulphuric acid on the sugar. 



(b) RED WINE. PROVISIONAL. 



Clarify with lead subacetate and re*move the excess of lead with sodium 

 sulphate as directed under the determination of sugar ("VI. General Methods," 

 P. -KM. Filter and treat a few drops of the filtrate as directed under (a). 



23. Detection of Foreign Coloring Matter. Provisional. 

 Follow the directions given under " XXVIII. Coloring Matter," page 190. 



24. Detection of Preservatives. 



Follow the methods given under " XXVII. Food Preservatives," page 179 and 

 allowing. 



The detection of added boric acid is somewhat difficult because a small 

 amount of it is normally present in certain wines. To be of practical value, 

 therefore, this test should be quantitative. The determination of sulphurous 

 arid must also be quantitative. A small amount of salicylic acid is also normal 

 in wine, and for that reason not more than 50 cc of the sample should be used 

 in testing for that preservative. 



