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Les diagrammes suivants illustrent la mdthode. 1 2 3 1 2 3 4 5 6 MICROCOPY RESOLUTION TEST CHART (ANSI and ISO TEST CHART No. ?.) 1.0 I.I 1.25 afi|2.8 ill 2.5 |M l"^ IIIIIBBB 1^1^ 2.2 143 ^^ «S 14.0 2.0 l£ 1* u Ulftu 1.8 1.4 1.6 ^1 A >^PPLIED IM/IGE Inc 1653 East Main Street Rochester, New York 14609 (716) 482 -0300 -Phone (716) 283- 5989 -fax USA **-?■'• ~m^^ ?' Il; j EXPERIMENTAL CHEMISTRY. J. V • S- «a9c & (Bo.e €bnrational §ttit0. EXPERIMENTAL CHEMISTRY FOR JUNIOR STUDENTS BT J. EMEBSON BEYNCLDS, M.D, F.R.S^ VICB-PRBSIDBNT CUmiCAL SOCIETY OP WXdON PaomsoB OF camsTav. wnivemitt or dublut. ce:4P. /. TO xvL limed to cover work in IL Form of Sigh School Course* TORONTO: ^' J. GAGE & COMPAI^Y, 1886. If Entered according: to Act of Parliament in the oflSce of the Minister of Agriculture, iu the year of our Lord, 1886, by W. J. Qaqi St Co. PREFACE TO THE SECOND EDITION, The necessity for the issue of a Second Edition of ' Parts I. and II. has given me the opportunity to make a few verbal corrections, and some addition, required by our advancing knowledge. Otherwise the work retains the form in which I am glad to know ,t has proved acceptable to teachers and Students. November, 1882, J. E. R \ PREFACE TO THE FIRST EDITION. This work ,s identical in plan with my Six Ledum on Expenmental Chemistry, but different in style and much extended in ^ge, so as to include the amount of knowledge of fact and principle usually expected from junior Arts, Medical and Pharma- ceufcal StuJents, as well as from the higher classes in Intermediate Schools. The system pursued in this book is designed to pelts r' """^'^ ^ ^'' "" --ecffe ! h.mT r ^""'-'i"^'"'^ ■•" -m-and to assist 1 ^ wterpreution of his results, and in devi- drawn from them. Thus while acquiring a tolerably amomuTf ■°''^'^^ ''^ ^'"''^ '-eifes a cenat rZ. / '"^'" "'^ P"^^'y 'experimental method of mveshgating Nature. If this trainin.. be mea"ns' of' ^'""^V^/'^^-'-y "-t prove a valu^ab^ means of mental education. How far the particular P^ pursued in the following pages is liketyto con tribute to such a result, I must leave «th<..= L .•,.^-. . • •• VI 11 Preface, I ! but a reviewer of my Lectures was so good as to say : — * In these Lectures the author departs widely from the usual routine of elementary treatises. . . . We believe that he. is right in the plan he has adopted, and that instruction of this nature would greatly facilitate the acquisition of clear and distinct ideas of the leading facts and laws of Chemistrjr.' (Chemical News, vol. xxix. page 227.) This work is divided into four parts, each one being, as far as practicable, complete in itself. Part I. is introductory, and deals with first principles, and with the chemistry of the typical elements, hydro- gen and oxygan, and their compounds; Part II., with the rest of the non-metals ; Part III., with the metals ; and Part IV., with organic chemistry. The experiments described are, Whenever possible, those easily performed ; in some cases, however, methods are necessarily detailed which the student may not have either the skill or the means to cany out, but he should endeavour to see these operations carefully conducted. It is assumed throughout that the reader can obtain some practical instruction in glass working and the construction of apparatus. It is only necessary to add that the complete work will contain the solutions of all the problems in my Lecture Niote Book, J. E, R. CHERflCAL Laboratory, Trinity College, Dublin i Xvovember, 1880. I J CONTENTS. -•o*- CHAPTER r. Prenminary experiments-Difference between physical '^"" change Che .^'f^^-^^^- ^f effecting TeS Change-Chemical attraction -Mechanical mixtures and chemical compounds . . «iixtures CHAPTER II Experiments with Silver Nitrate and Magnesium-The :Ste";-:r^ot^-^^^^^^^^ CHAPTER III. ^'kS'^w^^ ""^^^^""^ -^ Hydrogen-Equiva- lents-^Chief characters of Jlydrogen gas . . . 12 21 CHAPTER IV. Experiments with Hydrogen and Oxygen gascs-Con^n • tion of water-Electrolvsis rhI5 ^^'^^^'"'^P^si- _ ^*c^ifOl> sis — Chief Drnnpwioc ^c r\ gen-uombustion of candle in air ^"-"-'"^" "' '"^^■ 30 X Contents, CHAPTER V. Experiments with Hydrogen and Oxysen continued- Specific gravities of gases— Effects of changes of tern- perature and pressure on gases— Avogadro's law — Dual character of elementary molecule — Gay-Lussac's laws — Atoms — Atomic weights of gaseous elements determined — Atomic Theory PAGB 44 CHAPTER VI. Experiments with Silver, Copper, and Magnesium— Capa- city for heat— Specific heat— Dulong and Pedt's law- Atomic heat ••••.... 56 CHAPTER VII. Table of Atomic weights— Distinction of metals and non- metals — Electro-cht nical changes — Chemical for- mulae, how deduced — Empirical and rational formulse —Atomicity or quantivalence — Equations • • • 63 CHAPTER VIII. Experiments with Acids, Alkalies, nnd Salts— Bases — Classes of acids — Radicles of salts — Simple and com- pound radicles .••••••• 80 CHAPTER IX. Farther experiments with Hydrogen — Preparation — I ro- perties- /lame tests — Hydrogen as a reducing agent — i^er riduit •••••••• 86 Cofttents. XI CHAPTER X. Experimental determination of the volume occupied by one centigram of Hydrogen gas -Correction of gaseous volumes— The VoL-Calculations— Absolute tempera- ture— Law of Charles .... PACK 95 CHAPTER XL Further experiments with Oxygen gas- Preparation -Pro- perties— Oxides— Acid producing and basic Oxides or Anhydrides-Indifferent Oxides -Oxyhydrogen flame —Ozone— Preparation — Characters— AUotropism— Isomerism • , . . io8 CHAPTER XIL Experiments with water-Purification of water bydistilla- tidn-Latent heat of steam-Effects of cold on water —Maximum density of water- Latent heat of water- Solvent action on solids, liquids and gases-Water supply-Hardness of water-Mineral springs-S°a water-Peroxide of Hydrogen -Preparation-Proper- fA7P'?'^'°" °^~'^'^'' ^^^ ^/^^^-Hydroxyl-Law of Multiple Proportions . . / ;' 'iw 125 APPENDIX. Modes of chemical change-Laws of Berthollet 143 PART IL CHAPTER XIII. Experiments with nitrogen — Atmospheric air — Its an- alysis — Composition by volume and weight — A mechanical mixturje— Effects of animals and plants upon— Changes in, caused by burning candles, gas, or coal— Causes of uniform composition — Graham's law of diffusion of gases — Impurities in air, how detected • rAGB HS CHAPTER XIV. Experiments with compounds of nitrogen— Nitric acid — Its preparation, properties, and tests — Nitre— Gun- powder —Nitrogen peroxide — Preparation and pro- perties—Nitrogen sesquioxide and nitrous acid — Preparation and properties —Nitric oxide— Preparation and characters— Nitrogen monoxide — Laughing gas — Preparation and properties— Physiological effects — Ammonia — Prep-^'-ation and properties — Ammonium hydrate — Salts a., -erivatives . • • • . 167 CHAPTER XV. Experimsnts with hydrochloric acid — i reparation and characters— Analysis oi—Aqua regiu—QYiXoxvat — Pre- paration and properties — Synthesis of hydrochloric Contents. xin acid-Chlorine water-Bleaching action of chlorine '''°" ~?ertr'r ^'"^'"^ li-e-Potassiu.n c rests for chlorates-Potassium perchlorate- Pr. paration and tests^Series of chlorine'acids " ,^^ CHAPTER XVI. Experi„,ents with iodine- Separation of iodine- Manu facture from kelp-Its characters -Hydriodl acid Preparation and properties - Iodides - T sU for odiT acid and anhydride . -resistor iodic 232. !: il' INTRODUCTION 10 EXPERIMENTAL CHEMISTRY. PART I. CHAPTER I. PRELIMINARY EXPERIMENTS. ChemVry has for its object the discovery of the laws which govern the composition of all material things and the action of one kind of matter upon another in all cases mvolving change in composition. This knowledge is acquired by experiment, accurate obser- vation of the phenomena presented during an experi- ment, and careful reasoning upon the result. The lollowing pages contain numerous illustrations of the application of this experimental method of inquiry in the study of chemistry. ^ Experiment l.-Let us commence our course with a simple experiment. Hold by means of a small pincers or tongs a piece ot thin wire of the metal njntinM • «• \tt.i\. xitmiv \jk (( B li' Fig. I. 2 Introduction to Experimental Chemistry. spirit lamp, as in fig. i, or in that of a Bunsen gas< burner. Observe that the wire soon becomes red-hot and glows as long as it is held in the flame ; but, when removed and allowed to cool, it resumes its original appearance, and if weighed before and after the experiment, no difference is observed. Therefore the change from cold to red-hot platinum is but a temporary one, the metal remaining un- changed in form and sub- stance. Experiment 2. — Now make an identical experi- ment with a piece of mag- nesium wire or ribbon. Ob- serve that the metal # soon begins to burn and emits much light, even when removed from the source of heat. It also gives out white fumes .and leaves a white substance behind which, though retaining some of the form of the original wire or ribbon, can be easily powdered when cold, and is seen to be utterly unlike the metal which produced it. Moreover, the white substance is found to iveigh more than the magnesium originally taken. In this case, a change has taken place on heating, and it is per ma?ient. The temporary alteration of the platinum wire is not accompanied by any difference in composition, aftd IS spoken of as a pJiysial change ; that of the magnesium, as a chemical ^nange, and the action, as Prehminary Experiments. ^//«W«^//i,„, because a material alteration in com- position has taken place, as shown l,y the gain in weight; and a new body has been produced, evidently possessing characters which serve to distinguish it completely from the metal magnesium, and, indeed. Irom all other known substances. All observed changes in matter can be placed in one or othe' of the above classes, but it is with chemical change and chemical acti.m that we are principally concerned. .h /?u"'^ experiment with magnesium it was sho«n that the application of heat served to bring about chemica change, but we shall find as we proceed that chemical action can be determined by other agents— namely, \>j Mechanical Mce, Light, £/eetricit_y, and a peculiar force called Chemcat attraction, or 'affinity ' which acts on ly at excessively minute distances. Expenment a-Place two or three small crystals (not more) of the salt called potassium chlorate in a stone-ware mortar, powder the substance and add half as much sulphur, also in powder. Mix gently and then give the mixture a sharp blow with the peslle. A report follows, indicating that chemical action has jaken place, in this instance determined by mechamcat Experiment l-Again, dissolve a few crystals of s^ver nitrate in half a test tube of water and paint the liquid over some ordinary writing paper in a darkened room. Then divide the paper into two parts : preserve one in a .irawer, and immediately ex- pose the other to full sunlight or diffused daylight. .^,._„ ^^^^, ,,,,, s.^ortiy aiscoiour and assume ^2 4 lutrodiiciion to Experimental Chemistry, a cliocolato ])rown tint, or even a bronzy black colour --the result of chemical change brou^Mit iibout by the ac;ency of j//////i^///, lor the paper preserved from light does not suffer any api)areni. change in the same time. The art of photography depends upon similar changes brought ab(yijt h\ light. Experiment *). ^ rrw take the little galvanic cell described isl pugc 6 ^ ee fig. 2, a; and attach a small slip of sheet platinum to the end of the wire from Z;/, F,o. 9. and connect a slip of copper with C«; dip bo'h in a strong solution of copper sulphate contained in B. Remove the slips after a few minutes and observe that a reddish deposit has formed on the slip connected by wire with tlie zinc plate Zn, of the cell. If the action be continued for some hours, a considerable layer of red tfieta ic copper is obtained on the slip as the result of chemical change determined by electricity in the solution of copper sulphate. The art of electro- typi)-ig de):)ends on this power exerted by electricity. Experiment 6.— Finally, if we add to a small globule of the liquid metal mercury, or quick- silver, contained in a mortar, a few fragments of iodine, and mix them together with the pestle, the metal and iodine gi .dually disappear and a powder is formed. If the proportion of iodine used ht-. larfyp • * " CJ-7 Zn. ■Vv Preliminary Expcrinients. 5 the resulting powder is red in colour ; if little iodine be enij)loyed, the colour is a dull green. Here the two bodies named produce a new substance when brought near to each other, and this change is alone due to the chemical attraction of one body for the other. The exercise of this attractive forcp is facilitated bv tie liquidity of the metal, and the c.ange is hastened ^y the addition of a fc v drops of spirit of wine, which dis- solves some of the iodine and thus enables the par- ticles of the latter to move more freely. 1 nis chemical attraction differs from other forces in the important particular that it only acts at excessively minute dis- tances. This may be further illustrated in the following way : — ® Experiraent 7.— Mix in any dry glass vessel, such as a benker or a tumbler, a tea-.spoonful of 'bread soda,' or sodium bicarbonate, and the same quantity 01 hnely powdered tartaric acid.' However closely the solid particles are brought together by stirring or rubbing, no action takes place, provided the mixture is dry. Add now some water to the powder, and violent effervescence ensues, indicative of chemical action. Water added to die acid or the soda separately does not cause any effervescence and merely dissolves each body, the violent action observed on addition of water to the mixed powders must therefore have been due to the mutual attraction of the two solids leading to chemical action ; but that action could only take place v,rhen, by solution in water, the particles of each body were endued with greater mobility than in the 'Or the contents of the two papers sold as powder • may be mixed instead of the above. ■ Seidlitz ;N 6 Introduction to Experimental Chemistry, solid state, and were thus enabled to get within the sphere of each other's attraction. We thus learn that chemical action is greatly facili- tated by the solution or liquidity of one or all of the bodies engaged. We shall find later on, Experiment 53, that a fine state of division of a solid tends to a similar result. In some of the experiments already cited, the student will have observed the evolution of heat and light during chemical action. Thus, when the magnesium wire burned in air, much heat and an intense light were proauced. But electricity is also freely developed in certain chemical actions, and in fact the source of electricity in an ordinary galvanic cell is chemical action. Experiment 8.— The simplest form of galvanic cell may be easily made thus : — Take a glass vessel, such as a tumbler (a, fig. 3), and fill it about two-thirds with water, to which one-tenth part of A oil of vitriol (sulphuric y acid) has been added. Next cut a slip of clean sheet zinc, Zn^ a little longer than the glass ; its width may be equal to half the diameter of tlie vessel. Make a hole through one end of the slip, pass a piece of bright copper wire through it and fasten securelv hv twisfinor th^ wirp Prpnnr** -" J -• ^o — _ .^^.-^^ Fig. 3. Preliminary Experiments. a similar slip of clean copper, Cu, with its wire, and , he apparatus ,s complete. M'hen the two ^2 are connected, as shown, and the plates immer 7d m the hquul, wuhout touching one another, ,he znc a^one dissolves m the acid, the copper not being cTe! n^ically acted on, while a current of electrici.yVows ^ong the w,re, and may be easily detected by bringin; m of a toy compass. The needle tends to se ction be"f ""f r "" ''"'' ""' -^ »•- 'hemi ' action be stopped, by taking the plates out of the 1-qu.d, and the connecting wire be brought over the -leedle as before, no motion takes place! as°he JJe no onger conveys electricity. The compass need e therefore, serves as a detecter of electric cu^ents' circulatmg through copper wires. ' as Z"\T^: T^ "' '""" =™P'« g-^'vanic cells «ay that the zinc plate of one cell is coupled with the copper plate of the next, a ^afyanu MttfJ of Z simplest kind is obtained; but for details conceit n' Again turning to the experiment with burning magnesium, we rind that it is capable of afford"" uf another Item of information. We pointed out fha the white substance produced when the met^I bums ^Ue to Itself some' oth/r ITdy thS cTi^d'r ^^ derived from the air in wl^vi, .u , .^ ^^ The chemical action th^indu'c^aVh^.-ri 8 Introduction to Experimental Cheynistry. \\\ • ill I combination^ or the union of unlike kinds of matter. Experiment 9. — The same agent — heat— is capable of effecting the reverse change. If we take a small quantity of the well-known white, crystalline and trans- parent substance called silver nitrate^ and heat it gently in a small dry test tube, the body is seen to melt to a yellowish liquid, and, on continuing the heat, bubbles rise through the liquid and ruddy fumes pour out of the mouth of the tube. If we continue to heat until all action is over, and brcalc the tube when cold, the residue is seen to consist of pure white metallic silver. In this case the chemical action brought about by heat resulted in decomposition^ or resolution, of the silver nitrate into the metal silvt ;, and some other kind of matter seen to be driven off as coloured vapour or gas. Since chemical action may result either in com- bifiation or decomposition, it follows ihat chemical substances may be conveniently divided into two great groups: first, those forms of matter which do not suffer decomposition by the exercise of any force at our command; and, secondly, those bodies capable of resolution into some two or more members of the first group. The forms of matter included in the first group are called elements, and those in the second, compowids. The decomposition of a compound into its elements is spoken of as a process of analysis, and the production of a chemical compound from its elements is termed synthesis. The researches of chemists up to the present time Preliminary Experiments, names of the most important of these are given in the table, which will be found at page 64. But it is necessary to guard carcrully against the idea that the ' elements ' so-called are certainly simple bodies- we cannot at present prove them to be compounds -that IS ail we can say. All known chemical compounds are the result of union bet^'een some two or more elements; but the important question now arises whether this union is m the nature of a mere mixture, or of sometlung much more intimate. ^ Experiment lO.-Make a mixture of iron filings with about two-thirds of their weight of sulphur (the flour of sulphur ' of the druggists). A greemsh-grey rowdei results, but distinct particles of iron and of sulphui can be easily recognised in it, not only with ' the aid of a magnifying glass, but also by stirring some of the powder into a considerable quantitv of water, when the heavy particles of iron fall quickly to the bottom of the vessel, while the lighter sulphur more slowly subsides and collects as a distinct layer. Or the iron can be still more easily separated from the sulphur by means of a small horse-shoe magnet If the latter be passed through some of the powder' the particles of iron are attracted by the poles of the magnet, and attach themselves so firmly that the particles of sulphur-which are not attracted but mechanically adherent-may be blown away, leaving the metallic iron behind. ^ The constituents of this mixture can therefore be separated by mechanical means. Moreover ,>. r..^_ perties partake of those of iron and sulphur. ' ^ '" \ I 10 Introduction to Experimental Chemistry, iii ' Experiment ll.-Nowheat very strongly a portion of the original mixture in a tube of Bohemian or hard glass ; note that the mixture becomes pasty and then gloivs for a short time. Cool and remove the result- ing dark substance from the tube. When examined with a magnifying glass, no particles of iron or sul- phur can be detected, if the mixture was sufficiently heated ; moreover, it is noc attracted, or but slightly by the magnet, and therefore does not any longer contain/;r^ metallic iron. The iron and sulphur are no longer separable by mechanical means, and the properties of the body resulting from the fusion do not partake of those of free iron or free sulphur. In fact, the glowing observed on heating the mixture was due to chemical combination between the two ^ elements, and the product of that union-a body termed iron sulphide— possesses a definite group of characters which not only serve to distinguish it from the free elements iron and sulphur, or a mixture of them, but from all other known bodies. Experiment 12.— Mix twelve parts by weight of finely-powdered charcoal (a form of the element carbon) with sixty-four par^s of sulphur, also in a fine state of division. The mixture is an opaque, almost in- odorous, dull, yellowish powder that may be exposed to the air for an indefinite time without loss of weight or other alteration. Now obtain a specimen of the liquid termed ' carbon bisulphide,' which is a chemical com- pound of carbon and sulphur in exactly the same propor- • A glass which fuses with great difficulty, and hence may be suitably used in operations requiring a temperature so high as to easily melt ordinary glass tubing. Preliminary Experiments. II tions as the mixture of the two elements already made. I his liquid IS perfectly transparent and colourless, and has a most disagreeable smell, while it is so volatile that a few drc . let fall upon a plate disappear m a very short time. We thus learn still more clearly that a w;de difference in properties may exist be- tween a definite chemical compound and a mere mechanical mixture of its constituents. The special properties of the elements can be easily recognised in the mixture, but not in the definite chemical com- pound, unless we decompose the lattei and sever the union of Its components. .n J''"^^/'^"-"^ ""= "y"*^^''^ °f ^ "ew chemical compound from its elements, the philosophic chemist performs an operation which approaches more nearly than any other to a creative act. ' For the preparation of this body see Part Tr „,™ It must be handled with c»re. » it is Zr^lZJ^^^ "^^ 12 Introduction to Experimental Chemistry, ! 11 III CHAPTER 11. . EXPERIMENTS WITH SILVER NITRATE AND MAGNESIUM. A KNOWLEDGE of the chief Laws of Chemistry can be more simply and naturally attained by the study of chemical compounds in the first instance than by the detailed examination of simple bodies or elements, 'I Fig. 4. BininmiBiiuoiniiiinininiiminiinmBiinimnnimMiiiiufliifiiffiiniiufflirmiimniir^ and the most easily managed compound with which the beginner can experiment is the silver nitrate. It has been already proved by Experiment 9 that Silver Ni crate is resolved into metallic silver and coloured gas, when otrongly heated in a glass tube. Silver Nitrate ami Magnesium. 13 Let us now examine this case of decomposition with the aid of a balance or delicate scales, one of the best forms of which valuable instrument is repre- sented in fig. 4.1 Experiment 13.— Break up in a perfectly clean mortar some clear and pure crystals of silver nitrate ; =» then press the powder between folds of white blotting- paper, in Older to remove any trace of moisture. Next take a stout test tube of /lani glass, measuring 12 centimeters long and 12 millimeters in diameter ; take care that it is clean and dry; then place it oti' one pan of the balance and counterpoise by placing a small pill box on the other pan, and adding grains of shot or pieces of tinfoil until equilibrium is estai)- lished. Next place in the pan, along with the shot or foil, weights representing 170 centigrams (=17 grams), and now pour into the test tube on the other pan the powdered siher nitrate until the weights are balanced. The test tube then contains 170 centigrams of the silver compound; Now support the tube in a slanting position in the wooden clip shown in fig. I, and gently heat the bottom of the tube with a spirit lamp, or a Bunsen gas-burner of the icjtm shown in fig. 5. The silver nitrate melts quietly to a » ' Much cheaper balances than that figured can now be ob- tained, which will indicate less than i milligram when loaded with 25 grams. When the student cannot obtain the use of a balance, he should perform the experiments as described without weighing the materials or products. * The crystals are alone certain to give satisfactory results, as the ' Lunar Caustic,* sold in sticks, is sometimes adulterated and often ia.pure. i m M' ' 14 Introduction to Experimental Chemistry. clear liquid. If the temperature be now increased by bringing the flame closer, sHght effervescence is ob- served— due to the escape of bubbles of gas. Soon reddish brown fumes appear, and these pass away mto the atmosphere, while the residue in the tube loses much of its transparency owing to evident dep<)sition of solid matter. The heating must be continued in such a way as to prevent any loss by spirting solid particles out of the tube, , and until the ruddy fumes are c<:>mpletely dissipated and pure silver alone remains; finally, let the flame play on the sides of tiie tube so as to ensure the decomposition of any particles of the nitrate that may have yet escaped the full action of the heat.» When cold, replace the tube oii the pan of the balance and adjust the weights in the other pan so as to restore equilibrium ; the weights required represent the pure silver thus obtained from 170 centigrams of silver nitrate. Two separate experiments made in the way de- scribed afforded the following results : • Weight of metallic silver obtained from 170 centi- grams of pure silver nitrate. I St experiment 2nd 108*22 c.grs. 108-40 c. grs. The second experiment was made by a young student but little skilled in chemical manipulation. ' The ultimate decomposition may be thus represented : AgNO.-Ag-tNOs + O. f « Silver Nitrate and Magnesium. j t Now, it is found that the more carefully the experi- ment IS .na.le, the nearer does the result approach to io8; we may therefore say that 170 c. grs. of pure s. vtr nurate contain 108 c. grs. of the n.etallic element silver. W hatever may be the source of the .silver nitrate taken, pMd it be pure, and whatever the quantity employed m the experiment, provided the decompo- smon be carefully conducte"'"''<'" -1^0. between the silver defin t. ■""" ^^^^ °"g'"'"'y "^^^^ place in aehnite proportions. r = m Again, the change consequent unon the action of and of combmation, for while the silver n,>r„. „J V • »«vtvu rros ca 20 Introduction to Experimental Chemistry. decomposed And. its silver separated just as completely as by heating the body alone, the 12 c. grs. of magnesium W/;/../with the 62 c. grs. of Miitrate,' and in fact the solution contained at the end of the experiment magnesmm nitrate weighing 74 c. grs. (12 + 62 c. grs.), and that weight of the new compound thus formed could actually be separated from the litiuid. w I m i :! I 'i ■\ ■ i j: f \ 1 i 1 M % i 21 CHAPTER III. EXPERIMENTS WITH MAGNESIUM AND HYDROGEN. Experiment 16.-Half fill a test-tube with water to which two or three drops of oil of vitriol (sulphuric acid have been added. Now plunge into Ihe liquid a shp of magnesium ribbon and note the result' Brisk effervescence takes place, and the metal .peedily tZlZ'- ^'^^t---"« ■»-' be due 'to Z of he tube the gas takes fire and burns with slight explosions, but emits very little light while it burns silver fror "fSnesium, which displaces metallic Silver trom silver nitrate causes the evolution of an in-' flammable gas from acidulated water. The next step is to collect some of this gas and examine its properties. Experiment 17.^Take a glass tube closed at one end and about 20 centimeters long, and 2 centimeters in diameter, /, fig. 6; fill it com- pletely with water acidulated withyjjth of its bulk of sul- phuric acid; thennlacen mW^^r^ — au^.^j ._i a ground glass plate, over the mouth of the tube and Fm. 6. 22 hitrodttcHon to Experimental Chemistry, invert it. Next bring the month under the surface of a larger quantity of the acidulated water contained in the wideglass beaker,^, and support by means of the stands. So long as the mouth of the tube is under the surface of the liquid no air can enter, as the water is retained in the tube by atmospheric pressure. Now take a piece of magnesium ribbon about 20 centi- meters long, crumple it up and rapidly pass it through the water and under the mouth of the inverted tube. It will ascend into the tube and cause effervescence as before, but the gas cannot escape into the air and therefore collects in the upper part of the tube, while It displaces a corresponding volume of water. As the magnesium dissolves add fresh pieces until the tube is filled with the gas. Pass the plate under the water and close the mouth of the tube, then detach the latter from the stand, remove the tube, still closed with the plate, from the water, and examine the contents. a. Note that the gas is free from colour. b. Turn the mouth of the tube up quickly and apply it to the nose, No peculiar odour is perceived. c. Refill 1 the tube with gas as before, and apply a Fig. 6 b. ' Instead of refilling the large tube, the charge of gas collected in it in the first instance may be transferred to three small test tubes, if the latter are filled with water in a large dish or trough, inverted and held with the mouth of each under the surface of the liquid. 1 he large tube of gas is carried lo the wat«»r- nn/l fKo i^^.,>u 1 1.. . - - .-# ii._ «_i„, „„^ „,^ Mivuwi wiwu^iii unaer one oi the Mag7icsium and Hydrogen. S3 flame to the mouth. The gas takes fire and burns witli a pale l,lue flame. c.fL ff '"f " "v "'' '"^" with gas, turn the mouth of the tube up-.c.ards and remove the thumb. After a few seconds brmg a flame to the ,ou,h of the tube No combustible gas is found in the tube. We are therefore, warranted in slating that the g.as produced when metallic n.agnesium acts^on a idu! lated water ,s colourless and inodorous. We may further assert that it cannot be soluble in water to any extent as we are able to collect it easily over hat quite nsoluble m water. It is combustible and is much hghter than atmospheric air, as evidenced by he rapidity with which it escapes on holding the tube wuh Its mouth directed upwards. The gas possessing these properties chemists call RvbrogS and regard it as an elementary body. Although hydrogen is an extremely light bodv- m fact the lightest ku<,w„ form of matter- t admits of bemg weighe, „ Silver nitrate. The numbers so obtained are called equivahntSy because they represent weights which are of equal value in chemical changes. In all such changes hitherto examined, hydrogen has never been found to directly displace or combine with less than its own weight of any other element or compound, or indeed with less than three times its own weight of any other form of matte hence it is properly taken as tlie unit of a scale of equivalents, which really includes all the simple and compound bodies known. On this scale, magnesium, silver, and the compound silver nitrate occupy the positions assigned to them above. A familiar illustration will probably render the meaning of the term 'equivalent' clear. A single brilliant diamond of purest water, weighing but one grain, has approximately the same purchasing power as the weight of Gold represented by . '. 3 sovereigns. Silver „ „ . . 60 shillings. Bronze (an alloy of tin and copjier), by 720 pence. A diamond of a certain quality will purchase more iv.3 \jv!:i.i. wci^lit ^" of any uthcr substance s the Magnesitim and Hydrogen. 27 economic value oidi unit weight of diamond in exchange is therefore greater than that of any other material found in commerce. Similarly the chemical value of a unit weight of hydrogen in exchange is gieater than that of any other element known to chemists. As 170 c. grs. of silver nitrate are equivalent to i c gr. of hydrogen, the student will now understand our reason for selecting the weight of the silver compound that we operated upon in the first quantitative experi- ment. Experiment 19. — The mo«it convenient method for . the preparation of considerable quantities of hydrogen Fig. 8. gas for experiment is the following. Take a glass bottle of the form shown in fig. 8, place in it some clippings of sheet zinc and sufficient waterlo occupy about one-third of the bottle Replace the cork and pour some oil of vitriol — about a teaspoonful— down the thistle funnel. Chemical action quickly commences and hydrogen gas is freely evolved ; for zinc, like magnesium, easily dis- « 28 Introduction to Experimental Chemistry, places hydrogen from acidulated water— i centi- gram of the gas being set free by 32-5 c. grs. or one equivalent taf pure zinc. Tne gas is conducted by means of the glass delivery tube under the water in the ' pneumatic trough,' and it is there collected in glass jars or bottles previously filled with water and inverted, keeping the mouths under the liquid in the trough. A small shelf supports the jars over the delivery tube. It is advisable to allow the gas to bubble through the water for some time before collect- ing it in jars, or uniil the air is judged to be expelled from the gas bottle and its place taken by hydrogen, as the latter forms an explosive mixture with atmo-' spheric air. a. Remove a jar full of hydrogen from the water, keepmg its mouth downwards. Take a piece of Fig, 9. Fig. io. mi lighted taper attached to a wire and pass it rapidly up into the jar, as shown in f^g. 9. The gas takes fire at the month c\^ fJio fnK^ „.^^ 1 ^1 ' "* ^"'- ■'"'-■^ «ii^ uuiiib there Willi a paie Magnesium and Hydrogen. 29 blue flame, but ihe taper is extinguished ; on brinmntj It down to the moutli of the tube again, it can be re! kindled there. Therefore hydrogen, tliough a com- bustible gas, does not support the combustwfi of a taper which burns readily in air. b. Take a dry glass jar, hold it with its mouth downwards and V^ring under it a jar full of hydrogen carried from the trough with its mouth downwards! Now invert the jar of hydrogen, bringing its mouth under that of the dry jar, as shown in fig. 10. After ten or fifteen seconds remove the lower jar and bring the lighted taper under the upper one :^a slight explosion occurs, and fl^me is observed, indicative of the pr^^- sence of hydrogen ; therefore the latter body is so much lighter than air that it can be poured up through the latter, and will nccumulate in the upper part of any vessel previously fuli of air. c. The same point can be elegantly demonstrated by removmg the gas delivery tube from the water drying u, and introducing the end into the neck of a small collodion balloon. If any zinc remains undis^ solved in the generating flask, a few drops of fresh acid added through the funnel will hasten the evolution of gas, and the latter passing into the ballon will expand It. When fully distended, detach the balloon from the tube and set it free. It will ascend rapidly through the air of the room until arrested by the ceiling, and will remain there untii much of the gas escapes and the residual hydrogen is no longer sufficient to buoy up the balloon. The latter then falls and may be re- served for another experiment i 3© Introauction to Experimental Chemistry. Fig. it. CHAPTER IV EXPERIMENTS WITH HYDROGEN AND OXYGEN GASES. Experiment 20.— As we have already proved that hydrogen gas bums in air, we may evidently .construct a small apparatus which can afford us a stream of the gas for combustion at a jet. 'i'he most convenient form is that rcpr^ented in fig. ii. The gas delivery tube of fig. 8 is replaced by a short piece of straight tube, which passes through the cork of the generating bottle and through the cork of the wide tube, /, which latter is filled with fragments of calcium chloride, a powerful absorbent of moisture. Through the second cork of / there passes a small glass tube, drawn out so as to form a rather fine jet. The flask contains strips of zinc, and water, as before, and on pouring oil of vitriol down the funnel tube, hydrogen is evolved. Let the stream of gas issue freely from the jet for some time before a light is applied,^ else an explosion will occur; then kindle the gas. ' It is well to cover the jet with an inverted test tube, and to remove the latter, mouth downwards, when it is desired to test the gas, and then to apply a flame to the test tube. If Hydrogen and Oxygen Gases. 3 1 a. Note that the hydrogen flame is of a pale bhnsh colour, and emits very little light ; but it is intensely hot, for if we introduce a Hne platinum wire into the flame it becomes nearly white hot, and emits much light. l>- It we take a glass ti;be, oi)en at both ends, about one centimeter wide and 30 centimeters long and pass the jet up into it, the flame is seen to sud- denly elongate and a musical note results. The note emitted by ihis chcmual Imrwonicum depends on the dwmetcr and length of the tube; consequently tubes varying m these particulars may be used to produce diflerent sounds. c. It will be observed in these experiments that the glass tubes are bedewe,i when they approach the hydrogen flame. Next place the flame under a large W /""■' n-, '"'^"■' °'^' " ^ '"g'^ ^'y wide-mouthed bottle. The inner surface of the bottle is quicklv bedewed with moisture, and presently drops of liquid rickle down thfe sides and collect at the shoulder. When some drops of the liquid have been collected It can be examined, and is then found to possess all the properties of water. Now, since the calcium 'Chloride m the drjing tube completely removes moisture from the nnbumed ,as, and the latter does not bedew a coKl surface against which we may allow U to impmge, the liquid we observe to be deposited from the flame must be a product of the combustion of hydrogen in air, just as the white substance, see the gas burns quietly, it may be safely kindled at the jet ; but rf with explosion, it is still unsafe, and the testing must be re- i^vaicu uucr a icw minutes. 32 Introduction to Experimental CItemistry, Kxpcriment 2, is a product of tlic combustion of mag- nesium in air. • By means of the next experiment we can prove that the water prcduced in the combustion of hydrogen weighs more tlian the gas l)urned, and there- fore that the process is one of chemical combination in progress between hydrogen and some constituent or constituents of atmospheric air; the resultant water is consecpiently a compound of hydrogen, or of the water generator (l^cwp, water; yeriuw, I generate), with some other kind of matter. Experiment 21.— Take aU tube of the form of ^, fig. 12, fill the wide limb very loosely with fragments Fig. 13. of zinc and insert the cork b whicli serves to prevent the zinc falling out when the tube is inverted, but which should be perforated so as to allow liquid to flow freely in and out. Pass the narrow limb of the U tub«i ihrou£;h a good cork c which fits a test tube I Hydrogen and Oxygen Gases, 33 about 2 centimeters in diameter. The cork also carries the glass tube s provided with a fine glass stopcock which can regulate the supply of gas to the jet in which the ti;be terminates ; the wide end of this tube is sufficiently large to pass through the cork c to the bottom of the test tube /. The latter is now filled with fragments about the size of a pea of dry and porous calcium chloride, and by turning the tube nearly on its side and tapping, the tube of s can be passed down along the glass and the cork inserted as shown. Now pass the wide limb of a through the neck of a light flask of about 80 or 100 centimeters' capacity, containing diluted sulphuric acid, and secure the tube a in the neck by means of slices of rubber cork, but without interfering with access of air. On turning the stopcock s the acid rises in a and acts upon the zinc, hydrogen is evolved and passes through the drying tube / before it can escape from the jet. The evolution of gas is allowed to continue until all air has been expelled, then the hydrogen can be kindled at the jet, and once it is found to burn freely, the stopcock is turned off, the evolution of gas ceases, because the latter has now no exit through s^ and accumulates in a, forcing out the acid through the perforated cork b, and therefore away from contact with the zinc. Before the experiment, th*" appaiatus is accurately counterpoised, and a quantity of dry gas is then burned at the jet, under conditions to be presently described, and the stopcock again closed. If, when cold, the apparatus be replaced in the balance it will, of course, D i 34 U I Introduction to Exftrmenial Chemistry. weigh less than before, and the weight lost is the weight of dry. hydrogen burned. ' '°'' " «"« Another piece of apparatus is now to be prepared" This consists of a small paraffin lamp . himney "fig ..connected by means of a corl, as shown, « th tht U tube V filled with calcium chloride. This is our water collector, and is to be attached by the w" e hook to the arm of a balance and carefully counTer! poised before an experiment. counter- Diec« "nf"'' "" ^''P^"™^" f'us : counterpoise both flexible tube w.th an aspirator^ p, as shown, so that a stream of air may be drawn slowly through the water collector during the combustion of thf hydroTeT Now turn the stopcock .. immediately kindl7"e hydrogen, and pass the flume well up into the tube i chiefly m v. When the hydrogen has burned for some mmutes. dose the tap ., and stop the current of a.r through i.; allow both pieces of apparatus to cool —r'T^l' *^".'''— « -1 weigh each separately. The gam m weight of the dryins in paratus represents the weight of water prXfd t tJe jet"! ° "' ""*'"' °' ''^^^"e- burned at When the experiment just described is conducted Hydrogen and Oxygen Gases. 35 with great care, it has been found that for every centi- gram of hydrogen burned almost exactly 9 centigrams of water are obtained in the drying apparatus ; thus it can be proved that the hydrogen gains in weight • on undergoing combustion in air; and, further, that the product of combustion weighs 9 times as much as the hydrogen burned. The next step clearly is to resolve water into its constituents, or to decompose it, in order to isolate the matter which hydrogen must have obtained from air. The conipound water, whether in the liquid con- dition, or when gaseous (as steam), withstands a com- paratively high temperature without decomposition; similarly light alone is without action upon it, but electricity is found to decompose it with facility, and the current derived from a Grove's or Bunsen's gal- vanic battery consisting of two cells is sufficient for the purpose. Experiment 22.— If we attach to the copper connecting wires of such a battery small slips of platinum (taking care that the connections are per- fectly clean and bright), and then plunge the platinum terminals or * poles' into some water acidulated with a few drops of oil of vitriol, in order to make it a good conductor for electricity, bubbles of gas are seen to rise from each pole. Note that more gas seems to be evolved at the pole connected with the zinc end of the battery than at the other. In order to collect the gas it is only necessary to arrange the apparatus shown in fig. 13. The vessel v contains the acidulated water. The two test tubes are tilled D 2 • i rl 'W 36 Introduction Jo Experimental Cliemistry. Fig. 13. with some of the same water and then inverted with the mouth of each below the level of the water in the vessel V, and supported close together by clamps. The platinum poles are now arranged as shown, their wires being attached to the binding screws s, s, which latter are also connected with the battery. The wires are dried and then com- Pletely coated with sealing wax, from the platinum slip to the point c, so as to pre- vent any escape of electricity, except through the plates when they are immersed in the water. Each platinum' pole IS then brought under the mouth of a test tube and secured m position. Gas bubbles arise from the pole, as before but mstead of escaping into the atmosphere they collect m the tubes placed to receive them A marked difference is observed in the amount of gas g.ven off at each pole, and it .s presently seen TO fuT"' ' ' " "'" '"" °' ^^ "^^ ""'«''' "^"^ In order to examine the gas in each tube, remove the wires, then close the mouth of the tube containing the largest volunie of gas with the thumb passed under the surface of the water in the vessel v. Invert the tube shp as.de the thumb, and quickly apply a flame o the mouth of the vessel ; the gas takes fae.nd ' burns with a pale blue flame, and this gas is hydrogen A similar experiment is made with the contents of the second tube, but the gas it contains does nnf tot. Hydrogiii and Oxygen Gases, 17 fire. If, however, we dip into the gas a splinter of wood with a glowing tip, the wood bursts into flame, and active combustion ensues. This gas is, therefore, incombustible in air, but is a supporter of combustion. This body, like hydrogen, is an element and is called Oxygen. The process of analysis by electricity just used is termed electrolysis, and is often employed in effecting the decomposition of chemical compounds. During the electrolysis of water we have already observed that twice as much hydrogen is evolved as oxygen, and the presumption is that those are the proportions by volume in which the two gases unite to form water.* But we have not yet proved that water consists of hydrogen and oxygen ofily. If, then, we take the mixture of gases evolved from water, consisting, as we know, of two volumes of hydrogen and one volume of oxygen, such a mixture must be capable of repro- ducing water // the latter consists exclusively of these two elements in tl proportions stated. Experiment 23.— Take a stout wide-mouthed phial of about loo c.c. capacity. Fit it with a caoutchouc - -zk and, having bored a hole axially through it, a.^^ert the short limb of the narrow but strong delivery tube bent in the form shown at d, fi'g. 14. The wider tube shown can be filled with fragments of calcium chloride when a supply of the dry gaseous ' 100 cubic centimeter-, of water dissolve only 2 989 c. cs. of oxygen at mean temperature and pressure, and 1 -93 of hydrogen gas under the same conditions ; the solubility of each gas is therefore so low and so nearly the same, that the above in- ference may be faiiiy drawn. i\ 38 Introduction to Experimental Chemistry. mixture is reouired. Then pass two stout wires of platinum through the cork on each side of, and close to the glass tube, and attach small slips of platinum ton to the ends of the wires that project within the bo tie. Nearly fill the vessel with water containing a little sulphuric acid arid insert the cork, connect the wires projecting from the cork with the terminals of the battery, as shown, and a steady supply of an electrolytic mixture of hydrogen and oxygen will be Fig. 24. Fig. 15. obtened When .t ,s judged that all air has been expelled from the bottle and tubes, collect some of he mixed gases m a small test tube over the liquid meta mercury, contained in a small and strong plass rough, as m fig ,5. This mechanical mixture^? he two gases may be kept for an indefinite time without comb,„at,o„ taking place, but if we remove the tes tube from the trough and apply a flame to the momh -a flash of hght, and a rather violent exolosion i;jiiniv. irini.-Mfirirr ♦u ,k -.i = ... - follow, u -iojcuting that chemical union has taken place.' Hydrogen and Oxygen Gases. 39 We thu", learn that combination of the gases can be determined by heating them sufficientlj.^ Experiment 24.--A stout glass tube closed atone end IS now taken ; it should be about 50 centimeters long and i centimeter in diameter. Two thin platinum wires pass through the sides and are sealed mio the glass near to the closed end, and opposite to each other ; but their extremities within the tube must be kept at a very short distance apart. The object of this arrangement is to leave a gap so that an electric spark may be sent between the wires within the tube, and thus, by heating the mixture of gases, determine their combination. Such a tube is called a eudiometer, and must be stout so as to resist the force of the explosion that ensues ; it is shown at b, fig- 15- Fill the tube with mercury, and when quite full, close the mouth with the thumb, and bring it under the surface of some more mercury, contained in the small trough /, fig. 15. Now half fill the tube with electrolytic gases from the apparatus shown in fig 14. Then remove the generator and pass a pad of india- rubber under the mercury and under the mouth of the tube. Press the pad against the bottom of the trough with the tube grasped firmly by the hand. When the tube is in this position, pass a spark from a coil, a Leyden jir, or a small electrophorus, through the gases by means of the wires sealed into the glass, one of them being connected with the earth by means of wire, the other with the apparatus that is to afford the 1 Qaa r'linnf.av TV t^ : » f.1 .. I en name* \i' 11 ' 40 Introduction to Experimental C/iewistry. spark. A flash of light passes down the gas in the tube and a jerkT is felt by the hand, and then all is over On relaxing the pressure and moving the moutli of the tube from the pad, but keeping it under the surface of the mercury, the latter rushes up so as to fill the closed end almost completely ; the gases have therefore been condensed,' or rather, the product of their union is not a gas, but must b. either a liquid or a solid occupying an exceedmgly sniall space as compared with that previously filled by the generating elements. If we examme the upper part of the tube carefully with a lens, we can detect between the mercury and the glass mmute drops of liquid. This liquid can be proved to be water. It is therefore certain that water con- sists only of hydrogen and oxygen, and that those elements combine to form water in the proportions by volume mdicated by the results oi electrolysis. Experiment 25.— A similar experiment to that just described may be performed with the apparatus shown mfig. 16, termed a 'Cavendish eudiometer' because itw.swith such a vessel that the Hon. Henr^ Cavendish demonstrated the composition of water in the year 1781. The strong glass vessel, fig. ,6 IS provided with a glass stopcock c and a stopper through which wires of platinum p p pass, and th.s stopper IS retained in the neck of the vessel by means ' As a matter of fact a small bubble of hydrogen remains after explosion ; this is chiefly due to the loss of a little oxvtren by solution in the water of the bottle d, fig. 14. and further bv conversion of a very small proportion of the element into a body called 'ozone.' If all the oxygen wore evolved as gas there would not be any free hvdiofri>n a(t^r th» «».,x!» .:-.- Hydrogen and Oxygen Gases. 4t of the damp a. The brass stopcock b allows the apparatus to be screwed to the plate of a good air- I)iimp, and when exhausted of air, B and c are closed, and not opened until the tube is screwed to the brass stopcock of a bdl jar similar to that shown in fig. i8, but containing some of the electrolytic gases. On opening the taps the mixiure of gases rushes in to fill the vacuum. The stopcocks are again closed, the eudiometer screwed to its stand, and a spark passed through the mixture. A brilliant flash of light accompinies combmation, and the sides of the glass vessel are bedewed with the water resulting from the combination of the gases. The experiments hitherto made have led directly to the conclusions we have already drawn from them respecting the composition of water, but they also afford complete proof that atmospheric air contains oxygen ; and we thus learn in addition that the great heat evolved "during the combustion of hydrogen in air is due to the chemical union of hydrogen with the oxygen of the air. Finally, we are led to suspect that all ordinary cases of combustion which come under our notice are due to ihe rapid chemical combination of atmospheric oxygen with the body burned. Under Experiment 2 1 a method was described by which the ^ Wcigut Oi water produced during the combustion of I c. gr. of hydrogen was determined, and it was stated K: ll m.v'*,%:m\ if: iili 42 Introduction to Experimental Chemistry, that 9 c. grs. of water resulted. Since we now know that the gam in weight could only be oxygen derived from the air in which the gas burned, the equivalent of Oxygen must be 9-1=8. When the metal magnesium burns in air, a white solid only IS produ. _d, and it is found that 12 centi- grams of. the metal afford 20 c. grs. of the white body, that IS to say an equivalent of the element magnesium (12 parts) unites with an equivalent of the element oxygen (8 parts), and produces an equivalent (20 parts) of the compound body termed magnesium oxide or * magnesia '—for 12 + 8=20. The truth of the statement is not so evident in the case of a candle, for when the latter burns per- fectly m air, the matter of the candle is apparently destro3^ed. But since we know that matter is inde- structible, we conclude that the candle is resolved bv combination with oxygen into invisible products. These products we can actually collect if we burn a candle m the apparatus, fig. 17. Experiment a'J.-Attach the small paraffin candle c to the peiforated cork, and insert in the lamp through which a bent tube passes which serves to connect the lamp glass with the U tube. The limb t^L T\ ''.^'''^V *^^ ^^"^P g'ass is filled with lumps of calcium chloride, and the second limb with fragments of caustic soda When the cork c is placed m position, the apparatus, with the rp.nH!- ic amch-d to one arm of the balance and carefully' counte'rpoi'sed. Hydrogen and Oxygen Gases. 43 The tube / is then connected by means of a flexible tube with the aspirator a, and a current of air gently Fiu. 17. n \ ' ^ VaI \ ^ c^^ 1 ( [] ^ A ^£±11^ 1 J yf 4 M\ • Ml 11 drawn through the apparatus. The candle is removed, lighted and replaced, and then burned within the lamp glass, while the products of combustion are obliged to pass over the absorbent materials in the U tube. When the candle has burned for five minutes or so, put it out and allow the whole apparatus to cool down to the ordinary temperature. Then replace in the balance and observe that the weight has increased. Therefore, not only has no matter been lost during the combustion of the candle, but it has actually gained, and, as we shall see at a later stage of our study, the gain represents oxygen derived from atmosnheric air, and chemically combined with the matter of the candle during combustion. ;i l!i 44 Introduction to Expetimental Chemist. ry. \\m\ CHAPTER V. EXPERIMENTS WITH HYDROGEN AND OXYGEN G/.SES {continued). 11^7 ^T ''?"-'''^ "^" ""^S^" S^^ '■' - con- stituent of atmospheric a.r-though it is not the only one-and of water The study of the composition o^ he latter has further made kno.vn the curious fact that oxygen requires twice its volume of hydrogen gas to forni water, and only i„ this proportion does a,rect combmation take place between those elements Iherefore the two gases unite in as definite propor-" tions by volume as by weight, and it is evidemlv probable that an intimate connection exists between weight and volume combination in this case- hence we must investigate the point more closely ' Experiment 27.-The first step in this direction ts to select a globe of about ,l literi' capacity Z^Z with a stopcock, and to exhaust it of air a' com P ete ly as possible, by means of a good aTr pi >To' the plate of which it can be screwed ; then cTo e' 'th^ tap securely, remove and counterpoise carefully on the balance. The globe is next taken from the balance and connected, as shown, with a vessel containing pure hydrogen gas, and the stopcock opened, hy _- -^_„ . ....„€. „, auu uiib tnc giobe. The stopcock is Hydrogen and Oxygen Gases. 45 Flu. 18. again closed, after the levels of licjuid within and without the jar have been equalised, and the vessel re-weighed. The increase in weight is that of the hydrogen which has entered. The globe is again ex- hausted to the original point as determined by the gauge attached to the pump, and again filled with gas, but this time with pure oxygen, whose weight is then determined. Now if care be taken to exhaust as completely as possible each time — certainly to the same extent — and that the bodies are pure, and the temperature does not vary so as to unequally expand or contract the gases, the weights obtained are those of equal volumes of the two gases. In a particular experiment con- ducted in this way the hydrogen weighed 11 centi- grams, and the oxygen gas 1 74 centigrams. The specific gravity of oxygen as compared with hydrogen, or the ratio of the weights of equal volumes of the two bodies ^ when hydrogen is taken as the standard, and =1, is or as nearly in the ratio of i : 15-96 — the true ratio • — as can be expected in a rather rough experiment. Therefore oxygen gas may be said to be 16 times heavier than hydrogen. Now since one volume of oxygen requires two volumes of hydrcgen for the production of water, it follows that 8 centigrams i:i 46 Introduction to Experimental Chcmislry, by weight of oxygen must unite with i centigram of hydrogen to form 9 cc.uigrams of water- -a result Identical w.th tluit ol)tained by the direct weighing of the water produced in the combustion of a mven we-ght of hydrogen. Therefore, a very close connec tion exists between combination by weight and hw vohime. ^ It may be added that the specific gravities of all gases can be determined by the method just described, and smce hydrogen .s the hghtest gas known, it is taken as the standard for reference. ' The experiments already made with the two gases hydrogen and oxygen, place beyond doubt the fact that they are perfec Jy distinct forms of matter as far is chemical characters are concerned, but they evidently resemble each other in certain physical cluu racters, for they are both colour- less, invisible, and inodorous. Let us now see whether this re- semblance extends farther. Experiment 28.— Take two tubes of as nearly as possible the same diameter and length. Close each at one end and bend to the form shown in a and b, fig. 19. The short limb may be about 20 centimeters, and the longer i meter, in length, lake one of \ . A -1. ,M ^^^ *"^^^' ^^* ^^'^^^ water acidu- iated with dilute sulphuric acid and invert over the po.e ^iig. 13) froi-a which electrolytic hydrogen is Fig. 19. li Hydrogen anU Oxygen Gases. 47 being evolved ; collect enough of the gas to about half fill the shorter limb of the U tube, then close the njouth with the thumb, remove aiul make the gas pass' completely into^he closed limb: this can easily be done by bringing the tube to a horizontal position while the shorter limb is uppermost. When the gas has been transferred, bring the a|)paratus into the position shown, and adjust the level of the liquid in both limbs ot the u by sucking out the water in the long limb by means of a pipette wi»h a flexible tube attached, which latter should be of sufficient length to reach nearly to the bend. Fill the second tube to the same extent and in the same manner with electrolytic oxygen, and tie the two tubes securely together as shown. When the apparatus is plunged up to the point a in a large beaker nearly filled with water at the boiling temperature, the gases in the tubes are found to expand considerably. The expansion cf tho hydrogen is seen to be the same in amount t^ that c^'the oxygen. Simi-arly in cooling down again tO he te nperature of the air they contract equally. We learn from this experiment that the two gnses resemble each other in another particular, namely, that they are eff"ected to the same extent by equal al- terations of temperature^ when observed under the same conditions. Now replace the hot water in the beaker by some at the temperature of the room, and leave the tubes undisturbed for several minutes, in order that the gases may acquire the temperature of the water in the large vessel ; then pour mercury into each wide tube until nearly full, and the column in each is of equal length. --^i % ni 4? Introduction to Experimental Chemistry. Wd InH "' n' '°'"'"'"' °f "'^•^"'y rise to the same lrl!i 1"' "^ P'"'''""* ">^°" ">« g^^es equally in- creases, they contract to the same extent If we remove the mercury, the gases expand equally and regam their original volume when the pressure is reduced to that at which we commenced Therefore hydrogen and oxygen gases, when com- pared under the same conditions, are affected in the same way and to the same extent Oy cjual alterations 0/ pressure. When the same n,ode of investigation is applied to other gases, whether elementary or com- pound, they are found to sufTer very nearly equal changes of volume when subjected to equal variations of temperature and of pressure. _ The conclusion to be drawn from all the data before us ,s that all gases ^«<^t\n physical constitution, however niuch they may differ in chemical composition. This conclusion is independent of any hypothesis that may be founded upon the facts, but a most impor- tent one has been based on them by the distinguished physicist Avogadro. He assumed that all gases (as wel as solid and liquid forms of matter) are made up of almost numberless, separate little particles, termed molecules (from molecula, a little mass), and that e^ual volumes of gases ontain the same number of mole- euies, when compared at the same temperature and pres- ol'; \TT '^ '1""""""' "f Avogadro's, or, as it is often called. Ampere's law, for to the last-named philosopher IS due the credit of having specially drawn he attention of scientific men to .he importance of the principle enunciated by Avogadro, when the t!at«m'>tropoiiiun lu tne vuiuuica oi gases or vapours from which it has been formed. £3 \\ m in* 1 |i 52 Introduction to Experimental Chemistry, Reasoning upon this result, it is perfectly clear that each molecule of wa.er-gas so produced must contam oxygen, and, if the law of definite proportions be true, as we know it is, each molecule of water-gas must contain the same quantity of oxygen, conse- quently a semi-moleciile of that body. Hence*, though the free molecule of oxygen is not divisible by any known physical means, it divides under the in- fluence of chemical attraction into t^vo parts. Now the weight of oxygen corresponding to the semi-molecule of that body is the smallest quantity of it that takes part m chemiral change, and as it cannot be further divided, even by chemical means, it is called the atom^ O! oxygen. Later on we shill find that the molecule of hydro- gen IS also chemically divisible in two parts or atoms Now, \{ the weight of the molecule of hydrogen be taken as = i, the weight of the atom of hydrog-n must be represented = \, but since less than i part by weight of hydrogen is not known to act in chemical change, it is convenient to take i as the atomic 7vei^ht, or vveight of the semi-molecule, of hydrogen. The weight of the molecule of hydrogen is therefore =rr 2. As we have already seen from Experiment 27, the oxygen molecule is sixteen times heavier than tliat of Hydrogen ; therefore, since the molecular weight of hydrogen=2, that of oxygen must=32, while the atomic weight of oxygen is 16. If, then, we desire to know the atomic iveight of an elementary gas, it is only necessary to find its specific gravity, /.^,, to weija:h it as in ExDerimpnt '>n affainc* «« ' &ro/ios, indivisible. Hydrogen and Oxygen Gases. 53 equal volume of pure hydrogen under the same con- ditions. The weight obtained, referred to hydrogen as the unit, is the atomic weight of the body. But the information that our experiment affords us does not end here, for we can deduce from it the specific gravity of water-gas, referred to hydrogen as our standard. We have already learned that two molecules of water-gas, which must contam the hydrogen in two molecules (i.e., 4 atoms) of that body, and the oxygen in one molecule {i.e., 2 atoms) of that element, occupy the same volume as two molecules of hydrof^en. Therefore one molecule of water-gas occupies the same volume as one molecule of hydrogen. Now, one molecule of water-gas must have the relative weight 18 (16, weight of the semi-molecule of oxygen + 2, weight of the molecule of hydrogen) referred to the hydrogen molecule=2 ; this gives the ratio of 9:1; therefore 9 is the S[)ecific gravity of water-gas compared with hydrogen gas as the unit. It may be useful to add the following definitions ; — A molecule of an element or compound is the smallest portion of a body that can exist in the free state. An atom of a chemical element ' is the smallest portion of it that is known to take part in chemical change, and is almost invariably the semi-molecule. An (quivalent of an element or compound is its replacing or combining value compared with an unit weight of hydrogen. liiv, sn.vjf.j.iix. liic-wiy \}i uic ujiistn.r'"^ pniiosopner^ * A chemical compound has not atomic weight. 11 M' If et ij n- S4 Introduction to Experimental Chemistry, Dr. John Dalton, of Manchester, was one of the first substantial attempts ' to account for the law of definite proportions t^iat we have seen to so remarkably govern chemical changes, and we may now state the theory and the differ eiice ;n form between it as enunciated by Dalton (in 1804-8), i lid as adapted to the present state of our knowledge. Dalton supposed, as Avogadro did, that with all matter a point c^ i be reached at which further mecbmical subdivisoa is impossible, and it was to tliese ..timate particles he applied the tetm atom— the atomic weight being a constant for each element. The molecules of the present day are the representatives of the atoms of Dalton, and we have already learned from our expei iments that the molecule of an element, though physically indivisible as we suppose, can divide under the influence of chemical attraction into two— but rarely laore or less than two— pa»ts, and to each part we now apply the term atom. Dalton further ass-med tAat chemical action takes plact only beu^h^-n the .doms of matter, and in proportions by weight -^^kic^ are determined by the relative atomic tvei;:his of the detnmts. In the Daltonian tlieorv- as tl us modified ^± have an explaiiation of the law of definite proportions, but it is necessary to guard against the supposition that tie law of definite proportions depefids on this hypothesis. As we have seen, the theory is founded on two assumptions, both reasonable, it is true, but which are not at present capable of direct proof. We ' The fundamental conception in the • Atomic Theory » was distinctly enunciated by two Dublin chemists—Kirwan in 178.1. and Hiji-lns s.i 1789. ' "" Hydrogot and Oxygen Gases. 55 may, therefore, use the theory as an important help in our inquiries, but not as a support on which we may rest in full confidence. If, however, we desire to go still farther, and to enqui-e how it is that these elementary atoms possess the power of uniting with each other, we must simply confess that this is one oi the many mysteries that still lie hidden from the view of man. m H 56 Introduction to ExperimSttal Chemistry. ¥ CHAPTER VL EXPERIMENTS WITH TdE METALS, SILVER, COPPER, AND MAGNESIUM. It is obvious that the method of weighing an element in the form of gas against the same volume of hydro, gen, when we desire to determine atomic weight, is only apphcable in those cases in which the element IS either a gas at ordinary temperature and pressure or in which it can be converted into gas, or vapour, at a moderate and manageable degree of heat. Neither Sliver nor magnesium can be vaporised at even moderately low temperatures: hence we must seek for some other mode than that above referred to of hxing their atomic weights. The equivalent, or re- placing value of silver stated in terms of the hydrog'^n unit, we have already proved to be io8, and that of magnesium 12. Now it is evident that the atomic weight in each case cannot be less than those values but It may be more, for we have already seen that in the case of oxygen the least weight of that body that takes part as a whole in chemical change (the atom) IS twice the equivalent. ' ^ Experiment 30.-Make the following curious and mstructive experiment. Take a five shilling piece » ^ ' Although the coin is not pure silver, it is sufficiently nur- ior liiiit lough experiment. ' *" Stiver, Copper, and Magnesium. 57 and fasten it securely to a piece of fine binding wire, lake a piece of copper of the same ^veiirht and thick- ness, and attach it to wire. Now, while holding the wires dip the two pieces of metal into some water boihng in a kettle, or other vessel. After ten minutes or so remove the pieces, let them drain for a few seconds and attach the wires to a rod. At first the metals arc equally hot to the fingers, for they-Iiave evidently been heated to the same extent; soon, however, the silver will be cool enough to be held between the fingers, and to be pressed against a piece of phosphorus without igniting it, while the copper will be still too hot to hold, and will easily kmdle a test of the same kind. The silver, there- fore, cools more rapidly than the same weight of copper under the same conditions. As the two metals do not differ materially in conducting power we infer from this experiment that silver at koo° c' (the tempcnmire of boiling water) contains less heat than the same weight of copper at the same tempera- ture---in other words, a less quantity of heat is re- quired to raise the temperature of a given weight of silver to the same extent as an equal weight of copper, hence the eapacity of copper for heat is greater than that of silver. » If we could conveniently replace the th.t'o?siL'' *°w ^ '^! '^'"^' ^''' "^ ^^Pf^^^ '' greater than hat of silver Water has the greatest capacity for heat of any reftrred to that of an c.^mi .vei^rht of water as unity : thus the capacuy of sUver for heat is about ,Vth that of an e'ual weight ih.Z7.'r"7 T^Tl '""^ """^ '^5701 : I. This ratio is the spa^fic heai of silver. The a^oruu; heat of aa, element U ^•} \ ' e stated thus: -77/^ atoms of elementary mat*er have the same capacity for heat. If this law be true, toS centigrams of pure silver and 12 centigrams of pure magnesium when heated to 100° C— the tempf.)ature of boiling water— and then allowed to cool, ought to give out on cooling to the same extent the .ame quantity of heat^ if the above numbers represent tl e relative weights of their atoms. Experiment 31. — By the method now to be de- scribed we can apply this test to the two mttals. The atometer, fig. 21, is really a large spirit ther- mometer with a test tube inserted in the bulb, as shown, and hermetically sealed therein. The shaded portion is full 9f alcohol, coloured red in order to the product of the specific heat by the atomic ^veight, and if about 60. Thus '05701 x 108 =»6i S7. % Fig. ai. Silver and Magnesium. 59 make its motions in the stem more evident. Tlie stem s should be about 30 centimeters long, graduated clearly in milli- meters. The in- strument ought to be so constructed that the t^read of liquid should ad- vance through a length of fully 30 millimeters for an increase in tem- perature of one degree centigrade. The bulb of the atometer is bed- ded, as shown, in cotton uool contained in any con- venient beaker, or better still, a heavy tumbler. A small piece of cotton wool is passed down to the bottom of the test tube /, and ont ubic centimeter of water accurately delivered into the previously dry tube from a measuring pipette, or dropping tube, fig. 22. The whole apparatus is left in a cool place until the thread of liquid i the stem becomes steady, i.e. until the ii. 'ument acquires the same lem- peratiire. Now taker ^jiece of pure metallic silver weighing exactly j centigrams, and of such a shape that it cau easily pass mto the *^ -. xxxvsx, -. v: Liis. aiuincic,. i'iace tile centigram atOLi of silv r in the test tube //, which passes rather Fig. 2a. ee fc Tftirodndion to ExpcrimcnUtl Oicmistrv, II ' \\r-.\ Fiu. aj. loosely through the cork of the flask / fig 23 The test tube sho^uld be closed by a small stopper of cork or vulcanit»\ Throu^jh the cork of the fla>k another tube passes which is open at both ends, and which gives exit to the current of steam produced when the water in the flask is boiled vigorously. The test tube and the con- tained silver are thus heated to the tempera- ture ot steam, i.e. 100° C. if the pressure be 760""". After ten minutes heating in the steam bath the metal will have acqirred the tiesired temperature: then remove the tube // quickly, bring its mouth near to the mouth of the tube / of the aiometer, withdraw the cork /, and so invert h that the lump of silver s may ciuickly drop into the water in /, where it parts with its heat. The little piece of cotton wool prevents the lump of silver from breaking the glass. If the temperature, as indicated on the stem s, be noted just before the introduction of the silver, the thread of liquid will be seen to. rise almost immediately after the silver has been dropped in, and will continue to rise imtil it reaches a maximum. In an exj^eriment made in this way the thread of liquid in the atometer rose from 10 to 30 (20 divi'clrknc\ qft-Av »ka t,*o ,. ./••i _«_•> 7\y '■ "-'^-- ■•"■- •-■« ^. ©la. oi siivci iiau ueen mtro- duced. Silver and Mag.Hsium. 5| luIt.Z^f'^^^ centigra>ns of pure >„a«ne.ium i,> JTrooo r ?,"' '•'•■''"^ ■' '" '•'' '"'»-• '> ""'' heat u,i •? ^' ""•' ''"'"^ '^■•■'y ''s 'he silver. . h.„r . u "'"Snesium is heating, pass a wire with a hook a the en.l nuo the tube of the atomcter and Z:^ '° ''^" T •\°'' ""= ■-- '" ™"- woot 1 er h H ^ ;""' " "'" '"■"" "' ^'l^*^^- After the silver with a force,« and push the cotton Lack under the water then remove the wire. At this time the liqutd m the stem . will be still above the point fro.u whtch It started in the experiment with si ver tl er" ore remove the bulb . and blow upon it, or o cool l"rlou;:l''''"''r'""'^'^'"'''°-'n-inttl"an we re,,u,re; now replace in the wool, an.l allow the temperature to gradually rise, until the silver starting, pomt .s reached. By this time the magnesium wm have been heated to .00° C, and it is now to be plunged into /. as in the former experiment, and the nse in temperature noted. t In the particular experiment above referred to. the .quid expanded from .0 to only aj (,5 division ) or as o ,oT" "/'f ""^ '=«'■""' """ " ^^ -the case 01 108 c. gis. of silver. The conclusion we draw from this result is that l» c. grs. of magnesium at .00° C, contain but half the quam.ty of heat that 108 c. grs. of silver do at the same temperature. We therefore infer that the weigh of magnesium that would contain the same quantL of heat at loo" C. as ,08 c. grs. of silver is 24 c. grs and Z^T^l^.^^^-^ 'his larger'weight. - «:..;.; uic 5an.c conuitions as betore, we get an I : til III % I 62 Tiitroduction to Experimental Chemistry, expansion winch is nearly equal to that caused by the silver. Now, according to our definition of the term e '""^ '^ for Aun^mf and ekht c ur^ ^e\? f ' ^^' ^''^ /-c. grs. Of ACsit": ?hrz;::i!!«:/---: m aiph.bet.cal order in the .ablerbu t ilTs ^I^ 64 Introduction to Experimental Chemistry. Name I i i Aluminium Antimony {SfiNiim) Arsenic Barium Beryllium . Bismuth . BOROV Hromink . Cadmium . Calciuri! Carhon CHl-ORFNii . Chromium . Cobalt Copper {Cuprum) Fluorine . Grold {Anntut) Hydrogen. Iodine Iron (t'enitm) Lead {Plumbum) Lithium Mag^nesium Manjg^aness Mercury \ llyiirar^yntm) Nickel Nitrogen . Oxygen Phosphorus Platinum . Potassium {Kalium) Selenium . Silicon Silver {Argentum) Sodium {Natrium) Strontium . Sulphur . Tri.i-urium Tin {SUxnnum) . Zinc . Symbol Atomic Weiijht Al'' Sb' As' Ha" «e" Hi'" B" Br' Cd" Ca" C" cr Cr" Co" Cu' F Au'" H' r Fe"' Plj" Li' Mg" Mn»' Ilg" Ni" N" O" P' Pt" K' Se«' Si" Ag' Na' Sr" Te" Sn" Zn" 27.3 122.0 750 1370 9.2 210.0 II. o 80.0 112.0 40.0 12.0 35.5 524 58.6 63.0 19.0 196.2 I.O 127.0 56.0 207.0 7.0 24.0 SS.o 200.0 58.8 14.0 16.0 31.0 196.7 39.1 79.0 28.0 108.0 23.0 87.2 320 128.0 1 18.0 6;.o Experiments with Metals and Non^ Metals. 65 divide them in two great groups, of metals and non- metals, respectively. The names of tiie former are printed m the table in strong Egyptian type, and those of the latter m capitals, in order to facihtate reference. J he most strongly marked members of each class admit of easy distinction. Experiment 32.^Take a slip of copper, about ten centnneters long, and a roll of *cane brimstone' or sulphur, of the same length. Compare them and note:— ti. That the red-coloured copper exhibits that peculiar lustre termed metallic, while the yellow sul- phur has a greasy lustre of a perfectly distinct kind. Fic. 94. ^^-^^^SS^ b. That when one end of each specimen touches the surface of some boiling water, the fingers which grasp the other end quickly feel the heat conducted hy the copper, while those holding the sulphur have not any sensation of warmth conveyed to them. c. That the copper, O/, fig. 24, when used to connect the terminal wires of the galvanic battery B With the galvanometer o in the circuit, conducts the electricity along it, as shown by the ctrnn« d--. flection of the needle. When the copper is removed, m L 66 Introduction to Exi^erimental Chemistry, and the wires connected by sulphur, the needle is not affected. I'he metal copper is therefore distinguished from the non-metal hulphur— by the metallic lustre, and by conducting heat and electricity freely. These broad distmctions are sufficient for the present, but it must be stated that the members of each group cannot all be so sharply defined, and in some few cases it is by tio means easy to determine whether in the free ele- ment-arsenic, for example— we have to deal with a metal or wiih a non-metal. Experiment 33.--Again, take some crystals of blue vitriol,' or copper sulphate, and dissolve them in some hot water; now plunge into the solution two platmuin slips attached to the terminal wires of a strong galvanic Imttery. Immerse for a minute or 80, and observe that bubbles of gas separate from one of the plates; withdraw the slips, and note that a red deposit of metallic copper is obtained on the slip connected with the zinc end (the negative pole) of the battery. No deposit takes place at the other- pole, but It was from this that bubbles of gas were separated, and this gas could be shown to be oxygen if collected and tested. We learn, then, that when a compound of copper with a body which certainly contains oxygen is elec- trolysed, the metal makes its appearance at the negative pole, /.^ that connected with the zinc end of the bat- tery The reason commonly assigned for this selection of the negative pole by the metal is, that the latter t»etng electro-positive is most strongly attracted by the unhkepole, while the non-metal, oxygen, being elecint. Experiments tvifh Metals and Non-Metals, 6y negative, makes Us appearance at the unlike, in this case the positive pole. This is true, not only of the copper compound, but of other compounds of a metal with a non-metal, when subjected to electrolysis ; thu«. while the metals are electro-positive elements, non^ metals are electro-negative. Experiment 34.-Make a fresh solution of copper sulphate and place it in a phial; suspend a clean strip of iron wire mthe liquid by means of a string fastened o the cork of the bottleJ A deposit soon forms upon the iron, and if the bottle be shaken it falls to the bottom ; when the iron is taken out of the liquid it is seen to be coatea with copper, and the deposit in .nni n .J' """''"•' "^PP"'- '^^'^ ^^''^^ SO^^ on until all the copper has been separated from the solution by the iron, the latter metal dissolving in the liquid. Metallic iron therefore displaces copper from solution without the assistance of a battery Experiment 35.-Next dissolve a small quantity of the poisonous 'corrosive sublimate,' or mercuric chloride m hot water in a test tube, and plunge into the liquid a clean strip of copper. The latter soon becomes coated with a greyish deposit, and if we remove the copper, wash it with water and rub it. a bright silvery surface is obtained due to the separation of the nietal mercury, or quicksilver, from the solu- tion by the copper— the latter metal dissolving Experiment 36.-Again, dissolve a few crystals of silver nitrate in some water in a small phial, and pour a few drops of pure liquid mercury, or quicksilver, into i- - «.*can oieKi kuiic ra If 6S Introduction to Experimental Chemistry. ,1 Fic. »s- the solution, and allow the latter to stand for a day or so. At the end of that time beautiful needle-like crystals of metallic silver will be seen in the liquid, separated out from the solution by the mercury. We thus learn that the metals are not equally electro-positive, thus iron being more tlectro-positive than copper displaced the latter from the solution •, for a similar reason copper displaced mercury, and mercury the silver. Experiment 37. — The displacement of silver by magnesium already effected in Experiment 14, is another case in point, and the well- known ' lead tree ' is a further illustra- tion. In order to prepare the latter, dissolve about twenty grams of * sugar of lead,' or lead acetate, in half a liter of water and place the solution in a white glass flask. Seaire a piece of dean zinc to a string and suspend the metal in the solution as shown (fig. 25). The metallic lead separates from the solution after some hours in beautiful plates or leaves, while the «inc slowly dissoWes. From the results of experiments of the kind just described, we can draw up the following table of four- teen metallic elements arranged in electro chf»mical order. Each metal is electro-positive to those above, and electro-negative to those below it in the list. Chemical Formul= ''■°"nula,' exnr^i T "'"'"'"'"' '=°"'P°'"'«I. and such an expression mforms us of what kinds of matter the body ,s composed, and in what proportions the several constuuents are present. Thus 'the formula NaC expresses the composition of rommon salt, H,0 tha of water, and AgNO, that of silver nitrate If we desire to find the formula by which the composmon of common salt is to be expres ed, we have to ascertain in the first instance o/'what e^! mentary forms of matter it con.sists. With the aid of Je methods of ,uaUt,Uive a^alysn we can pH that .t consists of the two elements, sodium and ^onn^ Our next step is to find the proportion of e«h element pre^^t, and this is accomplished by II ; Si ' fO Introduction to Experimental Chemistry, the methods of quantitative analysis^ and the results are stated below in percentages. 100 parts of common salt afforded on analysis : — Chlorine . • • , 60*62 Sodium ..... 39-38 1 0000 These are facts, quite apart from any hypothesis ; but in order to fin' I the relative number of atoms of each element present in the compound, we divide the percentage of each constituent by its atomic weight, thus— 6o'62 35"5» :i7 and 39*18 ----1=17 Hence there is an equal number of atoms of each element in the compound, aiitl the ratio of Na to CI is I : I. The formula of the body ij, therefore — iNa : iCl, or, more simply, NaCl, for each symbol represents one atom of the element, and the approximation of the symbols without any sign between indicates that the definite compound, called common salt, is the product of the chemical union of the two elements sodium and chlorine. .The chemical name ofihis compound is sodium chloride. Again, 100 parts of water afforded on analysis — Hydrogen . , . irir-f- ix=ii«iiora. Oxygen . . . _88^ -4-16= 5-55 or i. 1 00 00 • The atomic weight of chlorine. t The atomic weight of sodium. "f^ Chemical Formulce. formula - ^^ ' ^ ^^'^ '^ expressed by the analysis- ^ °^ "'*'" ""^"e aflorded on Silver , Nitrogen Oxygen ^3'5»- 08=: 588, or I. f'^-^ 14= -5878 „ X. 28^25^ '6=17656 „ 3. 100.00 The quotients, •c88i and -eft^a equal that we n,ayVa.rly set Ij h'e 'sliX d^"'"'" luent ; it is therefore a miH«,. ,.r • i- ^ cxperi- tennwe employ to divide rUlr'"''""^' ''•'''^'' the quotient is a's ne^;' pLs'sS , h'""'' Tf we have the same numl.er'^f ato„, 0^!",'' "h nrnfonrn-tTtr-?"-'^^^^^^^^ expressed by the foSl '••"" "'°"'"= ^*"°-'' *«» AgNO,. cal ro^i ^Tfb^ran^ r «'■"" °"'^ *"■'-'• its percentage compo L:!." be^'^I^h '" >"' "'"l this problem is exceedinX i^l i^;/"'"""" °' m &,i steg k to find the mo/auMr weigJU . the sum of the atomic weights of its consti- tuents—thus : — Ag . . . . N . . . . 03(16x3) Weight ot molecule Three sums in simple proportion then obtain the desired information. «=io8. = 14. « 48. = 170. 170 : IOC.-. 108 : 63 52 the percentage of Ag. 170 : IOC.-. 14 : &.23 „ „ N. 170 : 100/. 4S : 28-25 „ n O. lOO'OO The symI)ol AgNO., is called an empirical formula, because it ex|)resses only the atomic ratios of the con- stituents, ;ind iJoes not convey any idea as to the way in which the elements are grouped within the molecule. Jf however wc write silver nitrate thus, Ag-O-NOa, we seek to convey the idea that the atom of silver is united by means of one oxygen atom to an oxygenated group, NC)^, and this is termed a rational formula. We shall presently meet with -mmy such expressions. If we examine lists of cIh mnal formuije, we can easily select a number oi ^ .mplet;, such as the following : — Fonnuloe. Names. ^ j HCl • , • Hydrogen Chloride. (HF , , Hydrogen Fluoride. «. HjO • , Hydrogen Monoxide. f'h Atomiciths of Elements, Forniultv. 3. AuCI, 4. CCI4 5. PCI. ^5 MnF. 71 Gold Trii hloride. Ca bon Tctratl, ride. I'hosphorus Pentachlo- ride. Manganese Hexafluoridp All these compounds are binary ronpounds or .K«... Con,amn,g only t«o ki, ,1, of nfatter Tn ,'.,rce dis met elen.ents unite, they forma /-«„n.c!,", o 'd «,' B.H er nura.e, AgNU It is to be no,e.l that "re ter this o-Turs only m the names of bijry eompo.m". Aga,n the syml.ol written ,0 the left han.l fn S formula ,3 , at of the ..ost .l^tro-posiUr. J " w and th.s ., also a general rule, Ihou.h there a rZ excepttons ,0 it. Lastly, the mm.I.er „f a^om. , the bX^er " '=°"^"r "' '" ""^ -'-"'euLiii i!.l the consideration of these formula; leads u. H and CI, as well as H and F, comhine atom (or atom (anu as a matter of fact, in no other prop.-rtiS Ind are therefore .said to be e,,ual in chen.i^al po," r B« a s-ngle atom of oxygen can a.tntct and a'tach'o itself t^oo, but not more than two, atoms of hydrogen Ist water. Again, one atom of the metal^on U! Cham as u were three, but not more than three atom .ton. LT'"\" " «."" '"'^"'"'''^^■- «in.ilarly one atom of ca bon can fix the maximum number of four atoms of chlonne, as in carbon tetrachloride . .h. ..IT pno^piiorus atom, five of chlorine, as in 'the "pento! I Al MICROCOPY RESOLUTION TEST CHART (ANSI and ISO TEST CHART No. 2) 1.0 I.I 1.25 ■^ 1 M ■ 50 ""== 14.0 tb u KUU 1.4 II 2.5 1 2.2 2.0 1.8 1.6 jd APPLIED INA/^GE Inc ^^ 1653 East Main Street r^^ Rochester, New York 14609 USA ''^ (716) 482 -0300- Phone SSS (716) 288- 5989 -Fax 74 Introdjtction to Experimental ChemUry. chloride ; and the manganese atom, six of the element fluorine. We thus learn that the atoms of the elements differ widely in chemical power. The atom of man- ganese resembles in this respect an open chain of six hnks, each one of which can attract and hold strongly one atom of the element fluorine ; phosphorus, a five hnk Cham ; carbon, one of four links ; gold, one of three ; oxygen, one of two ; while the hydrogen, chlonne, and fluorine atoms are represented by single Imks. ° We can thus divide all the known elements into those whose atoms are I link, or Monad, like Hydrogen. Diad „ Oxygen. Triad „ Gold. Tetrad „ Carbon. Pentad „ Phosphorus. Hexad „ Manganese. This hydrogen or chlorine fixing power of an ele- ment IS often spoken of as the ' atomicity,' ' quantiva- lence,' or 'valence,' of its chemical atom, and is thus mdicated m the symbols by the marks shown •— H' 0",Au^Ov,pv, Mnvi.i ' But the atom of an element does not always act with Its full chemical effect : thus nitrogen acts as a pentad m sal ammoniac, NH.Cl, as a triad in am- monia, NH3, and as a monad in nitrous oxide, N,0 or laughing gas. Returning to our simile of the'chain] » The atomicity of each element is marked in the Table of Atomic Weights. 2 3 4 5 6 si Atomicities of Elements. 75 we say that the five link nitrogen atom may also act with but three hnks or one, the other links {i.e. centresof attraction, ' bonds,' ' equivalents,' or 'atomicities ') be- com,ng.atem or inactive in pairs, owing to mutual sa- tisfaction. If we regard the atom of nitrogen as a chain of five equivalents or links, we can easily illustrate the suppression of links in pairs. Let the following diagram represent the nitrogen atom, acting as a pentad, by an open chain of five l.nk« each one having but a single free point of attachment, i.e., at a bend or angle ; the chain should therefore consist of oval and triangular links. Fig 26. thus Ifwe close the chain by connecting the oval links, Fig. 27. three points of attachment are still free, and we have a representation of the atom of nitrogen acting as an apparent triad. s » ^n The next diagram represents the monad condition ot the nitrogen chain, in whiVh hn* rsr.^ k^^j • free for attachment. J i\ il: mm H 76 Introduction to Experimental Chemistry, The. disappearance of the points of attachment in Fig. 28. pairs is thus seen to be a mechanical ne- cessity in the case of the hnks of the chain. A triad clement, such as gold, would be represented as a chain of three links —one triangular and two oval, and this chain when closed would represent a seem- ingly monad gold atom, thus— Fig. 29. I' '1' We are acquainted with a number of compounds, in which the gold atom acts as a monad elem/int. An ekment which is never more than a monad, such as hydrogen, is best represerced as a single circular \v[i\., as if^has but a single centre of attrac- tion. In this way we can symbolise the elements of uneven atomicity, or pcrissads. The atoms of elements of even atomicity, or ajtiads, may be represented in a similar way. Thus the manganese atom acting as a hexad — Fig. 30. -yvvv\- Atomicities of Elements, 77 as a tetrad— Fig. 31. as a diad — Fio. 3» The element carbon is a good example of a tetrad atom, and may be represented by a chain of two tnangular and two oval Imks ; the closed chain corre- sponds to the carbon atom acting as a diad An element which is always diad can be best representeu by a chain of two oval links, as in the next figure, in this we represent the composition of the molecule of water, which, as we have already ZTr:. ''Tn """"^ ^'^"^ oio^yg^x, in union widi two aioms of hydrogea * Fig. 33. 0= Ma w 78 Introduction to Experimental Cltemistry. The circular links are atoms of liydrogen while the pa.r of oval links represent the .torn of oxygen" Such representations of monad, diad triad i^. elements may be easily made in a h;rr^me b^ cuttmg some stout copper wire into equaT e gThs o'f about lo centnneters, and bending each inf^ or other of the forms of hnk JTIZ Z^ can then be permanently coupled np into chai s so a' to represent .uoms ; and the latter can be employed ' m ,lh,stratmg chemical combinations in Zlt already pointed out. ^ In using these aids to study the hpamn«. carefully ayoid regarding them as tpr^f " LT'ol Sciairr"^^' "'' ■" ^^^'' - -'- ''^^ -e The student will do well to attach the 'atomicity' marks, as ,n the table, to all chemical symbol t w.ll thus be<:ome soon familiar with the relcL and combining values of the atoms. ^ ^ ^ SrequSn-"""""'^ '' ''""'"' ^^''^-'"- 2H' + 0"*=H'20". is intended to represent that two atoms of H and one .hat every „„k of e.ch cha,„ is'.llv e^d. ' " """"■ lhe//«jsign + signifies 'added to 'or ««,i,o« j II 4- Chemical Equations, yg of O, when brought together under the proper con- l^'tions, unite and produce the compound water. The number of atoms of each kind of matter on one side of an equation must evidently be equal to that on the other hence we say-//,. .,,,4./,,, o/lAepro^.a or products of a gtven change, must be equal to the sum of the weights of the bodies taking part in the reaction. Again — indicates that the compound water has suffered de- composition, and that the products are cne atom of O and two atoms of H. In other words, 18 c. grs of water can afford on decomposition 2 c. 2xs of H and i6c.grs. ofO. fc> • ^^^ xi, These examples are sufficient for the present, but many otners will be given as we proceed. It mu^t be added, however, that the student should not look upon every equation that complies with the above me as bemg necessarily a correct one ; it must not only equate, but represent the facts as accurately as possible: therefore the quantitative experimental test IS the only true one of the accuracy of an equation. i ' ' 1 f . II '5 \ «0 Introduction to Expr. imental Chemistry. Ill m CHAPTER VIII. EXPF.niMRN-TS WITH ACIDS, ALI'.AI.,ES, AND SALTS. Experiment 37 A-Take some common hydrochloric or 'muriauCaad, dilute it with about twenty bes' tnste and that a piece of blue litmus paper is red- dened when dipped into the liquid. Then add a small quantity of common • bread soda,' and note that brisk effervescence takes place, much gas being evolved. acid and Tf ^^■~'^t^ '°'"' '^"'' -f"''"' °' """c ac.d, and dilute it to the same extent as the former acid with water. Note that it also tastes swir ^^T Tf' '"^^ ^^"'"^ effervescence when bread soda is added to it. Experiment 39.-Again, take some ' oil of vit iol • or sulphunc acid, and dilute it with twenty times it's bulk of water, adding the strong acid to the water arjjp by drop, and stirring witli a glass rod. This solution is also sour, reddens litmus, and sets up ef- fervescence when bread soda is added to it ...H T^ ^^"'^"ded our experiments to all known ac ds which are soUible in, or can be easily mixIS with, water, we should find them to possess in a greater or less degree the characters detected in the All!,''"" ''•?'^'' "''■''''' '=''"'*'"' " '""'y <=al'=d acetic acid ^l^su™gac,dsm„Mbcca„,io„s1yha„med,«.hey«ege„e:r,t i t \ I Adds, Alkalies, and Salts. gj HCI . HNO3 H,S04 . HydrocI'loric acid. . Nitric acid. . Suiphuric acid. tasu ; that it does not redden blue litmus Daner hm ../^^^the colour of the paper .Xr.^C^X cause anv Iff' "'°" °^ " ^""'^'"^ ^^"^ ^^^s "Ot Ss appl;""^"^^""' °^ ''•" '^ -^ ^- -bb.es of Experiment 41.-DissoIve in a similar way a small t'st t r/ r"'" P"'^^"'' °^ potassium hydrLe,an1 test It in the same way. calle?'thr,''!f !j"rfP'^"'"^"'^'''^«h are often caJied the l.^ed alkalies,' or ' bases,' the latter term being generally applied to bodies which posset characters opposed to those of an acid. The foraute of the two bases are the following- NaOH . Sodium hydrate, or caustic soda. *^UH . Potassium hydrate, or car tic potash. canSlTlX';'''''""'' ^'"''^ ^'' '" ^h^^^«-^^ 'hey can easily netiirahse one another Experiment 4a.-Take a piece of caustic soda .1 ' I ti l\^ f M' j . ^jg Iv ■ ■* 82 Intf-odnction to Experimcutnl Chemist}'}'. about the size of a bean, dissolve it in about 30 c cs of water. Pour the liquid into an evaporatin- basin' f>^ fig. 34, and throw into the liquid a strip of blue litmus paper. Now. add, drop by drop, colourless hydrochloric acid, stirring the liquid in the basin after each addition until the litmus parser begins to assume a reddish colour. Tf we now taste the solution it has a salt taste, the action of it on litmus paper is neither acid nor alkaline, and the solution is said to be ;/^///r.//; the acid character of the hydrochloric acid iias been exactly counter-balanced by the alkaline Fig. 34. property of the caustic soda, and a salt is the product. If now we place the basin on the ring of the retort stand and apply heat, as shown in fig- 34, the solution soon boils, and the water is gradually converted into steam or vapour, and is driven oflf, or evaporated. When the liquid has been thus reduced to a very small bulk, little granular crystals separate. Pour off the liquid and allow the crystals to dry. They will then be found to possess the familiar characters of common salt. Therefore that body is produced when we neutralise hydrochloric acid by caustic soda. The formula of common salt is NaCl. The following equation expresses the change :»— ' If 'bread soda' instead of caustic soda be treated with hydrochloric, or other soluble acid, a gas- carbon dioxide, or Carbonic acid '— is evolved, as in Experiments 37, 38, and 39, AciJs, Alkalies, and Salts. Na^03 + «'C1' = Na'Cr 83 Sodium hy. drate, or caustic soda. Hydro- chloric acid. Sodium chloride, or common salt a-, or H in HC, b^he'Z"?:::™' "^""^ is con,n,on ni"e. ' "'"" '""^ '"^ "^"'''" »°'"tion £53 + g-No, = K,V0, + n^ Water. Potassium hydrate, or caustic potash. Nitric acid. Potassium nitrate, or * nitre.* the solution and hard crystal nf .1! , ^^^^"''^^ sulphate, K,SO., separate"': in Ims Ta';!!'-'- y^'OH) + H^^SO, = K.SO. + .„,o. ^•""^ ^SSr- ^ ^ requires for neutrahsation twice as ^!!!3 *Ji2L ■ NaCl . H,0 . CO. B-d^a. Hv.^ co;;;^„ ^^ ^-^^ '**"• add gas" Hydro- chloric acid. ■1: t ! ■J G2 I 11 m- i S4 Intyoduction to Experimental Chemistry. much (/>., two molecules) caustic potash as the mo ecule of nitric acid did. The reason for this is that the molecule of sulphuric acid contains two atoms of H, and, as we have already seen, each atom of H requires an atom of monad metal such as K to replace it .-. two molecules of KOH were required because the necessary number of atoms of K could not be obiamed in any less quantity. But, as we shall find later on,*it is possible to displace only half the hydrogen by K in such an acid as sulphuric and to form an acid salt, KHSO,, or acid potassium sulphate-a body which still contains hydrogen capable of replacement by a metal The compound, K,SO„ is the neutral or 'normal' salt » ^ Although It is not desirable to go much further in this direction at present, we can evidently draw the following conclusions from the foregoing experiments aad statements. 1st. That acids do not necessarily contain oxygen else the undoubted acid HCl could not belong to that class of bodies. ^ 2nd. That the acids used contain H replaceable by a metal, with the production of a salt This is true of «// acids. ^rd. That all acids do not contain the same number of atoms of replaceable H within their molecules. 1 hose acids containing one atom of replaceable H, ' A group of bodies termed * double salt. ' is known ; com- Z^^lT IS a good example of such a salt, for in it we have suTohate''%rr '^^''>f\^'^^^^^ sulphate and aluminium K ^n A . Tc^^?'"""'^ °^ anhydrous alum may be thus writtea- Acids, Alkalies, and Salts. or.bas,c hydrogen; as it is sometimes called are . ™ed mouobosic acids, and those containing two t^'acids^ir'-'^'""^^'''^- ^'*'- -d''-^- "a, ac ds, likewise exist, containing respectivelv three and four atoms of basic hydrogen. General ' monobasic acids are the only members of the clas ' which do not form acid salts. It may be added that we can recognise in all salt, an electro-positive constituent-the metal Vltl tld S/r"!"" f ^'-"-%'ative constituent or actd,a,/Hlc When the latter ,s an element such a, ™o J?' " '^ " '"'"' """'■' ""' '^ -^ "" •« KNO,, or SO, m K,SO,. it is called a cou^ln^ / I Ji;! 86 Introduction to Experimental Chemistry. CHAPTER IX FURTHER EXPERIMENTS WITH HYDROGEN. HvDROGEN. Symbol H'— r T l^.t «^«^/if^ _-.2. — ihis element, which wae discovered by Cavendish in X766, has already bl^ expenmented with, and we have found it to be " colourless modorous, and extremely light gas which s.af rL^vsnrirweZhr^ ^'- ^--•^ een'SrIt''* ^ ''■'''^' terrestriarstorehouse of hydro- fart'h « ^ ^ °'''" '" "'^ fr«« ^'^te upon the volcanoes. It is a constituent of animal and veeetable tissues, and of all true adds. vegetable The hydrogen can be liberated from water as we Which case the compound is resolved into its consti- H20=2H + 0. wate^'^whl"*"'* ^'•rH>''J^°gen is also separated from .Te s ze o " 7eZ?"' " ^'''' °' "^^ ■"''-' ^odinm dish Th/ K^ i°™^ '=°''^ '^^'^^ contained in a a *« amplest expn^ssion If I I * i \\ HN 94 Introduction to Experimental Chemistry. body left in the tube chiefly consists of metnllic iron in a very fine state of division, in which condition the meta eastly takes fire, if the warm powder be poured out through the air.'- In this condition the metal is said to \i& pyrophoric. Fej03+6H=2Fe + 3H20. Thus prepared from pure oxide, the metal ronsti- tutes the Ferreduit, or Fenum rcdactum of the British Pharmacopoeia. Hydrogen gas is absorbed by water in very small proportions, loo cubic centimeters of the latter dis- solve only 1-9,^ c. cs. But some soli.i metals absorb hydrogen, noiably the metals platinum » and palladium. The atter take up no less than 370 volumes of the gas at ordinary temperatures. M ^lt?7r^^" ''"' ''"'" '■'•^^""y condensed by M P ctet of Geneva to a liquid, exhibiting steel-blue metallic \^,r^, under the enormous pressure of 650 atmospheres, and at a temperature of 140° C. below v^o: 1 ^t' u'f' *''"■'*''""'• *° ^ ^^Sarded as the vapour of a highly volatile metal. ' The same weight of iron in the form of wire would but slowly rust or oxidise when exposed ,0 the air, the Ibove ex penment therefore well illustrate., the effect of a fine s,I!e"; division in determining rapid chemical changes For a descripUon of the Dobereiner lamp see Platinum. 95 CHAPTER X. EXPERIMENTAL DETERMINATION OF THE VOLUME OCCUPIED BY ONE CENTIGRAM OF HYDROGEN. Tlt^r ^^"'^^^ ^'^'""^ ^'^"^ Experiment i8 that ac d"^&:r' H '' '^'^^^^" ''' '^ -^1-d from aciauiated water dunng the solution of 122 c grs of pure metalhc magnesium; we, therefore know h^w to get our unit weight of hydrogen. In he exnen ment cited we allowed the gas to escape we 3,l"i now collect the gas and measure it. Experiment 54.-Obtain a tube about 40 c ms long and 2 c. ms. internal ^ ^• c'lameter, graduated into 130 cubic centimeter divisions, a, % 39- Dilute 50 c. cs. of oil of vitriol with about a liter of water in a jug, and throw into the liquid a few scraps of metallic zinc. Hydrogen will be developed and the liquid will have nearly or quite satu- rated itself with the gas in a few minutes. Next pour some of the diluted acid into a tall -ffow „ea.er i, a„u, naving filled the graduated tube Fig. 39. IM I i il .1' 111! • . 11 ,t 96 Introduction to Experimental Chemistry. completely with the same liquid, invert it in the acid in the bjaker and support it as shown. Now weigh out 12-2 c. grs. of pure and clean metallic n)agnesium— the weight of the metal that we know will liberate i c. gr. of hydrogen—and place it in the bottom of a narrow test tube, c, to the middle of which a wire is attached to serve as a handle. The tube is then filled with water and plunged under the surface of the acid in b, and the upturned mouth of tiie test tube rapidly brought under the mouth of the graduated tube, and even passed up into the latter. •Very soon the acid liquid displaces the water in the test tube and th6 metal is attacked ; the hydrogen gas evolved passes into the inverted tube and there collects. When the last trace of magnesium disappears the action is at an end, and we have confined in the tube the volume of pure hydrogen gas that weighs i centigram. Now depress the tube in the acidulated water until the liquid within and without the tube stands at the same level, and read off the volume of the enclosed gas. Immediately afterwards read the tewpmitiire as indicated by a thermometer in the neighbourhood of the apparatus, and the pressure as indicated by a barometer. A more precise experiment can be made with the apparatus, fig. 40. The stand a supports a tall glass cylinder, r. Through the large india-rubber cork which closes the lower opening of the cylinder the U tube c is passed, great care being taken to avoid breaking the small t connector c. The outer limb of the U tube is provided with a glass tap t. The limb within the tall glass cylinder is sufficientlv wide t^o/ume of I c. gr. of Hydrogen. to contain 150 cubic centimeters in the ex- panded portion, which, in our apjmratus, measures sixty centi- meters in lent^th. The graduation cannot be conveniently carried beyond fiftlis of a cubic centimeter. At the point shown an india- rubber tube ,g is at- tached, whicli can be closed at will either by a good clip or by a stopper of glass rod. The glass side tube c serves to connect the measuring apparatus, filled to o with water, with the generating vessel D, which is a long and wide glass tube placed within the cylinder. The glass t tube E is connected by means of rubber tubing with r, while one limb passes through the india-rubber cork of d, and the other is con- nected by another Fig. 97 98 Introduction to Experimental Chemistry. piece of rul)bcr tubing with a fine tube of the long pipette F (of about 20 c.cs. capacity), which {)rojects through the cork. .This connection must be suffi- ciently long to admit of the clip being applied as rhe large glnss cylinder b is filled with water, in ordei a maintain a steady tcmpeniuire, the value of which can be known by means of a thermometer immersed in the water. A determiiiation is made with this apparatus in lie following way: — H.vjng disconnected the T tube E from c and removed the clip, the tube d is taken out of the water of the cylinder, the cork carrying the pipette, &c., withdrawn, and then 12*2 c. grs. of magnesium introduced into the tube d. Before re- placing the cork the pipette f is filled with diluted sulphuric acid by suction at e, while the small glass tube opening on the under side of the cork is closed by a finger: the clip is then applied. The exterior of the pipette is now washed with a little water, and the cork, with the apparatus attached, is then replaced in position; the tube d again immersed in the water of the large cylinder, and the joint between e and c securely made. Before making the connection the water in the graduated tube should stand at the zero of the scale, but after securing the joint the pressure within the apparatus is usually greater than that without. As the air in the tube D cools down to the temperature of the surrounding water, contraction takes place; but should the water not return to the zero, equilibrium is at once restored hv nnpninor the finp ir: '!a-r!ihh*»r fnK* • t (^K^^TA VVtl,^^ ^' I a few S *i Volume of I c. gr. of Hydrogen. 99 seconds, and then closing in such a manner as to prcyciu any imssible escapf of gas. The acid is brouglu in contact with the mai^ntsinm by removmg the chp fron. the india-rubl,;, ,2 connected wuh the p.pette; the r .. nt then fa upon the metal at the bottom of the tuOe D. Hydro gen >s volved and .1 .places water from ., the Ikp °d the U tube by a!lo«i„g the water displaced to run off by means of the tap t. When the evolution of gaf tt ?r • '. r'"" '"'^' '^ "^^"■^''^'1 by .neans of r!!-t '' T^ '^\ '°'"'"^ °f S^^ P™fl"<^"l "> the reacfon then read off on the graduated tube ; the tet.perature of the water in the cylinder . i, ,1 en thTti'r '/' '"'!,'' **^ '"-"'S'^' °f "^^' baron,cterat cIlcuTatS'™^^"""^-^"'*'^---''--''/ A student obtained, as the result of an exi eriment madetn this way, xai cubic cemimeters of "c bu moist hydrogen, measured at 16° C. and 7s= milli meters pressure, during the solution of 12-2 c l s ■ of magnesium in acidulated water. • fc • "i So far for our experiment : we now have to find he volume this gas would occupy if dry and measured at o C. and 760 millimeters-the ' standard temp, ra- corrected, for reasons that will presently appear The corrections are three in number-namely: fo, temwn of aqueous vapour, iox pnssure, and iox tem. r . ^, .xxi^^uiiiy m rne saiupie of metal. H 2 I S t * I ! ,J 100 Introduction to Experimental Chemistry, perature, and we shall deal with each in some detail in order to illustrate the method of solving such problems. I. Correction for tension of aqueous vapour.^ — We find from the annexed table of tensions for different temperatures that at i6° C. the pressure exerted by vapour of water =13-5 mm., that is to say, the pressure exerted by the aqueous vapour within the tube tended to balance the atmospheric pressure to the exter.t of a column of mercury of 13*5 millimeters in height ; therefore the actual pressure under which we measured the confined gas was 755 — 1 3 "5 =74 1 "5 millimeters of mercury. Tensions of Aqueous Vapour. Degrees Centigrade O 5 10 II 12 ^3 15 16 17 18 Degrees Centigrade M i riitii Tensions in millimeters ot mercury 4'6o 19 6*53 20 9-16 30 979 40 10-45 50 iit6 60 II "90 70 1 2 '69 80 13*53 90 I4'42 100 15-35 2. Correction for pressure. — We learned from Ex- periment 28 that when a confined mass of gas was ' The student must refer to a work on Physics for full details of corrections of ffasos^ Tensions in millimeters of mercury i6'34 i7'39 31*54 54-90 91-90 14870 23300 354'6o 525-40 76o'oo Correction of Gases, loi compressed, its volume or bulk diminished with in* crease of pressure, and conversely, increased in volume as the pressure diminished Thus, if the pressure on a given mass of gas be doubled, the volume is reduced to one-half, and if trebled, to one-third, and so on. When the original pressure is restored the gas returns to its original volume. If now we reduce the pressure to^ one-half, the volume of gas is doubled-, if to one- third, the volume is trebled, and so on. These facts' find expression in the law of Boyle or Mariotte : * The volume 7c>hich a gas occupies is inversely propor>. tional to the pressure to which it is subjected: Now 741-5 mm. being a lower pressure than the standard 760 mm., our gas would occupy a less volume at the greater pressure ; how much less we find thus— 760 : 741-5 /. 121 : X (>,; =118-5 CCS.). 3. Correction for temperature.— Eyi^&x\m^\\\. 28 also showed us that gases expand equally when heated, and contract when cooled. If we begin with a given volume of gas at the temperature of melting ice, i.e. 0° C, and measure the gas as we raise its tem- perature at a definite rate, we find that for each rise m temperature by 1° C. the gas expands ^|,rd of its volume at 0° C. That is to say, 273 c.cs. at o°-C. expand to 274 c.cs. if the temperature be raised to 1° C. ; or to 280 c.cs. if heated to ')° C. ror to 289 ccs. if heated to 16° C. ; the pressure throughout being constant. • Similarly, 289 c. cs., cooled too° C. contract to 273 c. cs. Hence we can easily find the volume that 118-54 ccs of gas at 16° C. would occupy if cooled ii tilUb- 289 : 273 ••. 1185 : X (K=iti-9c.cs.). I I' f iff i mm i'"- * 102 Introduction to Experimental Chemistry. The final result is that i centigram of pure dry hy- drogen, when measured at o° C. and 760 mm. pressure, occupies as nearly as possible 112 ccs. As we have already adopted the centigram as our unit of weight, we may conveniently take the bulk of i c.gr. of hydrogen, measured under standard conditions, as our unit of volume, and call it briefly a vol. Thus when we speak of i vol of any gas, we mean 112 ccs. of it measured at 0° C. and 760 mm.' The zW as thus defined is a small and convenient quantity of a gas, which is well within the capacity of the ordinary measuring vessels used in laboratories ; moreover it possesses the great advantage over the liter as a unit of gaseous volumes, that its weight in hydrogen is identical with the atomic weight of that body in centigrams; consequently a vol of any other elementary gas weighs the number of centi- grams indicated by the atomic weight of the element. Thus — Name of gas Hydrogen Oxygen . Nitrogen Chlorine Atomic weight I.O 16.0 14.0 35-5 Weight in centigrams of I 7W(at o°C. and 760 mm.) or 112 c. cs. 1.0 c. gr. 16.0 „ 14 o 35-5 A number of^/^/ tubes may be prepared by cuttin- a good cylmdncal glass tube 4.2 centimeters diameter into lengths of 7.8 centimeters, one end of each tube is then close 1 by a glass plate which is cemented on. Each tube or jar should hold 112 c cs of water We have a number of these jars prepared and hlled with different coloured wool, in order to illustrate the volume reiauons of elementary and compound gases. Chemical Calculations. 103 Hence in order to find the weight of a given bulk of gas, for instance, of 900 cos. of hydrogen at stan- dard temperature and pressure, it is merely necessary to proceed as under :-^ ^ 112:900/.! : X(X=8o3c.grs.}. But if the gas were oxygen— ii2:9oo.M6: K(K = 128-57 c.grs.) ^. n X at. wt. Generally — K = 112 Smce the w/ of hydrogen represents the semi- molecule of that element, the molecular weight being renrZn, T ^'''''''' '"'" '^''^ ^'^^ 5^)' ">^ ^'"^"'^o represents the sem.-molecule of any compound gas- water gas for example-consequently the weight of one po/ of a compound gas is half the molecular weight m centigrams. Thus— Name of gas Molecular Molecular I roimula i weight Hydrogen "Water gas Hydrochloric gas . Ammonia , Marsh gas Carbon dioxide Carbon monoxide acid H, ii:o HCl NH3 CII, CO., CO" 2 18 36.5 17 16 44 28 Weight in centi- grams of one 7JoI (at o"C. and 760) or 112 C. CS- I 9 18.25 8.5 8 22 c. gr. >> I) >i if tt it The numbers in the fourth column are identical kMI Tl''".. S^^^''!- °/ the gases referred To 111 S ffll I; V 104 Introduction to Experimental Chemistry, in centigrams of a given hulk of a compound gas—^ox instance, of 1200 c. cs. (=i'2 liters) of ammonia gas at standard temperature and pressure— we say 112 : I200.-.8-5 : K iX=9i c. grs.). If the gas were hydrochloric acid gas— 112 : I200.M8-25 : x (X = i95-5 c. grs.). Generally — K «_x sp. gr. 112 when n = the number given in cubic centimeters of dry gas at 0° C. and 760 mm. Instead of the' z/^/, we may use the liter as our unit of volume. The weight of a liter of pure dry hydrogen at o°C. and 760 mm. is -08936 (this weight is called by Dr. Hofmann a crith), A liter of oxygen weighs 16 criths, of chlorine 35-5 criths, of nitrogen 14 criths, &c. A liter of water-gas weighs 9 criths, of ammonia 8-5 criths, of hydrochloric acid gas 18*25 criths, &c. We have already learned from Experiment 29 that the specific gravity of the compound water gas is half its molecular, weight; and the above table tells us the same thing for other compound gases. If then we have presented to us a gas of unknown composition, we can determine its molecular weighthy first taking its specific gravity, as in Experiment 27, and that vakn, when doubled, should give the molecular weight of the com- pound. Thus, ammonia gas has the specific gravity Z'^, its molecular weight is therefore 8-5x2= 17. ^ Hydrochloric acid gas has the specific gravity i8-2^ ; the molecular weight of the compound is therefore 18-25x2= 36-5. Absolute Temperature. Fig. 4t. There are a few exceptions to this important rule, Which u'lU be noticed in the proper place ^ ExperimentSS.-TnkeaUtubeoftheformshown m lig. 41, with Innbs 60 centimeters long. Let one Jimb be hermetically sealed at the top and the other open. A stopcock is provided near to the bend of the open linib- Now fill both limbs completely with mercury so as to expel all air, then insert the cork u through which passes the end of a small tube open at both ends, and filled with fragments of calcium chloride. Now open the stopcock s, and allow about ' half the mercury to flow out, while //ryair enters through the drying tube c. Next transfer this dry air to the closed lirub by inclining the tube suffi- ciently. Then bring the mer- cury in both limbs to the same level by drawing off some through the stopcock. Should the volume of air in the closed limb be less than half the tube full, after levelling, transfer sufficient to make up the de- sired volume, and level again, but this time by remov- ingf the cork and nnnrinrr ;«f^ 4.1 !• , ^ . ---— r --o "^«-^ i"c open iimo suJiicient mercury. T he cork and tube c need not be replaced w di Ml i>, ' . I- « • I iiiii 106 Introduction to Experime?ital Chemistry, We have now a confined xnass of dry air in the closed limb. Place over this tube a glass jacket/, which IS stopped below by (he cork /, through which the closed limb passes, and the small side tube m. Fill up the space between the exterior of the U tube and the jacket with pounded ice. This will soon cool down the air in the tube, and the gas will con- tract m volume. When no further contraction takes place, again adjust the level of the mercury in the two hmbs, and mark off as accurately as possible in the outer tube the position of the mercury in the closed hmb. This iparks on the tube the volume occupied by the dry air at the temperature Ox melting •• ^, i.e. at 0° C. Now pour tepid water into the jacket/ ; this will melt the remaining ice,' and the water will flow off through the side tube m, which is opened or closed at pleasure by the pinchcock or clip/, that compresses a piece of india-rubber tubing attached to m. When the ice has melted, and the water been drawn off, remove the pmchcock/, and connect the tube h, by means of vulcanised tubing, with a flask from which a good cur- rent of steam can be obtained by rapidly boiling water contained in it ; the steam rushes through the jacket and the excess may be allowed to pass off into the air through the tube in. As the air n the clos'id hmb becomes heated it expands until it has acquired the temperature of the steam. When it ceases to ex- pand, adjust the level of the mercury as before, and mark on the tube the volume occupied by the dry air 9X the particular temperature. Now divide iha interval between the two points Laiv of Charles. xty marked into loo equal parts, by transferring the length to cardboard, and plotting ofif the intervals With the scale thus obtained, measure the distance from the position occupied by the mercury when the gas was cooled to the temperature of melting ice, to the sealed top of the tube, and it will be found that the end of the tube is reached, as nearly as possible at 273 DIVISIONS of the scale. This point is termed the absolute zero, for it is evident that the contraction of the gas could not go beyond this point, even {{ it con- tracted with regularity nearly to its limit. U then we represent the top of the tube as absolute zero, or 00°, the enclosed air at the temperature of melting ice will occupy the position 273°, and that of free steam the position of 373°, on such a scale of absolute temperature ; hence the ' law ' enunciated bv Charles that the volume of a given mass of gas, under constant pressure, ts directly as its absolute temperature, i.e., as Its temperature measured from absolute zero. This IS 273+/, t being the number of degrees above the freezmg-pomt on the scale of the centigrade ther- mometer. f f i X08 httroduction to Experimental Chemistry ill i I I t CHAPTER XI. EXPERIMENTS WITH OXYGEN AND OZONE. OxYGEN-«5>w^^/, 0"=i6. I F^/ wei^r/is i6 e. grs. Molecular wei^ht=^2,—\N(t have already proved conclusively that oxygen is not only a constituent of water, and that it forms |ths of that body by vei-ht, but also that it is present in atmospheric air. Later on, we shall find that it is met with in most of the chemical compounds of which the solid crust of our globe is composed, but in the air alone do we find the element m a free state (/. e. not in chemical combination), though mixed with four times its volume of another gas called nitrogen. We do not possess a convenient process for the direct separation of oxygen from air, hence we always prepare it from one or other of its compounds. Oxygen can be '• prepared from water by electrolysis, as already described, Experiment 22, H,0=2H + 0, or more conveniently by heating certain bodies which easily yield oxygen— ior example— mercuric oxide, or the salt called potassium chlorate. Experiment 56.— take a tube of hard glass, /, fig.^ 42, closed at one end, and fitted with a cork and delivery tube as shown. Place in the tube about 200 Fig. 42. Experiments zvith Oxygen, 109 c. grs. of red oxide of mercury, the * red precipitate ' of ihe druggists. Heat gently at first, and then increase the temperature. Gas will soon escape from the delivery tube and bubble through the water in the pneu- matic trough. After expulsion of the air, the gas collected is found to have the property of rekindling a match with a gib wing tip, and is oxygen ; at thesametimeitwillbe observed that bright metallic globules con- dense on the sides of the tube /, and, if the heat be contmued long enough, the pure mercuric oxide is wholly resolved into oxygen gas, and globules of the liquid metal mercury or quicksilver. Thus :— Hg" O" = ^-^ , Mercuric oxide. Mercury. + o Oxygen.' This process is not an advantageous one for the preparation of oxygen in quantity, but it possesses special interest, since it is the method by which the element was first prepared by its discoverer, Dr. Priesttey, in'1774. Oxygen can also be obtained by heating manga- . o.e ^xw ^. i;.a. ui ngu anord i6 c. grs. of O, the weight of one vol at o°C. and 760 mm. , .;: \.:. 1 1 !l II 1 1 o Introduction to Experimental Chemistry, nese dioxide, in which case the following decom- position takes place— 3MnO,=:Mn3 04-f2 0. Barium dioxide and other similar bodies also afford the gas, and the processes will be described under the respective compounds; but the most convenient method is the following : — Experiment 57.— Fit a flask— a clean Florence oil flask answers well— with a cork and delivery tube Fig. 43. as shown in fig. 43. Break up some crystals of the salt potassium chlorate (KC102)in a mo.tar, then mix with about one-third of its weight of black oxde of mang:anese (manganese dioxide), and pour the mix- ture into the flask, but resen'e a small portion and heat the latter strongly in a test tube before applying heat to the contents of the flask. If no violent action takes place when the small quantity is heated, the manganese used may be considered free from any dangerous impurity, such as charcoal, soot, or lamp th which it is sometimes accidentallv mixed KIm.I ui.13.-^ n., TV 1 Preparation of Oxygen, III or even adulterated ; ' then heat the flask. After expulsion of the air, the gas can be collected \\ several jars or in w'"de.mouthcd bottles over the water )n the pneumatic trough, as ico ^ CCS. of water dissolve but 2*989 ccs. of \ wimmm W^ gas at 15° C. If it be desired to store a (]uantity of the gas for a number of experiments, the gas-holder shown in section, fig. 44, is to be emi)loyed. The heat resolves the potassium chlorate into oxygen gas and potas- sium chloride, which latter remains in the flask at the end of the operation along with the black oxide of manganese ; for the latter body is not known to undergo any chemical change during the operation, though its presence undoubtedly enables the oxygen to separate at a lower temperature than it other- wise would. The following equation represents the ultimate change : — K'C1'0"3 = K'Cl' + 3O Potassiijm chlorate. Potassium chloride. The potassium chloride left is easily soluble in water, whereas the black oxide of manganese is insoluble ; we can take advantage of these facts in order to sepa- rate the two bodies. Add some warm water to the contents of the flask, allow the mixture to stand for half an hour or so, and thf n throw the dirty black mixture on a paper filter. The clear liquid passes ' Several fatal accidents have resulted from such admix- ture. I¥ y M '..fl .S&.i 112 Introduction to Experimental Chemistry, through and is collected in a l)eaker, while the solid pnrticles of the insoluble manganese dioxide are retained by the filter and thus separated. When aH the liquid has passed through the filter, place the dish on a ring of a retort stand, and evaporate (as in Expeninent 50) until all the water is removed, and a i!ridf '""^ ^"""^^ ''"''''"'• '^^''' '' '^^ potassium With the aid of the equation just given we can easily calculate the weight and the volume of pure oxygen gas, at 0° C. and 760 mm. that a given weight say 100 cgrs., of the pure potassium chlorate can aficrd T J°"?^^^^^ '^^''^^P^^'tio"- '^he molecular weight of K UO3 is 122-6, and this is found by the general method of adding together the weights of the con- stuuent atoms, /.. K=39T, 0=35-5, 3 0=48 ^10 X 3}. bince all the oxygen is evolved when the salt is strongly heated for a suflicient time, it follows that 122-6 cgrs. of K CI O3 can afford 48 cgrs. of O. Hence the weight of gas 100 cgrs. can yield is— 122-6 : ICO.-. 48 . K ( K =39-15 cgrs. Arts.). We have now to find the volume:- 16 cgrs. of oxygen at 0° C. and 760 mm. measure 1 z'^/( = ii2 c cs ) • now ' 'I > 16 : 39-I5.MI2 : K (X=274 ccs. Am.). The general answer therefore is- 100 cgrs. of pure potassium chlorate afford 39-15 cgrs. of oxygen gas, which occupies the volume of 274 ccs. at 0° C and 760 mm. The same method is employed in all similar calculations, as for instance in the calculation of the Experitiieiits toit/i Oxygen. »I3 volume of oxygen that can be collc< ,cd on heatins a given weight of red oxide of mere ury ' VVe already kno^v that oxygen gas is colourless, in- o< orous. and a powerful supporter of .omhustion. th^l '' '•■"■' °' °"' -^fsas already collected n,ake tne lollowino experiments -^ Experiment 58 -Take a small Unnp of charcoal and tw,st a piece of copper wire round it. Hold the char, oal m the spirit or gas flame tmtil it is kindled, and then plunge it into a jar of oxygen. The char co^ burns energetically in the pu'fe gas, enii fng much hght and heat. In this and si.„ilar experf men s it is well to provide a cover for the jar of cardboard, through a hole in which the wire passes. VVhen the combustion is at an end remove the char- coal ami pour into the jar some clear lime water- no e that the latter becomes milky when the mouth shaken. The reason is that the product of the com- bustion of charcoal (carbon) in oxygen is a gas called carbon dioxide, this forms insoluble a,/i, or calcium carbonate, when it meets with lime water (solution of caelum hydrate); the latter is, therefore, a Ust for the gas. 1 hese reactions are thus represented— C + 2O = CO2 " ^ ' ^ , — ' Carbon. _ ^ Carbon dioxide. weight of a body required to afford a given volume of gas. ... , " '""" "^.^^^^ ^« '^^^<^^ in a jar of pureoxv^en it do.« iiut Dccome lurbid. " '" li t li '^1 m 1 14 Introduction to Experimental Chemistry. Then— CO2+ Ca"(0Hy2 = Ca^'COa + HgO. Calcium hydrate. Calcium carbonate. Fig. 45. The chalk is the calcium salt of an acid HXO3 formed by the action of water on the gas CO.,. Experiment 59. — Place a small quantity of sulphur in the iron spoo'.i, fig. 45, and kindle it, when feebly burning plunge it into a jar of oxygen. The sulphur burns with a beautiful blue flame, and )\ gas — sulphur dioxide— havi. g "N-' A a suffocating oclour, is the product. Remove the spoon, pour some water into the jar, close the mouth with the hand and shake. Now test the water in the jar with some blue litmus paper. It ill be found to redden the paper, and to have a sour taste. In the first instance — S +20= SO2. Sulphur. Sulphur dioxide. The sulphur dioxide gas when dissolved in water pioduees sulphurous acid, thus — SO2 +H20=^ H.SO.,. Sulphur dioxide. Sulphiircus acid. Experiment 60.— Clean the spoon used in the last exnerilYient nnd nlnrp in if n vprt/ email Ar^r .^."^ Experiments with Oxygen. 1 1 5 of phosphorus.' Kindle and plunge into a jar of oxygen. It burns with great brilliancy and produces white fumes in abundance; these deposit a. a white l)owcler on the sides of the jar, if the latter be nearly dry. Remove the spoon and pour some cold water into the jar and shake as before. The white sub- stance disappears, dissolving in the water; this solution also is found to contain an acid. The first change is' thus expressed — 2P- ,+ 50"= Then— Phos- ohorus. Phosphorus pentoxide. P2O5 +H20= 2(HP03). Phosphorous pentoxide. Metaphos- phoric acid In each of these experiments, then, an oxide was the product of combustion in oxygen, and the oxide produced an acid when added to water. The name of the element^ signifying 'acid producer' was given m allusion to this property, but it is now known to be only one amongst several elements which can give rise to compounds exhibiting acid characters. Experiment 61.— Take a piece of thin iron wire and coil it into a spiral, twist one end of the spiral round a small sfjJinter of wood coated with sulphur. Now set fire to the latter and plunge the coil into a ^ ' Take care to cut this under water, as phosphorus is easily Ignited by friction, and it burns with great violence xa '^ i. Fig. 46. 316 Introdtiction to Experimental Chemistry. large jar of oxygen, as shown in fig. 46. The sulphur and the match burn and soon raise the temperature of the iron to such a point that it undergoes strong combustion, molten drops falling from the point of wire into the water covering the bottom of the jar. When the combustion is ended, the jar is removed and the solidified drops examined. They con- sist of an oxide of iron, but they do no^ produce an acid with water under any conditions, nor do they exhibit any alkaline or basic characters. 3Fe + 40=Fe304. Again, when hydrogen burns in air or in oxygen, it produces 7vater, which we already know to be a liquid that does not present the ordinary characters of an acid or of a base. We thus learn that all oxides do not produce acids, though some do; further that some oxides do not produce either acids or bases, and may be classed as indifferent oxides. Experiment 62. — Place a small piece of the metal sodium in the little spoon, shown in fig. 45, heat the metal until it fuses and begins to burn, plunge then into a jar of oxygen. The sodium produces a white or nearly white body (NajO) which dissolves in water with a hissing noise and produces a liquid which ia strongly alkaline to test paper. Thus — 2Na' +0"= Na'oO". • Sodium. Sodium oxide. Then — Experiments with Oxygen. ny Na^O +H20= 2(NaOH). Sodium oxide. Sodium hy drate, or caustic soda. A similar experiment can be made with the metal potassmm. Experiment 63.~Finally, burn a piece of mag- nesium wire or ribbon in air or oxygen, and throw the white sohd produced (magnesium oxide, or magnesia, ) into a small quantity of water. » Although he body does not seem to dissolve in the water the latter acquires an alkaline reaction if allowed to stand for some time, and a piece of reddened litmus paper left m the liquid becomes blue. Mag- nesium Magnesium oxide. Then— Mg'^O :'0" +H20=Mg''(0H)V Magnesium oxide. Magnesium hydrate. oxid'e-^'cao'''„l,'""'' "^ '""""°" * l'"^'''™^.' or calcium oxide CaO-used in morlar, when added to water falls to powder and dissolves to a small extent, uflording an a'ka ine ol ^ ovTr :L: t: X"\ '' .""^ ' '""''' "-"'"^ °f watt be poutd over the lime, it is absorbed and the mass crumbles to a ^wder zrVh :tri^.^'!-:.s^'"")c™-H hea.r:tg Part III.) ""'"" " '"'' """^ """ ''^^^'- i^ee *""her 11 1 1 8 Introduction to Experimental Chemistry, % RwhIBSb i ■P? Our results may be thus tabulated — Acid producing Oxides — Carbon dioxide Sulphur dioxide Phosphorus pentoxide Indifferent Oxides — Water Iron oxide . • , . Basic Oxides — Sodium oxide .... Potassium oxide Magnesium oxide CO2. SO2. P2O5. 'H,0. Fe304. Na20. K2O MgO. The members of the first class are termed acid anhydrides, and those of the third class, basic anhy- drides, because the corresponding acids and bases can yield these oxides when the elements of water are abstracted from them. Experiment 64.— Fill a stout gas jar with water,i and invert in the^pneumatic trough in the usual way, introduce oxygen until one-third of the water has been displaced, and then hydrogen until the jar is filled with gas. Slip a glass plate under the mouth of the jar, remove the latter from the trough and apply a flame. A violent explosion takes place, as in the .similar Experiment 23, and water is produced, as we nave already proved by Experiments 24 and 25, when we exploded the mixture of "gases under such conditions that the resulting water could be observed. lA/P cV»oll -n/Mir «-Mol:r£> fU^-v ^,.^^^.._ l-.x. 1 • .1 Fig. 47. Oxyhydrogen Flame. 1 19 Experiment 65.— Connect the tube h, fig. 47, with a small rubber cloth bag full of hydrogen by means of a flexible tube, and with a similar bag containing oxygen gas, the stopcocks s and s' being closed. Apply ^^//.^/ pressure to the bags, and turn on a little hydro- gen by cautiously opening the stopcock s ; the gas passes through the meslies of the wire gauze g, placed over th^ opening of both tubes, and enters the little chamber c, whence it passes by the narrow tube t, to the jet at which it is to be kindled. While the hydrogen burns, producing a flame 3 or 4 centimeters long, turn on tlie oxygen gradually by opening s'. The flame shortens considerably as the proportion of oxygen increases, up to a certain point, but if too much oxygen be introduced, it is extinguished with a snap, then the stopcocks must be turned off and the same plan of lighting repeated. When burning properly, the oxyhydrogen flame is of pale blue colour, and emits little light, but it is intensely hot—in fact the hottest Vxio^fxx flame. a. Introduce into the flame the end of a piece of platinum wire. The metal melts eae:ily to a globule, though it is almost infusible in our most powerful furnaces. ^ b. Introduce an iron or steel wire ; it also melts quickly, and burns, emitting brilliant sparks. - ^.^-.-^ ix. tii^ liaiiie a picLu 01 quickiiiiit;, or one of the cylinders of the same material, commenly sold If 1^ 120 Iniyoduction to Experimental Chemistry, for the purpose, /, fig. 47. The lime does not m-It, but it becomes intensely hot, ahnost white hot, and emits a brilliant light. This is the oxyhydrogen, or * limelight,' which is used for various illuminating^ purposes. ** Ozo^Y.— Symbol, O3. Molecular weight^^%. Experiment 66.— Pour a layer of water on the bottom of a tall and wide-mouthed bottle, and intro- duce a stick of clean, freslily-scraped phosphorus, takmg care that the latter shall not be immersed in the water through more than one-third of its length. Partiafly close the mouth of the vessel with a piece of card-board, and let it stand for half an-hour or so. i\1iitish fumes soon appear, and ultimately fill the bottle : on opening the latter, a strong and peculiar smell is perceived, and when a strip of moist starch and potassium iodide paper » is plunged into the air of the bottle, it is quickly discoloured, while pure air is almost without action upon the paper. The peculiar smell and the effect upon the test paper are alike due to the presence of a small quantity of a body discovered by Schonbein in 1840, and named by him Ozone? The strong smell noticed when an electrical machme is worked, or electric sparks are passed through air, is due to the formation of a little ozone ; and if the oxygen evolved on the electrolysis of water' as m Experiment 22, be examined with the test-paper] » Easily prepared by soaking pieces of white bibulous paper in fodide"'' '^""''^ ^^''^' """^ ^'^"'''"' '°^"*^°" ^^ potassium * ''O^w, I smeii. Experiments with Ozone. 121 it will also give the colour change just observed. Dr Andrews, of Belfast, has proved that ozone is nothing but free oxygen in a remarkably active condition, for pure, dry oxygen can be partially converted into ozone by the silent electrical discharge, • and the oxygen dunng conversion is found to contract in volume In fact, It has been shown that three volumes of ordinary oxygen form t^^ o volumes of ozone ; the molecule of the latter therefore contains three atoms (unlike so many other elementary molecules, which contain two) • hence, ozone may be correctly spr^ken of as a chemi- cally condensed and active modification of ordinary oxygen, and its symbol written O3. On heating ozone to 260^ C. it is reconverted into ordinary oxygen, and the gas returns to its original volume, while It loses the power of afiecting the test paper. 1 his remarkable instance ol" what is termed alhtro. ptsm s not the only example of an element occurrinff m two forms which differ in physical and chemical characters, and yet consist of the same matter : for we shall meet, later on, with analogous allotropic forms of phosphorus, sulphur, and of carbon-the black and dull charcoal and the colourless and brilliant diamond being but allotropes of the element carbon. Isomerism in compounds is the condition analo- gous to allotropism of elements ; we are acquainted with pairs of compounds which contain the same ele- ments m the same proportions, but exhibit different ' - ^^7 '^'^^^-^ favourable circumstances the proportion of ozone formed m a given volume of oxygen rarely exceeds one-tenth of the whole, ev^n w>,«. „ c:„lT__. I '-^ceeas electrical ozoniser is employed. 122 Introduction to Experimental Chemistry. ill \ physical and chemical characters ; for example, lactic acid, met with in sour milk, and solid grape sugar. But we have in two bodies, whose empirical formula is in each case CON2H4, illustrations of a special kind of isomerism. One of these substances, ammonium cyanaie, is easily converted l)y heat into the second, a jDody termed tirca, and the latter is identical with a well-known product of the animal organism. (See Appendix aud Part IV. for details.) Experiment 67.— Pour a small quantity of per- fectly bright c}ean mercury into a short wide test tube, and lower the hitter by means of a string into the jar containing ozone used in the last experiment. Note that a very short exposure to the ozonised air suflices to render the surface of the mercury dull, owing to the production of a film of dca oxide of mercury. Pure oxygen does not afifect pure mercury under the same conditions, but the mo'e energetic ozone rapidly tar- nishos or oxidises the metal. A piece of rubber tubing is also quickly attacked by ozone. Experiment 68. — Bend a tube about 50 centi- meters long and 1-5 cms. diameter into U form. Fit one opening with a cork carrying the bent gas de- livery tube, as shown, fig. 48, and through the cork pass a stout platmum wire terminating within the tube Before inserting - - ^ Fig. 48. in a strip of foil of the same metal Experiments with Ozone. 123 the cork, coat it (but not the platinum) thoroughly with moMtx, paraffin, as the latter is not affected by ozone, and serves to prorect the cork from the in- fluence of the gas. Let the end of the small gas de. livery \ ibe dip under the surface of a small quantity of ether contained in the phial p. Now connect the wire w with the platinum end uf a small two-cell Grove's battery, and insert the other pole in the open side of and well down into the bend of the U tube, the limbs ot which have been previously half filled with water acidulated with chromic acid, or, if the latter IS not available, with sulphuric acid (one volume of strong acid to three of water). Oxygen containing a little ozone will be evolved from the plate iv but haying no exit save from the gas delivery tube, will bubble through the ether. The latter dissolves the ozone, and after some time becomes so charged with that body that it instantly discolours the ozone test paper when a strip is dipped into the liquid. Moreover, when some of the ozonised ether i? shaken up with water, coloured of a pale blue tint by * sul- phate of indigo,' the colour is destroyed, and the liquid thus bleached. Ozone is also soluble in turpentine and several essential oils, but it is dissolved to a very -mall extent by water : according to Carius only o'5 c.c. in 100. Experiment 69.-Expose a piece of ozone test paper freely to the outer air for a few hours, shading It, however, from sunshine. Even prolonged exposure to the air of a large city rarely produces discolouration of the paper, but pure country air usually causes a uistmci browiiish colouration in a {q\j minutes. It 124 Introduction to Experimental Chemistry, has been proved that ozone is present in pure air in . mmule proportions, though other .bodies are occa- sionally met with which hkewise discolour the paper. It IS supposed that the bkie colour of the ' sky ' is due to the presence of ozone. It is not surprising that city air should contain but httle ozone, as the organic and other impurities destroy, and, we may add, at the same time are de> stroyed by the ozone, which latter, therefore, acts as a natural disinfectant by reason of its extremely energetic oxidising power. ^ When highly 'ozonised oxygen or air is inhaled into the lungs, much bronchial irritation results; but* a small proportion does not produce any sensible efifect We have thus studied in some detail the two strongly contrasted and typical elements hydrogen and oxygen— the former a type of metals, the latfer of non-metalsT The products of theifurfion irow require further examination at our hands, in order that we may complete the first stage of our inquiry. lil 'try. 125 re air in e occa- ' paper. ' is due I ■ contain purities are ele- cts as a lergetic inhaled ts; buf ensible le two drogen itfer of •eqiiife lat we CHAPTER XII. EXPERIMENTS WITH WATER AND HYDROGEN PEROXFDE. Our previous experiments having placed beyond doubt the composition of water by weight and vokime and its molecular weight (H20=i8), we have now to examme some of the more prominent characters of this most important of all liquids. Experiment 70.— Arrange the stoppered retort a. Fig. 49. fig. 49, Liebig's condenser, b, and receiver c, as ™^ Siiown. iiitroduce some rain or river water into a, ii^ ll<< » If 126 lutroductm, to Expenmcnlal C/ia,nstrj, . s,tf '„!"""<=''""' "^'-' P'-n-ose, a„.I apply „,e heat of a s mt or gas flame, taking care to n.ove >he la.ier about at l.rst an.] to wipe off drops of moisture 1 form on the bottom of the retort VV|,en t he v te has l,een ,l,u, warn.ed at first, the hu,.p flam , Uy allowed to play steadily on the retort. After a hort time the water ^w/.i vigorouslv and ,h. ! into fh,. i,„.i, r .1 "^'t'"'""'*'/' and the steam passes nto the beak of the retort, and idtimately in o the ■n'^^r glass tnhe ^, of the condenser ; here il is cl ed [he in nhf t '">"=' I"««i"g water-tight through the tin plate jackety.hs cooled by a current of rolH ::L?of tT "-'""^ '''""'' ''"^ f'-nel/arthe 10 2 poin of the apparatus, whUe the warmer and there- most of Its heat, is carried away by the tube t it ,h^ "pper part of the condenser. "iL first po toin of e condensed steam, or &////„/ „,„,,,., ^ J ,„ "f^^ ' n away and the rest collected in the receiver b Tt^^ not advisable to continue the distillat L" 'aSr 1 e quid in the retort has been reduced to one fifth of 1^ original volume. The water thus colleaed is almost chemically pure. "'■cttea is ,nH^^'"'''j'"" "'"' P'""' '' ^ C"Io"rless,« inodorous and msipid „c,md, which at ordinary iemperIrS .he .„nosp„er^ a. the .! IfH:':::':?;':"",:' '" """ °' ture is ico° C at -76-. n, '"i,"^ ^'^^^ «fwatc this tempera- .iscs .™„ fans With increased I J:^^^^^:^"' """' Great ,«as.,e. of pure water have a distinct bluish co,„,ar. Experiments with Water. 127 gives off invisible vajraur, and diffuses into the sur- roundms air ; hence, water can be slmvly but whoilv evaporated by, simple exposure to the air. When heat IS applied it can be rapidly and completely converted into steam-one volume of water affordiuR nearly 1,700 volumes of steam at 100° C and a pressiire of 760 mm. One gram of steam at 100° C passed into ice-cold water can raise the temperature of S37 grams of the latter i» C. The ' latent heat of steam is, therefore, 537 thermal units. Water . becomes solid when sufficiently cooled, either by its own rapid evaporation, or by the application of external in ,^Ti,*"f°* "-I''^^« '^ f-^w drops of pure water in a watch-glass and suspend the latter over a basin containing strong oil of vitriol, standing on the plate of an air-pump. Now cover the whole with a small bell jar and exhaust the air. As the pressure diminishes, rapid evaporation of the water takes place while the vapour is absorbed by the oil of vitriol' The quantity of heat abslricted by rapid conversion mto vapour is sufficient to cool the water down to he freezing point in a. very short time, and a small piece of ice IS qu.cKly produced. Several ingenious ice- prkciple."'" ' ''''' ''''" ^°"^'™^<^d o" this Exneriment 72.-Take a tube about 30 c ms long and 4 ,„m. internal diameter. One end musi be closed and expanded into a bulb. Pour in water the bulb and half the stem in a beilcpr nf ,.„.„ ;.. cold and containing ke. The water in the stm fir« i ; t St f "f" Si^.j' f il^ 128 Introduction to J'.xperivtcntal Chemistry rises, owing to the contraction of the glass on cooling diminishing the c ijucity of the vessel and pushing up the column of water ; as the water cools, however it contracts more rapidly than the glass, and the level of liquid sinks below the starting point until it be- comes stationary and, if the external water be really ice cold, then rises acr(mi in the tube. If a thermometer could be plunged in thc^ water within the bulb it would be found to mark about 4° C when the liquid commenced to rise. Now remove the bulb and plunge It into a 'freezing mixture'' of ^Glauber's salt' and common ' muriatic acid/-the salt just covered with acid. The expansion of the liquid goes on until a sudden check is observed ; if the bulb be then re- moved, it will probably be found cracked and con- tainmg ice.2 l^hus water, when cooled down, contracts until the temperature of 4° C. is reached; then it ex~ pands axain up to the soluiifying point, and still greater expansion at that point suffices to burst the containing vessel, if it offers any obstacle to the free motion of the ice, for the latter occupies, ^weight for weight, more space than water at 0° C. The temperature of maximum density of water is 4° C, or that temperature at which one cubic centimeter of water has the greatest weight, i.e., one gram. ' Poumled ice mixed will, half its weight of common salt may be used instead, but the mixture given above ii convenient and eflective. « This sudden expansion on freezing aids materially in the d.smtegration of rocks, as the water contained in the cavities and hssures, wlien converted into ice, expands with great force, and breaks up successive layers of the material. The same Cause Ifii ' • ■ ' • kIc i,-\ »K< ig of Watcr-pi pes. Solution of Solids. , j. If similar experiments are made with alcohol oil, .and other hqu.ds, they will be found to contract £ not to expand again as the temperature >s r^du Id hus water .s the great exception to this gene^lTat' and m thts respect stands alone amongst the hautl' hitherto examined. "quids seem toTT' ""'"^'' "''^ P^P^"^ "^ "«'« may seem to be, its consequences are of ereat mnm-.„. . mankind Thus, if water obeyed L^ZC^ ^ nvers and lakes would s,K,n become mCeT of Lud .ce, their fish would be destroyed, anftte heaTt^ summer would be unable to undo the effm rfth^ ioTlXbir" ''"^ -'' equatorial regiL ai- We thus have 'evidence of design ' in this excen honal property of water, which exceeds in im~t' any a orded by the animal or vegetable ki gdC When .ce at o°C. melts, it absorbs without el J^tion of temperature ^^ much heat as would raise thHet perature of an equal weight of water from o»C to L-C ^ Lm STr '"; "' "^"^'^^ ^° ^"^"^e '"/L^e irom solid to liquid water, and is spoken of as its latent heat, ,>, hidden (insensible) heat place m each ,00 c. cs. of cold water. Weigh out "noer" sH ^T °[ ' "'"^ ^■''™' ' ^"y»''"""d copper sulphate), and introduce into one of the' a2l;'°fr'' °' "' P"'^"'"'" ^'•'•"-"'^e, into anoUier ; and 50 grams of common salt into the Of 79 tinicfc Its weight ol water i^C, *!' h M: i'llf 1 30 Inirodticiion to Exp^imental Chemistry, third. Now boil the contents of each flask : note that the copper and bichromate alike dissolve com- pletely on boiling, each body communicating its colour to the liquid. But even long continued boiling fails to dissolve all the common salt There- fore common salt is less soluble than the other two bodies in boiling water. As a mitter of fact, bodies vary greatly in solubility : some dissolve to such a small extent that they are commonly spoken of as insoluble, for example, chalk and glass ; others so freely that they are almost indefinitely soluble, for example, caustic ptotash and calcium chloride. When the contents of the three flasks are quite cold, it will be found that beautiful crystals have separated in the copper and the bichromate solutions, and these crystals can be made to disappear and re- appear by alternate heating and slow cooling of each liquid. It is therefore evident that heat increases the solubility of both solids in water, and that the ex- cess of solid ' over and above that which the cold liquid can dissolve separates out, thus leaving a solution which cannot dissolve more of the particular body at the given temperature, and is therefore said to be a cold saturated solution. A hot saturated solution is obtained by adding the desired substance to boil- ing water until the solid ceases to dissolve. The • When decomposition does not accompany the act of solu- tion, the crystals which separate from the hot sohition h-we the same composition as the body originally dissolved. If d« com- position precedes solution, as when sodium and potassium dissolve in water. Experiments 45 and 46, the body in solution must be different from thar intrrMhirnd. Solids and Liquids. x\\ solubility of a non-volatile solid is usually determined saturated a a known temperature, until the solven IS completely expelled ; the dry solid residuum ,s then accurately weighed and the ratio ol the solid to the solvent l,q«,d thus directly determined. ' Experiment 74.-Pour off into a large test tube some o the cold and clear saturated soluL of com! mon salt prepared m the last experiment, now boil dol'no.''^"^'''^'^'"""'"" ^^"' the latter evidemy the solubility of common salt in water is nmrly the ^««.ath,ghand low temperatures, and in this respec S ' i ,M ''■""''^'''^ ^^<^^Ption to the general ?ule that solids are more soluble in hot than cold liquids. I.m. ^vater (seepage 117) in a flask, and note that the ome of T" '"'''• , '"''= '^ '"^ '° "-^ separationbf some of the previously dissolved lime, its solubility . ; boiling water being little more than hllf that nea to on to the general rule, as it is las soluble at h.gh than at low temperature. '' .,.K^''-l'^*°* 7e.-Take four test tubes and half fil' each with water. A.Id a k^ drops of alcohol to one, of chlorofor,n to another, of oil to a third, and o g ycenne to a fourth. Note that the alcohol and glycerine read.ly dissolve in, or mix with, the wa.e" «he„ the contents of the tubes are shaken up, and «,..' ^"'" "fU'^'ed with one salt can dissolve others • thus . rrrrlr.^"^ -""•.--■'- stilldis^tveeithercoi: r- •-. "i i^u turoinaic oi potasoium. K3 ' 11 III i s '"^^ I 132 Introduction to Experimental Chemistry, t1>e water can take up an indefinite quantity of each. On the other hand, agiiati.on fails to make the chloro- form or oil disappear, but when the clear water is poured off from the layer of heavy chloroform, it has the odour and sweetish taste of the latter : therefore chloroform is shghtly soluble in water. The oil, on the other hand, fails to dissolve to any sensible ex- tent Hence water is a good solvent for some liquids as well as for solids. Experiment 77.— Obtain a bottle of* soda water.' * On removing the ffressure of the cork, a rush of gas takes place. Whtin effervescence has subsided, pour some of the liquid into a flask anc^heat : effervescence recurs, and a cork lightly inserted in the neck of the flask is quickly blown out, owing to the es- cape of much gas. If the liquid be boiled and then allowed to cool, it will be found to have lost its brisk taste, due to the presence of the gas, for the latter has been wholly expelled by heat. Place another portion in a beaker or tumbler, and the latter on the plate of an air-pump, cover with the bell-jar and exhaust. As the pressure within the receiver diminishes, strong effervescence commences in 'fhe liquid and continues as the exhaustion proceeds, until all but the most minute traces of gas are removed from the liquid.' It is clear, then, that the ' The amount of ' soda ' present is usually so small that we may regard it as a solution of carbonic acid gas in water. ' Although the weight of any gas dissolved does not, gene- rally speaking, diminish regularly with increase of temperature, {■Va/er Supply. jj^ gas present in this solution-called 'carbonic acid gas -i« rather freely soluble in water, unlike hydro- gen and oxygen,' which we have already found to d^lve to an almost insensible extent; an.l later on a art II ) we shall meet with much wider differences n solubihty; but the fact is that all gu.es are n.ore or Jess soluble in water^ .nd „1 our experience proves it to be the most general solvent known. ° Owing to the general solvent power of wate. it is from ,r r «r°"'''"d ^ven solid impurities from the air through which it passes, and from the soil on which it falls. The prime source of all water supply is ua- doubtedly, the ocean, since in nature thirl is a c^ ttnuous circulation from the sea to the air, then frol air to rivers, and, finally, to sea again. The air a contact with the ocean becomes quickly .saturated with the vapour of water, and then, bemg carried by currents over the earth and suddenly cooled, lets faU ^e, u.kiU ,H. ../„„,. ,v M. sam^M all fr^^ura (Henry-. H„.?° IT'"''!."''' °' 2" '" *•■"" "" ^ determined by „p,a. tiogtogelher known volumes of gas unci wa.er i„ a graduTced tube elosed by :nercury, and „, ii„g the volun.e abLbei it constant l.mpcrature and pressure. •■'■'«)ri«j at • At„,osph..ric air is soluble to a very small e.v:e:,t in water loo CCS. of the latter dissolvin,; only ,., c es of .|p 1 ' ' te;nperature. Small ,h„„g„ .bis amoL. L",: to be it sTrl" ^.s source that «sh obtain the air neces^rv for thl Ml*!;™ % v% fiil u - 134 Tntroduction to Experimental Chemistry, much of the aqueous vapour in the form of rain.* If the soil be not very porous, small streams are formed (which wash out soluble impurities from the surface soil), and these flowing into a common channel produce a river. If the soil be porous, the water percolates through it, and may drain away again at a lower level and form rivulets and/ivers, or it sinks into the subjacent permeable strata, thus serving to main- tain the supply of wells and of natural springs, often situated at a great distance from the place of rainfall. If the permeable strata are not overlaid by those only slightly pervious, \ land-springs not rising above the surface are obtained over the district ; but if the strata dip between two impermeable beds, an Artesian spring is obtained on boring, at a lower level, through the upper bed to the water-bearing strata. Water in its passage through the rock strata, often under con- siderable pressure, dissolves out more or less of the soluble constituents of the strata, and makes its appearance in land-springs and natural or artificial Artesian wells or springs as a mineralised water. If the rocks, through whose substance cr fissures it passes in its downward course to find its level, happen to be the older metamorphic, granitic, or quartzose rocks, or green-sand beds, but little impurity is taken up, and the springs usually yield a supply of very pure water. If the rocks are cretaceous, or magnesian, or both, the water is then charged with lime and other salts, to an extent dependent on the particular * If the rainfall of a district be known, the calculation^ for the catchment area can be easily made, if it be remembered that a fall of lo inches of rain yields 226, 170 gallons per acre. Mineral Wafers. 135 of the latter inhelinnln K ''"^ '^''^°'^'^^ l'"' ""'e acid, since tie ami of chalr^f' -"-""onic taken up bears a dire rehtfon J H "'"" '"'""^"=> ciis.solve(l carbonic !"] I ''"''"'''^ °'" ''"^ of the Cnrara snrin!« I ^°""'™«' as in the case probably Tder fs Ire LT'" '"",""' '^''"^=^^. acid and with chalkln!; " """'"'■'' ^^"^n' ""1' loses much of its f ko"f °"r"':« '"™'" 'he sot.rce is the depos,°[o^oT.t°"chal\ oL"' 'T\ "' ""^ '°- tion by the acid in !! ? •' P'«^'°"sly hel.l in solu- Mme, '2Z^t:'T^. '"-"gh stmta containing with carboni :'c°; ^^iTin't' !'' "^.'" '''^'^^^ Posable ferruginous ~th°Cr Ten'"""- portion of their iron as ll.^ I ^^''' "I' * dissolves in the excess of IT- ^"'^°"''"^. 'vhich the water of a chaj:! IpT Tt "''' ''"'^ ^°™' meet with in volcanl dttr Cj aJd aT "^"^T" °'''" bourhood of the coal measTres' In .h T '" '^ ""'s''- -e rarely fai, to „,eet not oX' ^Uh st""' '"^'""''^^ less worthy of the name rh, , '^'"'springs, more or > ot tne name chalybeate, but we also find carbonate dissolved by carboni, \°\ "" ''''"'' "'••'gncsi,,,,,) water, and is called ■ ,emD„;m' " ""'"""=^ "J' •»"i"S 'he boiling is . perma en, h"Ie7. and T ' ' """ ""' '""»'='' by or sulphate of calcinn. ll" 1!'! '"'' " ''"* '° *»«"'«! chlorid; Calcium, and I'art IV ,' Soap'^""'"'"' '^'' ''""""• P"' "I-, lu' h I'. h : 136 Introduction to Experimental Chemistry, the sulphur spas, the sulphuretted compounds of which have been ctuctly derived iroui the decomposition of SI piiidcs, always present in the shales and true coal beds, by infiltrating water charged with carbonic acid. The most celebrated of tnese rnmeraiised waters of medicmal value may be thus grouped, accordmg to their chief constitueiits : — Carbonated ami Alkaline^ as those of Vichy, Bilin, Ems, and Malvern. Sulp/iatcdi^o(X\\va\\ Carlsbad, Cheltenham, PuUna (Magnesium), Epsom, Sedlitz. Sulphuretted, iJarrogate, Aix-la-Chapelle, Lucan, Lisdoonvarna Chlorinated^ Leamington, Harrogate, Clielteaham, Wiesbaden, Homburg, Kissmgtn. ChalyOeate, iSpa, Tunbndge, Harrogate, &c. In addition to these, we meet with special pro- ducts of the action of volcanic gases and steam in the — Siliceous waters of the Icelandic Geysers. Boracic waters ot the Tuscan lagoons. Sea water is the product ot continual land wash* ing, and m it enormous quantities of saime matter are stored.-* An analysis ot the water ot the Iristi Channel, made by Messrs. 'I'horpe and Moreton, afforded the following results ; — > Sea water is easily rende,red potable by Dr. Normandy's process for providing pure water lor ships at sea. Salt water i$ distilled, as iii Experiment 70, but in l.ri;e iron reiuiis (or ttiUs), the salt- are Icli in tiie retort, and uit condensed and pure water, wl. Ji is flat and insipid at hrst, is rendere ^ bri:,k and agreeable by .rcing it to di .solve ome atmospheric au m « i>|)cciai apparatus. Peroxide of Hydrogen, 137 n n looo parts gave — Sodium chloride Potassium „ Magnesium chloride bromide sulpliate >» nitrate . Calcium sulphate , V carbonate Lithium chloride . Ammonium „ Iron carbonate , Silica , Water . • « 26.459 0.-/46 0.070 .'^.066 0.002 ^•331 0.047 traces >» 0.005 traces 966.144 volumes) of the water .s 1024.8, if pure water =,000 the Dead Sea is so large that the specific cravitv of a AsX:r'? ''''■'' '° '' "'*■ (-'- = oooj foil" tt^'" ■'''•''"'''• '^ '"^'y ^-'Sh^rlLn xroo. if follows that an average man wouM be buoyed ud !h n' r''' f '^' ''^"^ Sen, and could not sink wholly beneath its surface without some effort Peroxide OF HvDRoGEM (Oxygenated WaterW^,«. Experiment 78.-Add, with frequent agitation about 5 grams of barium peroxide (liSTbi ^u"'"!_' ^- <^- ."'^ '"-""g a-:"! ; filter, and add som. "..=1 to a portion of the filtered liquid and a fe^ H- I'^I 138 Introduction to Experimctttal Chemistry, drops of solution of red potassium bichromate, and shake. Note that the ether (which is but little miscible with water) rises coloured of a magnificent blue tint, which is evanescent. . Barium peroxide and sulphuric acid afford hydro- gen peroxide (or oxygenated water) and barium sulphate. The latter body being insoluble is filtered off. BaOa + H2S04=EaSO4 + HjOa. The chromic compound serves to detect the pre- sence of the peroxide of hydrogen formed in this re- action,* as it is characteristic of that body to produce an unstable and highly oxidised blue chromic com- pound which is soluble in ether, and less quickly changes in that liquid than in any other. The solu- tion of H2O2 made as above is dilute; when carefully prepared in the first instance, and then evaporated oyer oil of vitriol in the exhausted receiver of the air pump, a syrupy liquid of specific gravity 1452 (water =1000) is obtained, which is colourless and inodorous, but has a strong somewhat metallic taste, and can be cooled down to — 3o°C. without freezing! This is the pure peroxide, but so unstable is it that a slight heat suffices for its decomposition into water and oxygen, and even the dilute solutions of the body sold are easily decomposed in the same way. Experiment 79.— Take a long and moderately A'7^^ peroxide, like ozone, sets free iodine fr-rm potassium iodide, and therefore colours the ozone test paper This colouration by the peroxide takes place even in presence of •green vitriol ' or ferrous sulphate, unlike that due to o.nn« Peroxide of Hydrogen, j 39 thin glass tube, scaled at one end, tliree-fourths fill It with mercury, and the remainder with as stromr 1 a solution of the peroxide as can be obtained : then in- Z% "!. """TT' ^' '''°^^'"' ^S 50. If the tube be inchned, and the portion occupied by the peroxide gently heated by f.c 50. means of a spirit or gas flame, bubbles of gas will quickly make their appearance. When sufficient gas has been collected, pass the thumb under the mercury, close the mouth of the tube, remove from the - mercury, invert, and test for oxyiren by plunging a match with a glowing . tip into the gas. HaC^HgO + O. This decomposition of peroxide of h3'drogen into aTd of reir^"" ^"' ^^" '^ ^^^---^^^ -t'out h: aid ot heat by mere contact with— and^arf f rrf"'"''''-.''° ""' "'''"^^'^<='' '''«^' -change and are therefore said to act catalytically Mox exaunt -gold sUver, platin.™, charcoal and fibrin o b ood b. Bodies wh,ch lose oxygen at :he same time ^ give a substanfi'al *.vr^I-,„»..•„• _r ., . i''^"^"^ unable to Tha. brings aSuTc^eS^han' "in'Xerit °' "^"^ itself suffering sensible alteration ^ ""' *"^<"" 140 Iniroduction to Experimental Ckanistry, Experiment 80. —Moisten a sheet of writing paper with a solution of lead acetate, and expose it to the fumes arising from a few drui).s of ammonium sulphide sprmkled over the bottom of a shalluw dish. The paper becomes quickly chscoloured, owing to the production of the dark-coloured lead sulphide (PbS). When stained a dark brown, remove the pai)er and dry It, then charge a brush with a solution of peroxide of hydrogen, and draw a design on the stained surface. The (lark lead sulpiide will be rai)idly bleaclud by the perox'de, and the^ design will appear in white on a dark ground. In this case, the peroxide actsas a power- ful t?.r/^/>///<,r agent, converting the dark lead sulp///^^ into white lead sulp/z^/^, (PbSO^), thus— PbS + 4HaOa=PbS04 +4H2O. In a similar way, discoloured oil paintings and engravmgs can be bleached by careful treatment with dilute solutions of the peroxide. The latter has also been largely used to bleach dark hair, and change it to the golden colour, lately fashionable. The chromic test, described under Experiment 78, is another example of oxidation effected by the per- oxide, but in that case cdlour is developed not destroyed.' * ' Another case of oxidation by the neroxide accompnnied by a colour change is the following :-Add a {tsv drops .of a fresh alcoholic solution of guiacum nsin to a few c.cs. of water, then a few drops of solution of the peroxide to the turbid liquid If to the mixture a little colouring matter of blood be added a beautiful turquois blue tint is soon develo; ed. In this case the blood determines the decomposition of the peroxide whose ^ Hydroxy!, 1^, Although the peroxide cannot be converte(! into gas, and have its specific gravity taken in that con- dition so as to determine its molecular weight its analysis, and the reactions already cited, leave no doubt that its formula is H^O,. Its relation to water may be thus shown — Water. H-O-H Peroxide. In the peroxide we assume that the two double- link oxygen atoms are united, and form a chain, to each end of which IS attached a single-link hydrogen atom. If we break this chain at the dotted line, it is evident that we get two -r'..ups, each containing one atom of oxygen and of lydrogon, and each group is expressed by the symbol III. Ve should not expect, and do not find, these i m..j,s to exist in the free state, because each wouid have one link of oxygen free, and that is contrary to the general rule ; but we might look for OH in combination. As a matter of fact we meet with the group OH in an immense variety of oxygenated compounds, and this group acts like a single atom of a monad or uni-link element, and is commonly spoken of as the * compound radicle,' hydroxy!. The molecule of the peroxide of hydrogen contains two hydroxyl groups, and therefore is to be regarded as the free molecule of that body. The study of water and peroxide of hydrogen —two distinct compounds of the same elements— l^ds atom of available oxygen at once oxidises the finely divided resin into the blue coloured body. This is Dr. Day's, of r^dnn., test for biood. ' ' "*' J • f ' . i J42 Introduction to Experimental Chemistry ot fcis *.;;:■ "'"'« «i>™"> ««,.««: I' i 11 ' '" f ' l^.<' I APPENDIX. may be referred to one or other of the following divisions As one or „,ore examples of each kind of changroccur ofe eacrcaTe^KT""™'^' '"^ '^'"^^ '' ""vised o rcier each case he has met with to its proper division In order to acilitate this process of general isa^n a smgle exan,p,e. with its reference, is Jven uXTach I. Cases 0/ direct combination of elements, (Experiment a.) Mg + ^ - MgO Magnesium. Oxygen. Magneslu^xid.. 2. Cases oj simple decomposition, (ExPBrtlMBNT aa.) H^ - 2H + o Water. Hydrogen. Oxyien. 3- ^<^e5 of double decomposition, (Experiment 14.) AgNO, + NaCl » 8U AgCl ver nitrate. NaNO, ^L"r„*'.°n?« Sllv.rclUor.d.. Sodiun.' Jit 1 lit/-. mumtaw Js! 144 Appendix. 4. Cases of decomposition by substitution. (EXPERIMUNT 19.) Zn + H,SO, - ZnSO Zinc. Sulphuric acid. ^ ^ + 2H Zinc sulphate. Hydrogen. 5. Cases qf decomposition by reduction. (EXHEKIMBNT SaX CuO + 2H - Cu + W.iter. Copper oxide. Hydrogen. Co^cr. 6. Cases of rearrangement, or isomeric change. J (Pack laa.) Ammonium cyanate. Urea. Two conditions tend so materially to determine double fng Ta^.T "' *""'" *"" '"""""'"=" '"« fo""- I. Two bodies in solution will always decomoose each other, .f it be possible, by double declmposiS, : produce a new body to soluble than either of the two original substances. ** • ''<•'■ e'"»n>Ple-silver nitrate and common salt orodur* insoluble silver chloride. (Experiment ,4.) alwnv. 7 "^'^ *''*" """^ "■■ heated together will ^-Tm j'"^'""f«''« ^^-^h other, if i, be possible bv double decomposition, to produce a n^w k!S ^ ^olaHU than either of the tw^o :^;"arsubsTanc:s.'' '""'" car^It rd'K.^^t-c^td' "/""r ''^''™«- -lo.de at ordinJir;::,-;^. ''t^^Z\T'' PART IL Fic. SI, CHAPTER xm. EXPERIMENTS WITH AIR AND NITROGEN. abn.^r^*''*/^-^"' " P'^^^ °^ phosphorus Swlf z. V as ' '' -'^ ^-'^ ^~ paper, and place it in the small porcelain capsule r, fig- 5i» which floats on the water in the pneumatic trough. Fire the phosphorus by the touch of a hot wire, and immediately invert over it the bell-jar, which is at first full of air. The mouth of this jar must be under the surface of the water so as to completely inclose the gas it contains. Bubbi*a ^f «•- ^s.-^^-^ ^^ i:_ * " '^ "''■ i''- «*i msi, Owing 4 ,■ 1 i 1 : f ■ ■1 146 Experimental Chemistry. to expansion by the heat, hut soon contraction takes place and the water rises in the jar. The white fumes produced during the cornbustion of the phosphorus are the same in composition as those formed in Ex- periment 60, i.e. P2O5, and we already know that they dissolve in water and form phosphoric acid ; thus the oxygen of the confined mass of air is removed in the form of solid oxide of phosphorus, and the latter is washed away by the water \ the gas in the jar there- fore contracts in volume. Now it is obvious that if air consisted only of oxygen, and we used sufficient phos- phorus in our experiment, all the gas would disappear and water would completely fill the jar ; but, as a matter of fact, the phosphorus soon ceases to burn, and then, on allowing the jar to stand over water until the white fumes disappear, we find that a consider- able volume of colourless gas remains behind. Now transfer this gas to smaller tubes in the manner directed in Experiment 17, and make the following,' observations : — a, A tube full of gas when turned up is found to be free from smell, if it has been washed ihoroughly from all fumes. b. A burning taper plunged into another tube full of the gas is immediately extinguished. c A little Mime-water' shaken into another jar of gas is not rendered milky, unlike the result ob- tained with the carbon dioxide gas formed in Ex- periment 58. Therefore air from which oxygen has been re- moved is colourless and inodorous ; it is incom- bustible, does not support the combustion of a taper, Experiments with Nitrosen. 147 and does not render lime-water turbid. This gas Nitrogen' — Svml>ol fi^ — t . , rr t •• Molauiaru'ei<;/itz=2S. Nitrogen does not support anima! life, and is sometimes called azote » in con5Pn„„n tI • ^li<.l-.l« .„i, ki consequen ;. It is very sligl.tly soluble m water ; i cc. of water dissolves only 001478 cc. at 15° C. ais.olves Free nitrogen is one of the most indifferent gases Mof Indf.orf '"'"P"^"^'^- A similar, but muchlwe f^foCrw:;™' '''^'""'"" -^ '^ -"^^ - ^^ Experiment 82.-Fill the gra.'uated tube a, fig. ,3 wuh .00 CCS. of air, taking care that the vo nme s' measured when the water stands at the same height confin.? '".'r.'- ""*' P"^' ''•Sh up into, the confined air a small stick of phosphorus at arhed to a stout copper wire Secure the wire in its place ^d ' From ►iT(>w, nilie, and y,n«,, I generate. J- •fc. f r lj i 148 Experimental Chemistry, leave t^e whole for twenty-four ^ ours. The phos- phorus slowly combines with and removes the oxygen, and leaves onlv nitrogea In order to measure the Fig. 53. PtG. 5«. ' \~<$ latter, withdraw the phosphorus, adjust the water, level again, and read the graduation. If the temjjera- ture and pressure are unchanged, the residual nitrrj^f^n — ■ a- — Anafysis of Air. ,_j„ th,,^d.ference. or oxygen absorbed, is, thcr.forl! nearly' Or another, and very rapid, method of anilvsis hv S.orpyro.UoU.sorJ::eCnrs:rS IcJ^^fT""^ 83.-Take a cylindrical tube, , meter tong and about i6 millimeters diameter nL j h "corLdl,'"'''^'^ r '"^ '"•-• ^- -o e drops to rail into the J^Z d7„ t 'I ai ra^r a1> rau rj' a?;' ^^ T^c °T ^^ '""^ ■"-" ^'^ tX back .„°h ' '"•°" "^ "'^ ""''"■'^ Bring the riXThumbCnT.lr'"';' 'I' ""'^™-'- liquid rapidly runs rfr™;Th.TT"''*' "l^"-'" ^^ "'« tion h-« fl-nn 1 . ^ '^""' "°«'- as absorp. before Re" ^!T ^'''''" ^'°'^ ^ ""^ P^°<^eed is -Uthi;.;^^e;;;;rh'lbr:brb.f'^b — ^. «ii the bulb co«,ple,ely with waterrdos^^; A p '; * ^ I., I 5#i I ' 1 50 Experimental Chemistry. • with the thumb, and invert in a tall vessel of water On opening 5 the heavier dark liquid flows out, and is soon replaced by pure water. Adjust the liquid to the same level within and without by depressing the tube to the reciuisite extent The water should'then stand above the second ring, or, on a graduated tube, at 209 divisions out of too of air. Experiment 84.--Fill the eudiometer used in Experiment 23 with water in the large pneumatic trough, and allow about one-third the water to be displaced by air ; adjust the water to the same level withm and without the tube, and note the volume. Now pass in half the volumo of pure hydrogen gas, level again, and read the total volume. The hydro-en ^n be easily obtained from the apparatus used'' in Experiment 68 if dilute sulphuric acid be employed m It and the wire w be connected with the zinc end of the battery ; gas should not be collected in the eudiometer until sufficient has been separated by electrolysis to expel all traces of air from the apparatus. 1 he tube instead of passing into the bottle, as shown, should, of course, dip under the surface of the water m the pneumatic trough. Press the mouth of the eudiometer on an india-rubber pad placed between It and the bottom of the trough ; now grasp the tube, hold It firmly against the pad, and pass a spark between the internal wires. After explosion rela. the pressure on the tube and allow water to enter ; adjust levels again and read. One-third of the total contrac Uon observed represents oxygen present in the air. for we already know from Experiment 23 that two volumes of hydrogen and one volume of oxygen unite Analysis of Air. 'Sr to form water, which latter condenses at ordinary tem- perature. If, in a particular experiment, loo parts of air are mixed with 50 of pure hydrogen, and after explosion the residual gas measures 87-3 parts, the pressure and temperature being the same at the beginning and end of the operation, we can calculate the composition of air by volume thus :~The contraction after explosion IS 150 - 87 '3 ^627 parts. Then «^ = 20-9 - the Tie. 54. proportion of oxygen gas in the original 100 parts >- volume of pure air. The difference, or 100-20-9 — 79"i, IS the percentage of nitrogen gas. Experiment 85.-FiIl the tube of hard glass, a, fig. 54, with bright copper turnings, support it 'as shown, and heat with a large gas or spirit flame • connect the end by rnean^ of an india-rubber tube with a glass delivery tube, /, which latter dip under the water in the pneumatic trough. The flask/ s. yii^ onlv contain water efQUf^* ^'^ r>^..«.- ^u^ .^ j _/• .. ;«i ; 1 i < ' ^L^^ 'Hi i i w t$2 Experimental Chemistry. funnel tube. Now apply heat to the tube contalnine the copper turninss and when a red heat is reached pour water into the limnel tube of the flask ; air is thus mnde to pass over the calcium chloride in ..,itiop of air by weight. They caused pure dry air to pass over red- hot coj.ptr contained in a glass tube, and thence into an exi;.- psted glass globe ; each portion of the appa- ratus w^^ accurately weighed before an ex|,eriment itie Pbe and globe were separately weighed after an exper,n,ent. The former gained in weiglit, owing to the combination of the copper and oxygen, and the gam of the globe was due to nitrogen ; the sum of «iese quantities was the weight of air operated upon. The mean of a number of Laborious experiments of this kmd, m vhich every possible precaution against error was adopted, gave the following results, which for convenience, we compare with those of the volu- metric analysis of air already de'^cribed ;— Percenlage of By w. ,h. By volume Nitrogen . . 76-995 . . \^.^ Oxygen. . , ,3.00. . , j^.^ If nitrogen and oxygen were of the same specifio AiraMixtun. 153 gravity the percentage composition of air by weinht and volume would be the same; but we have already O- r /u"" '''^"' ''"■"'"y °^ N = i4 and of , ^"7'^' '"="■= "S oxygen is, volume for volmne, a lutle heavier than nitrogen, it follows In" fi'J!!! ^fT^ °' *'''>*'^" """ «<='K'^ """•' than one-fifth of the total weight of five volumes of air although oxygen forms but one-fifth by volume of the gas. m ^^\ '^^n?^" ^'^'''^y ^^ P"*-^ ^^y ^'r is 1447 1447 cgrs.''^'"'"' ''"' ^'^ ^''- "' "•"'•> ^^^'Shs Atmospheric air is ^..^r/^ constant in composition, ihe results of numerous precise analyses of pure air collected at various and widely-separated points of the earth's surface, and at considerable heights above sea-level during balloon and mountain ascents, prove that the variations in the proportion of oxygen are well wuhiu one-fifth per cent, by volume In tropical countries, however, the oxygen has been ob- served to drop suddenly as low as 20-3 per cent owing to some hitherto undetermined cause. ^f//*^^ air were a definite chemical compound of nitrogen and oxygen it shuuld be absolutelv constant in omposition, and we know that it is not quite on- 8U ^>^^^^^ox^ it is not a definite chemical cow tound. Again, oxygen and nitrogen are not present in sim- pie atomic proportions in pure air, the ratio b. mg ro atoms of nitiogen to i of oxygen. If the inclusion just stated be true, a mere mixture of the v..o gases in the proportions indicated' by analysis ought to fwsic^ -Oi the propertit ii of air. To test this, make— % if if i 'S4 Experimental Chemistry. >n ert ,t ,„ ,he pncu.na„o .rouf,h : introducr as nn.ch n.trogon gas (prepared as in Kxperimcnt 8,)\r will d>sph,re four-nrths of „,e „,ter, and a, m„c ^ vgl fill llie jar. I his .» an evi.lfnt mixture of the two gases, and no heat i. develo,,ed, nor .:an «c find . nt ease, M„„ ''''■"'-' l>^«>»«-'en the two Tand ,f '^™°''-' "" ■"•" '" ""^ "'"='' «-.-.v, invert t TnotT? "..T" "•'"' '"°*'"e .ip into the j.ar1 ■t .8 not rekindled as it would be in pure ox>4a to bTn^ "r?/"'"' '"'° '"^ «^^- ^"'' " -«^"- lo Durn a.^ it did in air In fart .« «n .his mixture or the two galL at lljXo! t o,e of"o "' •■"' ".^ '^•'"•■'^'=" '^f "^« '=•«--« ndfferent h'T" '""'=' ,''"""•■'' *'"' J"« ^"^h an ndiflerent body as we know nitrogen to be We .M,^ have ,,.«M./,. evidence in favour of the mix.i: rath!''^'*^T *''-T'"on dioxide is (piickly absorbed by the alkali in the pro- duction 01 potassium carbonate, thus :— £0a + 2KOH = K.COa Carbon diuxide. Caustic I^tash. Potassium carbonate. mg for ievcJ, gives tlie proportion of carbon dioxida Inve'r.Il'in'^h'"'""'"','"'". ''"''' """' "'"' "•""^'''X ""d then rr he „'LT'« ''""*■ .'^ '"'" "f 8la»». curve,] a, one end nnJintoTTK « '-'• "•""'^ '" """'r ">« «ir from >h. hinp. mo / I he hm ,k„.,o„s of air expelled from the mouth forcing it tlirouah the ae"".". L-u- . " """"™' '•J' ' 58 Experimental Cfiemistiy. If a small quantity of strong solution of pyrowllic pi^,:"" '"f-t"^--d, a further conirJZ S ™ thi"' '" ^''''«""'<="' «3, to absorption of ox)gtn , th.s ,s measured, and the residual .as is nurosen, whose volume is then deter.nined In h , way the com,K>sition of a sample of air exuirel h! , man was foun-i to be. in too volumes- ' ' Nitrogen Oxygen . Carbon dioxide 79-58 16-04 ^4-38 lOO'OO evwinlv in i T" •' '°"'""'"^'* '" 'he proces^ evidently m the combustion of tarbomsed n ateriaL evolved. An adult man thus expires about 450 liters of COj in twenty-four hours. Experiment 90. -Pour 30 or 40 cc^ of lime-water >nto a w.de-mouthed bottle ; now plunce a burinl burn for a short tm,e ; then remove the tauer do,! the mouth with the hand, and shake. The lime-w tl becomes very turbid, therefore carbon diSe w^l produred durmg the combustion of the taper A snfljlar experiu,ent may be m.ide with the flame of a small i^etroleum lan.p or of roal-c^s o w , h Pjece of red-hot coal. In' all these ,^es carl o„ dmuie .s a product "f the combustion, and the r tec on of tins particular nro.luc, proves he pescnce of the element carbpn in ne br^y burned. ' We have thus detected several sources 0/ con- Fig. 58. ^cf^on 0/ Plants on Carbon Dio:ade. ,59 We knoi that y^'r . i!r f""""^ '° '"-• process of purification mth^ "' *'''"' "'""'"' ■i-|.e next e!y.ri„,enrwm Lp '"0'""'^ •'' "■°^''- nature of this process. ^ understand the Experiment 91._vVe tair» t^. other of the following JZV- °" ^"''^^^ °"= °' the common .4««./}<,„i, /j,,^;,^. 5f ; ""'''""• to te found in our ditches and rivers, Ehdea cana- 1'nus, OratophyUum, if.uoma, Sp,rogyra, or any whose leaves have large stomata % 5«) with water saturated wKh carbon dioxide by the method described later' oa Attach a ,^„,on of the p,ant, *'th as many fresh leaves as Pos'-ble. ,0 a piece of ^Z f„ order .0 sink it in the water ,n " - and secure Tin d^1o„ h ' '" "^^'"^"^ ^^^^< Fill a test-tube wi,r«a° ^ '"'""■"' °^ *"^ ^'^J'* over the tube ofX ^n '..rir 'S '""^ '"-"^ 'hat no change takes pla;e in 7^1, r'? T c^'I'ose the whole arranceml. . ./ ^^ '*'"• ''"« »ome houi. =^-. ..,;!''''""*"* •" ''"Kht sunshine Mr ""•' """"'«* "f Ijas will J,e evolved, and i6o Experimental Chemistry. will rise through the funnel and collect in the test tube. When a sufficient quantity has been collected, remove the tube in the usual way, invert it, and plunge into the gas a match with a glowing tip ; note that it is rekindled. The gas can be easily identified as pure oxygen thus evolved from the plant. A care- ful examination of this process of separation of oxygen has shown that the latter is a product of the decom- position of CO, in the green or chlorophyll cells of the leaves ; in these cells the carbon is fixed and em- ployed in the production of various carbonised bodies, starch, woody fibre, &c, while any oxygen not re- quired for similar purposes in the plant -organism is returned to the atmosphere in the gaseous form, as we have seen.' We learn, thus, that the carbon dioxide which issues from the lungs of a man or other animal, from the burning candle, the factory fire, and many other sources, and that would, if allowed to accumulate, soon render the atmosphere deadly to the higher animals, is rapidly decomposed by vegetation under the influence of the solar rays. Thus man is saved from slow poisoning by the depurating action of vegetation on impure air, and this action is, moreover, the chief cause of the nearly constant composition of ' In additifjn to this decomposition of cariion dioxide, which hi only eflfecttd in the chlorophyll cells under the influence of light and chiefly of the yellow rays a process of nsptration analogo' ."^ to that of animals takes place in all parrs of the pian», and is not dependent on the action of light ; but this ah- «<».ption of oxygen and evolution of carbon dioxide is so very /eeble that the loss of carlxjn involved is insignificant when ciimpofeil with the enormous gain of carlx»ii l»ydecuuipoiU»ono/ its dioxide in the chlorophyll cells. the test )llected, it, and p ; note lentified A care- oxygen decom- cells cf nd em- bodies, not r«- nism is » form, carbon »r other re, and wed to f to the ;etation man is :tion of •reover, ition of B, which lence t)f pimiion i of the this ah- «o very It when mXMM of Fk;. 5^ Diffusion of Gases. i6i the air, aided as it is by the action of atmospheric currents arismg from alterations of temperature, and the operation of a curious physical law in virtue of which the constituents of a gaseous mixture tend to diffuse or distribute themselves eciually throughout the mass. This principle can be easily illustrated by the following experiment. Experiment 92.-Fit the doublc-riecked bottle h as shown in fig. 59. The tube / passes through the cork nearly to the bottom of the bottle, where it dips just under the surface of some water coloured with litmus or co- chineal ; this tube is drawn out to a rather fine jet at the end c Both corks are best of india-rubber ; through the second passes the long tube m ; this, hke /, should just dip under the surface of the water in h. The end outside the bottle passes airtight through the cork c, which closes the porous earthenware cell s. The latter is one of the small porous cells used for galvanic batteries, and should be new md clean. AH the corks, if not of rubber and very tight, must be coated with paraffin. Having prei)ared the api^aratus, fill a rather large jar with hydrogen, and bring it mouth downwards over s. Almost immediately gas bubbles from m through the liquid in the bottle, and as it has no exit It w confined in h and exerts considerable pressure upon the surface of the coloured water, whu b latter is, in consecpience, driven up through / ?.nd ia^ucs from <, iarawng a temporary fountain. On 3^ I I t '^, 162 Experimental Chemistry, withdrawing the jar the reverse action takes place—air enters through /, and the liquid rises in ;//. The reason for the accumulation of gas within the apparatus at first, and consequent increase of pressure IS that the hydrogen rapidly diffuses itself through the air m the cell and vice versd, while the porous cell walls do not oi)pcise material obstacles to mis process of diffusion, though sufficient to intercept mere currents. But hydrogen gas, Jx^ing so much lighter than air (in the ratio of i to 14-47), rushes through the pores at a higher rate than the heavier air can pass in the oppo- site direction-corisequently gas accumulates in the cell and the evidence of this is the increased pressure withm the apparatus, which suffices to raise a column of liquid to a considerable height. If oxv^rcn wer^ present at first in the cell, the pressure would he still higher, owm^j to the greater specific gravity ot that gas^ The law regulating this diffusion of gases is allied 'Graham's law,' as it was di3covered by the late Professor Graham, the last scientific Master of the British Mint, and its statement is that Mv diffmion rates of two misses of gas in contact are inversely pro^ pomonal to the spmre roots of their spmfic gravities, 1 hus, comparing hydkogen and oxygen, the specific gravity of the latter is 16, and the square root of 16 is 4-therefore, according to the faw, four times as much hydrogen as oxygen will pass through i\xt cell wall in a given time. In the case of air the two constituents do not diffuse out into the external hydrogen at the same rate the heavier oxygen passing out in the above proportiorL una the somewhat lighter nitrogen nt « hii/iu-- ^-^-^ ■Q-.NM. ««*tp4M Carbon Dioxide in Air. iMruRiTiEs IN Air. "5.^ The impurifics commonly met with in air are the noatmg solid parti,:lcs~the 'motes in the sun- beam beautifully seen when a beam of sunlieht passe, through the air-and the gaseous or vaporous bodies we should expect to find, viz., ,arlm.. dioxide water, ammonia, and ozone; while we , «:casionallv meet with carbon monoxide, marsh gas. and other hydrocarbides, sulphur dioxide, sulphuretted hydrogen t^T.^ t-'™^'"; ,''"°"""' ""'^ "^^""''^ emanations fron the skms and lungs of men and other animals. Experiment 93.-Exposc in a dish a quantity of lime water to the air of some open space for a few hours • the water will soon be covered with a white pellicle' owing to the formation of chalk arising from the action of the carbon dioxide, always present in ordi- nary a,r, upon the hme in the water (see Experiment 50;. The usual proportion of CO, in good fresli air is from C-033 to 004 percent, i.e. 3t0 4partsm ,0,000, bm tJie a.r of confined and ill-ventilated sp.tces ,s often much less pure, as it is rapidly alie.red by animaj respiration and burning illuminating material An adult man exjnres about sixteen cubic feet of a|r per hour and about ,«,th of this 1. carbon dioxide. A single gas-jet which consumes three cubic feet of coa gas per hour (equal to about ,50 grams of oil or mt) uses up more air th^m two men. When the proportion of carbon dioxide reaches 0-C9 to 01 per cent, the air is clogft and * fu=tv ' £0 — - senses, and is unwholesome. The late Dr! VmhL Ma I *? 1 1 li 164 Experimental Chemistry. held, and we think rightly, that air should be con- sidered unwholesome for" human beings when the carbon dioxide present exceeds 006 |)er rent., or 6 volumes in iq,ooo, the carbon dioxide being in this case taken as a measure of the general purity of the atmosphere. • Good ventilation aims at keeping the atmosphere of a room well under this standard, and for this purpose 3,000 cubic feet of fresh air must be introduced per head every hour, and about twice this volume of fresh air per hour for each gas-burner that hourly consumctJ three cubic feet of coal gas, un- less the products of combustion arc removed by special means.* Experiment 94. —Take two plates ; expose to the air on one some lumps of calcium chloride, and on the other some common pearlash— impure potassium carbonate. After a time both substances will [)e found in a moist condition, having absorbed aqueous vapour from the atmosphere and dissolved in it, or deli- quesced ; if exposed long enough each will become completely liquid, and a strong solution of calcium chlorfde be formed in one case and of potassium car- bonate in the other. Both substances are spoken of as hy^roscopii\ or moisture-imbibing bodies, and thus serve to prove the presence of water in the air. ' Two methods will t)e found in Chapter XX. for the esti- mation of CO., in air. » The amount of air-space required for healthy adults in a foom is at least 300 cubic feet per head \ hut it is well to aim at a hijiher proportion. A room la feet long, lo feet wide, and 10 feet high contains, when free from furniture and inhabitants, I.aoo cubic feet of air, and mil therefore accommodate four Sviiithy udutis if uu^ajuaic veniiiaiion be provided. Moisture and Ammonia in Air. 1 65 Experiment 95._Piace a few pieces of .ce in a N-.st..ube ; the sides of ,l,e lat.cr are soon cookd down nearly ,0 the .em,,era.ure of m.hing ice. and m tun ,hcy cool the a,r immediately m contact wnh the exte nor of .l,e tube : moisture is then seen to be de posited on the glass, because a,r nearly saturated wuh aqueous ■ .our at a comparatively h,..h tem perature deposits much of its water when cooled neaHy th. !, \'^'r« P"'"'- " '° ''ny temperature k-low would suffi ■ """""" °^ ^■"'""' """•'•"y P^'"^"' salumtion point is passed, the excess semrates in he form of dew, cloud, or rain. Therefo e. by the atracuon of deliquescent bod.es and by the method of coohng, we learn that ordinary air contain, aqueous vapour , the amount of this is. however extremely variable. "uwcver, of h^owr"^'"* °''-: ''"' " '^^8^ S'-^^' beaker capable of holding two or three liters with fresh and clean am w^ter ; add to the water about ,0 c.cs. TnI^Z /«/ solution,' and let the mixture stand after mixinr Few samples of rain water fail ,0 show a pale yel ot colour when treated with the test, which lit, r is hi moisitirp in nJr « .u '-naptir A\. for estimation of 1 Ti t»'^"«'»i iiufyect of liyi^rometry. io<,i„i'"sr,i;r;z. °' "" "'"""" " ""^^-^ ""'" ' *>0 delicate Is this tt^t fW •'♦ »':" J-Js • __ I part of .mrnonia 1„ io.ooo:couorwa.e;r"" "' '"""""' "* 166 'I Exfierimem, Chemistry. Jht animoma (NH,) in air rarely exceeds one ^^en c tnH A T ^- ■"'""' "f ''""• ''"'°""'» '° be- tween 5 and 6 lbs. per acre annu illy, and from this source vegetation on uncultivated soils derives some Of the nitrogen necessary for healthy dew! mment. though ao the elaborate experiments of Mess,.. Lawej and Gilbert at Rothamstead have shown, the agrirul- tural importance of this aerial ammonia has probably been exaggerated. ""luiy VVe have already (Experiment 69) learned how to test for ozone in air, and the characters of the other accidental constituents of the atmosphere already enumerated will best be dealt with under the severi compounds. >- waj If Exftrimtt CHAPTER xrv. «XPEH,ME.T. W,T„ COMPO^NOS OP K.TROCEN. f IS. io. nitrogen, potassium, and oxvirpn in n,<. indicated by the iorrc^Z^Zl' '''°''°«'°"' NtTRic Ac.n= HNO,.-J/,w^^ „^,i^,= 6, _ Experiment 97.— Plar^ in , ...i...i-._. . % 60. about 30 gran, of nitr^ and ;:;;'';" e7hwit;' '4 W' • k-»1t*'j MICROCOPY RESOLUTION TEST CHART (ANSI and ISO TEST CHART No. 2) 1.0 I.I 1.25 15.0 "" ■■1 yy 3 A no ■■ 1 4.0 •A u ■iUU i" 11111= |2.2 2.0 1.8 1.4 1.6 ^ /APPLIED \^J\A\3E Inc S^. 1 653 East Main Street r.,S Rochester. New York 14609 USA SS: (716) 482 -0300 -Phone SaS (716) 288 - 5989 - Fax 1 68 Experitnental Chemistry. \ ' ■ strong sulphuric acid; connect the retort directly with the receiver /, which latter is supported by the dish d containing cold water ; gently heat the retort and raise to the boiling point; a heavy fuming liquid of a yellow colour distils over and collects in the receiver, which latter should be occasionally cooled by pouring water over it. When the distillation is at an end allow the apparatus to cool, when the residue in the retort will solidify to a crystaUine mass easily dissolved out by water, and consisting of acid potassium sul- phate, KHSO4. The contents of the receiver are now to be examintJd. a. Allow a drop of the liquid to fall on a piece of blue litmus paper ; the latter is instantly coloured red and then bleached, while the paper is soon de- stroyed—therefore the liquid is a strong and corro- sive add. b. If a piece of white silk, some wool, or coVk be immersed in the acid it is quickly coloured yellow, and, in the case of the cork, soon destroyed. The skin is likewise corroded and stained yellow by the acid. c. Add a few drops to a solution of indigo ; the blue colour of the latter is instantly changed to a dirty brown. d. Place a few fragments of copper in a test-tube and pour over the metal a small quantity of the acid. Deep ruddy fumes are rapidly evolved, and a blue liquid remains in the tube. The acid possessing these characters is nitric acid, or aquafortis, whose formula when pure is HNO.3. A he foiiowmg equatioii represents the change liia-t Experiments iviik Nitric Acid. i6g takes place when nitre and sulphuric acid are heated together — J^NOa^ + £^J^ = ^NOa + KHSO4 Potassium Sulphuric Nitric Potassium and nitrate. acid. acid. * hydrogen sulphate. On the large scale the cheaper sodium nitrate (NaNOg) or * Chill nitre' is used instead of the potas- sium compound ; moreover, in order to avoid wa{;ve of sulphuric acid, two molecules of the nitre for one of acid are used, but the heat required to complete the operation is much higher than that employed in the Experiment 97, and the residue in the large retorts used is neutral sodium sulphate, Na2S04— 2(NaN03) ^ H2SO4 = 2(HN03) + Na2S04. Pure nitric acid has a specific gravity of 1-510 (water = i -ooo), ^ The best commercial acid is a colourless liquid of specific gravity 1-420, and contains about 30 per cent of water. When exposed to the air it emits an acrid corrosive vapour, and begins to boil when heated to 121° C. The acid is distinguished by the characters and tests already observed, and we have in the copper test (d) an experiment illustrating the fact that nitric acid is a powerful oxidising agent, since it easily suffers deoxidation to a low oxide of nitrogen, to- • The colour of the ordinary acid is due to the presence in solution of oxides of nitrogen ; these can "be removed by making a stream of air bubble through the acid. Other impurities OiiSn lOUHvi jn t«v eoinmercial acid arc sulphuric aod hydiO- chloric acids ; for their tests see the respective acids. I' ill; Jill 170 Experimental Chei,nistry. gether with loss of hydrogen. In the case of copper the reaction in the strong acid may be thus written— f.^ + ^J^3 = N2O3 + 2(Cu(NO,)2) + 3H2O. Copper. Nitric 'Nitrogen Copper Water' Nitric acid. 'Nitrogen sesquioxide. Copper nitrate. The ruddy fumes observed in the experiments con-' sist in part of the sesquioxide of nitrogen, and the blue liquid formed contains in solution the blue-coloured copper nitrate,* which latter can be separated by evaporation and crystallisation. Experiment 98.— Put a lump of red-hot charcoal on any suitable support under a flue. Take up a few drops of strong nitric acid in a long glass tube and allow the acid to fall on the charcoal. Note that violent action at once takes place, the charcoal burn- ing rapidly in the oxygen of the acid. Experiment 99.— Add some of the acid to a solu tion of ferrous sulphate or 'green vitriol;' it at once communicates a black colour, which is changed to brown on boiling. 2 This is the iron test for nitric acid. Experiment 100.— Place a crystal of the alkaloid Brucia on a white plate and let fall a drop of the strong acid upon it Note that a fine orange redzoXom is developed. Experiment 101.— Place a few cubic centimeters of nitric acid in a capsule, and add caustic potash solution until the acid is neutralised ; then evaporate ^ For the action of tbe weaker acid on copper, see page 179. * Foif the explanation of this, see page 180. Experiments on the Basicity of Nitric Acid. i;i until a peilicle forms and allow to stand On cooling crystals oi nitre separate— HNO3 + KOH = KNO3 + H^O. The analyses of nitric acid and of nitre lead to the formulae just given as the simplest expressions for their composition ; but the discussion of the analytical data cannot tell us whether nitric acid may not be represented by the symbols ^ H^N^Oe, and nitre by K2N2O6, or some multiples of these values. Moreover the vapour of nitric acid is so easily decomposed by a high temperature that Avogadro's law cannot help us to decide between the above formulae. How then are we to pro.-eed in order to determine which of the formulae, HNO3 or H^N^Og, for example, is correct- m other words, whether nitric acid is mono- ordt-basic} (See Part I. page 84.) A little consideration will satisfy us that if the acid be di-basic and its formula H,N,0, , It ought to be possible to form a second potassium salt-one containing KHN^O^. We must, therefore, make an expeiiment calculated to deiermine this point. Experiment 102.-Take two porcelain capsules perfectly clean and dry, and place one on each pan of the balance and counterpoise exactly; then mark one capsule A and the other B, so as to know which pan it belongs to. Remove the capsules and place In each 10 CCS. of the same strong solution of causti6 potash coloured blue by the same quantity of solution of litmus. Now neutralise the potash in A by nitric acid added gradually, without loss, from any convenient measanng vessel Note the quantity required for this i-h ^72 Experimental Chemistry. purpose. Next add to the caustic potash in B double the quanuty of the nitric acd required to just neutra- lise the first. Place the two capsules dose togetiier on a small tray of sheet iron, the bottom of which is covered w,th a layer of sand, and heat this 'sand bath' ZZT\^ V ^"f """'P'"' "'^'"^ underneath, so as l^Vh . K r """^ '" ^""""^ '^•'"'^"''^ »'°»''y evaporate without boilmg or spirting. When the solutions have been concentrated to the some extent small crystals separa'^ ' "o difference is observed in the appearance of these or m their apparent amount, but during evaporation acid fumes are freely evolved froin left ?r T \ ^'""' '^^'■' """• ^ dry mass is left m each capsule and acid vapours are no longer given off; then when cold, replace the capsules t Aei respective balance-pans. If the operations have been carefully conducted the capsules should still counterpoise, proving that the same weight of matter was produced in each case ; and when each residue .s carefully examined it is found to possess all the detected there by a great gain in weight and by differences m the characters of the safts obtained m the two capsules. No new salt is separated, but merely a mixture of nitre and excess of nitric acid is obtained, and the latter being volatile is dr ven off during evaporation. Therefore nitric acid is a monr! basic acid, and its formula must be written HNO, ?'.-.p,nment I03.-Introduce into a test-tube some solve the latter, and heat No fumes will h^ <.v.i„„^ B double t neutra- together which is id bath' \ so as ^^aporate •ns have crystals earance during i from mass is » longer ules in IS have Id still matter residue all the rm the Band nd by •tained :d, but acid is en off mono- tsome o dis- Dlved. Gunpowder, its Composition, 1/3 Cool the liquid and add a cubic centimeter or so of oil of vitriol ; violent action soon begins and ruddy fumes are freely evolved, just as in Expernnent 97, d. In this case the metallic nitrate is inactive ; but on addition of the powerful sulphuric acid the salt is decomposed as in Experiment 97, and the nitric acid thus set free at once produces its characteristic effects. For a similar reason a metallic nitrate reacts, as in Experiments 99 and 100, only after the addition of^ sulphuric acid ; hence this addition cannot be neglected in testing a salt of nitric acid. Experiment 104.— Mix a very small quantity of nitre with about one-third of its weight of powdered charcoal in a small porcelain crucible, and apply heat Violent action almost amounting to explosion takes place ; the mxture is said to * deflagrate '—the carbon or charcoal burning in the available oxygen of the nitre. All nitrates » cause this deflagration. When sulphur as well as charcoal is mixed with nitre, gun- powder is produced The proportions of the ingre- dients differ somewhat, according to the purpose for which the powder is to be employed, but the per- centage composition of good rifle powder is— Nitre ..... 75 Sulphur . . . .10 Charcoal . , , .15 Such a powder when fired affords about 280 times its volume of gas, corrected to o" C. and 760 m.m. ; and this gas is found to be a somewhat variable mixture of nitrogen, carbon dioxide, and ' For the characicrsi of particular nitrates, see Part 111, ii m. :' 174 Experimental Chemistry. carbon monoxide gases, with much smaller pro- portions of other gaseous bodies. A solid residue rich m potassmm sulphide, results from the decom' position, and this, when blown out into the air from the muzzle of a gun, quickly burns and forms potas- smm sulphate, of which the white smoke chiefly consists. v-'iiciiy By the aotion of phosphoric anhydride on strong nitnc acid colourless crystals can be obtained con tammg N,0, This is nitrogen pentoxide, or nitric SS'th^s-'^" '''''' '° -^- " «-- NsO, +*H20 = 2HN03. The same anhydride is produced when dry chlo-' rme gas is conducted over dry silver nitrate: silver chloride and oxygen are likewise obtained- 2AgN03 + 2CI = 2 AgCH- N2O5 + O. Poisonous action -Strong nitric acid is a powerful corrosive, colouring the skin or mucous membrane yellow, and destroying the tissues. When swallowed It acts as a strong irritant poison and produces violent vomiting, great pain, loss of voice, difficulty of breath, ing, and ultimate death. When much diluted with water the acid can be safely taken in small quanri ty ^«A^<,*..-Calcmed magnesia or dilute solution of borax, followed by oily or mucilaginous- drinks. Nitrogen PERoxiDE=NO,orN,0,.J/^/;K,«^/,/=46. I^perLment lC5.-Take a tube of hard glass closed at one end ip, fig. 6.). Having introduced Experimefits with Nitrogen Peroxide. 175 about 10 grams of dry and powdered lead nitrate into a, bend the tube in the form shown ; then apply heat to the salt ; presently deep orange fumes are given off, and these pass down the tube b\ if che bend r be immersed in ^ freezing mixture of ice and salt, or a mixture of hydrochloric acid and sodi'iru sulphate, Fig 61. the fumes condense and form drops of a blue liquid, which solidifies to a white crystalline mass if cooled to - 10° C. This body is an oxide of nitrogen whose formula in the state of gas is NOg,* though often written N2O4 for reasons that will be stated when con- sidering another oxide of 'nitrogen. • When electric sparks are passed for some time through dry air, a mixture of oxides of nitrr»oron jc fx—v-r^,! . i. . ., . body occurs. ml 176 Experimental Chemistry prcsIL'r"'"""" ^' '''' '^^^ "'^-'^ - thus re. ?b;W03), = .NO, + PbO + o Lead nitrate. Nitrogen peroxide. Lead oxid£. Oxygen. • oxid?' '''^'" ^'^ ^-^ "^'^'^^ "^^h the nitrogen per- .> KnKM ' 'u^ ^""^ '''"^' ^'^'^ the delivery tube make t bubble through .// ./ ,//././. Note that much of the ruddy fumes dissolve in the acid th.T escaping. ^^^^' the oxygen Of n^^ietlTl'"^"'^ ^^^'^^ '° '- -'>-^"- ^NO, + H,0 = HNO3 + HNO, Nitric acid. Nitrous acid. N,TK0GE._S.SQ„,0X^, OR N.TROUS AnhvorzoB Nmous Acm=HNO, J/./,^/,,, ^.^^/^^^ blue hqu.d, or when passed into ice-cold waTekfbiue ft* thus re- 'e make nuch of oxygen ^assium ed. :e-cold tained. lixture oxides \ )US I. 3RIDE vo of ^6i ; ne of rown brda blue Experiments with Nitrous Add. ij^ solution is obtained. The formula of the body is N.O The reaction ,^hich affords u .s thus expressed^: " AS2O3 4- 2H.,0 ^ -f- 2(H3AsO,) Arsenic acid. 2HNO3 + Nitrogen sesiiuioxicle. The arsenic acid remains in the tube. We have'alre.rfv anMride, ,i.e N^O,. and^SI dSrbut te" events o?r:r '^''^ "'-^ -•-'' ^'^^^^^ N30a + H,0 = 2HNO, Nil acid. rous rt will be remembered that this is one of the two aads^a^ady known to result from the action o/no: b. Add a few drops of the solution of nitrous acid ° pot'i'umT' '^ ' ""'^ ^""'^^'^ """^ »n whh wh chT P'™^"«'''"^'^' ^ body rich in oxygen v.ith which ,t easily parts, and then loses its fine pu^l" tc. ^ In the above case, nitrous contains less nwl' .L?^f J° N 'i ' 78 Experimental Chemistry. HNO, + O = HNO, mikfnU correTpondrJ:"''' ""^ Pe"nan,a„ate. by ^ '-urresponding experiment. or Joo ci' of^wat"'' °' "" ""^""' "^'^ '° "° i„jj "'"^'^ containing a little Doh«,„m IJiuuucea Jt the so ution be vrrv Hi'ii,*^ 'iodidrof s'ta'ch . 'fn th"'" ^^'^-g'y ^o'o-ed hydrate. oxide Nmic Ox,BK=NO or N,0. Mol. ..^,,=3, ,,,,. Expenment 107.-Take the bottle, fig. 6.. used water ihe ,.e,„ „„, beir^dt .'::;::" "''-*" '- -» le nitrous disinc: or in dilute nate, by to 200 otassium v^ colour ite, or a e to 'the I of the oloured acts as NO Nitric oxide. n atom f nitro- nitrous in the ' or 60. , used 5n, and means, in well Experiments with Nitric Oxide. ,;g '" tJie preparation ot hydroecn oas nn^ • . j some copper turnings or v.refmo^r.. "•'"''"'* with some warm water and in 1-t 'l "'"'' \ "'«••" the thistle funnel. NoV ?i" 1 ^^°l^ ™^^>'"« a liU>e strong nitn^Idr ct ^ a^'"''^' '"'- commences and „n,<:h gas is evolved ?hl r '''°" are allowed to escine m,l .^ ' '^'''■■" P"""'"^ usual i„ the ars As' 2 , ^'' " "'"" ^""""-•'ias jars. As the evolutiot, of gas slackens, a Fig. 6a. little more acid will make it brisk arrafn Ti. • . gas should be allowed to ^fJZ ^ i ^^ ^^'' ""^ short time in order Zf h T ""''' '^' ''''''' ^^^ ^ generally a^X ma^SSth^ ""^^^ ''''' leave the gas colourless. ^ ' '" '^' ^^^^^ ^"^ follcSli^JLnilii^r^^^ P^°^"-^ - the g reaction with the somewhat if//u/e^ acid— SCu'' + 8HNO3 == ^Cu'YNO ^ ^ ^Tr^ -» • IV oxide. :' S: i8o Experimental Chemistry. iln Fig 63 a. Remove a jar full of the colourless gas, covered with itf glass plate as usual. Withdraw the plate and note that brownish fumes are instantly produced when the gas meets the air. This is the most characteristic property of the gas, as it rapidly passes into one or other of the higher oxides of nitrogen— N.Og or NO — on meeting with a sufficient proportion oV>.. oxygen This property is of the utmost importance in the manufacture of ojI of vitriol. A Place a piece of phosphorus in the spoon, lig. 63, and touch it with a warm wire ; while it is just kindling or burning feebly, plunge it into a^jar of nitric oxide— the flame is almost or quite extinguished. Now withdraw and again kindle, but let the phosphorus burn briskly, then plunge into another jar of the gasj vivid combustion now takes place. In the first case, the temperature was not sufficiently raised to decompose the gas and render its oxygen available; in the second this decomposition occurred, phos- phoric anhydride was produced, and free sTnZrVt ^r ^'^ -^Pe^n^^ents may be made with sulphur and wood. c. Make a strong solution of ferrous sulphate (green vitriol) m water and pour the solution into a jar of the gas, close the mouth quickly with a glass plate or the hand, and shake. Note that absorption occurs, as the plate or hand is drawn tightly up to the mouth of the jar, and the contents of the latter become dark-coloured. Therefore the gas is easily soluble in solution of ferrous sulnh.-.fp .j,„„„i, , / Fig. 64. Experiments -mtk Nitric Oxide. igj of pure water dissolve only ? c r. nf ,1 definite comtwunrl i- f„ j • '''^ S^^' A niula is no' FeSO ^ If'Th !," f ''"'°" ^^ose for- the nitnc ox de ifdriven off' ''"''' ^' "'""^'^ brownish solution le Th f '' ""'^ " ^°'"^^^''« compound is fo med in.^ 7 '. "^"^ dark coloured the nitric acid and the rv'J f '" <^^°'<'d'ses nitric oxide-then d«!>l '^1°'^"" "^ reduction- ExpertaenJ "oa-F ;r: L'eVf^r f ^""*^'^- %• 64, with mercury, and "n vert in ™ '^°""' stout tumbler ; now in ™^'''^"y '" '^ troduce as much nitric oxide gas as will about half fill the tube. Pass tip into the gas, through the mercury, a pellet as large as a pea of the metal potassium (iiie ,at. ~y Jfth 'r fhS:,Tf -^^^^^ sium can be thrown ilth/"''."^ ' ^'"'' '"^^ P"'^^" any mercury theT p T^ " ™'''°"t "saving tube still uLer the furfur V'\""™''' ^''^^^ "^«' end a depressed 1 1 f "'" "'^'■^"^y ^"d the potassium the m!,^''°""' "'^" "PP'V heat to the with the oi r/l'":L^lt1?^ ^°"''"^^ mtrogen gas. Allow the apmrntus t ' f"^. ^"^ that the mercury has r^^ZT. ^^'^L""'^ "°^« Penment be properly co„du«,,Th;- ^^' -J- ii'i 1 82 ■■'' Experimental Chemistry, .assuming that it contlt , "^S^^^"'"' Justified in Heat the copper stronp^v = ^ Experiment 52. Fig. 65. nitrogen when co.,:ct;d'l1i:Ld^ 7^ '" °^ IS abstracted by the copper just TsTn ih ? °''^^'" but to find the eXL tl ^ ''"°^"' *^ have Cotnposiiion of Nitric Oxide, n specific grav r i! o„ ' °^'" t"'' '"'>'^^"' ""^ its .4'99 X 2 -J:.'s f ; ' "■■'"^ ""^ conclusion, for gasfor the ^ekhfof two /'"°'''"'" "^'^ht of the and one ^/l erSrffrc 't-""''«^-^- certainly NO. '^rmuia ol the gas is But the nitrogen atom is pentad nr fi i- i and that of oxveen H,-o^ Pentad, or five-hnk, ..^ -ui ^-xygen diad, or two-linV o«^ unatticJr/.''Ir:eTarrrer2^ ^"^ °"^ """^ the general rule that frle J.T } I ^^^^V^^ou to links (i.e., centres of atacSnih"' '" *•='' atoms enga-ed Som/ll ^ • ''^"" ^mponent this ^^X-J:2:^z2^o'': " ^" °-' weight acc:<;::;T: i::;s:r,r^ r'^^r far above its conde„t^ ^f"^ ^' '^-"P^^^^^^ NO, whicl! sTrlTlkf^^^^^^ '° '"^^ ^"""""^ is cooled down 7fs t V / ' •'"" ''''''" '"^^ gas ^3 (H = r) t^nVr ;K cE Ir^"!: ^^'"^ Point-the latter number gvesth. °ot' 7"'^"^'"^ 92 and the formula N„0.^ t,! .! l","'*^^"'" weight assumed in the ca0 by ue Experiments with Nitrous Oxide. , gj when cold, is removed from th^ hn.- ^ 'n a well-closed bottle ITw^a ^"" ^"'^ Preserved Experiment 11 If t Vn o f ''^"''''"' ^y- the preparation of oxyg n L 6,^'^ "'''' ""' '°' the flask about 30 grams of fh ^'^^ "''°''"'" "«° prepared as just descr L ^ ^^mmonmm nitrate, corlc carr,ing\he dS^'^bfanHll '^T' ''' matic trough with /,^, . ' , '""^'^ 'he pseu- The salt mf,„,?d etlr ^f' '^' ^^P'^ ''^^t. the temperatur; Shes "o c" rf '"'•^'^''" ^^ -^30 u The gas is termed Fig. 67. cloudy at fir.f „, ^ ^ ^"'■^ "^ generally carried oyer ^ .11"^ '° "'''''''' °^ =^""« "'«'er colecule oi this g^ u«at of nitric oxide, contains ... ^. if^; By the method adopted in Experiment 109 it can be shown that this gas, like nitric oxide, contains hd" 3-.6/c".:nhf^""'""" '"^-^ '-perature abscbs fo Physiological Effects of Nitrous Oxide, 187 its volume of oxygen. It therefore contains, for the same volume of oxygen, twice as much nitrogen as nitric oxide, and its formula is N^O. The change that takes place on heating ammonium nitrate is therefore represented by the equation— NH4NO3 = N,0 + 2H,0 Ammonium nitrate. Nitrous oxide. The molecular weight of the body should be 44 = (14 X 2) + 16, and its specific gravity (H = i) ought to be —= 22. The experimental number is 21-99 ; therefore the above formula is correct. Consequently I vol weighs 21 '99 c.grs. at 0° C. and 760 m.ms. Experiment 113.— Take a jar, that we may call A, containing only air, and hold it mouth upward. Take a jar, B, of NgO, and turn it mouth upward also and remove its plate. Now slowly pour the gas from B into A, just as you would pour a liquid from the vessel, and test both jars with a taper having a glowing wick. The taper is re-kindled in A, but not in B, thus proving that the gas is so much heavier than air (1-52 times) that in can displace the lighter air just Hke liquid. The gas cannot be retained in an open vessel for any length of time, as it escapes by diffusion (see Experiment 92) into the atmosphere. It is liquefied by a pressure of 30 atmospheres at 0° C. The gas is often termed laughing gas, in allusion to the curious property Sir Humphry Davy found it to possess, when mixed with some air and inhaled of causing temporary excitement and a sense of p. i88 Experimental Chemistry. PC! H exhilaration. When unmixed with air or oxygen, and pure, nitrous oxide produces insensibihty if inhaled tor a short time ; at first ringing noises are heard and a general sense of pulsation ' is experienced, then sleep supervenes, during which any short operation, such as the extraction of a tooth, can be and frequently is performed. A few full respirations of pure air restore the patient, and no unpleasant after-effects follow the administration. In the latter respect nitrous oxide IS superior to ether and chloroform as an anesthetic U.e., a body used tp procure insensibility to pain) but the gas can completely suffocate if too long inhaled Ringer says of it : ' It appears to me to produce its anaesthetic effect by preventing oxidation of the ner- vous centres, and this chieiiy by depriving the blood of its supply of free oxygen from the air.' Although there is more oxygen in nitrous oxide than in aiN it IS chemically combined with nitrogen, and thu's we have, m the comparative action of nitrous oxide gas and air on the animal economy, a remarkable illus- tration of the wide difference in characters that may exist between a chemical compound and a mechanical mixture of the same elements. We have thus recognised the existence of five oxides of nitrogen, two of which are anhydrides of distinct acids. If we assume that the molecule of n„rL^'^^"' '''''^^ ^'' '"^'"^'^ ^°^ '"^^1'-^^'°" should be purified from ammonia and higher oxides of nitrogen by Gb hging It to pass in succession thro«gh sulphuric acid and uLkT . r? ^^"'P'^^^' "^ S'-^^" -^"°'' contained in suitable wash -bottles. • 53*$ pe? omU hy weight, as against 23 per cent, in air. %'. air,' N2O N2O2, or NO. N2O3 N2O4, or NO2 NoOv Experiments with Ammonia. 189 each oxide contains the same weight (i.e., 28 parts) of nitrogen— althv u.jh we know this is not quite true in one instance at least-it follows that the group of known oxides of nitrogen is a complete series of com- pounds resulting from successive additions of single oxygen atoms to the lowest term-i.e., nitrous oxide. Thus — Nitrous oxide , , Nitric oxide .... Nitrogen sesquioxide, ornitrous anhydride .... Nitrogen dioxide . : Nitric anhydride . In this group of bodies we therefore have additional evidence in support of the law of multiple proportions already deduced from the examination of the two oxides of hydroi^en. ( Vide Part I. under Experiment 80.) Ammonia = NH3. \ Vol iveighs ^-^ c.grs. Molecular weight =-17. Experiment 114.~Boil some metallic zinc with strong caustic potash solution in a large test-tube • the metal slbwly dissolves and a gas is evolved which burns at the mouth of the tube, and can be easily shown to be hydrogen, and zinc potassate is left— Zn + 2KOH = Zn''(0K)2 + 2H. On the addition of a few drops of nitric acid or a little mtre to the solution anH ckn^\r^ i,^«*.«„ *u "ft""' "^avijig, tiic pun- gent smell of hartshorn is noticed, and a piece of i: J Itl J 90 Experimental Chemistry. pour We r ''"'• ''''''"'' °' "" """"'"' ^^- the hydrogen, 'no'lo^^e^::;; ; Vufwh/nT "he' «<,...«/ .state, quickly deoxid.ses , he nitre form „! nitrogen of he nitre and forms ammonia gas which lajter^ evo,.d^.hi,e potassium hydrateTiSt KNO3 + ^H = mi^+ KOH + .H,0 Potassium nitrate. Ammonia. Potassium hydrate. Experiment 115.— Pass a rnrr^nf r hydrogen through a hot aiic^iin^e sX To ofnitfe^d ra e':/r 1? ''' "'* ^^'^'^-^'^ litmus-paper No trace of allcahne ammonia can be detected if tZ materials employed are pure, and care be Ikl t^ prevent any of the liquid reaching the paper '° ^^«.f fo experiments well illustrate the difference rJ TJ .''"'"""" ""' comparatively stable free mole condhL;'':rf "^ *^ "^^ ^■^"^"' - *~' condmon-i.e., at the moment of liberation of its atom from a compound, and, as some suggest before It can meet with another atom in orderTform °he ^rb:r:-r,atey--'^-----='"^^^^^^ Experiment I16.-Take a tube of hard gia.s closed at one end, and one-third fill it wirpites of horn, bone, gelatine, feathers, wool, hair, or, if the From naxrn^. l-rt K/» 1 y ■»--- s^« uvm. Experiments with Ammonia. Fic. f S. 191 Teat \L '"^' ""'• ^"^'"^"'^ °^ '°=^'. and apply heat. The organic or carbonised matter soon ri7 voTErtt r '""'ir^^ °^ '"^ heatand variot to bluu All the bodies mentioned agree in cnn taming nitrogen-even coal contains from to 2Z Wise present,ii^:;^:rmlT 7.1 '''-'-' "^^" nitrogenised animal and vegetable bodies afford more or less ammonia m this way, not only at high but at ordinary temperatures, when they undergo slow putrefactive change or decomposition in presence of mois- ture-in fact, much of the atmo- .spheric ammonia is derived from the-e sources. ^ Most of the ammonia employed in the arts is obtained from the tarry ammoniacal liquors collected during the manufacture of coal gas. The pre paration of sa/-ammomac and similar ji^ TndSs oH '""'^^ .'^'-''^--^ will be referred to unoer baits of Ammonia ' in Part III aJo!^T' '^^-^---^y powder some ../. with rather more than its own weight of slaked '' Or distillation attended by decomposit ion. X ig2 M Experimental Chemistry. hme in fine powder, quickly transfer the mixture to the flask / fig. 68,. insert the cork carrying the delivery tube d, -nd invert over the free end of the latter the dry h tie On applying a very gentle heat to clrr mixti, n , / abundnnre of ammonia Kas fs evolved, \ht pungei.^ smell ot which is quickly perceived, ^vhiie red litmus-paper passed up into the gas is instantly rurned blue, .md white fumes are pro- duced when a glass rod," moistciied with hydrochloric or acetic acid, iff I'lfought to the mouth.' Note that the pure gas is colourless. 2NH,C1 + Ca(0H)2 = 2NH3 + CaCl., + 2H,0 Ammonium chloride. Calcium hydrate. Ammonia. Calcium chloride. Fig. 69, a. Pass up a lighted taper into a jar full of am- monia. The flam- is extinguished without igniting the gas. A Take a dry gas jar and at- tach a piece of red litmus-paper near the top inside by means of gum. Invert the tube, and bring under its mouth a rather larger tube full of ammonia gas, as shown in fig. 69, and slowly invert the latter. The colour of the litmus in the upper jar quickly changes, proving the ascent of the ammonia, and the flame of a taper is ex- tinguished if passed up into the gas. Therefore am- ' Any other ammoniacal salt may be used instead of the chloride, aad potassium or sodium hydrate instead of lime. I mixture ying the id of the ry gentle onia pjas quickly into the are pro- ochloric fote that f- 2HnO I of am- guished and at- is-paper cans of d bring ■ larger 5 shown 'ert the litmus hanges, imonia, is ex- )re am- d of the ue. Experiments with Ammonia. 193 monia {slighter than air, and displaces the latter from the upper jar. Its specific gravity is 8-5 (H = i) or but httlc more than half (0-586 if air = ,) as heavy rri air. ^ c. Fill another stcit bottle with the gas, close with a glass plate, and remove, still mouth downwards to some water ; withdraw the pla! « when ti.e mouth Fig. 7a IS under water. Note that the water rapidly rushes into the jar and nearly fills it ; therefore ammonia gas IS very soluble m water-in fact, i c.c. of water at 15 C. and 760 m.ms. dissolves 783 ccs. of ammonia gas, or 783 times its volume. ^^ SAperiment I18.-Prepare ammonia gas as be- fore, .-ut wasli it from impurity by making it pass" ' '94 Experimental Chemistry, through the small quantity of water ' in the little wash- bottle z£/, fig. 70, and then conduct the gas into a measured quantity of water contained in the bottle b, which latter is cooled by immersion in a beaker of cold water, as heat is evolved during absorption of the gas. Apply heat to the flask/ and pass the gas through the water in b as long as it is absorbed, but when bubbles pass through without sensibly diminish- ing m size it may be concluded that all the gas has been dissolved that the water can hold at the particular temperature and pressure. Measure the bulk of the liquid in b after Ijhe experiment, and it will be found to have increased to the extent of about one-half its volume.2 This 'solution of ammonia ' is colourless, with a characteristic and very pungent smell, and strong alkaline reaction to test-papers. The specific gravity of the solution is about o-88 (water = i). When the solution is heated, ammonia gas is expelled, and after boiling for a short time almost every trace of the gas is removed ; thus ' solution of ammonia ' is a very convenient source of the gas, and we shall use it presently for this purpose. Ammonia gas is also easily soluble in alcohol. The extraordinary solubility of ammonia gas in water, accompanied as it is by considerable evolution of heat, IS commonly regarded as due to true chemical combination— a new body being formed which closely ' Rather more than 50 c.cs. of water should be used for every 100 grams of sal-ammoniac. ''The process employed on the large scale in the manufacture of liquor ammonia fortior-^ of the British Pharmacopoeia is identical with that given above. ExperimenU with Ammonia. 195 resembles potassium and sodium hydrates in its h^hly alkalme character and power of neutralising acids (e.g. „,tr,c acd, Experiment .10), and forming hence the liquid may be fairly regarded as a hydrate similar to those of the metals above named, in which hydroxylis united to a monad compound radicle NH „ which acts like a monad metal and is termed ammonium.^ Thus— 'c.mcu J^ + HjO = NH'.OH Ammonia. ^T '"~ — "" Ammonium - ' hydrate.* Water saturated with ammonia gas at o° C and under the pressure of 760 m.ms., may be regarded as nearly pure ammonium hydrate, since it contains a weight of ammonia equivalent to about 96 per cent, of JN II4OH. But a slight elevation of temperature suffices to decompose this body, and nearly all the gas can be expelled before the liquid reaches 100° C Thus- NH,OH = NH3 + H20. From the above experiments we learn how to pre- J's'oLt. f"" "^"''^"^ ^^"'^^^^ ^"^' ^"d '^ obtain solution of ammonia 'of the British Pharmacopoeia, or ammonium hydrate. Ammonia can be condensed to a colourless liquid by cooling the gas to a temperature of - 40° C or F. ' See further, Experiment 124. .Z ^"lf^\ compound is known, which is intermediate in composition between NH, and NH.OH ; its composition is represented by the formula NH..OH. and ,> i= ..^^TuTJ^ been replaced by the group OH or hydroxyl. 02 li f , i: ! 196 Experimental Chemistry, (and, it may be stated, this particular temperature is the only one indicated by exactly the same value on the Centigrade and Fahrenheit thermometer scales) by means of a freezing mixture of two parts of snow and three parts of crystallised calcium chloride. The comparative ease with which ammonia gas can be liquefied by cold leads to the presumption that it admits of liquefaction by very moderate compression at ordinary temperatures. By means of the following Fig. 71. cheap and effective apparatus we can reduce the gas to the liquid form. * Experiment IW.-A species of U tube of stout wrought uon is made of the form shown in fig. 71, ALB. A IS about 40 centimeters long, B 30 centi meters, and each is 2 centimeters internal diameter • C is about 25 centimeters and 5 or 6 milhmeters internal tubes. The whole is fastened to the wooden stand A A is provided with ucv^uw a;.icw-cup n^ tne joint Liquefaction of Ammonia, 19; being rendered gas-tight by a leather washer. B is also fitted with a strong screw-cap with a deep head, through which a conical hole is bored ; the long glass tube t of the apparatus / passes through this hole to the expansion c, which should fit into thg cone and be there secured by any good cement. The screw-cap m therefore carries the glass apparatus, which latter is a form of pressure tube now easily obtained through good instrument-makers. The liquefaction is to take place within the glass tube /, which must of course be very strong ; the length of this tube is about 25 centi- meters, and at first it is open ; the wide reservoir o must have at least ten times the capacity of / ; the reservoir terminates below in a rather narrow curved tube w, which is always open. The glass apparatus must be filled with dry ammonia gas by connecting w by means of a flexible tube with/ fig. 70, affording a current of ammonia gas, but freed from moisture by passing through a long tube packed with fragments of fresh quicklime. When all air has been expelled— and a good current maintained for ten minutes is sufficient to effect this— the flow of gas is allowed to slacken and the capillary end of / securely sealed at the blowpipe ; the tube is removed from w and the latter at once dipped in mercury, which enters and prevents escape of ammonia. Now remove the cap n, and • pour mercury into A until the metal rises nearly to the top of B ; then introduce mto B, allowing the mercury displaced to overflow into a vessel placed to receive it, and screw home thp rnn ttl l\u\\\r\\ r\f f^rxuraa. uc piOViuec with a good leather washer). We have, therefore^ '.nl V Is 198 Experimental Chemistry. nothing but mercury between the gas in and the sur- face of the metal in A. Next remove enough mercury from ^ by a pipette to leave a space of some 1 2 centi- meters between the surface of the metal and the cap ; then fill up to the top with the strongest 'solution of ammonia,' and screw down the cap n, and the apparatus is ready for experiment, which is performed in the following way : — Gradually heat the portion of A -containing the solution of ammonia by a Bunsen flame occasionally applied; as the temperature rises, ammonia is expelled from thg solution, but since the gas has no escape, considerable pressure is exerted in A on the surface of the mercury, and the latter, acting as a fluid piston, compresses the gas in 0, which steadily diminishes in volume until at last the mercury rises into view in / ; > and if the heating of A be now care- fully managed, the compression proceeds until a layer of colourless liquid is seen to form on the surface of the mercury in /. This is the liquefied ammonia, and IS obtained when the pressure reaches about 6-5 atmospheres at mean temperature. If the joints are well made and the heating well managed, it is easy to maintain a steady pressure for a considerable time, but anything like violent heating must at all times be carefully avoided. On allowing the apparatus to cool, the mercury recedes in /, and the liquefied ammonia disappears. This apparatus is always ready for experiment, though it is desirable to 'It is well to cover / with a large cage of fine wire gauze, lest the glass should give way when first subjected to consider- Su»e pressure. Covibustion of Ammonia. 199 unscrew the cap of J occasionally and change the kSbV. '"""""'^ " ^""^ '^^"^^S^ ^^^ '^ i' Experiment 120.-As we have already seen ^x- penment 117, <.) ammonia does not burn when a light .s appued to the cold gas. Now pass it through a narrow glass tube heated to redness near to the point at wh.ch gas issues, and it can be easily :gnit"d burn- 2' It :ror""'-^^"°" "^-"^ '" the'oxygen'ofX Z^^ K i""^"'^^^ ""roge" gas and water, hence a Sed'asrj"'° *^. "^^ ^^ ^'-^^y ^ 2NH3 + 3O = 2N + 3H2O. somr'.^i 5 ' "l '""'^^"^^ ^"^ (^b^^i^^d by heating some solution of ammonia ') issuing ^ from a jet be surrounded by oxygen gas and then ignited. The little ap- paratus, fig. 72, enables this experi- ment to be easily performed. ^ is a short brass tube into which oxygen gas can be admitted through the side tube ^ ; « is a glass tube delivering ammonia; this passes through the cork . which fits the brass tube a. Ammonia is allowed to flow through n, and then oxygen gTs de nved from a bag or gas-holder, is turned on camiously, this' fppamtur if ' ^•'''"'■' P""^P ^' "'^^g^^'^^^ ^^-ided in tms apparatus, it is inexpensive. Before usinjj any form ,°'„??!!^i"\^«^^^P--"^« o-he kind described.1t Z,d T !*' Fig. 72. a n 1j< ■>1 I 200 Ej^periinental Chemistry. while a flame is applied to the jet. When the propor- tions of the two gases are properly adjusted a tolerably steady flame can be obtained.' If in the last two experiments, but more especially in Experiment 120, we dry the ammonia by passing the gas through a tube filled with fragments oi quick- lime (CaO), the appearance of water as a product of combustion is proof that hydrogen is a constituent of ammonia, while the mode of generating the latter from nitre adopted in Experiment 114 leaves little doubt that nitrogen is another constituent of the body ; but the following experiment affords us complete evi- dence of the composition of ammonia. Experiment 122.— Fill the eudiometer (fig. 73) one-fourth -h say 20 ccs. of dry ammonia gas over mercury. Measure the volume and pass a series of sparks from an induction coil between the wires within the tube.2 The confined gas is thus intensely heated ' In these experiments the rapid oxidation of ammonia in- volves complete decomposition; but when slowly oxidised, especially in aqueous solution, it first affords nitrous acid, thus— NH3 + 30= HNO, + H,0. The nftrous acid then unites with another atom of oxygen, and produces nitric acid, thus — HNO2 + O = HNO3. The organic matter of sewage readily affords ammonia on decomposition, and the latter then undergoes slow oxidation as just stated ; hence in sewage -contaminated water nitrites and nitrates are usually to be found. 2 In this case a Leyden jar must be placed in circuit in order that the maximum heating effect may be obtained. For this pur- pose it is merely necessary that one of the coil wires should be in metallic connection with the knob, and the other with the external coatinL-^ of the ian Analysis of Ammonia. 201 and decomposed, and if the sparks are passed for a sufficienttime the volume of gas increases to 40 c.cs., or IS doubled. Having obtained the maximum expansion note the volume, and introduce 20 ccs. of pure oxygen and explode in the usual way. After correcting for al- teration of level, the residual gas wiU measure only 15 CCS.; therefore 60 - 15 = 45 ccs. of gas have dis- appeared, two-thirds of which, or 30 ccs., must be hydrogen and the rest oxy- Fig. 73. f^~~-^~ gen (see Experiment 24). As 20 ccs. of oxygen were introduced, and 15 ccs. have thus disappeared in union with hydrogen, the residual gas in the tube must contain 5 ccs. of oxygen. This residue measures, as we have seen, 15 ccs. ; hence 15 — 5 = 10 ccs. of ni- trogen left. J To sum up, then, our experiment proves, firstly, that ammonia gas contains only nitrogen and hydrogen ; secondly, that it is completely decomposed into its constituents at a high temperature ; thirdly, that the resulting mixture of gases occupies twice the volume of the original ammonia ; fourthly, that this gaseous mixture contains one volume of nitrogen and three of hydrogen— consequently the molecule of am- ' By passing up a few drops of caustic potash, followed by a strong solution of pyrogallic acid (see Experiment 83), the that it can be easily identified. i Fig. 74. 202 Experimental Chemistry. nionia gas contains one atom of nitrogen and three atoms of hydrogen, and must be represented by the formula NHg,^ and its molecular weight by 17 (14 + 3). This result is confirmed by the specific gravity of the gas, which, as we have already seen (page 49), is 8-5, and 8*5 x 2 =17. I vol of ammonia gas (112 ccs. at 0° C and 760 m.ms.) weighs 8*5 cgrmr Experiment 123.— Pour a few drops of strong commercial hydro- ^ chloric or 'muriatic acid' into a wide-mouthed bottle ; cover with a glass plate and turn the bottle about so as to distribute the acid over the sides. Fill another bottle with ammonia gas, bring its mouth down on the glass plate that covers the first, as shown in fig. 74, and then remove the plate from between them so as to leave them mouth to mouth. White fumes are instantly formed in abundance, and they deposit a white saline body on the glass after a time which is ' We can recognise the nitrogen acting as a one-link, or monad atom, in nitrous oxide, N'-0"-N', or N.,0 ; as a threes Imk, or triad, in ammonia, N'^H',, and as a five-link, or pentad m ammonium hydrate. N'H',(OH)', the monad group hydroxy]' OH',^ satisfying the fifth link. In the case of sal-ammoniac,' N'H'^Cr, we also have evidence of the five-link or pentad character of the nitrogen atom. In all these cases the links or bonds appear or disappear in pairs. Ammonium Amalgam, 203 identical with sal-ammoniac or ammonium chloride for ^_NH3_^+ HCl = NH'4C1 Ammonia. Hydrochloric Ammonium • ' acid. cliloride. Thus at the commencement of our experiments we decomposed or analysed sal-ammoniac, and now we have reformed it or effected its synthesis, and we have written the formula of the body in such a way as to indicate that it is the chloride of the compound radicle ammonium NH'4, already referred to under Experi- ment 118, rather than NH3HCI, the formula directly justified by its mode of formation. Now the former view assigns to the group NH'^ a pseudo-metallic character, and it may be fairly asked whether am- monium has been isolated, and, if so, whether it pre- sents any of the metallic characters. As a matter of fact, ammonium, NH'4, is not known in the free state, but a curious body can be prepared which is supposed to be a solution of ammonium in mercury. This body is easily obtained ir the following way. Experiment 124.— Introduce about one cubic centimeter of mercury into a wide test-tube ; gently warm the metal over a lamp an'', directing the mouth of the tube away from the person, drop in a fragment of clean metallic scditwt about half the size of a pea. If the mercury be warm enough, the sodium will at once dissolve in it with a little explosion— if not, heat gently. Then introduce another piece of sodium of the same size, and after its solution a third. A Slavery white amalgam of sodium is thus prepared 204 Ex'perimental Chemistry. which retains the metaliic lustre' Now pour out the warm and still liciuid amalgam (for if allowed to become cold it will become pasty or solidify) into about 250 CCS. of a cold saturated solution of sal- ammoniac (see Experiment 73). The amalgam quickly mcreases to at least 15 times its original bulk, and ultimately becomes a large pasty mass, light enough to float on the surface of the liquid. This mass can be removed and washed with water; it presents a brilliant metallic appearance, but it is very unstable and soon decomposes, evolving ammonia and hydrogen gases, and after some time nothing remains but the original mercury. This body appears to be a true amalgam of mercury and the metal-like am- monium, the latter taking tlie place of the sodium • thus— ' JlgxNa^ -f NH.Cl = Hg^^NH^ + NaCl Sodium Ammonium amalgam. ' amalgam. The amalgam then breaks up in the following way-^ Hg^NH^ ^ Hg^+ NH3-f H. There is therefore some experimental evidence as to the existence of the compound metal ammonium, and the close analogies traceable between its saline and other compounds and those of potassium and sodium confirm this view; but it would lead us too far out of our course to examine this question here ; ' Alloys of metals with mercury are termed amalirams ; in some cases these are mere mixtures of metals, in others feeble chemical union takes place, but the product in all cases retains the •metallic appearance. • Expenmcnts with Iodide of Nitrogen. 2c ^ hence we- shall reserve this part of our study until we have to deal with the compounds of the alkali metais in Part III. Experiment 125. - Powder half a gram or so of iodine and add it with frequent stirring to 20 ccs. of ammonium hydrate solution ; allow it to stand for half an hour until a black powder has completely subsided, then pour away the clei\r liquid and dis- tribute the black residue on pieces of bibulous paper. Put these in some safe airy place to dry. When the black substance is dry, a touch suffices to make it explode, when violet vapours of iodine are evolved. If small quantities are operated upon and reason- able care exercised, the experiment is not attended with danger. The black substance is called iodide of nitrogen, and is really a mixtute of ammonia derivatives. Dr. Gladstone's formula for the chief substance is NHIj, or ammonia in which two-thirds of the hydrogen has been replaced by iodine. Analogous bodies are pro- duced by the action of chlorine (chloride of nitj-ogen) and of bromine (bromide of nitrogen) ; but these are amongst the most dangerous explosives known, and have caused so many serious accidents that any de- scription of their preparation is undesirable. Many other derivatives of ammonia are known in which various groups of elements replace one dlhiore atoms of hydrogen in NH3 ; these will be met with later on in our course, but wt may here give the formulae of three of these important bodies— Ethylamine. Diethylamine. Triethylamine. NHalC^Hs)', NH(C2H,)'2 N(C2H,)'3. !ipi iir: 206 Experimental Chemistry, ■ ^ CHAPTER XV. EXPERIMENTS WITH HYDROCHLORIC ACID AND CHLORINE. Hydrochloric Acid (Afuruitic add) = HCl i Vol of gas weighs i^i^'ic) c.grs. Molecular weight ^ 2>(,-c Experiment 12a-Mix some sal-ammoniac-am. monmm chloride, as we shall term it for the future- with strong sulphuric acid in a test-tube. Even with- out heat a quantity oj-gas is evolved which has a very pungent smell and fumes in the air ; it does not burn or support combustion of a match, but it reddens blue • litmus-paper, and produces whitg clouds if a rod moistened u'ith ammonium hydrate be brought near the mouth of the tube. ' ^ ^ The gas evolved is therefore an acidg2.^ capable of uniting wuh the alkaline ammonia, and' this 'body is termed hydrochloric acid, and its symbol is HCl Thus in Experiment 1x7, we liberated ammonia gas from NH.Cl, and m Experiment 123 re-formed the latter by effecting the combination of ammonia -with hydrochloric acid. We have now broken up the compomjd agam, but in such a way as to make it yield itTacid constituent ; thus— 2NH,C1 -f £,S0, = (NH,)^4 + 2HCI Sulphuric Ammonium Hydrochloric acid. sulphate. acid In this case, each group, NH„ takes the place in Ammonium chloride. Hydrochio.ic Acid Gas. 207 the sulphuric acid of ont. atom of H, and the latter unites with the CI of the ammonium salt and forms the acid. Ihe specific gravity of hydrochloric acid gas, detcrmmed as in Experiment 27, is 18-19 (H = i) • and I vol weighs 1819 c grms. Its molecular weight is therefore 36-5 (if CI = 35-5). Experiment 127.-Make a similar experiment with common salt or sodium chloride, and note that the same acid gas is evolved. In this case 2NaCl + H,80, = Na^SO^ + 2HCI <^*^lo'''^e. sulphate. Lower the test tube from which HCl g2i% freely issues into a small dry gas jar standing mouth upwards, and loosely cover with a glass plate. After a minute or two slip aside the glass plate, rapicly remove the test- tube, and pour in a few cubic centimeters of water ; cover the mouth with the hand and shake up. Note that a vacuum is produced, as evidenced by suction of the hand, indicating that the gas has been absorbed by the water ; now test the latter with blue litmus- paper and note that it has acquired an acid reaction. Therefore hydrochloric acid gas is soluble in water and produces an acid liquid. As a matter of fact, the gas is very soluble in cold water, as we shall find presently, for I c.c. of water at 15° dissolves 450 ccs. of the gas at the same temperature. It is a strong solu- tion of the gas in water that constitutes the liquid hydrochloric acid ('muriatic acid' or 'spirit of salt') of commerce. Experiment 128.— A glass flask, / fig. 75, is provided with a cork through which passes" the^gas ,f 208 Experimental Chemistry. delivery tube bent twice at a right angle and passed to the bottom of the wash-bottle w, which contains a very little water, which a tube leads from 70 into a bottle b containing cold distilled water. Place about co grams of common salt or sodium chloride in /and \o c cs. of water in /;, and connect the apparatus as shown Measure 50 ccs. of oil of vitriol and add it gradually Fig. 75. and with stirring to an equal volume of water contained ma porcelain dish ; when cool, pour into the flask, and then, if necessary, apply a gentle heat to/. HCl IS freely evolved as a colourless gas and passes through the water in w, where the first portions are absorbed, and then into ^he water in b. When all air has been txpelled from the solution, the bubbles that pass into the water disappear before they reach the snrfarP fhe Hydrochloric Acid Solution. 209 gas is so easily soluble in water ; but when the latter IS saturated they pass through without apparent diminution of bulk, and thus the end of the process can be recognised. The bottle b must be kept cool throughout, resting in the beaker of cold water. » When the gas is being freely evolved it is well to remove the delivery tube from b, dry it, and pass it to the bottom of a gas jar placed mouth upwards and partially covered ^^ith a glass plate. When the jar is judged to be full of the gas, remove the tube, close the mouth and bring it under water. The latter quickly rushes up and almost fills the jar, or quite fills It if all air has been expelled. . ^ The solution ultimately obtained in the bottle b is a nearly colourless and strongly acid liquid, emit- ting white fumes which have a pungent smell. Its specific gravity is about i-i6 (water =i-o), and it contains about ^2 per cent, by weight of actual HCl. When heated this acid loses gas until the percentage of HCl is reduced to 20-24, and a solution of this strength boils at a constant temperature of 110° C if the pressure does not vary from the normal (760 m m) The common ' muriatic acid ' of the shops always has a yellow colour, owing to the presence of iron - other impurities commonly present are free chlorine' arsenic and sulphur compounds. Appropriate tests for these impurities will be found under their respec- tive heads. ' The process given above is that directed by the British Pharmacopoeia for the preparation of the pure acid. The crude commercial acid is chiefly obtained as a by.product in the manufacture of 'salt-cake,' or crude sodiuL su//>Ta)e!'' sL irart III. p. 283. ■II 210 Experimental Chemistry. Experiment 129.-Mix a few drops of the colour- less acid prepared as above with ten or twelve parts of water, and add to the diluted acid a few drops of silver nitrate solution. Note that a white precipitate IS produced that becomes curdy on shaking. Let the precipitate subside, pour off most of the liquid and then divide the precipitate between two test-tubes. a. To one portion add some moderately strong nitric acid and boil Note that the precipitate does not dissolve. b. To the other part add NH.OH solution ; the precipitate soon dissolves completely, and can be repreclpitated wheh the ammonia is neutralised by nitric acid. The precipitate possessing these characters is silver chloride, which is formed when silver nitrate is added to free HCl, :r to any soluble chloride such as ammonium or sodium chlorides— HCl + AgNOg = AgCl + HNO3 Hydrochloric acid. Silver nitrate. Silver chloride. Nitric acid. Experiment 130.— Add a few drops of solution of lead nitrate (Pb(N03),) to some diluted hydrochloric acid ; a white precipitate is obtained if the liquids are not very weak, and the body dissolves to a consider- able extent in boiling water and separates out in white crystals on cooling the solution. This body is lead chloride, thus formed— ^^^^li3 + 2HCI = PbCl, 4- 2HNO3 Lead nitrate. Lead ^1,1, ...:.4_ Experiments with Hydrochloric Acid. 2 1 1 For another useful test of hydrochloric acid or a chlonde, see Experiment 137 ; and for the distinction of the acd from free chlorine, see E neriment 147 acid wrh""?* ^^^r"!;'"'^ ^°"'^ ^''""S hydrochloric acid with water, and add caustic soda until the acid IS neutrahsed, as m Experiment 42. The solution cTrairoffh" " '"°"'!' °^'°""^" ^^''' '^"d affords crjstals of the compound on evaporation - HCl + NaOH == NaCl + H^O. ■ Other metallic hydrates afford corresponding chlo- ndes when used to neutralise the acid Experiment 132.-Add some black oxide of copper to a lutle of the acid in a test-tube ; the oxide dis- solves easily and forms a green-coloured solution which contams copper chloride— Cu"0 + 2HCI = Cu"Cl3 + 2H,0. Other basic oxides are acted upon in a similar way by hydrochloric acid, and produce metallic chlorides and water; b.-t certain peroxides, such as MnO„ give chlorine in addition (see Experiment 137) '' Experiment 133,-Plunge a strip of zinc into some of the diluted acid in a test-tube. Brisk efc vescnce takes pbce, and the gas evolved burns when a flame is applied to the mouth of the tube. The eas is hydrogen resulting from the reaction- + 2H'a' = ZnXT^ ^ 2H Zinc chloride. Zn'' r If iron be used instead of zmc, hydrogen is also Pa I ! I I I F 212 Experimental Chemistry. evolved, but ferrous chloride ^ferrum^;,^^) is ob- tamed in solution— Fe" + 2HCi ^ Fe"Cl2 + 2H Ferrous chloride. In each case thg. solid salt can be obtained by evaporation, of the solution ; for details, however see the respective metals in Part III. ' Experiment 134.-Take two' test-tubes, pour into one 3 CCS. of strong nitric acid, and into the other 4 C.CS. of strong hydrochloric acid. Put into each acid some pieces oi gold-leaf '^nA apply heat. Neither acid IS able to dissolve the gold, or ' royal metal ': but on mixing the contents of the^est-tubes the panicles of gold disappear almost immediately; hence the mixture of acids is called aqua regia, because it alone dissolves gold or platinum, which latter is also classed ad a noble metal. When the two strong acids react, particularly on heatmg or long standing, the following products are obtained — aHQ 4- RNO3 = 2CI + NOCl + 2H,0 Chlorine. Nitrosyl- chloride. The solution of the gold (or platinum) is due to the action of the chlorine on the metal -^ Au'"-f 3Cr = Au"'CI'3. '^\sftdilutednitro-hydrochloricacid{^. P.) is prepared by mixmg the strong acids in the above proportion (3 •' 4), standing for twentv-fouf honr« tn nArrp.v v,«.-i.. Fro. 76. Analysis of Hydrochloric Acid. 2 1 3 complete change, and then diluting with .5 parts of assmJf r° r"'^""^"' ''^P""'"" ^e have hitherto L "rnont ? ""^^ *""' "^^ ^as evolved when sa -ammoniac or when common salt is heated with ^ulphuncactd. We must now examine this bodjmore use thiTITf """"^ '" '^°'"'"°" «"• "'« ^hall now aadJas ln^ 1 T°\^ '"^'"""^ f^°'" hydrochloric ac d gas. Kill the U tube, fig. 76, with hydrochloric acid by passing a rapid current of tlK gas throuX t for some time ; then close the .stopcock . ^ and immediately pour sufficient mercury into the open limb to close the bend / and partially fill the tube as shown. Now adjust the level of mercury by opening the stopcock for an instant, as the gas must be under a little pressure, then mark he position of the mercury in the closed limb and fill up o completely with mer- cury containing some sodium amalgam, rrf "J '" E-"''^"'"^"' '^4. Next g asp . firmly m he hand pressing the thumb on the opening Tnd tailrth ^ '' "'"'^^ "'^°"g'' 'he mercury con- tain ng the sodium, at last transferring all the c"s not t'hat r J""'- ''T ^^-"^^^ *' 'humb ^^ the mercu ; thTr'^""'''. '" "' ='<^J"« '^e level o<: «">b occupies only /..// ti." ;;L.^rof' thT h^r 214 Experimental Chemistry. chloric acd. Fill up o with plain mercury brinir , flame near to the jet, and cau iously openT-the 1 Sidual gas ru*es out and burns for anfnstant T t Experiment ISe.-Bend a tube in U form as in ^5f SI"? •E.ri ri-r£» Fig. ^^, Now plunge the carbon poles ^ into the arM Jn fi, tt tube OS «h^«r« r- • , ^ ^^^^ ^" the U tube as shown. Gas is evolved at each pole-colour £^hfb:-r^-r^2-5 and neither burns nor rekindle J^tcT ^aS 2r^^l f however, a piece of moistened blue litmu! paper be Ia.d over the mouth of the tube it is soon mll^Z tT T' *" "''''• ''''"•'== P'^'i"'™ would be ^.acked by the chlornK evolved during elcc.oly.. of ,he Experiments with Chlorine. 215 allusion to its greenish-yellow colour ; its symbol is CI and atomic weight 35.5. The voU mes o7the two gases evolved during electrolv.ic; . " "" eoual whpn fi.^ V \ ^'^^"oosis are approximately equal uhen the hquid becomes saturated with chlo- rine. The specific gra^ ity of chlorine gas, determined as m Experiment 27, is ^r.,8 m - r\ .u "-'"'^^'"^^ r=ii2 r pc: \ „,„• t ^o "^ ^ ')' therefore i w/ ^-112 CCS.) weighs 35-38 cgrs. wethfis , l"-\°"^ ''*°"'' °f '^"'^^g"'' -hose c%ni IS I cgr. Now, since 36-? - i = ,c-c «r almost exactly the weight of x t./ of chlorine we conclude that the molecule of hydrochloric add Is consists only of hy< ogen and chlorine, and of bf^h chemical y combined without condensation. AkhoS this proof IS complete, it is well to coni^rm 1he co„ ThlorTne i» o '° °'^'''''" ''''^8^^ ^"'-'"i'ies o that demenr "7 ''"'\'"^ ''"^^ "'^ -characters of that element. (For synthesis see page 219.) Chlorine a.=35-S. i ^^/«'«^/« 35-36 ..^. Molecular weieht =. 7io_n io „k ■ , , " rhlnri^ o„-j u ''°- " 's obvious that hydro- chloric acid ought to afford an abundant supply of chlorine rf we can remove its hydrogen and avoid mon salt. ■"' """"-^ ''"'"' ^^'^*""» in com- 2l6 1 b i i Experimental Chemistry, presenting at the same time a body that can combine with all the chlorine. Experiment 132 proves to us that a vionoxide like copper oxide will not suit our purpose, since the metal can unite with all the chlorine displaced by the oxygen, but if we use a peroxide of a metal whose atom requires but two of chlorine to satisfy it, the excess of chlorine should be obtained in the free state. We shall, therefore, make the follow- ing experiment vvith a body of the kind referred to that we have already used, viz., manganese per- oxide. Experiment 137.— Heat a little manganese per- oxide (MnOa) in a test-tube with strong hydrochloric acid ; note that a greenish-yellow gas of suffocating odour is evolved which rapidly bleaches moist litmus- paper laid over the mouth of the tube. The gas is chlorine, resulting from the following change— Mn^vQ^a + 4H'Cr= Mn^d'a + 2QV + 2H,0.» The manganese chloride (MnCla) remains in solu- tion. Experiment 138. — Mix a little manganese dioxide with common salt and sulphuric acid in a test-tube and note that chlorine is evolved. In this case HCl is first formed by the action of sulphuric acid on common salt, as in Experiment 127 ; the hydrochloric acid then acts as above on the manganese dioxide. Experiment 139.— Fit a Florence flask with a delivery tube bent twice at right angles, as shown • According to Dumas, MnCI, is first formed and then de- composed by heat into free chlorine and manganese dichloride. Experimoits with Chlorine. 217 in fig. 78. Introduce into the flask about 20 grams of MnO.2 in lumps, and 100 c.cs. <^i crude but strong hydrochloric acid solution, and apply a gentle heat. Chlorine gas is so much heavier than air' that it Fir.. 78. can be easily (ollected by displacement of air as shown, the colour c^i the gas enabling the experi- mentalist to observe the rate of filling. As each jar fills,, remove it and at once cover with a glass plate slightly greased so as to enclose the gas se- curely. Fill several jars in tliis manner, and make the following additional experiments, which, as well as the generation of the gas, should be conducted near to a good draught, as the inhalation of chlorine is attended with danger, owing to the irritant action of the gas on the delicate tissues of the lungs. ^ Experiment 140.— Plunge a burning wax taper into a jar of the gas (see fig. 79). Note that while com- bustion continues iis character alters, for the flame is dull reddish, and much black smoke arises from it, acid fumes bein^ freely produced. The latter ' As already stated (p. 215), it is 35 -5 heavier than hydrogen, and, since air is 14-47 times heavier than hydrogen, it follows that chlorine is almost 2\ times heavier than the same volume of air. 2l8 Experimental Chemistry. consist chiefly of HCl gas ; and the study of the change leads to the conclusion that the combustion in chlorme is due to the rapid chemical union of the latter with the hydrogen of the wax (a compound of hydrogen, carbon, and a little oxy- gen), but the carbon does not unite directly with chlorine, and therefore most of it separates, and in the finely- divided state of black smoke or soot. The attraction of hydrogen for chlo- rine must therefore be very great ; but the following experiment illus- trates this important point still more clearly. Experiment 141.— Moisten a strip of blotting-paper with a few drops of turpentine (C.oH.e), previously warmed, and, holding the paper by tongs, plunge it into a jar of chlo- rine. Spontaneous combustion soon takes place and torrents of black smoke and acid vapour are evolved as before. ^ Experiment 142.-Take. a strong and well-filled ' ^ jar of chlorine, and another of the same size full of hydrogen gas. Bring them mouth to mouth, and keeping them close together, invert several times so as to mix thoroughly, then separate and cover with glass plates. The mixture has a yellowish colour. Remove the cover from one of the jars and apply a flame ; an explosion results, and acid fumes of HQ are produced. Bring the second jar, which should be very securely closed bv a wPiL^r^oo.^ . Synthesis of Hydroc/Uonc A cid. 2 \ 9 glass plate, into diffused daylight, but not into direct sunlight.' Note that the yellow colour slowly dis- appears, and when the contents have become quite' colourless, carry the jar to (he mercury trough, bring the mputh under the mercury, then remove the plate and note that the gas has not changed in volume, as gas does not escape, neither does mercui-v enter to any extent. Now pass up a few drops of water by means of a curved pipette, and note that the mercury now rises in the tube and will completely fill it if the original gases were pure and mixed in equal volumes We have thus effected the synthesis of hydrochloric acid referred to under Experiment 136, and equal volumes have united without change of bulk, and the fact of their union is proved by the solution of the product in a small quantity of water, by which a mere mixture of hydrogen and chlorine would be very slightly affected. Synthesis therefore completely con- firms the conclusion drawn from the analytical data. In these cases H + CI = HCl. Experiment 143.-Plunge a small piece of dry phosphorus into a jar of CI, using the long spoon _ 'If the tube were exposed to direct sunlight, almost instant combination of CI and H would have taken pice with exr^osion. Small and thin glass bulbs are sold ready fdled with the mixture of gases, and when exposed to direct sunlight (or to the light emitted by burning magnesium, which is also rich in chemically active violet and ultra-violet rays) the bulb is sha teied to fragments, owing to the sudden expansion of the contents ].y the heat evolved on the combination < of rh. ._ r 'I 'i fi i ' 1 ^^i. 220 Experiiuental Cheviistry. for the purpose. The phosphorur. soon takes fire , in the gas, and produces a mixture of chlorides of phosphorus, PCI3 and PCI.,. Cl^ can also be made to unite with sulphur, though heat IS necessary, but it does not directly combine with either oxygen or carbon, though compounds with these elements can be obtained by indirect means. ^ Experiment 144. -Powder some metallic antimony very finely, and shake the powder into a jar of CI As the particles of metal fall throu-h the gas they burn, evolving much light and producing a most irritating vapour of antimony trichloride— Sb'" + 3CI' = Sb'"Cr, Chlorine acts upon arsenic with equal energy and when aided by heat, on all the true metils also,' forming therewith chlorides, in which it acts as a smgle-link or monad element. Experiment 145.~-Write across the printed matter on a piece of newspaper a word or two in black writing ink, and plunge the paper into \ jar of CI. After a short time the writing ink, whose colour is due to gallo-tannate of iron, will be bleached, while the printing ink is unaffected, as the colouring matter of the latter is finely-divided solid carbon, which IS not attacked by chlorine. Chlorine is therefore not an universal bleaching agent. Experiment 146. -Remove a jar of dry gas to the pneumatic trough, and, having allowed some water to enter, close the mouth with the hand and shake up the gas and water ; the hand is drawn in. nrr.vJn. Chlorine Water. - 23, that absorption has taken place, and on renmving the hand under water the hitter ri.es in tl,e jar-there- fore CI IS moderately sohihle in water, i cc of water at 15- diss6lves 2-368 ccs. of CI fras. 'surh a saturated solution of CI in water forms the Z,-pu,r CA/on of the British Phannacopa-ia, and is easily obtained by passing chlorine gas evolved from hydro- chloric acid and manganese peroxide through a little water in a wash-bottle (as in ng. 75), and then through distilled water, until gas ceases to be absorbed. A hquid IS thus obtained which rapidly bleaches indigo solution, writing ink, &c., and possesses the character- istic odour of the gas. If this solution be cooled by surrounding the bottle that contains it with melting ice, fine white crystals slowly separate which, when drained froni the liquid in which they are formed and analysed, are found to consist of Cl'sH O Very slight rise of temperature suffices to decoinpose this body into chlorine gas and water. Faraday first succeeded m obtaining liquid chlorine by sealing up some of these crystals in a strong glass tube anS melting the solid, when two layers of liquid were obtained, the lower and heavier consisting of liquefied chlorine, the lighter of a solution of chlorine in water Experiment I47.-Take two to ^ tubes half full of distilled water, add to on . few drops of the solution of rhiorine, and to t.. other a similar quantity of diluted hydrochloric acid. Kow add to each a little silver nitrate solution and note that a similar white precipitate is produced in each case. Repeat the ex periment with fresh solutions, but add potassium locliae instead nf <.iKro». „.v^^*.„ ^„j . , _. ...,,^^ xiitiatw aim note limt no 222 Expei'iniental Chemistry, change follows its addition to the hydrochloric acid, while a strong brownish yellow colour is developed in the free chlorine solution, and a black precipitate if the solutions are strong. This change is due to the separation of iodine (see Ex- periment 159), and serves at once to dis- tinguish free chlorine from pure hydro- chloric acid. "Experiment 148.— Take a tube of the form shown in fig. 80 and quite fill it with solution of chlorine ; ' now expose it to strong sunlight and observe that bubbles of gas are evolved and collect in the top of the tube, while the liquid gradually loses its yellow colour. Note that the liquid acquires a strong acid reaction. Since we have only chlorine and water present, and a colourless gas is separated, there is a strong presumption in favour of the gas being oxygen liberated from the water by the superior attraction of chlorine for hydrogen, and in accordance with the equation — 2CI + H2O = 2HCI + O. We have already found the acid ; we now test the gas by filling up the little side tube with water, if it be not already quite fulL then closing the mouth with a finger and so inclining the tube as to oblige the gas collected to pass into the small limb. Then have a match ready with a glowing tip, remove the finger and • In this experiment the chlorine solution could not be con- fined in a tube over mercury, as the latter is quickly attacked by free chlorine. Bleaching Experiments. 223 test the gas, when the wood will be rekindled and the presence of oxygen ascertained. In the absence of light the same change can be effected by passing a mixture of chlorine and steam through a red-hot porcelain tube.' The ease with which chlorine decomposes water and sets free the oxygen leads us to e'nquire whether water plays any part in the bleaching action of free chlorine. Experiment 149.-Take two perfectly dry stop- pered bottles, warm them and fill each with chlorine by displacement of air, but dry the gas before it reaches the bottles by making it slowly bubble through some strong oil of vitriol. Now place in each bottle a strip of red flannel (madder-dyed) previously dried thoroughly by heat, insert the stopper and expose the flannel to the action of the chlorine for half an hour If proper care was taken to exclude moisture, no material bleaching effect will be observed. Now in- troduce a few drops of water into one of the bottles and the colour of the flannel will slowly fade while the dyed stuff in the dry chlorine will retain its colour. In this case, then, the bleaching effect of chlorine is indirect, and due to the powerful action of the nascent oxygen (see page 190, and note) derived from water • and similar experiments have shown that in most cases the presence of water is necessary, though we shall meet later on with some exceptions to this rule. » We infer from these H. >ts that chlorine does not tend to unite with oxygen directly, and it is not known to do so ; never- theless many oxygen compounds of the element are ohfnmaKU oy mairect means (see lixperiments 151 ^/ seq.) 224 Experimental Oiemtstry. Chlorine is used in enormous quantities as a bleaching agent, but neither the free gas nor its solution in water are now employed for the pur|)ose, as It is more convenient in practice to liberate the body from ' bleaching liriVe ' and analogous compounds in contact with the materials to be bleached (see Experiments 151 and 152). Experiment 150.— Introduce a few drops of am- monium sulphide— 2i yellow liciuid of very offensive smell— into a bottle and gradually add chlorine water to it with agitation. Note that the unpleasant odour disappears, and the smell of chlorine is not detected unless too much of the latter has been added. In this case, then, the free chlorine acts as a deodorant, and it is commonly used for removing un- pleasant smells, for which purpose a small cjuantity is generally sufficient. It is, moreover, believed to act as a disinfectant, either by direct corrosion of disease- particles or by its indirect oxidising action, though it is improbable that it usually produces much effect unless employed in large quantities. The most con- venient source of chlorine for these purposes is ♦bleaching powder,' which affords the gas when a little acid of any kind—vinegar, for example — is added to it (see Experiment 152). Experiment 161.— Instead of dissolving CI gas in water, pass it into cold solution of potassium hy- drate (KOH)'— the Liquor Potasses (B. P.) answers ' If NH^OH be substituted for KOH in the above experi- ment, a very different change occurs, for a quantity of nitrogen gas is obtained instead of a bleaching solution, thus - 4NH.OU + aCl - N + iNHf-i J. aU n Experifnents with Hypochlorites. 225 well; when partially saturated with the gas, stop the current. The solution so obtained is colourless, and smells somewhat like ' bleaching lime.' A few drops of any acid added to a portion causes the evolution of chlorine, which is easily recognised by its colour and odour. The action of CI on KOH in the cold results in the production of a mixture of potassium chloride and hypochlorite in solution, thus — 2CI + 2 KOH =r KCl + KOCl + H,0 Potassium chloride. r Potassium hypochlorite. If into this liquid a piece of madder-dyed wool be stirred, the red colour is not destroyed, as the alkaline hypochlorite does not bleach, but, on the addition of a few drops of dilute hydrochloric or other acid, the colour is discharged. In this case the bleaching agent is chiefly chlorine, resulting from the following reaction — KOCl + 2HCI = KCI + 2CI + HA Potassium hyp : jrite is therefore a convenient ^ source of chlorine for bleaching, deodorising, and disinfecting purposes, but in all these cases acidulation is necessary in order to obtain the bleaching or de- odorising effect. The solution of chlorinated soda (B.P.) is obtained by passing CI gas through solution of sodium car- This is, in fact, a good method for the preparation of nitrogen gas, but the ammonia must always be present in excess, else there is risk of forminc the damreroua chloridp n( nJir.uro,, ^e»- under Experiment 125). 226 Experimental Chemistry, "$ bonate, when sodium hypochlorite and chloride are formed, and carbon dioxide gas is evolved — Na^COa + 2CI = NaCl + NaOCl + CO2. Experiment 152. — If we line the interior of a wide-mouthed bottle with moist slaked lime (Ca"(OH) ,) and pass a slow current of CI gas mto the vessel, the gas is absorbed and combmes with the lime, forming the ' bleaching lune' or chlorinated lime , of the B.P., commonly called 'chloride of lime' » :— Bleaching lime. 4CH-3Ca"(OH)'2 = cH^T^c^ciwr+liEo Calcium Calcium chloride. Calcium hydrate. chloride. chlorhydrate. On the large scale the slaked lime is spread in thin layers on shelves in large chambers to which Cf gas is admitted ; the latter is absorbed (just as in the bottle), and ' bleachmg lime ' obtained as a dull white powder with a feeble odour like chlorine and only partially soluble in water, calcium hydrate separating and im- purities in the lime used remaining undissolved. The aqueous solution contains the two calcium salts above named. Bleaching powder or its solution affords HOCl and CI gas on treatment with any acid (as in the case of KOCl), and is therefore a most convenient source of those bodies for bleaching or deodorising purposes. The three bleaching salts above referred to are derived fron^i the acid named hypochlorous acid, H'0"C1', which is best obtained by the action of ' Its empirical formula is Ca^Cl.O.H,, which requires ^9 per cent^of chlorine. ^ The best samples rarely contain more than l^'% percent., and aiwap contain mere or ics.s caiciuai chlorate. Potassiu7tt Chlorate, 22J its anhydride upon water. The anhydride is prepared by passing dry chlorine gas over dry mercuric oxide,' placed in a tube which is cooled. An orange yellow gas results from the action of the CI on the oxide, and this is the anhydride Cl.^0, which can be easily liquefied by reducing the temperature to — io'» C. 4CI + 2HgO = Cl^O^^ + Hg^Cl^O Hypochlof-ous anhydride. Mercury oxychloride. Tlie gas is very explosive, the heat of the hand being often sufficient to decompose it into 2CI and O ; it is therefore not a safe body for the junior student to prepare, i c.c. of water dissolves 20 ccs. of cthe gas, and forms solution of hypochlorous ax:id— CljO + H2O = 2HOCL The solution is a powerful bleaching agent Experiment 153.— Instead of dissolving CI gas in cold potassium hydrate, pass it into the boiling solution until gas ceases to be absorbed, and allow the liquid to cool. If the potash solution were originally strong, colourless crystalline plates will separate out even before the liquid is quite cold ; but if these crystals do not separate on cooling, evaix)rate the solution down to half its bulk and then cool , collect the crystals deposited on standing and throw them on a suitable filter ; pour a small quantity of cold water over them to wash away impurity, repeat the washing if necessary, and then dry. This body, » Prepared by precipitation. See Tart III: 228 Experimental Chemistry. when pure, has a cool saline taste and is sparingly soluble in cold water, though easily dissolved with the aid of heat ; its name is potassium chlorate and its formula KCIO3 or K'-O"— O"— O"— CI', the body from which we have already prepared oxygen gas (see Experiment 57). In its preparation »— 601 + 6K0H = KCIO3 + 5KCI + 3H,0 Potnssium chlorate. Potassium chloride. The KCl is a very soluble salt, and therefore remains in solution, while the slightly soluble chlorate crystallises out. When the latter is heated in a test- tube it melts and gives off oxygen, which can be easily recognised by its property of rekindling a match with a glowing tip. Here — KCIO3 = KCl + 3O. The white residue in the tube consists of potassium chlorid(, which is easily distinguished from the chlorate by its solution affording a white precipitate of silver chloride (AgCl) when tested with silver nitrate. Potassium chlorate does not give a precipitate with ' Instead of pure caustic potash, as above, the B. P. directs CI g,ns to be passed through a mixture of solution of potassium carbonate (K.CO,) and slaked lime {Ca(OH),). In this case- I3C1 + K,CO, + 6Ca(OH), = 2KCIO, + CaCO, + sCaCL + 6H,0. The mixture is afterwards boiled, then filtered from excess of slaked lime and the chalk (CaCO,) produced in the process, concentrated by evaporation, and the chlorate crystallised out from the solutioiL Tests for a Chlorate. 229 sil /er nitrate, because silver chlorate is a very soluble salt. • ' Experiment 154.— The ease with which the chlorate parts with its oxygen renders it a very power- ful oxidising agent ; hence, if a few grains are mixed with a little powdered charcoal and heated on a knife blade, explosive combustion ensues. Experiment 165.— Pour five or six drops of strong sulphuric acid into a test-tube and add a very small crystal of the chlorate, and gently warm ; the mixture becomes yellow, and a yellow gas is evolved which explodes very easily ; hence a loud crackling noise occurs on heating. The gas is a mixture of oxides of chlorine, which decompose into their constituents with explosive violence on gentle heating. This effect is very characteristic of a chlorate, but in apply- ing the test direct the mouth of the tube away from the person. Experiment 156.— Powder separately a gram or so of potassium chlorate and of dry loaf sugar ; mix the powders on paper with a glass rod, place the > F-ee chloric acid (HCIO3) is obtained by adding to a saturated solution of potassium chlorate a strong solution of hydrofluosilicic acid (HjSiF,, see page 267) ; the potassium unites with the latter, forming the sparingly soluble salt KjSiFg, which is precipitated, while monobasic chloric acid remains in solution — 2KCIO, + H,SiF, = 2HCIO, + IC.SiF«. No anhydride of this acid is yet known. We are ac- quainted with another body, chlorous acid (HCIO,), which is intermediate between hypochlorous and chloric acids, but, like the latter, it is not as yet of any practical importance. The anhydride CljjO, is known. 230 Experimental Chemistry, mixture on a metal plate and touch the powder with a rod dipped in oil of vitriol; violent combustion en- sues, the sugar (a compound of carbon, hydrogen, and oxygen) burning in the available oxygen of the chlorate. Experimei t 157. — Dissolve some of the chlorate in water, add a few drops of indigo solution, and then some strong sulphuric acid. Note that the blue colour is destroyed ; as might be anticipated, this bleaching action is due to oxidation. Experiment 168. — Again heat some potassium chlorate in a tube of hard glass. The salt fuses as before, and oxygen is given off ; but, if the heat be steady throughout and not very strong, the contents of the tube become solid, and the evolution of gas ceases. On raising the temperature still higher, gas is again evolved, and in larger quantity than before. The check just observed occurs when only one- third of the total oxygen has been driven off as gas, and the residue is found to consist of two salts, potassium chloride and potassium perchlorate— a body which is very slightly soluble in cold water, and which is therefore left behind to a great extent when the cooled mass is digested with cold water. The following equation represents the change — 2KClOa = KCl + KCIO4 + 2O Poiassium chloride. Potassium perchlorate. The perchlorate is much less easily decomposed than the chlorate, but ultimately yields up all its oxygen like the chlorate. Hence, in ureuariiiff oxy. Oxides and Acids of Chlorine, 2^ i gen gas from potassium chlorate, the decomposition takes place in two stages, though we commonly express the change by means of a single equation. When potassium perchlorate is heated with strong sulphuric acid, an acid distillate is obtained which Roscoe found to contain perchloric acid, HCIO,— one of the most powerful oxidising agents known, as mere contact with it suffices to kindle paper oi woodJ No anhydride corresponding to perchloric acid has been obtained. Neither the acid nor its potassium salts are as yet of any practical importance, but much interest attaches to the former as the highest term of the following series of chlorine acids- Hydrochloric acid Hypochlorous acid Chlorous acid , Chloric acid , Perchloric acid . Acids. HCl HCIO HClOa HCIO3 HCIO4 Anhydrides. C1,0 Cl.Oa C1A(?) CI2O; (?) All these acids contain but one atom of hydrogen within the molecule replaceable by a metal, and are therefore monobasic. They may be regarded as successive oxides of hydrochloric acid (HCl), and their formulae will be most easily remembered when they are thus viewed. Moreover, the series of bodies may be cited as remarkable illustrations of the Zavt of Multiple Proportions, " The perchlorate does not bleach indigo in presence of SUipisunc aciu, and « ihus caaiiy diaUuguishcu from the chlorate. 232 Experimental Chemistiy. CHAPTER XVL EXPERIMENTS WITH IODINE. Experiment 159.— Dissolve in water, in a test- tube, a few crystals of the salt potassium iodide (KI), and add a few drops of chlorine water to the liquid. Note that a brown-red colour is immediately produced, and black, heavy particles separate from the liquid if the solutions are strong and sufficient chlorine is added. When the particles have subsided, pour off the coloured liquid, and drain it away as completely as possible from the deposit. Now, with- out drying, apply a gentle heat to the black substance ; a violet-coloured vapour is produced, which condenses on the cool upper part of the tube in black, shining metallic-looking scales, the water present volatilising and condensing at the same time. This metal-like substance (or ' metalloid '), characterised by its easy volatility and beautifully coloured vapour, is an ele- ment, and is called Iodine — F =127. The compound with potassium used in this experiment is easily decomposed by chlorine, as we have seen ; the latter seizes the metal and forms potassium chloride, while iodine is displaced, thus — K I^ -h Cr = K Ci' + V. Preparation of Iodine. ^l^ Experiment 160.— Potassium iodide and chloride are obviously analogous bodies ; hence the method already used for the separation of chlorine from its metallic compounds (Experiment 137) might serve for the separation of iodine from the metallic iodide. Mix the latter, or its solution, with some manganese peroxide (MnOj) in a test-tube, add a few drops of strong sulphuric acid, and apply heat Violet vapours of iodine are given off, and condense on the sides of the tube as before ; the by-products manganese and potassium sulphates are left — 2KI + MnOa + 2H,S04 = 2I + MnS04 + K2SO4 -h 2H2O. The reaction is therefore precisely analogous to that in which chlorine is evolved by the action of MnOj and H2SO4 on common salt. Iodine is widely distributed throughout nature, but in small quantities, and always in combination, though chiefly with potassium, sodium, or magnesium, and sometimes, though rarely, with silver. It is present in many mineral waters, and in sea water ; ^ from the latter the iodides are extracted by various sea- weeds, and these, when collected, partially dried, and burned, afford an ash which is termed 'kelp,' and from this ash much of the iodine of commerce is extracted. The process of extraction consists in di- gesting the kelp with water, which dissolves out a considerable number of soluble salts, including the iodides (and bromides, see page 250) ; the solution ' It is also present in small quantity in 'Chih nitre '—sodium nitrate — in cod-liver oil, sponge, &c. 234 Experimental CJumistry, is filtered, evaporated, and the kss soluble salts crystallised out and tlius separated from the very soluble iodides. I'ho remaining licjuor is treated with strong suli)huric acid, and some sul[)hur is then sepa- rated and removed 'I1ie acid li()uid is next poured into large stills or retorts, manganese dioxide added and heat applied Iodine is separated from the iodide as in the above experiment, and distils over ; Fig. 8i *' ^* condensed in a number of tubular receivers, from which it is removed, and, when sufficiently dry, is sent into commerce in a somewhat crude condition. Free iodine and some of its compounds are largely employed in medicine, but it is desirable that the crud€ element should be purified before it is so used. Experiment 161.— Place a few grams of crude iodine in a cru- cible, which is to be covered as shown (fig. 8i) with a flask con- taining cold water. A gentle heat IS applied to the crucible, and after a few minutes the flask IS removed ; then the small (juantity of iodine deposited upon it, with a few whitish needle-shaped crystals of ' iodide of cyanogen,' which usually accom- pany It, must be scraped off; the flask is replaced and gentle heat again applied. After some time large crystalline plates of pure iodine will be found attached to the bottom of the flask ; these are to be removed and preserved Tf fh*» i/v^in^ ^^^r.A ;« ^.u- £__. • Experiments with Iodine, 235 were pure, no residue should be IcP. in the crucible at the end of the operation. This process is one of sublimatwn—m which a solid is deposited from a state of vapour. The specific gravity of pure solid iodine is 4ot; (water=i). The element gives off vapour at ordinary tern- peratures, and it becomes a li(juid when heated to ri4° C. ; it boils at 200° C, and afTords its mag- nificently coloured vapour in abundance, as wc have already seen. The specific gravity of the va|)our is 125-9, but the atomic weight is slightly higher, or 127. Experiment 162.— Add to some water in a test tube a few fragments of solid iodine ; shake, and allow to stand for some time. The water gradually acquires a brownish yellow tint, but the proportion ultimately dissolved is very smal', a$ nreful experi- ments have shown that iodine r„H njres learly 6,000 time^ its weight of water at rnti's^ ter; perature for solution. Experiment 163.— Add some litmus to a pi»rtion of the dissolved iodine ; little or no bleaching is observed, unlike the rapid decoloration that takes place with chlorine. Experiment 164.— Rub a few pieces of common starch with water in a mortar, and pour the mixture into a capsule. Heat nearly to boiling, with constant stirring, and when the mixture thickens and becomes gelatinous remove the source of heat. Stir the ' made starch' up with warm water until a thin 'mucilage' "•" ^-' """ j-scricivc iiiis lor use. /Aod a few drops of the mucilage to half a test-tube full of 236 Experimental Chemistry. aqueous solution of iodine, and shake ; a beautiful bl«e l,.,u.d ,s obtained, owing to the formation of an Ill-defined compound of starch and iodine. This is an excellent and most characteristic test for the free element. Heat the contents of the test tube nearly to boilmg, note that the colour disapfears, but, or, cooling .t reappears. Therefore the starch test should always be applied in cold liquids. JExp3riment 165,-Add a drop or two of starch mucilage to a solution of potassium iodide.' No change whatever is observed ; therefore iodine in NoTn*;! r?i '•'°" ^"^^ "" eive the reaction Now add to the mixture a drop of chlorine water, or of strong brownish-coloured nitric acid ; iodine is instantly set free and the blue compound formed. Experiment 168.-Again, put some pieces of lodme into a test-tube with .some water ; we already know that very little dissolves, even on long standing ; but now throw m a few crystals of potassium iodide and observe that on agitating the liquid it becomes of a deep reddish-brown colour, and the solid iodine disappears as the potassium iodide dissolves. The 10 .de solution han in plain water. In this case so- ution IS probably due to the formation of a potassium tri-iodide of the formula KI I2. of the T'"^" '' !f'''" °^ "^'^ ^"^' '" "^^ preparation spirit of wine is the solvent, the solubility of iodine » A very dilute solution. Experiments with Iodine, 237 Fig. 8». in alcohol also being increased by the presence of potassium iodide. Experiment 167.— Add a few drops of chloroform to a simple aqueous solution of iodine, and shake. The chloroform subsides on standing, and has a fine purplish colour, as it carries with it the iodine, which is very soluble in it, and is thus easily removed from the water. lodme is also soluble with ease in ether and in carbon disulpiiide. Iodine does not burn in, neither does it directly combine with, free oxygen ; but it readily unites with many metals and non-metals. Experiment 168.— Rub a frag- ment of iodine with some mercury in a mortar ; a reddish powder is first produced, which becomes green if a little more mercury be added and the trituration be continued for a sufficient time. * The resulting com- pound is 'green iodide of mercury' — Hg"2l'2 — thus formed by direct union of the elements. Experiment 169.— Take a large . and wide test-tube— about 10 ccs. long by 3 CCS. diameter; introduce a few frag- ments of iodine, and support the tube in a convenient holder. Apply heat to the tube so as to convert the iodine into vapour, and when the latter half fills the ' The addition of a few drops of alcohol hastens the process Dy uissuiViiig MJin-^ ui Ulc UXItiic utiu mUa iciCutiaiiii^ Cficuiiw&i action, as in Experiment 6, I'urt I. eiG. 83. 23 8 Experimental Chemistry, tube plunge into the vapour a very small piece of (fi« E7 Tr 'r'^r' ^" ^'^ ^^^-g^ating spoon (ng. «2). 1 lie phosphorus takes fire in the iodine vapour and burns for some time ; if the phosphorus be in excess,' the colour of the iodine vapour disappears, owing to complete combination of the latter with the phosphorus, an iodide of the latter body being formed— thus, P + 3I = PI3. If, when the tube and its contents have cooled down, a few drops of cold water 'are allowed to fall upon the dark- coloured body left in the tube, a fuming gas that reddens blue litmus-paper will be given off- H xynAt^r i\\et etirAir>A n.C ^\s.st .js.~*-s- -i-_ ^' . ^ Salts of Hydriodic Acid, 241 would take place so rapidly that the solution would rush back into the flask. A liquid can be obtained containing 57 per cent, of hydriodic acid, whose spe- cific gravity is 1*9, or almost double that of water. The aqueous solution and the gas are easily decom- posed when exposed to air and light, iodine being liberated and water formed— 2HI + O = H2O + 2L The iodine is not deposited from the aqueous acic' unless decomposition has proceeded very far, but ib dissolved by the acid, in which the element is very freely soluble. £zperi]r.ent 175. — Pour into a capsule some of the dilute solution of hydriodic acid prepared in the last experiment, and just neutralise with solution of caustic potash ; then evaporate the solution until a crust begins to form on the surface of the liquid, and allow to cool. Small cubic crystals separate out which are identical with the potassium iodide employed in Experiment 159. The following change takes place on neutralising the hydriodic acid with the alkali — HI + KOH = KI + H2O. This is the easiest mode of preparing potassium iodide and many other iodides (Le., by saturating the acid with the hydrate, oxide, or the carbonate of the metal or other basic radicle), but much of the com- mercial potassium iodide is prepared by the method employed in Experiment 1J81. • We have already seen that potassium iodide and diluride are analogous bodies, and can aiford the 242 Experimental Chemistry. non-metallic radicle by similar treatment. Now we know from Experiments 126, 127 that a chloride affords hydrochloric acid v/hen treated with oil of vitriol ; we have therefore to ascer^^b.ab]e cause of this is hyd iodic add, which, as we uready k?iow, puts easily with itf. hydrogen, and tht latti- then available forms water with more or less of the oxvge-. of the sulphuric acid, and iodine is set free. Here ,, though hydriodic acid is doubtless Ibrmed according to the equation KI + H2SO4 « HI + KHSO,, H is inirnediately de.^tfoyed in the way just indicated ; but the ietailed exami?\ation of the reaction must be reserved ui til w, study oil of vitriol. If this view be correct, we ought to get hydriodic acid gas alone on heating the iodide with a strong acid not so readily reduced or deoxidised as sulphuric acid Experiment 177.— Heat a few crystals of the potassium iodide as befhr<*. wirh ct/ntt^ j.Lj^..j.l..^^ h^^ Tests for Iodides. 243 acid} and note that hydriodic gas is evolved and little if any iodine is sei)arated. Experiment 178— Add a few drops of silver nitrate to a solution of potassium iodide, and note that a pale yellow precipitate of silver iodide is formed— AgNOg + KI = Agl + KNO3. The precipitate is insoluble in dilute nitric acid, and IS very slightly soluble in anmionia solution. ^ •Experiment 179.--Add to some disscaed potas- smrn jodidea few drops of lead nitrate solution. Note tha: a fine bright yellmv precipitate of lead iodide IS ai once obtained — 2K'r 4- Pb" (NO3)', ^ Pb"I, + ,KN03. This precipitate is somewhat soluble in boiling water and separates out on cooling in fine golden spangles. ' experiment 180.- To another portion of the iodide solution add mercuric chloride (Hg^Cl^) or *corro.sive sublimate.' By the addition of the first drop, a precipitate, varying in tint from salmon colour to bright scarlet, is obtained, but this dissolves on shaking the liquid. On continuing the addition of the mercury solution, a point is reached at which a scarlet precipitate is obtained which does not dissolve on agitation ; this is scarlet mercuric iodide— Hg"Cl, + 2KT = HgIa + 2Ka This scarlet iodide is easily soluble in excess of potassium iodide, producing a col'ourless solution, as we have seen ; the latter contains a soluble and colourless double iodide of mercury and Dotassinm Ua\ * See Phosphorus. 244 Experimental Chemistry. A strongly alkaline solution of this double iodide constitutes Nesslet^s test^ for ammonia (see page 21). Hydriodic acid and iodides are thus easily dis- tinguished by the reactions we have learned in the course of these exper'ments. Experiment 181. — Warm some caustic potash solution in a test-tube, and add iodine, in small portions at a time, until the liquid assumes a per- manent yellowish colour. The element dissolves and forms two salts— one potassium iodide^ KI, the other potassium iodate., KIO3, thus — 61 + 6K0H = sKI + KIOj + 3H,0. This reaction is precisely similar to that which occurs when chlorine acts on a hot and strong solution of caustic potash, as in Experiment 153, but the iodate cannot be separated from the iodide^ quite as easily as can the chlorate from the chloride. Pour the solution into a small porcelain dish and evaporate to complete dryness. Remove a small portion of the dry residue, which is a mixture of the ' NessUr's test solution is thus made — Dissolve 5 grams of potassium iodide in a very small quantity of hot water ; add to the liquid a saturated solution of mercuric chloride until the red iodide just ceases to redissolve. Now add 12 grams of caustic potash, previously dissolved in a little water ; mix and make up the total volume to 100 cubic centimeters .vith distilled water ; finally add a few drops more of the mercuric chloride solution, allow to stand, and draw ofT the clear liquid for use ; but it must not be filtered through paper. For the action of the test see under Mercury Salts, Part III. p. 104. « The separation is best effected by evaporating the solution to comolete drvness and dicestincr the residue with stromr alco. . . .. .. — J, hul, which dissolves the iodide but not the iodate. Preparation of Potassium Iodide. 245 ^vo iodine salts ; dissolve in some water in a test- tube, add a drop of starch mucilage and then some dilute acetic acid. Note that a blue colour is quickly developed after the addition of the acid, proving that lodme has been set free. In this case the acetic acid displaces hydriodic acid from the iodide, and iodic acid from the iodate, and the two acids thus liberated at once react, producing free iodine and water thus — * HI03 + sHI = 6I-}-3 HjO. Now return to the dry residue of evaporation ; powder It m the dish and mix with one-fourth its bulk of powdered charcoal. Heat the mixture until It is seen to melt, before which it glows for a short time, owing to the combustion of the charcoal or carbon m the oxygen of the iodate, carbon dioxide gas being formed and evolved, while the iodate is reduced to potassium iodide— 2KIO3 + 3C = 2KI + 3C0^ Then allow the mass to cool, add some hot water and filter from residual charcoal. The solution now contains only potassium iodide (which can be crystal- lised out), for on adding starch and acetic acid no olue colour is produced. Most of the potassium iodide of commerce is prepared by the process just followed, and samples of the iodide can be tested for iodate by the method mdicated. Potassium iodate is sometimes used as a test foi sul- Dhuroiis ac'd ''«'*» fKnf k^^.a : .r^ s _ • * " ''^'" "' '■""■- '■^-^j) i" ucciiv, rtuu uluer acids : the iodate used for this purpose may be separated from 246 Experimental Chemistry. iodide as stated, or, better still, may be sperially pre- Tn H ,7 .":^ /""o^ing instructive method directed m tlie Br tish Pharmacopteia Experiment 188.- Heat together in a fla.k two or three grams of powdered iodine «ith an oiual wei-ht of potassium chlorate and ab„ut .0 ccs. of wa'ier acdulated with 5 or 6 drops of strong nitric acid. Lhlonne gas is evolved, and the mixture is diffested untd ,he colour of the iodine ^n- ■' Hisap,,ears ; then bo>l for a minute or two , ,( 'Jj „„j' mto a capsule, and evaporate to dryness at a gentle heat 1 he residue consists w!,;,lly of potassium iodate, the chlorine and the nitric acid having almost coml pletely disappeared. This amounts to p replacement of chlorine in potassiu.n chlorate by iodine, thus— KCIO3 -; i = KIO, + CL The small anaount f f nitric acid used facilitates this replacement by libeniting small successive quantities This decomposition is remarkable, because it proves that chlorine is displaced by iodine from its ^«°'?f".'''"'.^?'"P«"*'''« Examinations reaching at least the standard of the Matriculation Examination of tho Univcraity of Londwi. The Shorter English Grammar. Islntended for learners wfio have but a limited amount of time at their dis- posal f..t Eng MhHtiHics; but the experience ..f s. lu.oM In which it lias been tho otily KngliHl. ..ramtnar u«ok will not have da„,aged eye«i,ht through 1 p^„V '* What it is. ° It K. a iK,rie« of Kradecl le«K)n.. oo„talnln.r the wo«I, in T""*'.^""- with ahhrevlatlon, etc. .; won,, o, ..„„ar P«>n:;„:;:ti: td .Iff^^.: i^^^ iiijf a collection of the nicwt difflcuK wordn in th* i«.. "'"«'«•«* "Ih-"- ...;.«„,,„,.„«„„.„,,,, vb.':x,uir«™rr;,rK.*r::^ Ui.l to uieuiory by the pupil* ' " wmmii Hlvery teacher should IntroduceTit Ca »» m . » o It I, an hnproveuient on tha old "^ H ^ hook ZTJL^J''T'"- lMtroduc« it into hi. cliw^e, * ' ^'*' ^^''^'^ *««'»>«»' •*>«"» The best yet seen. -— o— « HAMnrJW RMITI-'S MATHEMATICAL WORKS ~ Hamblin Smith's Arithmetic. 12th Edition, B • «« ^ ^ - Price, 75 Cent*. KEY.— A complete K«y to (b9 ftiwve Arithmetic, by the Authon. Price, $a.oo. 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D. 43 to 1870, In- teresting alike to young and okl. A mvorlte. Londom Aovrrtisrk. The iMjok will prore a favorite' with toachom preparing pupils for ?.he entrance exauiiuations tc th« High Schools. Vesy attractive. BRmsn Wmo, Kiwobt«)i». This little book, of on« hundred and forty pages, presents history in a very attractive shape. Wisely orransred. ^"^ Cakada Prsssytrrsah. The epochs chosen for the division of English History atti well marked -nol nure artiflt lal niUt-Ktones, arljltmrily erected by the author, b:ir reai natuml landntarka, consisting of groat and important events or remarkable chaniret. Interesting. Yarmoitii Trihcni, Nova Sootia. With a iMsrfect freedom from all loowsncNs of stylo the Interest is so well sustaltiod throughout the narrative that those whp comnience to road it win find it difflcuU to leave oH with its p«nisal inwnnplcte. Comprehensive. Litrrart World. 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