Page images

7. The lower oxidizing flame. Suitable for oxidation of substances in borax or other beads.

8. The lower reducing flame. Suitable for reductions on charcoal, and in fused borax or other beads.

. The upper oxidizing flame (obtained by admitting the maximum of air). Suitable for oxidation at lower temperatures than are found at ß and y.

n. The upper reducing flame. Suitable for reductions ; possesses greater reducing power than &

Metallic films.The more volatile metals, such as arsenic, mercury, and zinc, are reduced from their compounds when these are heated on an asbestos thread in the upper reducing flame (n). If a small porcelain basin, filled with cold water, be held just above the substance to be examined, the volatilized metal condenses on the cold basin as a metallic film.

Example.—Place a minute quantity of any arsenic compound on a thread of asbestos. Hold this in one hand, and in the other a small porcelain basin filled with cold water. Now place the basin just above the upper reducing flame, and then the asbestos thread immediately below. In a few seconds the reduction will be complete ; remove the basin and observe the brown film of metallic arsenic. Moisten the film with cold dilute nitric acid, and observe that it is scarcely soluble ; moisten now with solution of sodium hypochlorite, and observe its instant solubility.

Metallic beads.-The less volatile metals may be obtained as beads, when their compounds are heated with sodium carbonate on a small charcoal rod held in the lower reducing flame (8).

Example.-Hold a crystal of sodium carbonate in the lamp flame for a few seconds till it begins to fuse ; then rub the fused salt thus obtained over a common wooden lucifer match, and burn this until it is converted into a rod of charcoal. Then allow a single drop of the fused sodium carbonate to fall on the palm of the hand, mix this intimately by means of a pen-knife with a small quantity of silver nitrate, and then place a very small portion of the mixture on the point of the rod of charcoal. Allow the mixture to melt in the lower oxidizing flame (y), and then push the charcoal splinter into the lower reducing flame (8). When the reduction is completed, remove the splinter and examine the point with a lens. Minute beads of fused silver will be seen, which may be further examined by breaking off the end of the splinter, and crushing it, along with a few drops of water in a small agate mortar. Pour off the water (which will carry the charcoal with it), and examine the metal thus obtained in the same way as the bead obtained by the mouth blow-pipe (56, a).

58. Compounds of the following metals form metallic films :—ANTIMONY, ARSENIC, BISMUTH, MERCURY, THALLIUM, CADMIUM, ZINC, INDIUM, and LEAD. They may be further distinguished by the following tests :



Antimony. Black film, thin part brown luble in cold


dilute HNO3. Bismuth. Black film, thin part brown With diffiMercury. Grey non-coherent thin film! culty soluble

in cold dilute Thallium. Black film, thin part brown HNO3. Cadmium. Black film, thin part brown

Instantly soZinc.

luble in cold Indium.

dilute HNO3. Lead.

Compounds of the following metals give no film, but are reduced to metal on charcoal splinter :COPPER, TIN, SILVER, GOLD, PLATINUM, IRON, NICKEL, and COBALT. They may be further distinguished as follows :Copper. Red bead, soluble in HNO3

Fusible to Tin. White bead

metallic Silver.

beads. Gold. Yellow bead, insoluble Platinum. Non-magnetic powder Not fusible to Iron. Magnetic powder

beads, but obNickel.

tained as meCobalt.

tallic powders.

[ocr errors]

59. Additional tests for the compounds of the following metals :

Antimony.On asbestos thread in upper reducing flame, pale green coloration, unaccompanied by smell. Reduced on charcoal splinter, yields white brittle metallic beads.

Arsenic.-On asbestos thread in upper reducing flame, pale blue coloration, and characteristic smell (garlic). Reduced on charcoal splinter, yields no metallic bead.

Bismuth, — Reduced on charcoal splinter, yields shining yellowish brittle splinters of metal. Dissolve in HNO3, add SnC, and NaHO, yields black precipitate of Bi, 02.

Mercury.—Mixed with dry sodium carbonate and potassium nitrate, in a small thin test-tube (5 millimetres wide and 15 millimetres long), and held in the flame (by a platinum wire coiled round it) just below a small porcelain basin filled with water, yields grey film, which, on rubbing with a piece of filter paper, is collected into small globules. If the quantity of mercury be large, globules form at once.

Thallium. — Flame coloration bright green. Reduced on charcoal splinter, yields white ductile bead, which quickly oxidizes, and is acted on by HCl with difficulty.

Cadmium.-Reduced on charcoal splinter imperfectly to a white ductile bead.

Zinc.-On asbestos thread in upper oxidizing flame, yields white film of ZnO on the porcelain basin. Moisten a square centimetre of filter paper with HNO3, and rub it over the surface of the basin so as to dissolve the oxide film; roll this up and place it in a coil of thin platinum wire. Now burn the paper in the upper oxidizing flame at as low a temperature as possible, and observe that the colour of the ash is yellow, while hot, and white on cooling. Moisten his ash with a drop of a very dilute solution of cobalt, heat in the lamp flame, and observe the green colour produced.

Indium.Flame coloration, intense indigo colour. Reduced on charcoal splinter with difficulty to silverwhite ductile globules, slowly soluble in HCl.

Lead.—Reduced on charcoal splinter, yields soft ductile metallic beads, soluble in HNO3. Add H2SO4 yields white precipitate of PbSO4

Copper.-Reduced on charcoal splinter, yields ductile metallic beads of a red colour. Dissolve in HNO, and add K Fe (CN)., yields chocolate coloured precipitate of Cu, Fe(CN)

Fuse a small quantity of borax on a straight piece of platinum wire (of the thickness of a horsehair), and, having obtained a clear bead, add a trace of any copper compound, and observe the blue bead obtained, which does not alter in the lower reducing flame. Add a trace of tin or any tin salt, and heat in the lower reducing flame; observe the change of colour to red, owing to the formation of Cu,O.

Tin.-Obtain a borax bead coloured faintly blue by copper, and add the tin compound; proceed just as described under copper. The change of colour from blue to red indicates presence of tin.

Silver.--Reduced on charcoal splinter, yields white ductile beads. Dissolve in HNO3 and add HCI, yields white curdy precipitate of Ag Cl.

Gold.--Reduced on charcoal splinter, yields yellow

« PreviousContinue »