4 BULLETIN 448, U. S. DEPAETMENT OF AGEICULTUEE. 



occasionally as a more homogeneous product of similar properties. 

 Tlie most objectionable of the impurities of gasohne may be removed 

 by washing it a few times with concentrated sidphuric acid. 



Ether. The alcohol in the commercial product may be removed 

 by washing. 



DicMorhydrin. Most commercial C. P. products contain free acid. 

 This is seldom harmful, but a freshly washed preparation may be 

 preferred occasionally. 



Ethyl acetate. Apparently this is usually impure and before use 

 should be washed with water to remove alcohol, etc. 



Arayl acetate. Amyl acetate is suited to the same uses as ethyl 

 acetate. It is, however, a less active solvent for many dyes, partly, 

 no doubt, because it dissolves less water. Commercial C. P. prep- 

 arations show great variability, apparently from the presence of 

 large amounts of impurities and not merely from difference in the 

 proportion of isomers present. The impurities, especially amyl 

 alcohol, are much more difficult to remove than those hkely to be 

 found in commercial ethyl acetate, so that the latter solvent has been 

 used for the work described in this bulletin, notwithstanding its 

 solubihty and ease of saponification. 



Anilin. Unless recently distilled, anihn is usually strongly 

 colored; but the coloring matters present differ widely in solubihty 

 from the sulphonated dyes for whose separation it is most frequently 

 employed. The colored impurities do not interfere fm^ther than by 

 inconveniently masking the com'se of the fractionation. 



PJienol. This must be colorless and should be free from mineral 

 acid. 



Carbon tetrachlorid. 



Methyl alcohol. 



PRELIMINARY TREATMENT OF FOOD PRODUCTS. 



It is usually necessary to begin examination of the color or colored 

 material by treatment with some solvent that will bring the coloring 

 matter into solution. 



Commercial food colors if soluble are dissolved directly in water, 

 care being taken that the solution, to be examined according to the 

 scheme described on pages 9 to 20, inclusive, be not made too concen- 

 trated. Solutions of suitable concentration contain from 0.05 to 0.01 

 per cent actual coloring matter. If the coloring matter is a powder, 

 blowing some of the substance from the tip of a spatula over a sheet of 

 moistened filter paper,^ or over the surface of concentrated sulphuric 

 acid contained in a fiat porcelain dish, ordinarily will show if it is a 

 mixture made from dry colors. 



1 O. N. Witt, Z. Anal. Chem. 36 (1887), 100. 



