An Introduction to Chemical Science Part 2

Lead Pb 206.II, IV ... ... ... "

Lithium Li 7.I ... ...... "

Magnesium Mg 24.II ... ...... "

Manganese Mn 55.II, IV, VI ... ... ... "

Mercury Hg 200.I, II 100. Liquid Nickel Ni 59.II, IV ... ... ... Solid Nitrogen N 14.(I),III,V 14. Gas Oxygen O 16.II 16. "

Phosphorus P 31.(I),III, V 62. Solid Platinum Pt 197.(II), IV ... ... ... "

Pota.s.sium K 39.I ... ...... "

Silicon Si 28.IV ... ...... "

Silver Ag 108.I ... ...... "

Sodium Na 23.I ... ... ... "

Strontium Sr 87.II ... ... ... "

Sulphur S 32. II,IV,(VI) 32(96) "

Tin Sn 118. II, IV ... ... ... "

Zinc Zn65. II 32.5 "

If more than one atom of an element enters into the composition of a binary, a prefix is often used to denote the number. SO2 is called sulphur dioxide, to distinguish it from SO3, sulphur trioxide. Name these: CO2, SiO2, MnO2. The prefixes are: mono or proto, one; di or bi, two; tri or ter, three; tetra, four; pente, five; hex, six; etc. Dia.r.s.enic pentoxide is written, As2O5.

Symbolize these: carbon protoxide, diphosphorus pentoxide, diphosphorus trioxide, iron disulphide, iron protosulphide. Often only the prefix of the last name is used.

16. An Oxide is a Compound of Oxygen and Some Other Element, as HgO. What is a chloride? Define sulphide, phosphide, a.r.s.enide, carbide, bromide, iodide, fluoride.

In Experiment 6, where S and Fe united, the symbol of the product was FeS. Name it. How many parts by weight of each element? What is its molecular weight? To produce FeS a chemical union took place between each atom of the Fe and of the S. We may express this reaction, i.e. chemical action, by an equation:--

Iron + Sulphur = Iron Sulphide Or, using symbols Fe + S = FeS Using atomic weights, 56 32 = 88.

These equations are explained by saying that 56 parts by weight of iron unite chemically with 32 parts by weight of sulphur to produce 88 parts by weight of iron sulphide. This, then, indicates the proportion of each element which combines, and which should be taken for the experiment. If 56 g. of Fe be used, 32 g. of S should be taken. If we use more than 56 parts of Fe with 32 of S, will it all combine? If more than 32 of S with 56 of Fe? There is found to be a definite quant.i.ty of each element in every chemical compound. Symbols would have no meaning if this were not so.

Write and explain the equation for the experiment with copper and sulphur, using names, symbols, and weights, as above.

CHAPTER V.

MANIPULATION.

17. To Break Gla.s.s Tubing.

Experiment 8.--Lay the tubing on a flat surface, and draw a sharp three-cornered file two or three times at right angles across it where it is to be broken, till a scratch is made. Take the tube in the hands, having the two thumbs nearly opposite the scratch, and the fingers on the other side. Press outward quickly with the thumbs, and at the same time pull the hands strongly apart, and the tubing should break squarely at the scratch.

To break large tubing, or cut off bottles, lamp chimneys, etc., first make a scratch as before; then heat the handle of a file, or a blunt iron--in a blast-lamp flame by preference--till it is red-hot, and at once press it against the scratch till the gla.s.s begins to crack. The fracture can be led in any direction by keeping the iron just in front of it. Re-heat the iron as often as necessary.

18. To Make Ignition-Tubes.

Experiment 9.--Hold the gla.s.s tubing between the thumb and forefinger of each hand, resting it against the second finger.

Heat it in the upper flame, slowly at first, then strongly, but heat only a very small portion in length, and keep it in constant rotation with the right hand. Hold it steadily, and avoid twisting it as the gla.s.s softens. The yielding is detected by the yellow flame above the gla.s.s and by an uneven pressure on the hands. Pull it a little as it yields, then heat a part just at one side of the most softened portion. Rotate constantly without twisting, and soon it can be separated into two closed tubes. No thread should be attached; but if there be one, it can be broken off and the end welded. The bottom can be made more symmetrical by heating it red-hot, then blowing, gradually, into the open end, this being inserted in the mouth. The parts should be annealed by holding above the flame for a short time, to cool slowly.

For hard gla.s.s--Bohemian--or large tubes, the blast-lamp or blowpipe is needed. In the blast-lamp air is forced out with illuminating gas. This gives a high degree of heat. Bulbs can be made in the same way as ignition-tubes, and thistle-tubes are made by blowing out the end of a heated bulb, and rounding it with charcoal.

19. To Bend Gla.s.s Tubing.

Experiment 10.--Hold the tube in the upper flame. Rotate it so as to heat all parts equally, and let the flame spread over 3 or 4 cm. in length. When the gla.s.s begins to yield, without removing from the flame slowly bend it as desired. Avoid twisting, and be sure to have all parts in the same plane; also avoid bending too quickly, if you would have a well-rounded joint. Anneal each bend as made. Heated gla.s.s of any kind should never be brought in contact with a cool body. For making O, H, etc., a gla.s.s tube -- delivery-tube--50 cm. long should have three bends, as in Figure 6. The pupil should first experiment with short pieces of gla.s.s, 10 or 15 cm. long. An ordinary gas flame is the best for bending gla.s.s.

20. To Cut Gla.s.s.

Experiment 11.--Lay the gla.s.s plate on a flat surface, and draw a steel gla.s.s-cutter--revolving wheel--over it, holding this against a ruler for a guide, and pressing down hard enough to scratch the gla.s.s. Then break it by holding between the thumb and fingers, having the thumbs on the side opposite to the scratch, and pressing them outward while bending the ends of the gla.s.s inward. The break will follow the scratch.

Holes can be bored through gla.s.s and bottles with a broken end of a round file kept wet with a solution of camphor in oil of turpentine.

21. To Perforate Corks.

Experiment 12.--First make a small hole in the cork with the pointed handle of a round--rat-tail--file. Have the hole perpendicular to the surface of the cork. This can be done by holding the cork in the left hand and pressing against the larger surface, or upper part, of the cork, with the file in the right hand. Only a mere opening is made in this way, which must be enlarged by the other end of the file. A second or third file of larger size may be employed, according to the size of the hole to be made, which must be a little smaller than the tube it is to receive, and perfectly round.

CHAPTER VI.

OXYGEN.

22. To Obtain Oxygen.

Experiment 13.--Take 5 g. of crystals of pota.s.sium chlorate (KClO3) and, without pulverizing, mix with the same weight of pure powdered manganese dioxide (MnO2). Put the mixture into a t.t., and insert a d.t.--delivery-tube--having the cork fit tightly. Hang it on a r.s.--ring-stand,-- as in Figure 7, having the other end of the d.t.

(Fig 7.)

under the shelf, in a pneumatic trough, filled with water just above the shelf. Fill three or more receivers--wide-mouthed bottles--with water, cover the mouth of each with a gla.s.s plate, invert it with its mouth under water, and put it on the shelf of the trough, removing the plate. No air should be in the bottles.

Have the end of the d.t. so that the gas will rise through the orifice. Hold a lighted lamp in the hand, and bring the flame against the mixture in the t.t. Keep

the lamp slightly in motion, with the hand, so as not to break the t.t. by over-heating in one place. Heat the mixture strongly, if necessary. The upper part of the t.t. is filled with air: allow this to escape for a few seconds; then move a receiver over the orifice, and fill it with gas. As soon as the lamp is taken away, remove the d.t. from the water. The gas contracts, on cooling, and if not removed, water will be drawn over, and the t.t. will be broken. Let the t.t. hang on the r.s. till cool.

With gla.s.s plates take out the receivers, leaving them covered, mouth upward (Fig. 8), with little or no water inside. When cool, the t.t. may be cleaned with water, by covering its mouth with the thumb or hand, and shaking it vigorously.

What elements, and how many, in KClO3? In Mn02? It is evident that each of these compounds contains O. Why, then, could we not have taken either separately, instead of mixing the two? This could have been done at a sufficiently high temperature. Mu02 requires a much higher temperature for dissociation, i.e.

separation into its elements, than KClO3, while a mixture of the two causes O to come off from KClO3 at a lower temperature than if alone. It is not known that Mn02 suffers any change.

Each molecule of pota.s.sium chlorate undergoes the following change:--

Pota.s.sium Chlorate = Pota.s.sium Chloride + Oxygen KClO3 =KCl + 3 O.

Is this a.n.a.lysis or synthesis? Complete the equation, by using weights, and explain it. Notice whether the right- hand member of the equation has the same number of atoms as the left. Has anything been lost or gained? What element has heat separated?

Does the experiment show whether O is very soluble in water? How many grams of O are obtainable from 122.58 g. KCIO3? PROPERTIES.

23. Combustion of Carbon.

OXYGEN Experiment 14.--Examine the gas in one of the receivers.

Put a lighted splinter into the receiver, sliding along the gla.s.s cover. Remove it, blow it out, and put in again while glowing. Is it re-kindled? Repeat till it will no longer burn. Is the gas a supporter of combustion? How did the combustion compare with that in air? Is it probable that air is pure O? Why did the flame at last go out? Has the O been destroyed, or chemically united with something else?

Wood is in part C. CO2 is formed by the combustion; name it. The equation is C + 2O = CO2. Affix the names and weights. Is CO2 a supporter of combustion? Note that when C is burned with plenty of O, CO2 is always formed, and that no matter how great the conflagration, the union is atom by atom. Combustion, as here shown, is only a rapid union of O with some other substance, as C or H.

24. Combustion of Sulphur.

Experiment 15.--Hollow out one end of a piece of electric-light pencil, or of crayon, 3 cm. long, and attach it to a Cu wire (Fig. 9). Put into this a piece of S as large as a pea, ignite it by holding in the flame, and then hold it in a receiver of O.