13 



In doubtful cases the ammoniacal solution should be acidified, shaken out with 

 ether, and the melting point of the vanillin, obtained by evaporation at room tem- 

 perature, determined. 



Following the above, under section "4," insert Leach's test for 

 coumarin as a provisional method: 



(b) DETECTION OF COUMARIN (LEACH's METHOD ). 



Applied to dry crystals or to the residue from the ether extract of the dealcoholized 

 ammoniacal sample of vanilla extract, in the gravimetric determination of coumarin, to 

 confirm its identity. Dissolve a few of the crystals or the small crystalline residue in 

 a few drops of hot water, filter if necessary, and add to the clear solution a little 

 iodin in potassium iodid reagent. & In presence of coumarin a brown precipitate 

 will form, which on stirring or shaking will soon gather in dark-green flecks, leaving 

 a clear, brown solution. The reaction is especially marked if the iodin reagent is 

 applied with a glass rod to the few drops of solution to be tested on a white plate or 

 tile. 



a Leach, Food Inspection and Analysis, p. 738. 



b Dissolve 2 grams of potassium iodid in 100 cc of water and saturate solution with iodin. 



Under heading "4," and following section "(b)?" insert the colori- 

 metric ferrous-sulphate method for the determination of vanillin as a 

 provisional method: 



(c) DETERMINATION OF VANILLIN (COLORIMETRIC METHOD 65 ). 



Measure 2 cc of the vanilla extract into a test tube and add about 5 cc of lead 

 hydrate reagent. & Mix thoroughly and pour upon a small wet filter and collect 

 filtrate and washings in a 50 cc graduated Nessler tube. Add an excess of bromin 

 water (three or four drops), and sufficient freshly prepared 10 per cent ferrous sul- 

 phate solution to produce the maximum bluish-green color that will result if vanillin 

 is present, and fill to the mark with water. 



Prepare a standard solution of vanillin by dissolving 50 mg of pure vanillin in 

 25 cc of alcohol and make up to 100 cc with water. Make up a series of color stancU- 

 ards, taking for instance, 0.5, 1, 1.5, 2, 2.5, 3, . . . cc of the standard vanillin solu- 

 tion in 50 cc Nessler tubes, each being treated with two or three drops of bromine 

 water and with an excess of ferrous-sulphate solution, and made up to the 50 cc 

 mark. Match the color from the sample extract with the appropriate one of the 

 color series and thus calculate the amount of vanillin present. 



If, for example, 2 cc of a sample extract, treated as above, are found to give a 

 color corresponding in depth to that produced by 5.5 cc of the standard solution, the 

 amount of vanillin would be thus calculated: 



100 cc of standard vanillin solution contain 0.05 gram vanillin. 



1 cc of standard vanillin solution contains 0.0005 gram vanillin. 



5.5 cc of standard vanillin solution contain 0.00275 gram vanillin. 



Since 2 cc of the sample are equivalent to 5.5 cc of the standard solution, it follows 

 that 2 cc of the sample contain 0.00275 gram of vanillin; therefore 100 cc of the sample 

 contain 0.1375 gram of vanillin. 



"Leach, Food Inspection and Analysis, p. 735. 



b Dissolve 200 grams of lead acetate in 850 cc of water, filter, and add an excess of potassium 

 or sodium hydroxid. Let the precipitate settle and wash thoroughly by decantation with 

 repeated portions of water till perfectly neutral. Keep in 500 cc of water in the reagent 

 bottle, and shake to form an emulsion-like mixture before adding to decolorize. 



