4 BULLETIN 448, U. S. DEPARTMENT OF AGRICULTURE. 
occasionally as a more homogeneous product of similar properties. 
The most objectionable of the impurities of gasoline may be removed 
by washing it a few times with concentrated sulphuric 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. 
Amyl 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 likely to be 
found in commercial ethyl acetate, so that the latter solvent has been 
used for the work described in this bulletin, notwithstanding its 
solubility and ease of saponification. 
Anilin. Unless recently distilled, anilin is usually strongly 
colored; but the coloring matters present differ widely in solubility 
from the sulphonated dyes for whose separation it is most frequently 
employed. The colored impurities do not interfere further than by 
inconveniently masking the course of the fractionation. 
Phenol. This must be colorless and should be free from mineral 
acid. 
Carbon tetrachloride 
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, 1 or over the surf ace of concentrated sulphuric 
acid contained in a flat porcelain dish, ordinarily will show if it is a 
mixture made from dry colors. 
i O. N. Witt, Z. Anal. Chem. 26 (1887), 100. 
