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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 .,o. 2) 1.0 I.I 1.25 1^ ill 2.8 11 2.5 |M '"" 11111^= ■a m IIS Sli^ £ 1^ 2.0 IS. ^^= ^ u ■uuu 1 1.8 1^ 1.4 1.6 ^ APPLIED IN/HGE Inc =^ 1653 East Maiii Slreel r.a Rochester, New York 14609 USA ^= (716) 482 -0300- Phone == (716) 288 - 5989 -Fax <-wiSK '< '^ l^ ,T /*'& * > 1-, i*, A-"y5 ',/ ^•'■/r.J II 7 thWtj ^y^g^a^JM -r •'^Sii^iAKRKn MtfH wvs-'; ^-i? i«.5*« «'iVS«.iKV'>f^i'»F.'^:. ,i«i , f^v*- 1 SV*/,i'--W, *■ ,v gKc'-i-^ '/. '^V';v''^'^''!'"?'.<^' J 9p ^ //^^ ^ I hp' H A HAND-BOOK FOR TEACHERS OF CHEMISTRY IN SECONDARY SCHOOLS BY J. A. GIFFIN, B.A., LL.B., COLLBOIATB INSTITUTE, ST. CATIIARI.NE8, ONT. TORONTO WILLIAM BRIGGS 1900 '■T / ^«>^o t::::''-'-«:'.;'':,:r::':,:: > „„„ '"^' '" Hi,, J,, ■ ono ■ '^''''"'fiji,.,,! of PRF.FACn. :• '" ""■ voar one ''^" ^'^'l»m,u,nt of Tins little book has been pivpared for the use of teachers of Chemistry in our secondary schools, in the hope that it may be helpful in presenting a dimcult sul)ject. It is a cause for regret that many teachers are obliged to give instruction in Chemistry with very limited apparatus, an.l, what is even worse, to perform experiments in laboratories which are not properly ecpiipped with draft cupboards. To add to these difficulties, text-books often give very imi)erfect directions for performing many important experiments, and if those experiments are attempted by large classes, as directed in the text-books, they become a source of danger to the health of both students and teachers. This i« pai ; icilarly the case in studying the properties of gases, ^\'e ca ^not hope for a remedy for this state of affairs until we have more stringo/.t school regulations in regard to general health, as school boards are very often unwilling to supply even the most necessary, to say nothing of efficient, appliances for teaching the subject.' It is to aid in overcoming these difficulties by means of inex- pensive apparatus, that these hints and suggestions are sub- mitted for the consideration of Science teachers. The methods employed, and the experiments and liiodifica- c PREFACE. "^^roducr/'t^'";"''; """ ^"'' '^'' "^ost part o • • ."•^"""'ion of o„e of „„ f """"■■™ '•' >««ed „„ ,^1 "^'^ '" teaching the , """'' '""her, of Ch "" new Tl ■ • "■" '"^'hod of ™! , '"boratory General Hinf. "^ ""^S-estions ,„ „ ^"""''e «on on G ■■"'" ^"'^"'''d fro„ ™; '" "^ "l-apeer of wi Graphic Pori.inJ • '^^^us sources Ti. Chemistry, "'"^"^^^^ ^ taken ft,., Baiiey J' . ^ " ^"- J n^aj not ha ''''''^ *^e«e experinient,"^' P''^^ented the best wav nf *'"'•'» «' 'i>e „.eth: InVTV'*'" '" -^^ro:. I s^ °«t part original. The '' ^^''^ «« the recom- ;^««^d be introduced ^^-^hing the equation ■^^^^^ntheJaborator; '•^«a^J«is, are entirely '^^"« of experin^ents ^ be added, however' I '« ^'-^ed on a n^ethod ' '"^^^'^is. All except S '^ I'aw of Definite ' "^ ^be chapter of I «««'-ces. The«ec- ' Bailee's "Tutorial ""y of perform ^ittJe booJc proves ins 3verconiin- Tlie Law of Charles §6 The Percentage of Oxygen;,,,,; " " " §^.lhemsionofLi,ni.san.l.a.ses .* * ' §«• The Muhility of Air an.l Ammonia .as in Water' CHAPTER IV. J Oa.s Analysis. A New and Simple Aletho,! CHAPTER V. General Hints. §1- ^'^"y General Suggestions § !^. Cements . ' * * • . § 3. How to Remove Stains .''"'■•• I'AOK . 54 . fle . 58 . 60 . 62 . 63 . 64 . 65 66 72 73 74 I. ITUS, »llowing : I'AOt • • . 54 Jrochluric Acid . 56 . 58 • • , . 60 * • • . 62 • • , . 63 IS in Water . 64 . 65 66 72 73 74 A HAND-BOOK OF CHEMISTRY. CHAPTER I. THE CHEMICAL EQUATION: HOW TO TEACH IT. Si. Introductory Work. A TEACHER of Elementary Cliemistry finds many difficulties in his work, and one of the greatest he encounters is in teaching junior students to write a chemical equation, and to have a proper understanding of what it denotes. The reason for this is quite apparent. To successfully express a chemical fact it is necessary to have a comprehensive idea of the theory of the constitution of matter, without which a begin- ner will not make much pi-ogress in his work. Among the many plans suggested for teaching equations, by writers of text-books, none are satisfactory. The intro- ductory work is not always arranged in logical order, nor with a view to giving the student a clear conception of the atomic theory. Many points are omitted which give con- siderable trouble, and the teacher is left to work out his own plan to overcome these difficulties. Jt may be argued that this is not within the province of an elementary text-book, but surely anything which will aid the student in getting a better grasp of the subject should have a place in such a work. One important reason why the beginner has «u nmch diffi- 7 8 A HAND-BOOK OF CHEMISTRY. making ptcturerto ; ""Tf" """«''''' """ ">e power o and hyd.«e„ eo„.JL'\:t "wTt; ":r7l%^' "^«™ expressed by an equation R 7 . ' f "' ""' """^ be mental picture of hetZ f ■ " '""*'' "«" '" '"'™ » i»g so a^ to for:'a ' :' uT : :r ?„;r ;*?• -" -""- arc the forces wl,iel, hrin !' '"''' ''""' wnderful loves dry fact ; „ Lsri; I ™°'' " "''"«*• "N» »"^ love the truths tlZ^ if :f ''T *'* ■■^»' '"^-S and as teachers fail „'„!;, J! ".f '° .''"J"^ --»-•" « we our student, look upon'cheltv " ; ™' ^"'""-htag 'hat because they find it neTes arv to "' ""'""'«'"■>■' ■""* ''"^^ " not because thev eniov lelrnf '""' T' *'"""i™'i°''. and covering its aec^ts ' ' ""'"' "'"'•" ""'>'- »d dis- bootr?hiehTa"d ;: t"^' '""°™*' °™" - »- ^e^t. foots UichaidTnelhrZr •''".' ™"^ ""'»''-' duced until the student ^ °""° '^ ""^ ""' '"''•"■ ' ino.^anic CeJ^s^Tl:^"! 7"'rf<='«'' '"s study of ' elements may combine t^ f ^^^ "'^' '™ "■■ -ore pounds, but L noTgiven a r Zat "™''"' „"' *'f"^-' «- should be formed rather T T" '"''^ ""<' impound placed before ht: 1 tm I'T'l'"" '^''^ "<> »»' -ay take place when he peXj::"''/™.'° ""■""' "'"" fl.™ his results aft*r he hi I t^''"""''"'' "■• ^o -^on- statements are made whlh t T ^" *"*• Sometimes cbemists, and thTb gil f isTke ""^ ^" "'^"""^ "^ which might be much b.,T„ '^'"'" ""ny things - -mo^y with ri!rrd:r:vi— tif^; , CHEMISTRY, HOW TO TEACH THE CHEMICAL EQUATION. 9 te7Z!^Jr "" f"' "'^ "'^'^^^ '^ ^'^^^^^>'^"^ ^»- ^^«"-"t« -to monads, is i^t nl 7' ""T"'' ^^"'■^' '"^^^' ^*"' ^^^'^ ^^^" -^'-^^"^^1 - -"^^ text-books, so ^ imal T .r''' '^' *''"' ''•" •'^'"^^"'^ "^^^^' ^^ ^'"'^^^^^^^ to write the compouncls of .at wh^^ " the powe, of the elements. It is worth while asking if this is not only . forexamnirl r"^ '^ Unnecessary but misleading. Would it not be one hundred er anrm ''''^^'" *•"""' ''"""'' ^^ «^^« the san.e information by means of Men- t is bettT nf! T^ ^" ^"^"^'^'' ^'^««'«^^tion ? Why should we leave the introduc- - eaeh nf I.. T ? '' *'"" ""^ '""^^^ ^"^ important law until we have studied the more nd to ^^T "7 J" l"'P«^^^"t elements and their compounds? From the table ^nc,:Z':: T^':^:' t^/r"^ ^^ ^^« ^^«^-t oxides n,ay be seen at a glance, m wifh rooi^ ■ . 5^ ^"^ ^"""^ ""'^^y 't IS to write the sulphides, sulphates and to en^ov ?• '"''^TV"^ Carbonates. The classiHcation further indicates the way in itisnr;tl!r'\- . ^ '^^''"^ the other elements combine with hydrogen, and when 'sZXeZ f?."' ^' '"'" ^"" ^^^^^"«^^ ^°'"'»"- -^th oxygen, it is not dilH- : some exam r'^ '' ^"^' to determine how many atoms of hydrogen the metals e ZltZ ": "f ^"P^'^' ^" '^^ ^y^^'-^^^" compounds, and how the metals and nature and dis- metalloids form their chlorides, bron.ides, hydrates, nitrates, ies occur in ^^'^' ^'^"^ ^^ ^^^^^ '^ ^^""^^^ ^^^ rational method of writing i and mn ''^™^ ^^''^' ''"^ ^^^ "^""''^ important compounds of the elements, and at ni'^cT^ ''"r''"' '^'' '""^^ '^"' "' '"'^^ ^'•^^ ^"^"^-" to many other features c^?^ T """' T'"" ^"^ '"' "^ '^' ^'''''''' discoveries of chemical ^ience. ZXltVr ' "' ' '' '^^ ^^"^ ^^^" ^^^^ «P^-^^ «f the best teachers of mber of Jff ""^ """'' '■ ^^''""'^'''y ^^^^t the principles underlying the subject should be "n ll^ ^f " ""■ >^-^"-d - -rly as possible. For that reason, in the plan on w^ one compound | here submitted, the Law of Constants, the Law of Defhiite .Vand tacts are not I Proportions, the Law of Multiple Proportions, some features I of the Periodic Law and Avogadro's Law have been intro- I duced at the very beginning of the work, and in practice the result has been exceedingly satisfactory. Experience has : shown that in carrying out this or any other plan, the aim ; should be to give the student experimentally, and as quickly I as possible, a comprehensive notion of the atomic theory. In I so doing, care should be taken not to make use of experi- him to predict what experiment, or to con- his work. Sometimes ig been discarded by to learn many things by introducing facts )veries. For example, 10 A HAND-BOOK OF CHEMISTRY. bul„:!' 7°""" "^ T"f'"-»". ""•'.ich ™„M become IrZ ■ °",^ '"'■'' ""I'""'™"''' - would have .,o„„ " v„,„e .„ .„„,t,.ati„« tl,e principle, »,erl,i„, t,„ the student ha., a knowledge of elcuientary physic, or i„ would aid in introducing the atomic theory. a taowietrrr',""?";"?'"' "■" '^^*'""-'- ■''""■'" »•""- oon,hV S f ^^""'"' '■■'"'■'«'=> " chemical chan.-e tl,. alsoTeci^^a. "'■*," " °°"'''"""''' '■'"• '^"O""" ""Sl" compo „d, Th 'r «'■'="">'■""''«-"' variety of cheiiiLil compound.,. Then the question naturally arise., are the suh ^Unces which enter into a combination themsehe m „u s ^ not Len T ^ ", '^"""'- "'" '■""' "'"' ""= <■'«"-«'« have j general way into metals and non-metals; and further i, brings up the important question, how dodemen s^^bii^^ I answered by tae analysis and .synthesis of water o. the analysis and synthesis of hydrochloric acid. In the* exned ments the studenf v^,^p« fy,„f ^.i expen- portant question,, Are compounds constant in co-L„,Lo' and IS 1 a fixed law that other gases unite in defln" ~' unite in definite proportions by weight! Manifestly the CHEMISTKY. It has been assumed that elementary physics, or in HOW TO TEACH THE CHEMICAL EQUATION. 11 :, or which would become Jnswer may be obtained by means of some ^ood experiments le beginner should perform *> 'Ih'^*^''-"*^" <^»-- T en. , , . "^ i ^Apeumtnts ments us would have some ' principles underlying th .> ;ii ^ / .^1 T " -"•"-. ,m^uu L-Aperimencs o Illustrate the Law of Constants and the Law of Definite roportions. We will now consider a few such expe.iments. §2. Some Expehimevts to Illustkate the Law op Constants and the Law of Definite Proportions. I . , — -^ - ' 1 (^''''''—^"««sy'"«thod of filling the eudiometer to which bysical properties of liquids Jpecial attention is directed, is described in 01,-^ ill c'twf «on.e facts whicli ^.. 1. Decompose water with an electric cun-ent, collecting ,, , ^" , r ^"'''' '" '"^^''^^'^ test-tubes, so as to compare their vol .a chenucal change, th. ff apparatus for this purpose is described in Chap III .. 3 ) change, and the difference jCollect the gases in one test-tube and ignite. If 'the s^uden ^d, etc. Attention might |s not satisfied that n.oisture is forn.e,!, it will be necessary to r and variety of chemical prepare dry hydrogen and burn it in air or oxygen, col e ing turally arises, are the sub- ihe product in a cold dry bottle collecting on themselves compounds:! ^^.2. Pass some pure dry hydn,gen and oxygen into a V number, their symbols eudiometer over mercury. Take cai^^ that ih^ f ' pf fi.nf fK„ 1 , *i , ^ ^"'^^ '"^ gases are at ct tlidt the elements have ^he same temperature. Measure the volume of e-ich .^l. ..n^ ey niay be divided, in a ^plode. Eepea. the experiment until ::::lZ:!::t :' -nietas; and further, it ^i"ced that tiie gases unite in the proportion of 2 to 1 no low do elements combine ^'atter what volume of each gas may be present ^on may most easily be | From these two experiments it will be seen (1) that water Uies. of water, or the r --^ant in composition. (2) that water is a compound, (3) e acid. In these experi- fat a definite volume, and hence a definite weight, of hv;]ro es oxygen and h3^rogen, |en unites with a definite volume and weight of oxygen to aetinite proportions by form acjueous vapor. Jft " ^e^ty unite in definite | Let us now consider the question. Do other gases unite in naturally, come the im- ^-finite proportions by volume? To obtain a satisfactory onshiivt m composition, |i^«wer, use diy hy.lrogen chloride. There are two very unite in definite propor- ^portant advantages in using this gas to demonstrate these s? Do other elements facts. In the first place, only inexpensive apparatus which .ght ^ Manifestly tbe ^ to be i^uiid in almost .ny laborlry, is ZeJary t^,t 12 A HAND-BOOK OF CHEMISTRY. form the experiments, and for this reason, the laws may be demonstrated, in this way, by any teacher, while more elabo- rate and expensive apparatus, such as an induction coil, a battery, and a delicate pair of balances are required for other experiments of this kind. . Secondly, the experiments may be used for the purpose of showing that molecules of hydrogen and chlorine each contain two atoms, but at a later stage in the work. The next experiment is' taken from Reynolds' " Chemistry." Ex. 3. {a) Open the stopcock (Fig. 1), and pass a current of hydrogen chloride gas tla-ough the U tube for some time, then (juickly close the stopcock and pour mercury •^ into the U tube to close the bend, and half fill the open arm. Open the stopcock slightly, and allow the gas to escape until the mercury stands nearly the same height in both arms. Mark the height of the mercury in the closed arm. Next drop into the open arm sodium amalgam, and fill to the top with mercury ; close the open end with the thumb and pass the gas backward and forward a number of times through the mercury by tilting the tube. Finally hold the tube erect, raise the thumb and allow air to enter the open arm. Pour in or re- move mercury until it is the same height in both. The gas in the closed arm should now occupy half the volume that it did at first. Tilt the tube so that the mercury will press on the gas in the closed arm, cautiously open the stopcock and hold the nozzle to the flame. (See also experiment 7, and the chapter on the analysis of gases.) (6) A modification of the same experiment may be per- formed as follows: Into a bent tube (Fig. 2), filled with mercury conduct dry hydrochloric acid gas, and then intro- FlG 1. e laws may be lilc moro elabo- iduction coil, a [uired for other riinoiits may be es of hydrogen t a later stage from Reynolds' 1 pass a current for some time, d pour mercury and half fill the htly, and allow y stands nearly lark the height Next drop into id fill to the top with the thumb [•ward a number tilting the tube, the thumb and Pour in or re- height in both, low occupy half Tilt the tube so the gas in the opcock and hold iient 7, and the at may be per- 2), filled with and then intro- Kk;. ■.'. HOW TO TEACH THE CHEMICAL EQUATION. 13 duce in the bend of the upper part a little piece of dry metaUic sodium. On heating the latter with a lamp, the hydrochloric acid is decomposed, the chlorine combin(!s with the sodinin to form a sodium chloride while hydrogen is set free. Upon measui-- ing the residual hydrogen, it will be found that its volume is exactly half of the HCl introduced. In preparing the gases for the next experiment use appara- tus descrilH>d ir. Chap. III., ^2, Fig. 14, and Chan. Ill ii3, Fig. 1.5. 1 •. Ex. 4. Pass eciual volumes of pure dry hydrogen gas and chlorme gas into a graduated tube or eudiometer, oxer mer- cury, as in Fig. .3 About 6 c.cm. of each will be sutticient. Place the graduated tube in a very dim light while mixing the gases. When the tube is ready, place in the sunliglit, or burn magnesium ribbon near it, and chemical union will ensue. If a eudiometer is used, an electric spark from an induction coil may be passed through it. Some water may be passed into the tube by means of a pipette, if considered Fui. ;<. advisable, when the hydrochloric acid gas will be dissolved. An instructor in chemistry may find it an advantage to demonstrate that the laws hold true when solids, or a solid and a gas combine. The three following experiments are recommended, but must not . be attempted unless with a delicate balance. Ex. 5. (a) Into a hard glass tube, which ha« been weighed (Fig. 4), introduce a weighed (quantity of copper oxide. About one gram is a convenient amount. Pass dry liydrogen through this tube, and, after all air is expelled, heat the tube 14 A HAND-BOOK OF CHEMISTRY. Fi(i. I, and containcfl oxide to rodnoss. W«'i;L(lj tlio tnho nnd con- tents, and find tlic weight of the remaining coppei. Calculate the combining weights of oxygen and (-(.iipci'. It is best to liave a piece of rubber tubing on the end of the glass tul)ing, so as to drive off moisture without igniting the sur- plus gas. (h) Heat the copper that is left in th(! tube in a curn'ntof air, and find the weight of CuO that is formtid. This may best Ite done by attaching an aspirator, or a rubber bulb with valve similar to those used in a rubl)er syringe. if.r. G. The following very simple and inexpensive experi- ment was designed by the writer to illustrate this law, by burning magnesium ribbon (Fig. 5). Take a clear sheet of mica about eight inches h>ng, and four or five inches wide, roll in the form of a cylinder, ha\ing the ends overlap aliout one - inch. Firmly fasten the ends together with any good cement. xVround the cylin- der place a couple of fine rubber bands, to hold it securely. Take two small pieces of mica, to place on toj) and bottom of the cylinder. These need not be secui-cd. Through a small apertin-e, made Avith a fine needle in the centre of one, place a piece of platinum wire about one and a half inches long, and fastened at one end to close the I'lu. 5. [Y. le tnho and con- >l>I)<'i. Calculate I', it is host to the ^'lass tuhin*;, io as to (li'iv(! off noisturo without giiiting the sur- )lus gas. (h) Heat tlie oppcr that is left n thr tu])t' in a urrcnt of air, and ind the weij;ht if CuO that is ornitMl. This may »est be done hv I valve similar to xpensive experi- ate this law, by a clear sheet of )ng, and four or the form of a verlap about one i ends together round the cylin- rubber bands, to o small pieces of :1 bottom of the lot be secured, le needle in the about one and id to close the HOW TO TEACH THE CHEMICAL EQUATION. 16 apertu:-e. On the other end of th Weigh the a[)parati K' wire make a small hook S including the cylinder, tw mica, and platinum wire. Now weiirl ribbon, about two inches 1 hook, and place it throu"h tl o pieces of 1 a piece of magnesium ong, hang it very looseJy on th . , - „ " ^'"' "I"'.i,'I't cylinder. Do not let the lower end of the ribbon extend below the lower aperture of the cylinder. Now ignite the magnesium ribbon, and in- str Uly place on the piece of mica. Press on the upper surface o tne apparatus, so as not to allow any of the fumes to escape. This IS very important. It is best to j.lace the apparatus on a piece of glass or porcelain while burning the magnesium, as the mica becomes quite hot. Weigh the apparatus when cool, and calculat(. the combining weights of O and M.r The accuracy of the e.xperin.ent largely depen.ls upon u^ighi,,.. be ore and after ignition, at about the same ten.peratuiv and with the same weight of air present in each case. Tt may be repeated a numbc^r of times without trouble, since it is neces ^y to shake off only the loose powder before repeating. AN ith a little practice and a delicate balance, this experiment can be <|uickly and easily done. £:x. 7. The following experiment is also simple and easily per ormed. The apparatus is similar to Fig. 1, used in the analysis of hydrochloric acid, and, still more important, may be used in tho analysis of gases. The reader's attention is directed to the chapter on this subject. The piece of apparatus described here is sometimes used as a eudiometer. Take a U tube similar to Tig. 1, with one arm drawn out to a point, so that a piece of rubber an.l damp may be attached, or better, having a stopcock. It is best to haNe the base of this arm nearly level, as in the diagram, and the base ot the second arm rounded. It would also be an advantage to have the arm graduated, but this is not necessary. One 16 A HAND-BOOK OF CHEMISTRY. nvvf) of the tu»)e mmi not hold less than 75 or 80 c.cni. Close the stopfwk. Pour in 'listilled water, ami l)y tilting com- pletely fill the elosed arm, atid have the water rise a few inches in the open arm. Now carefully weigh out from .150 to .200 gms. of zinc, imd drop it into the open arm, and cause it to rest on the level h a under the closed arm. A few scraps of platinum might be added. Now pour some strong sulphuric acid into the ojien arm, and let the gas collect in the closed aru). If the tube is not graduated, place it in a tank of water, and over it a graduate filled with water, and allow the gas to pass into the graduate, so that it can be measured. Bring the water to the same level both inside and outside t)ie graduate. In calculating allow for the tension of the afjueous vapor, the temperature and atmos[)heric pressure, and deter- mine the weight of H displ-iced by Zn in H.SO^. Other methods of performing the same experiment will be found in Reynolds' " Chemistry," Chap. X., page 95, Experi- ment 54 ; also Remsen's " Chemistry " (Advanced), page 754, which it might be well to consult. Ex. 8. A method of detejininiiig the amount of oxygen in a weighed quantity of potassic chlorate is described in Rem- sen's "Advanced Chemistry," page 745. § 3. How TO Rkpuesent Molecules and their Reactions upon One Another. From our experiments we have learned that two or more elements may combine to form a compound. For example, O and H unite to form water, and H and CI combine to form hydrochloric acid. Now, the smallest ])irticle of any com- pound or element which can exist by itseii, or vu a free stpte and which still retains the propertier^ nf that, substance, is called a molecule. Hence it follows that a molecule of water must contain at least two parts, or combining units of hydro- J STRY. 5 or 80 c.cin. Close uul by tilting com- ,ter riHo a few inches 1 out from .150 to 3n arm, and cause it arm. A few scraps Diiic stronf]; sulphuric colltx't in tlio closed ice it in a tank of ivat(a', and allow the t can be measured, side and outside the nsion of the ac|ueou8 pressure, and deter- H,SO,. experiment will be X., page 95, Experi- dvanced), page 754, mount of oxygen in described in Rem- ES AND THEIR TIIER. d that two or more ind. For example, CI combine to form nxticle of any com- t'j O)' ii. a free stn te ■ that- abstance, is a, molecule of water ling units of hydro- HOW TO TEACH THE CHEMICAL EQUA'i^W. 17 gen, and on,, part, or combining unit of oxygen : and a mole- (Ule ot HCl must c.ntain af least one part, or combining unit of hydrogen, and one part or combini.ig unit of chlorine, hach particle of hydn.gen, oxygen or chlorine which . r.ters into the composition of the moleeuK-, is called an atom A molecule of water, then, must contain at h-ust two aton.s of hydrogen and one atom of oxygen ; a molecule of hvdrochlonV acu must contain at least one atom of hydrogen and one atom of ciaorino; and a molecule of cupric oxide must contain at l"ast one atom of copper and one atom of oxygen. Molecules of these compounds are usually written H.,0, HCl, CuO, etc but it is best also to represent them by diagrams', somewhat as follows : H H H 01 Cu O Mg O By means of these the beginner may form a mental picture of how the atoms are held together in the molecules. Just at this stage in the work the student should learn wiat the symbols of chemical notation, such as CI, H O etc denote; what is indicated by the formula of a compound' as, H,0, CuO, MgO, etc.; and further, that the electro- positive element stands first in the formula. This should be followed by the preparation of hydrogen gas from the acids and such metals as zinc, magnesium, etc. ; also from water by using potassium and sodium, as these experiments will best serve the purpose we have in view. Having performed these experiments, it will be an advan- tage to make diagrammatic representations of the molecules of substances used and formed, when these chemical changes took place. For example, potassium hydrate, sodium hydrate. K I Na 2 H OH, and other formulae not in the 18 A HAND-BOOK OF CHEMISTRY. previous paragraph, might be written out. The transmuta- tions in these experiments might now be represented some- what in this way : (1) When potassium is thrown on water, hydrogen and potassium hydrate are formed. Ek X[7 O V_ H O H H H 1x. K O H K O H (2) When sodium is thrown on water, hydrogen and sodium hydrate are formed. This may be represented by a diagram similar to the action of potassium on water (1). For a representation of this see § 10 of this chapter, page 37. (3) When hydrochloric acid is poured on zinc, hydrogen and zinc chloride are formed. r H ( CI Zn ~^-[- CI Zn CI ^~^^-- H t CI ^ H H -—-"^ . ater, hydrogen and ydrogen and sodium on zinc, hydrogen HOW TO TEACH THE CHEMICAL EQUATION. 19 (4) When copper is heated in a current of air, oxide of copper is formed. (5) When hydrogen is passed o^er CuO, water and copper are produced. For a diagram of this reaction see § 10 of this chapter page 38. ^ ' (6) When magnesium is heated in air, oxide of magnesium is formed. This may be represented by a diagram similar to the action of oxygen on copper (4). (7) The synthesis of hydrochloric acid may be. represented : H ^__^ H __^^ ■1 — .. ' — ^ H CI _— u— » CI CI CI (8) The analysis of hydrochloric acid may be demonstrated as m diagram, § 10 of this chapter, page 36. (9) The synthesis of water may be represented as in dia- gram, § 10 of this chapter, page 37. A HAND-BOOK OF CHEMISTRY. (10) The analysis of water may be represented : Many other illustrations might be added, such as the action ot sulphunc acid on zinc, and on magnesium; the heathn^ of potassic chlorate, mercuric oxide, etc., but enough have Ln used to indicate the method. In the preparation of hydrogen, and in many other intro- T.T^ ."TT""^'"' '^' '""'*' ^"^P^'-^^"* ^*^ids have been nl;r tI ^^""r "'" ^^ '"""^^^ -^^h ^heir common names. These may be used to good advantage to introduce the formuhe of compounds. § 4. Thk Formul.e op Compounds. Like water the acids are compounds of hydrogen, or con tain displaceable hydrogen, as shown in the preparation of hydrogen gas; and such comp, unds of hydrogen may be written somewhat as follows • Besides the common names, water, hydrochloric acid, nitric acid, eC, these compounds are called hydrogen oxide, hydro- gen chloride, etc. *^ When potassium was thrown on water, an atom of K took the place of one atom of H. and formed F^h t^ ... ., atom of K were to take the place of the atom of hydrogen, ■EMISTRY. represented : H H O O H H Ided, such as the action tiesium ; the lieatiug of but enough have- been in many other intro- tant acids have been r with their common dvantage to introduce MPOUNDS. I of hydrogen, or con in the preparation of of hydrogen may be ^03, H,S, H,SO„ drochloric acid, nitric rdrogen oxide, hydro- •, an atom of K took 16 atom of hydrogen, HOW TO TEACH THE CHEMICAL EQUATION. 21 !we would have K,0, the oxide of potassium. Other com- I pounds of potassium may be formed by disphicing the hydrogen of the acids with K, one atom of K taking the place of one I atom of hydrogen. In this way we may write down the compounds of potassium corresponding to those of hydrogen • KCl, KI, KNO,, KBr, K.,S, K.,SO„ K,CO,, K.3PO,, etc" In the same way the compounds of sodium may be written out. Now let us look at magnesium. The oxide is written MgO. Then an atom of Mg just takes the place of two ' atoms of hydrogen, as the oxide of hydrogen is written H..0. Hence the sulphate of magnesium will be MgSO,, its s"ul- phid3 MgS, and its carbonate MgCO,. Since one atom of hydrogen combines with one atom of chlorine to form HCl, an atom of magnesium will combine with two atoms of chlorine to form magnesium chloride, MgCU. Then it* other com- pounds will be written Mg(OPI)„ MgL,, MgBr,, MgNO.,, etc. The table, as it appears on the blackboai-d, will be : Oxides. H.O KoO NaoO Mgb Iodides. HI KI Nal Mg(I), Hydrates. HOH KOH NaOH Mg(OH), Nitrates. HNO., KNO. 3 NaNO, Mg(NO,), Chlorides. HCl KCl NaCl Mg(Cl), Suljjhides. H.S K.S Na.^S MgS Bromides. HBr KBr NaBr Mg(Br), Sulphates. H.,SO^ K^SO, Na.SO, MgSO, Zinc and copper might be added to this list as practice for the student, but before writing out any more compounds it will be necessary to get a clear idea of how the elements combine with one another, and this can be done by a study of Mendelejeff's classification. 22 HAND-BOOK OF CHEMISTRY. CHEMISTRY. HOW TO TEACH THE CHEMICAL EQUATION. 23 05 05 SO ^ In studying this table with the class it is best to have a large chart made, showing the ele.iients with their atomic weights, and have it hung in a conspicuous place. The elements are arranged, in the classification here presented, in eight vertical columns, representing eight groups ; while suc- cessive series are presented in horizontal lines. (These may be made to incline slightly, so that on rolling the table Na will immediately succeed F, K will succeed CI, and so on, in a spiral line. See Shepherd's "Chemistry," page 221.) The first eigl i present very marked individual characteristics. The teacher should not draw attention to too many facts at first, but only give such information as will be useful in illustrating the way in which elements unite to form com- pounds. If too much is attempted it niay lead to confusion, and the teacher must use his own judgment as to what is necessary. The following might be made clear : 1. The elements are in the order of their atomic weights. 2. The meaning of RO, R.,0, R.^O.^, etc., RH,,*RH,„ RH„RH, etc. ' 3. The elements of each group have a series of compounds corresponding to the oxides. 4. One atom of CI, Br, etc., unites with one atom of H, and hence with one atom of each element in Group I. The other groups form similar compounds. 5. The position of the metallic and non-metallic elements in the table. The next step in the work is quite plain. The student should write out a series of compounds, or at least one element in each group, similar to those of H, Na, etc., already given, but it should be made plain that many of these have com- pounds corresponding to the elements in other groups, and that the elements of each group should be memorized. In connection with this study the subject of valence, and the 24 A HAND-BOOK OP CHEMlSTRr. '"«««■ '» «on, -h-h the aton, „, radicaHan coL^ "' '''""'«''•' «"> Pl^oe. The combining capacltv T^T "" "''"'''> " «•■'« re- »mt, hence hydrogen i.sZflX '"^"'^'"' '" '"k™ as the ■' -« be seen tha't the att rvt™'™^^ °' ■'"^■" ^^ compoMtion of the hydride 1 ^ "scertained from the hen the most sUbletfd'or'hrid™"'' ""'«>""'= ^'^ '■3'Cndes .n Mendeieje., ,,, ^:^^^ ^e used, .he % writing dowL fhp K i^'j ^^-' ^H. 'heir aton-ic Wit ^el :tr 't e*r" ^"™™'^ »<> of the elements for hydrogen dimti.h "^ ^™"P ""e affinity ■ncreasing atomic we^ht neverth' " t" ''^ ^'^P ^''h the «en atoms which combine w"th?r' *' """"her of hydro! e -ents is constant for ^h t ! "'T' ""'' »' '"^ °*: valence or atomicity, and may be L„3 " *""" '^ """ed affimty of an element i„ it, relt,„ * ' "" """e function of to the combining power rhydZe ''"'""''" ^ -^-ed rame, then, the valency of the '? '' " """• T" deter- y the more .mp„rte„t elementa, let CHEMISTRy. HOW TO TEACH THE CHEMICAL EQUATION. 25 tnvalent element*? of X "ecs chemieaJ nom'en! I 'I' ^""^"^'""^ *^'''' ^^^"^"'^ °^' •^^'^"^^''^- ^'^^ ^^^oni of hydro- educes ChemieaJ nomencla- ' ^''« n^'nes of compounds ^^ncy,. which is condensed 'k;s of chemistry, indicates '«^denng the subject. AI] E. has demonstrated clearly ' Property of combinin.. ^••adicals in definite and f this property is com- l^toms of hydrogen with b^ne or which it can re- ydrogen is taken as the valence of one." Thus 'e ascertained from the such compound exists The ie may be used fesonted RH. different elements and each group the affinity step by step with the the number of hydro- ' of each of the other his IS what is called i as -the function of ^drogen," or referred ' a unit. To deter- oortant elements, Jet - en unites with one atom of each element of the chlorine roup. Hence the halogens possess one affinity unit and are nonovalent. Sulphur and oxygen each unite with two atoms »f hydrogen or chlorine, and since they possess two .iffinity inits they are divalent, i.e., an element which will not com- bme with more than two atoms of hydrogen or chlorine, or will not displace more than two atoms of hydrogen is divalent For similar reasons nitrogen and arsenic are trivalent, and carbon and silicon tetravalent. "Nor can one atom of fchlonne, sulphur, nitrogen or carbon be made to combine I with more than one, two, three and four atoms of hydrogen ' respectively, to form stable and definite compounds. They are satisfied, or saturated, and these compounds are termed saturated compounds." "Chemical affinity, however, must not be confused with valency. Valency is quite independent of affinity, and pecu- liar to individual elements." Carbon combines with four atoms of chlorine, sulphur with two, and hydrogen with one atom to form saturated compounds, but this does not indicate that carbon has a greater affinity for chlorine than sulphur or hydrogen. Very often the opposite is the case. "Those elements which have the greatest chemical affinity have often the lowest valency, and inert bodies, such as those of Group IV. and Group VIII., have often the highest valency." A study of the equivalent weights of the elements will also aid in determining their atomicity. It has been found by actual experiment that 23 grams of sodium liberate from water 1 gram of hydrogen; 24 grams of magnesium or 65 grams of ^.ac displace 2 grams of hydrogen from the hydrogen com- pounds, and 27 grams of aluminium liberate 3 grams of hydro- gen ; also 12 grams of magnesium displace 108 grams of silver from silver nitrate. The weight obtained in each case is 26 A BANB-BOOK OF CHEMlSTRr. ^«'g''ts; andtho.se j;, ^^'"P^'-^^«'''-^l to half 2 !, the atomic weiJ,? l''^""""'"'« ^nd Group ITT. '''^'"' J^n the casp ,.f I • *^'*'»Gnts of Groun it , '^^"t.j the. '^Ju'Jiiniuni, the ^f» • ^ ^- "^^^ divalent 1 t'^e equivalent wei™lent, Groun do this chemisf^ I? ^'^""^^^ compounds " T ""^^ r- ar ir^^^^ - .-™rrr c tneir modeof off u ^^oms within f ho > ''^' '^"t of the Write" tt^"""' "" """ mother » n ,"""'' "" ^rite a chemical equation. P CHEMlSTRr. when referred to hydrogen an'i the other elen.ents of -^;^ntieai with the atoj ^fnm^noszum and the other ^:^-^^^ to ha]f the aton. . n Group Ul. to one-third "^v Law of Multiple roportions, which forn.s an essential amplification of the .aw of Definite Proportions; an,l perhaps the I^iw of Multi- . e Proportior,s can best be explained by calling attention to [the oxides of nitrogen. A study of this law leads us to a consideration of the most iDOrtant nrinpinloa ,.f «l, • .^..^ t^ , . . . tilp H. . •"' '^"'J wif ?. , : . -"■• —^'^ "■-'''""' ^""SKieration ot the most f. equivalent weight ; T^'P^''*^"^ principles of chemistry. Dalton ma.le the groat .^'oup II. ^,^ ^j.^,^j^^^ I discovery that "elements unite in definite proportions by »« we,ght is tliree times r'^^''' ^"'^ ^PP^^^'l ^o his discovery the atomic theory. This ""»nmm and the other ^<^^iJl ^>e seen that there '^y and atomic weights " ■.a'-e monovalent, Group -alent, Group IV. J for twvalent. Group P ^n. are heptavalent talent or divalent. It here are compounds ^ai statement, and to bj^^t we must study pounds." In order to ^olic method of repre- ' ^'^'e expression not ^ments combine, but Z V^" "molecule, and • ^^ IS the opinion ^»ee graphic formuhe a chemical equation s i '■ ^ ^ ""' '"-"^"veiy uiie atomic theory. This , j^'rewoutof acrude analysis of matter, which proved tolas : mind, at least, that the same substance always had precisely the same composition, as Proust and other investigators had a ready written on the '-constancy of the relations by weight of the component parts of boenta unite,), a„d' the cH ^'"^ T"""'"" '" -hioh tht "■*""''' "f " compound 2i^. t '"! '™^"-' particle 1 add-ng together, the wei-d," of >'''"'"■' "^ "^^'"'^ by '-ch a basi, we see that theoonft * ""'"'"^"* ""'"'- O" be^constant." -n^t.tuents of compounds should ihe consideration of thp t bnngs out the fact that thel,^" °' ^""-'P^ Proportions ""'y one proportion, and 'he ' i'"'"' """* "'* M^genTn ! ;::: :"Th'"^"'^"'» -t; wirtr'^r"^-"-""-^- 'orced to the conclusion th»t • "■ densities, we are • "^'ary gases there is conwLT "'""' ™''""« "^ hese e" ' »r combining units. Ifto ""V" '"'"'" »™ber of atoms 1 pie, there are 1000 ,7 "" ™''">« "f l>ydro<^n f." ' 1 ^""Oaton.s.whiche^ual/oooCigl:::;':;] f CHEMlSTfty. f .°^ the existence of atoms ' -Ki olefiant ,,as that tJ^ oDalton. He calculate.! ^' «^ these compounds wea. :"^'';>' gas contained twice -;'ehantgas. He further 'yS^n ,n carbonic acid ^jas ''" o^icle gas (CO). These , ^' '^P^^-^ned by assun,- '^'Jy smali particles which ^em.cali^ ar mechanicaJlv ■ ^•'f '^ of adorns possessing ;'^\eou.ia be denoted by hjd'ogen being taken «; • the atoms of different .^nd alJ atoms of one yht and are like each ^toms with one another proportion in which the tJ^e smallest particle or ^refore be obtained by constituent atoms. On »ts of compounds should ' Multiple Proportions ^n>te with hydrogen in ^are the proportions in heir densities, we are • ' volumes of these ele- T! T'^^' of atoms, f hydrogen, fc,r exam- '^ 1000 weight units. HOW TO TEACH THE CHEMICAL EQUATION. 29 nd in a like volume of chlorine there are 1000 atoms of .lonne, which = 1000 x 35.45 weight units, then it is evident 'liat the relation between the atomic weights and that be- tween the densities must be the same, or one volume of hydrogen = 1000 X 1, and one volume of chlorine^ 1000 x .35.45. Hence the atomic weights of the halogen elements are proportional, or eciual to their densities if n-ferred to the same unit. We arrive at a perfectly similar, but much more general conclusion, by the consideration of the physical proi,erties of gases or vapors. According to the law of Mariotte and lioyle, "the volume of a gas at constant temperature varies mversely as the pressure," and from the law of Charles and Gay Lussac we learn that, "the volume of a given gas at a constant pressure varies directly as the absolute temperature " etc. From this we infer that when we have the smallest particles which can exist in a free state, and the gas expands irom an increase of temperature, the particles do not increase in number, nor do they increase in size, but the spaces be- tween the particles must become larger. In other words when heat or energy is transferred to a volume of gas the temperature increases, and each particle receives the same amount of energy. Hence, according to the kinetic theory of gases, they are driven apart, or aiiected, to the same extent, so that the spaces between the particles must increase to the same extent. Now, it necessarily follows that if equal volumes of different gases change to the same extent when subjected to equal alterations in temperature and pressure "there must be an equal number of particles contained in equal volumes." From this it is inferred that their relative weights are proportional to their volume weights, or gas densities. Now we can appreciate the historical order of these dis- 30 A HAND-noOK OF CHEMISTRY. iTon, t ,es„ ex,,eri„,e„ta we I„„,,, the foU.w 1 1 volume of I! + | volnnio nf CI « , * ■ «H2vo,„,,,e,„„^,,ire:?o; :::;::: ™^ As a oonHnnauon of „u,. exneri,n * '""■"<'»'" H.O. Gay Lume discovered ( 1,,!,^ ' """^ »«"'■■« th, pie volume ratio,, „"d (1/ 1 7" 7"" ''™''^'""« '° '"' body bears a si.nl ,„t o to h! 1 "'"" "' "" ■■•'"""" Dalton discoveredt ,at tl '""""' "' "'" ""'""'"ont, bini„« e,e™e„.ralo :, Vi'.m"r''"T ''. "'">"" "' '"^ ™- wo grant ti.e „,„„io ^ Z^"""" ° ""." ""»">=. I Avogadro-s hypothesis foiC : :;;trr 1 "',"""■ of gases under the sn,„e conditionr„f 1 ' ' "''"""~ -re eontain the sa.„e nuX tf II . ""P-"'""" ""d Pr- Having proved the tru ho tf'" °'' "'"''■■""''•'■" cerning hyjroehlorie „o d t ' '" " "" '""■^' '"'"' «°"l 'aw, ..e,„:, voiu J or;! ' X"rhr '^ ^™«'^"''' perature and pressure ennt .? "' """ditions of ten,. Then . n,i:: ' fTy;;^;r''''r'r^f '"°'^""'-- molecules of HCl ; "y"™*™ + > molecule of chlorine = ij of Hc"" - " ■""'"'""" "' « -^ ^* « -'-"'e of CI . , „„,ec„„ ^ Therefore a moleculp nf ni ,.„^ , tain at least two atoms ' '"""'""^ °' « -^l' ~" ) syrnS^""^ "^^ •« ■'-- '-- *e analysis and { oules™ 'Zt: vap!f ;"°="'" ^ • '"*™"' 0' -^«e„ = 3 mole- j Therefore 1 molecule of hvdrofrnn x i o i , d = 1 molecule of water vapor ; * " "'''"'^ ^' ^^^>'-"-' 1 Hence we infer that a molecule of oxvffen i. Hi -^ , • ^^ 2 parts, or contains at least 2 atoms. ^^'"^ ^"'' - P CHEMISTUV. )stion again nriHes, Ho - d analysis and synthesis o, fi this point plain, irn the following : f CI = 2 volumes of HCl ; )f = 2 volumes of H„0. ?riments, we are aware tha 1 asos unite according to aim ''« volume of the resultin; olumes of the constituents cities by weight of the com ratio to one another. J !ir constitution of mntte. mely, " that equal volume s of temperature and prt> articles or molecules." t'se laws we may infer con' !e, according to Avogadro' ;he same conditions of tem ime number of molecules,' 1 molecule of chlorine = 2 oleculeof CU 1 molecuh molecule of H each con n from the analysis and cule of oxygen = 2 mole- f- 1 a molecule of oxygen^ oxygen is divided into HOW TO TEAOn THE CHEMICAL EQTtaTION. 31 .^ H. Mo,,KruLAR Volume and Atomic Wkkjut. We have already pointed out that ihe relative weights of ,8es are proportionate to their densities, and in determining eir densities that hydrogen is taken as a unit. In other 3rd8. to obtain the density of any gas, we divide the weight a certain volume by the weight of an equal volume of hydro- n at the same temperature and pressure. It will be mani- st, therefore, from Avogadro's liypothesis, that if we divide ^e weight of a certain number of molecules by the weight of . equal number of molecules of hydrogen, we also get the nsity ; and, further, we arrive at the sam(> result by divid- ig the weight of one molecule of the gas by the weight of a olecule of hydrogen. It is quite apparent, then, that we ay obtain the weight of a molecule of any gas by multiply, ig the density of the gas by the weight of a molecule of lydrogon. The reverse of this is also true ; we may obtain he density from the molecular weight, which is verv import- it to the beginner in studying the properties of ^m^es To determine the weight of a molecule, however, we must ■ow the number of atoms in a molecule and the weight of atom. It is certain, then, that the student will need to ve a clear conception of "molecular volume " and "atomic 'eight," and it must be made plain that the molecule exists Wily in theory, but that the assumption of its existence frves, at present, as the best means of explaining chemical |henomena. We are ignorant of both the form and charac- T of the molecule, and any measurements which have been lade of its volume are approximations. To say that a olecule IS invisible to the highest powers of the microscope loos not by any means give an idea of its volume Sir W hompson estimated the diameter to be about one ten-nwl- x)nth of a millimeter J but it would take a considerable stretch the imagination to even conceive of a particle of such 32 A HAND-BOOK OF CHEMISTRY. minute dmiensions. S„cl, measurements are interestin. I of matter, though extremely small, have a definite size. W.I1 be quite apparent, then, that the weight of an a cannot be actually determined, but the height of anl' ydrogen has been adopted as unity, and fll measurem hove been made relatively to its weight. Since ther molecule of hydrogen contains two atoms, and a"' atm hydrogen weighs one, its molecular weigh is two Td molecular weight of any gas is equal to the density ;f he m IS relation to hydrogen multiplied by two. Then ^ must be apparent that if we take a volume of hydr" which weighs two (its molecular weight), an equal vime any otl^-r gas at the same temperature and pressure m weigh molecular weight. Therefore, if a volume o h^d gen weighs two pound,,, grams or ounces, an equal vo urn' any gas at the same temperature and pressure willweTg, number of pounds frnma ,^.. "'oi^i molecular weight ""'' corresponding to We ,„ight very properly at this point discuss the metho of determming the atomic weight of an element, but it w be suftcient for our purpose to state that in dete mWnl I weight of all compounds containing the element by the methc ah^ady indicated, and then (2) from an analysis of irs c pounds calculate the smallest amount of the loment t moleeular weight of each of its compounds. This wilT. the atomic weight, which may be defined as " the smafl weight o that element which enters into a mol 1 „ compounds.' j Now we are in a position to appreciate a simple method } determming the molecular weight of any gas. 22.4 litres hydrogenatOoO. and 760™"barometricpLLe weigh gl OF CHEMISTRY. HOW TO TEACH THE CHEMICAL EQUATION. 33 sureinents are interesting, ho« , o • *u he view that ultimate particlf , "', '" "^^^^^ular weight of hydrogen, and since by Avo- mall, have a definite size i'''''' y'^^' "^qu^-l volumes of gases under the same condi- that the weight of an atof f !, ^^P^''^^^''^ contain the same number of molecules," but the weight of an atom 1;'''.'''^^ *''^<^ ^^'^ ^'^^^^ oi any gas at 0^ C. rnd 760""" baro- unity, and all measureraentf ?• ^'^'"1"'^ "'"'^ '''^'^^' '^^ molecular weight in grams. ' its weight. Since, then f I V '^'^^""" ^* ^" ^- ''^"^ 760-"' weigh 71 grams, two atoms, and an atom WTu '' '^' molecular weight ; 22.4 litres of amdionia cular weight is two, and tl ^^^J^'''^ temperature and pressure weigh 17 grams, and jqual to the density of the JI '' , ™olec"lar weight of ammonia. On the other hand, tiplied by two. Then too '"f , ^^'"^ ''""'^^''' ^^ ''^^'^™^ ^^ ^ molecule, and the take a volume of hydrog J"^ ^^""^ ''*'''"'' ""'^ "'''' calculate the weight of 22 4 r weight), an equal volume '''' "^ ^'f ^""^ ""* standard temperature and pressure. In iperature and pressure muT"'''"'*'' ^^^™P^^' ^here are three atoms of hydrogen and ierefore, if a volume of hydrf "" ""^T '''*'''^''' ' '''" ^^^"^ °^ hydrogen weighs 1 and an V ounces, an equal volume f T. T.^'''^^'' ^''^^'' ^'^' ^^'^'^^""'^ ^he molecular weight is ■+14= 17. Hence it follows, from what has been said, that 4 litres of ammonia gas at standard temperature (0^ C ) d pressure (760""" B. P.) weigh 17 grams. For the same >ason 22.4 litres of marsh gas (CH,) at standard tempera- 're and pressure weigh 12 + 4=16 grams. For the above reasons, it will be important to know the must (1) find the mole°culI?'" ""^ ^^°'"' '" ^ molecule of the diiferent elements, ig the element by the metlil ^'^ ^'^'^ *^''°'' '"^ "" molecule of each of the more com- from an analysis of its co*? ^^'^'' '"'*" """ "' ^^' ^' ^^'- ^^^^^^i"-"- sodium, zinc ount of the element in tl ^^«''«"''y have one atom in a molecule, and recent inves- ■gations on the new gases, argon and helium, indicate that ere is but one atom in a molecule of each of these elements IS interesting here to note that recent investigations idicate that arsenic is not an element, but a compound of [hosphorus. re and pressure will weigh ounces corresponding to ii lis point discuss the methorj t of an element, but it w iiate that in determininws the Law of Multiple Proportions in forming its com- oends, as for example, H.O and H.,0„. ^.Hydrogen occupies a definite position in Mendeleieff's issification, and its atomic weight is such as to lead us to lieve that it is an element, from its relation to other atomic ignts in that classification. It forms a series of compounds similar to those of Group 'f Mendelejeff's classification, and it may be displaced in .se compounds by many other substances which we believe 'be elements; and both hydrogen and its compounds have ^perties similar to those we would expect an element and compounds to have which would occupy the position it !s in the table. 'or similar reasons other substances are classified as iments. ^Vhile studying the relation of hydrogen to other elements > other point should be made clear. Is hydrogen a metal' |a non-metal ? The answer we get will aid very materially (understanding its compounds, and their relation to the ipounds of other elements. For the following and other ^sons, It IS believed to be a gaseous metal at ordinary nperatures. ^ Hydrogen is absorbed by the metal palladium, and the snm.'™'"* at hydrogi- -^ -..„„., „.„^„,„eu uy tne metal palladium, and the some reason, but any o.fpouad conducts taelf like an alloy of two nnetll, 1.! reason in itself. jg ~, -..i.ig 36 A HAND-BOOK OF CHEMISTRY. metallic in appearance, and having the power of conducti neat and electricity. 2 When water is decomposed hydrogen appears at tl electro-negative pole, as other metals when their salts a decomposed. 3. It possesses the power (in marked degree for a iras) o conducting heat and electricity. 4. Hydrogen is absorbed by the n.etals potassium an, sodium, forming alloys, in which the density of H is 6'^ 5. Liquid hydrogen is said to have a metallic appear ance, etc. ^^ 6. The element displays the character of a metal in ij chemical deportment. 1 § 10. The Chemical Equation. We are now in a position to write and understand what a denoted by a chemical equation. Let us begin by writir" out what took place in the analysis and synthesis of hyd. chloric acid, as we had evidence in those experiments that molecule of H and a molecule of CI each contained two aton (At this point the signs should be fully explained ) (1) When hydrochloric acid is decomposed, hydrogen ar chlorine are formed. H -.*^^_^^ 1 CI t*""**'***...^ 1 ci ^ H CI ^ — r^ CI ^ — - H H "T^ This may be expressed : 2HC1 = CI.. + Ho. H O H F CHEMISTRY. I HOW TO TEACH THE CHEMICAL EQUATION. 37 ing the power of conductiiiB ^2) ^^^'^ hydrogen and chlorine combine, hydrochloric Kid is formed d hydrogen appears at tli 1 ^^^ ^ diagram of this reaction see § 3 of this chapter, p. 19. netals when their salts ar 1 '^^'^ '"^y ^® ^"^ten : Ho +Clo = 2HC1. I (3) Now represent wliat take^ place with water. When larked degree for a gas) ^ ^^^ ^ combine HoO is formed. the metals potassium an. the density of H is .62. ) have a metallic appear; haracter of a metal in it^ tL Equation. ■ite and understand what Let us begin by writij | is and synthesis of hydi ti those experiments that I each contained two aton: fully explained.) decomposed, hydrogen ai; H H ^-\ ^ O H ^^.^^ O H H O H This may be represented : 2Ho + Og = 2H..U. The student writes out the molecular equation, and does lot need to write the equation in the atomic form, to which »> many chemists seriously object. Further, he is able to iderstand everything that is denoted by the equation, and should be fully explained that what is represented by the juation is true both by weight and by volume. (4) When sodium is thrown on water, hydrogen is formed. Na H O H v^ ^ 0- H O H An + Ilg. y Na O H 1 H 1 N Na O H This is expressed : 2Na + 2H ^0 = H.. + 2NaOH. 38 A HAND-BOOK OF CHEMISTRY. replied" ''''"°"°" '' '^"" "''' ""P"- »"" '* ™a 2CuO + iH,_iH,0 + 2Ca. All the student will need now is s„n,e practice in writi out a few simple equations in this wav Th„„ l „ "" be surpns,ng how quietly he gets over the difficulty ^ plan has never been found to fail ""nculty. 11 .eance:thttrup:i2:! 'rt"""- "•- ^^^ - Change are always placed atTe ^^^JltZTT ^.on and the compounds produced are pla d to tht r 'h! The s.g„ + ,„d,cates that the substances are brought tlo^u, under such conditions that thev react „„„ "^'"'«'" ^S""'. OF CHEMISTRY, d over copper oxide it may 2H„0 + 2Cu. HOW TO TEACH THE CHEMICAL EQUATION. 39 rabol denote the number of atoms of that particular ele- ent in a molecule; thus, 2H,0 denotes that there are two ioleoules of water, and each molecule contains two atoms of ydro^en and one atom of oxygen ; KCIO, indicates that ^.ere is one molecule of potassic chlorate, which contains one ^om of potassium, one atom of chlorine, and three atoms of ■ygen. Further. KCIO, indicates that a molecule of potassic lorate weighs (39 + 35.4-^3 x 15.96) or 122.28, which is the #m of the weights of the atoms ; 2KC10, would be twice tans amount. ^ Let it not be forgotten that an equation is based on the ^destructibility of matter; in other words, matter may be tansform. but cannot be destroyed. The total weight of e substances reacting on one another must be equal to the V is some practice in writinin, 'Z,. ',:""'"« °" "'« '">°"«'- ""-st be equal to the is way. L. „e :m:t fl 1 ^l^l^'^ "^ ^^^ l'"«'^-- P™""-". ""'I '» obtain used a^d produced It il , "T : ""^ """"^ °" ""^ ""■"• "'-"'- -'»« ats over the diCltv T t tt "?'' ™"'''°'""''' """^ "<• P^^uoed are in the , dittculty. ai,|a sous state, the numbers indicating the n.olecules used ,vill Jlete «-ithout answering tlMir.T''Al P^P"""™" ''y ™'™<' i" which the gases com- tion does a typ^l eTuat IdL^ tf ' "7''"' ''"'°""« "" "'°''^""'- P-du-d will ypioal equati.#dicate the volumes produced when in the gaseous state ■ or example, introduction, that the sulf ofj +o = '>H ther to produce a chemic J This expresses what we learned" 1^ experiment • ^1^"^^ ^^rl ' ?^^^-^-- ofhydrogenj voCin^Xgen pro- brought to^etl. t|erature and pressure. The water must be in the gaseous I 2. Hence, from Avogadro's law 2 molecules of hydrogen + 1 Necule of oxygen produces 2 molecules of water vapor at he same temperature and pressure. 3. 4 by weight of hydrogen (2x2U31.92 (2x15 96) by eight ot oxygen produces 35.92 by weight of water vapor. itances are brought togetli eact upon one another, an. ^e" or "produce" the su he equation. The numbei r formula denotes the nun placed at the base of eac 40 i A HAND-BOOK OF CHEMISTRY. IZ' III: '''." "' "^"^^ ''^ ^^^^ denomination weights are expressed-pounds, ounces, or grams. The proportions by volume do not hold true unless substances are in the gaseous state. This should be followed Iw f v,z. • i woblpn^ ,-n ni '"'"o^^'c' ^y the consideration of a piobJems in chemical arithmetic. §11. Graphic Formula op Volatile Compounds* ompounds. The valency is indicated by means of ]inp« P_y to the symbol, and may be dra/n ^^ 0!':- The'molcule of hydrogen is H-H. the atom H- oxygenis 0=0, „ 0=or--0 XT \/ N= or N I \/ nitrogen is N=N, or N^N, the atom =N= or — N— Compounds may be represented . Marsh Gas. Watpr n i ^^ .. water. Carbon dioxide. Ammoni, H H H „ I H-C— H A H~0-H 0=0=0 Nitrogen pentoxide. O O N-O-N \/ N Unsaturated Compounds.—We have alr.n^ saturated compounds There Z ''"'l^ ^^''""^ y ^onsidere, * Fioni Bailey's '•■ Tutorial Chemistry. " OF CHEMISTRY. HOW TO TEACH THE CFEMICAL EQUATION. 41 er m what denomination tMer, in which valency is not exercised to the full extent • , ounces, or grams. |ese are termed unsaturated compounds. For example, in do not hold true unless th ate. arsh gas carbon is associated with four atoms of hydrogen, , . ^^^"^ ^" ethylene each atom of carbon is associated with two the consideration of a h^ o^^ of hydrogen, and in acetylene with one Thus • H-C-H C-H *" Volatile Compounds.* udy the graphic formultii , :licated by means of lines i y be drawn in any convenier [ — H, the atom H =0, r, 0= or —O- ^N, XT \/ N=orN I atom =N^ or N Ammonia H H \/ N i H Carbon dioxide. 0=0=0 toxide. \l N have already considerecj certain compounds, how al Chemietry, H-C-H C-H Ethylene. Acetylene. It is assumed in such cases that certain valencies are sup- essed or latent. Carbon monoxide and nitric oxide are 10 examples of latent valency. =C=0 ~N=0 Carbon monoxide. Nitric oxide. Such bodies are usually characterized by the ease with *hich they enter into further combination with elements groups of elements to form saturated compounds. Ethy- ne in the presence of chlorine gas forms ethylene dichloride, oH.Clo, commonly known as "Dutch liquid," and chlorine bites directly with carbon monoxide to form (COCl.,) phos- ene gas ; nitric oxide unites readily with ferrous salts, and ith chlorine ; in the former case it is used as a test for nitric -ide, and in the latter it forms nitrosyl chloride (NOCl). There is another problem which every teacher must have et. Why, for example, does the body A react upon the ody B, and produce the bodies C and D ? Few students |ave not asked the questions. How can I predict when A will •^.act upon B 1 and, If the bodies A and B react upon one tother, what substances will be produced ? The answer lies the very foundation of analytical chemistry, and it may be long time before we can say to the beginner, "This reaction ■ill take place, because," etc. Nevertheless, every teacher iould become familiar with the developments in physical hemistry throwing light upon this interesting question. 42 A HAND-BOOK OF CHEMISTllY. CHAPTER II. HOW TO HANDLE NOXIOUS GASES IN THE OPEN LABORATORY. This i, a very important question, as tl,e health of exper,„,enter often depends upon the judicious handlin,. noxioU, j,ases produced in his work. No student or teac can retam h,s health in an atmosphere which is vitiated w sulphuretted hydrogen, chlorine, nitric oxide, or with torT tf ""i""'"' """'' "'•'"'""'"'"•tly "«1 in the labo tory. When the general health of a class in practical ch, istry ,s impenlled, it becou.es a very serious question. So ms ructors may not be willing to admit it, but it is nev ^eless, a fact, that any teacher who attempts to h:;,dTe perm,ts h,s pupds to study, „„.i„us gases by following \ methods descr.bed in our ordinary text-books, takes a su ourse of destroying his own health and that of the stud he has under h,s charge. Since this is the case, it is , urp™,ng to find that many contend that prac ical w should not be attempted in a laboratory which is not ,u phedw,th suitable draught cupboaris; and I am incled , think that IS the proper position to take, if other means ca not be found to overcome the difficulty. Having had son mThTol '" '""" "■ '"T "'■^' ' "' ■"»"' "> -^-'^ " ^i so far as i T™ bl"' "" """""^' """ '"'Pl'"^ -«-< so far as it ,s possible to succeed withont incurring very ^rJ expense, as the following plan will show. * OF CHEMISTUY. ER II. CIOUS GASES IN THE ORATORY. uestion, as the health of t on the judicious handling kvork. No student or teacl, )sphere which is vitiated wn 3, nitric oxide, or with constantly used in the labui of a class in practical cIk very serious question. Sou admit it, but it is, nev< who attempts to handle, i aous gases by following tlij iry text-books, takes a siifj 1th and that of the studtnti e this is the case, it is noi ontend that practical woi iboratory which is not sn )ards ; and I am inclined to take, if other means ca ifficulty. Having had soik; set about to devise a simp ilty, and happily succeede vithoMt incurring very gr 1 show. HOW TO HANDLE NOXIOUS GASES. 43 1. Sulphuretted Hyi,uo(;kn in Qualitative Analysis. Sulphuretted hydrogen, for example, is used so extensively analytical work, that it becomes absolutely necessary to tve a convenient method of disposing of the surplus gas. fhis IS the end T have had in view in all experiments described this chapter. To overcome the difficulty, I have found it »80lutely necessary to use rubber tubing and rubber stoppers may not always be easy to make the tubing and corks to ; but some hints are given at the end of the book which ill aid in this respect. ^ Take a large glass jar, and fit it with a double perforated P»l.ber stopper, or what is better, use a Wolff bottle, with *^o necks, which will hold one or two quarts. Place in the necks of the bottle (Fig. 6, a), perforated rubber stop- pers (i) and (c). Through one (b) pass a glass tube (d), which fits tightly in the stopper, and which passes to the .« /^\ -T-u . , bottom of the r (a). Through the other stopper pass a short glass rod M connect this rod by a rubber tube (e) about twelve inches ng to a test-tube or bottle (A), in which the solution to be ecipitated is placed. In the mouth of this test-tube or >tt e place a double perforated stopper. Through one per- .ration pass a long glass tube (g), which reaches nearly to .e bottom of the test-tube, and through the other perfor^ Fro. 6. 44 A HAND-HOOK OF CHEMISTftY. tion a piece of tuhinj,' (/), long enough to connect with tubing (.3) of the WolflF bottle. Connect the longer glass I ( mother bottle full of water. be prepared in this way. Wh idvantage to remove the stopj the thumb over the aperture it into a bottle of water. 11 ingling with the prepared - one of the bottles, and shak )lubility in cold water. Obser the tube (/). tBON Dioxide, Olefiant ETC. HOW TO HANDLE NOXIOUS GASES. ^t in Fig. 7. The copper, waJ Jlaced in the test-tube (a), a [o), as in the case of nitro^ • be left in one of the bott^ t it may be tested with litm ' is allowed to mingle with t^ r when reaction ceasf s, procci ise of nitrogen monoxide. Fi periments see any practic It is best to have a jar e ready, with tube and corj i in Fig. 9, so that when tl onnected the surplus gas mi into the Wolff bottle if tl' ■s not ceased. If care oxide may be prepared wit! cape into the room. :ide, marsh gas, olefiant g: ' the same way. It is sorai 47 ies desirable to show how marsh gas and olefiant gas act t tu"""t J" '*" '''' ^' """'^ ^^«' '' - l-«tl. par. I^y fil a bottle or jar with the gas. Then remove the fcper from the generating flask and place in a test-tube in ch chlorme IS generated, and fill the bottle by forcing I the rest of the water. Quickly attach the generating to surplus jar (Fig. 9). In the case of ethylene, it is to have the olefiant gas and the chlorine prepared in irate bottles, using apparatus Fig. 7. 4. Carbon Monoxide, when Prepared from Oxalic Acid. ^^hen carbon nmnoxide is prepared from oxalic acid, it is d with carbon dioxide. A good method of showing that f are equal in ° [me is to pre- a quinine le full of the Is, as in Fig. Ind insert a ile perforat- Irubber stop- Through one [•ture pass a lel (with a Icock if possi- jand through «r tub „g to a wash bottle (test-tube) containing KOH then to another quinine bottle filled with water, and \-j' laKe the precaution to determine the 48 A HAND-BOOK OF CHEMISTRY. volume of tlie bottles (a) and (/>) when filled with wat, means of a graduate. The quantity of water remaining may be ipeasured after the gas has been washed, if the'b are not equal in size. A still better method of perfor th,s experiment would be to fit up apparatus as describ, the chapter on Gas Analysis. § 5. Chlorine, its Preparation and Properties. In handling this gas it is best to use apparatus Fig 6 however, only one bottle is required, it may be prepared" apparatus Fig. 7, and then attach the generating fla. surplus jar Fig. 9, but experience has shown that* stud are not likely to prepare more than one bottle without a] ing the gas to escape when using apparatus Fig. 7. For reason it becomes a necessity to use apparatus Fig 6 experiments with chlorine may be divided into two series in the first series of experiments use a test-tube or qui bottle in place of (/.) Fig. 6. Fill the large jar (a) . water. Prepare the gas by placing manganese dioxide hydrochloric acid in the test-tube (k). Let the gas ; through the empty test-tube (h), or better, have a little w! m the bottom of the test-tube or bottle, but not enouo-h have the gas bubble through it, and permit the surplus ^.v pass into the jar (a). Quickly remove the test-tube, place thumb over the mouth, and shake up with the cold wa- and quickly insert a test-tube or bottle full of water in place, and let the gas bubble through this for some ti When showing that the gas is soluble, without removing thumb mvert the test-tube and drop it into a bottle of wat After the water in tho second test-tube is saturated rem It, and put test-tubes containing solutions of logwood indigo in Its place, to show the bleaching properties of gas. Into a fourth test-tube place a piece of printed paj OP CHEMISTRY. HOW TO HANDLE NOXIOUS GASES. ARATIOV AND PrOPERTIKS. St to use apparatus Fig. 6. [uiied, it may be prepared \vl _ _^. 49 I (h) when filled with water, |ch has Iipph m,^;o* j antit, of water remaining illeX^^^^^^ ^''''' ^^^'^ ^^ -^"- . up apparatu. as ^^^^^^l^^^JZ^ :-^- the oxides of lead, what happens when it is ^ aced " l«^en .is .nixed with a solution of sodi^^i: Utach the generating flas,:^ the second u-st^ube Into tH slst't f " ""' ^"^^ Bnce has shown that stu,Mi.o, and let the gas pL ov r ,'^ j^^*'*"'- .P"^ - P-- of than one bottle without alla|ve the calico Listen it I. """'" *'™'' ^"^^^'^ ig apparatus Fig. 7. For r'Tt anv .^ LZ T ' '"^'''''^ '" ^^" ^'•>' ^^^^"ne- to use apparat:s Fig. 6. f W ' gleTaL ^rr "^f ^'^ ^^^ ^^^^^^ ^^ -- be divided into two series.^tween the te^t^be andTe ^uVusT ''' "''" '"'^"«" ents use a test-tube or quiaeWs to becomp m . 7 , "^ ' '^ ""^ ^^^ ^« ^"o^ Fill the lar^e jar (^ ^hi^I V:; t:^^"' '^^^ ''' ^"^^ ^" ^^^ --^- lacing manganese dioxide In the second series of evnprJn. . tube ik). Let the gas ^e place of test-tuC/.f and rr"' '"^" », or better, have a little w. Jar Quicklv rlnv Tk , ' "' ^"*^ '^^ ^"'■plus .r bottle, but not enou, jce of t^l^l^ n^:t^t it t V^^^^ " ^^^' and permit the surplus guf and out .n .J!I!Ll"^ ^'^^!' "^ "L°'^^^ P-P^''. -emove the test-tube, plac. lake up with the cold wa r bottle full of water in through this for some ti soluble, without removing 3rop it into a bottle of wat est-tube is saturated ren ig solutions of logwood bleaching properties of ace a piece of printed pamo. i,. , — '• oiiccu ui mouse paper and put an empty bottle in its place. Test bottled It '^'f \P''^P^''^'^ i" this way, by shaking into I powdered arsenic, and by lowering into it a piece of glowing charcoal and a lighted taper den TTt ^" '"" '^'^'^ ^'"P'-^^^^d "P^'" the stu- piace of {},) as soon as it is removed. If this pre caution IS taken, the gas can be handled without allowing any of it to escape. To show the action of sunlight upon chlorine water, invert a test^ube full of the solution in an ilil' 50 A HAND-nOOK OF CHEMISTRY. evaporating dish, or use a tube sealed at one end, similar Fig. 11. Fill with chlorine water and place in sunligli This experiment, which is recommended in some text-hooks is more interesting because it illustrates an important prin ciple in physics. Hydrochloric Acid Gas. — To prepare this gas use apparati) Fig. 6, and as in chlorine, use the test-tube {k) as a general (i( Fill as many bottles as required, by placing empty bottles i| place of {h). To neutralize caustic soda place the solution i| the test-tube or bottle Qi), and let the gas pass through it tVj some tinie, allowing the surplus gas to pass into the receive For further experiments see any Practical Chemistry. i Potassic Chloride and Potassic Chlorate. — When prepariij KCl and KClO.j use apparatus Fig. 6. Place the hot or cofc caustic potash in the test-tube (A), and let chlorine gas p.ij through it as long as desired. It will be observed that tij potash may be kept hot while the gas is passing through it. ', Bleaching Pon-der may also be prepared by using the saij apparatus, Fig. 6. Cover the inside of the bottle (A) wil slaked lime, and pass chlorine gas through it as long as necil sary, collecting the surplus gas in the receiver (a). < § 6. HYDHOfiEN' Sulphide, its Puepakatiox and Pkopehties. \ The Preparation of the Gas. — It is sometimes difficult i prepare hydrogen sulphide quickly and in small (juantiti< but the chief ditliculty, no doubt, arises from the sulphide( iron. The following is a simple method which I saw apple recently, for the first time. Take some powdered sulphidct iron, and prepare the gas in the ordinary way, or pour sn) water upon it and let it stand for a time — a few hours,}i possible. Then pour off the surplus water, just leaving \ sulphide covered. Now add a few drops of sulphuric .".'"J CHEMISTRY. aled at one end, similar bar and place in sunligli| (lended in some text-ljook| istrates an important prii ^pare this gas use apparatii test-tube (k) as a generato jy placing empty bottles c soda place the solution the gas pass thi'ough it in as to pass into the receivt Y Practical Chemistry. Chlorate. — When prepariij ig. 6. Place the hot or ci ), and let chlorine gas p;i It will be observed that i\{ gas is passing through it. prepared by using the san iside of the bottle (h) wii| through it as long as nee the receiver (a). ITS Pkeparatiox and IKS. It is sometimes difficult dy and in small quantiti' :, arises from the sulphide' nethod which I saw applio] e some powdered sulphide ! ordinary way, or pour so for a time — a few hours, plus water, just leaving 'ew drops of sulphuric a HOW TO HANDLE NOXIOUS GASES. 51 without heating, the gas instantly comes off. When action has ceased, pour off the surplus solution, and pour to the test-tube a quantity of clean water, and let it stand Itil next required. Now pour off the surplus water and add Id. This is an excellent plan where the gas is frequently luired and in small quantities. It not only saves the buble of heating, out always ensures success. It may be pessary to prepare the gas by heating the first time ; after it, wash and keep the sulphide covered with clean water, )d no trouble will be found. ^'he Properties of the Gas.~In handling thir, gas always use jaratus Fig. 6. Prepare the gas in the test-tube (k). Fill receiver (a) with water, and use test-tubes or quinine ttles in place of (h). Quinine bottles are in many respects ^ter than test-tubes. Into the test-tube (h) place a small intity of water, but not enough to have the gas bubble jough it. Now fill the test-tube with gas, by forcing the into the receiver (a). Remove this test-tube, put the Imb over the mouth, and quickly put another test-tube in jplace. Shake up the gas in the first test-tube, to show its ibility, and, without removing the thumb, invert the test- - and drop it into a bottle of water. Dip some pieces of Ite paper into a solution of lead acetate, and place one of Se into another test-tube. Now remove the second test- of gas, and put the one containing the paper soaked in iate in its place. Bring the second test tube as quickly as lible to the flame of the gas jet. When the hydrogen Inrle ignii es place over the burning test-tube a dry quinine lie, and obf^^rve that moisture and sulphur dioxide are Jed. Remove the third teat-tube and put in its place a jtube full of water, and let the gas pass through it for a Now remove the sulphuretted hydrogen water, and |in Its place soluuoas of copper aulphate, mercuric chloride, JgKirr- -: 52 A HAND-BOOK OF CHEMISTRY. lead acetate, etc. Replace the generating flask with one gen-j erating chlorine, and pass some chlorine into the receiver,! and through a solution of H\.8. Let a drop of the solutioiil fall on a silver coin, and use some of it to precipitate acid and alkaline solutions of different metals. Some ammonium sul-j phide might also be prepared by passing the gas through! ammonium hydrate. Do not forget to replace one test-tube] by another as quickly as possible ; upon this will depend your! success in handling the gas. Tight-fitting rubber stoppers! must be used in these experiments. Never leave the appara-l tus open for an instant. § 7. Sulphur Dioxide : Its Properties. The same apparatus must be used in handling this gas asj in hydrogen sulphide and chlorine (Fig. 6). Use test-tube orj quinine bottle in place of ^ V). Fill the receiver (a) with water. Heat copper clippings and sulphuric acid in the test- tube {k), and proceed as in other gases. Place about half an inch of cold water in the test-tube (A), and force the air into the receiver, without allowing the sulphur dioxide to bubble through the water. Quickly remove the test-tube, placing the thumb over the mouth, and put a second test-tube in its place. Shake up the first test-tube, to show the acidity and solubility of the gas. Replace the second test-tube with one containing a highly colored flower. Test for the inflamma bility of the gas. Remove the third test-tube containing the flower, and put in pure air. Quickly replace this test-tube ■with solutions of logwood, indigo and potassium permangan- ate in succession. Now pass the gas through a test-tube full of water, and when it is saturated replace it with an empty test-tube. Test for the properties of sulphurous acid. This gas is much easier to handle than hydrogen sulphide, and for that reason it is best to study its properties before m HOW TO HANDLE NOXIOUS GASES. 53 attempting to prepare sulphuretted hydrogen. The student I needs some practice before studying gases like chlorine and I hydrogen sulphide. If only one bottle of sulphur dioxide is required, it may be prepared by using a test-tube and a bottle arranged as in Fig. 7. Other gases may be studied in the same way. Enough has I been given to show the plan. Properties. ¥ 54 A HAND-BOOK OF CHEMISTRY. 1 CHAPTER III. HINTS ON APPARATUS. § 1. Apparatus ro Illustrate Combustion. It is very important to have good experiments to sho that combustion is a chemical action, in which at least tvv substances ai'e equally concerned, but the descriptions of sue experiments are not always satis<-actory. I have found tli following method, which I devised, to work exceptional! well. • *^ 1 For this purpose use WolfF bottles (a) and (c) Fie. V One jar should hold about one and a half or two quarts,' aJ the other about one quart. fJ the necks of the larger jar arJ one neck of the smaller jaf with perforated rubber stoppei| Through one neck of the large! jar (a), place a funnel with stojj cock (b). To the other neck at tach rubber tubing of good lengtl and a Jass rod eighteen inche ^, ^ ^ong drawn out to a iine point (d Through one neck of the smaller jar place a wide glass tub {e)~a part of a medium-sized test-tube does very well Fi It tightly, by placing around it some adhesive plaster * Thi IS to prevent the bottle breaking when the gas is burning If you wish to burn oxygen in coal gas, connect the n.cl (/) of the jar (c) with the gas supply, and when the air i Fig. 12. F CHEMISTRY. R III. PARATUS. 3TRATE COMDUSTION. good experiments to shoi 3tion, in which at least tw but the descriptions of sue 'actory. I Imve found tli ied, to work exceptional! )ttles (a) and (c), Fig. h'l id a half or two quarts, am ber about one quart. F: cks of the larger jar an eck of the smaller j.v erforated rubber stopper h one neck of the larg place a funnel with stof ). To the other neck atj bber tubing of good lengt ,lass rod eighteen inclie iwn out to a fine point ((/ ir place a wide glass tub tube does very well. Fi ne adhesive plaster. Tlii len the gas is burning, coal gas, connect the mc ply, and when the air i HINTS ON APPAHATUS. 55 Iriven out ignite the gas at the tube (e). Fill, or partly fill, .e Wolff bottle or jar (a) by forcing out the water, as in FL^s and '.Pour water into the funnel (b), and force the g;^s hrough the tube (d). .Slowly lower it through the tube (.). k^knig care that it ignites as it is passed down. To reverse .e experin>ent, connect the tube (d) with the gas supply id when Ignited lower into the jar of oxyc^en (.) A much more difKcult experiment is to burn chlorine in iydrogen. Arrange the apparatus as in Fig. 13. Fill the nr (a) with chlorine by displac- ig the water, and arrange the nnel (b), the rubber tubing id the glass tubing ( in the neck of (.), but be careful to see that it :mtes. Do not let the chlorine mingle with the hydrogen Uess It is Ignited. When the gas burns in (0) increase the ce in the funnel (/.). Jt is possible to burn chlorine in the ar (c) without having it connected with the flask in which 'lie hydrogen is generated, but it is not satisfactory. Air "^tice T,"' I' '"' '" ^" '^" ^'-^"^ ^^^^' -^h ; little 'ac ICO. The advantage of this method is that you can ■egulate the supply. ^ Fu;. 13. 66 A HAND-BOOK OF CHEMISTRY. ! § 2. How TO Fill the Eudiometer. The eudiometer commonly used in our schools consists of straight graduated tube closed at one end, and it is not cor venient to pass into it a fixed volume of gas. For example if a fixed volume of chlorine has been placed in the eudiom^ ter, it is not easy to pass into it an equal volume of hydroger In most cases the g;r ,„ay be passed through the wash bottle and drying tube and into t!ie eudiometer from the flask ii Flu. llrt. which it is generated. Arrange apparatus as in Fig. 14a As in the diagram, attach to the drying tube (a) a rubbei tube, in the middle of which is a rubber bulb (i), with oi without valves, which may be purchased from any druggist. If necessary, attach the other end to the surplus gas jar, "and let the gas pass through the apparatus until you are absolutely certain that the tube and bulb are filled with pure dry gaj. Then disconnect, and insert a short piece of glass tubing" ir the end of the rubber tube, and put it into the dish contain ing the eudiometer. Close the stopcock (c). When the rubbci bulb is full of gas, press gently, so as to drive out any [r- hi the glass tubing. Then insert the tube under the mouth of the eudiometer, and press on the bulb. Even the smallest volume of gas may be passed into the eudiometer in this way. CHEMISTRY. HINTS ON APPAUATUS. 67 Thia is the case even if the generator has ceased to give off tas. he careful to see that the stopcock is closecrbefore kressing on the bulb. After forcing out the gas pinch the lubber at the end nearest the eudiometer, so as not to allow |ie mercury to flow back ink) the bulb ; if the generator has eased to act, pour water or acid into the funnel, so as to fill fie bulb with gas. Even a gas like chlorine may be passed ito the eudiometer in this way. When it is desired to repeat lie experiment a number of times, fill a juinine or other wide-mouthed bottle (Fig. lib) with gas. To do this, insert a rubber popper with three perforations. Through le pass a funnel. Into the second perfora |ion put a long glass tube, reaching nearly the bottom of the bottle, and into the piird place the drying tube, to which is jttached the rubber bulb. The long tulie aay be connected with the generator, and 111 the air driven out of the apparatus. If this is not satisfactory, fill the bottle l^ith water or mercury. Attach the rubber tube with bulb the wash bottles of the generator, and force out the liquid Jirough the long tube. Now disconnect the rubber with the lulb from the generator, and insert in the dish .-ontaining •le eudiometer. Place a short piece of rubber over the long ibe, and clamp it. Pour mercury into the funnel, open the topcock, and let some of it drop into the bottle. When the jibber bulb is full of gas, close the stopcock and insert the ibe under the mouth of the eudiometer. Press gently on H' bulb. While the hand is still on the bulb, pinch the ibber near the eudiometer, so as not to allow the mercury to low back ; pour more mercury into the funnel, so as to force lie gas into the bulb. The reason for using a rubber cork Fkj. l\h. 08 A HAND-HOOK OF CHEMISTUY. with three perforations is hecuuse it is dillicult to insert tl funnel without allowiii;f air into the hottlo after it has hw filled with gas. When passing air into the eudiometer it niiglit 1.0 coi veniont to have a hull) with valves, l,ut it is not ahsoUite] necessary. Use a drying tuhe and a rubber tubing with bull Place the finger over one apertu.e of the drying tube, aiij force the air out through the (.(her end by pressing on tl bulb. Pinch the ruljber tubing near the end, and let the a pass in through the drying tube. If x ulves are used on tl bulb, they may be arranged as in an ordinary atomizer. § 3. Apparatus to Illustrate tiik Decomposition OF Water and Hydkociiloric Acid. The apparatus usually sold for the decomposition of watt gets out of repair very easily. Fig. 15 shows a piece ( apparatus, designed by the writer, which may be used for th purpose. Take a piece of glass tubing about tlie size of test-tube or dry in tube, and have mad as in Fig. 1 5. Leuv tubes (a), (h), (c) am (d)open. Havefittt? into {[>) and (c) twi uniform test-tubes ( equal size which wi slip up and dow easily, without pe mitting water to escape when the apparatus is filled. Us pieces of electric-light carbons, about one inch long, for ele( trodes, to place in the tubes (a) and (d). Make a groove i the carbons, to attach the copper wire, and insulate the wii with sealing wax. Have air-tight stoppers, through whici i at the opening of the tubes [a) and ((/■ I' lU. 16. the conductors pass CHEMLSTUV. it is ), (c) anJ |^(D) ((/)open. HavefittJ / into {b) and {c) twl uniform test-tubes (I equal size which wij slip up and dowj easily, without pel i apparatus is filled. I" ut one inch long, for elec id (d). Make a groove i] tvire, and insulate the wii] ; stoppers, through whicl g of the tubes (a) and [di Vhen making the gases (in the dark, if necessary) invert the •st-tubo in (c), so that the sealed end will come down nearly - the carbons. Now incline the apparatus, and the mixed s will pass up (A). Attach a drying tube, rubl)er tubing id bulb (as in Fig. Ha), and pass th.^ gasen into the eudiome- fr and explode. Thus it will be .seen that tiie analysis and rnthesis of a compound may be shown in one experiment, his can.iot be done unless the gas^^s co^ne ofT in the i)roper roportions. When ilecoraposir- hydro hloric acid, some kxt books recommend mixing one volum of concentrated drochloric acid with U'n volumes »? a .sn.arated solution of >mmon salt. This is not satisfaci >ry, unless the current wses through the mixture until it becomes thorougl.ly .satur- fced with chlorine, which takes considerable time. In most bes It will be found more convenient to prepare the gases Iparately, and pass into the eudiometer. The best method oi filling the apparatus is to put a stopper the aperture (a), put the test-tubes into place ; pour the Hution into (h), slightly tilting, until completely full. Then lowly slip the electrodes into position, as in the diagram "^ig- 15). .Should the apparatus be used to decompose salts, fuse [eces of platinum, one inch long and half an inch wide, to '>mv wire, and insulate the wire. Place the platinum tips ■ the apertures (a) and (d). This apparatus can be cheaply iide by any glass-blower. It prevents leakage, etc. The apparatus can- 't be used without stand. Figs. IG id 17 show conve- ient stands for this jurpose. Take two llocks of wood of 60 A HAND-BOOK OF CHEMISTRY. ra la s,.e, ami cut grooves in them, as in the diagran that the apparatus will be held i„ pkee when the bLk h ought together. They ,„ay he held in place by wo dnven .nto „ne side, and holes placed opposite in'thro, The apparatus stand will then 1 the appearance %'■ 17. It wil observed that a] ratus Fig. 15 can J Fi(i. 17. used for the dec position of water j of hydrochloric ai and .0 show there is a back current whct'dt^oll^ect^i I the battery and attached to the galvanometer. § 4. Apparatus to Iilustlate Boyle's Law ated support etc Tnl.» f» j ^" ^ *"" ** S™' I h«vl r . ^^ ''^'^^'^S "^ ^''« barometer. is m ch elTr tT ; "''^'^' '^^"^ ^' ^^^^ '^P^-'^^- -'- support t1 '". ' " ^' '"^^ '^"^>^ *^^^' ^J- g-clua,i support. TaI-3 a uniform tube sealed at one end ihonfin J mer:;'^L""* '"'^ -'"■ -p-i. el:::'*." , appLt::wS;::tp;;:;':rVirr^"^«'-- ^ Wrap the Joints firmly with string. A, it is necessary / OF CHEMISTRY. n tliem, as in the diagrams, d in place when the blocks !■ he held xx\ place by two pt ^ placed opposite in the otii The apparatus m stand will then ha the appearance 17. It will observed that aj ratus Fig. 15 can used for the deoi position of water an of hydrochloric aci electrolysis of sal rent when disconnected fro galvanometer. HINTS ON APPARATUS. Gl 'STKATE Bo VLB's \,k\\\ ended for this experiment Jngth, and closed with a stu| >er tube not less than 50 c 'm- long. Place on a grai iing of the barometer, form of this apparatus wlii )e8 away with the gradual, lied at one end, about 30 cii stopcock. Connect this I ibout 30 inches long witli length. Take narrow sti i entimeter scale. Place tl I paste or fish glue. Thl Fig. 18. mg. As it is necessar) the tube wth pure dry air, attach a rubber bulb ami .Irv tube, a, ,r, F.g. U, to the longer tube, and force the dry through ,t and the rubber tube until y„„ are sure the .aratu, . fi„ed with dry air. I.ow Co^e'the stoplk If the tube (b) IS sealed at the end ill be necessary to fill the longer glass 'e and rubber with air before attaching tube {h). Now fill the tube {h) with ircury and attach the rubber tube. Firmly wrap the joint with a string •ur some mercury into {a\ but in doing do not allow the air in the room to gle with the dry air in the tube ce the tube {h) on the floor. Hold {a) •ight and gently raise the tube {h) and ^n the rubber tube alternately until the un-ed amount of air is in {h). When n^ this lift the rubber about the tre. In this way it will be easv to get required amount of air in {h) ' -et us suppose we have 10 c.cm. when •or:::?t.nds"r-"^ '^""t ^^^ ^^^^ ^^^^'-^ ^^-^ ti. omeer stands at ,o cm. Pour about 50 c cm intn (n\ ^^' t '""" <'\"""' '"" ™'"-" °^ "" ^^ 8 ^ ccm The apparatus will now be as in Fi.. 10 '-e a, the barometer. ' ''"'' "'"'"''' "« "•» [Now Wer the tube („> as in Fig. 20. Observe the differ. ■e m the level of the mercury in («) ,„, (,,j ^.^ Fl(J. 18. irr. 62 A HAND-BOOK OF CHEMISTRY. volume is 20 c.cni. This should be 37.5 cm. Use the t (a) as a graduate for measuring the difference in the level. When made in this way the apparatus need not cost m than 30 or 40 cents, and can be made any teacher. I think it is much hanc than with the stand. Flo. 10. Fio. 20. § 5. Apparatus to Illu.strate tuk Law op Ciiahles. .or this purpose use apparatus similar to Fi<^ 19 Tl tube (6) need not be graduated and n.ay be much shorto J^ill the tubes with dry air as in apparatus to illustrate Boyle aw and pour enough of mercury in (a) to bring it above .1, evel of the rubber. Fit a rubber stopper, with three perf..v tions, in a quinine or other wide-mouthed bottle. Through on aperture pass the tube {h). Through the other perforation )F CHEMISTRY. HINTS ON APPARATUS. 63 ^s short glass rods, one to allow steam to pass i„, and the f) |nds at the same level .ts when the air surrounded with snow. Observe the JTerence in the level of the mercury and culate the increase in volume for each ?''ee of increase in temperature. For |iinple, if the atmospheric pressure was ^ cm. and the tube (a) was raised 25.64 cm., the increase volume would have been ^^± had the gas been allowed [expand without increasing the pressure, because the lume of a gas varies inversely as the pressure OTK._lf the retort stamis are not heavy enough at the 3 they may be clamped to the table. .^ 6. The PERCKNTAfiK OK OXYCJKN IN AlU. Fn showing the composition of the atmosphere it is often lo-nmendod to invert a cylindrical jar over a jet of burning K'ogen, so that the mouth of the cylinder will be under er m the dislu This may i.est be done by filling a jar or M bottle with hydrogen. (A large bottle with a rubber k with two perforations does very well.) P„t the perfor- h corks with funnel having a stopcock and the connecting Mber tube m place. Pour water info fj,- t.,..^.^ -r-i " VUi. L'l. 64 A HAND-BOOK OF CHEMISIRY. U Fiu. 22. out the gas and ignite. Having placed the tube in positi. lower the cylindrical jar over the jet, Fig. 22. The instn the flame goes out turn the stopcock in the funnel. Tl will ensure success as the gas can be regulated when burnii which cannot be done if comes from a flask when t gas is being generated. If Florence flask is used to sic. erate the gas, have in t stopper a funnel with a sto cock. When the gas jui ceases to come off pour wati into the funnel and ign Arrange as in Fig. 22. gad may then be regulated with a Wolff bottle. It also saves the trouble of filling extra bottle. After the water has ceased to rise in the cy der, slip a cover glass or mica cover under the jar and ti mouth upwards. The capacity of the cylinder and t amount of water in it may be measured with a graduate. § 7. The Diffusion op Liquids and Gases. To show the diffusion of liquids through a membrane , osmose) it is sometimes ditJioult to tie a piece of parchmei paper or anin)al n.embrane over a funnel or thistle tub This may be conveniently done by tying on the membnii as tightly as possible with twine. Then take a piece sealing wax and place it in boiling water until it becor.)j plastic. While in this state remove it from the water ai quickly place around the funne at che point desired, th sealing the membrane to the glass so as to make it reasonah air-tight. The same difficulty is sometimes experienced in fittin "■; F CHEMISIRY. iiQUiDs AND Gases. HINTS ON APPARATUS. ({5 Irforated stopper into a porous battery cell to show" the p.ion of gases. It is best to have a rubber stopper for Is purpose but if one cannot be obtained an ordinary cork ly be made air-tight with plastic sealing wax. and fitted lo the battery cell. The SoLuniLiTY op Air and Ammonia Gas in Water. immonia Gas is Soluble in Water.-When working with large class, the simplest method of iliustratin^r this is to ice some aqua ammonia in a test-tube and over it place inverted empty test-tube. Heat the liquid until wa Ypty t,:be IS full of gas. Remove it, and drop it mouth •inwards into a bottle of water. Have each student do experiment. iiris Soluble in Water.~In class work one of the best Ithods ,s to half fill an evaporating dish or mortar with Iter and into it place an inverted test-tube full of water in lich no air is visible. Let the test-tube project over the |e of the dish. Gently heat the test-tube above the edge of d.sh until the water is converted into steam and descends |the test-tube. Now take away the lan.p and allow the ter to rise. Repeat two or three times and allow the ter to cool, A bubble of air will be found at the top of I test-tube. ^ Surface Tension.-To cause a drop of oil to float in a mix- ^ of alcohol ur.a water, half fill a test-tube with water put into It one or two drops of oil. Now pour in a little M The drop, of oil floats out into the mixture of the he density as itself where its form may be studied This iometimes used as an illustration of surface tension 66 A HAND-BOOK OF OHSMiSTllY. CHAPTER IV, A SIMPLE METHOD OF GAS ANALYSIS. Pmnki>8 the simplest and most complete method of gj - alym. is the one originated hy Prof. Hemphill, but t|l toucher of chemistry in a secon.iar ,• school very often do^ not receive sutKcient grant from .. school board to purcha the most necessary apparatus, and .dthough there are mar times in his work when he wouM like to determine tl different gases in a mixture which comes under his notic he has not the means at his disposal of satisfying h curiosity. If he wishes to overcome the difficulty, he mu eitlier work with inferior apparatus of his own constructit and be satisfied with unsatisfactory results, or he mu purchase rather costly appliances .uch as Prof. Hemphil at his own expense, and this is something very often IS ill able to afford. * ^ This is the only excuse for submitting the followir simple and original method of gas analysis, as tl apparatus employed is such that most teachers have a their disposa. or that can be purchased at a small cos Take two U tubes used for drying gases with calciu, chloride. The shape of the tubes is :,..material, but it woul be convenient to have one of the.- nilar to (b) Fis - having the neck between the bulbs :.rrow so that the" Z will .V pa^s through it when Wn. washed. It is best t ha/e ... other tube with a st^ ...k in one arm similar <. F CHS^^riSTIlY, •R IV, 'F GAS ANALYSIS. ost complete method of g by Prof. Hemphill, but tl dary school very often doi a school board to purchaj id il though there are maij oulfl like to determine tl ch comes under his noticl disposal of satisfying h ome the difficulty, he mul us of his own constructia Jtory results, or he mui 3 Guch as Prof. Hemphill something very often submitting the followii >f gas analysis, as tlj J most teachers have urchased at a small cos| rying gases with calciuj is i.'rinaaterial, but it woul e.>' nilar to (6) Fig. i .a.irrow so that the f,M ir'g washed. It is best i\ ^k in one arm similar ti A SIMPLE METHOD OF GAS ANALYSIS. 67 .t used for the analysis of hydrochloric acid. Fig. 1. or of , size and shape recommended for the determination of drogen m sulphunc acid, Ex. 7. ,. 2. One arm of each tube y be drawn out to a point so that the rubber tubing y be slipped over them ^ aveniently. If the arms the tubes are not drawn to a point and one of bm does not possess a stop- fek, they may connected I rubber stop- and a brt piece of ping with a ap placed Iween them |ich serves purpose ic well. The size of the tubes will ►end upon the quantity of to be analyzed, but a tube ich holds 7.5 or 80 c.cm. and 'ing stopcocks and graduated in Fig. 23 would be the most ivenient form. 'ill the tube (a) Fig. 23, with mixture to be analyzed. fs may be done by connecting tube with a generator or gas Hnd letting the gas pass through it until all the air linven out. Pour water or mtxroj—- U' -■ wtttei or mercuij mtu one open arm. Fig. 23. 68 A HAND-BOOK OF CHEMISTRY. Then disconnect from the generator and allow the liquid become level in the two arms and close the stopcock. Another method would be to close the stopcock and [ tilting fill the closed arm with mercury or water so that will rise to the point (d) in the open arm. Then conne with the gas jar and open the stopcock. The liquid used w come to a level in both arms. By regulating the quantity liquid with the stopcock or by removing some with a pipe; from the open arm, the volume of gas desired will be obtain in the closed arm. Connect the tube (h) to (a) and by tilti. fill the closed arm with the solution to be used in washin until it reaches the point (c) in the open arm. Now open t stopcock and pour liquid into the open arm of (a) until all t gas has passed into (b). The solution will slowly rise in t open arm of (/>). If all the gas does not pass over readi. remove some of the solution from the open arm of (b) with pipette. When the gas is in (6), the tube should be lar enough so that the bulb of the closed arm will t atain so solution. Place the thumb over, or put a rubber stopper i. the open arm of (b) and by tilting wash the gas thorough Close the stopcock in (a) and remove the solution from open arm until it stands at (d). Now open the stopcock and pour some of the solution u in washing into the open arm of (b). By regulating quantity of liquid in the open arm the gas will pass back i. (a). If it is desired to accurately determine the volume gas remaining and (a) is not graduated, the gas may passed into a graduate and measured, making allowance the tension of the aqueous vapor, temperature and pressu. The solution for washing the gas may now be removed ail another solution put in its place for determining the next j.' J in the mixture. By having pieces of platinum wire fused into the gradui CHEMISTRY. tor and allow the liquid close the stopcock, close the stopcock and uercury or water so that open arm. Then conne •cock. The liquid used w regulating the quantity noving some with a pipeti ?as desired will be obtain ihe (h) to (a) and by tilti on to be used in washiii ! open arm. Now open t >pen arm of (a) until all t tion will slowly rise in t oes not pass over readi A SIMPLE METHOD OF GAS ANALYSIS. 69 jbe (a), it may be used as a eudiometer to explode marsh Is, etc. Eudiometers are sometimes made in this way This is not a book on gas analysis and these suggestions 'e only intended as an aid to those with limited apparatus. )ll mformation on the subject will be found in Hemphill's ks Analysis, translated by Dennis and published by Mac- fllan & Co. ; also, Winkler's Hand-book of Technical Cas ^alysis. translated by Lunge and published by John Van Dorst, London. [The following may l,e used in determining the more com- pn gases : jA solution of pyrogallate of potash dissolves oxygen. I " " caustic potash „ qq _ [An amraoniacal solution of cuprous chloride dissolves CO C^Hjj. the open arm of (6) withfculphuric acid dissolves ammonia gas. the tube should be lar sed arm will <. atain so r put a rubber stopper iv wash the gas thorough!; ove the solution from t mmoniacal solution of silver nitrate dissolves C,H, le gas IS also very soluble in water. ^Vrous sulphate (concentrated) dissolves NO. ^old water or alcohol dissolves N.,0. 'xygen may also be determined by placing a piece of P in tube containing the gas and setting the apparatus in the light. ^i/drogen is absorbed by palladium asbestos. Some of the .stances may be put into a U tube of fine bore and placed a beaker of water kept at 100° C. while the gas is passing rough the tube. Place this tube between the tubes de ibed for the analysis of gases, in this chapter, and make ' connections with short pieces of rubber tubing. Force gas slowly backwards and forwards over the palladium estos three or four times. f„ , w .u , m^'''''^' ^"* (^^^*) ^*« "« absorbent and is determined b^ fused into the graduHiJlnbustion u.n „.i e- , J" >« determined by = ■ "••'"'"^«"^ iiicoraoustibJe gas are taken for ' some of the solution u ' (6). By regulating the gas will pass back i determine the volume iduated, the gas may •ed, making allowance fi emperature and pressu may now be removed a determining the next g 70 A HAND-BOOK OP CHEMISTRY. 26 to 37 volumes of methane and oxygf-n to prevent tl combustion of nitrogen. Ethylene (CgH,) Is absorbed by bromine water or 1 fuming sulphuri .i^. li.c, ar-" 1 must be so concentnit* that when the temperature is lowered crystals of pyrosulphui acid will separate. SuiphwHted Hydrogen (H^S) is determined by lei acetate, also by drawing the gas through iodine water, ai; potassium iodide with starch in it. The operation is stopp« as soon as the liquid becomes colorless. Nitrons Acid (HNO.,) is determined with concentrat HjjSO^, or a solution of potassium permanganate acidulat with H^SO^. ' Sulphur dioxide (S0„) is determined with KOH, or solution of iodine. Bromine, hydrochloric acid and chlorine are also absorb by KOH. Nitrogen has no absorbent. A solution oi" KOH for testing is usually made by mixi one part of caustic -^otash aad two parts of water. ^nammcniacal )lution of silver nitrate is made bye soh xg some crystals of silver nitrate in distillef' water a adding just enough aqua ammonia to redissolve the preci] tate ^r»rj.i!jd. An timmoniacal or acid solution of cvprou 4 chloride may made as follows : Cc: the bottom of a bottle i two litn capacity with a layer of coppei oxide thret fightli of an iiK deep. Place i a '^l tie a number )f pieces of rather stoi copper wire re;., ng om top to bottom. The bundle shou be one inch in diameter. Fill the bot ^ with common hy) is det«rmined by leJ I through iodine water, ail i. The operation is stoppd •riess. ermined with concentrat n permanganate acidulati 3rminfc>l > .th KOH, or ^ I chlorine are also absorb] A SIMPLE METHOD OF GAS ANALYSIS. 71 [it the copper wire does not become entirely dissolved, and bt the stopper is grease.l to keep out the air, as it turns the ution brown and weakens it. To make annnoniacal cup- l>s chloride, treat the acid chloride with ammonia until a Int odor of ammonia is perceptible. Copper should l,e kept lit as in the acid solution. |For a number of reasons the alkaline solution is preferable [the acid solution in determini' CO. yroynllate of Potash.-W eigh out" 5 grams of the solid \ (pyrogallic). Plac.. it in a reagent bottlr, and pour upon 100 com. of potassium hy.lrate, made as a; eady described. is usually made by mixi| parts of water, er nitrate is made by fll rate in distillet; water ai la to redissolve the precij 1 of cuprou eh I ride may I >m of a bottle f two litre ide thre* eighth- of an inij ler )f pieces of rather stoj Dottom. The bundle shoul bot ' with common hyi ottle is o casionally shakt ir nearly so, it is poured iitj i^ire. Care should be tak^ 72 A HAND-BOOK OF CflEMISTRY. CHAPTER V. GENERAL HINTS. ) § 1. Many General Suggestions. To perforate a rubber stopper, take an ordinary cork bore used for perforating cork stoppers, and heat it in the laiii] flame until it becomes quite hot. The stopper n)ay then 1 easily and (juickly perforated. A nmch better method is I use a solution of caustic potash as a lubricant on the borer. It is sometimes difficult to attach a piece of rubber tubiii to glass tubing. This may be done by wetting the gli? tubing with witter. The rubber will then slip over thn gla quite easily. When a piece of rubber tubing is larger than the gL W tubing it is best to first place a short piece of rubber tubi half an inch long over the glass tubing. The first pii bj of rubber should be about the same size a« the glass tubin.cs Then place the larger rubber tubing over the smaller pio tl This will make the joint quite air-tight. „,- Adhesive or surgeon's plaster will be found very valuali i in the laboratory. It may be used to tighten stoppers i^ beetles or to make a piece of glass tubing air-tight in M stopper. There are many ways in which it will be foun useful in fitting up apparatus, but it cannot be used wh' heat is applied to the glass vessel. In filling a narrow glass tube closed at one end wi ha mercury or any other liquid, will often be found conveniong CFIEMISTRY. GENERAL HINTS. 78 R V. INTS. 8U0GK8T10Na. ike an ordinary cork borf and heat it in the lam] rhe stopper may then much better method is t| I lubricant on the borer. I a piece of rubber tubit ►ne by wetting the gliu II then slip over tho ghu ? is larger than the gla^ t piece of rubber tubir tubing. The first pieci e size as the glass tubing ig over the smaller piet ght. 1 be found very valuali d to tighten stoppers il ass tubing air-tight in n which it will be fouiil it cannot be used whel closed at one end wit jften be found convenieiJ connect a thistle tuhe or funnel to the glass tube by means a piece of rul.ber tubing. When the narrow tul.o hecomes kged w.th the liquid and the air cannot force its way up las to allow the liquid to descend, shove into the tube a ^.t piece of iron or copper wire of a zigzag outline. The bre regular the undulations of the wire the better Hun ¥ wire up and down quickly a few times. The liquid will cend quite rapidly and the tube may be filled in a short fice of time. iMost noxious gases, such as carbon dioxide, frealy dissolve Icold water. That is why a room which is much occupied ^h a« a school-room or a bedroom, may be almost completelJ h-vted by having a pail of cold water left in it over night k the same reason the apparatus descril,ed in anothe^ ^pter for handling noxious gases may be constantly used pjiout having any gas escape. to toughen glassware, lamp chimneys, etc., immerse them Ico d water to which some common salt has been added 1.1 the water well and cool slowly. Glass treated in thi« IJ will resist any sudden chan-e of temperature. lA burette or bottle, which is wet with water, may be dried rinsing with alcohol, and then with ether, and blowing a rent of air through or into it. Sometimes alcohol is all ►t 18 necessary if the glass is allowed to stand for a few I'lites after rinsing. healing wax mny be made plastic by placing it in boiling i^r. When in this state it may l,e used for many purposes ittmg up apparatus and malung a air-tight. § 2. Cements. ^W P,.oo/ ^^ai^,, Acuis.-T^k^ some India rubber nielt It Add about 6 or 8 per cent, by weight of acid keep stirrpH -NTo,,* A„,. -,]j 1- ^- ,...•', * ^ ~ "' ""> "-'^ ^*Hiu until n becomes a soft 74 A HAND-BOOK OF CHEMISTRY. paste and, lastly, add enough red lead to make it dry an harden. s I A Fire-proof Cement for China and Glassware.— Into ^ thick solution of gum aral»ic stir plaster-of-Paris until becomes the consistency of cream. Apply with a brush t i both edges. In about three days it cannot be broken. TIk « cement is very white. ' I § 3. To Remove Stains. I | The teacher of science is so frequently asked for metho(' of removing stains from clothing that the following whit ' have been collected from various sources are given here. Silver nitrate stains may be removed from the hands c from goods by washing in a strong solution of potassiir tl iodide or ammonia. Potassium cyanide is sometimes usff but it is a violent poison and its use is attended with dangt , The most obstinate stains of iodine may be removed I soaking them for some time in cold water' and then soakirt them over night in starch paste and rubbed. They may al* be removed by a strong solution of sodium bicarbonate. Stains caused by sulphuric acid and hydrochloric acid m-r be removed by treating them with dilute ammonia or bicai^ bonate of soda to neutralize the acid, and then sponge wit J chloroform to restore the color. This will not do for nitr| acid. Ammonia or bicarbonate of soda sets the stain. Wht nitric acid falls on cloth thoroughly sponge it, as quickly possible, with water and then with a little chloroform. li\ nitric acid stain is already formed there seems to be no w^ of restoring the color. Cream of Tartar and alcohol will remove grass sttiins frc the daintiest goods, as it never stains the most delicate shao A strong solution of borax will remove oil stains frcj cotton and linen. CHEMISTRY. lead to make it dry anJ and Glassware. — Into plaster-of-Paris until Apply with a brush cannot be broken. Tlij Stains. uentlv asked for method hat the following whit irces are given here, loved from the hands ig solution of potassiuj anide is sometimes usei ) is attended with dange ine may be removed water' and then soakinj rubbed. They may als odium bicarbonate, id hydrochloric acid majl lilute ammonia or bicml d, and then sponge witS is will not do for nitrif •da sets the stain. Whu sponge it, as quickly I little chloroform. lil )here seems to be no wi GENERAL HINTS. 75 Boihng water poured through a cloth for some time will kmove tea stains, cherry and many other fruit stains. If ^18 does not succeed, turpentine will remove obstinate stains. Stams of iron rust may be removed by placing on then> ht some common salt and then some lemon juice. Wash at bee with cold water. Ink, fruit and mildew stains may be removed by putting keni first in cold water and then in half a pint of water to jhich a teaspoonful of lemon juice and half a teaspoonful of Jahc acid have been added. Afterwards wash with clear later. jSulph'.rous acid will whiten undyed goods, straw, etc. , Goods dyed with aniline dyes and faded from exposure to le sun should be sponged with chloroform. remove grass stains frc ) the most delicate shao remove oil stains frcl