LEAD COMPOUNDS.

29

pidinium, Pb,O,, is a bright red powder, which is not wcted by water, but evolves the smell of chlorine when naled with hydrochloric acid, and is slowly converted into pride of lead. Dilute nitric acid only partly dissolves it, ving a brown powder (peroxide of lead).

te.

tic Peroxide of Lead, or Binoxide of Lead, PbO,, is a dark on powder, which is insoluble in water and in nitric acid, dissolves slowly in boiling hydrochloric acid, giving off smell of chlorine, and forming chloride of lead, which stallizes in needles from the solution as it cools. Acetate of Lead, Pb2C,H,O,3Aq., forms white needlee crystals, which have a faint odor and an intensely sweet When treated with water it dissolves, but yields a ky solution, especially with common water, from the sence of a little carbonate of lead, formed from the caric acid contained in the water; nitric acid clears it up at When acetate of lead is heated on the point of a e, or on a slip of glass, it melts, and gives off an inflam›le vapor with a very peculiar smell, leaving a gray resicomposed of carbon and minute globules of metallic , easily changing to yellow oxide of lead.

2.

Perchloride of iron (ferric chloride), added to a solution acetate of lead, produces a white precipitate of chloride lead, and a red solution of ferric acetate, which is clearly after the precipitate has subsided.

White Lead, or Basic Carbonate of Lead, 2PbCO,,PbH2O2, heavy earthy powder, soon becoming gray when exposed ir, from the action of sulphuretted hydrogen. It is inble in water, and effervesces with hydrochloric acid, dising when heated, as chloride of lead, which crystallizes Needles on cooling. Dilute nitric acid easily dissolves

nate of lead, with effervescence caused by the escape rbonic acid gas. When heated on a knife, or slip of it becomes yellow.

romate of Lead, PbCrO,, is commonly sold as a bright or orange red powder or cake (the orange chrome

is the basic chromate or dichromate of lead, PbCrО, but fused chromate of lead has a brown color. It is i ble in water, but dissolves slowly when boiled with s hydrochloric acid, evolving chlorine and yielding a solution. If it be heated with hydrochloric acid and a alcohol, a bright green solution of chlorides of chro and lead is produced, which deposits crystals of chlori lead on cooling. Nitric acid scarcely affects chroma lead. If the yellow chromate of lead be heated on a k or slip of glass, its color changes to a red-brown.

unless heated.

Nitrate of Lead, Pb2NO,, forms hard white crys having a sweet taste. It dissolves in water, but not e When heated on a knife, or slip of glas crackles or decrepitates violently. If previously powde to prevent its flying off, it evolves suffocating brown fu (nitric peroxide), and leaves a yellow or red residue.

Chloride of Lead, PbCl,, is a white powder, somet crystalline, which dissolves slowly when boiled with wa the solution easily depositing crystals on cooling.

Iodide of Lead, PbI,, is a bright yellow powder, wi dissolves sparingly in boiling water, but more readily adding a little hydrochloric acid, yielding a colorless s tion, which deposits brilliant golden scales on cooling. W boiled with nitric acid, iodide of lead gives off the pu vapors of iodine.

Oxychloride of Lead is either white (Pb,OCl) or br yellow (Pb,O,C1), according to the mode of preparingi It melts easily when heated, the white oxychloride become yellow. It is insoluble in water, but dissolves sparit when boiled with hydrochloric acid, the solution deposi crystals of chloride of lead on cooling.

Sulphate of Lead, PbSO, is a white powder, which not change when heated, is insoluble in water, but diss slowly in boiling. hydrochloric acid, the solution depo crystals of chloride of lead as it cools.

Sulphide of Lead or Galena, PbS, is a dark, gray, i

e

LEAD COMPOUNDS.

31

pietallic-looking substance, the masses of which may be easily wit or cleaved with a knife-blade into rectangular fragments. nater has no effect upon it, and diluted hydrochloric acid 3sy little, but nitric acid gradually dissolves it, brown fumes с ting evolved, resulting from the decomposition of the nitric tid. Strong hydrochloric acid also dissolves it on heating, ducing the offensive odor of hydrosulphuric acid. Phosphate of Lead, Pb,2PO,, is described at (112).

1.1

re

32

15. Detection of a Metal belonging to the Hydrosulphuric Acid Group.

TABLE C.

Probable presence of
Arsenic (33, 34, 35).

solution is meant that to which no test has yet been added.

n

WASHING PRECIPITATES.

piecXPLANATIONS AND INSTRUCTIONS ON

wit nc

as

th

tion

L

lr

er

y

ur

TABLE C.

33

To wash a precipitate. The precipitate having been ted upon a filter (4) may be washed by filling the filter or thrice with distilled water, and allowing it to run through. A washing-bottle (fig. 12)

G. 12.

will be of great assistance in washing FIG. 14.
precipitates, the stream of water be-
ing directed so as to wash the pre-
cipitate from the sides towards the
apex of the filter.

When a precipitate is very heavy and subsides readily, it may be washed by decantation—that is, by

Png-bottle. shaking it up with successive quan

g the liquid without disturbing the precipitate.
Heating solid substances in tubes.-Ordinary
bes should not be used for this purpose, but
smaller tubes, which are made, with the help
blowpipe, from a piece of (German) glass
ree from lead, of the size represented in fig. 14.
iddle of this piece of tube is softened in the
pe flame (fig. 15), and quickly drawn out.to
wo tubes connected by a mere thread of glass,
is then detached from each tube, as shown at
ing the finished tube of the shape shown at b.