EXPERIMENT LXVII.

CADMIUM.

Materials. Cadmium sulphate, hydrogen sulphide, ammonium sulphide.

a. Dissolve completely not more than 1 c.c. cadmium sulphate, CdSO4 in 5 c.c. water, and add hydrogen sulphide in excess. Result? The visible product is cadmium sulphide, CdS. Color? Equation? What other sulphides of the same color have you had? Wash the precipitate by decantation, and treat it with 5 c.c. ammonium sulphide. Result? How distinguish between cadmium sulphide and other sulphides of the same color?

EXPERIMENT LXVIII.

MERCURY.

Apparatus. Pipette (medicine dropper).

Materials. - Mercury, concentrated nitric acid, hydrogen sulphide, hydrochloric acid, sodium hydroxide and potassium iodide solutions, ammonium hydroxide, zinc, and copper.

Caution. Before working with mercury remove all rings. Do not throw mercury away; but ask what you are to do with it.

a. By means of a pipette take from the mercury bottle a globule three times as large as an ordinary water drop; add to it 2 c.c. water and 2 c.c. concentrated

nitric acid. Result? Let stand until action stops; this may take some hours.

b. While waiting for a, dissolve a globule of mercury the size of a water drop in concentrated nitric acid; this gives mercuric nitrate, Hg(NO3)2. Equation (cf. Experiment XXXVII, g)? Dilute with 15 c.c. water.

c. To 2 c.c. mercuric nitrate solution (b) add hydrogen sulphide. Result? The precipitate is mercuric sulphide, HgS. Equation?

d. Add to separate portions of the nitrate solution, hydrochloric acid, sodium hydroxide solution, and potassium iodide solution, respectively. Results? Add the potassium iodide drop by drop, noting changes. Write equations where possible.

Note. - With sodium hydroxide we should expect mercuric hydroxide, Hg(OH)2; this, however, decomposes into the oxide and water.

e. Note the result of a. The crystals are mercurous nitrate, HgNO3; pour out into a beaker, and add 15 c.c. water and a drop of strong nitric acid.

f. To 2 c.c. of the mercurous nitrate solution of e add hydrogen sulphide. The precipitate is mercuric sulphide and mercury. Write the equation.

g. Repeat d with the mercurous instead of the mercuric nitrate. Results? With sodium hydroxide the precipitate is mercurous oxide, Hg2O. Write the equations. Treat the precipitate produced by hydrochloric acid with ammonium hydroxide. Result?

h. Into the rest of the mercurous nitrate put a strip of zinc and a copper wire. Results? Now rub them dry. Results?

i. Classify the results of c, d, f, and g in five vertical columns.

EXPERIMENT LXIX.

COPPER.

File or sand-paper.

Materials. Copper wire, concentrated hydrochloric acid; solutions of cupric sulphate, ammonium hydroxide, sodium hydroxide, and cupric nitrate; grape-sugar; iron nail.

a. File a piece of copper bright. Color? Is it hard or soft? From Experiment LXV give its fusibility compared with zinc, etc. By holding one end of the wire in the flame determine if it is a conductor of heat.

b. From Experiments XXXVII and XLII tell the action of nitric and sulphuric acids upon copper. Find out if copper reacts readily with concentrated hydrochloric acid.

c. To 2 c.c. cupric sulphate solution add ammonium hydroxide solution in excess. Result? Repeat with sodium hydroxide instead of ammonium hydroxide.

Result? Repeat, having the cupric sulphate hot, and then add the sodium hydroxide. Result? The last precipitate is cupric oxide, CuO. How formed (cf. Experiment LXVIII, d and g)?

d. From Experiment XLI, b and c, tell the effect of hydrogen sulphide upon cupric sulphate. Equation? Pass hydrogen sulphide into cupric nitrate solution. Result? Equation? What is the effect of heating blue vitriol (cf. Experiment XVII, d)?

e. Dissolve half a c.c. powdered grape-sugar, C6H12O6, in 2 c.c. water, and add it to 5 c.c. cupric sulphate solution. Now add sodium hydroxide solution, shaking until the precipitate first formed is redissolved. Color? Warm carefully, noting changes. Let stand. Results? Color of product? It is cuprous oxide, Cu2O. What effect had the grape-sugar?

f. Put an iron nail into cupric sulphate solution. Result?

EXPERIMENT LXX.

SILVER.

Materials. Silver foil, silver nitrate solution, nitric acid, sodium thiosulphate; solutions of sodium chloride and potassium bromide, iodide, and cyanide; filter paper; hydrogen sulphide.

a. In a test tube treat a piece of silver foil with 2 c.c. concentrated nitric acid. Result? Equation? Dilute with water to 10 c.c.

b. To 2 c.c. of the solution of a add 5 c.c. sodium chloride solution. Result? Equation (cf. Experiment

XXII, j)? Boil the contents of the tube. Result? Get the precipitate on filter paper, and expose it to sunlight. Result?

c. To 5 c.c. of solution a add 1 c.c. potassium bromide solution. Result? Heat to boiling, pour off the supernatant liquid, and add to half of the precipitate sodium thiosulphate solution, Na2S2O3 (make this by dissolving the crystals in water). Result? Expose the other half on filter paper to sunlight. Result?

d. To 1 c.c. silver nitrate solution add 1 c.c. potassium iodide solution. Result? Equation?

e. To 1 c.c. silver nitrate solution add hydrogen sulphide. Result? Equation?

f. To 1 c.c. silver nitrate solution add potassium cyanide solution, drop by drop. Result. Equation? Continue adding it, shaking, until it is in excess. Result? The solution contains the double cyanide, KCN.AgCN, i. e., KAg(CN)2. Add sodium chloride solution. Result? Explain the result in terms of the ionic theory (cf. Experiment XXX).

EXPERIMENT LXXI.

ALUMINUM.

Apparatus. Test tubes, tongs, blast-lamp.

Materials.

Aluminum wire and filings, white muslin, hydrochloric acid; solutions of sodium hydroxide, aluminum sulphate, sodium carbonate, alum, ammonium hydroxide, and cochineal; powdered alum, sodium bicarbonate, potassium sulphate, ammonium sulphate, aluminum sulphate.