20 BULLETIN 1390, U. S. DEPARTMENT OF AGRICULTURE 
N titanium trichloride solution (p. 24), using 5 grams of ammonium 
thiocyanate as indicator. Calculate the iron as ferric oxide (Fe,O,). 
To calculate the quantity of aluminium oxide (Al,O,) deduct the 
weight of ferric oxide from the total weight of mixed oxides. Cal- 
culate the percentage of iron and aluminium from the weights of 
the oxides. 
To the other reserved portion add 250 c. c. of water to insure a 
low concentration of magnesium, if present. Heat to boiling and 
add 3.5 grams of ammonium chloride and 1 gram of oxalic acid. Add 
ammonium hydroxide solution (1+99) until the solution is just 
neutral. Cool and let stand for an hour. Then filter through an 
asbestos mat prepared on a small Witt plate in a glass funnel and 
wash with very little water, reserving the cote liquids. Place 
the mat in a beaker and add 100 ¢. c. of water and 2 ¢. c. of concen- 
trated sulphuric acid. Heat gently until the calcium oxalate dissolves. 
Titrate with 0.1 N potassium permanganate solution. Calculate as 
percentage of calcium. 
Heat to boiling the reserved filtrate and washings and add N 
sodium ammonium hydrogen phosphate solution until there is no 
further precipitation. While stirring add about one-third the vol- 
ume of ammonium hydroxide solution (1+9). Let stand three 
hours, filter through an ashless paper, and wash with ammonium 
hydroxide solution (1+49). Convert to magnesium pyrophosphate 
by the usual method. Cool in a desiccator and weigh the magnesium 
pyrophosphate. Calculate as percentage of magnesium. 
ARSENIC 
REAGENTS 
girl ang mitric acid.—Arsenic-free and having a specific gravity 
or 1.42. 
Concentrated sulphuric acid.—Arsenic-free and having a specific 
gravity of 1.84. 
a hydroxide.—Arsenic-free and having a specific gravity 
of 0.90. 
Dilute hydrochloric acid.—Arsenic-free and containing 10 per cent 
by weight of hydrogen chloride. 
Dilute nitric acid.—Arsenic-free (1+ 9). 
Sodium phosphate solution.—Arsenic-free and containing 100 
erams of the crystallized salt per liter or an equivalent quantity of 
phosphoric acid. 
Meanie meaxture.—Arsenic-free and containing per liter 55 grams 
of hydrated magnesium chloride, 55 grams of ammonium chloride, 
and 88 c. c. of strong ammonium hydroxide. 
Saturated bromine water. 
Zinc.—Break arsenic-free stick zinc 6 mm. wide into pieces approxi- 
mately 1 cm. long. 
Lead acetate paper.—Soak heavy filter paper in 20 per cent lead 
acetate solution, ae and cut into pieces about 4.5 by 16 cm. 
Lead acetate cotton.—Soak absorbent cotton in 5 per cent lead 
acetate solution. 
Mercuric bromide paper.—Cut heavy, close-textured drafting 
paper into strips cattle 2.5 mm. wide and about 12 cm. long. Soak 
