28 BULLETIN 139, U. 8. DEPARTMENT OF AGRICULTURE 
DETERMINATION 
For yellow A B and yellow O B.—To a capillary tube of 1 mm. or 
smaller internal diameter, sealed at one end, transfer a small portion 
of the sample by inserting into the sample the open end of the capillary 
tube, removing, inverting, and gently tapping until the loosely packed 
substance fills the bottom of the tube to a height of 2 to 4 mm. 
Attach the capillary tube to the thermometer C by means of a small 
rubber band, so that the sample is placed at about the middle of the 
mercury bulb. Replace the thermometer in the tube, connect the 
tube A to the air blast, and force a not too rapid stream of air 
bubbles through the bath. Raise the temperature of the bath 
rapidly to within 5° of the approximate melting point of the sample. 
Keep the temperature constant until the thermometer reading is 
within 1° of that of the bath. Then raise the tem- 
perature slowly until melting is observed. On ap- 
proaching within approximately 0.5° of the melting 
point the substance darkens; true melting is indi- 
cated by the formation of a meniscus on the upper 
surface. When this condition is observed record 
the temperature. Keep the temperature as nearly 
constant as possible until the whole of the sample 
has liquefied; then record the temperature again. 
LOWER SULPHONATED DYES 
For amaranth and tartrazine.—To that volume of 
the master solution which contains 0.2 gram of the 
dye add 1c. c. of strong hydrochloric acid and bring 
to a volume of 50 ¢.c. Extract the lower sulpho- 
nated dye by shaking the solution successively in 
three separatory funnels, each containing 50 c. c. of 
amyl alcohol. Wash the amyl alcohol extracts by 
shaking successively with three 50 c. ¢. portions of 
approximately 0.25 N hydrochloric acid, passing 
each acid portion through the three funnels in the 
order used for the original solution. (One volume 
_ of strong hydrochloric acid, diluted with 50 volumes 
Fic. 3.—Melting point of water, yields a solution of about 0.25 N strength.) 
ies aha Dilute the amy] alcohol in each funnel with 100 ¢. ¢. 
portions of gasoline (specific gravity 0.65), and remove the lower 
sulphonated dye by washing with several 10 c. c. portions of water, 
passing each portion through the three funnels in an order the reverse 
of that previously followed. odie 
Determine the dye in the water extract by titration against 
standard titanium trichloride solution (p. 24), using 15 grams of 
sodium acid tartrate and having a volume of 100 c. ¢. Run a blank 
determination on the same weight of tartrate and the same volume 
of water, using 1 mg. of the dye. Calculate the result to percentage 
of fast red E in amaranth and fast wool yellow G in tartrazine. One 
cubic centimeter of 0.1 N titanium trichloride solution is equivalent 
to 0.01256 gram of fast red E and to 0.01081 gram of fast wool yellow 
G. If the quantity of dye is very small, it may be determined 
Siibiaeaattidally: using the original dye as a standard. 
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