6 BULLETIN 1390, U. S. DEPARTMENT OF AGRICULTURE 
Place an aliquot part 3 of this solution in a colorimeter tube and 
dilute to a definite volume with distilled water. Then prepare 
standards 4 containing known quantities of lead for comparison. To 
these add the same quantity of ammonium acetate as was used for 
the unknown and dilute to the same volume with water. Add a 
few drops of acetic acid, 1-1, to each and stir the contents well 
with glass rods. Then add 10 c. c. of freshly prepared hydrogen 
sulphide water to each tube and again stir the contents equally. 
Place the tubes over a white surface *and estimate the quantity 
of lead by comparison with the standards. 
Blanks. — Make a test for lead on the acids used, employing the 
procedure for the unknown here reported, 0.2 gm. of pure anhydrous 
sodium carbonate being added to the acids in order that the conditions 
obtaining in the blank may be somewhat similar to those in the 
unknown. 
COLOR ACID AND PURE COAL-TAR DYE 
For amaranth and ponceau 3R substitute the following method 
for that given in Department Bulletin 1390 (revised) (2). 
For amaranth and ponceau 3R. — Proceed as for ponceau 3R, etc. 
(Bulletin 1390, 2, p. 28, par. 2), substituting 10 gm. of sodium citrate 
for sodium acid tartrate. 
WATER EXTRACTIVES 
The following optional method for determining water extractives 
may be used: 
For yellow AB and yellow OB. — To determine the neutral extractives 
proceed as follows: Place 5 gm. of the well-powdered dye in a 300 c. c. 
separatory funnel and add 100 c. c. of benzene. Shake until the dye 
has dissolved. Extract with two 100 c. c. portions of water. 
Evaporate 100 c. c. of the extract in a weighed platinum dish on a 
steam bath. Dry in an oven at 100° to 105° C. Cool in a desiccator 
and weigh. Report the percentage increase in weight as neutral 
water extractives. Test small portions of the remainder of the 
extract for chlorides, sulphates, and nitrates. If more than traces 
are present, make the proper analyses on aliquot portions of the 
filtrate. 
To determine the acid extractives, proceed as directed in Bulletin 
1390 (2, p. 29, last paragraph), except that for "wash once with 25 
c. c. of benzene," in line 5, substitute "wash with 25 c. c. portions of 
benzene until the benzene is practically colorless." 
ANALYTICAL CONSTANTS 
Table 4. — Sulphur, nitrogen, and sodium content 
Color 
Sulphur 
Nitrogen 
Sodium 
Ponceau SX 
Per cent 
13.35 
14.18 
12. 13 
Per cent 
5.83 
6.19 
Per cent 
9.57 
Sunset yellow FCF 
10.17 
Brilliant blue FCF. 
3.53 
5.80 
8 In case very small quantities of lead are present, it will be necessary to use the 15 gm. charge of dye, so 
that a 10 gm. aliquot may be obtained. 
* From pure crystallized lead nitrate dried over sulphuric acid, prepare a standard solution containing 
1 mgm. lead per c. c. From this solution prepare another solution containing 0.01 mgm. per c. c. and use 
this solution for preparing the standards. Make up this dilute solution just before it is to be used. 
