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TESTS FOR LEAD. 
ART. XXI.— NOTE ON TESTS FOR LEAD. 
BY AMBROSE SMITH, 
Having recently had occasion to examine acetate of po- 
tassa, which was contaminated with lead, and finding that 
the lead, although readily recognized by means of sulphu- 
retted hydrogen, could not be detected by iodide of potas- 
sium, we were induced to make a few experiments, with a 
view of determining the relative delicacy of some of the 
tests for this metal. 
Iodide of potassium. — We found that a solution of ace- 
tate of lead containing one part of acetate in 900 of water 
could be distinguished by iodide of potassium, striking a 
greenish yellow. When the solution contained one part in 
1000, the iodide of lead entirely dissolved, forming a co- 
lourless solution. Iodide of lead is stated to dissolve in 
about 1200 parts of water, but we find it to be soluble to 
a somewhat greater extent when in the nascent state. 
Ferrocyanide of Potassium. — One part of acet. lead 
in 10,000 water, formed on the addition of ferrocyan. po- 
tass, a white opalescent turbulence; one part in 15,000, a 
milkiness scarcely apparent. 
Sulphuretted hydrogen. — One part acetate in 100,000 
water, showed distinctly with sulphuretted hydrogen, the 
solution becoming brown; with one part in 120,000, a 
change was produced that could be recognized. A. test 
tube i inch in diameter was employed in each experiment. 
Hence it appears that ferrocyanide of potassium as a test 
for lead is tentimes,and sulphuretted hydrogen one hundred 
and twenty times more delicate than iodide of potassium. 
The difference is still greater when the solution contain- 
ing the lead, contains also a salt of potassa or soda. In 
a strong solution of acetate of potassa, containing 1-1 00th, 
of acetate of lead, no change was produced by iodide of 
potassium. When the solution contained l-60th, it was 
