An Introduction to Chemical Science Part 16

We know but little of the molecular condition of solids and liquids, since we have no law to guide us like Avogadro's in gases; but, from the density of S vapor at different temperatures, we infer that liquids and solids have their molecules very differently made up from those of gases. The least combining weight of S is 32. Its vapor density at 1,000 degrees is 32; hence its molecular weight is 64, i.e. vapor density x 2; and there are 2 atoms in its molecule at that temperature, molecular weight / atomic weight. At 500 degrees, however, the vapor density is 96and the molecular weight 192. At this degree the molecule must contain 6 atoms. How many it has in the allotropic forms, as a solid, is beyond our knowledge; but it seems quite likely that allotropy is due to some change of molecular structure.

The above experiments show two modes of obtaining crystals, by fusion and by solution.

187. Occurrence and Purification.--Sulphur occurs both free and combined, and is a very common element. It is found free in all volcanic regions, but Sicily furnishes most of it. Great quant.i.ties are thrown up from the interior of the earth during an eruption. The heat of volcanic action probably separates it from its compound, which may be CaSO4. Vast quant.i.ties of the poisonous SO2 gas are also liberated during an eruption, this being, in volume of gases evolved, next to H2O. S is crudely separated from its earthy impurities in Sicily by piling it into heaps, covering to prevent access of air, and igniting, when some of the S burns, and the rest melts and is collected. After removal from the island it is further purified by distilling in retorts connected with large chambers where it sublimes on the sides as flowers of sulphur (Fig. 43). This is melted and run into molds, forming roll brimstone. S also occurs as a const.i.tuent of animal and vegetable compounds, as in mustard, hair, eggs, etc. The tarnishing of silver spoons by eggs is due to the formation of silver sulphide, Ag2S. The yellow color of eggs, however, is due to oils, not to S.

The main compounds of S are sulphides and sulphates. What acids do they respectively represent? Metallic sulphides are as common as oxides; e.g. FeS2, or pyrite, PbS, or galenite, ZnS, or sphalerite, CuFeS2, or chalcopyrite, etc. The most abundant sulphate is CaSO4, or gypsum. BaSO4, or barite, and Na2SO4, or Glauber's salt, are others.

The only one of these compounds that is utilized for its S is FeS2. In Europe this furnishes a great deal of the S for H2SO4. S is obtained by roasting FeS2. 3 FeS2 = Fe3S4 + 2 S.

188. Uses. -The greatest use of S is in the manufacture of H2SO4.

A great deal is used in making gunpowder, matches, vulcanized rubber, and the artificial sulphides, like HgS, H2S, CS2, etc.

The last is a very volatile, ill- smelling liquid, made by the combination of two solids, S being pa.s.sed over red-hot charcoal.

It dissolves S, P, rubber, gums, and many other substances insoluble in H2O.

189. Sulphur Dioxide, SO2, has been made in many experiments. It is a bleaching agent, a disinfectant, and a very active compound, having great affinity for water, but it will not support combustion. Like most disinfectants, it is very injurious to the system. It is used to bleach silk and wool--animal substances-- and straw goods, which Cl would injure; but the color can be restored, as the coloring molecule seems not to be broken up, but to combine with SO2, which is again separated by reagents. Goods bleached with SO2 often turn yellow after a time.

190. SO2 a Bleacher.

Experiment 107.-Test its bleaching power by burning S under a receiver under which a wet rose or a green leaf is also placed.

Chapter x.x.xVIII.

HYDROGEN SULPHIDE.

Examine ferrous sulphide, natural and artificial.

191. Preparation.

Experiment 108.--Put a gram of ferrous sulphide (FeS) into a t.t.

fitted with a d.t., as in Figure 32. Add 10cc. H2O and 5cc.

H2SO4. H2S is formed. Write the equation, omitting H2O. What is left in solution?

192. Tests.

Experiment 109.-(1) Take the odor of the escaping gas. (2) Pour into a t.t. 5cc.solution AgNO3, and place the end of the d.t.

from a H2S generator into the solution and note the color of the ppt. What is the ppt.? Write the equation. (3) Experiment in the same way with Pb(NO3)2 solution. Write the equation. (4) Let some H2S bubble into a t.t. of clean water. To see whether H2S is soluble in H2O, put a few drops of the water on a silver coin.

Ag2S is formed. Describe, and write the equation. Do the same with a copper coin. (5) Put a drop of lead acetate solution, Pb(C2H3O2)2, on a piece of unglazed paper, and hold this before the d.t. from which H2S is escap- ing. PbS is formed. Write the equation. This is the characteristic test of H2S.

193. Combustion of H2S

Experiment 110.--Attach a philosopher's lamp tube to the H2S generator, and, observing the same precautions as with H, light the gas. What two products must be formed? State the reaction.

The color of the flame. Compute the molecular weight and the vapor density of H2S. 194. Uses. -Hydrogen sulphide or sulphuretted hydrogen, H2S, is employed chiefly as a reagent in the chemical laboratory. It forms sulphides with many of the metals, as shown in the last experiment. These are precipitated from solution, and may be separated from other metals which are not so precipitated, as was found in the case of HCl and NH4OH.

The subjoined experiment will ill.u.s.trate this. Suppose we wished to separate Pb from Ba, having salts of the two mixed together, as Pb(NO3)2 and Ba(NO3)2.

195. H2S an a.n.a.lyzer of Metals.

Experiment 111.--Pa.s.s Some H2S gas in to 5cc.solution Ba(NO3)2.

No ppt. is formed. Do the same with Pb(NO3)2 solution. A ppt.

appears. Now mix 5cc.of each of these solutions in a t.t. and pa.s.s the gas from a H2S generator into the liquid. What is precipitated, and what is unchanged? When fully saturated with the gas, as indicated by the smell, filter. Which metal is on the filter and which is in the filtrate? Other reagents, as Na2CO3 solution, would precipitate the latter.

196. Occurrence and Properties. -- H2S is an ill-smell- ing, poisonous gas, formed in sewers, rotten eggs, and other decaying alb.u.minous matter. It is formed in the earth, probably from the action of water on sulphides, and issues with water from sulphur springs.

A characteristic property is the formation of metallic sulphides, as above. A skipper one night anch.o.r.ed his newly painted vessel near the Boston gas-house, where the refuse was deposited, with its escaping H2S. In the morning, to his consternation, the craft was found to be black. H2S had come in contact with the lead in the white paint, forming black PbS. This gradually oxidized after reaching the open sea, and the white color reappeared.

Chapter x.x.xIX.

PHOSPHORUS.

NOTE.--Phosphorus should be kept in water, and handled with forceps, never with the fingers, except under water, as it is liable to burn the flesh and produce ulcerating sores. Pieces not larger than half a pea should be used, and every bit should finally be burned.

197. Solution and Combustion. Experiment 112. -Put 1 or 2 pieces of P into an evaporating- dish, and pour over them 5 or 10cc.CS2 carbon disulphide. This will be enough for a cla.s.s. When dissolved, dip pieces of unglazed paper into it, and hold these in the air, looking for any combustion as they dry. The P is finely divided in solution, which accounts for its more ready combustion then. Notice that the paper is not destroyed. This is an example of so-called "spontaneous combustion." The burning- point of P, the combustible, in air, the supporter, is about 60 degrees.

198. Combustion under Water.

Experiment 113. -Put a piece of P in a t.t. which rests in a receiver, add a few crystals KClO3 and 5cc. H2O. Now pour in through a thistle-tube 1cc.or more of H2SO4. Look for any flame.

H2SO4 acts very strongly on KClO3. What is set free? From this fact explain the combustion in water.

199. Occurrence.--P is very widely disseminated, but not abundant, and is found only in compounds, the chief of which is calcium phosphate Ca3(PO4)2. It occurs in granite and other rocks, as the mineral apat.i.te, in soils, in plants, particularly in seeds and grains, and in the bones, brains, etc., of vertebrates. From the human system it is excreted by the kidneys as microcosmic salt, HNaNH4PO4; and when the brain is hard- worked, more than usual is excreted. Hence brain-workers have been said to "burn phosphorus."

200. Sources.--Rocks are the ultimate source of this element.

These, by the action of heat, rain, and frost, are disintegrated and go to make soils. The rootlets of plants are sent through the soil, and, among other things, soluble phosphates in the earth are absorbed, circulated by the sap, and selected by the various tissues. Animals feed on plants, and the phosphates are circulated through the blood, and deposited in the osseous tissue, or wherever needed.

Human bones contain nearly 60 per cent of Ca3(PO4)2; those of some birds over 80 per cent.

The main sources of phosphates and P are the phosphate beds of South Carolina, the apat.i.te beds of Canada, and the bones of animals.

201. Preparation of Phosphates and Phosphorus.--Bone ash, obtained by burning or distilling bones, and grinding the residue, is treated with H1SO4, and forms soluble H4Ca(PO4)2, superphosphate of lime, and insoluble CaSO4.

Ca3(PO4)2 + 2 H2SO4 = H4Ca(PO04)2 + 2 CaSO4. This completes the process for fertilizers. If P is desired, the above is filtered; charcoal, a reducing agent, is added to the filtrate; the substance is evaporated, then very strongly heated and distilled in retorts, the necks of which dip under water. It is then purified from any uncombined C by melting in hot water and pa.s.sing into molds in cold water.

The work is very dangerous and injurious, on account of the low burning-point of P, and its poisonous properties. While its compounds are necessary to human life, P itself destroys the bones, particularly the jaw bones, of the workers in it.

Between 1,000 and 2,000 tons are made yearly, mostly for matches, but almost all at two factories, one in England, and one in France. 202. Properties.--P is a colorless, transparent solid, when pure; the impure article is yellowish, translucent, and waxy. It is insoluble in water, slightly soluble in alcohol and ether, and it readily dissolves in CS2, oil of turpentine, etc.

Fumes, having a garlic odor, rise when it is exposed to the air, and in the dark it is phosph.o.r.escent, emitting a greenish light.

203. Uses. -The uses of this element and its compounds are for fertilizers, matches, vermin poisons, and chemical operations.

204. Matches.-The use of P for matches depends on its low burning-point. Prepared wood is dipped into melted S, and the end is then pressed against a stone slab having on it a paste of P, KClO3, and glue. KNO3 is often used instead of KClO3. In either case the object is to furnish O to burn P. Matches containing KClO3 snap on being scratched, while those having KNO3 burn quietly. The friction from scratching a match generates heat enough to ignite the P, that enough to set the S on fire, and the S enough to burn the wood. Give the reaction for each. Paraffine is much used instead of S. Safety matches have no P, and must be scratched on a surface of red P and Sb2S3, or on gla.s.s.

205. Red Phosphorus.-Two or three allotropic forms of P are known, the princ.i.p.al one being red. If heated between 230 degrees and 260 degrees, away from air, the yellow variety changes to red, which can be kept at all temperatures below 260 degrees.

Above that it changes back. Red P is not poisonous, ignites only at a high temperature, and is not phosph.o.r.escent, like the yellow. 206. Spontaneous Combustion of Phosphene, or Hydrogen Phosphide, PH3.

Experiment 114.--Put into a 20cc.flask 1 g. P and 50cc.saturated solution NaOH or KOH. Connect with the p.t. by a long d.t., as in Figure 44, the end of which must be kept under water. Pour 3 or 4cc.of ether into the flask, to drive out the air. It is necessary to exclude all air, as a dangerously explosive mixture is formed with it. Heat the mixture, and as the gas pa.s.ses over and into the air, it takes fire spontaneously, and rings of smoke successively rise. It will do no harm if, on taking away the lamp, the water is drawn back into the flask; but in that case the flask should be slightly lifted to prevent breakage by the sudden rush of water. On no account let the air be drawn over.

The experiment has no practical value, but is an interesting ill.u.s.tration of the spontaneous combustion of PH3 and of vortex rings. What are the products of the combustion? An admixture of another compound of P and H causes the combustion.

Chapter XL.

a.r.s.eNIC.