GIFT OF PROF. W.B. RISING INTRODUCTION TO INORGANIC CHEMISTRY With 82 Engravings on Wood BY WM. GEO. VALENTIN, F.C.S. \\ PRINCIPAL DEMONSTRATOR OF PRACTICAL CHEMISTRY IN THE ROYAL SCHOOL OF MINES AND SCIENCE TRAINING SCHOOLS, SOUTH KENSINGTON. LONDON J. & A. CHURCHILL, NEW BURLINGTON STREET 1872 PREFACE. THE encouraging reception which my Laboratory Text Book met with in this country, as well as in America, and the expe- rience which I since have had of its working with a large class of chemical students, have induced me to render the book still more generally useful by publishing it in two parts, and by somewhat enlarging the first part. I am in hope that this first volume may now take rank as a suitable text book for elementary classes preparing for the chemical examina- tions which are held annually under the Science and Art Department. The admirable list of experiments, sketched out by Dr. Frankland, in the Syllabus issued by the Depart- ment, will be found interwoven throughout the text. This I was able to do without deviating from the original plan of the book, which consists mainly in deducing the fundamental laws of chemistry from experimental facts, and thus to lay a sound foundation for qualitative and quantitative analyses. From my own laboratory experience, I can confidently recom- mend this experimental method of teaching. Large classes of students can be instructed with comparative ease, and theoretical difficulties, which are usually overcome only by a long course of chemical study, may be grappled with at the earliest stages even. I have found the theory of atomicity of chemical elements remarkably conducive to a quick and thorough understanding of chemical* changes. Graphic illustrations, I need scarcely remark, may be discarded as soon as they have fulfilled their purpose, and as soon as the pupils have become familiar with the use of the constitutional bymbolic formulae employed in this work. 237359 IV PREFACE. The Questions and Exercises, placed at the end of most of the chapters, constitute an essential feature of the book. They will be found of great use if the written answers are examined by the teacher, and any shortcomings discussed with the pupils. This en t ails \ no doubt, much labour, but it forms, in my experience, the only safe means of controlling and rendering the laboratory teaching thoroughly efficient. Most of the experiments can be readily performed by beginners, if the directions given in the text are attended to, others again, are perhaps more suited to the lecture-room. The selection may, however, be safely left to each teacher. When the chemical instruction in schools or elementary science classes has, of necessity, to be conducted by lectures only, this little book will, when placed in the hands of the pupils, also form a useful companion and guide for private study. The final chapter contains a brief summary of all the previous experimental facts, classified under four chemical changes, a summary which, I trust, will recommend itself to the practical teacher. In conclusion, I have to thank Mr. A. J. Greenaway, Junior Assistant in the Laboratory, for his kind help in pre- paring a number of new wood-cuts. CHEMICAL LABOEATOEIES, SCIENCE SCHOOLS, SOUTH KENSINGTON, Oct. 18, 1872. TABLE OF CONTENTS. CHAPTER I. PAGE Hydrogen. Properties of Hydrogen. Compound of Hydrogen with Oxygen. Water . . . . 1 CHAPTER II. Oxygen. Properties of oxygen. Nitrogen. Composition of air. Com- pounds of oxygen with metals, Oxides. Compounds of oxygen with sulphur and phosphorus. Combustion of carbon in oxygen. Yolume combination of hydrogen and oxygen . . . . . . . . . . 6 CHAPTER III. Physical states of matter solids, liquids, and gases. Mechanical mixture. Chemical combination. Chemical reactions (combinations and decom- positions). Binary compounds. Names and symbols of elements . . 19 CHAPTER IY. Eeductions. Chemical affinity. Indirect oxidation. Eeciprocal affinities 26 CHAPTER V. Electrolysis. Constant volume proportions. Eudiometer. Composition of water by weight and by volume. Allotropic state of oxygen. Ozone, its preparation and properties . . . . . . . . . . . . 31 CHAPTER VI. Constant combining proportions. Atomic theory. Table of combining weights of the most important elements. Yolumetrical composition of steam. Molecular volumes. Multiple proportions . . . . . . 37 CHAPTER VII. Water. Natural waters. Distillation. Metallic and non-metallic oxides. Acids. Alkalies. Salts. Basic oxides . . . . . . , . . . 45 CHAPTER VIII. Sulphur : its occurrence and properties. Allotropism. Dimorphism. Volume combination of sulphur with oxygen. Compounds of sulphur with metals, Sulphides. Compounds of sulphur with non-metals. Volu- metrical composition of sulphuretted hydrogen. Metallic sulphides. Precipitation, &c. .... . . . . . . . . . . . . 51 VI TABLE OF CONTENTS. CHAPTEE IX. PAGE Chlorine. Properties of chlorine. Preparation of chlorine water. Action of chlorine upon water. Hydrochloric acid. Metallic chlorides. Hydrogen compounds of bromine, Iodine, and fluorine. Properties and volumetrical composition of hydrochloric acid gas . . . . . . 62 CHAPTER X. Application of the theory of constant chemical combining proportions. Quantitative chemical calculations . . . . .... . . 71 CHAPTER XI. Atomicity or quantivalence of atoms. Volumetrical composition of hydro- chloric acid. Polyad elements. Hydrogen, the unit of atomicity. Representation of the atomicity of elements. Graphic representation of atoms and molecules. Classification of elements according to their highest atomicities. Use of thick type . . . . . . . . . . 75 CHAPTER XII. Hydrates, metallic and non-metallic. Peroxides. Hydroxyl. Formation of acids from anhydrides. Reactions in the wet way. Compound radicals and metalloxyls . . . . . . . . . . . . . . 83 CHAPTER XIII. Hydrochloric acid. Conversion of metallic oxides into chlorides. Prepa- ration of metallic chlorides. Action of hydrochloric acid upon metals. . 92 CHAPTER XIV. Formation of ternary oxy- compounds from metallic hydrates and oxy- acids. Sulphurous and sulphuric acids and their salts. Haloid salts. Oxy-salts 96 CHAPTER XV. Carbon, its occurrence and properties. Preparation and properties of its oxides carbonic anhydride and carbonic oxide. Carbonates, their formation, and action of acids upon them. . . . . . . . . . 102 CHAPTER XVI. Oxides of nitrogen, their direct formation by electric discharges. Prepara- tion and properties of nitric acid. Nitrates. Nitric peroxide. Nitrous acid. Nitrites. Nitrous anhydride, its reducing and oxidizing action. Preparation and properties of nitric oxide. Action of nitric acid upon metals. Compounds of nitrogen and oxygen. Aqua regia. Chloro- nitric gas. Use of nitric peroxide in the manufacture of sulphuric acid. Metallic sulphates 109 TABLE OF CONTENTS. Vll CHAPTER XVII. PAGE Ammonia. Preparation of ammonic nitrate and laughing gas. Properties of nitrous oxide. Composition and properties of ammonia. Ammo- nium. Ammonoxyl. Preparation of ammonic hydrate. Ammonium compounds . . . . . . . . . . . . . . . . . . 124 CHAPTER XVIII. Oxides of chlorine. Chlorates. Hypochlorites. Hypochlorous, chlorous, chloric, and perchloric acids. Perchlorates 131 CHAPTER XIX. Phosphorus. Phosphoric anhydride. Orthophosphates. Pyrophosphates. Metaphosphates. Phosphorous anhydride. Phosphoretted hydrogen. Arsenides. Oxides of arsenic. Arsenites and Arseniates . . . . 137 CHAPTER XX. Boric anhydride. Orthoboric and metaboric acids. Borates . . . . 144 CHAPTER XXI. Construction of the blowpipe. Nature of a candle flame. Oxidizing and reducing flame. Construction of gas lamps. Charcoal supports. Platinum supports. Blowpipe reactions. Fluxes . . . , . . 146 CHAPTER XXII. Silicic anhydride. Orthosilicic acid . . . . . . . . . . . . 152 CHAPTER XXIII. General properties of salts. Solubility of salts. Crystallisation. Water of crystallisation and of constitution. Colour and taste of salts . . 155 CHAPTER XXIV. Reaction of salts. Definition of a salt. Normal, acid, and basic salts. Double salts. Alums . . . . . . . . . . . . . . 159 CHAPTER XXV. Definition of chemistry. Modes of chemical action . . . . . . . . 163 INTRODUCTION TO INORGANIC CHEMISTRY. CHAPTEE I. HYDROGEN. Experiment 1. Fill a glass cylinder or test-tube with water, and invert it over a basin containing water, by first closing its mouth with a glass plate (Fig. 1). Wrap up a small piece of the metal sodium in a little fine wire gauze, fas- tened to a piece of wire. In- troduce the sodium rapidly underneath the mouth of the cylinder (Fig. 2). Gas bub- bles are observed to ascend through the water, and to collect in the upper part of the cylinder. The evolution of gas ceases after a few moments, and the sodium is found to have disappeared entirely. By repeating this operation, if necessary, the whole of the water in the cylinder may be replaced by a colourless gas. This gas is hydrogen. A. few other metals, such as potassium, ba- rium, strontium, cal- cium and magnesium, decompose water like- wise at the ordinary temperature with the evolution of hydrogen, but the action is, for the most part, much slower, and has, in the case of the latter metal, to be assisted by em- ploying hot instead of cold water. Some metals, such as aluminium, iron, FIO- 2. DECOMPOSITION OF WATER BY SODIUM B FIG. 1. PREPARATION OF HYDROGEN. manganese, cobalt, nickel, zinc, cadmium, tin, and antimony, which, when cold, are, for the most part, without action upon water, are yet capable of decomposing it when water, in the form of vapour or steam, is slowly passed over the metals heated to redness in a por- celain tube. They decompose it r however, more or less rapidly in the cold, if a little hydrochloric acid be added to the water. A brisk evolution of hydrogen ensues. Other metals, again, such as copper, mercury, gold, and platinum, even when placed in acidulated water, do not evolve any hydrogen. Experiment 2. Larger quantities of hydrogen are most conveniently pre- pared by acting upon zinc or iron with dilute hydrochloric acid. An apparatus, represented in Fig. 3, consisting of a two-necked bottle so-callecl Woulfe's bottle is employed, fitted up by means of perforated corks with a funnel and delivery-tube. The funnel-tube reaches nearly to the bottom of the Woulfe's bottle, and serves for the introduction of the acid. The delivery-tube, which has been bent, as seen in Fig. 3, in the gas-flame of an ordinary fish-tail or bat's- wing gas-burner, is fitted into the other hole, so as just to pass through the cork. Sound and well-fitting corks should be selected for such experiments, and they ought to be well squeezed before being bored. The glass funnel and delivery- tube should readily pass through the holes, and yet fit perfectly air-tight. It is best, therefore, to bore the holes by means of a sharp cork-borer of the size of the glass tubing to be employed. The delivery-tube dips under the water, and delivers the gas into the cylinder inverted over water in a pneu- matic trough. Q-ranulated zinc (or strips of sheet zinc) is introduced into the bottle, and the cork and delivery-tube adjusted properly. Moderately concentrated hydro- chloric acid is then poured through the funnel-tube, when the evolution of hydrogen begins at once. The gas finding no other outlet, passes through the deli very- tube, and forces its way through the water. The air contained in the Woulfe's bottle must first be displaced before any of the gas is collected. In order to ascertain whether the air has been sufficiently dis- placed, some of the gas is col- lected over water in a test-tube in the manner already described. When quite full, the tube is withdrawn by closing the mouth with the thumb, or with a small watch glass or glass plate. If the enclosed gas burns quietly, on applying a light to it, whilst the mouth of the tube is held downwards, with a blue lambent flame, it may be considered safe to collect the gas ; but should the gas in the tube burn with a slight explosion on applying a light to it, it may be taken as an indication that the air has not been sufficiently displaced from the generating apparatus. In the place of the zinc we might have employed iron scraps, nails, borings, or filings. Hydrogen gas, generated from impure iron, possesses a most disagreeable odour, arising from the pre- sence of carbon and sulphur in the iron, which elements, by entering into combination with a portion of the hydrogen, form FlG. 3. PREPARATION OF HYDROGEN FROM ZINC AND HYDROCHLORIC ACID. COLLECTION OF HYDROGEN. gaseous compounds, called carburetted and sulphuretted hydrogen. Pure hydrogen is inodorous, and is but very slightly soluble in water ; 100 volumes of water dissolve only 1*93 volumes of the gas. For storing up larger quantities of hydrogen, a gasholder, repre- sented in Fig. 4, is usually employed, consisting of a cylindrical vessel, A, made of zinc or copper, connected by means of two tubes, a and b, with the open vessel, B, and supported by one or two more tubular stays, c and c', as shown in Fig. 4 ; a and b can be shut off by means of stopcocks. A glass gauge, as seen in g g' , indicates the height of the column of water in A. By closing the opening, d, fitted with a screw'-plug, and turning on the taps at a and b, as well as the de- livery-tap at e, water which is poured into the vessel B makes its way into the vessel A, till it fills it entirely, and runs over through e. The taps at a, b, and c are then closed, and the gas- ' holder may be charged with gas by inserting the delivery- tube through the opening at d, after the removal of the screw-pi Qg. The water runs out from d as fast as the gas enters. When full, the screw-plug is replaced, and the apparatus is ready for use. By keeping the top ves- sel, B, always well supplied with water, the gas can be discharged at pleasure from A by turning on the tap a, which conveys the water down to the bottom of A, and opening the tap e partly or fully, as may be required. The water which flows from B to A presses upon the gas, and forces it from .e. The top vessel, B, may also serve the pur- poses of a pneumatic trough, and gas may be filled directly from the gas-holder into an inverted cylinder by opening the tap 6, and allowing the gas to escape through the water into the inverted cylinder. Now, what are the properties of the gas which has been collected ? Experiment 3. The hydrogen gas collected in a test-tube, or glass cylinder, as described in Experiments 1 and 2, can be readily removed from the basin (Fig. 5), or pneumatic trough, by closing the opening of the cylinder with the thumb or a glass plate. On applying a lighted candle to the mouth of the cylinder, Fig. 6, the gas burns quietly with a lambent, non-luminous flame. It is an inflammable gas. On introducing a wax taper, as shown in Fig. 7, into the cylinder, the gas burns at the mouth quietly with a bluish flame, giving very little light, whilst the taper, on being moved upward through the flame into the hydrogen, as shown B 2 FlG. 4. GASHOLDER. PROPERTIES OF HYDROGEN FIG. 5. in Fig. 8, is immediately extinguished ; on withdrawing the taper again, it ignites once more when it readies the burning gas at the mouth of the cylinder. The taper may be thus extinguished and rekindled several times in succession. This proves that hydrogen cannot support combustion ; also, that it burns, but only where it is in contact ivith the air (at the mouth of the cylinder). Experiment 4. A strong soda-water bottle, filled to about one-third its bulk with water, is inverted over the gas delivery tube, Fig. 3, until all the water Fl0 ' 6 - FIG. 7. . . . expelled by the bubbles of gas. A mixture of air and gas in the proportion of 8 ' " ta^explodes This proves that a mixture of hydrogen gas and air does not combine he ordinary temperature, but explodes with violence on coming in contact with a light. ansm^ 5 ,'~ A fc e8t-tube or cylinder full of air is held, mouth down- , ar some hydrogen is aUowed to pass into it from another tube, somewhat COMPOUND OF HYDROGEN WITH OXYGEN. WATER. FIG. 8. FIG. 9. inclined, as shown in Fig. 9. On applying a light -to its mouth, an explosion takes place, showing that this cylinder, which originally contained only air, con- tains now a mixture of hydrogen and air a mixture which is highly explosive, as proved by Experiment 4. This shows that the gas ascended from the lower into the upper cylinder, and that it must therefore have been lighter than air. Accurate determinations have established the fact, that the gas is ah out 14 times lighter than air, its specific gravity being '0691, as compared with air = 1. Owing to its lightness it is sometimes used for filling balloons. Coal gas being, however, more easily procurable, although about 8 times heavier than hydrogen, is now usually employed for this purpose. Experiment 6. The delivery tube of the gas-generating apparatus is con- nected with a drying tube (containing calcic chloride, a substance which possesses a strong affinity for water), and a glass tube drawn out to a point (Fig. 10). After allowing the hydrogen to escape for some time, the jet may be lighted without any danger of an explosion. 9 The gas burns with a pale blue flame, which, how- ever, is exceedingly hot. Invert a dry bell-jar over the flame. It soon be- comes covered with mois- ture on its inner surface, and drops of condensed water collect and run down. The same may be shown by holding a wide glass tube, about " , half an inch in diameter, over the jet. A musical note, high or low, according as the tube is wide or narrow, will be heard, arising from a series of small explo- sions, which follow one another in more or less rapid succession, as the tube is raised or lowered over the gas flame. The upper part of the tube contains the condensed water. This proves that water is formed by the combustion of hydrogen in OXYGEN. air. Hence the name hydrogen given to the gas (from vSup, water , and ryei/i/aw, I generate), represented shortly by the symbol H. Bodies which consist of hydrogen, together with another element capable of burning in air, viz., carbon usually termed hydro- carbons such as oil of turpentine, paraffin oil, petroleum ; and, again, others which contain a third element, viz., oxygen, such as common tallow, spirits of wine, wood, etc., produce all more or less water, besides some products of combustion, which will be explained hereafter. A tallow candle, ex. gr., produces rather more than its own weight of water ; alcohol, or spirits of wine, yields a still larger amount. This may be seen by holding a wide glass tube or a bell- jar over a burning candle, in the manner shown in Experiment 6. It is also perceived whenever water, or some, other cold liquid, is heated over a spirit-lamp or gas-flame in a glass vessel (a retort or flask). Drops of water produced by the combustion of the alcohol or gas condense on the outside of the glass vessel, until the vessel has been heated sufficiently long to prevent the condensation of the water vapour or steam. Summary.* Hydrogen is a very light gas. When pure it is colourless, tasteless, and inodorous. It is inflammable, evolving much heat, but giving little light ; it does not support combustion. Water is formed by its combustion in air. Although it has no poisonous properties, it cannot support life. CHAPTER II. OXYGEN, NITROGEN, AIR. FlG. II --OXIDATION Of MKIU'IRY. Experiment 1. Heat a little mercury nearly to boiling in a small flask (Fig. 11) pro- vided with a long glass tube, and shake fre- quently. The bright metal gets slowly coated over with a reddish-yellow film, which, on shaking, adheres to the sides of the flask, and, after heating for some hours, a portion of the metal is converted into a red powder. (The vapour of the metal mercury being poisonous, care must be taken not to allow any to escape into the room through the open condensing tube.) On weighing the flask and metal be- fore and after the conversion of some of the latter into the red powder, an in- crease in weight is observed. A ponder- able substance must have been added during the heating, which can only have come from the air. * The summaries placed at the end of this, as \vc-ll as the next following seven chapters, should be committed to ineivovv. PREPARATION OF OXYGEN. 7 Experiment 8. Introduce a weighed quantity of the red powder so obtained into a tube of hard G-erman glass (Fig. 12), and connect by means of a cork with a delivery tube, which dips under water in a pneumatic trough. On applying a strong heat to the tube by means of a Bunsen's gas burner, the FlG. 12. PREPARATION OF OXTOKN FROM MERCURIC OXIDE. expands, and is forced out through the delivery tube. After a little time a metallic coating is observed to form in the bend of the tube, and gas bubbles begin to come off more briskly. Test the gas which bubbles up through the water in the pneumatic trough by bringing a glowing chip of wood near it. If the latter bursts into flame, this is due to the gas which comes off from the red powder, as air would not inflame it. A glass cylinder, full of water, is then inverted over the mouth of the delivery-tube, and some of the gas collected. The cylinder becomes gradually filled with a colourless invisible gas. The metallic mirror in the bend of the tube increases, and collects in heavy drops. This liquid metal is mercury. When the whole of the red powder has been volatilized, and converted by heat into a gas and a liquid metal, the lamp is removed, and the delivery-tube taken out of the water. The condensed mercury may now be weighed in a little counterpoised porcelain dish. It weighs less than the red powder employed. Something, then, has been removed from the latter, viz., the gas collected in the cylinder. If the experiment be conducted with proper care, and in a per- fectly suitable apparatus, it will be found that 100 parts by weight of the red powder leave invariably 92 '59 of metallic mercury, or in the proportion of 216 : 200, and conse- quently yield 16 parts by weight of oxygen gas from every 216 parts of the red powder. The latter is a compound of mercury and oxy- gen, and is called mercuric oxide. What is this gas, and what are its properties ? By closing the cylinder with a small glass plate, the gas can be removed without loss, and on introducing a glowing taper or ignited chip of wood into it, the taper or wood bursts into flame (Fig. 13), and burns very brilliantly. This gas, therefore, supports combustion much more readily than the air from which it was originally derived (comp. Exp. 7). It is Flo> 13> 8 COMPOSITION OF AIR. called oxygen, or acid producer, from ov9, sour, acid, and generate (because chemists thought, at one time, that oxygen entered into the composition of every acid), and the symbol has been assigned to it. The metal mercury, .symbol Bg, from hydrargyrum, by combining with the gas oxygen forms an oxide, mercuric oxide (red precipitate), and the symbol HgO is used to express its composition. Experiment 9, Introduce a small piece of phos- phorus, dried between filter papa*, into a porcelain cruci- ble, which floats on water, as seen in Fig. 14. Set fire to the phosphorus, and rapidly invert an empty bell- jar over the burning phosphorus, so that the combustion can only take place at the expense of the air confined over water under the bell-jar. The latter becomes filled with dense white fumes, which gradually sink down, and are absorbed by the water. A diminution of about one-fifth in the volume of the air takes place, and in proportion as the air disappears, the water rises in the bell-jar. As soon as the combustion has ceased, the crucible may be removed from beneath the glass vessel. By slipping a glass plate over the mouth of the jar, it can be readily _^ removed, and its contents examined. This is done by FIG. 14. - PREPARATION OF introducing a lighted taper into the colourless gas left in NITROGEN. the bell-jar. The burning taper is immediately extin- guished. The gas, therefore, no longer supports combustion. It is no longer air. The phosphorus possessed a strong affinity for that constituent of the air, which is alone capable of supporting combustion, viz., the oxygen, an affinity which is greater than that which the metal mercury exhibited in Experiment 7. The air must, therefore, be a mixture* of a gas which supports combustion, viz., oxygen and another gas which does not sustain combustion. This latter has been called nitrogen, i.e., generator of nitre, also azote (from a pri- vative, and &m/ro's, belonging to life), and is represented briefly by the symbol N. Air, according to this approximate determination, consists of about one volume of oxygen and four volumes of nitrogen. Exact experiments have shown that air contains : By volume. By weight. Oxygen 20'9 23'2 Nitrogen 79'1 76'8 100-0 100-0 These proportions of oxygen and nitrogen in air have, moreover, been found to vary but little all over our globe. The specific gravity of oxygen and nitrogen is readily deduced OO.O y'A'Q from these numbers, viz.,^r_^ !], an a /0 = -97. A(j'& 79*1 * "When a mixture of nitrogen and oxygen, in the proportions in which they are present in air, is made, no chemical combination takes place between the two gases. The mixture has all the properties of atmospheric air. COMPOUNDS OF OXYGEN WITH METALS. 9 Air contains, besides these two constituents, a small proportion of a gas called carbonic anhydride,'* and more or less vapour of water. The porcelain crucible generally contains some remnants of un- burnt phosphorus, which should be kept covered with water, as the affinity which phosphorus possesses for oxygen is so great that it cannot be kept in air, and great care ought to be taken to prevent rntaneous inflammation whilst operating with it. Phosphorus uld, therefore, not be touched with the fingers, but should be taken out of the water with a pointed knife, or a pair of crucible- tongs, and cut into small pieces of the size of a pea under water. The white fumes, or the product of the combustion of phosphorus in air, called phosphoric anhydride, will be explained more fully hereafter. Experiment 1O. Expose a few thin strips of bright metallic sodium to the air in a flat porcelain dish. The metal tarnishes rapidly, and becomes coated with a dirty white layer of oxide, by abstracting oxygen from the atmosphere. The metal sodium oxidizes, in fact, slowly in air. The crust of oxide attracts moisture from the air, and speedily deliquesces. Thick pieces of metal on becoming coated over with oxide thereby become protected from the further action of dry air. On removing the layers of oxide and dissolving them in a little distilled water, a clear liquid is obtained, which feels greasy to the touch, tastes very caustic, and turns red litmus-paper llueft i.e., it has an alkaline reaction. The powder is in fact an oxide of sodium, or soda, also called caustic soda, and sodic hydrate. The symbol for sodium is Na ; from Natrium, the name given to the metal by German chemists. Instead of the metal sodium we might have employed the metal potassium with similar results. An oxide of potassium, or potassa (potassic hydrate), would have been left in the dish. The symbol for potassium is K (from Kalium) . On account of the great attraction which these metals possess for oxygen, they have to be carefully kept in a liquid which does not contain oxygen, viz., petroleum. Sodium being so much cheaper and less oxidizable than potassium, is now almost invariably used, since it exhibits similar properties, only in a less marked degree. Sodium may be cut with a knife, and can be handled with dry fingers, with- out danger of its bursting into flame from too rapid oxidation. The oxides of both metals attract moisture from the air most eagerly, and are gradually converted into thick oily liquids containing sodic and potassic hydrates. Experiment 11. We are acquainted with other metals which are acted * The term anhydride is applied to oxides which form acids by combining with water, or salts, when added to a base. It will be explained more fully in a subse- quent chapter. f Litmus, a vegetable colouring matter found in many lichens, is employed for preparing test-papers. The blue colouring matter is easily extracted by water from the litmus sold in commerce six parts of water to one part of litmus or very dilute solution of ammonia. Sheets of unsized paper are dipped into the filtered solution and dried. To produce red litmus-paper, the aqueous solution of the colouring matter is first turned red by the addition of a few drop's of very dilute sulphuric acid. 10 COMPOUNDS OF OXYGEN WITH METALS. upon by atmospheric air. A piece of magnesium wire or foil can be kept in the air without undergoing much change! It tarnishes only slightly. Hold the metal, however, for a moment in a flame, and it burns most bril- liantly, i.e., it deprives the air of one of its constituents Oxygen, with which it forms an oxide of magnesium or magnesia. Symbol MgO. The symbol adopted for magnesium being Mg. The wire continues to burn after its removal from the flame. Magnesia is a white earthy-looking powder, which is but little soluble in water, has only a feebly alkaline reaction on red litmus- paper, and little attraction for water. This experiment proves that the metal magnesium has at the ordinary temperature much less affinity for oxygen than either sodium or potassium. Some metals which volatilize at a high temperature burn vividly, and with a flame, i.e., in the finely divided condition of vapour they combine readily with the oxygen of the air. Experiment 12. Heat metallic zinc in a porcelain crucible over a gas flame (Fig. 15). It melts and becomes coated over with an iridescent film of oxide. On raising the temperature the metal volati- lizes, and its fumes burst into a dazzling bluish-white flame, giving rise to white smoke of zincic oxide. Thin sheet-zinc burns hi a Bunsen flame as fast as it melts. The oxide may be collected. It is not soluble in water, and shows no action upon litmus-paper. The symbol for zinc is Zn, and for zincic oxide, ZnO. Experiment 13. A piece of thin steel wire, when kept in dry air, remains bright and unchanged. On raising the temperature of the wire to intense white heat, by holding it in the flame of a gas-burner, it be- gins to burn, and to cast off brilliant sparks, i.e., the 15^-coMBusTioN OF m etal iron (steel is almost pure iron) combines with the ZINC IN AIR. oxygen of the air at a white heat, and forms with it an iron oxide resembling the black iron scales that fall from a smith's anvil when a hot piece of iron is hammered out. On removing the steel wire from the gas flame, however, the combustion ceases immediately. The symbol for this iron oxide is Fe 3 O 4 , the symbol for iron being Fe, from Ferrum. This oxide is not soluble in water, shows no alkaline reaction (in fact no reaction at all) with red litmus-paper, and is only slowly affected by water in the presence of air and car- bonic acid, being converted into iron rust. These experiments prove, then, that the metal iron has less affinity for atmospheric oxygen than either sodium, magnesium, or zinc. Experiment 14. Heat a piece of lead in an iron spoon over a gas-burner ; the metal melts, the surface of the molten metal is at first bright, then becomes covered with a yellowish film. The oxygen of the air by combining with the lead, forms lead oxide, or plumbic oxide (from Plumbum lead, symbol Pb), the symbol of which is PbO. It is insoluble in water, and has no action on litmus-paper. Experiment IS. Heat some bright copper turnings in a gas flame ; they become rapidly covered with a black film of copper or cupric oxide, CuO (from PREPARATION OF NITROGEN. 11 Cuprum, symbol Cu), which peels off readily (copper scales), and is obtained as a black powder, insoluble in water, having no action upon litmus -papers. The action of atmospheric air upon the nietal copper may be illustrated further by a simple experiment, showing conclusively that only one constituent of the air, viz., its oxygen, is capable of combining with the copper to form the black oxide of that metal. Experiment 16. Fill a glass combustion tube, ef, with bright copper turn- ings, and heat the tube in a small charcoal (or, if procurable, gas) furnace (Fig. 16). FlG. 16. OXIDATION OF COPPER IN AIR. Pass a current of air from the gasholder, A. The air is made to* pass through two U-tubes, T and T', before it enters the combustion-tube at e. The first U-tube contains small pieces of pvirnice-stone moistened with a solution of caustic potash, which absorbs the traces of carbonic anhydride contained in the air. The second U-tube contains pumice-stone saturated with concentrated sulphuric acid,* which possesses a powerful attraction for water, and retains every trace of moisture which the air carries along with it. Connect a delivery-tube with the end Jt /, of the combustion-tube, for the purpose of collecting the gas which passes off over a pneumatic trough, as seen in Fig. 16. Pass air over the copper without applying heat to the tube. No action takes place, the copper retains its metallic lustre. Collect some of the air in a glass cylinder over water and introduce a lighted taper. The taper continues to burn quietly. Heat the copper next to bright redness by heaping ignited charcoal all round the combustion-tube. The metallic copper remains unchanged. Now turn on a slow current of air, and the metal is seen to blacken from the anterior end of the layer of copper turnings onwards. Collect the gas, which issues from the delivery-tube under water, in a glass cylinder, and test it again by inserting a lighted taper : it no longer supports combustion, for the taper is extinguished. The gas is no longer air, it is in fact nitrogen gas. This constitutes, then, a ready method of obtaining pure nitrogen gas. When thus obtained it is a colourless, tasteless, and odourless gas. It is a non-supporter of animal life without, however, being directly poisonous, for we inhale it constantly in atmospheric air, in which it moderates the action of the oxygen. Water dissolves nitrogen only to the extent of about one-fiftieth of its own bulk. Nitrogen has never been liquefied by cold or pressure. It is slightly * The pumice-stone and sulphuric acid are heated together for a short time in a porcelain, dish, and the excess of acid drained off before the U-tube is filled. 12 PROPERTIES OF OXYGEN. lighter than air, its specific gravity, compared with that of air, being '971, or 14, as compared with hydrogen. Pass air till the whole of the metallic copper has been converted into the black oxide, which can readily be ascertained by collecting from time to time some of the gas over water, and testing it with a lighted taper. The oxidation is finished as soon as the gas supports o'nce more the combustion of the taper. By weighing the copper turnings previous to their introduction into the combustion-tube, and weighing again after complete oxida- tion has been effected, we find an increase in weight. The copper, like the metal mercury in Exp. 7, has attracted some ponderable matter from the air. The increase in weight remains proportionally the same, however frequently the experiment may be repeated. The weight of the metallic copper to that of oxide is as 100 : 125'2, or (for reasons to be explained hereafter) in the proportion of 63' 5 of copper to 79'5 of oxide, i.e., 63*5 parts by weight of metal combine with 16 parts by weight of oxygen. Experiment 11. Heat gold or platinum wire, or foil, in a Bunsen gas flame. Neither of these metals is affected by the oxygen of the air. Gold and platinum exhibit, under these circumstances, no affinity for oxygen. Summary* Some metals can take Oxygen from the air and form Oxides. Combustion and oxidation are, chemically speaking, the same operation. Combustion in air or oxygen does not imply destruction, but merely conversion of the combustible substance into a new body, into an Oxide. Some mefals possess a great affinity for Oxygen, and form Oxides readily ; other metals combine with Oxygen only at a high temperature ; others, again, do not combine directly with Oxygen at all, possessing but a very feeble affinity for that element. These latter metals are sometimes called noble metals. Atmospheric air consists mainly of two gases, of Oxygen and Nitrogen, in the proportion of about one-fifth to four-fifths by volume. Oxygen sustains combustion and animal life. Nitrogen is a non- supporter of combustion, and cannot sustain animal life. Properties of Oxygen. Experiment 7 has shown that oxygen can be removed from atmospheric air, and obtained in a pure state. It would, however, be both expensive and tedious to obtain large quantities of oxygen by the method described. We avail ourselves in the laboratory, therefore, of the property which a certain salt, called potassic chlorate, possesses, of readily parting with its oxygen when heated, leaving another salt, whiqh does not contain oxygen, viz., potassic chloride. This salt is as yet of interest to us only as a convenient source of oxygen. PROPERTIES OP OXYGEN. 13 Experiment IS. Heat in a Florence flask or test-tube (Fig. 17) a few grammes of potassic chlorate, KOjCL Collect the gas over water by means of test-tubes, or cylinders. By first powdering the salt, and then mixing a small Fie. 1 or OXTGKS ram roTAanc CHLORATE. quantity of red oxide of iron (iron rust) or black oxide of manganese with the powder, and heating such mixture in the flask, or test-tube, a far more ready evolution of oxygen is effected than by heating the salt by itself. For the purpose of collecting a larger volume of gas, sufficient for several experiments, it is preferable to employ a gasholder, as shown in fig. 18. In order to examine the gas, it will be found most convenient to first transfer a portion from the gasholder to wide-necked glass bottles, closed by means of a cork. The bottles are completely filled under water, in the Tessel B of the gas- holder (Fig. 18). On placing them over the central tube, which connects the lower " A of the gasholder with the upper water reservoir B, and opening first the FlG. 13. rUPAJUMIOK OF OXTGBJf. 14 OXIDES. stopcock at , which allows the water to flow from B to the bottom of the vessel A, and then the stopcock at b, the column of water in B forces the gas rapidly into the bottles. In the absence of a gasholder, the gas may be directly filled into the glass bottle or cylin- der, .from the evolution flask or retort (Fig. 19). The bottles containing the oxygen are then removed from the water. For this purpose their wide mouth is closed under water by means of a cork, and their contents can now be ex- amined at pleasure. Experiment 19. Heat a piece of magne- sium wire in a gas flame, till it bursts into flame. Introduce it rapidly into a bottle filled with oxygen ; the combustion becomes of a most dazzling brilliancy, and the resulting white oxide (magnesia) is identical with the white powder obtained on burning magnesium in the air (comp. Exp. 11). Experiment 2O. Zinc turnings, slightly dipped into sulphur, burn on ignition of the sulphur with a dazzling white light, when plunged into a bottle containing oxygen. The result of the com- bustion is the same as in Exp. 12, viz., zincic oxide. Oxygen is capable of combining with all elementary bodies, ex- cept fluorine. Substances which burn readily in the air, burn with still greater energy in oxygen gas ; this may be illustrated further by the fol- lowing experiments. Experiment 21. A thin watch-spring is fastened to a cork, which fits loosely into the mouth of a wide-necked bottle, Fig. 20. The steel spring must be heated first, before it can be coiled up into a spiral form. In order to cause the oxygen in the bottle to act upon the iron of the watch-spring, the temperature of the latter must be raised by fastening to the end of the watch-spring a piece FIG. 19. FIG. 20. FIG. 21. of tinder or dry charcoal. The tinder or charcoal is ignited, the cork which closes the bottle is removed, and the cork with the watch-spring rapidly inserted. The tinder or charcoal, which at first only glows, burns vividly, and quickly raises the temperature of the watch-spring, till the latter burns likewise, and gives a most dazzling light, throwing off sparks of melted metal and of oxide, which fall with a hissing noise into the water left in the bottle, in order to pre- vent the globules of molten iron from breaking the glass. This experiment proves that iron, which in the form of thin wire COMBUSTION OP CARBON IN OXYGEN. 15 can be burnt in air, by holding it in a gas flame, burns in free oxygen with great brilliancy, and gives off much heat. The product of its combustion in oxygen is the iron oxide FeaC^. Experiment 22. Another bottle (Fig. 21) is filled in a similar manner with oxygen. A wooden cover is fitted to its mouth, through which passes a stout wire, to the lower end of which a small iron spoon a so-called deflagrat- ing spoon is fastened. A few pieces of sulphur are placed in the spoon, and inflamed previous to their introduction into the oxygen gas. The sulphur burns in the air slowly, with a pale blue flame. As soon as the ignited sulphur comes in contact with the oxygen of the bottle, it burns brilliantly, with a dazzling blue flame. On examining the bottle after the combustion is over, a suffocating gas is found to be left, having the odour of burning matches. Introduce a piece of blue litmus-paper into the gas. It is turned red instantaneously. On intro- ducing a lighted taper, the light is immediately extinguished. The gas does not support combustion. This gas has received the name sulphur dioxide or sulphurous anhydride (S0 3 ). Experiment 23. Fill another bottle with oxygen, and introduce in like manner a piece of phosphorus, another elementary body, as we have already seen, which possesses a great affinity for oxygen. The small piece of phosphorus to be employed is dried rapidly between folds of filter-paper, and then placed in the iron spoon, ignited, and rapidly introduced into the bottle. Phosphorus burns with most intense light in oxygen gas, producing at the same time great heat. Should any of the burning phosphorus be spurted from the iron spoon, and come in contact with the glass, it will cause the glass to crack, without doing, however, any further harm. The whole bottle is filled with clouds of a heavy white compound, which gradually subside. On letting it stand for a little while, these white clouds disappear. They combine with the water, with which they form an acid substance. Test the water with litmus-paper ; it turns blue litmus red. The liquid possesses an acid taste. The white compound formed by the combustion of phosphorus in oxygen gas is called phosphorus pentocdde or phosphoric anhydride (P 2 5 ). The product of the action of water upon this compound is called phosphoric acid. Experiment 24. Arrange apparatus in such a manner as to pass a current of oxygen gas from the delivery-tube of the gasholder over pieces of ignited charcoal placed in a piece of combustion-tube, connected by means of corks and india-rubber tubing into a glass cylinder, as shown in Fig. 22. Previous to applying heat to the charcoal, and before turning on the oxygen gas from e, introduce a lighted taper into the glass cylinder. It continues to burn. Apply heat to the tube where the charcoal rests ; it begins to glow. Now pass a slow current of oxygen gas, the charcoal imme- diately burns most vividly, and the combustion goes on wthout any external ap- plication of heat. When the combustion has proceeded a few minutes, introduce the lighted taper again into the glass cylinder which received the gaseous product of com- bustion. The light of the taper is extinguished. The gas in the cylinder is neither air nor oxygen. A series of burning tapers fixed on wires at various heights may also be introduced into a second wider cylinder. The taper placed lowest will be extinguished first, then the next above it, and so on, till all are extinguished. The charcoal in the combustion tube is gradually consumed and carried away as gas. It burns at the expense of the oxygen, i.e., it combines with the latter and forms an oxide of carbon, called carbon dioxide or carbonic anhydride (C0 2 ). 16 COMBUSTION OF CARBON IN OXYGEN. This experiment proves then clearly that the colourless gas which results from the combustion of carbon in oxygen does not support combustion. FlG. 22. COMBUSTION OF CARBON IN OXYGEN. Combustion, in the sense used to express this and some of the preceding chemical changes, is accompanied by the phenomenon of light and the evolution of heat. The body to be burnt requires to be heated first to the initial temperature at which a chemical change can take place ; sufficient heat is afterwards given out to keep up the combustion, and to carry it on- provided a free supply of oxygen or air can be obtained till the body is consumed, i.e., altered in form, as in Experiment 24, when the solid carbon vanished gradually and was converted into the gaseous body carbonic anhydride. An analogous instance we have in the case of an ordinary coal fire burn- ing in a fire-grate. The amount of heat actually produced by a given weight of carbon, no matter whether burnt quickly, in oxygen, or slowly, in air, is the same. The sensible heat, however, was greater in our experiment, because there was no nitrogen to dilute the oxygen, as when carbon is burnt in atmospheric air, and when the non-combustible nitrogen has to be raised to the temperature of the flame, without itself contributing any heat to the combustion. Consequently the more the oxygen the element which supports combustion is diluted, the less energetic becomes the combustion. The charcoal in the glass tube burnt more or less energetically, in proportion as the admission of oxygen from the gas-holder was increased or decreased. A coal fire is quickened by forcing air into it by a pair of bellows ; not only is fresh air supplied more rapidly, but the chief product of the combustion, carbonic anhydride, which is a non-supporter of combustion, is carried away more rapidly. A PROPERTIES OF CARBONIC ANHYDRIDE. 17 good chimney draught accomplishes the same. Compressed air, as used to feed blast-furnaces, acts for like reasons more energetically than ordinary air. Combustion is accompanied by flame only in the case of bodies which are converted into vapour previous to their burning. Instances : steel wire and coke, compared, with zinc, sulphur, phosphorus, or bituminous coal, all of which are volatilized before they burn with a luminous flame. Experiment 25. Collect some carbonic anhydride in a cylin- der over warm water in a pneumatic trough. Remove the cylinder when full of gas by closing it with a glass plate. Pour the gas into another cylinder in which a small burning taper is placed, Fig. 23. The taper is extinguished, and it can be clearly seen how the carbonic anhydride by falling through the air of the up- right cylinder, at first forces down the flame, till at last it entirely ex- tinguishes it. This proves that carbonic anhydride is heavier than air, and that it consequently falls Fl - 23. through the air. Experiment 26. In like manner fill a stoppered glass cylinder with car- bonic anhydride, close the mouth with the ground glass stopper under water, and remove the cylinder to a trough containing cold, but recently boiled water. Open the cylinder under water. The water rises slowly, the gas being absorbed by the water. This absorption may be accelerated by vigorously shaking. The water now tastes slightly acid, and a strip of blue litmus-paper is slightly reddened. This proves that carbonic anhydride is absorbed by water, and that its solution is a weak acid, which is called carbonic acid. Heat expels it again. Natural waters contain carbonic acid. Experiment 2*J- Pass the carbonic anhydride generated by the combus- tion of charcoal in oxygen from the combustion-tube, directly into a test-tube containing lime-water (i.e., a clear solution of slaked lime in water). The first bubbles cause a milkiness, and in a few minutes a quantity of a heavy white powder is formed, which on interrupting the current of gas, gradually falls to the bottom of the test-tube. This powder is evidently the result of the action of the gas upon the lime dissolved in the water. If the gas is passed somewhat longer, the white powder gradually dissolves again. This proves that the latter is soluble in excess of carbonic aci:l. On adding lime-water, the clear liquid becomes once more milky. The same happens when heat is applied. In the latter case some of the gas is seen to come off. It has been already shown that water is formed by the combus- tion of hydrogen in air, and that a mixture of hydrogen and air, when ignited, explodes with great violence and forms water. A mixture of hydrogen and oxygen gas explodes with still greater violence, especially if the mixture consists of one volume of oxygen to two volumes of hydrogen. The heat produced by the combustion of oxygen and hydrogen is 18 VOLUME COMBINATION OF HYDROGEN AND OXYGEN. very great. A jet of oxygen directed into a flame of hydrogen causes sufficient heat to melt a platinum wire. Experiment 28. Soak a good sized bladder in water till it is quite soft. Insert into the neck of the bladder V a tube provided with a stop-cock r, shown in- Fig. 24. A, tubulated bell -jar is fitted with a stop-cock s. By plunging the jar C into the water contained in the upper vessel B of the gasholder, it can be filled entirely with water by simply opening the stopcock at s, and allowing the air to escape. The stopcock is then shut off and the bell-jar connected with the tube 'of the empty bladder by means of a piece of india-rubber tubing. The bell-jar is next filled with oxygen, as described under Experiment 18. By opening the stopcocks * and r, the gas is transferred to the bladder V. By filling and discharging in like manner the same bell- jar twice with hydrogen gas from another gasholder filled with hydrogen, the bladder can be charged with a mixture of one part by volume of oxygen, and two parts by volume of hydrogen. According to a beautiful law of nature, the two gases rapidly diffuse and intermingle most intimately, and the gaseous contents of the bladder now constitute a highly explosive mixture, the explosive nature of which may be shown by filling soap-bubbles with the gas. A solution of soap and glycerine is most suitable for this purpose. The cup at the upper end of the tube which delivers the gas from th3 bladder, is dipped into the soap- solution. The stopcock is then opened, and, by applying a gentle pressure to the bladder, a bubble can be blown and shaken off by a slight side-movement of the tube. The bubble ascends rapidly, because the gaseous mixture with which it is charge 1 is lighter than air, and can be exploded by applying a light to it as it ascends. Each bubble bursts with a sharp report. If no gasholders ar3 at the operator's disposal the two gases may also be filled in the proper proportions, one after another, directly from the generating flask and retort into the bell-jar, which for this purpose is divided into three equal parts, and is placed full of water over a pneumatic trough. This experiment shows that hydrogen and oxygen do not com- bine at the ordinary temperature, but if the temperature of a very small portion of their mixture be raised by applying a light to it, the heat which is produced by the chemical combination of hydrogen and oxygen communicates itself with great rapidity to the rest, and the whole mixture explodes. Water is formed by the combination of two volumes of hydrogen and one volume of oxygen. The combination of hydrogen and oxygen in these proportions can be shown in many other ways, but the highly explosive nature of the mixture renders it advisable for the operator not to attempt at first any more elaborate experiments. Some of the elementary bodies hitherto treated of possess pro- perties which appertain only to metals, others again lack such properties entirely, e.g., carbon, sulphur, phosphorus. These latter bodies are called non-metals or metalloids.* Some of the elementary * From julraXXov, metal, and eldog, form. It is difficult to draw the line of demarcation between metals and metalloids very sharply. Metals are opaque bodies, having a peculiar lustre, known as metallic lustre, and are good con- ductors of heat and electricity. Metalloids do not possess these properties in the same degree. PHYSICAL STATE OF MATTER. 19 gases already examined, viz., oxygen, hydrogen, nitrogen, belong likewise to the non-metals. Summary. Pure oxygen combines energetically with metallic as well as non-metallic elements. Oxygen mixed with nitrogen, as in air, combines less energetically. The nitrogen acts as a diluent. Heat is produced by the combination of oxygen with other elementary bodies. Such combination is frequently accompanied by the pheno- menon of light. The oxides of metallic bodies are solid bodies, either soluble in water and of a caustic or alkaline nature, or insoluble in water. They are also called bases. The oxides of non-metallic bodies are either gaseous, liquid, or solid bodies. They dissolve for the most part in water, and many possess acid properties. CHAPTER III. PHYSICAL STATE OP MATTER. MECHANICAL MIXTURE. CHEMICAL REACTIONS (Combinations and Decompositions). ELEMENTS. THE physical condition of everything around us, no matter whether of a simple or compound nature, depends mainly upon temperature. Water is a liquid body at the ordinary temperature. If the tem- perature fall below Centigrade (32 Fahrenheit) this liquid solidifies and becomes ice.* Again, if the temperature of the water be raised by the application of heat, the liquid becomes converted into water vapour, or steam. It forms then a clear, 'transparent, colourless gas, devoid of smell or taste. That temperature is indi- cated on the thermometer scale at 100 Centigrade (212 Fahrenheit) at the ordinary atmospheric pressure. Water remains unchanged in composition, i.e., it is still composed of hydrogen and oxygen, in the proportion by volume of two to one respectively, whether it exist in the solid, liquid, or gaseous form, as ice, water, or steam. It merely changes its state of aggregation, and this change is dependent upon a loss or gain of heat alone. It is a mere physical change. Most simple bodies occur at the ordinary temperature and pres- sure of our atmosphere as solids ; two only, viz., mercury (quick- silver) and bromine exist as liquids, but solidify respectively at 40 C. and 24'5 C. Four are known as gases, viz., hydrogen, oxygen, nitrogen, and chlorine, the last only being condensable by great cold and pressure ; all others are solids. Many solids may * Water maybe cooled to 12 C. without freezing, if it be left perfectly undisturbed. c 2 20 PHYSICAL CHANGES. either be converted into liquids and gases by raising the tempera- ture, as e.g., the metal zinc (compare Exp. 12) ; or reversely, gaseous bodies into liquids and solids by lowering the temperature. All solid elementary bodies, with the sole exception of carbon, have been melted or- liquefied, tjiough some of them require a very high degree of heat, such as the metal platinum. The alteration in their physical condition does not affect their weight. Solid elementary bodies which cannot be liquefied or volatilized by the heat of our ordinary furnaces, melt and vaporize readily when exposed to the extreme heat of the voltaic arc or the electric current produced between the poles of a powerful voltaic battery. Liquid bodies contract on passing from the fluid to the solid form. Water forms a remarkable exception. It reaches its maximum density at 4 C., and below that temperature it gradually expands again till it reaches the freezing point C., when, as ice, it sud- denly expands still more. Ice, therefore, floats upon the surface of our rivers and lakes, its density or specific gravity being '918 com- pared with I'OO, the sp. gr. of water at 4.* The temperature of the water below remains constant. Animals living in ice-bound waters are thus protected from the most severe winter frosts. Solid and liquid bodies alter their bulk but slightly by heat or cold, or by compression ; gases, on the other hand, are elastic bodies, which can be visibly compressed, and which contract or expand at a given constant ratio by cold or heat. By the united action of cold and pressure, most gases are reduced to the liquid state, some even to the solid condition ; a few gases only, among which are oxygen, hydrogen, and nitrogen, have never been liquefied, although there * Tlie density of liquids, as well as solids, is measured by taking the density of water at 4 C. as th3 standard unit. One litre of water at 4 C. weiglis exactly 1,000 grammes or 1 kilogramme (about 2lb. English). The advantages which French measures and weights possess will become readily apparent, if we bear in mind that a litre is a cubic decimetre, equivalent to 1,000 cubic centi- metres, both these measures being derived from the French unit of length, the metre (equal to 39'37 English inches). The unit of length, the metre, and the unit of capacity, the cubic metre, or, in the simpler forms, the decimetre and the cubic decimetre or litre, or the centimetre and cubic centimetre stand in a simple relation to the unit of weight most frequently used by chemists, viz., the weight of 1 cubic centimetre of distillel water at 4 C., called a gramme (= 15'432 English grains). To determine the density or specific gravity of a liquid body, we have merely to ascertain the weight of a given bulk, say 50 cubic centimetres, at 4 C., and to divide the weight found by 50 grms., i.e., the weight of the same bulk of distilled water at 4 C. It is usual, however, to weigh the liquid at 15 '5 C. (60 F.), the process of weighing being thus rendered so much more easy, and to divide the weight by the weight of the same bulk of distilled water at 15'5 C., when of course the relative specific gravities remain unchanged. Solid bodies heavier than water displace a certain amount of water ; and by ascertaining the weight of the water so displaced, and dividing it into the actual weight of the solid body immersed (which has to be ascertained previously by direct weighing) , we arrive at the specific gravity of the solid body. Grold, for example, has been found to displace 19'34 times the weight of its own bulk of distilled water at 4 C., i.e., it is 19'34 times heavier than the latter, or its specific gravity is 19'34. Mercury displaces 13'59 times its weight of distilled water at 4 C. ; its specific gravity is therefore 13'59. . MECHANICAL MIXTURE. 21 can be little doubt that their liquefaction is merely a question of intenser cold and .greater pressure than physicists can at present command. Experiment 9 has shown that air is a mechanical mix- ture, mainly of two gases, of oxygen and nitrogen. Nature supplies us with numerous other instances of mere mixtures. Muddy water holding particles of solid matter in suspension yields, on freezing, pure ice, any suspended solid particles being thereby removed. On filtering dirty water through a little white sand or filtering-paper, the water becomes clear, the solid ingredients being left on the filter. Experiment 29. Place a little ordinary gunpowder on a filter and wash it with warm distilled water. It leaves a black residue on the filter, which, when dried, no longer deflagrates like powder, but burns with a bluish flame, giving off the pungent odour of burning sulphur. On evaporating the clear filtrate in a small porcelain dish over a spirit lamp, or a small gas flame, a white crystalline salt is left, known as nitre. If the residue on the filter be thoroughly dried, by ] lacing the filter in a warm place, and then treated in a test-tube or flask with a little carbonic disulphide, heated by placing the test-tube into some warm water, and the extraction repeated several times with small quantities of the disulphide, we obtain at last on the filter a black carbonous residue, which on drying in a warm place and ignition no longer burns with a bluish flame, nor emits the odour of burning sulphur. This residue consists now only of finely divided char- coal. By placing the carbonic disulphide liquid into an evaporating dish over some hot water (without applying a direct flame) near a good chimney draught, a yellow crystalline residue (octahedral crystals) of sulphur (brimstone) is obtained, which on ignition burns with a bluish flame, and gives off the characteristic suffocating odour of burning sulphur. Now, gunpowder is manufactured by intimately grinding together in a moist condition finely divided charcoal, nitre, and flowers of sulphur. The moist mass is strongly compressed, formed into grains, and then cautiously dried. However carefully the in- gredients may have been ground together, they will always remain only mechanically combined, for we have seen that the two soluble bodies, the nitre and the sulphur, the first soluble in water and the second in carbonic disulphide, can be separated consecutively from the carbon, this latter not being soluble in any known solvent. Gunpowder is in fact a mere mechanical mixture of these three solid bodies. But if a spark be allowed to fall upon a little gunpowder, it is converted with a sudden flash mainly into gaseous bodies, which become diffused into the surrounding atmosphere, or which, when confined in a gun barrel, can be made to drive a bullet with considerable force. The black carbon, the yellow sulphur, and the white salt, the nitre, exist in fact no longer as such, but their elements have entered into fresh combinations, and have formed new bodies, partly gaseous and partly solid, perfectly different in their properties from the ingredients employed in the manufacture of the gunpowder. The change which took place is no longer a mere physical change, it is called a chemical change. Experiment 3O. Mix about equal parts by weight of fine iron filings and flowers of sulphur in a mortar. Shake a portion out on a sheet of white paper, and bring a magnet near the mixture ; the iron filings are attracted by the magnet, and can be almost entirely separated from the sulphur. H>at another portion of the mixture in a tube closed at one end (a test-tube), and powder up the fused mass ; the magnet no longer separates the iron from the sulphur. Heat 22 CHEMICAL COMBINATION AND DECOMPOSITION. has in fact effected a chemical combination between these two elementary bodies. On treating another portion of the mixture with carbonic disulphide in the manner explained in Exp. 29, sulphur is dissolved out, and the iron filings are left behind. On treating in like manner the fused compound of sulphur and iron, or a little of the natural compound (known as iron pyrites), no sulphur is separated. Mere mechanical mixture is therefore readily distinguishable from chemical combination. Heat is mainly employed by the chemist-, to induce chemical changes, to combine elementary substances, and to break up com- pound bodies. A piece of platinum wire when heated in a flame remains un- charged (Exp. 17). A piece of magnesium wire similarly treated bursts into flame (Exp. 19). A piece of dry phosphorus, when exposed to the air, emits white fumes ; it undergoes slow oxidation. On placing, however, a red-hot bar of iron at a distance of several inches even, the phosphorus ignites and burns with a brilliant flame. A mixture of sugar and potassic chlorate is unaffected by holding a glass rod dipped into oil of vitriol over it, but inflames as soon as the acid is dropped on it, owing to the heat produced by the chemical action. We have become acquainted with some changes produced by heat alone, and shall have occasion hereafter to examine many more. Chemical study, to a large extent, consists in fact in combining elementary matter, whereby new compounds are obtained, totally differing for the most part in their properties from those of the separate elements, as well as from the mere mixture of the elements before they were chemically combined. Many elementary or compound substances cannot be mixed together without inducing at once a change. The metal sodium in Experiment 1, on being brought into contact with water, decomposed it rapidly. Hydrogen gas was evolved, and the oxygen went to the metal sodium, and formed with it a new body, soda, or an oxide of sodium, differing essentially in its properties from the metal itself. A new body was formed, viz., soda, ~by the combination of two distinctly different bodies : the sodium, in fact, entered into chemical combination with the oxygen. In Experiment 8, we saw that red oxide of mercury, when heated, gave off oxygen gas and mercury. One uniformly constituted body thus broke up under the influence of heat into two new bodies, differing entirely from each other. The chemical change arose from the break- ing up of one body into two. It was a chemical decomposition of a compound body into its constituent parts. Chemistry deals thus with simple bodies and compound bodies. A compound body which consists only of two simple bodies, is called a binary compound. Water is a binary compound, and so are the metallic oxides called bases, e.g., cupric, ferric, plumbic oxides. The names of binary compounds are constructed by using the names of the metallic element adjectively with a terminal ic, and giving to the non-metallic element the terminal ide. Carbonic anhydride is a binary compound, BINARY COMPOUNDS. ELEMENTS. 23 for Experiment 24 lias shown that it is the result or product of the combination of the element carbon with the element oxygen. All combinations of oxygen, either with metals or non-metals, are called oxides, and the chemical change which gives rise to the formation of oxides, is called oxidation. Since at least two substances are required to produce a new body, the one acting or reacting upon the other, such chemical changes are also called reactions, and the bodies which act or react chemically are termed reagents. By way of chemical decomposition simpler substances are obtained from compound bodies, as in the case of red oxide of mercury, yielding oxygen and mercury. Metals and metalloids are always simpler bodies than their oxides (bases, acids). The question naturally arises, what are the simple bodies which constitute these metals and metalloids ? The answer must be, that it has hitherto been found impossible to decompose these bodies into simpler substances. Such substances, then, which cannot by any known process of decomposition in the present state of chemical knowledge be split up or decomposed into still simpler bodies, must be taken to constitute absolutely simple bodies. It does not, however, follow that at some future time means and ways may not be discovered, whereby these metals and non- metals may be decomposed into still simpler bodies. Such abso- lutely simple bodies for the time being are called elements. They form the basis of all chemical compounds. The endless variety of animate and inanimate forms in nature might at first sight lead us to think that there must be an innu- merable host of elements, and that to fathom them all in their manifold and varying characters must be all but impossible to the human mind. Does it not strike us, for instance, that the infinite varieties of form, colour, odour, taste, &c., which consti- tute the main portion of our experience as regards matter, must be due to an equally varied number of elementary constituents ? And yet there are but a few elements which, by combination with each other, make up all the objects that surround us in nature from the wonders that lie hidden beneath the surface of the earth, even to the very glories of the distant star world above. Although we are as yet very far from knowing every chemical compound that exists in nature, it may safely be stated that no element of any import- ance has escaped the searching eye of the chemist in that portion of our globe which is accessible to chemical investigation. The result of such investigation has proved that only a limited number of elements exists. Up to the present time we have become acquainted with 62 elements, of which about one-half occur in nature in such small quantities, and so locally, that a limited share of use- fulness only can be ascribed to them in the mineral kingdom, as well as in the economy of animate life. Others again are of the utmost importance, and appear to pervade almost every nook in nature, viz., oxygen, hydrogen, carbon, iron, aluminium, calcium, potassium, sodium. Some of these stand out in truly gigantic proportions, overshadowing all others. We need only refer to oxygen and nitro- gen, which form the principal constituents of the mixture of gases, 24 NAMES AND SYMBOLS OF ELEMENTS. termed atmospheric air ; to oxygen and hydrogen, the constituents of water, and to carbon, the element entering into every organic body, as well as into numerous mineral bodies. Only a few of the elements are met with in nature in the uncombined or native condition, and then only to a .limited extent, viz., oxygen and nitro- gen in the air, sulphur, carbon (blacklead, diamond), copper, bismuth, mercury, silver, gold, and platinum. Some of the more extensively occurring elements are invariably found in the combined state. The crust of our earth, as far as it has been penetrated and examined, consists to a large extent of oxygen, combined with a comparatively limited number of elements, mainly with silicon, iron, aluminium, calcium, magnesium, potassium, and sodium. The sea, which covers the greater part of our globe, contains, independently of the oxygen and hydrogen of the water, soluble compounds, con- sisting mainly of the elements sodium, potassium, magnesium, calcium, and chlorine. It will on this account be quite legitimate if a larger share of our attention be bestowed upon the more plenti- fully occurring elements. In the following table, arranged in alpha- betical order, the 36 most important elements are distinguished by black type ; those next in importance, 10 in number, by italics ; whilst the rest of the elements which occur, either to a very limited extent in nature, or of which we possess as yet a very imperfect knowledge, are printed in small ordinary type. The Latin names a few of the names are of Greek origin, but have become latinized are given wherever the English names of elements differ materially therefrom. Chemists have, moreover, adopted a kind of symbolic language by writing merely, as has already been shown, in the place of the full name, the first letter of the Latin name of each element. Sometimes, for the sake of distinguishing between two or more ele- ments beginning with the same letter, the first and second letter, or the first letter together with some leading letter out of the middle of the Latin name are used ; thus Sn stands for stannum, tin ; Pt stands for platinum ; Pb for plumbum, lead ; As for arsenic. TABLE OF CHEMICAL ELEMENTS. Aluminium . . Antimony (Stibium) Arsenic Barium Bismuth Boron .. Bromine Cadmium Caesium . . Calcium Carbon Cerium . . Chlorine Chromium Cobalt . . Symbol. Al. Copper (Cuprum) Sb. Didymium .As. Fluorine Ba. G-lucinum Bi. Gold (Aurum) . . B. Hydrogen Br. Indium Cd. Iodine Cs. Iridium Ca. Iron (Ferrum) C. Lanthanum Ce. Lead (Plumbum) Cl. Lithium Cr. Magnesium . . Co. Manganese . . Symbol. Cu. Di. F. G-l. Au. H. In. I. Ir. Fe. La. Pb. Li. Mg. Mn. NAMES AND SYMBOLS OF ELEMENTS. TABLE OF CHEMICAL ELEMENTS (continued). Symbol. Symbol. Mercury (Hydrargyrum) Hg. Silver ( Argent um) Ag. Molybdenum Mo. Sodium (Natrium) Na. Nickel , . Ni. Strontium Sr. Niobium Nb. Sulphur S. Nitrogen N. Tantalum Ta. Osmium. . Os. Tellurium Te. Oxygen O. Thallium Tl. Palladium Pd. Thorium Th. Phosphorus P. Tin (Stannum) Sn. Platinum Pt. Titanium Ti. Potassium (K Hum) K. Tungsten (Wolframium W. Rhodium Rh. Uranium TJ. Rubidium Rb. Vanadium V. Ruthenium Ru. Yttrium. . Y. Selenium Se. Zinc .. Zn. Silicon (Silicium) Si. Zirconium Zr. In order to distinguish different kinds of elementary (as well as compound) matter, it is necessary to study carefully the prin- cipal physical properties as they present themselves to our senses, such as the state of aggregation, colour, lustre, hardness, density, crystalline structure, the fracture of solid bodies, and lastly, the impression a substance makes upon our sense of taste, odour, and touch. Among the most important of these physical properties are those which can be expressed by figures, such as the specific gravity or density of a body, the temperature at which it passes from one state of aggregation to another, and the crystalline form which it exhibits. Summary. Elementary as well as compound bodies exist, either in the solid, liquid, or gaseous state. Changes in the mere state of aggre- gation of bodies are termed physical changes. Mixtures of two or more elementary or compound bodies, unaccom- panied by any chemical change, are termed mechanical mixtures. Changes which give rise to a new body or bodies, differing essen- tially in properties from the original bodies, are called chemical changes. The new body or bodies may be formed 1st. By the com. bination of two (or more) simple bodies, perfectly distinct in their pro- perties ; or, 2nd. By the decomposition of a compound body into two (or more) simpler bodies, differing in properties from the former. Bodies reacting upon each other are termed reagents. TJie change itself is called a reaction. Bodies which cannot be decomposed by any known process into simpler bodies, differing essentially in properties, are called simple substances or elements. Sixty-two elements are known up to the present time. 26 REDUCTIONS. CHEMICAL AFFINITY. CHAPTER IV. REDUCTIONS. CHEMICAL AFFINITY. OXIDES are binary compounds. Most oxides hitherto referred to were obtained by a simple process of addition of element to element. A further step towards enlarging our chemjcal knowledge will naturally be gained by ascertaining whether these binary compounds can be broken up into their component parts or elements ; whether, in fact, the elements contained in oxides can be isolated again. Che- mical processes of this kind are termed reductions. Experiment 8 showed clearly that heat alone can split up an oxide into its two component elements, into mercury and oxygen. Reductions of so simple a nature are, however, rare ; and it happens more frequently that the affinity which holds elements together in binary compounds is much greater than what we find in the case of the red oxide of mercury, and that heat alone cannot overcome it. In such a case we make use of the stronger affinity which a third element may possess for one of the elements of a binary compound. Adhesion or cohesion exists between bodies or parts of bodies, and enables them to hold together without altering their properties, and to remain what they are. A chemical change, we have learned, produces new bodies, different in properties from the original bodies. Hence a chemical compound must form a far more intimate com- bination, and the union of the elementary component parts must necessarily extend to the smallest possible particles of the body. On this account a distinct name has been given to this uniting force, viz., chemical affinity. It may be defined as a force which draws together the elements of a compound, firmly linking particle to particle, and which opposes itself to their separation. Chemical affinity varies in degree with the temperature. Lime and carbonic anhydride, e.g., combine readily at the ordinary tem- perature to form chalk (calcic carbonate), but at a red heat (e.g., in lime kilns) this latter is decomposed again, giving off carbonic anhydride and leaving lime. Experiment 10 has shown that sodium and potassium possess a greater liking or attraction, or, as we must now call it, a greater affinity for oxygen than either magnesium, iron, lead, mercury, or copper. We infer, therefore, that it will be easier to remove the oxygen from mercuric oxide than from soda. This is actually the case, as Experiment 8 proved. If only a slight or weak affinity has to be overcome between the elements composing a binary compound, as in the case of mercuric oxide, heat alone may overcome the force which is opposed to their separation. If, on the other hand, the elements of an oxide are held together by a powerful affinity for each other, inherent in each element although heat will certainly help to overcome the opposition to overcome it entirely we must REDUCTION OF CUPRIC OXIDE BY HYDROGEN. 27 call into action other elements possessing a still stronger affinity for one or other of the component elements of the oxide. Now, to dis- cover the different degrees of affinity which different elements exhibit towards one another, and to be able to select the right element for the purpose of breaking up a binary compound, is a matter of pure experiment. Such knowledge, in fact, constitutes our chemical experience. It is possible to reason from a knowledge of well-established affinities, and frequently to predict by reasoning from analogy, what changes will take place when an element acts upon a binary body. The experience gained by the few simple experiments which have hitherto been described has already taught us that potassium, sodium, and phosphorus possess great affinity for oxygen. Next to these we must classify sulphur, carbon, hydrogen, magnesium, aluminium, zinc, iron, tin, lead, copper, mercury, silver, platinum, gold ; and we perceive at once why silver, platinum, and gold are noble metals, namely, because of their extremely slight affinity for oxygen. Experiment 31. Introduce some cupric oxide or black copper scales (see Experiment 15) into a bulb-tube of hard glass, and pass dry hydrogen over it, as shown in Fig. 25. For this purpose the gas may be generated from zinc and FIG. 25. -REDUCTION OF CUPRIC OXIDE IN A CURRENT OF DRY HYDROGEN. dilute hydrochloric acid in the "Woulfe's bottle A. Commercial zinc is, however, never obtained pure, but contains invariably small quantities of carbon and sometimes of arsenic and sulphur which form gaseous hydrogen compounds possessing a very disagreeable odour. In order to remove these impurities, the hydrogen gas is passed through a Woulfe's bottle, B, containing water a so- called wash-bottle and then through several U-tubes, ODE, filled with small pieces of pumice-stone, before it passes over the cupric oxide in F. The pumice- stone in the first U-tube is moistened with a concentrated solution of caustic potash ; that in the second with a solution of corrosive sublimate ; and that in the third with concentrated sulphuric acid, which retains every trace of moisture which the gas carries with it. The cupric oxide in F is heated by a spirit lamp or gas jet, and is connected with a small two-necked receiver, G-, in which the 28 INDIRECT OXIDATION. greater part of the water which is produced by the deoxidation or reduction of the cupric oxide is allowed to condense, and with a U-tube, II, filled with pumice-stone soaked in concentrated sulphuric acid, which absorbs the remaining water. The bulb-tube is first weighed empty, then with its charge of about 4 grammes (or 60 grains) of previously ignited pxide. The difference in the weight gives the amount of cupric oxide. As soon as the air has been completely displaced from the tube, the gas which issues from the glass jet,/, may be lighted and heat applied to the cupric oxide. When the oxide has become sufficiently hot, a change is observed. It begins to glow, the hydrogen flame becomes smaller and smaller, and dies out at last. Moisture condenses in the two-ntecked receiver, G, and in the TJ-tube, H, the weight of which has been previously ascertained. If the lamp be removed from time to time the formation of steam ceases, and the hydrogen can be lighted again. By continuing the application of heat, whilst passing a slow current of hydrogen, it is possible to obtain finely-divided metallic copper in the form of a red spongy powder. The experiment is continued till the whole of the oxygen of the cupric oxide has gone to the hydrogen to form water. The bulb-tube is allowed to cool in a current of dry hydrogen. It is then disconnected, the hydrogen displaced by dry air, and the bulb-tube weighed again as speedily as possible. The difference in the weight indicates the loss which the cupric oxide has suffered. The loss is the same, however often the experiment may be repeated.. It is in the proportion of 79'5 to 63*5, or, if we express it in percentage numbers, every 100 parts by weight of cupric oxide lose 20'13 of oxygen. It is obvious that the water left in the receiver G and the U-tube H must be the result of the oxidation of the hydrogen gas by the oxygen removed from the cupric oxide. The increase in weight, which can readily be determined by a second weighing, consists in fact of the oxygen so removed, and the hydrogen with which it combined to form water; and for every 8 parts by weight of ponderable matter lost by the cupric oxide in the bulb-tube F, we find an increase of 9 parts by weight in the receiver Gr and U-tube H. We are therefore justified in concluding that oxygen and hydro- gen combine in the proportion of 8 to 1 by weight to form water. This experiment proves clearly that the affinity which hydrogen possesses for oxygen is not sufficient to break ^up cupric oxide (a binary compound) in the cold, but only when aided by heat. On comparing the change that took place when red mercuric oxide was heated, with the change which took place when hydrogen was passed over cupric oxide, two things become apparent, viz. : 1st. Both changes are reductions. 2nd. The second reduction is accompanied by an oxidation. Chemically combined oxygen, as well as free oxygen, or oxygen mixed, with nitrogen as in air, can therefore oxidize hydrogen and convert it into water. It is of interest, moreover, to observe, how a gaseous body, oxygen, becomes converted into a solid by combining with copper ; and on leaving the copper and combining with the gas hydrogen, is converted once more into a gaseous body, steam, which condenses into a liquid body, water. The oxidation of the hydrogen by means of the oxygen in the cupric oxide, is termed an indirect oxidation. RECIPROCAL AFFINITIES. 29 Other metallic oxides can, in like manner, be reduced, and this process of reduction is actually resorted to when pure iron and zinc have to be prepared. Some oxides, such as magnesia, soda, potash, cannot, however, be reduced in this simple manner. These metals have too strong a hold upon the oxygen ; or, in other words, the chemical affinity which they possess for oxygen is greater than that which hydrogen possesses for oxygen, even when aided by strong heat. From Experiment 1, we have seen that the affinity of the metal sodium for oxygen is sufficiently powerful to decompose water, i.e., to deprive it of its oxygen, and thereby liberate the hydrogen in the gaseous form. The oxidation of the metal sodium was in that case likewise an indirect oxidation. Experiment 32. Introduce into the bulb of a hard glass tube (Fig. 26) a small piece of sodium, and pass slowly over it dry carbonic anhydride, ob- tained as shown in Experiment 24. No change takes place. Heat the metal contained in the bulb. It is rapidly converted into the oxide of sodium or soda at the expense of the oxygen of the carbonic anhydride, and carbon separates and remains inti- mately mixed up with the oxide. Allow to cool and add a little water. The soda dissolves and the carbon floats on the liquid and may be sepa- rated by nitration. FlG - 26. REDUCTION OF C0 2 BY SODIUM. This experiment, viewed in connection with Experiment 24, proves that carbon can be oxidized directly by passing oxygen over charcoal heated in a tube of hard glass ; and that the carbonic anhydride so formed can indirectly oxidize sodium, leaving free carbon. It becomes also apparent that the metal sodium possesses a stronger chemical affinity for oxygen than the non-metal carbon ; and yet sodium and' potassium are obtained in the metallic state by this very action of carbon upon the oxides of these metals. Here then is an apparent contradiction. It may be readily explained, however, if we take into account the part which heat plays in these reactions. Carbonic anhydride yields up its oxygen to the metal sodium, when the latter is gently heated, as in the preceding experiment, because at this temperature the affinity of the sodium for the oxygen is sufficiently excited to cause the decomposition of the carbonic anhydride. The finely- divided carbon does 'not, however, react upon the sodic oxide formed, the heat not being sufficient ; but if a mixture of soda and carbon be exposed in an appropriate furnace, and in suitable iron vessels, to a strong heat, the affinity of the carbon for oxygen be- comes stimulated to a sufficient degree to deprive the sodic oxide of its oxygen. The gaseous product of the indirect oxidation of the carbon escapes, together with the vapour of the metal sodium. 30 RECIPROCAL AFFINITIES. The latter can be condensed into a solid body, whilst the carbonic oxide can no longer exert any action upon the metal at a low temperature. Such chemical changes depend upon reciprocal affinities. Phosphorus, we have seen, ppssesses, like sodium or potassium, a strong affinity for oxygen. But by mixing its oxide, phosphoric acid, or substances containing phosphoric acid, such as ground bones with charcoal, and exposing the mixture in an iron retort to a strong furnace heat, phosphorus distils off, ami can be condensed in water, whilst the oxides of carbon escape as gases. It is evident then that the easy volatilisation of sodium and phosphorus facilitates the process of reduction ; whereas metals, such as magnesium and aluminium, which possess less affinity for oxygen, but volatilise with more difficulty than sodium or phosphorus, cannot be reduced from their oxides by the action of carbon. Summary. Oxides are binary compounds, formed by the direct or indirect combination of oxygen with another element. The opera- tion by which a compound body is resolved into its elements is called a reduction (resolution). The force which draws together bodies of the same or of a different chemical nature, and which opposes itself to their separation, is called chemical affinity. The intensity of a chemical reaction depends upon the strength of the chemical affinity which exists between different kinds of elementary matter. Elements which possess the greatest affinity for oxygen constitute the most powerful reducing agents. A reduction is frequently effected by the displacement (substitution) of one element in a binary body by another element. Such displacement depends not only upon the degree of affinity, but also upon the temperature, state of division, 8fc., of the bodies reacting upon each other. Reactions are termed reciprocal, when the result of one reaction constitutes the basis or starting-point of another, e.g., AB + C = AC + B A C + B = A B + C. ELECTROLYSIS. 31 CHAPTER V. REDUCTION BY MEANS OP ELECTRICITY (Electrolysis). OZONE. THE reductions hitherto studied have been of a twofold nature : 1st. A simple decomposition of an oxide by heat into its com- ponent parts or elements. 2nd. A decomposition by the aid of an oxidizable body, either without heat or assisted by heat. Electricity furnishes us with additional means of splitting up many chemical compounds into their elementary component parts. Voltaic electricity* is almost exclusively used for this purpose. On plunging the electrodes of a voltaic battery (consisting of two zinc-carbon cells at least) into water to which a few drops of sulphuric acid have been added, decomposition of the water takes place. Oxygen escapes from the positive electrode connected with the carbon end, and hydrogen from the negative electrode connected with the zinc end of the battery. If the end of the wire of the positive electrode consists of a readily oxidizable metal, such as iron or copper, no oxygen is evolved, as the gas combines with the metal the moment it leaves the hydrogen of the water, and forms with it an oxide. Hydrogen, 011 the other hand, is evolved at the negative pole in the free state. In order to obtain oxygen likewise in the free state, platinum electrodes are employed, and both gases can thus be collected either separately or mixed together in the same vessel. Experiment 33. On introducing the platinum electrodes into water, the conductive power of which has been increased by the addition of a few drops of sulphuric acid, we observe immediately small gas bubbles forming on the strips of platinum, and escaping through the liquid (Fig. 27). FIG. 27. * The student should study in some good manual of Natural Philosophy the laws of the electric current, and make himself familiar with the apparatus employed for producing voltaic electricity. 32 ELECTROLYSIS OF WATER. Experiment 34. A small bottle (Fig. 28) is fitted with a cork and a short glass tube, bent at a right angle. Two platinum wires pass likewise through the FIG. 28. cork, and end in small strips of platinum. The bottle is nearly filled with acidu- lated water, and the platinum electrodes are connected by means of copper wire with the voltaic battery. Gas bubbles are instantaneously seen to form on the platinum strips, and to detach themselves gradually ; they rise through the liquid and escape through the delivery-tube into the cylinder, C, placed full of water over the pneumatic trough. The gas so collected detonates with great violence when a light is applied to it. It constitutes, in fact, an explosive mixture of two volumes of hydrogen, and one volume of oxygen. Experiment 35. These volume proportions are shown by introducing the platinum electrodes, resting on a piece of gutta-percha, into separate cylinders of equal diameter, as shown in Fig. 29. The gas arising from the negative FIG. 29. electrode occupies twice the space from that given off at the positive electrode. On examining the gas. s in the usual way, by applying a light, the larger volume of gas burns with the characteristic flame of hydrogen ; the smaller volume does not burn, but supports combustion ; it is oxygen gas. Experiment 36. In order to show that the gases evolved at the positive and negative electrode always come oft' in the proportion of one volume of oxygen to two volumes of hydrogen, an apparatus proposed by Dr. Hofraann (Fig. 30) may be used with great advantage. It consists of a TJ-tube, connected from its bend with an equally wide long upright tube. The two tubes of the U-tube nd in two narrow tubes, provided with glass stopcocks. The apparatus is filled with acidulated water, so that the U-tube is quite full up to the stopcocks. The CONSTANT VOLUME PROPORTIONS. 33 main tube must be long enough to receive the liquid contained in both limbs of the U-tube. The two electrodes are introduced from below into the U-tube. On completing the circuit oxygen is seen to be evolved at the positive and hydrogen at the negative pole j the quantity of the latter is, moreover, seen to be always just double that of the former gas, however much or however little water we may decompose by the voltaic current. The gases collected in the limbs of the U-tubes are tested by open- ing the stopcocks, applying successively a glowing chip of wood or a lighted taper to the gas which issues from the narrow tube. Our attention is at once fixed in the two last experiments by the co%- stant volume proportions in which the two gases are obtained on electro- lysing water. In fact, as often as the experiment is repeated, one volume of oxygen and two volumes of hydrogen are invariably obtained. We have, then, a right to infer that the two gases are really combined in water in these proportions. Experiment 3*7. It remains now only to prove that two volumes of hydrogen and one volume of oxygen, when mixed and ex- ploded in a eudiometer-tube,* a (Fig. 31), combine in the very same proportions to form water. We employ for this purpose a narrow glass tube, a, accurately graduated for holding the explosive mixture, and place the tube in mercury contained in the glass cylinder, e. The electric spark is made to pass between two platinum wires, fused into the upper part of the tube at b and c, which nearly touch each other within the tube, and end outside in two small loops, one of which, b, is con- nected by means of a small chain with the outer coating of a Ley den jar, charged with electricity : and by touching the other loop, c, with the knob of the jar, a spark passes through both platinum wires, and fires the gaseous mixture. The heat which is produced by the chemi- cal combination of the hydrogen and oxygen, momentarily expands the steam, the product of the chemical combination, considerably. The eudiometer should, therefore, never be more than half full of gas, and should, more- over, be pressed down firmly upon an india- rubber pad at the bottom of the mercury. As soon as it has sufficiently cooled, the steam condenses on the sides of the eucometer, and the mercury rushes in and fills nearly the whole of the space occupied previously by the two gases. If the mixture be diluted with a large excess of either hydrogen * So called from tvdia, calm air, and perpov, a measure. FIG. 30. FIG. 31. 34 EUDIOMETER. or oxygen, the explosion becomes less violent, and less heat is given out. The hydrogen gas may in this manner be burnt almost with- out explosion, and if the dilution be carried sufficiently far, the gases combine only locally when a light is applied, and the combustion does not spread to the surrounding gaseous mixture. The excess of oxygen or hydrogen is found in the eudiometer-tube unacted upon after firing the mixture. One volume of oxygen unites exactly with two volumes of hydrogen, no matter in what proportions these gases may have been previously mixed. By rarefying the gaseous mixture before exploding it by means of the electric spark, the violence of the explosion is likewise considerably reduced. This leads us to consider the combining relations between ele- mentary bodies, of which, in the processes of oxidation and reduction hitherto studied, no account was taken, viz., the quantitative propor- tions in which elements combine. The combination of water by volume may be represented by the following scheme : H 2 The small squares are made to represent the volume units of the elementary gases ; and to represent water symbolically we should write OTT, or OH 2 , the formation of water by the combina- tion of oxygen and hydrogen being expressed symbolically by the equation + H 2 = OH 2 . Now if two elements such as oxygen and hydrogen are found to combine invariably infixed volumes, it is clear that these two gases must also combine infixed proportions by weight, for each of these gases has its own weight or specific gravity. Hydrogen has a specific gravity of 0'0691, and oxygen of 1'1056, when compared with air; hydrogen is therefore 16 times lighter than oxygen, thus : 1-1056 0-0691 10 " If 1 litre of hydrogen gas weighs 1, a litre of oxygen must weigh 16, and since always two parts by volume (2 litres) of hydrogen are required to combine with one part by volume (1 litre) of oxygen, two parts by weight of hydrogen will be necessary to combine with 16 parts by weight of oxygen, and in order to express symbolically the combination by volume and by weight by one and TT the same scheme or formula, water is written OTT, or OH 2 , in widen formula each H not only expresses hydrogen, but one part by weight COMPOSITION OF WATER BY WEIGHT AND BY VOLUME. 35 and one part by volume, and the not merely oxygen, the element, but 16 parts by weight and one part by volume of oxygen. Water is then composed as follows : By volume. By weight. 2 vols. of H 2 parts by weight of hydrogen. 1 vol. of O 16 parts by weight of oxygen. Or in 18 parts by weight of water (say 18 Ib.) there are 21b. of H, and 161b. of O ; and as this composition of water is constant, we can readily calcu- late from these figures how much hydrogen or oxygen is contained in any given quantity of water. In order to know, e.g., how much hydrogen is contained in 100 Ib. of water, we have the proportion 18 : 2 : : 100 : x x = ll'lllb. of hydrogen. The percentage composition (by weight) of water is therefore Hydrogen 11 '11 Oxygen 88'89 100-00 Now, in Experiment 31 we likewise obtained water, as the product of the reduction of cupric oxide in a current of dry hydrogen gas, and we found that the oxygen and hydrogen combined in the pro- portion of 8 to 1. It is obvious, however, tbat the water so obtained had the same composition as the water decomposed by electrolysis in Experiment 36, and we have, therefore, no hesitation in altering the above figures to the proportion of 16 of oxygen to 2 of hydrogen, so as to represent by the same formula, volume combination as well as combina- tion by weight. Ozone. It will probably not have escaped notice that a peculiar odour was produced when water was decomposed by voltaic elec- tricity in Experiment 33. A similar odour may be noticed whenever an ordinary frictional electrical machine is set in motion, an odour which strongly resembles the sulphurous smell perceived in the air after some vivid lightning. A special apparatus constructed for electrifying air produces a like odour. Schoenbein first noticed the similarity between the odour produced by chemical discharges, and that which accompanies the electrolysis of water, or when phos- phorus is slowly oxidized. Experiment 38. Cleanse a few short sticks of phosphorus under water from, any adhering white oxide, and place them at the bottom of a perfectly clean large flask (Fig. 32) with enough water to cover about half of the phos- phoru's. Loosely cover the flask with a glass plate, and let it stand quietly for half an hour at the ordinary temperature, then invert it over water and allow the phosphorus to fall out. Replace the glass plate and remove the flask from the D 2 36 PREPARATION OF OZOXE. water. Introduce now a broad strip of freshly-prepared, moist iodized starch paper.* The paper immediately turns blue owing to the liberation of iodine, which forms with the starch a blue compound. Ordinary air or oxygen is without action upon iodized "starch-paper, showing clearly that the 'air has befen chemically acted upon by the phos- phorus. The paper remains unchanged if the phosphorus" be left too long in the flask. Several other methods for the prepa- ration of ozone will be*- referred to here- after. It has been found that only the oxy- gen of the air and not the nitrogen is chemically altered by the action of the phosphorus ; that its properties become, so to speak, intensified. Hence ozone has also been called active oxygen. On ac- count of its odour it has received the name ozone from ow, I smell. Ozone FIG. 32.-pRErA*ATiosc OP OZONE, . differs from oxygen by being denser, it is half as heavy again, three volumes of oxygen furnishing by condensation two volumes of ozone. It has, however, never been obtained free from admixture with a very large proportion of air or oxygen. Ozone is not soluble in water. Oil of turpentine absorbs the ozone only from a mixture of ozone and oxygen, leaving the oxygen untouched. The density of ozone has been determined by observing the diminution in the volume of the mixture of the two gases. When ozonified air is inhaled it produces a feeling of irritation in the lungs. When heated to 290 C., or when passed over black manganic oxide or similarly constituted bodies, ozone is changed into ordinary oxygen, without these oxides undergoing any per- manent change. It exerts a powerfully oxidizing action upon substances which are not acted upon by ordinary oxygen. It im- mediately oxidizes the common metals as well as dry mercury, and even silver when moist. It has a powerful bleaching action, and destroys effluvia far more effectually than any other deodorising agent known. Traces of ozone are usually present in country air, especially after a thunderstorm, but more so in sea air when the wind blows off the sea, rarely, however, in the atmosphere of crowded towns ; in damp and foggy weather less ozone or none at all is found in the air. Most plants whose growing is favoured by bright sunlight give it out, mixed with oxygen, although in ex- ceedingly small quantities. Summary. Voltaic electricity constitutes a powerful reducing (resolving) agent. * Prepared by soaking unsized paper, e.ff., some strips of Swedish filtering paper, in a cold dilute solution of starch (1 part of starch dissolyed in 10 of boiling water) and potassic iodide (KT) (^th of a grm.), and drying by suspend- ing the moist strips of paper over some white cotton yarn. Keep the dried papers in the dark in a well-stoppered bottle till required for use. CONSTANT COMBINING PROPORTIONS. 37 Gaseous elements combine in very simple definite proportions by volume and by vjeight. These proportions ojre constant. Symbolic representatimi of chemical changes expresses by one and the same formula both volume combination and combination by weight. CHAPTER VI. CONSTANT COMBINING PROPORTIONS, ATOMS AND MOLECULES, ATOMIC, AND MOLECULAR WEIGHT. CHEMICAL FORMULA. SYMBOLIC EQUATIONS. WE have jnst established experimentally that the combination by vohime of hydrogen and oxygen remains invariably the same, whether large or small volumes of the two gases enter into chemical combination, that the combining ratio of two volumes of hydrogen to one volume of oxygen gas remains in fact constant, and that the combining proportion by weight must, for the same reason, be like- wise constant, viz., as 2 to 16. We can conceive, moreover, that chemical combination does take place between minutely small proportions by volume of the gaseous bodies hydrogen and oxygen between quantities far beyond the reach of experiment and yet be convinced that all such combina- tions, even between the smallest imaginary gaseous particles of these elementary bodies, must take place in a like ratio of two volumes of the one to one volume of the other, and that the water so formed must possess properties perfectly identical with those observed in the water resulting from the combination of large volumes of hydro- gen and oxygen. It can be proved experimentally also that when a mixture, containing an excess of either element, is exploded in a eudiometer, chemical combination takes place only so far as to satisfy the requirements of this law of definite proportions, viz., between two volumes of hydrogen and one volume of oxygen ; and the portion of the element that happens to be in excess of this ratio, will remain in a free or an uncombined state mixed with the aqueous vapour. The combining proportions remain constant. The composition of water by weight and by volume is capable of being demonstrated by the two methods usually pursued in chemical investigations : viz., by the analytical* method, for we can break up water (comp. Experiment 36)^ into its constituent parts ; and by the synthetical^ method, for we are able to obtain water by the direct union of the two gases hydrogen and oxygen in the eudiometer tube. We have learnt to destroy water and build it up again. The means at our disposal for proving the chemical composition of water * From dvdXvertg, a loosening. f From avvOtyig, a putting together. 38 ATOMIC THEORY. are in fact more ample than those we possess for demonstrating the constitution of most other bodies. We can break up bodies readily enough into their constituent elements, but are sometimes unable to build them up again. If water, then, results- from the (jhemical combination of smallest particles of two kinds of gaseous elementary matter in immutably constant proportions, it may legitimately be conceived, that chemical combination always takes place between such smallest particles of matter, and that every process of chemical combination between large or small bulks or volumes of gaseous matter is, in fact, merely a repetition of a process of combination between smallest possible gaseous particles or volumes ; also, that chemical bodies generally consist of a number of smallest particles of matter, capable of entering into combination with smallest particles of other kinds of elementary matter. We have no conception what these smallest particles are, nor do we know what is their size, shape, etc. Matter itself being as yet unknown to us, need we wonder that the very existence, size, shape, etc., of the smallest particles of matter should not be capable of experimental demonstration ? Where experiment fails to throw light upon the absolute nature of the constant chemical combining proportions, and can at best only supply us with relative data, hypothesis steps in. Dalton assigned to the smallest particles of matter, between which chemical action takes place, finite proportions, and called them atoms;* assuming them to consist of the smallest particles of elementary matter which are capable of existing in chemical combi- nation. According to this theory, known as the atomic theory, all elementary matter consists of atoms which, on entering into combi- nation with other atoms of similar or dissimilar elementary matter, form molecules, i.e., little masses, from moles, a mass. A molecule of matter is the smallest quantity of a substance elementary or compound which is capable of existing in the free state. The weight of hydrogen which combines with or is expelled from other gaseous, liquid or solid elementary matter, being relatively smaller than that of any other elementary body known to us, has, on this account, been adopted by chemists as a convenient unit or standard for determining the relative combining weights of ele- mentary bodies. The smallest proportion by weight in which an element enters into or is expelled from a chemical compound the smallest weight of hydrogen so entering or leaving a chemical com- pound being chosen as unity constitutes the relative combining weight of such element. The observation f that the weight of an element in the form of gas or vapour, under like conditions of temperature and atmospheric pressure, occupies the some volume as one part by weight of hydrogen, corroborated the relative combin- * From aro/ioe, indivisible. t Other considerations have guided chemists in the determination of atomic weights upon which we cannot, however, touch, as we lack as yet the necessary experimental data. ATOMIC THEORY. 39 ing weight. These proportional numbers are called atomic weights. They are purely arbitrary numbers. The atom weight of any other element might have been chosen as the standard in fact, oxygen at one time constituted the standard and had the combining weight 100 assigned to it without in the least disturbing the law of constant combining proportions. By making the atomic weights of other elements the standard of comparison, as many series of atomic weights might be obtained as there are elements; and yet all would satisfy the requirements of the atomic theory, since they would all express correctly the relative combining weights of elemen- tary bodies. In water, we have already seen, there are two parts by weight of hydrogen or as we must now call it, two atom weights combined with 16 parts by weight or one atom weight of oxygen, the gaseous atom oxygen weighing, as we have seen, 16 times heavier than an atom of hydrogen. In like manner we have found by experiment that the metal mercury combines with oxygen in the proportion of 200 to 16, and we have no hesitation to assign to the metal mercury the atomic weight 200 : that is to say, one atom of mercury, weigh- ing 200, by combining with one atom of oxygen, to form 216 parts by weight of mercuric oxide, takes the place of two atoms of hydro- gen in water. Copper, we have seen, combines with oxygen (com- pare Experiment 31). The increase in weight was invariably as 63'5 of copper to 79 '5 of the oxide. The atomic weight of copper must therefore be 63' 5 ; i.e., one atom of the element copper, weigh- ing 63' 5, entered into combination with 16 parts by weight of oxygen and replaced two atoms of hydrogen in water. It is obvious that we should have no difficulty in fixing the atom weight of copper if this elementary body could be obtained like hydrogen in the gaseous condition. We should simply have to determine the specific gravity of a given volume, say one litre of gaseous copper, and divide the weight of such volume by the weight of an equal volume of hydrogen. We should next have to double the number so obtained, because the atom copper takes the place of no less than two atoms of hydrogen. We can conceive, however, that the oxygen gas which existed in a solid condition in combination with the metal copper, and which was removed in Experiment 3 L by the action of the gaseous hydrogen in the form of water, leaving behind solid metallic copper, was attacked by one hydrogen atom after another, and that for every two atoms of hydrogen, with which an atom of oxygen combined, one atom or 63 '5 parts by weight of copper were set free, so as to leave for every 79 '5 parts by weight of cupric oxide which were acted upon, 63 '5 parts by weight of metallic copper, and 18 parts by weight of water. If, then, combination between smallest particles by weight of oxygen and hydrogen can be conceived, it is equally conceivable that smallest particles (or atoms) of the solid body copper were combined with smallest particles (or atoms) of oxygen, and that the binary com- pound cupric oxide consisted likewise of smallest particles (or atoms) of copper and oxygen, combined in immutably constant proportions by weight. 40 TABLE OF ELEMENTS. Now, in anticipation of experimental confirmation, we may say that the same holds good for other elements. The atomic weights were found to differ for every element, and had to be determined in every single case by experiment. Such quantitative experiments are among the most difficult and delicate chemical operations ; let it suffice, then, to remark that the law of combina- tion according to constant proportions by weight and by volume, has been established experimentally with the utmost precision, and that we shall have frequent opportunity, as we enlarge our knowledge of chemical compounds, to satisfy ourselves of its perfect consistency. The symbols which have hitherto merely represented the indi- vidual elements gain thus in interest, since they not only recall the name of the element, but indicate at the same time one atom of such element, together with its particular combining weight and, with few exceptions, its combining volume. The following tables give the names, symbols, and atomic weights of the 86 most important elements : NON-METALLIC ELEMENTS (Metalloids). o 16 N 14 Su.lpb.ur s 32 P 31 Chlorine Cl 35-5 C 12 Bromine Br 80 B 11 I 127 Silicon i Si 28'5 Fluorine F 19 H 1 METALLIC ELEMENTS. Ught Metals: Potassium K 39 Heavy* Metals: Cr 52-5 Na 23 Iron Fe 56 Zinc Zn 65 Mff 24 Manganese ...... Mn 55 HS Cobalt Co 58-8 Barium Ba 137 Nickel Ni 58-8 Sr 87-5 Calcium Ca 40 Tin Sn 118 Gold Au 1967 AlvnrPviiuTn .... , . Al 27-5 Pt 197-4 Pb 207 Hff 200 Silver Aff 108 cS 63'5 Cd 112 Bi 208 As 75 Sb 122 * The metals which possess a higher specific gravity than 5, and which are not acted upon at the ordinary temperature, by the oxygen of the air, are called heavy metals. VOLUMETRICAL COMPOSITION OF STEAM. 41 Combination by volume, we have seen, takes place in accordance with the law of constant combining proportions by weight ; i.e., two volumes of hydrogen will invariably combine with one volume of oxygen to form water (steam). What volume, however, does the steam so formed occupy? This question can only be answered experimentally. In order to measure the volume of steam left in the eudiometer- tube (Experiment 37), hydrogen and oxygen gases must be exploded at a temperature at which the steam produced cannot condense. Dr. Hofmann has devised an apparatus* which accomplishes this in a very elegant manner. Experiment 39. A mixture of two volumes of hydrogen and one volume of oxygen is introduced into a U-tube A (Fig. 33), the eudiometer-tube is, how- FlG. 33. VOLUMETRICAL COMPOSITION OF STEAM (HOFMANN). ever, surrounded by a jacket consisting of a wider glass tube, B, fixed over it air- tight by means of corks. The vapour of amylic alcohol, a liquid boiling at 132 C., is made to pass from the flask through the intervening space, and out at b, d, to be condensed in the worm D. The gaseous mixture acquires thus rapidly a temperature of 132 C. It is then exploded in the usual manner. The two gases combine and form water, which remains, however, as steam, and is found when the pressure in the two limbs of the apparatus is equalized, to occupy only two-thirds of the volume which the mixture of hydrogen and oxygen occupied before explosion. Consequently three volumes of gas contract into two volumes. * Modern Chemistry, page 53. 42 MOLECULAR VOLUMES. A molecule of steam occupying two volumes is, therefore, made up of two volumes of hydrogen and one volume of oxygen, and the weight of one volume of steam must be the weight of one volume of hydrogen and half a volume of oxygen, or 1 + 8 = 9. The specific gravity of steam is therefore 9 ; i.e.^ one litre of steam is nine times as heavy as one litre of hydrogen gas the unit of comparison adopted for gas volumes and its actual weight will be found by multiplying the weight* of a litre of hydrogen "0896 grm. by 9 : 0896 x 9 = -8064 grm. A similar contraction of volume frequently takes place, when other gaseous mixtures combine chemically ; the resulting gaseous volumes are (with a few exceptions) two-volume vapours. Compound bodies can have no atom volume, they possess only molecular volumes. Hence if we wish to compare gaseous elements and compounds with each other, we have to adopt molecular weights, both for elements and compounds, as the measure of the combining quantities. Thus, in order to compare the volume of the element hydrogen with the gaseous compound body, steam, we have to com- pare the molecular volume of hydrogen with the molecular volume of steam and Other reasons, also, to which we cannot refer here, render it desirable that hydrogen, when regarded in relation to other gaseous bodies, should be expressed as the molecule H H, or H 2 , and not as H, the atom. The same applies to other gaseous elements. Since the volume of a gas varies with the pressure of the atmosphere and the temperature, these molecular gas volumes would necessarily be of variable dimensions, a conception which runs counter to the idea we have formed of the constitution of atoms and molecules. All gases expand, however, under the influence of heat in the same ratio. For every degree of the centigrade thermometer scale above C., they expand '3665 per cent., or, less accurately, ^-^-3 part of their bulk at 0. The average weight of the atmosphere at the level of the sea is that of a column of mercury 760 millimetrest high. Now, according to the law of Boyle and Marriotte, the volume of a gas is inversely, and its density directly, as the pressure which it sustains if the temperature remains constant. We have, therefore, no diffi- culty in reducing gases to the standard agreed upon by chemists, viz., a temperature of C. and 760 mm. atmospheric pressure, at whatever temperature or barometrical pressure they may have been measured. * Dr. Hofmann assigned the name crith (from KpiOrj, a barleycorn) to the weight of 1 litre of hydrogen, '0896 grm. at C., and 760 mm. barometrical pressure. t The student should make himself familiar with French weights and measures. (See Tables in Appendix.) MULTIPLE PROPORTIONS. 43 EXAMPLE. A gas volume, say 100 cubic centimetres, was measured when the temperature of the gas was 15 C., and the atmospheric pressure 770 mm. What volume will the gas occupy at C. and 760 mm. pressure ? Correction for temperature 1 cc. at expands into 1 + (15 x -003665) at 15 C. 1-054975 : 1 : : 100 : x x = 94*7889 cc. Correction for pressure 760 : 770 : : 94*7889 : x. Ans. = 96'0360 cc. Multiple Proportions. If the conception which, we have ac- quired of atoms be correct, it follows of necessity that only whole or undivided atoms can combine with each other. There is no reason, however, why several atoms of one element should not be capable of entering into combination with one or several atoms of another element to form a new compound. Such compounds can be represented symbolically by writing the symbols of the com- ponent elements side by side, indicating the number of atoms by placing a small figure after the symbol to be multiplied. When two or more elements combine in single or multiple proportions, the symbolic expression of such combination constitutes a chemical formula. A figure placed on the left of the formula or group of elements multiplies every following element, or the sum of all the component parts of the chemical formula. The sign + is employed to indicate the addition to, the sign the removal or subtraction of one elementary or compound body from, another elementary or compound body. The sign = should be interpreted by furnishes, rather than by the arithmetical meaning equal to. Thus 2 atoms of hydrogen, plus 1 atom of oxygen, furnishing water, are expressed symbolically by the equation H 2 + O = OH 2 . With the experimental data which are at present at our com- mand, we must content ourselves with merely stating that sulphur and oxygen combine in the proportion of one atom of sulphur to two atoms of oxygen to form sulphurous anhydride, SO 2 (Experi- ment 22). The change is expressed by the chemical equation: S + O 2 = S0 2 . Two atoms of phosphorus unite with five atoms of oxygen to form phosphoric anhydride, P 2 5 (Experiment 23), equation : P 2 + O 5 = Pz0 5 ; carbon with two atoms of oxygen to form carbonic anhydride, C0 3 (Experiment 24), equation: :C + 2 = CO 2 , and we shall hereafter have to consider many more instances of combination in multiple proportions of a similar nature. We shall also shortly learn that sulphur can combine with three atoms of oxygen, and carbon with one atom as well as with two, that in fact several combinations are possible between two elements, without prejudice to the law of constant combining proportions by weight. There exist scarcely any chemical elements between which at least two combinations could not take place, whilst there are many elements which can combine with others in three, four, five, and more proportions. As the number of atoms accumulates in a com- 44 MULTIPLE PROPORTIONS. pound, its molecular structure becomes more and more complex, but the combining proportions by weight and by volume stand in a simple ratio to one another, and will be invariably multiples of the simpler combining proportions. Summary. Law Of Constant Combining Proportions. All elements combine according to constant proportions ~by weight. The numbers which express the respective weights of the elements so com- bining are proportional numbers. The unit of comparison accepted by chemists is the weight of hydrogen, on account of its being less than that of any other element. The smallest proportion by weight in which an element enters into or is expelled from a chemical compound constitutes its atomic weight, the weight of hydrogen being taken as unity. An atom is the smallest particle of matter capable of entering into, or existing in a state of chemical combination. A molecule is the smallest particle of matter capable of existing in the free state. A molecule consists, except in a few cases, of at least two atoms. The atoms of each kind of isolated elementary matter exist, with few exceptions, in combination with each other or are associated in pairs, and constitute then an elementary molecule. The molecular weight of a compound is, with few exceptions, identical with its atomic weight. The molecular volume of a compound equals, with very few excep- tions, the molecular volume of hydrogen at the same temperature and pressure. Hence the laiv : Equal volumes of all gases and vapours contain at the same temperature and pressure an equal number of molecules, and the molecules of all compounds in the gaseous or vaporous condi- tion, no matter how great may be the aggregate volume of their con- stituents, occupy, with very few exceptions, one uniform, volume, when compared at the same temperature and pressure, viz., that of two volumes', or one molecule of hydrogen. Law of Multiple Proportions. When two elements combine with each other in more than one proportion, the quantities by weight of the one element, which combine with a constant quantity of the other, are invariably integer multiples of its smallest combining quantity. COMBUSTION OF HYDROGEN IN OXYGEN. 45 CHAPTER VII. WATER, METALLIC AND NON-METALLIC OXIDES. ACIDS. ALKALIES. SALTS. BASIC OXIDES. WATER plays a most important part in nature. Its great importance was recognised long before its chemical composition was under- stood, for it was one of the four elements of which, before the dawn of modern chemistry, matter was supposed to consist. Water covers the greater part of our globe ; it forms part of most mineral, vegetable, and animal bodies, and is, like air, absolutely necessary to vegetable and animal growth. Small quantities of pure water may be prepared synthetically by the direct combination of hydrogen and oxygen (comp. also Experi- ments 6, 28, 37, 39). Experiment 4O. Introduce a jet of burning hydrogen into a bell-jar sup- plied with oxygen in the manner shown in Fig. 34. Both gases should be carefully dried, and the glass jar kept cool by means of a damp cloth. In a short time the inside of the jar becomes overcast with watery-vapour which condenses and runs down in drops, the wat, r accumulating in the lower vessel. In this manner a quan- tity of water may be procured sufficient to study its properties. Larger quantities of pure water are usually obtained by a process of distillation,* i.e., by condensing steam by means of a Liebig's glass con- FlG 34.- COMBUSTION OF HYDROGEN IN OXYGEN. FIG. 35. DISTILLATION OF WATER. * This chemical operation effects the separation of a volatile from a less 46 DISTILLATION OF WATER. denser (Fig. 35), or a tin worm (lead is perceptibly dissolved by pure water). Distilled water thus obtained is a limpid colourless liquid, without odour or taste. It has no action upon test papers, and can be volatilised without leaving any residue. Water evaporates at all temperatures, and passes off into^the air as an invisible vapour (steam). The evaporation is more: or less active all over the surface of our globe, so that the atmosphere is everywhere charged with aqueous vapour. The quantity of moisture in the air varies, how- ever, according to the natural conditions which favour or retard the evaporation of the water. The vapour of water being lighter than air (the sp. gr. of steam is only '622 as compared with air), rises till it reaches the upper and colder regions of the atmosphere, where it is condensed into masses of clouds which float on the air, till they become too heavy to be supported any longer, when the water is returned to the earth in the form of dew, mist, rain, snow, hail, etc., etc. A natural process of distillation is thus constantly going 011 all over the globe, and rain water stands in point of purity next to dis- tilled water. It contains, however, the gases of which our atmo- sphere is composed, dissolved in it, usually to the extent of 3 to 5 per cent, of its own bulk, besides traces of ammonic nitrate and nitrite, and particles of solid suspended matter washed out of the air. The presence of air in rain water is necessary for aquatic vege- table, and animal life. Rain water exerts a certain solvent action on the surface matter of our earth, varying in degree according to the nature of the soluble matter with which it comes in contact. Granite, sandstone, slate, and other hard rocks are but little acted upon. Rain water falling upon mountainous formations mainly composed of these rocks, runs off the surface almost pure, generally holding in solution only a little organic and mineral or saline matter. Such waters we meet with for instance in the Welsh and Cumber- land lakes, and in Loch Katrine, from which Glasgow draws its water supply. The waters of lakes and rivers contain, as a rule, less mineral matter in solution than spring waters. Rain sinks into the earth through porous mineral strata of various composition, upon all . of which it exerts more or less solvent action, and when the collected waters issue again in natural or artificial springs, they are charged with varying quantities of mineral (saline) substances. Waters coming from the chalk formation contain chiefly chalk or calcic carbonate, as well as magnesic carbonate in solution. These mineral bodies are held in solution by gaseous carbonic anhydride. Strata of gypsum yield gypsum or calcic sulphate to the water ; others are acted upon in an analogous manner. The amount of solid matter which different spring waters hold in solution varies considerably. A water is considered no longer volatile or fixed body (in the case of natural waters from the mineral or saline constituents which are left behind). The distilling apparatus, flask, retort, etc., must be provided with a condenser only, if the substance becomes vaporized at a low temperature. The product of the distillation is called distillate, and is usually received in a flask or other vessel, called a receiver. NATURAL WATERS. 47 wholesome if it contain more than 1 grm. of mineral matter per litre (=70 grains per gallon) in solution. Good potable waters should never contain more than a few grains of saline matter per gallon, and should be all but free from readily decomposable organic matter. River and spring waters often contain large quantities of organic matter, if the water which they receive runs over manured and well-cultivated land, or if, from gross ignorance and culpable neglect, sewage is allowed to flow into them. Nature has happily provided running streams with the power of destroying soluble organic matter a power which is due to the oxygen of the air dissolved in the water. The organic matter is rapidly oxidized, and is converted into harmless products of oxidation, viz., water, car- bonic, nitrous, and nitric acids (nitrites and nitrates). When natural waters are charged with still larger quantities of mineral substances, such as common salt or sodic chloride, sodic sulphate (Glauber's salt e.g., Cheltenham waters), magnesic chlo- ride or sulphate (Epsom salts), calcic chloride and others, they are termed mineral waters. Waters which hold iron salts in solution (carbonate or chloride) are called chalybeate waters. They have an inky taste, and on exposure to the air deposit iron rust. Others are called mineral waters, because they hold large quantities of gaseous matters in solution, such as the well-known acidulous Seltzer water, which is strongly charged with carbonic anhydride, a gas which causes the water to effervesce strongly. Sulphurous or hepatic waters, such as the water of Harrogate, exhibit a strong odour of rotten eggs (sulphuretted hydrogen) . Inland lakes which have no outlet are usually found charged with very large quantities of saline matter. The water of the Dead Sea contains as much as 12,600 grains, and that of the Great Salt Lake 22,000 grains per gallon. Some springs such as the so-called Geysers of Iceland and California, issue boiling hot from the earth, and deposit silica on cooling. The density of all such waters is considerably greater than that of pure water. The chemical composition of water has already been established both synthetically and analytically. It is a binary compound, an oxide of hydrogen. Other elementary bodies, we have seen, com- bine likewise with oxygen to form oxides bodies which differ, how- ever, very much from each other in their properties. The metals sodium or potassium when burning in dry oxygen form the binary compounds potassa or oxide of potassium, and soda or oxide of sodium. Both these oxides, together with the oxides of a few other metals, viz., barium, strontium, calcium, and magnesium, combine more or less eagerly with water. Experiment 41. Pass a slow current of air over fused calcic chloride con- tained in a U-tube, and then over a piece of sodium placed in a bulb-tube (comp. Fig. 26), and apply a gentle heat till the sodium bursts into flame. Remove now the lamp, as the combustion goes on without the application of external heat. When it has ceased, the sodium will be found to have been converted into a white powder, which attracts moisture very rapidly from the air. On moistening it with a little water it gets very hot, and is rapidly dissolved to a colourless liquid, which, when concentrated enough, corrodes the skin, whilst in a 48 OXIDES, METALLIC AND NON-METALLIC. dilute state it produces a peculiar soapy feeling when rubbed between the fingers. The liquid has a soapy disagreeable taste and a peculiar smell. A minute di*op of the liquid turns a red litmus solution instantaneously blue, i.e., it restores the natural blue colour of a litmus solution reddened with a drop of very dilute sul- phuric acid. This is due to what is called the alkaline property of soda, a property pertaining also to various other metallic oxides, especially to potassa. These oxides are called alkalies, from Kali, the name given by the old alchemists to the ashes of plants (potashes). Hence also the name Kalium, used by German chemists instead of potassium, and Kali in place of the oxide or potassa. Experiment 42. Burn a little magnesium wire and place the oxide of magnesium, or magnesia, on moistened red litmus-paper, or on yeUow turmeric- paper. It is sufficiently soluble to change the portion of the litmus-paper with which it comes in contact to a blue colour, or that of the turmeric-paper to a red- dish brown. MgO is soluble only in about 50,000 parts of water. Experiment 43. Aluminium, except in the form of very thin leaf, be- comes only superficially oxidized when heated in air or oxygen. On placing some aluminium-leaf in a jar containing oxygen, and touching the metallic leaf with a glowing splinter of wood, the aluminium burns with a sudden flash of dazzling white light. Put some of the white oxide formed on moistened litmus-paper. The paper remains unacted upon, showing that the oxide of aluminium, or alumina, is not soluble in water. No action is observed if some other metallic oxides, e.g., the oxides of iron, zinc, copper, be placed on litmus-paper. There are only comparatively few metallic oxides which are soluble in water, the greater number being insoluble ; they neither corrode the skin nor exert any perceptible action upon vegetable colouring matters, and yet a remarkable analogy is perceptible in their chemical composition and deportment. There is another class of oxides, viz., most of the oxides of the non-metallic elements, which differ greatly in properties from, and are chemically opposed to the oxides which the metals form. We have already seen that the oxides of the elements sulphur and phos- phorus combine freely with oxygen (comp. Exp. 22 and 23), and form oxides which are readily soluble in water, the solution possess- ing a sour or acid taste. We meet with acid bodies in fruits (e.g., red currants, lemons, apples, &c.), in wine, in sour beer, etc. The acid taste of these substances is owing to a few so-called organic acids, such as citric, tartaric, malic, and acetic acid, or vinegar. Mineral substances, such as phosphorus and sulphur, by combining with oxygen and water, form acid bodies which are readily distinguish- able from the acids just mentioned by their intensely sour and burning taste. They instantaneously tarn blue litmus solution red. Other non-metallic elements, with the sole exception of fluorine, are likewise capa- ble of forming with oxygen compounds which are for the most part soluble in water, and constitute, when so dissolved, powerful FIG. 36. acids. BASIC OXIDES. 49 Experiment 44. Add slowly and cautiously, by means of a pipette, (Fig. 36) some dilute sulphuric acid to an alkaline liquid a dilute solution of soda tinted blue with a solution of litmus till a point is reached when the blue colour disappears and the liquid becomes reel. One drop of the alkaline liquid restores the blue colour, or one drop of the acid liquid turns the blue solution red. There must, however, be a point at which the two fluids may be so mixed as to completely neutralize each other, i.e., at which the solution neither turns blue litmus-paper red, nor red litmus-paper blue. This neutral point can be readily- ascertained. The compound produced by the action of an acid upon an alkali constitutes what is usually called a salt* The solid oxides of zinc, iron, copper, when treated with an acid liquid, such as a solution of sulphuric acid, dissolve readily ; a point is reached, however, at which no more oxide dissolves, when, in fact, the acid body has 'be- come neutralized by the metallic oxide, and when a single drop of an alkaline liquid, e.g., soda, will turn the solution blue. It is evident, then, that an acid may be neutralized by the alkaline solu- tion of a metallic oxide, as well as by a solid oxide, devoid of any reaction and insoluble in water, and salts in general may be formed by the mutual action of an acid upon certain metallic oxides termed bases.'f Such bases are for the most part the mono- or protoxides, and in a few cases the suboxides of the metals, also termed basic or salifiable oxides, having the formula R 2 or HO, a few only being combined in the proportion of two of the metal to three of oxygen, forming the so-called sesquioxides of the general formula, R 2 O 3 (B standing for metal). The terminals ous and ic are now generally used, when a metal forms two basic oxides, containing different proportions of oxygen. Copper, e.g., forms two basic oxides, CuO, or cupric, and Cu 2 0, or cuprous oxide. Iron forms two well-defined salifiable oxides, FeO, or ferrous, and Fe 2 3 , or ferric oxide, &c. Some metals are capable of forming other oxides, besides the one or two so-called basic oxides already enumerated. Lead and manganese, e.g., form oxides of the formula RO 2 , viz., manganic dioxide, or black oxide of manganese, MnO 2 , and plumbic dioxide, PbO 2 , which are usually termed indifferent oxides, because they do not enter into chemical combination with acids without first under- going decomposition into lower oxides of the formula HO. The intermediate oxides of the formula R 2 O 3 are mostly weak bases which frequently play the part of weak acid bodies towards strong bases, or towards a salifiable oxide of the same metal. Higher metallic oxides of the formula RO 3 , such as Mn0 3 , Cr0 3 , etc., act like true acids ; they combine with bases and form salts. The following is a list of some of the more important basic or salifiable oxides. The asterisk indicates the oxides which occur more or less abundantly in nature. Most metallic oxides are insoluble in water. * A definition of the term salt will be given hereafter. f As most of the bases insoluble in water form, with acids, salts which are acid to test-paper, it is frequently advisable, in preparing such salts, to use slight excess of the insoluble base, and to filter off before crystallising the salt. E 50 TABLE OF BASIC METALLIC OXIDES. TABLE OF THE MOST IMPORTANT BASIC (OR SALIFIABLE) METALLIC OXIDES. Lower, or ous Oxides. Higher, or ic Oxides. [CrO, chromous oxide.] FeO, ferrous oxide. MnO, manganous oxide. CoO, cobaltous oxide. NiO, nickelous oxide. Cu 2 O,* cuprous oxide. (Red copper ore, or ruby ore.) HgoO, mercurous oxide. Bi 2 O 3 ,* bismuthous oxide. (Bismuth ochre.) [Sb 2 O 3) * antimonious oxide.] ( White antimony.) SnO, stannous oxide. PtO, platinous oxide. OK 2 , potassaf (potassic oxide). ONa 2 , soda (eodic oxide). BaO, baryta (baric oxide). SrO, strontia (strontic oxide). CaO, lime (calcic oxide). MgO,* magnesia (magnesic oxide). (Periclase.) A1 2 O 3 ,* alumina (aluminic oxide). Cr^Os,* chromic oxide. (In chrome iron ore.) Fe 2 O 3> * ferric oxide. (Red hcematite.) Mn 2 O 3 ,* manganic oxide. (Braunite.) [Co 2 O 3 , cobaltic oxide.] [M 2 O 3 , nickelic oxide.] ZnO,* zincic oxide. (Red zinc ore.) CdO, cadmic oxide. PbO, plumbic oxide. CuO, cupric oxide. HgO, mercuric oxide. SnO 2 ,* stannic oxide. (Tinstone.) PtO 2 , platinic oxide. [Au 2 O 3 , auric oxide.] OAg 2 , argentic oxide. Summary' Natural waters are more or less impure. They con- tain certain gases, together with soluble organic and 'mineral matter. Rain water is the purest natural water. Waters containing large quantities of gaseous or mineral matter are called mineral waters (acidulous, chalybeate, hepatic waters^). Pure water can be obtained artificially by the direct combination of hydrogen and oxygen, or by a process of distillation (vaporisation) and condensation. Salts are formed in general by the mutual action of an acid upon certain metallic oxides, called basic or saliflable oxides. f The old special names for some of the more important oxides (at one time looked upon as elementary bodies) are still retained by chemists. SULPHUR. ITS OCCURRENCE. 51 CHAPTER VIII. SULPHUR Its Occurrence and Properties. ALLOTROPIC STATE OF MATTER. DIMORPHISM. SYNTHESIS OF SULPHUROUS ANHYDRIDE. SULPHURETTED HYDROGEN. METALLIC SULPHIDES. OXYGEN is one of the most widely diffused elements in nature ; it forms a most important constituent of a great portion of inor- ganic or mineral nature, and is likewise of paramount importance in the animal and vegetable economy. We have seen that it combines chemically with other elements often with great energy and that it forms compounds of a well defined chemical character. 'No other element equals oxygen in this respect. Many, espe- cially the metals, possess only a limited combining power, and among the metalloids there are only two, sulphur and chlorine, which, if we merely consider their power of forming well charac- terized inorganic chemical compounds with other elements, are of like importance. Sulphur is at the ordinary temperature a solid body of yellow colour. It occurs in nature more or less pure in the free state, par- ticularly in volcanic regions, e.g., in Sicily and other places. It may be purified by distillation from any mineral non- volatile ingre- dients with which it occurs mechanically mixed. By far the greater quantity of sulphur is, however, found in nature in the combined state, especially with metals (as blende and pyrites). Combined with lead it furnishes the well known mineral galena, with zinc the brown mineral zinc blende, with iron the yellow brassy looking mineral known as iron pyrites. Combined with oxygen and water, it forms an acid, known as sulphuric acid, which is some- times met with in waters from volcanic regions, or which when com- bined with bases forms salts known as sulphates, the most important of which are the sulphates of the metals calcium (gypsum and anhydrite), barium (heavy spar), magnesium (Epsom salts), sodium (Glauber's salt), and others. Several of the soluble sulphates are also found in most springs and river waters. In combination with hydrogen, it occurs in sulphurous or hepatic springs. It enters likewise into the composition of many plants, and forms a constituent of many vegetable and animal substances, such as oil of mustard, of onions, of garlic, white of egg (albumin), muscle, casein, gall, hair, and many others. In commerce it is commonly obtained in the form of flowers of sulphur or roll sulphur (brim- stone).* * Specimens of native sulpliur, of flowers of sulphur, and roll sulphur ; of various metallic sulphides and sulphates should be examined by the student. E 2 PROPERTIES OF SULPHUR. The physical properties of sulphur are of considerable interest. Sulphur is not soluble in water, but can be dissolved to a slight extent in ether, or hot alcohol ; it is, however, readily soluble in oil of turpentine, benzol, or carbonic disulphide, CS 2 a volatile liquid analogous in composition to carbonic, jdioxide, C0 2 . Experiment 45. Introduce some powdered sulphur into carbonic disul- phide, and warm gently by plunging the flask into warm water ; the sulphur dissolves readily (100 parts of CS 2 dissolve 73 of sulphur). Pour out into a warm evaporating dish, and allow the carbonic disulphide to eyaporate spontane- ously. Orthorhonibic-octahedral crystals of sulphur are obtained which arc identical with the sulphur crystals observed in native sulphur. Experiment 46. Heat a few pieces of roll sulphur in a small beaker or crucible imbedded in warm sand on a sand-bath. Without first becoming soft or pasty the sulphur is seen to pass at once from the solid to the liquid state, and to form a clear amber yellow liquid ; the pieces of unmelted sulphur remain at the bottom of the glass vessel, being, unlike ice, heavier than the liquid sul- phur ; or, in other words, sulphur on melting expands and occupies a larger space in the liquid state. Allow the thoroughly liquefied sulphur to cool until a solid crust forms on the surface. Pierce with a glass rod two holes through the crust near the edge on opposite sides, and pour out through one hole the still liquid sulphur, the other hole serving for the admission of air. When the mass is quite cold, remove the solid crust carefully with a knife. A network of long transparent honey-like prismatic needles, will be left behind, as seen in Fig. 37, which belong to a different crystal- lographic system, viz., the monoclinic system. Their specific gravity, 1*98, differs likewise from that of the orthorhombic octahedral crys- tals which have the specific gravity 2*05. The respective fusing points are 120 and 115 C. ,. 37,-pRisMATic SULPHUR This var i et y O f sulphur is insoluble in carbonic CRYSTALS. disulphide. The needle-shaped crystals are slightly elastic at first, but become rapidly brittle and opaque ; they acquire then a somewhat lighter colour, and at the common tem- perature they pass slowly, more rapidly at a higher temperature, back to the first or octahedral variety, and become soluble in car- bonic disulphide. Experiment 4"J. When sulphur is heated in a retort, it passes from the solid to the liquid, and lastly to the gase- ous state. Flowers of sulphur can be heated over boiling water in an open vessel, e.g., a porcelain dish, without melt- ing, it merely agglutinates ; at 111*5 C., however, it melts to a honey-like liquid ; on heating somewhat more strongly (to 250 or 260 C.) the colour changes to red brown, almost black, and the liquid be- comes very viscid, so that the open vessel may be turned upside down without any of the liquid sulphur running out. If sul- FIG. 38. DISTILLATION OF SULPHUR. phur be heated in a retort (Fig. 38), the DIMORPHISM. ALLOTROPISM. 53 same changes will be observed, and if the application of heat be continued longer no further change of colour is seen, but the sulphur becomes less viscid, and begins to sublime, and at about 440 C. it boils and distils. When the liquid sulphur is allowed to drop into water, threads may be obtained of a pure pale amber colour, by regulating the temperature carefully. The strings of distilled sulphur remain for several days quite soft and elastic, but become gradually hard, opaque, and brittle. This third variety of sulphur also called viscid, plastic or amorphous sulphur (from a privative, and popi] form) in distinction from the two crystalline varieties, is insoluble in carbonic disulphide, and passes slowly back into the soluble varieties, rapidly when heated to about 100 C. The change becomes then so sudden, that the temperature rises speedily from 100 C. to 110 C. The explanation of these different crystalline forms may be sought in the different states of tension produced by the different temperatures at which the sulphur molecules rearrange themselves, when passing from the liquid to the solid state. Bodies which possess the power of crystallising under varying conditions in forms belonging to two different crystallographic systems, are called dimorphous bodies, and the property itself is called dimor- phism. The vapour of sulphur is brownish yellow. Heated to about 500 C., it is 6'654 times heavier than air, or 96 times heavier than hydrogen. The specific gravity of the sulphur vapour does, how- ever, not remain constant, but decreases at higher temperatures, till, at 860 C., it is only 2 '21 times heavier than air, or 32 times heavier than hydrogen. After this (between 860 and 1040 C.) it remains constant. Two rare elementary bodies, Selenium and Tellurium, which resemble sulphur in most of their properties, show at low tempera- tures similarly abnormal vapour densities. The explanation of this is that the vapours of many bodies behave like true gases only at temperatures far higher than the temperature at which they pass from the liquid to the gaseous condition. Octahedral, prismatic and plastic or amorphous sulphur, are merely three modifications of one and the same element. A fourth may be obtained by dissolving the elastic strings of viscid sulphur, after they have again become hard, in carbonic disulphide, when a grey insoluble amorphous powder is left. The property which elementary matter, such as sulphur and a few other elements exhibit, of assuming forms physically differing from each other in crystalline structure, specific gravity, fusibility and solubility, is termed the allotropic state of matter. Ozone, e.g., is viewed as the allotropic form of oxygen. The following table shows the allotropic modifications of sulphur : Solubility in carbonic Sp. gr. Fusing points. disulphide. 1. Octahedral .......... 2'05 115 C. Soluble. -r, . , nr . n 2. Prismatic .......... 1'98 I Insoluble before its ( transformation. 3. Plastic ........... 1-95 J *" Averted into lnsoluble . 4. Amorphous powder... 1-96J ' 54 VOLUME COMBINATION OF SULPHUR WITH OXYGEN. Heated in air, or in oxygen gas, sulphur bursts into flame at about 270 C., and burns with a pale blue, slightly luminous flame, forming sulphurous anhydride (comp. Exp. 22), which is readily recognised by its odour. One atom of sulphur combines inva- riably with two atoms of oxygen. TJhe change may be expressed symbolically S + O a = S0 3J i.e., 32 by weight of sulphur combine with 2 X 16 = 32 by weight of oxygen to form 64 by weight of sulphurous anhydride. It may be instructive to prove synthetically by a simple experiment the volume composition of sulphurous anhydride. Experiment 48. Fill a glass flask, best a litre flask (Fig. 39), over mercury, with dry oxygen gas. Introduce a piece of sulphur, placed on a small iron cup fastened to an iron wire, and ignite the sulphur within the flask by means of a concave mirror and sunlight. The sulphur can only burn at the expense of the oxygen. It forms, as we already know, sulphurous anhydride. The bulk or volume in the flask remained the same no expansion or contraction took place. FIG. 39. VOLDMETRICAL COMPOSITION OF SO;;. This proves that sulphurous anhydride con- tains its own bulk of oxygen. Now the weight of sulphurous anhydride gas compared with atmospheric air has been carefully determined. It is 2 '247, air being 1. If we deduct, therefore, from the weight of one volume of the gas (represented by the number which expresses its specific gravity compared with air, viz., 2'247), the weight of its own bulk of oxygen (density 1*106), we must obyiously get the weight of the sulphur contained in the same volume of sulphurous anhydride Weight of one volume of sulphurous anhydride 2 '247 oxygen T106 1-141 A figure which pretty closely expresses the weight of & volume of sulphur vapour (the specific gravity of gaseous sulphur being 2*21 2'21, as compared with air), viz., = 1'105. 2 Half a volume of sulphur vapour cannot, however, enter into chemical combination, any more than half atoms can exist ; and we get, therefore, by doubling the volume proportions 1 volume of sulphur vapour and 2 volumes of oxygen gas ; which we may express thus S 2 COMPOUNDS OF SULPHUR WITH METALS. SULPHIDES. 55 The molecular weight of S0 2 is 32 + 16 x 2 = 64 and 1 litre mast weigh 32 times as heavy as 1 litre of hydrogen or 32 X '0896 grm. = 2-8672 grins. Nearly all metals are capable of uniting directly with sulphur, when heated with it, or when the vapour of sulphur is passed over the ignited metal. The metal mercury alone combines with sulphur in the cold, on account of its being a liquid at the ordinary temperature. Sulphur forms with Metals Sulphides. Experiment 49. Cu/pric sulphide may be formed by heating together sulphur and copper turnings in a flask (Fig. 40) . The sulphide so obtained is a black hard substance insoluble in water Cu + S = CuS. Native copper sulphides are found in Cornwall and other places. Experiment SO. Heat in a test-tube (Fig. 41) a little sulphur till the sulphur vapour fills the greater part of the tube, then introduce finely-granulated FlG. 40. PBEPARATION OF CUPKIC FlQ. 41. PREPARATION OF STANNIC SULPHIDE. SULPHIDE. lead or tin, in small quantities at a time, and heat it still more. Combination between the metal and the sulphur takes place. A sulphide of lead or tin is formed according to the equations : Pb + S = PbS Sn + S 2 = SnS 2 , the plumbic sulphide being left as a non-crystalline, dull-black mass j the stannous sulphide as a greyish-black mass. Lead is found in nature chiefly in combination with sulphur as Galena, PbS. Tin occurs most frequently as oxide, but likewise as sulphide (together with copper, iron, and zinc). Experiment 51. A thin plate of wrought-iron (not cast-iron) is heated over a Bunsen lamp to white heat, and the heated part rubbed over with a piece 56 COMPOUNDS OF SULPHUR WITH NON-METALS. of roll-sulphur. Combination between the metal and the sulphur takes place. A ferrous sulphide peels off, and the plate appears as if burnt through. The sulphide is black and insoluble in water Fe + S = FeS. The natural compounds of sulphur and iron, such as iron pyrites, are of considerable interest. Experiment 52. When iron pyrites, FeS 2 , is heated in a test-tube or a piece of combustion-tube closed at one end, out of contact with the air, it parts with one-third of its sulphur. The change is expressed by the equation 3FeS 2 = S 2 + Fe 3 S 4 . Tl^e sulphur sublimes and condenses in the upper part of the test-tube or ignition- tube, in orange-coloured drops, which solidify on cooling into yellow masses of solid sulphur. Experiment 53. One part by weight of sulphur and about six parts by weight of mercury (i.e., atomic weights of sulphur = 32, and of mercury = 200) are rubbed together in a mortar. The little globules of mercury gradually dis- appear and a black powder is obtained. A partial combination takes place when the mercury and sulphur are rubbed together for several hours. As rubbing alone cannot, however, unite mercury and sulphur thoroughly, the black mass is cautiously heated in a porcelain dish or crucible, when further chemical combina- tion takes place with slight explosions, a clear instance of the difference between mere mechanical mixture and chemical combination. Mercury and sulphur form mercuric sulphide. A similar reaction takes place when sulphur is melted, and five to six times its weight of mercury gradually stirred into it, till 5 the. sulphur begins to get viscid. Combination takes place accompanied by a flash of light and a slight report, and not unf requently some of the mixture is violently ejected from the crucible. The mass which is left is dark-red. When cold it may be pulverized, and on mixing it with a little sulphur and heating in a flask with a long neck loosely closed with a conical piece of charcoal, the mercuric siilphide sublimes as a fine red powder called cinnabar. Cinnabar is also found as a mineral. It is insoluble in water. Sulphur combines likewise with Metalloids. The compound which it forms when burning in air or oxygen, viz., sulphurous anhydride gas, has already been noticed. Another gaseous compound of sulphur is of great importance, viz., the com- pound which it forms with hydrogen, called sulphuretted hydrogen, or hydric sulphide. These two elements combine directly with each other ; but only under exceptional conditions. Experiment 54. Treat some ferrous sulphide* (or any other sulphide of the same group of metals) with dilute hydrochloric acid or sulphuric acid in a generating apparatus! (Fig. 42), consisting of a tubulated glass cylinder (known * Native iron pyrites (FeS 2 ) cannot be employed, because it is not acted upon by dilute hydrochloric or sulphuric acid. The ferrous sulphide (FeS) is prepared by fusing in a Hessian crucible, heated in a fire, a mixture of 7 parts of iron filings or turnings and 4 parts of sulphur (i.e., atomic weights of iron = 56 and sulphur = 32). t This apparatus may obviously be employed also for producing a constant current of hydrogen, by charging it with granulated zinc. By shutting off the screw-clamp, placed on the delivery -tube, the acid can at any time be forced back again into the doubly tubulated bottle, and the evolution of the gas made to cease almost instantaneously. PREPARATION OF SULPHURETTED HYDROGEN. 57 by the French name eprouvette) which is charged with the ferrous sulphide (in moderate sized lumps) in the manner shown in Fig. 42. A small perforated disk of sheet lead placed just above the narrow part of the cylinder prevents the FlO. 42. PREPARATION OF SULPHURETTED HYDROGEN. sulphide from falling to the bottom. The doubly tubulated bottle on the left hand side is charged with the dilute acid, and on slightly opening the screw clamp which closes the india-rubber tube, as well as the clamp which shuts off the delivery-tube, the acid flows into the lower (empty) part of the eprouvette. As soon as it reaches the ferrous sulphide, a steady current of a colourless gas is evolved, possessing a most foetid odour FeS + 2HC1 = FeCl 2 + SH 2 . Sulphuretted hydrogen may be collected over tepid water, and several cylinders may be filled with the gas, as shown in Fig. 42. Close the cylinders under water with a greased glass plate before removing them from the pneumatic trough, and set them aside for experiment. On removing the glass plate and applying a light to the mouth of the cylinder, the sulphuretted hydrogen gas bursts into flame and burns (where it is in contact with the air) with a fine bluish flame, and partial separation of sulphur, which deposits on the sides of the cylinder. Sul- phuretted hydrogen, like hydrogen, is thus a combustible gas. The hydrogen is burnt or oxidized into water O + H 2 = OH 2 , and the sulphur into sulphurous anhydride s + o 2 = so 2 , the presence of which makes itself rapidly perceptible by its pungent and suffo- cating odour. The combustibility of the gas may likewise be illustrated in a striking manner by burning sulphuretted hydrogen from a jet in the manner illustrated in Experiment 6. The water which condenses on the cold bell-jar will be found strongly acid to the taste and to litmus paper, since the sulphurous anhydride combines with the water, and yields a weak solution of sulphurous acid. By moisten- ing another bell-jar with a few drops of a strong solution of ammonia, and holding it over the jet of burning sulphuretted hydrogen, white clouds are formed, consisting of a compound of sulphurous acid with ammonia. 58 VOLUMETRICAL COMPOSITION OF SULPHURETTED HYDROGEN. Experiment 55. Burn a little sulphur in a glass cylinder, and invert the cylinder containing the sulphurous anhydride, which is formed by the combus- tion of the sulphur in air over another cylinder filled with sulphuretted hydro- gen gas (Fig. 43) ; withdraw the glass-plates ; the two gases diffuse, react, and mutually destroy each other ; the oxygen of the sulphurous anhydride unites with the hy- drogen: of the sulphuretted hydrogen, and sulphur is deposited, thus : 2SH 2 + SO 2 = S 3 + 2OH S . (A secondary reaction takes place giving rise to the formation of a little pentathionic acid.) Experiment 56. Into another cylinder filled with sulphuretted hydrogen introduce a piece of delicate blue litmus -paper, moist- ened with distilled water ; the blue colour changes to red. Sulphuretted hydrogen is a feeble acid, also called hydros ulpliuric acid, and when acting upon bases forms true salts, the sulphides, sometimes called Tiy dr osulp h ates . Experiment 5 1 ?. Moisten some strips of filtering paper with a solution of sugar of lead, and hang up to drain. Plunge a strip of the moist lead-paper thus prepared into a cylinder filled with sulphuretted hydrogen gas. The paper is instantaneously blackened, owing to the formation of a compound of the sulphur with the metal lead, viz., plumbic sulphide, PbS. The presence of sulphuretted hydrogen in crude coal-gas, or in the exhalations from drains, cess-pools, can in this manner readily be demonstrated. When sulphuretted hydrogen is inhaled in somewhat large quan- tities it acts like a poison. Small animals die in an atmosphere con- taining as little as T ^Vo to T yVo ^ this poisonous gas. It is found wherever decomposition of organic compounds containing sulphur takes place, e.g., in sewers. Cold water absorbs from three to four times its volume of this gas ; and a solution of sulphuretted hydrogen in water forms one of the most important reagents in the laboratory. It is, however, rapidly decomposed when left in contact with air, finely divided white sulphur being precipitated. If we examine into the combination by volume which took place between sulphur and hydrogen, we have no difficulty in recognising a resemblance between the constitution of water, OH 2 , and that of sulphuretted hydrogen, SH 2 . The latter gas may in fact be viewed as sulphur water, or water in which the atom (or volume) of oxygen has been replaced by an atom (or volume) of sulphur. FIG. 43. ACTION OF 80s UPON SH 2 . METALLIC SULPHIDES. 59 Its molecular weight is 32 + 2 = 34. One litre of sulphuretted hydrogen compared with the volume unit (one litre of hydrogen) weighs 17 times as much, or 17 X '0896 = T5232 grm. The specific gravity of sulphuretted hydrogen compared with hydrogen is therefore 17, and when compared with air 1'199. The great affinity which metals possess for sulphur enables us to separate most metals from their saline solutions in the form of sulphides. Experiment 58. Dissolve a few crystals of the following well-kuown salts in distilled water (solutions 2 and 3, with the addition of a little ammonia), and pass sulphuretted hydrogen gas through their solutions, using test-tubes or bottles fitted with doubly perforated corks (Fig. 44). FIG. 44. 1. Blue vitriol (or cupric sulphate) 2. White vitriol (or zincic sulphate) 3. Grreen vitriol (or ferrous sulphate) 4. Sugar of lead (or plumbic acetate) 5. Alum 6. Epsom salts . . . . Kesult. a black precipitate, a white precipitate, a black precipitate, a black precipitate, no precipitate, no precipitate. The sulphur of the sulphuretted hydrogen combines instantaneously with the metal, and forms a metallic sulphide (1) Cupric sulphide, CuS ; (2) Zincic sul- phide, ZnS ; (3) Ferrous sulphide, FeS ; (4) Plumbic sulphide, PbS, whilst the metals aluminium in alum, and magnesium in Epsom salts do not possess sufficient affinity for sulphur to form a sulphide in the wet way. Most metallic sulphides (the alkaline sulphides excepted) are either insoluble or with difficulty soluble in water ; and it is obvious, therefore, why a precipitate appeared, as soon as the sulphur of the sulphuretted hydrogen combined with the metals copper, zinc, iron, or lead. The following is a list of some of the more important 'metallic sulphides, the asterisk indicating the sulphides which occur more or less abundantly in nature : 60 TABLE OF METALLIC SULPHIDES. TABLE OF THE MOST IMPORTANT METALLIC SULPHIDES. SK 2 , potassic sulphide. SNa 2 , sodic sulphide. BaS, baric sulphide. SrS, strontic sulphide. CaS, calcic sulphide. FeS, ferrous sulphide. T7 a / ferric sulphide, or 3sfe3 ' t diferric trisulphide. FeS 2 ,* ferric disulphide. (Iron pyrites, martial pyrites.) ZnS,* zincic sulphide. (Zinc blende.) MnS, manganous sulphide. (Manganese blende.) CoS, cobaltous sulphide. Co 2 S 3) * cobaltic sulphide. (Cobalt pyrites.) NiS,* nickelous sulphide. (Capillary pyrites, hair nickel.) NiS 2 , nickelic disulphide. CdS, cadmic sulphide. (Greenockits.) SAg 2 ,* argentic sulphide. (Silver glance.) * SnS, stannous sulphide. ' SnS 2 , stannic sulphide. (Tin pyrites, bell metal ore.) PbS,* plumbic sulphide. (Galena.) Hg 2 S, mercuro us sulphide. HgS,* mercuric sulphide. (Cinnabar.) Cu 2 S,* cuprous sulphide. ( Vitreous copper, or copper glance.) CuS,* cupric sulphide. (Indigo copper, or blue copper.) Bi 2 S 3 , bismuthous sulphide. (Bismuth glance.) Sb 2 S 3 ,* antimonious sulphide. (Antimony glance.) PtS 2 , platinic sulphide. Au 2 S 3 ,* auric sulphide. Solution, precipitation. We have repeatedly seen that bodies may be dissolved in water, forming what is termed a simple solution. The liquid in which the solution is effected is termed a solvent. Water (distilled) is most frequently employed for this purpose ; other solvents, e.g., alcohol, ether, chloroform, etc., are occasionally but rarely employed. A finely- divided substance dissolves more readily than a coarse powder or a crystalline body ; it also, with very few exceptions, dissolves more rapidly and to a greater extent in hot than in cold water. A solid body can be recovered from its solution by evaporation. This may be effected by heating the solution in a porcelain dish over a little copper water-bath (Fig. 45) or over the bare flame, by so regulating the heat as to prevent loss by spurting ; or it may be recovered by modifying or removing the solvent ; NaCl, e.g., which is soluble in water, is precipitated on the addition of concentrated hydrochloric acid ; calcic carbonate dissolved in carbonic acid by the removal of the gaseous solvent on boil- ing ; or, lastly, by the sudden conversion of the liquid into a solid body by the action of another body, induced by greater chemical affinity, one substance remaining in solution as a general rule. The body which is precipitated is termed the precipitate. It generally sinks to the bottom of the glass vessel (test-tube, etc.) on FlO. 45. EVAPORATION ON A WATER-BATH. PRECIPITATION, ETC. 6.1 account of its greater specific gravity. Stirring, as well as the appli- cation of heat, frequently promotes the subsidence of the precipitate. We speak of pulverulent (amorphous), crystalline, flaky, curdy, gelatinous precipitates, according to the appearance which they present. This and the colour of a precipitate assist materially in identifying a body. The body which precipitates another body is called the preci- pitant. QUESTIONS AND EXEKCISES. 1. How does sulphur occur in nature ? 2. What are the properties of sulphur 1st, at the ordinary temperature ; 2nd, when heated to 111 C. ; 3rd, at a temperature of 250-260 0. ? 3. Define a metallic sulphide. 4. Explain what changes take place when sulphur is heated, 1st out of contact with the air, and 2nd with free access of air. 5. Describe the allotropic modifications of sulphur. 6. What is understood by dimorphism? 7. In what proportions by weight does sulphur combine on ignition with oxygen, and what will be the yolume weight and the molecular weight of the product of combustion ? 8. How would you explain the fact that no contraction of volume takes place when sulphur and oxygen combine, and how does a knowledge of the density of oxygen and sulphurcms anhydride, as compared with air, enable you to prove the volume composition of SO 2 ? 9. Explain the terms roll sulphur or brimstone, flowers of sulphur, distilled sulphur, copper pyrites, galena, iron pyrites. 10. How is cinnabar prepared ? 11. Describe the preparation of sulphuretted hydrogen from ferrous sulphide, and state briefly its properties ; give equations. 12. What are the products of the combustion of sulphuretted hydrogen in air ? Express the changes by equations. 13. What change does a solution of sulphuretted hydrogen in water undergo when exposed to air ? 14. How would you extract sulphur from iron pyrites ? 15. Calculate the percentage composition of SH 2 . 16. State whether the atomic weights of SH 2 and SO 2 are identical with the molecular weights. 17. What is the density of SO 2 and SH 2 compared with hydrogen, and what is the weight in grms. of one litre of the respective gases ? 18. How would you demonstrate experimentally the action of SH 2 upon different saline solutions, such as a solution of sugar of lead, blue and green vitriol, etc. ? 19. You have given to you iron filings, flowers of sulphur, and dilute hydro- chloric acid : describe accurately the different chemical changes which, in your opinion, can be produced with these materials. 20. State how you would purify a sample of rough sulphur containing from three to four per cent, of earthy impurities ; also, how you would determine the amount of sulphur quantitatively. 62 PREPARATION OF CHLORINE. CHAPTER IX. CHLORINE, its Properties. CHLORIDES. Experiment 59. When a well known mineral called black oxide of man- ganese, MnO 2 , composed of one atom of the metal manganese and two atoms of oxygen, is gently heated with concentrated hydrochloric acid in a generating flask (Fig. 46), a yellowish green gas, called chlorine,* is evolved, which cannot, FlQ. 46. PREPARATION OF CHLORINE GAS. even when largely diluted with air, be inhaled without danger, on account of its highly poisonous nature, and the black oxide of manganese dissolves to a yel- lowish coloured liquid, containing manganous chloride, MnCl 2 . The reaction takes place in two stages 1. MnO, + 4HC1 = MnCl 4 + 2OH 2 . 2. MnCl 4 = MnCl 2 + C1 2 . Chlorine gas, like hydric sulphide, is soluble in water cold water dissolves at 10 C. nearly three times its bulk of chlorine and a solution of chlorine may be obtained by passing the gas for some time into cold water. The gas can be col- lected over warm water in a pneumatic trough, as seen in Fig. 46, or it may also be collected by displacement, i.e., the delivery-tube is passed to the bottom of an upright glass cylinder, or test-tube, till the whole of the cylinder is filled with the yellowish green gas. The lighter air is gradually lifted out of the cylinder by the heavier chlorine. The operation of collecting a highly poisonous gas like chlorine must be carried on in a well ventilated closet. Cylinder after cylinder may thus be filled with chlorine. Absolute displacement of the air is not possible, nor is it of much consequence. The edge of the cylinder is slightly greased, and a glass plate, when gently pressed down upon the opening, effec- tually shuts in the gas. Chlorine cannot, like some other gases, be collected over mercury, as it acts slowly upon this metal, forming with it a soluble salt, mer- curic chloride. Chlorine gas is considerably heavier than air, its specific gravity * From x^wpoc, yellowish green. Jl- Cl Cl PROPERTIES OF CHLORINE. 63 2'46 compared with air, is 2*46, or = 35*5, when compared with hydrogen gas. 1 litre of chlorine gas therefore weighs 35'5 criths, or 35jj^ x 0896 grm., = 3'1808 grins. It is a two volume gas and its molecular weight is 2 X 35 '5 = 71. Experiment 6O. Introduce into a cylinder charged with chlorine gas flowers of various colours, a strip of litmus-paper, a piece of moistened cotton print, printed and written slips of paper, and cover over with the glass plate. The colours of the flowers disappear ; violets, e.g., become quite colourless ; the cotton print is turned white ; the ink acquires a reddish-brown appearance ; the printing ink alone, or the finely divided carbon which it contains (lamp-black) remains unaffected. This proves, then, that chlorine is a powerful bleaching agent. Hence its application in the arts and manufactures. Linen and cotton goods are bleached by the agency of chlorine, and paper pulp is rendered white. Silk or woollen stuffs, however, cannot be bleached by chlorine, because the fibres of these fabrics are destroyed by it. Mineral colours, in general, are not affected by it. Chlorine water bleaches equally well. A solution of chlorine in water is a useful reagent in the labora- tory. Experiment 61. The solution is prepared by passing a ^current of chlorine gas through Woulfe's bottles, as seen in Fig. 47. The contents of the Woulfe's bottle nearest to the generating flask are generally contaminated with FlO. 47. PREPARATION OF CHLORINE WATER. some hydrochloric acid, which has been carried over by the chlorine, and are best rejected. A simpler method of making a saturated solution of chlorine con- 64 PREPARATION OF CHLORINE WATER. sists in passing the gas from the first Woulfe's bottle to a retort inverted, as seen in Fig. 48, containing cold distilled water. When cooled to near the freezing point of water crystals of a molecular compound of chlorine with water are formed, containing for every molecule df chlorine 10 molecules of water. Their composition is expressed by the formula C1 2 10OH 2 . If a strong glass tube embedded in a freezing mixture be nearly filled with the crystals, and if it be then drawn out before the blowpipe flame and carefully sealed, the crystals will melt as soon as the tem- perature rises, and yellow oily drops of liquid chlorine subside through the water. The pressure which the chlo- rine exerts upon the glass tube at 15 C. is equal to that of four atmospheres. Liquid chlorine has a specific gravity of 1'38. It does not solidify even when cooled to 110. Experiment 62. Place a cylinder filled with chlorine gas mouth to mouth with another cylinder (comp. Fig. 43) containing sulphuretted hydrogen gas. On withdrawing the glass plates with which they are covered the two gases mix, and sulphur is seen to be deposited. If the rims of the cylinders be slightly greased, they will adhere air-tight, and when detached from each other under water, the latter rushes in and speedily fills both cylinders. This shows that the new gaseous body is soluble in water. Test the water with litmus-paper. It is acid. The chlorine has formed with the hydrogen a gaseous binary compound, an acid, known as hydrochloric acid or hydric chloride, according to the equation SH 2 + C1 2 = 2HC1 f S. The action of chlorine upon sulphuretted hydrogen is analogous to that which chlorine water undergoes when exposed to sun- light. A solution of chlorine in water has the same yellowish-green colour as the gas itself. It should be kept in the dark, as it becomes gradually decomposed when exposed to sunlight, especially to direct sunlight. The hydrogen of the water goes to the chlorine to form hydrochloric acid, which remains dissolved in the water, and the oxygen is liberated OH 2 + C1 2 = 2HC1 + O. This action arises from the powerful affinity which chlorine has for hydrogen, an affinity which is greater than that which either of the elements oxygen or sulphur possess for that element. The bleaching action of chlorine depends upon the same chemical change ; it is an indirect process of oxidation. What is done slowly by sunlight may be effected more rapidly by employing heat. The apparatus required to illustrate the re- action renders the experiment, however, more fit for the lecture room than for the laboratory. Experiment 63. Pass a slow current of steam and chlorine simultaneously through a porcelain tube, loosely filled with fragments of broken porcelain, and heated to redness in a charcoal furnace (Fig. 49). The chlorine generated in the flask provided with the funnel-tube, by the action of hydrochloric acid upon DECOMPOSITION OF STEAM BY CHLORINE. 65 black oxide of manganese passes through a wash-bottle, containing water, into a second flask, in which steam is generated. The small Woulfe's bottle arrests any condensed steam. The rectangularly bent glass tiibe leading to the porcelain FlQ. 49. DECOMPOSITION OP STEAM BY CHLORINE. tube should be cut off slantingly, and should be as short as possible, to prevent ' any drops of condensed water from being carried forward into the porcelain tube, with the imminent risk of cracking the latter. Under the influence of a strong heat, and favoured by the gaseous condition of the two bodies, the chlorine breaks up some of the steam with formation of hydrochloric acid gas, and liberation of oxygen, which can be collected from the exit-tube in the usual manner over water, rendered alkaline by a solution of sodic hydrate, in order to absorb any undecomposed chlorine, as well as the hydrochloric acid which formed. The reaction is expressed thus : C1 2 + OH 2 = 2HC1 + O. Experiment 64. Place a burning taper in a cylinder and hold a second cylinder filled with chlo- rine gas to the mouth of the upright r" ider, as seen in Fig. 50. As the rine descends the taper con- tinues to burn with a feeble yel- lowish flame, and heavy clouds of smoke or soot are seen to separate. A candle, whether made of paraffin, wax, tallow, or sper- maceti, consists of carbon and hydrogen, or of carbon, hydro- gen, and oxygen, in varying proportions. The chlorine acting upon the hydrogen sets the carbon free in the form of solid particles or black soot. This then proves that the white material of which candles are made contains carbon, and that chlorine has a strong affinity for hydrogen FIG. 50. 66 HYDROCHLORIC ACID. METALLIC CHLORIDES. and none for carbon. The chlorine forms with the hydrogen hydro- chloric acid. This can be shown by rinsing out the cylinder with a little water and testing with blue litmus paper. Experiment 65. Powder some metallic antimony very finely, and place the powder in a fine sieve sufficiently large to cover the opening of a tall and wide glass cylinder filled with chlorine gal Shake the sieve gently. Some of the finely divided antimony falls through into the chlorine gas, and combines with it, giving rise to quite a rain of fire, and the cylinder becomes filled with thick white fumes. The chlorine gas combines directly with the metal antimony Sb + C1 3 = SbCl 3 , and the chemical change is accompanied by great heat, and the phenomenon of light. To prevent cracking the cylinder, it is well to place some white sand at the bottom. A similar but less energetic action is observed when chlorine is made to act in a retort or tube of hard glass upon copper-leaf, or upon Dutch metal, an alloy of zinc and copper. The reaction has, however, to be started and assisted by the application of heat. Flashes of light are likewise given out during the combination of the metals with the chlorine gas. The compounds so formed are found on analysis to be composed of 1 atom of the metal to 2 atoms of chlorine, e.g., CuCl 2 , ZnCl 2 . Experiment 66. Set fire to some magnesium wire and .introduce the burning magnesium quickly into a cylinder filled with chlorine gas. It continues to burn with great brilliancy in the gas. The product of the combustion o magnesium in chlorine is a white powder, magnesic chloride (MgCl 2 ), which on exposure to the air rapidly attracts moisture and liquefies. Test the liquid. It is neutral to test-papers. Experiment 67. Place a small piece of sodium in a deflagrating spoon ; ignite the metal and plunge it rapidly into a glass jar containing chlorine. The sodium burns brilliantly in the chlorine. Take some of the white powder which is formed by the combination of the sodium with the chlorine, and dissolve it in a little water. The solution shows no action upon either blue or red litmus- paper ; it is an indifferent or neutral liquid ; it tastes neither sour (acid) nor caustic (alkaline). It has the taste of common salt. In fact, by the combination of the metal sodium and the gas chlorine, we have produced common salt, and have proved thereby that our common table salt sodic chloride (NaCl) consists of two elemen- tary bodies, of sodium and of chlorine. Nature of Metallic Chlorides. As all metallic chlorides, with the exception of the chlorides of platinum and gold, can be prepared like sodic chloride (and several of the metallic chlorides produced in the previous experiments, e.g., SbCl 3 , CuCl 2 , ZnC] 2 , MgCl 2 ,) by the direct combination of a metal and chlorine, they must be analogous to this well known salt, and the latter may be regarded as the representative of metallic chlorides generally. From the most remote times sodic chloride has received the name of salt, and has always been known as " the salt." The same name in its generic construction is now assigned to other metallic chlorides. They are distinguished from the corresponding metallic oxides by their re- action on vegetable colours (litmus-papers). Not one metallic HYDROGEN COMPOUNDS OF BROMINE, IODINE, & FLUORINE. 67 chloride possesses an alkaline reaction, the chlorides of some of the heavy metals giving even an acid reaction ; whilst the corresponding oxides have either a strongly alkaline (caustic) character, or show no reaction at all with litmus. Sodic chloride is found in nature very widely distributed. From one of its sources, viz., sea- water, it is obtained by evaporation and crystallization. The so-called mother liquor (or concentrated saline solution from which salt has been removed by crystallisation) has been found to contain two other elementary bodies, bromine and iodine, which closely resemble chlorine in their properties. They exist chiefly in combination with magnesium, as bromide and iodide of magnesium. These elements can likewise be isolated. Bromine* (symbol Br), at the ordinary temperature is a dark brownish dis- agreeably smelling, very poisonous liquid. Iodine^ (symbol I) is a crystalline substance of dark steel or deep violet colour, subliming in beautiful violet vapour, when a small crystal of it is gently heated in a test-tube. These two elements, together with another elementary body, found in fluor spar, called fluorine (symbol F), (never isolated as yet), can likewise combine with metals, and are classed together with chlorine under the name of halogens or salt formers (from a\9, salt, and ryewdu, I generate). They also combine with hydrogen and form acids gaseous like hydrochloric acid gas, and eagerly absorbed by water. These acids are called Hydrobromic acid (Hydric bromide) HBr. Hydriodic ( iodide) HI. Hydrofluoric ( ,, fluoride) HF. Chlorine we have already seen combines with non-metals (metal- loids) as well as with metals. Chemical combination takes place between them with great energy, mostly marked by flashes of light and evolution of much heat. Phosphorus, sulphur, and carbon form chlorides, although the latter element cannot combine directly with chlorine. A knowledge of these compounds is, however, best acquired by attending a course of lectures, since the explanation of the chemical changes involved in their formation would, to a great extent, be a mere repetition of what has already been studied. The most important compound is that which chlorine forms by direct combina- tion with hydrogen. Experiment 68. A wide capacious flask (Fig. 51) is filled by downward displacement with chlorine gas. A gas-holder filled with hydrogen furnishes a steady supply of gas. A glass tube bent in the manner shown by the figure is drawn out to a jet, and connected with the delivery-tube by means of india-rubber tubing ; the gas is lit, and the burning jet rapidly introduced into the flask. It continues to burn for some time with a bright blue flame. The flame dies gradually away ; and on removing the delivery-tube and closing the mouth of FIG. 51. COMBUSTION OF the flask rapidly with the palm of the hand or a cork, HYDROGEN IN CHLORINE. From /Spwjuog, a stench. f From ludrje, violet-coloured. F 2 68 ELECTROLYSIS OF HYDROCHLORIC ACID. and introducing it, mouth downward, into cold water, and then withdrawing the hand or the cork, the water rushes into the flask and nearly fills it. Remove the flask by inserting the cork, and test its contents with litmus-paper. The liquid reddens blue litmus-paper instantaneously. This shows that it contained an acid gas which is eagerly absorbed by water. From its purely synthetical origin, it can only be hydrochloric acid gas or-hydric chloride, and the liquid a very dilute hydro- chloric acid solution. That hydrogen and chlorine in hydrochloric acid gas are com- bined in equal volumes may be roughly shown synthetically by charging a strong soda-water bottle with equal volumes of these two elementary gases, and applying a light. The bottle should be well wrapped up in a thick towel, as the experiment is not free from danger, owing to the violent explosion with which the two gases combine. As the hydrochloric acid gas is so very soluble in water, and as chlorine acts upon mercury, the synthetical experiment cannot be made with accuracy. It may, however, be shown analytically by decomposing a strong solution of hydrochloric acid by means of voltaic electricity in Hofmann's apparatus (see Exp. 36) used for the electrolysis of water, but somewhat modified, as seen in Fig. 52, by substituting a flexible india-rubber tube and a small glass globe for the long tube in Fig. 30. Experiment 69. Fill the apparatus (Fig. 52), instead of with water, with a concentrated solution of hydrochloric acid, and connect the wires with a vol- taic battery. Hydrogen is speedily liberated at the negative pole, whilst at first scarcely any evolution of gas is observed at the positive pole, owing to the solubility of the chlorine in the acid. The decompo- sition should therefore be started for some time so as to allow of the liquid to become well saturated with chlorine before the two gases are collected in the two limbs of the apparatus. The pressure should also be equalized in the limbs and the movable glass- globe, for the greater the pressure the more gas remains dissolved. By opening the glass stopcocks, the gases may be discharged as long as the evolution of gas from the two electrodes is not equally strong. Having collected equal volumes of the gases sepa- rately, their properties can be readily studied. One will be found by its ready combustibility to be hydrogen ; the other is non-inflammable, and pos- sesses bleaching properties : it is chlorine. Properties of the gas. Hydrochloric acid forms a colourless transparent gas of pun- gent acid odour. Its combining proportions by volume may be represented as follows : FlG. 52. ~ ELECTROLYSIS OF HYDROCHLORIC ACID. H H ii Cl Cl = 2 i.e., 1 molecular volume of chlorine gas on combining with a mole- cular volume of hydrogen, forms two molecular volumes of hydro- chloric acid gas. The two gases combine without contracting. PROPERTIES OF HYDROCHLORIC ACID GAS. 69 Combination takes place with explosive violence when a mixture of hydrogen and chlorine is exposed to direct sunlight, slowly only when left exposed to diffused daylight, and not at all at the ordinary temperature when placed in darkness. The specific gravity of hydrochloric acid gas compared with air is 1'262 and compared with hydrogen 7777^ = 18 ' 25 ' ^ e '' 1 litre of hydrochloric acid weighs 1 + 35-5 36-5 1C . OK ,. ~ = = lo'zo times as much as I litre of hydrogen or 18-25 criths, equal to 18'25 x '0896 grm. or 1-6352 grm. The molecular weight of hydrochloric acid gas is 36'5. It is most eagerly absorbed by water one litre of water is capable of absorbing 500 litres of gas at C. Water so saturated fumes in the air, the vapour of the acid combining with the moisture in the air, and the liquid constitutes the ordinary commercial fuming hydrochloric acid. Bromine, iodine and fluorine when combined with hydrogen form likewise acid liquids with water, which possess considerable interest ; they will be considered more fully hereafter. As these acids contain no oxygen, like the acids with which we have already become acquainted, they have been called hydrogen acids or simply hydro-acids, as distinguished from oxygen or oxy -acids. Oxygen then is not the only element which can by its combination with other elements form acids, as was thought at the time when this element was first discovered, and when it received the name oxygen or generator of acids. In fact, on comparing the compounds which oxygen forms with metals, such as potassium or sodium (which are perhaps only of a basic character, since these powerful metals neutralize arid actually overpower the acidifying properties of oxygen), with the compounds which potassium and sodium form with chlorine, it is obvious, that chlorine rather deserves to be called an acid generator : for the compound which it forms with hydrogen is a powerful acid, and its compounds with potassium and sodium are neutral or indifferent bodies, the metals obviously not being capable of overpowering to the same extent the acidifying properties of chlorine as they overpower those of oxygen. This acidifying property of chlorine becomes still more apparent, when we compare some of the chlorides of the heavy metals which are strongly acid, with the corresponding oxides which are mostly quite indifferent bodies. Metallic chlorides are soluble in water, with the exception of the chlorides of silver (AgCl), mercurosum (Hg 2 Cl 2 ), and lead (PbClo) ; the latter is difficultly soluble in cold, readily soluble, however, in boiling water. Cuprous (Cu 2 Cl 2 ), aurous (AuCl), and platinous chloride (PtCl 2 ) are almost insoluble in water. The following is a list of some of the more important metallic chlorides, the asterisk marking those which are found more or less abundantly in nature : 70 TABLE OF METALLIC CHLORIDES. TABLE OP THE MOST IMPORTANT METALLIC CHLORIDES. KC1,* potassic chloride. (Stassfurth salt.) NaCl,* sodic chloride. (Common salt.) BaCl 2 , baric chloride. SrCl 2 , strontic chloride. CaCl 2) * calcic chloride. (In many mineral waters.) MgCl 2 ,* magnesic chloride. (In sea water.) Al 2 Cl6, alumiiiic chloride. Cr 2 Cl 6 , chromic chloride. FeCl 2 , ferrous chloride. Fe 2 Cl 6 , ferric chloride. ZnCl 2 , zincic chloride. MnCl 2 , manganous chloride. CoCl 2 , cobaltous chloride. NiCl 2 , nickelous chloride. CdCl 2 , cadmic chloride. stannous chloride. j SnCl 4 , stannic chloride. PbClo, plumbic chloride. (In Mendipite.) Hg 2 Cl<>, mercurous chloride. (Calomel.) HgCl 2 , mercuric, chloride. (Corrosive Sublimate.) Cu 2 Cl 2 , cuprous chloride. CuCl 2 , cupric chloride. BiCl 3 , bismuthous chloride. SbCl 3 , antimonious chloride. Pt01 2 , platinous chloride. PtCl 4 , platinic chloride. AuCl, aurous chloride. AuCl 3 , auric chloride. AgCl, argentic chloride. (Hornsilver) It will be seen from this table that very few chlorides only are found in nature, but that they contain just those metals (K, Na, Ca, Mg) which are, for the most part, not met with in the form of native oxides or sulphides. QUESTIONS AND EXERCISES. 1. How is chlorine prepared ? Give equations. 2. Describe briefly the properties of chlorine. 3. Explain the bleaching action of chlorine. 4. State how chlorine water becomes decomposed when exposed to sunlight, or when it is acted upon by sulphuretted hydrogen. 5. Define a metallic chloride. Describe instances of the direct combination of chlorine with metals, and express the chemical changes by equations. 6. Show in what respect metallic chlorides differ from metallic oxides. 7. Explain the meaning of the terms chlorine, bromine, iodine, and fluorine. 8. Enumerate briefly the distinguishing features of chlorine, bromine, and iodine. 9. Explain the terms halogen, hydro-acid, hydric chloride. 10. How is hydrochloric acid gas prepared, and what are its most characteristic properties? 11. What is the volume weight and the molecular weight of chlorine and of hydrochloric acid gas ? 12. What is the weight of one litre of Cl and of a litre of HC1 in grammes ? 13. You have given to you black oxide of manganese, concentrated hydrochloric acid, and metallic antimony : state what chemical changes you can produce with these materials. 14. The density of hydrogen gas compared with air is '0691, that of chlorine gas 2'46 ; find, from these figures, the atomic weight of chlorine. 15. Calculate the percentage composition of HC1 and of NaCl. APPLICATION OF THE THEORY OF COMBINING PROPORTIONS. 71 CHAPTER X. APPLICATION of the THEORY of CONSTANT CHEMICAL COMBINING PROPORTIONS. SYMBOLIC formulae have hitherto served 1st. To represent bodies, elementary or compound. 2nd. To illustrate in the briefest manner, the play of chemical affinities, the breaking up of existing chemical compounds, and the building up of new bodies. They serve, however, another and most important purpose, for they also bear, as has been already remarked (Chapter VI), the impression of the respective atomic weights of the element or com- pound body which they denote. Equations illustrating chemical changes express likewise the relative quantities of the elements which form the compounds acting upon each other, or which take part in the changes, and hence they furnish the basis for qtiantitative chemical calculations. Thus the formation of cupric oxide by the action of oxygen on copper is expressed by the equation Cu + O = CuO which conveys to the mind at the same time the idea that one atom of copper combines with one atom of oxygen to form the molecule cupric oxide. The atomic weight of copper being 63'5, that of oxygen 16, our equation tells us, by a process of simple substitu- tion, that 16 parts by weight of oxygen combine with 63'5 parts by weight of copper, and that the two together must form 79 '5 parts by weight of cupric oxide. The symbolic equation is thus tran- scribed arithmetically 63-5 + 16 = 79-5 and it is easy to calculate the quantities of copper and oxygen in- volved in the formation of a given quantity of cupric oxide, and the quantity of cupric oxide obtained from known quantities of copper and oxygen. It will be found useful, for the sake of practice, to transcribe, both symbolically and arithmetically, some of the reactions already studied, e.g., the reactions involved in Experiments 7, 8, 11, 12, 13, 14, 15, 18, 22, 23, 24, 31, 40, 49, 50, 51, 52, 53, 54, 55, 59, 62, 63, 65, 66, 67, 68. This may be done somewhat in the following manner : Exp. 7. Mercury. Oxygen. Mercuric Oxide. Hg + O = HgO at. W... 200 + 16 = 200 + 16 ^ 216 72 QUANTITATIVE CHEMICAL CALCULATIONS. or expressed in words: 200 parts by weight (pounds, ounces, grains, grammes, etc.), of the metallic element mercury can com- bine, under favourable conditions, with 16 parts by weight of the gaseous non-metallic element oxygen, to furnish 216 parts by weight of solid mercuric oxide.- , Or Exp.,18. Potassic Chlorate. Potassic Chloride. K0 3 C1 = KC1 + at.W.. 39 + (3 X 16) + 35-5 = 39 + 35-5, + 122-5 or in words : 122*5 parts by weight of potassic chlorate furnish 74' 5 parts by weight of the salt potassic chloride, and 48 parts by weight of oxygen gas. Questions such as the following will now readily be answered by a mere calculation of rule of three : 1. How much Cu combines with a given quantity of O ? 2. O Cu? 3. CuO can be formed from ,j Cu ? 4. Cu is contained in a ,, CuO ? 5. O CuO? If we wish to know 1st, how much cupric oxide, CuO, we can get by the oxidation of 100 grains of copper, we have 63-5 : 79-5 : : 100 : %. Atomic weight Weight of a molecule of copper. of cupric oxide. Ans. = 125*19 grs. of CuO. 2. How much copper is left when 100 grains of cupric oxide, CuO, are reduced in a current of hydrogen gas? 79-5 : 63-5 : : 100 : x. Molecular weight Atomic weight of of cupric oxide. copper. Ans. = 79-87 grs. of Cu. 3. How much mercury, Eg, is required to form 20 grms. of mercuric oxide, HgO ? 216 : 200 : : 20 : x. Molecular weight Atomic weight of HgO. of Hg. Ans. 18'51 grms. 4. How much iron, Fe, has to be taken to produce 100 Ib. of ferrous sulphide, FeS ? QUANTITATIVE CHEMICAL CALCULATIONS. 73 88 : 56 :: 100 : x. Molecular Atomic weight of FeS. weight of Fe. Ans. 63-63 Ib. 5. How much ferrous sulphide can be obtained by the combina- tion of iron with 50 Ib. of sulphur ? 32 : 88 : : 50 : x. Atomic Molecular weight of S. weight of FeS. Ans. 137-5 Ib. 6. How much hydrogen by weight, and by volume (in litres), is required to reduce 25 grms. of cupric oxide, CuO, to metallic copper ? 79-5 : 2 : : 25 : x. Molecular weight Weight of the of CuO. molecule of H. Ans. '6289 grm. of H. On dividing '6289 grm. by the weight of one litre of hydrogen, measured at and 760 mm. barometrical pressure, viz., '0896 grm., or a crith, we obtain the number of litres of hydrogen gas at the same temperature and pressure Ans. 7-01 litres of H. 7. How much sulphurous anhydride, S0 2 , is obtained by the combustion of 10 grms. of sulphur in oxygen gas 1st, by weight ; 2nd, by volume (litres) ? 32 : 64 : : 10 : .. Atomic Molecular weight of S. weight of SO 2 . Ans. 20 grms. of $0 2 . The volume weight of S0 2 is 32 criths, or 2'8672 grms. and by dividing the total weight of sulphurous anhydride obtained, viz., 20 grms. by the weight of one litre of the gas, we have = 6-975 litres of SO,. 8. How much chlorine gas by weight, and by volume, can be obtained by the action of excess of hydrochloric acid on 16 grms. of black manganic oxide, Mn0 2 ? 87 : 71 : : 16 : x. Molecular The weight of weight of a molecule MnOg. of chlorine. Ans. 13-057 grms. of Cl 74 QUANTITATIVE CHEMICAL CALCULATIONS. Now one litre of chlorine weighs 35*5 criths, or '0896 x 35 '5 = 3-1808 grms. 13*057 - = 4*104 litres of chlorine gas. 3*1808 9. When carbon is burnt in oxygen gas it forms carbonic anhy- dride gas C0 2 . How much carbonic anhydride by weight, and by volume, can be obtained by thus burning 15 grms. of carbon ? 12 : 44 : : 15 : x. Atomic Molecular weight of C. weight of CO 2 . Ans. 55 grms. of CO*. One litre of carbonic anhydride gas weighs 22 criths, or '0896 X 22 = 1*9712 grm. and = 27*90 litres of carbonic anhydride gas. JL'i)7 LA 10. How much hydrogen and oxygen by weight and by volume can be obtained, by electrolysis, from 10 grms. of water ? 18 : 2 : : 10 : x- Molecular Weight of weight of OH 2 . mol. of hydrogen. Ans. 1*111 grms. of H. 8*889 grms. of 0. 'One litre of H weighs *0896 grm., hence 1*111 0896 = 12*4 litres of hydrogen gas. One litre of oxygen weighs 16 times as much as one litre of hydrogen gas, i.e., *0896 x 16 = 1*4336 grm. Q.QQQ 5|jL = 6*200 litres of oxygen gas. 11. You have given to you five litres of chlorine gas : how much metallic sodium is required to convert the whole of the chlorine into sodic chloride ? Ans. IQ'8Q4t grms. of Na. 12. 15 grms. of ferrous sulphide are treated with dilute hydro- chloric acid : how much SH 2 by weight, and by volume, can be ob- tained theoretically therefrom ? Ans. 5*795 grins, by weight, and 3*804 litres of SH 2 . ATOMICITY OR QUANTIVALENCE OF ATOMS. 75 CHAPTER XI. ATOMICITY OR QUANTIVALENCE OP ATOMS. ACCORDING to the law of multiple proportions, atoms can combine with atoms in more than one proportion, i.e., one atom with two, three, four, or more other atoms. Some few metals and metalloids can form only one oxide, sul- phide, chloride, others two or more. Thus we have seen that binary compounds, such as : FeO. FeS. MgO. MgS. CuO. CuS. ZnO. ZnS. FeCl 2 . MgCl 2 CuCl a . ZnCl 2 . are comparatively simple bodies. In fact, the number of atoms in the higher binary compounds of mineral or inorganic origin can mostly be expressed by the multiples 3, 4, 5. We have seen (page 64) that under the continued influ- ence of sunlight, chlorine water is decomposed into hydrochloric acid, which is absorbed by the water, arid oxygen ; and that for every two volumes of chlorine gas, when placed over water, one volume of oxygen will be found after some time. Two atoms of chlorine exert, therefore, the same combining power as one atom of oxygen. Experiment 62 has also shown that sulphur is displaced by chlorine in sulphuretted hydrogen with formation of hydrochloric acid gas without any change in the respective volume composition. Experiment. 2 has demonstrated that the action of dilute hydro- chloric acid on zinc liberated hydrogen, whilst the chlorine remained combined with the metal zinc, forming zincic chloride. "We have since seen that hydrogen and chlorine in hydrochloric acid gas are combined in equal volumes : : of the H ~i' Cl consequently we know that for every molecule H H if liberated hydrogen gas two volumes (two atoms) of chlorine remain in combination with the metal zinc, and that therefore two mole- cules of hydrochloric acid must have taken part in the reaction Zn + 2HC1 = ZnCl 2 + H 2 . Zincic chloride has the composition ZnCl 2 ; one atom of zinc accord- ingly possesses the chemical combining power of two atoms of hydrogen, and two atoms of chlorine are of the same chemical 76 VOLUMETRICAL COMPOSITION OF HYDROCHLORIC ACID. combining value as one atom of oxygen (comp. Exp. 63) ; they are in fact equivalence. The same holds good for other metals, such as calcium, iron, manganese, copper, mercury, i.e., they all unite with the same number of atoms of chlorine, viz., two. Experiment 1 has "shown tha the metal sodium decomposes water by taking the place of the hydrogen therein. Chlorine in Experiment 67 also combined directly with the metal forming common salt, NaCl, a compound which is in every respect analogous in con- stitution to hydrochloric acid, HC1. Sodic chloride can be readily prepared by the decomposition of this acid by means of sodium, hydrogen being evolved. Experiment flO. In order to illustrate this, collect by displacement some dry hydrochloric acid in a cylinder, by heating concentrated hydrochloric acid in a flask (Fig. 53) and passing the gaseous acid which comes off through a U-tube filled with pumice - stone, mois- tened with oil of vitriol. The gas being heavier than air, may be collected in dry cylin- ders by passing the delivery tube down to the bottom of the cylinders, loosely covered with a piece of card-board, or better still, over mercury. On introducing a small piece of ignited sodium, placed in a deflagrating spoon into a cylinder full of hydrochloric acid gas, the sodium which at first burns at the expense of the oxygen of the air con- tinues to burn in the hydro- chloric acid gas at the expense of the chlorine, i.e., it combines with the chlorine, setting free the hydrogen, and forms sodic chloride 2HC1 = 2NaCl + H 2 . Experiment 71- It may also be shown analytically, according to Hofmann, by filling a U-shaped bent tube (Fig. 54), open at one end with mercury, so as to displace all the air. By opening the compression clamp, the mer- cury is almost entirely run off from the open limb of the U-tube into a receiving vessel. Dry hydrochloric acid gas evolved as described in the previous experiment, is now introduced into the closed limb, which remained filled with the mercury, by means of a narrow delivery tube, provided with a piece of flexible india -rubber tubing, so as to be readily passed round the bend into the closed limb of the U-tube. Whilst this latter is charged to about two- thirds full with the dry gas, the mercury is allowed to run off from the little branch tube, provided with a compression clamp. With- draw now the delivery tube, and equalise the FIG. 54.-DEcoMPosmoN OF HC1 BY le ! of th( ? ^ercury in both limbs before sotJUM. tightening the compression clamp. Adjust the FlG. 53. COLLECTING DRY HYDROCHLORIC ACID GAS BY DISPLACEMENT. POLY AD ELEMENTS. 77 india-rubber ring, so as to mark the height of the mercury in the closed limb, and by means of another india-rubber ring, mark the line which divides the gas into two halves. Fill the open limb with sodium amalgam.* Close the tube with the thumb and transfer the gas into the limb containing the amalgam, and agitate it briskly. The sodium abstracts the chlorine from the HC1, forming with it sodic chloride, and leaves hydrogen. Transfer the latter back again into the closed limb, and remove the thumb. Equalise the level of the mercury once more in both limbs by opening the tap. It will now be found that the gas fills only half the space which it originally occupied, and that the mercury has ascended to the upper india-rubber ring. Fill the open limb again with mercury, close with the thumb, and retransfer the gas which is left to the open limb. On withdrawing the thumb and applying a light to the gas, it will be found to burn with a bluish flame where it is in contact with the air. It is in fact hydrogen gas, for neither chlorine nor hydrochloric acid gas is a combustible gas. This proves that two volumes of dry hydrochloric acid gas (or a molecular volume) contain equal volumes of hydrogen and chlorine. The metal sodium by combining with the chlorine, left the hydrogen in the free state. One atom of sodium possesses the same chemical displacing power as one atom of hydrogen, and two atoms of sodium must be required to combine with one atom of oxygen (in the same manner as two atoms of hydrogen were required to combine with one atom of oxygen in water), and the formula of the resulting sodic oxide must therefore be written Na 2 0. The same holds good for several other metals, viz., potassium, silver ; and the respective formulae of the chlorides and oxides of these metals are therefore NaOl. KC1. K 2 0. AgCl. Ag 2 0. Other metalsf again combine with 3, 4, 5, or 6 atoms of chlorine, or l, 2, 2, and 3 of oxygen ; such as the metals gold, tin, anti- mony, chromium. Their respective oxides and chlorides are thus written AuC] 3 . Au 2 3 . SnCl 4 . Sn0 2 . SbCl 5 . Sb 2 5 . CrO 3 . and Sb0 2J being inadmissible for reasons already stated. Sulphur forms with metals compounds almost precisely analogous to those which oxygen forms. In order to mark the binding capacity or atom-fixing power, [called atomicity or guantivalence] of the various elements, six divi- * Prepared by gradually dissolving about 10 pieces of sodium the size of a pea, in 50 c.c. of mercury. f The tables showing the most important oxides, sulphides, and chlorides, will furnish further illustrations of the combining capacities of the different metals. 78 HYDROGEN, THE UNIT OF ATOMICITY. sions have been adopted by chemists, of which the following metals may be regarded as the representatives : Na, Mg, An, Sn, Sb, Or. An element which combines with 1 atom of chlorine is monova- lentic or monadic; other elements "which combine w r ith 2, 3, 4, and 5 atoms of chlorine (or in the place of 6 of chlorine with 3 of oxygen), are di-, tri-, tetra-, penta-, and hexa-valentic (from valere to be of value), shortly called 'monads, dyads, triads, tetrads, pentads, and liexads. Elements with an odd number of bonds are called by Dr. Odling perissads (from Trepiaad?, uneven, odd) ; whilst those with an even number are termed artiads (from apnos, even). Oxygen, we have seen, is combined in water with two atoms of hydrogen : it is therefore divalentic, or one atom of oxygen is equi- valent to two atoms of hydrogen. Sulphur in sulphuretted hydro- gen is divalentic ; and one atom of sulphur is equivalent to two atoms of hydrogen. Boron combines with three atoms of chlorine to form boric chlo- ride, BC1 3 . Carbon combines with four atoms of hydrogen to form marsh-gas, CH4, one of the constituents of coal gas. Pentavalentic elements are the elements constituting the nitrogen group, N, P, As, and Sb. Hydrogen is thus called upon to perform fresh functions, for it forms also the unit of the binding or atom-fixing as well as atom- dis- placing poiver inherent in every elementary body, as it already con- stituted the unit of atomic and volume combination. This atom- fixing power of elements is well illustrated whenever elements com- bine directly with hydrogen ; as when oxygen attracts to itself two, nitrogen three, or carbon four, atoms of hydrogen. It must not be supposed that in the absence of metallic com- pounds with hydrogen, the combining capacity of metals (and non- metals) for chlorine the equivalent for hydrogen has been the only criterion for determining the atomicity or quantivalence of the different elements. Comparatively modern discoveries in the che- mistry of organic bodies, in which metals are combined with a certain number of atoms of the organic analogues of hydrogen, methyl, ethyl, etc., have but recently introduced this method of determina- tion. The coefficients of atomicity are, moreover, not yet deter- mined experimentally for all metals, and we have in many cases to assume them by reasoning from analogy only. But whilst the atomicity of many elements must still be considered as provisional, and open to revision, yet the system of classification founded upon atom-fixing power has so much simplified the study of chemistry, that its introduction, even in its present incomplete state, into text books, cannot fail to recommend itself strongly to the student, as it supplies him with a generalisation which greatly facilitates the comprehension of chemical phenomena. Moreover, the doctrine of atomicity is in strict harmony with the atomic hypothesis. We connect, then, with atoms not merely the notion of indivisi- bility and a definite relative atom- and volume- weight, but likewise REPRESENTATION OF THE ATOMICITY OF ELEMENTS. 79 varying degrees of inherent affinity and a capacity of fixing or dis- placing a definite number of other atoms. Thus the atomic theory gains in importance as it gains in extent. Symbolic representation of t he powers of Atoms infixing or displacing other Atoms. We represent to ourselves atoms as the smallest possible par- ticles of matter, and in the absence of any experimental evidence as to their form may, for the sake of convenience, view them as spheres. We explain chemical combination between two elements as arising from the intimate union which takes place between their atoms, owing to the chemical affinity peculiar to each individual atom. If an atom exhibits an affinity by which its atom-fixing power becomes exhausted by combining with an atom of another element whose atom-fixing power equals that of hydrogen, taken as unit, it is manifestly a monovalentic element or a monad, it can bind or satisfy only one affinity. The atomicity of an element such as hydrogen or chlorine may be represented graphically, thus : Monad Atom H- Molecule H-H. Cl- C1-C1. An atom of a element like magnesium, capable of fixing two monad atoms of chlorine, would then have to be represented graphically, thus : Dyad Atom -Mg- An element capable of fixing 3 atoms of chlorine, thus : Triad Atom Ns/ I An element capable of fixing 4 atoms of hydrogen, thus : Tetrad Atom I An element capable of fixing 5 atoms of chlorine, thus : Pentad Atom P I An element capable of fixing 3 atoms of the dyad oxygen, thus : Hexad Atom \S/ or == ^ == /\\ Symbolic notation conveys the same idea if we employ dashes, and for the higher atomicities Roman figures- placed to the right- hand side slightly above the symbols, thus : 80 GRAPHIC REPRESENTATION OF MOLECULES. Hydrogen. ... H' (written mostly without the dash). Oxygen O" Boron B'" Carbon C iv Phosphorus . . PY Sulphur S vi Other modes of graphic representation would answer equally well and have actually been used for this purpose, thus : [ -f | = molecule HH, or C1C1, HC1, ISTaCl, AgCl. = molecule OH 2 , or SH 3 , OAg 2 , OK 2 . = molecule CuO, or HgO. I - | , | I = molecule AuCl 3 . J__J = molecule CH 4 , or Sn01 4 . = molecule S0 2 , or C0 2 . This method of graphic representation possesses the advantage of setting forth in a marked manner the quantivalence of atoms as well as their molecular combining conditions. The second formula, e.g., shows at a glance that two atoms of hydrogen are combined with one atom of oxygen, and that, therefore, the atom oxygen is equivalentic to two atoms of hydrogen. Formula 5 shows in like manner that four atoms of hydrogen are combined with one atom of carbon, and hence that this latter element is equivalentic to four atoms of hydrogen or chlorine. At the same time this graphic representation is liable to mislead if the idea be entertained for a moment that an atom of carbon is four times, or an atom of oxygen twice as large as an atom of hydro- gen or chlorine ; and as no graphic representation whatever can claim to elucidate " either the shape or size of an atom or molecule, nor the relative position of the constituent atoms of any chemical com- pound," it will suffice if we simply link together their symbols by short connecting lines, in order to indicate their atom-fixing capacity. Thus we write : 01 Cl H O H CLASSIFICATION OF ELEMENTS. In the following table, taken from Dr. Frankland's " Lecture Notes," page 32, will be found the 36 most important elements, classified according to their atomicity or respective quantivalence. Metalloids are printed in italics. The different classes are again sub- divided into sections, representing elements closely resembling each other in their chemical character : Monads, or Monovalentic Elements. Dyads, or Divalentic Elements. Triads, or Trivalentic Elements. Tetrads, or Tetravalentic Elements. Pentads, or Pentavalentic Elements. Hexads, or Hexavalentic Elements. 1st Section. 1st Section. 1st Section. 1st Section. 1st Section. 1st Section. Hydrogen. Oxygen. Boron. Carbon. Nitrogen. Sulphur. Silicon. Phosphorus. 2nd Section. 2nd Section. 2nd Section. Tin. Arsenic. 2nd Section. Fluorine. Chlorine. Barium. Strontium. Gold. 2nd Section. Antimony. Bismuth. Chromium . Manganese. Bromine. Calcium. Aluminium. Iron. Iodine. Magnesium. Cobalt. Zinc. 3rd Section. Nickel. 3rd Section. Potassium. 3rd Section. Platinum. Sodium. Cadmium. 4ith Section. 4th Section. Mercury. Copper. Lead. Silver. The elements have been classified according to their highest atomicity or greatest number of bonds. Thus sulphur can be made to combine with 3 atoms of the dyad element oxygen, although under ordinary conditions it combines only with 2 atoms of oxygen to form sulphurous anhydride gas, SO 2 . In this instance the sulphur acts the part of a tetrad. Again, sulphur combines with two atoms of hydrogen, and is then for the time being a dyad element. The active atomicity or quantivalence of an element, therefore, principally depends on the nature of the elements with which it enters into combination. A hexad atom does not necessarily com- bine always with its maximum number of 6 chlorine atoms, or 3 atoms of oxygen, &c. ; it may bind only four atoms of chlorine or 2 atoms of a dyad element, such as oxygen or sulphur ; or 2 atoms of chlorine or its equivalent of a dyad atom : but a hexad atom will never be found to link itself to 5 or 3 or 1 atom of a monad element. Its atomicity co-efficient is invariably an even number. If the co-efficient be 2 or 4, instead of 6, 4 or 2 bonds respectively become, so to speak, dormant or inactive, and are indicated by dashes or Roman figures placed on the left-hand side, slightly above the symbols ; but the absolute atom- fixing power of the hexad remains the same, and the dormant, or latent bonds, as Dr. Frankland calls them, may be called into activity by fresh chemical agencies, 82 USE OF THICK TYPE. whenever it is desired. The sum of the active and latent bonds must evidently always be equal to the absolute atomicity of an element. Then, again, a pentad atom need not necessarily combine with 5 atoms of chlorine, &c. It may exist in combination with 3 atoms, or 1 atom, but never with 4 or 2 aj^ms of chlorine, or its equivalent. Its atomicity co-efficient is invariably an uneven number. Elements which in the above list are classified as monads, &c., may possibly be discovered to be capable of a higher binding power. Compounds may exist, or may yet be discovered, in. which the monad element exists as a triad or pentad, or the tetrad or hexad element as a hexad or octad ; but it may safely be predicted that a monad element will never bind 2 atoms of chlorine, but only 3 or 5, and that its atomicity co-efficient will be found to be an uneven nnmber, and that of a dyad always an even one. Use of Thick Type. The formulae of the different chemical com- pounds are, according to Dr. Frankland's system, written in such a manner as to denote "that the element represented by the first symbol of a formula, is directly united with all the active bonds of the other elements or compound radicals following upon the same line." Thus the formula of water, OH 2 , signifies that the dyad atom of oxygen is combined with the two bonds of the two atoms of hydrogen. The formula of carbonic anhydride, CO 2 , signifies that the tetrad atom of carbon is combined with the four bonds of the two atoms of dyad oxygen. The first symbol constitutes the grouping element, and whenever this element has more than one bond, it will always be printed in thick type. The element having the greatest number of bonds will, as a rule, occupy this prominent position. QUESTIONS AND EXERCISES. 1. How would you demonstrate analytically that hydrochloric acid consists of equal volumes of hydrogen and chlorine ? 2. Grive reasons why two molecules of hydrochloric acid (KC1) are required to act upon an atom of zinc. 3. How would you demonstrate synthetically that hydrochloric acid gas is com- posed of equal volumes of H and Cl ? 4. Assign reasons for the formulae NaCl and ONa 2 . 5. Classify the following elements according to their respective atom -fixing power : Br, B, C, N, Sn, S, Mg, Ag, Cd, Pt, Si, As, Mn. 6. Commit to memory the 36 most important elements as classified in the preceding table. 7. Explain the terms perissads and artiads. 8. How can the atomicity of elements be indicated, 1st symbolically, 2nd graphi- cally ? 9. Explain what you understand by absolute atomicity, active and latent bonds, grouping elements. 10. State how many atoms of the following elements Cl, O, S, you consider equi- valent to an atom of copper, of silver, or of antimony, platinum, gold, iron. 11. Represent graphically a molecular volume of HC1, OH 2 , SC1 3 , CH 4 , so as to indicate the atomicity of the respective elements, and state what objections can be urged against such graphic representation. 12. Place the atomicity co- efficient against the following elements : P, Hg, Sr, F, I, Cr, Au. 13. Place atomicity co-efficients against the elements constituting the oxides, sulphides, and chlorides enumerated in the tables on pages 50, 60, and 70. HYDRATES. REACTIONS IN THE WET WAY. 83 CHAPTER XII. H YDIt ATE S METALLIC AND NON-METALLIC. PEROXIDES, HYDROXYL. FORMATION OP ACIDS FROM ANHYDRIDES. REACTIONS IN THE WET WAY. COMPOUND RADICALS. IN most of the reactions hitherto described we have restricted ourselves to changes which take place in the dry way, between solid bodies. In the few instances in which a liquid body reacted upon a solid body as in the case where metallic sulphides were formed by the combination of a metal with the liquid sulphur, or where a liquid metal, such as mercury, or a readily fusible metal, like sodium, combined with oxygen or chlorine one of the reacting bodies was rendered liquid by the application of heat. Such changes are called reactions in the dry way. There are, however, a vast number of reactions, where the presence of water forms an essential feature, either by virtue of its solvent action (whereby substances are brought into more intimate contact), or by giving up a part or the whole of its constituent elements for the formation of the molecules of the new body. Such changes are termed reactions in the wet way. Certain bodies, as soda, eagerly attract to themselves the moisture contained in our atmosphere. There can be no doubt that a chemical combination takes place between these bodies and the water, ac- companied by the liberation of much heat. This is proved, more- over, by the difficulty with which soda gives up its water again when heated. Experiment 12. Evaporate a little solution of caustic soda in a small iron basin, or, better still, in a silver crucible or evaporating dish. It loses water, and acquires a syrupy consistency. On cooling, the mass solidifies. Quantitative experiments have shown that one molecule of water is retained by the fused mass for every molecule of soda, ONag. Dry soda., such as is formed by the oxidation of the metal sodium in a current of dry oxygen gas, combines with 1 molecule of water, and the change may be viewed as an .addition of two binary com- pounds according to the equation ON"a 2 + OH 2 = Na 3 H 2 O 2 , or 2]STaHo. The new ternary body contains the elements of soda and water truly chemically combined. In fact, soda acquires its characteristic caustic nature only by this very act of combination with water ONa 2 is without action upon dry litmus-paper. Experiment 73. Heat some finely granulated zinc or zinc turnings and a strong solution of sodic or potassic hydrate in a small flask provided with a gas delivery tube, and collect the gas which is slowly evolved over water. As G 2 84 HYDRATES. soon as a sufficient amount of gas has been collected, remove tlie test-tube from the pneumatic trough, and apply a lighted taper. The gas burns at the mouth of the tube v, ith the characteristic lambent flame of hydrogen. This shows that concentrated hydrated alkali is decomposed by the metal zinc with formation of potassic zincic oxide and evolution of hydrogen, thus : Zn + 2(OHK) = ZnK 2 2 (or ZnKo 2 ) + H 2 . The new body constitutes a quasi saline compound, in which the strong alkali acts the part of the base and the zincic oxide that of a weak acid. This may be shown by adding sulphuretted hydrogen water to the solution, when a white precipitate of zincic sulphide, ZinS, comes down. The metals aluminium, cadmium, and mag- nesium give rise to reactions of a similar nature. They dissolve even in the cold when placed in contact with platinum, iron, etc., in alkaline solutions with evolution of hydrogen. Experiment fl4. A little burnt lime, CaO (quicklime) is placed in a porcelain dish, and moistened with as much water as it will take up within its pores. The mass soon begins to get hot ; it gives off steam, and falls to pieces. Much heat is evolved by the chemical combination of lime with water. Quantitative experiments have proved that this reaction takes place according to the equation CaO + OH 2 = CaH 2 2 , or CaHo 2 . Numerous metallic oxides are met with in nature, both in the anhydrous and hydrated condition, e.g., the oxides of iron, man- ganese, aluminium, copper (comp. Table, p. 50) ; some combine with more than one molecule of water, and form more than one hydrate. Some hold the water with various degrees of force ; cupric hydrate, CuHo 2 , parts with its water at a very moderate heat, calcic hydrate at a very strong red heat, whilst potassic or sodic hydrate are not decomposed by the strongest heat which can be applied to them. A few only are readily soluble in water, and deserve our special attention, viz., the hydrates of potassium, sodium, barium ; others are moderately soluble, e.g., strontic and calcic hydrate. All these form strongly alkaline solutions. Others, again, are insoluble, or nearly so, e.g., magnesic hydrate, plumbic, mercuric, and argentic hydrate. Experiment *J5. Heat some plumbic oxide (Massicot), PbO, for several hours in a small porcelain dish or iron spoon below the point where it fuses (below 300 C.). Stir occasionally with a glass or iron rod. The bright yellow oxide absorbs slowly oxygen from the air, and is converted into a fine red powder, called red lead or minium, consisting of varying quantities of lead and oxygen, usually of the formula Pb 3 O 4 . This is generally done on a manufacturing scale by heating plumbic oxide in a reverberatory furnace with constant stirring. That oxygen has been taken up may be readily proved by heating some red lead in a tube (Fig. 55), when oxygen is given off again, and the yellow oxide is left, thus : Pb 3 4 = 3PbO + O. On account of the facility with which the red lead parts with a fourth of its oxygen, it is used as an oxidising agent in making PREPARATION OF HYDROXYL. 85 flint glass, the plumbic oxide combining at the same time with the white sand or silica. FIG, 55. Experiment 16. Treat some red lead with dilute nitric acid, and heat gently for some time in a porcelain dish. The brilliant red colour changes to a deep brown, owing to the acid dissolving out two parts of 3Pt)0, with which it forms a salt called plumbic nitrate, and leaving plumbic dioxide, PbO 2 . This, when filtered off, washed, and dried at a gentle heat, constitutes a dark purplish brown coloured body, which yields half its oxygen upon the applica- tion of a gentle heat, and is reduced to the yellow plumbic oxide. Experiment 17. Pass dry air or oxygen over lumps of baric oxide, BaO, heated in a porcelain tube to from 300 to 400 C. The baric oxide takes up oxygen, without altering its form, changing merely from white to a greyish colour, and forms a peroxide, BaO 2 , containing double the amount of oxygen. On heating this per- or dioxide (also called binoxide or hyperoxide) to full red- ness, it loses its second atom of oxygen again, and becomes reconverted into baric oxide. On treating it with a little water it forms a white hydrate, which is little soluble in water, and which gives off oxygen on boiling, and is converted into baric hydrate, BaO 2 H 2 , or BaHo 2 , which dissolves readily in water. It has been proposed to utilize this property of baric oxide of combining with oxygen at a low heat, and giving it up again at a high heat, for the wholesale manufacture of oxygen gas. This body possesses, however, additional interest, as it forms the usual starting point for the preparation of peroxide of hydrogen, or hydric peroxide, O 2 H 2 . Experiment 78. Suspend some finely divided baric peroxide in water, and pass a current of carbonic anhydride. The hydrated baric peroxide* breaks up into hydric peroxide and baric oxidjs, which by combining with the carbonic anhydride forms insoluble baric carbonate, which can be filtered off from the soluble hydric peroxide. The solution should be concentrated by slow evapora- tion, by placing it under a bell-jar in a porcelain dish 6*ver oil of vitriol. Hydric peroxide,* also called liydroxyl (molecule), forms a colourless liquid of syrupy consistency, and possessing a peculiar odour. Its specific gravity is 1'452. It does not solidify at * A solution of hydric peroxide containing a little free acid (hydrochloric or sulphuric), is now sold for medicinal and photographic purposes, also as a hair- wash, for it bleaches the hair, and produces a much admired golden yellow colour. 86 PROPERTIES OF HYDROXYL. 30 C. It is very unstable, and begins to decompose spon- taneously at 15 to 20 C., more rapidly so when heated sometimes with explosive violence. Dilute solutions of hydric peroxide, especially if they contain a little hydrochloric or sulphuric acid, are more permanent. Experiment *J9. Nearly fill a small flask, fitted with a narrow delivery - tube, with hydric peroxide. Add a drop of sodic hydrate, and heat gently in a water-bath till the evolution of oxygen begins. Collect the gas over water, and ascertain by the usual tests that it is oxygen. This experiment shows that heat breaks up hydric peroxide into water and oxygen, analogous to the change which plumbic dioxide and baric peroxide underwent when heated, only far more readily. On this account hydric peroxide constitutes one of the most power- ful oxidizing agents with which we are acquainted. The second atom of oxygen separates from hydroxyl under various and often enigmatical circumstances in the form of gas, the volume of which amounts to 475 times that of the liquid. Great heat is also developed, and when the experiment is made in the dark even light is ap- parent. Certain bodies, among which are charcoal, many metals, and some metallic oxides, induce by their mere contact a more or less violent decomposition of the peroxide into OH 2 and O, without themselves undergoing any change ; gold, platinum, and silver, particularly when in the precipitated or spongy state, act most violently, and cause a great disengagement of heat. This chemical decomposition by mere contact is termed catalytic action ; its nature, however, is not at present understood. Experiment SO. Allow a drop of hydric peroxide to fall upon brown argentic oxide. Decomposition takes place with explosive violence and great evolution of heat. The silver oxide loses its oxygen, and is reduced to grey metallic silver. The oxides of gold, platinum, or mercury are acted upon in a similar manner, likewise the peroxides of lead and manganese, as well as several other more highly oxidized bodies. The explanation for this interesting reaction, first minutely examined and explained by Sir B. Brodie, is that the second atom of oxygen in the peroxides of hydrogen and barium is not merely retained in an unstable state of combination, but that it is, by association with the oxide of an electropositive element like hydrogen or barium, thrown into a polar state, opposite to the polar state of the oxygen in unstable protoxides, and to that of the loosely combined oxygen in the more or less electropositive (chlorous) peroxides. Hence the two oppositely polarized oxygen atoms unite with one another, as indicated in the following equation : AgAgO + H 2 66 = AgAg + H 2 6 + 66. Hydric peroxide, which in the last experiment acted as a most powerful reducing agent, is frequently employed for purposes of oxidation. ' HYDRATED PEROXIDES. 87 Experiment 81. Soak some filter paper in a solution of plumbic acetate (sugar of lead), and expose the paper to sulphuretted hydrogen gas. Black plumbic sulphide (PbS) is formed. Wash and dry the paper, then brush it over with a solution of hydric peroxide. The black plumbic sulphide is instantaneously oxidized and converted into plumbic sulphate. Old oil paintings discoloured by the formation of plumbic sulphide, may be cleansed by washing with a dilute solution of hydric peroxide. Certain metallic hydrates are readily peroxidized by exposure to the atmosphere, more especially in the presence of an alkali (soda, lime, etc., etc.). Experiment 82. Dissolve some manganous chloride, lHnCl 2 , in water, and add a solution of sodic hydrate as long as a precipitation takes place. Filter and wash with a little hot water ; then take some of the flesh-coloured man- ganous hydrate, MnO 2 H 2 , or BInHo 2 , off the filter by means of a glass spatula, and spread it out in a thin layer on a porcelain slab or plate. The hydrate becomes rapidly brownish black, owing to the absorption of atmospheric oxygen, with which the manganous oxide forms a more highly oxidized body, of the com- position Mn 2 3 ,OH 2 , or { JJSoHo- This affinity for oxygen observed long ago by chemists, in the lower oxide of manganese, has been practically utilized of late for recovering the manganese from the chlorliquor, formerly run to waste by the manufacturers of bleaching powder. The oxidation is effected by blowing air through a mixture of milk of lime and man- ganous hydrate. The lower hydrated oxides of iron and of cobalt are acted upon in a similar manner by atmospheric oxygen, in the presence of an alkali (ammonia, soda). The oxides of non- metallic elements, such as of phosphorus or sulphur, exhibit the same affinity for water as some of the metallic oxides. Phosphoric anhydride, P 2 5 , absorbs moisture with great avidity from the atmosphere. A few flakes of the anhydride, when thrown into water, cause a hissing noise, and dissolve instantaneously, giving rise to an increase of temperature. Experiment 83. Sulphuric anhydride, SO 3 , is obtained as a white mass of crystals, resembling asbestos. When exposed to moist air the crystals fume, and rapidly deliquesce from absorption of aqueous vapour, and become converted into the hydrate, usually called sulphuric acid. Small portions of the anhydride when cautiously thrown into water, occasion each time a hissing sound, and the water gets intensely hot. The heat must have been stored up in the anhydride and in the water (both cold bodies at the ordinary temperature). The liquid reddens blue litmus-paper most intensely. On distilling the dilute acid in a retort, through the tubulure of which a thermometer is fitted air-tight by means of a soft cork, it yields first water, then hydrated acid, and the boiling- point rises gradually until it remains constant at 326 C. No further change is observed, and the remaining liquid rapidly distils over. Quantitative experiments have proved that this distillate is a ternary compound of S, O, and H, viz., SO 4 H 2 , or SO 3 OH 2 . The compound S^Os is represented graphically : ^8=0 88 ACIDS AND ANHYDRIDES. On passing sulphurous anhydride* slowly over plumbic dioxide, 3Pb0 2 , loosely spread out in a thin layer in a narrow tube of hard glass, the gas is eagerly absorbed by the binary compound, plumbic dioxide, with which it forms a white compound, called plumbic sulphate, S0 2 Pb0 2 . The same reaction takes place when manganic oxide, Billl0 2 , is employed manganous sulphate, S0 2 Mn0 2 , being formed. Experiment 84. Add to a concentrated solution of sulphurous anhydride gas in water, a solution of peroxide of hydrogen, O 2 H 2 , until the odour of the sulphurous anhydride gas has entirely disappeared. Sulphurous acid is instan- taneously converted into sulphuric acid on coming in contact with hydric per- dxide. S0 2 + O 2 H 2 = S0 2 H 2 2 , or S0 2 Ho 2 . Sulphurous Hydric Sulphuric anhydride. peroxide. acid. If we then regard the chemical compound which is formed when S0 3 and OH 2 are brought together, as consisting of sulphurous anhydride gas and hydric peroxide, we shall be able to represent it graphically as follows : O H S H and preserve in this manner the hexad nature of the sulphur atom. Manganous sulphate, containing in the place of the two atoms of hydrogen a dyad element, Mn, and plumbic sulphate, the dyad element, Pb, would then be written graphically O O 0=S S O O Mn O Pb The compound S0 2 is called sulphurous anhydride (from av, not, without, and v&up, water), and the compound SOa, sulphuric anhy- dride ; for oxides which form acids when they combine with water, or salts when added to bases, are termed anhydrides. Water is usually viewed as an oxide of hydrogen. It may, how- ever, also be regarded as a hydride of the semi-molecule HO. Many bodies of analogous nature occur among organic compounds, and we are, therefore, perfectly justified in taking this view of water, viz. : OH 2 = H HO. Hydric peroxide being then represented by H 2 2 = HO HO, * The preparation of this gas will be fully described in Chapter XIV. COMPOUND RADICALS. 89 the compound H 2 2 consisting of two parts of the binary compound HO, which has not as yet been obtained in an isolated condition, but exists merely in the form of the molecule. One of the semi- molecules, HO, in H 2 O 2 , takes the place of H in OH 2 , and it is, therefore, equivalentic to H ; i.e., it possesses the same binding power as hydrogen, or chlorine, or any other monad element." Such a group of elements which is capable of taking the place of one or more atoms of H is termed a compound radical. The radical HO has received the name of hydroxyl, and is conveniently expressed symbolically with a small o after the H, viz., Ho ; it must not be supposed, however, for a moment that a different atomic value appertains to the small o than the large 0. Hydric peroxide consists of two parts of the compound radical hydroxyl. Although Ho is a compound, it yet acts the part of a simple atom, because it enters into combination with other atoms, according to definite weight. Graphic representation illustrates clearly its monad nature, for we must write hydroxyl H only one hypothetical point of attachment of the oxygen atom being left by which it can join itself to hydrogen to form water, or to another hydroxyl radical to form hydric peroxide. In like manner there must be as many compound radicals possible as there are metals. A few may be said to correspond to the peroxides, but in most cases they are purely hypothetical creations, as the peroxides of many metals are unknown ; thus we have Compound radicals* corresponding to hydroxyl or its multiple. Ko (Potassoxyl). Bao" (Baroxyl). Mgo" (Magnesoxyl). Zno" (Zincoxyl). Feo" (Ferrosoxyl). Pbo" (Plumboxyl). Sbo'" (Antimonoxyl). Bio"' (Bismuthoxyl). Metals. Potassium. K Barium. . . Ba" Magnesium Zinc Mg" Zn" Iron Lead Antimony . Bismuth . . Fe" Pb" Sb"' Bi'" Ba0 2 Oxides. Peroxides. OK 2 BaO MgfO ZnO PeO PbO Sb 2 O 3 Bi 2 3 OK Ba The atoms of oxygen in these compound radicals are represented by a small o, indicating their binding function, as distinct from the atoms in the peroxides. In the peroxides the oxygen and metal * If it should be preferred to retain the large O for these compound radicals, they should be bracketed, and the atomicity coefficient placed outside the bracket, thus : (KO) (BaO,)" (Mg0 2 )" (Zn0 2 )" Potassoxyl Baroxyl Magnesoxyl Zincoxyl (Pb0 2 )" (Sb0 3 ) /// Plumboxyl Antimonoxyl Aluminoxyl 90 COMPOUND RADICALS. are connected by one bond only of the atoms, whilst the remaining bonds of the oxygen atoms satisfy each other ; this is indicated by bracketing the oxygen atoms. In the metalloxyls, on the other hand, the oxygen atoms are linked to one or more atoms of other elements, for example 01 I 9 Baric Peroxide BaX > Ba j ' O Baroxyl ...... Bao" Ba O The dashes and Roman figures after the small o indicate that the compound radicals which these metals form, are capable of replacing one, two, three, etc., of the monovalentic radical Ho. On viewing in like manner the sulphuretted hydrogen gas, SH 2 , which we obtained in Experiment 54, we may regard it either as water, OH 2 , in which the oxygen atom has been replaced by an atom of sulphur, or as the hydride of a compound radical hydrosulphyl, HS, analogous to hydroxyl, conveniently written with a small s, Hs, after the hydrogen, and represented graphically thus H S Only one point of attachment is left open in the dyad atom sulphur by which it can link itself to hydrogen to form sulphuretted hydrogen, or to a monad element, e.g., sodium, Na, potassium, K, to form Nails, KHs. The ternary chemical compounds which are obtained when water combines with metallic oxides to form hydrates must be expressed graphically in like manner. We may view potassic oxide, OK 2 , as composed of the compound radical potassoxyl " jo the radical in the molecule potassic dioxide QTT- or K 2 2 together with an atom of K, thus OK 2 = KKo; and potassic hydrate as a compound of K and Ho, the radical hydroxyl, Ho, replacing potassoxyl, Ko, in potassic oxide. K K, or K O K. K H, or K H. Metallic hydrates, then, may be viewed as binary compounds, in which one, two, three, or four parts of the compound radical hydroxyl are combined with one atom of a metal, according as the latter is of a monad, dyad, triad, or tetrad nature. Hydrates of monad metals Graphically KHo . NaHo . AgHo K Ho. HYDRATES. 91 Hydrates of dyad metals Ca"Hoa . Fe"Ho 3 . Pb"Ho 2 Hydrates of triad metals Au'"Ho 3 . Sb'"Ho 3 . Bi'"Ho 3 , Hydrates of tetrad metals Sn iv Ho 4 Sn iy = Ho 4 . Some of the metallic oxides possess little or no affinity for water, or, if they combine with it, form only weak chemical compounds, which are broken up again on the application of heat, into water, which is given off", and oxides. On the other hand, metallic oxides are often capable of fixing more than one molecule of water ; thus potassic hydrate (which is generally sold in the form of sticks, from having been run into cylindrical metallic moulds whilst in an oily condition ; or in lumps, from being poured into flat iron vessels and broken up when cold), if left exposed to the air attracts moisture very rapidly, and forms an oily liquid it deliquesces. Oil of vitriol, or sulphuric hydrate (which contains generally a little more than one molecule of water), also attracts moisture very eagerly. It is, therefore, employed for drying gases which are not acted upon by the acid. By passing gases through sulphuric hydrate, contained in a two-necked Woulfe's bottle, or through a drying tube filled with pumice-stone soaked in oil of vitriol, they are freed from moisture, and may be collected in a perfectly dry state. As the combination of a further molecule, or number of molecules of water with potassic hydrate or sulphuric hydrate is accompanied by a con- siderable rise in temperature, it is inferred that several hydrates of one and the same oxide may exist ; and this is actually the case. A tetrahydric sulphuric acid, for instance, exists, which boils at 242 C., and is formed from two molecules of water and one of sulphuric anhydride. Symbol S0 3 ,2H 2 O, or SOHo 2 Ho 2 , O H S H /\ O O / \ H H A natural compound, called gypsum (dried at 100 C.), is the acid salt of this tetrahydric acid, viz., SOHo 2 Cao" (dihydric calcic sulphate) . Ca /\ O \/ H O S H 92 PREPARATION OF HYDROCHLORIC ACID. It is usual to express dilute sulphuric acid by the formula S0 2 Ho 2 , and a solution of potassic hydrate or caustic potash, by the formula KHo, without regard to the amount of hydration which these bodies have undergone. The same formulas, however, possess likewise a definite meaning, expjeessing, as has been already shown, in the strict sense of our symbolic notation, sulphuric monohydrate, potassic monohydrate. QUESTIONS AND EXERCISES. 1. Define what is meant by reactions in the wet and dry way. 2. Give instances of combination between oxides and water, and state on what grounds you consider such compounds to be the result of a chemical and not merely mechanical combination. 3. Explain why hydrogen is evolved when zinc (Al, Cd, Mg) is acted upon by a concentrated solution of potassic hydrate. 4. How is red lead manufactured from massicot ? 5. How is red lead acted upon (1) by strong heat, (2) by nitric acid ? 6. How is baric oxide converted into baric peroxide, and how would you prepare from the latter a solution of hydric peroxide ? 7. Explain the action of heat upon a concentrated solution of hydric peroxide. 8. Mention instances of the oxidising action of hydric peroxide. Give equations. 9. Describe the action of air upon moist ferrous, manganous, or cobaltous hydrate. 10. What do we understand by the terms ternary compound, anhydride, peroxide, hydroxyl, catalytic action, hydrosulphyl, deliquescence 1 11. Give symbolic and graphic formulae of sulphurous and sulphuric anhydride, of dihydric sulphuric acid, of manganous sulphate, and of dihydric calcic sulphate. 12. Assign reasons for writing the symbolic formula of sulphuric acid, SO 2 Ho 2 , instead of SO 4 H 2 . 13. Define a compound radical. Give illustrations. 14. Write out the names of the compound radicals corresponding to hydroxyl, of the metals which are capable of forming the salifiable oxides enumerated on p. 50. Practise writing out symbolic and graphic formulae thereof. 15. Give symbolic and graphic formulae for baric peroxide, manganic oxide, plumbic dioxide, potassic dioxide, potassic hydrate, calcic hydrate, stannic hydrate, baroxyl, plumboxyl, argentic peroxide, argentoxyl, antimonious hydrate. 16. You have given to you quicklime, dilute sulphuric acid, and water ; what chemical combinations are you able to produce with these materials ? 17. Calculate the percentage composition of baric peroxide. 18. You have given to you 10 grms. of red lead and a solution of hydrochloric acid. State how you would prepare (1) oxygen, (2) chlorine, from these materials, and how much of each gas, by weight and by volume, you could prepare therefrom. CHAPTER XIII. HYDROCHLORIC ACID.-CONVERSION OF METAL- LIC OXIDES INTO CHLORIDES. Experiment 85. A flask fitted with a cork and delivery-tube is charged with a few pieces of fused sodic chloride ; oil of vitriol is added in sufficient quantity to cover the salt. On gently heating, a colourless gas is evolved, which, on coming in contact with the air, fumes considerably. CONVERSION OF METALLIC OXIDES INTO CHLORIDES. 93 The reaction is expressed by the equation NaCl + SO 2 Ho 2 = SO 2 HoNao + HC1. Hydric sodic sulphate. Hydrochloric acid gas can be obtained perfectly anhydrous by passing it through a U-tube containing pieces of pumice-stone, moistened with oil of vitriol (as was shown in Fig. 53), and can then be collected by displacement. For this purpose pass the delivery-tube to the bottom of a perfectly dry globular flask. The lighter air is gradually lifted out of the flask (Fig. 56) by the heavier gas (the sp. gr. of HC1 being T247, as com- pared with air), and its escape from the flask is marked by white fumes, produced by the combination of the otherwise trans- parent gas with the moisture of the air. Hydrochloric acid gas possesses a powerful attraction for water. In order to illustrate this, place the globular flask with its mouth downwards in a small capsule full of mercury. Trans- fer cautiously to a basin of water (Fig. 56), coloured blue by a few drops of litmus, and open the flask under water by raising its mouth out of the mercury. The water rushes in with great violence, for it is capable of absorbing 480 times its bulk of hydrochloric acid gas. The blue colour changes instantaneously to red. Experiment 86. Introduce a piece FIG. 56. ABSORPTION OF IIC1 GAS BY of freshly burnt lime (quick-lime) into WATER. dry hydrochloric acid gas, placed in a cylinder over mercury. The gas will be quickly absorbed and calcic chloride and water will be formed, according to the equation CaO + 2HC1 = CaCl 2 + OH 2 . Experiment 87. Introduce a lighted taper into a cylinder filled with dry hydrochloric acid gas. The taper is immediately extinguished. Hydrochloric acid gas does not support combustion, nor is it combustible. Experiment 88. Pass a slow current of dry hydrochloric acid gas directly from the drying tube over freshly ignited cupric oxide, CuO, placed in a porce- lain boat inside a tube of hard glass, in a manner similar to that shown in Fig. 22. The copper lays hold of the chlorine, and the oxygen combines with the hydrogen, according to the equation CuO + 2HC1 = CuCl 2 + OH 2 . The water is carried along and partly condensed in the further part of the tube, or carried with the undecomposed hydrochloric acid into a bottle contain- ing a solution of sodic hydrate. The black oxide of copper is converted into a greenish liquid, which is partly left in the boat, and partly volatilized and con- densed with a portion of the water. The reaction takes place in the cold, but much more rapidly when the part of the tube containing the boat is gently heated. On allowing it to cool, and dissolving the cupric chloride left in the boat by the addition of a little water, a green solution is obtained. The same change takes place when mercuric or zincic oxide is acted upon, according to the equation 94 PREPARATION OF METALLIC CHLORIDES. HgO + 2HC1 = HgCl 2 + OH 2 , ZnO + 2HC1 = ZnCl 2 + OH 2 , water being invariably produced, whilst metallic chlorides are formed. If no chloride exists corresponding to the oxide, part of the chlorine escapes, leaving a lower chloride of the metal as was the case in preparing chlorine 'from black oxide of manganese (Exp. 59), or when red lead is acted upon by hydrochloric acid. A solution of hydrochloric acid gas in water (sometimes called spirit of salt, muriatic acid, from the word muria,' brine, chlorhydric acid, and hydric chloride), is largely used in the laboratory, and constitutes one of the most indispensable reagents. Experiment 89. Put one part by weight of dry sodic chloride (common salt), and two parts by weight of concentrated sulphuric acid (previously diluted with one-third of water) in a flask (Fig. 47) , shake well up, connect with two or three Woulfe's bottles, and apply a gentle heat. Small quantities of sulphuric acid, which may be carried over, are arrested in the first Woulfe's bottle. The delivery-tubes should be adjusted so as to dip barely into the water, became the hydrochloric acid is so eagerly absorbed by the water as to cause the coflWmts of the Woulfe's bottles to recede, and because the acid liquid which is formed, being heavier than water, sinks rapidly to the bottom. A solution of pure hydrochloric acid should be quite colourless. Experiment 9O. Neutralize a solution of sodic hydrate, in the manner shown in Exp. 44, with dilute hydrochloric acid. The resulting sodic chloride, formed according to the equation NaHo + HC1 = NaCl + OH 2 . crystallises out on evaporation in a porcelain dish. Pour off the liquid and spread the crystals on filter-paper, placed on a porous tile, to dry. It follows from this experiment that a metallic chloride can be obtained also by neutralizing a solution of a metallic hydrate with dilate hydrochloric acid, and that such chlorides possess all the properties of chlorides obtained in the dry way. Metallic chlorides can, with few exceptions, be prepared, as we have hitherto* seen, 1. By the direct combination of chlorine with metals (comp. Expts. 65, 66, and 67), e.g., IVEg + 01, = MgCl 2 . 2. By the action of hydrochloric acid, either in the gaseous form or as dilute acid, upon metals (comp. Expts. 2 and 71), e.g., !STa 2 + 2HC1 = 2NaCl + H 2 . Graseous. Zn + 2HC1 = ZnCl 2 + H 2 . A dilute solution. * Other modes of forming metallic chlorides will be dealt with below. ACTION OF HYDROCHLORIC ACID UPON METALS. 95 3. By the action of hydrochloric acid, no matter whether as gas or in solution, upon metallic oxides (comp. Expts. 86 and 88), or sulphides (Exp. 54), e.g., CuO + 2HC1 = CuCl 2 + OH 2 . 4. By the action of dilute hydrochloric acid upon metallic hydrates (comp. Exp. 90), e.g., NaHo + HOI = NaOl + OH 3 . Methods 3 and 4 of preparing chlorides, moreover, are the most convenient and most generally adopted, since metallic oxides or hy- drates, which occur more frequently in nature than the metals, are much more easily and cheaply converted into chlorides than the metals themselves. This applies especially to the lighter metals, Na, K, Ba, Sr, Ca, Mg, Al. We can prepare in this manner potassic chloride, baric, and calcic chlorides, etc., by neutralising their corresponding hydrates with dilute hydrochloric acid, according to the equations KHo + HOI = KOI + OH 2 , BaHo 2 + 2HC1 = Ba01 2 + 2OH 2 , CaHo 2 + 2HC1 = CaCl 2 + 2OH 2 . Solutions thus obtained are termed chemical solutions, because the solvent, HC1, forms with the dissolved substance a chemical compound. It may be useful to examine for a moment somewhat more closely into the action of hydrochloric acid upon the more important metals (method 2), and to observe 1. That certain metals* are readily dissolved with evolution of ' hydrogen, viz., K', Na', Ba", Sr", Ca", Mg", Al 1 ?, Fe", Zn", Od", Ni", Co", and (pulverulent) Cr iv . 2. Others are only with difficulty soluble in boiling acid, viz., Sn". 3. Others again are but slightly attacked by hydrochloric acid, viz., Sb'", Pb", Ag', Bi'", Cu", and 4. A few metals are not affected either by cold or hot hydrochloric acid, viz., Au, Pt, As, Hg, and (crystalline) Cr. Hydriodic, hydrobromic, and hydrofluoric acid act in a similar manner upon metallic hydrates. They form iodides, bromides, and fluorides, e.g. KHo + HI = KI + OH 2 MgHo 2 + 2HBr = MgBr 2 + 2OH 2 NaHo + HF = NaF + OH 2 . * Practically no other but the few metals printed in thick type would ever be thus used for the preparation of metallic chlorides. The atomicity marks placed on the right hand side above the symbols indicate the nature of the chlorides which the different metals form under the given circumstances. Compare also table of metallic chlorides, p. 70. 96 FORMATION OF TERNARY OXY-COMPOUNDS. All metallic iodides and bromides, with the exception of argentic iodide and bromide, are more or less soluble in water or dilute nitric acid. Metallic fluorides, on the other hand, are for the most part insoluble in water, with the exception of the alkaline and a few other fluorides. The best known fluoride is calcic fluoride, or fluor spar, insoluble in water and dilute ucids. QUESTIONS AND EXEECISES. 1. How would you demonstrate the great solubility of hydrochloric acid gas in water ? 2. What is the action of dry HC1 gas upon dry metallic oxides? Give equations. 3. How is a concentrated solution of hydrochloric acid prepared ? 4. You have given to you a dilute solution of sodic hydrate and dilute hydro- chloric acid : state how you would prepare from these materials crystals of common salt ? 5. Explain the terms neutralize, chemical solution, evaporation. 6. Commit to memory the action of hydrochloric acid upon the more important metals. 7. Enumerate the different methods for preparing metallic chlorides, and state which methods you would follow if you had to prepare cupric chloride, mercuric chloride, zincic and ferrous chlorides, sodic chloride, stannous chloride. Give equations. 8. Give symbolic anCT graphic formulae for antimonious, cupric, magnesic, cobaltous, manganous, and argentic chlorides. 9. How much sulphuric acid (SO 2 Ho 2 , molecular weight 98) is required to de- compose 100 grms. of fused sodic chloride, so as to leave hydric sodic sulphate ? 10. How much metallic zinc can be dissolved by 50 grms. of hydrochloric acid containing 20 per cent, of acid by weight ? 11. How much dry hydrochloric acid gas by weight and by volume will be required to combine with 5 grms. of ignited cupric oxide ? CHAPTER XIV. FORMATION OF TERNARY OXY-COMPOUNDS FROM METALLIC HYDRATES AND OXY-ACIDS, SULPHUROUS AND SULPHURIC ACIDS, SUL- PHITES AND SULPHATES. SULPHUR combines, as we have repeatedly seen, directly with oxygen, and forms a binary compound, sulphurous anhydride, SO 2 , readily recognised by its pungent and suffocating odour. The gas is transparent and colourless, and does not burn nor support combustion (Exp. 22). It is soluble in water 1 volume of water dissolves at the ordinary temperature more than 40 volumes of the gas and furnishes by direct combination with it a ternary body, an acid, called sulphurous acid, consisting of sulphur, oxygen, and hydrogen, according to the equation S0 2 + OH 2 = SO 3 H 2 , or SOHo 2 . The aqueous solution acquires the taste and smell of the gas, and acts like a strong mineral acid. PREPARATION OF SULPHUROUS ACID. 97 In order to prepare a concentrated solution of sulphurous acid, we avail ourselves of the action which sulphuric acid exerts upon certain metals. Experiment 91. Introduce some copper clippings or "turnings into a flask provided with a funnel-tube and two delivery-tubes (Fig. 57). Add a little concentrated sulphuric acid, and heat gently over a sand-bath. As long as the glass stopcock on the left hand side delivery-tube, which dips into a solution of soda, remains closed, the sulphurous anhydride, which is copiously evolved, is forced to pass through a Woulfe's bottle containing water (for the purpose of arresting any sulphuric acid fumes), into a second bottle contain- ing distilled water. When the absorption of the gas ceases, and the glass stop- cock on the left is opened, the gas can be made to pass into the soda solution con- tained in the cylinder on the left, which absorbs it freely. Eemove the saturated solu- tion of sulphurous acid, and keep it in a well stoppered bottle for further use. FlG. 57. PREPARATION OF SULPHUROUS ACID. The reaction takes place according to the equation : Cu + 2S0 2 Ho 2 = S0 2 + S0 2 Cuo" Sulphurous Cupric anhydride. sulphate. 2OH 2 . The oxidation of the copper is effected at the expense of the sulphuric acid, with evolution of one molecule of S0 2 . A second molecule of SO 2 Ho 2 combines with the cupric oxide to form cupric sulphate, which is left behind in the flask, and which may be re- covered by diluting with water, filtering, and evaporating, when it is left in the form of fine blue crystals (S0 2 Cuo",5OH 2 ). Several other metals, e.g., mercury and silver metals, which, like copper, do not decompose water might have been substituted for the metallic copper. Non-metallic bodies, such as carbon (and various organic bodies), sulphur, etc., can likewise effect a partial deoxidation of the sulphuric to sulphurous acid. Experiment 92. Substitute for the wash-bottle containing water (Fig. 57) a Woulfe's bottle charged with concentrated sulphuric acid, and pass the dried sulphurous anhydride through a U-tube, tapped at the bend and surrounded by a freezing mixture consisting of ice and salt, at 10 0. The gas condenses readily to a colourless liquid of specific gravity 1*49, which becomes solid at 76. Draw off some liquid SO 2 , into a test-tube, and watch for the deposition of a hoar-frost. Add a little water, and observe the freezing of the water, and the vaporisation of the sulphurous anhydride, by the heat which it suddenly abstracts from the water. Liquid sulphurous anhydride may be preserved in sealed tubes. 98 SULPHUROUS ACID. Experiment 93. Collect some sulphurous acid by displacement (comp. Exp. 70) in a glass jar. Introduce a bunch of roses and stopper up the jar. The flowers -will become bleached, but their colours are not destroyed, as was the case with chlorine gas, for on adding either an alkali (a dilute solution of am- monia) it is at first restored, and then changed to a green ; or, on the addition of a stronger acid (sulphuric), -the colour is^agam restored. The same may be shown by means of q)n infusion of red cabbage leaf or log- wood. Experiment 94. Add to a solution of sulphurous acid, drop by drop, a solution of potassic permanganate (mineral chamseleon), and observe that the colour of the latter is permanently destroyed, for neither alialies nor acids can restore it. The change depends in this case upon the oxidation of the sul- phurous into sulphuric acid, whilst in the case of the vegetable colouring matters the acid does not appear to be acted upon, but seems rather to form colourless combinations with them. Stains of fruit, port, or claret, etc., can be removed from linen by treatment with a solution of sulphurous acid. Woollen goods, silk, straw, sponge, isinglass (glue), are bleached by exposure, in a moist state, to the fumes of burning sulphur, or by immersion in a solution of the acid. Sulphurous acid is likewise a powerful disinfectant. It is used for arresting fermentation in beer, wine, cyder, &c. An alcoholic solution of sulphurous acid is one of the most powerful disinfectants for sick-rooms. Although oil of vitriol may be broken up into oxygen and sul- phurous acid by allowing it to fall upon white-hot platinum, the combination of the sulphur dioxide, SO 2 , with a third atom of oxygen, so as to form sulphur trioxide, S0 3 , has to be effected by indirect means. Experiment 95. Expose a freshly prepared solution of sulphurous acid in a shallow vessel for some time to the oxidizing action of the air. Add then a few drops of a solution of baric chloride to the solution ; a white precipitate of baric sulphate, SO 2 Bao", insoluble in dilute hydrochloric acid, will be obtained, whilst the precipitate produced in the acid before exposure, consisting mainly of baric sulphite, SOBao", is all but soluble. Experiment 96. Add a few drops either of nitric acid, of chlorine water, or hydroxyl, to another portion of the aqueous sulphurous acid, and test in like manner. A heavy insoluble white precipitate is left. Neither of these oxidizing agents give by themselves a precipitate with baric chloride. Certain porous bodies, such as platinum Hack or spongy platinum, prepared by strongly heating platinic chloride (PtCl 4 ), appear by a kind of catalytic action to facilitate the combination of a third atom of oxygen with the sulphurous acid, by condensing the two gases within their pores. Experiment 91. Charge a piece of combustion glass, drawn out at one end to an open point, as seen in Fig. 58, with spongy platinum (a coil of fine platinum gauze or even platinized asbestos) . Heat the tube" to a low red heat, and pass a slow current of SO 2 and oxygen over it two volumes of the former to one volume of the latter. In order to regulate the two currents approxi- matively, the gases are each passed through a wash-bottle containing oil of vitriol, before they enter the empty three-necked Woulfe's bottle, where they mix (diffuse) previous to their passing over the spongy platinum. SULPHURIC ACID. 99 Dense white suffocating fumes are formed in the tube, and as soon as the gas comes in contact with the moisture of the atmosphere on issuing from the tube (both oxygen and sulphurous anhydride are colourless gases), which, when passed FlG. 58. SOa PREPARED DIRECTLY FROM 80-2 AND OXYGEN. into water, are absorbed. Hold a gas jar (comp. Exp. 6), moistened inside with water, or a dilute solution of ammonia, for a few minutes over the jet, and then test the condensed acid or solution of the ammonic salt by means of a solution of baric chloride. A dense white insoluble precipitate of baric sulphate is obtained. Filter and add some chlorine water to the clear filtrate. No farther precipitate (comp. Exp. 96) comes down. The whole of the sulphurous anhydride has been converted in the experiment into sulphuric anhydride, thus : SO 2 + O = SO 3 . The strongest sulphuric acid, so-called Nordhausen acid, from a town in Saxony, where it was mainly manufactured, is obtained by distilling well dried ferrous sulphate (green vitriol) in earthenware retorts, and condensing the acid fumes in glass or earthenware vessels. Heat liberates the acid, leaving Fe 2 3 as a red powder, known as colcothar (rouge), which is used for polishing plate glass, metals, &c. The change is pretty correctly expressed by the equation : 2S0 2 Feo" = Pe0 a + S0 3 + S0 2 . Sulphuric Sulphurous anhydride, anhydride. Some sulphuric acid is, however, always formed, since the whole of the water is in practice never driven off entirely from the green vitriol (SO 2 Feo",7OH 2 ) before it is submitted to destructive distillation, and the composition of the acid (called oil of vitriol, from its oily appearance), should, therefore, be expressed by the formula fS0 2 Ho S0 2 Ho 2 ,S0 3 , or^ O LS0 2 Ho This process, discovered four centuries ago by the German alche- mist Basil Valentine a discovery which had the greatest influence upon the progress of chemistry has now been almost entirely superseded by the so-called English process of manufacturing sul- phuric acid. The reactions involved in this latter process will be explained when a knowledge of the oxides of nitrogen has been acquired. H 2 100 SULPHITES AND SULPHATES. Concentrated sulphuric acid is a powerful dehydrating agent. It chars almost all organic substances by depriving them of their hydrogen and oxygen (or water). When mixed with water it gives out great heat, so that much care should be observed in diluting the strong acid. Experiment 98. Pour a little of the strong acid over some wooden shavings. The wood becomes blackened almost instantaneously. Experiment 99. Add one volume of concentrated sulphuric acid to two volumes of strong syrup of sugar placed in a capacious beaker on a plate ; stir up quickly. The liquid becomes intensely hot, and swells up to a bulky, black, porous mass of finely divided charcoal. Sugar consists of Ci 2 H 22 On, and is broken up by the acid into 12 atoms of carbon and 11 molecules of water, which combine chemically with the sulphuric acid. Hence the great heat which accompanies the chemical change. Both sulphurous and sulphuric acid, by combining with salifiable bases, form most important salts, called sulphites and sulphates, neutral if the whole of the hydrogen of the acids is replaced by a metal, as e.g. : 2ETaHo + SOHo 2 = S0tfao 2 + 2OH 2 . Sodic sulphite. 2KHo + S0 2 Ho 2 = S0 2 Ko 2 + 2OH 2 , Potassic sulphate. acid, if only one-half of the hydrogen is displaced, e.g. : NaHo 4- SOHo 2 = SOHoNao + OH 2 . Acid, or hydric sodic sulphite. KHo + S0 2 Ho 2 = S0 2 HoE:o + OH 2 . Acid, or hydric potassic sulphate. Potassic sulphate, like sodic chloride, has neither acid nor basic properties ; it is an indifferent or neutral body. Sulphates of the alkali metals are soluble in water. Baric sulphate is practically insoluble in water as well as in dilute acids ; strontic, calcic, and plumbic sulphates nearly so, argentic sulphate is difficultly soluble in water. All other metallic sulphates are soluble in water. Metallic sulphates can, with few exceptions, be prepared 1st. By the action of sulphuric acid upon the metals,* (a) with evolution of hydrogen when the acid is dilute, e.g., K, Na, Ba, Sr, Ca (the last three metals are imperfectly acted upon on account of the formation of insoluble sulphates). Mg, Al (requires the application of heat) Fe", Zn", Cd, * Practically no others than the metals printed in thick type would ever be dissolved in sulphuric acid for the purpose of preparing their sulphates. METALLIC SULPHATES. 101 Ni, Co, Mn, and (pulverulent) Cr, Sn (imperfectly acted upon by dilute sulphuric acid with evolution of hydrogen). (6) by the action of concentrated sulphuric acid with evolution of sulphurous anhyride, especially on heating, e.g., Cu", Bi'" Hg" Ag', Sb'" and Sn", Pb (slightly soluble only on heating). whilst a few metals, such as Au, Pt, As and Cr (crystalline) are not affected by concentrated sulphuric acid. 2nd. By the action of dilute sulphuric acid upon metallic owides, or sulphides, e.g. S0 2 Ho 2 = S0 2 Zno" + OH 2 . Zincic Zincic oxide. sulphate. PeS + S0 2 Ho 2 = S0 2 Feo" + SH 2 . Ferrous Ferrous sulphide. sulphate. 3rd. By the action of dilute sulphuric acid upon metallic hydrates, e.g. MnHoa + S0 2 Ho 2 = S0 2 Mno" + 2OH 2 , Manganous Manganous hydrate. sulphate. 4th. By the action of sulphuric acid upon metallic chlorides, etc., e.g. 2NaCl + S0 2 Ho 2 = S0 2 Nao 2 + 2HC1, Sodic Sodic chloride. sulphate. Metallic sulphites are readily produced by adding a solution of sulphurous acid to a metallic hydrate, oxide, etc. The grouping ele- ment sulphur acts as a tetrad element. Its bonds are satisfied in metallic sulphites by one atom of dyad O and two of a monad, or one of a dyad metalloxyl, thus : - Symbolically. Graphically. O SOHoNao Na O S H O SONao a Na S O Na SOCao" Sulphurous anhydride is readily liberated from metallic sulphites by the action of hydrochloric, or sulphuric acid. Potassic sulphate is the representative of a large number of 102 CARBON. ternary compounds called oxy-salts, because three elementary bodies enter into their composition, one of which is always oxygen. Salts may thus be divided into 1. Haloid salts (binary compounds), e.g., chlorides (bromides, iodides), etc. 2. Oxij-salts (ternary compounds), e.g., sulphates, sulphites, and many others, and the same nomenclature is used in the case of oxy- salts which was adopted for haloid salts, viz., the name of the metallic element is employed adjectively, and that of the acid substantively ; the name of the acid element of oxy-salts ending, however, as in potassic sulphate and sodic sulphite in ate and ite, in order to distinguish them from the acid element of haloid salts which terminate in ide, as potassic chloride. QUESTIONS AND EXEECISES. 1. You have given to you an alloy of silver and copper (e.g., a sixpenny piece) and sulphuric acid. State what chemical compounds can be produced from these materials. Express the changes by equations. 2. Describe how you would prepare liquid sulphurous acid. 3. How would you demonstrate the bleaching and disinfecting action of sul- phurous acid ? G-ive an explanation of it. 4. How is sulphurous acid acted upon by air, by nitric acid, by hydric per- oxide? 5. Describe how SO 2 and oxygen gas can be made to combine directly with each other ? 6. How is Nordhausen sulphuric acid obtained ? 7. Explain the action of concentrated sulphuric acid upon wood or syrup of sugar. 8. How would you prepare neutral and acid sodic sulphite or potassic sulphate ? 9. Describe methods for preparing magnesic sulphate, mercuric, and zincic sulphates. Express the changes by equations. 10. Explain what nomenclature has been adopted for distinguishing haloid from oxy-salts. Give illustrations. 11. Practise symbolic and graphic formulae of the following compounds : sul- phurous acid, hydric sodic sulphite, calcic sulphate, magnesic sulphite, ferrous and ferric sulphates, argentic sulphite. CHAPTEE XV. CARBON, its Properties. CARBONIC ANHYDRIDE, CARBONIC OXIDE. CARBONATES. Carbon is one of the most important elements with which we are acquainted. It occurs in nature mainly in combination with other elements, such as oxygen, hydrogen, etc. It constitutes the essential element of everything organic, both of vegetable and animal origin. We are familiar with three varieties three so-called allotropic forms of carbon, viz., (1) amorphous carbon mineral and artificially prepared ALLOTROPIC FORMS OF CARBON.' 103 charcoal, coke, etc., (2) graphite or black-lead (plumbago), "kish," the graphitic carbon which often separates from melted pig-iron, and (3) diamond, the hardest of known substances, consisting of crystallised carbon, brilliant, transparent, and generally colourless. In all these forms carbon is infusible and non- volatile, and appa- rently unalterable in the air and in water at ordinary temperatures. Combined with oxygen and hydrogen, a little nitrogen and sulphur, and more or less mineral matter (ash), it constitutes some of the most important natural substances, such as anthracite (culm), con- taining 90 94 per cent, of carbon and but little volatile matter ; house or pit coal, containing varying quantities (from 80 90 per cent.) of carbon, varying through cannel and bituminous coals of numerous varieties down to lignite or brown coal, which still bears the imprint of the fibrous structure of the wood from which it is derived. Experiment 1OO. Heat a small piece of wood in a test-tube, loosely kept closed with the thumb, and observe the changes. Some water and tarry matter pass off, which condense in the upper part of the tube, as well as some gaseous matter, which burns with a bright flame, and the wood will be found to be con- verted into charcoal. By heating bituminous coal out of contact with air, in so-called coke-furnaces, or, for the purposes of manufacturing coal-gas, in long iron or clay retorts, a large quantity of gas and of tar distils off, which are either for the most part consumed in the coke furnace or systematically collected, and the gas stored up in gas- holders for illuminating purposes. The coke which is left in these processes of destructive distillation constitutes a porous mass of carbon, resembling graphite in its properties, but retaining all the mineral impurities of the coal. Animal charcoal or bone-black, another variety of less pure carbon, is obtained by heating bones in iron retorts. It contains about 90 per cent, of mineral matter (calcic phosphate), and is largely used by sugar refiners as a decolorising agent. Ordinary wood charcoal, as well as animal charcoal, possesses a remarkable power of absorbing gases, owing to its great porosity. The latter especially is used as an energetic disinfecting agent. Foul gases are oxidized by being brought, within its pores, in close con- tact with the atmospheric oxygen. We have already become acquainted with a gaseous compound of carbon and oxygen, called carbonic anhydride, obtained by burn- ing carbon in air or oxygen (Exp. 24), and have experimentally established, both synthetically (Exp. 24) and analytically (Exp. 32), that these two elements enter into its composition. Traces of this gas are invariably found in the air ; the amount varies from '03 to ;06 per cent, in pure air, and from 3J to 4 per cent, in air which passes from our lungs. Experiment 1O1. This may be shown by exposing some clear lime-water in a shallow glass dish to the air, when it will speedily become covered with a white pellicle of calcic carbonate or chalk (comp. Exp. 27) ; or by blowing the breath, by means of a glass tube, fron*the lungs through lime-water. The 104 PREPARATION OF CARBONIC ANHYDRIDE. latter will even more speedily become turbid, owing to the formation of calcic carbonate. The reaction is expressed by the equation CO 2 + CaHo 2 = COCao" + OH 2 . Respiration in animals is always attended with the formation of carbonic anhydride. Combustion of organic (or carbon) substances, slow decay, fermentation of saccharine matter, etc., likewise give rise to its evolution, and the gas would go on accumulating in the air were it not for growing plants, which under the influence of sun- light decompose it by storing up the solid carbon and setting free the oxygen, and for the rain, etc., which carries it down again to the earth into springs and rivers, wherewith to feed and nourish the roots of the plants. Water, beer, champagne, lemonade, etc., owe their briskness and freshness to the presence of more or less carbonic anhydride which they hold in solution. Soda-water is spring water charged with the gas under pressure. At the ordinary temperature, and without any pressure, water absorbs about its own bulk of it. The setting and hardening of ordinary mortar (slaked lime mixed with more or less sand) is due to a great extent to the absorption of carbonic anhydride and the slow conversion of the caustic into carbonated lime or chalk. From this source, as well as from cer- tain mineral bodies con- taining it, such as chalk, marble, it may be readily obtained by the action of hydrochloric or other acid. Experiment 1O2. Intro- FlG. 59. PREPARATION OP CARBONIC ANHYDRIDE. duC6 into a Woulfe's bottle* (Fig. 59) a few pieces of marble, and add through the funnel-tube dilute hydrochloric acid. Effervescence ensues, and a colourless gas comes off. Fresh acid is added from time to time, as long as any marble is left undissolved. The reaction is expressed by the equation COCao" + 2HC1 = CaCl 3 + C0 2 + OH 2 . Calcic Calcic carbonate. chloride. We can readily collect some of the gas over water in glass cylin- ders, and have no difficulty in recognising it as carbon dioxide or carbonic anhydride, since it is acid to litmus-paper, extinguishes a light, is heavier than air, and gives a white precipitate with lime or baryta- water. Its specific gravity compared with air is 1'529 or 1*529 = 22, when compared with hydrogen. One litre of the two- '0691 * Instead of this simpler apparatus, we may also employ the apparatus described in Exp. 54, and secure thus*a constant supply of CO 2 . PREPARATION OP METALLIC CARBONATES. 105 volume vapour carbonic anhydride, consisting of one atom of carbon , , . , 32 -f 2 x 16 00 , . and two atoms of oxygen, weighs as 22 times as much a as a litre of hydrogen, or 22 criths, i.e., 22 X '0896 grm. == 1*9712 grm. The molecular weight of carbonic anhydride is therefore 44. It is written graphically O=C=O, carbon being a tetrad element. Subjected to a pressure of 38 -J atmospheres at C., it condenses to a colourless limpid liquid of specific gravity '83, and by allow- ing a fine jet of the liquefied gas to issue into the air, the rapid evaporation of one portion freezes another, producing a snow-white flocculent solid mass, which may be formed into balls like snow. The density of gaseous carbonic anhydride may be illustrated in various amusing ways. The gas may be poured from one vessel into another, drawn off by a syphon, ladled out, poured into a glass vessel accurately counterbalanced on a pair of scales ; soap bubbles of air may be made to float and rebound on its sur- face, etc. Experiment 1O3. Pass some carbonic anhydride into a solution of caustic soda, NaHo. The gas is absorbed. On evaporating the solution to dryness, and igniting gently in a porcelain dish, then dissolving the dry mass once more in hot water, crystals of a salt are obtained, which analysis has shown to be composed of three elementary bodies, viz., sodium, carbon, and oxygen. Its formation is explained by the following equation : 2NaHo + C0 2 = CONao 2 + OH 2 . The salt is disodic carbonate, and is one of a large and important class of salts called carbonates. The tetrad element carbon forms the grouping element, its bonds being satisfied by one atom of dyad oxygen, and two of the monad radical sodoxyl, Nao. It is ex- pressed graphically : O C Na. We have now to add one more method to the four methods enumerated above for preparing metallic chlorides, etc., viz., by tlie action of dilute hydrochloric acid upon metallic carbonates, e.g. COCuo" + 2HC1 = CuCl 2 + C0 3 + OH 2 . COMgo" + 2HC1 = MgCl 2 + C0 2 + OH 2 . It is obvious that metallic sulphites and sulphates may, in like manner, be prepared from metallic carbonates, by treating the latter with dilute sulphuric acid, etc., e.g. COFeo" + S0 2 Ho 2 = S0 2 Feo" + C0 2 + OH 2 , Ferrous Ferrous carbonate. sulphate. and as many metals occur in nature more or less abundantly in the form of carbonates (e.g., K, Na, Ba, Sr, Ca, Mg, Fe, Zn, Mn, Pb, 106 CARBONIC OXIDE. Cu), this method of preparing chlorides, sulphites, and sulphates, and, as we shall shortly see, other salts also, will at once recommend itself as the most convenient and cheapest, especially as carbonates are, for the most part, decomposed with great facility even by weak organic acids, such as ac.etic or tartaric acid. Experiment 1O4. Pass carbonic aijhydride gas through a solution of baric hydrate, BaHo 2 . The gas is likewise absorbed, and a white precipitate falls as soon as the first bubbles of the gas are passed into the solution. The precipita- tion ceases after a while, and by filtering off the white powder, which consists of barium, carbon, and oxygen, we obtain a salt called baric carbonate, insoluble in water. Its formation is expressed by the equation BaHo 2 + C0 2 = COBao" + OH 2 . On passing carbonic anhydride gas somewhat longer through the solution in which some of the precipitate is suspended, the latter disappears, and the liquid becomes once more clear. Excess of carbonic anhydride, then, dissolves the baric carbonate (comp. Exp. 27). It combines, in fact, with the caustic alkalies and alkaline earths in two proportions, forming either a neutral carbonate or an acid, or hydric carbonate respectively. The carbonates of the alkali metals are soluble in water, all other (neutral) carbonates are insoluble. One more compound only of carbon with oxygen exists, and claims a brief notice, viz., carbonic oxide, "C"0, containing just half as much oxygen as the oxide already described. Experiment 1O5. Pass a slow current of carbonic anhydride over lumps of charcoal contained in a porcelain (or iron) tube, and heated in a charcoal fur- nace, as seen in Fig. 49, or a Hofmann's gas furnace. Collect the gas in glass cylinders over water as it issues from the tube. Apply a light to the mouth of the cylinder : the gas will burn, at the mouth of the cylinder only, with a fine blue flame characteristic for carbonic oxide gas. The carbonic anhydride is deprived of half its oxygen by being brought into contact with ignited carbon, and becomes converted into carbonic oxide : C iv 2 + C = 2"C"O, in which two bonds of the element carbon have become latent. The volume of the gas is exactly doubled. This experiment explains some of the chemical changes we observe in ordinary coal fires, in blast furnaces, etc. Instead of preparing carbonic oxide by the action of carbon upon carbonic anhydride, it is usually prepared for laboratory pur- poses by breaking up certain carbon compounds, by acting upon them with sulphuric acid. Experiment 1O6. Heat in a flask (Fig. 60) some crystallised oxalic acid with about 10 times its weight of oil of vitriol. Pass the gaseous mixture, which consists of CO and CO 2 , through a wash-bottle containing a solution of caustic soda, in order to absorb the CO 2 (comp. Exp. 103), and collect the carbonic oxide over water. Oil of vitriol is, as we know, a powerful dehydrating agent, and by abstracting water from the oxalic acid the remnant C 2 O 3 imme- diately breaks up into CO + CO 2 . The reaction is expressed by the equation : PREPARATION OF CARBONIC OXIDE. 107 COHo + SO ' H 2 = " C " + CiV * + SOHo 2 Ho 2 . Oxalic Carbonic acid. oxide. FlG. 60. PREPARATION OF CARBONIC OXIDE. Experiment lO 1 ?. Another method of preparing this gas consists in heat- ing some sharply dried potassic ferrocyanide (or yellow prussiate of potash) with about 10 times its weight of oil of vitriol. Employ a flask with a wide delivery tube, as the gas comes off after a time very quickly. Collect over water. The composition of yellow prussiate is expressed by the some- what complicated formula, IQFeCeNe^OH^. On. heating the dried salt together with sulphuric acid, it breaks up into pure carbonic oxide, while the whole of its nitrogen remains behind as ammonic sulphate, and the potassium and iron likewise as sulphates. The reaction may be expressed by the equation : eNe + 6S0 2 Ho 2 4- 6OH 2 = 6CO + 2S0 2 Ko 2 + S0 2 Feo" Potassic ferro- Carbonic cyanide. oxide. 4- 3S0 2 Amo 2 . Experiment 1O8. Inflame a cylinder of carbonic oxide, and introduce a lighted taper. The light will be extinguished, but the gas will continue to burn, at the mouth of the cylinder, with a blue flame. It deports itself in this respect like hydrogen gas (comp. Exp. 3). Add now a little lime- water and shake up. A white precipitate of chalk will be produced. Experiment 1O9. Add lime-water to another cylinder filled with the gas, without previously inflaming it. Shake up. No precipitate will be produced. This shows that carbonic anhydride has been produced by the combustion of carbonic oxide in air. Two vols. of CO require one vol. of 0, according to the equation : CO + O = C0 2 , and are converted into 2 vols. of C0 2 , i.e., the 3 volumes of the two gases contract into 2 volumes. 108 PROPERTIES OF CARBONIC OXIDE. Carbonic oxide has a specific gravity of '967, as compared with '967 air, or = 14, when compared with hydrogen. One litre of the two volume gas weighs - = 14 times as much as a litre of hydrogen, or 14 criths, i.e., 14 -f '0896 grm, = 1*2544 grm. The molecular weight of carbonic oxide is 28. This gas has not been liquefied. It is but little soluble in water (1 vol. of the gas.dissolves in 40 vols. of water). It is colourless, possesses a faint oppressive odour, is totally irrespirable, and is very poisonous. One part of the gas in 100 parts of air speedily produces a sensation of giddi- ness, and when inhaled for any length of time proves fatal. Carbonic oxide dissolves slowly when agitated with a hydrochloric acid solu- tion of cuprous chloride, Cu 2 Cl 2 . Both carbonic oxide and dioxide are normal constituents of ccal gas. Carbon forms a compound also with nitrogen, called cyanogen^ with sulphur, with hydrogen, the so-called hydrocarbons which belong to organic chemistry, also compounds with many metals, termed carbides. The study of these compounds must, however, be left to a course of lectures. QUESTIONS AND EXERCISES. 1. How does the element carbon occur in nature ? 2. Describe the allotropic modifications of carbon. 3. Explain the action of heat upon wood, coal, coke, in close vessels. 4. Explain the decolorising and disinfecting action of wood and animal charcoal. 5. What changes take place when carbonic anhydride is successively passed into distilled water, into solutions of baric or calcic hydrate ? 6. Describe several sources of carbonic anhydride, 7. Find the volume weight of carbonic anhydride, and calculate the weight of 66'5 c.c. of the dry gas. 8. You pass 6 litres of oxygen over 5 grins, of carbon (charcoal). How much carbonic anhydride by volume and by weight can you obtain by the combustion of the carbon in oxygen, and how much carbon, if any, will be left? 9. How much carbon will be required to convert 10 litres of carbonic anhy- dride into carbonic oxide, and what will be the volume of the gas so obtained. 10. How much carbonic anhydride by weight and by volume will be required to convert 2'5 grms. of NaHo into disodic carbonate ? 11. Give the symbolic and graphic formulae of the following compounds : carbonic anhydride, carbonic oxide, baric carbonate, argentic carbonate, ferrous carbonate, hydric potassic carbonate. 12. Describe several methods for preparing pure carbonic oxide. Give equa- tions. 13. How would you experimentally distinguish CO 2 from CO ? 14. Describe the distinctive properties of both gases. 15. Explain the terms : plumbago, culm, kish, coke, lignite, animal charcoal, mortar, choice damp, yellow prussiate, cyanogen, hydrocarbon, carbide. OXIDES OF NITROGEN. 109 CHAPTER XYI. THE OXIDES OF NITROGEN. MANUFACTURE OF SULPHURIC ACID. Two important compounds containing 1 one of the oxides of nitrogen in combination with the alkali metals potassium and sodium exist in nature, and are known to us as potash nitre (or saltpetre) and soda nitre (Chili saltpetre, cubic nitre). The affinity which nitrogen possesses for oxygen is so feeble, that in atmospheric air (which consists of a mixture of these two gases) they exist side by side with- out combining ; and it is only by the most powerful agencies (such as electrical discharges) that very trifling quantities of an acid pro- duct of oxidation can be obtained. Nitre is principally found in tropical countries, where the rapid oxidation of certain organic nitro- genized bodies, such as animal excrements, and especially urine, under the influence of a hot tropical sun, notably in presence of porous lime soils and soils rich in alkalies, produces this most im- portant of nitrogen compounds in considerable quantities. We know of no reactions by which the oxides of nitrogen could be formed directly from their elements in appreciable quantities. The affinity which draws their component atoms together being found very feeble, their power of resisting decomposition is proportionally weak ; and hence it is that these compounds part readily with their oxygen, and that the different oxides of nitrogen are among the most powerful oxidizing agents known. The combustibility of a gas depends upon whether we can raise it to a sufficiently high temperature to cause it to ignite, i.e., to combine chemically with oxygen, etc., in other words whether it has a low or high ignition point. By employing the electric spark (which may be said to be as much hotter again, as a blast furnace is compared with ice) we can succeed in combining nitrogen with oxygen. Experiment 11O. Pass the electric spark through a mixture of nitrogen and oxygen, or through moist air, contained in a tri-tubulated glass globe (Fig. 61). Increase the pressure by connecting the open glass-tube with a forcing pump, since gases are known to burn more readily and with intenser light when under pres- sure. Place some damp blue lit- mus-paper into the glass-globe. In 5 to 10 minutes from the time when the electric spark has FIG. 61. COMBINATION OF OXYGEN AND NITBOGEN BY been first sent through the gase- ELECTRIC DISCHABGES. ous mixture, red fumes are ob- served and the blue litmus-paper is seen to turn red. An acid results from the combination of the two gases, called nitric acid. 110 PREPARATION OF NITRIC ACID. FlG. 62. PREPARATION OF NITRIC ACID. Rain-water generally contains traces of nitrous and nitric acid in the form of ammonic nitrite and nitrate, owing to the action of light- ning or atmospheric electricity. The quantities so found are greater in tropical countries, where electrical discharges in the air are more frequent and more powerful. Experiment 111. Introduce into a small retort (Fig. 62) a little nitre with sufficient concentrated sul- phuric acid to cover the salt. Care- fully prevent the acid and the salt from coming in contact with the neck of the retort. Apply gentle heat. A reaction is seen to take place, and ruddy vapours come off which condense in the neck of the retort. The receiving flask should be kept cool by partially immersing it in a basin of cold water, and by cover- ing it with a wet cloth or filter-paper. The distillation continues briskly for some time, and an orange-red liquid condenses in the receiver. The opera- tion may be discontinued when no more ruddy vapours are observed in the body and neck of the retort. The liquid in the receiving flask reddens blue litmus instanta- neously. It is an acid body called nitric acid. Analysis has proved that it is a ternary body, composed of nitrogen, oxvgen and hydro- gen, viz., N,0 3 ,H. Nitrogen being, however, a pentad element, it follows that in 2N0 3 H, which we may view as obtained by the com- bination of one molecule of N 2 O 5 with one molecule of OH 2 , six atoms of dyad oxygen and two atoms of monad hydrogen cannot be united directly to two atoms of nitrogen ; but that the two atoms of hydrogen link themselves to two atoms of oxygen to form two semi- molecules of the compound radical hydroxyl. This may be shown graphically as follows : 00 O 0=N N=O + H H = 20=-N H. Or, if we view nitric acid as the result of the direct combination of the next lower oxide of nitrogen, W 2 O 4 , or nitric peroxide (the prepara- tion of which will be explained below), with one molecule of the compound radical hydroxyl, Ho 2 , the equation will be N 2 4 + Ho 2 = 2W0 2 Ho. Nitric Hydroxyl. Nitric peroxide. acid. or expressed graphically 0=N=0 + H H = 20=N H, CONSTITUTION OF NITRIC ACID. Ill we find that one molecule of anhydrous N 2 5 , or one molecule of N 2 0, must give rise to two molecules of nitric hydrate or nitric acid, the atom group NO 2 remaining unchanged, like the group S0 2 , in S0 2 Ho 2 . The pentad element nitrogen links together two atoms of dyad oxygen as well as the monad radical hydroxyl, and we therefore write the graphic formula of nitric hydrate or nitric acid O 0=N =N H- The distillate collected in the receiving flask consists of a more or less concentrated solution of nitric acid. It attracts moisture from the air and holds it chemically combined, yielding it up again only by round-about processes, and not without suffering partial decomposition. On warming the flask ruddy fumes of a suffocating and poisonous nature are given off, and the remaining liquid becomes colourless or nearly so. The volatile gaseous portion consists of lower oxides of nitrogen. It is evident therefore that the affinity which nitrogen possesses for oxygen in nitric acid is not sufficient even to resist its partial decomposition upon simple distillation. The liquid remaining in the retort solidifies on cooling to a saline crystalline mass of hydric potassic sulphate. It is possible under given conditions, e.g., excess of acid, to obtain a sulphate in which only half the Ho is replaced by Ko. The nitric acid also comes off at a considerably lower temperature, and is therefore less coloured by lower oxides of nitrogen the products of the decom- position of nitric acid. Such a salt is called an acid salt. Only dibasic or dihydric acids are capable of forming acid salts. Mono- basic acids (such as nitric acid), containing one replaceable Ho, can only form one kind of salts. The action of sulphuric acid upon nitre or potassic nitrate is expressed by the equation N0 2 Ko + S0 2 Ho 2 = WOoHo + S0 2 HoKo. Hydric potassic sulphate. A more dilute nitric acid formed from one molecule of UT 2 5 , and four molecules of water is a much more stable liquid. The degree of hydration in the case of nitric acid, as in that of other acids, is generally not expressed by the formula assigned to the dilute acid. The strongest nitric acid is a fuming, intensely corrosive liquid, which stains the skin yellow and destroys the epidermis. It has a specific gravity of 1*52. Cooled to about 40 C., it freezes, and heated to 85'5 it boils, suffering partial decomposition. Many organic non-nitrogenous bodies, such as cotton, glycerin, sugar, benzol, carbolic acid, are converted by it into violently- explosive bodies. The acid of 1'4<2 sp. gr. has a definite boiling point of 120'5, but is not, therefore a definite hydrate. 112 NITRATES. NITRIC PEROXIDE. Nitric acid forms with metallic oxides, hydrates, or carbonates, salts called nitrates* which are all soluble in water, e.g., KHo + W0 2 Ho = N0 2 Ko + OH 2 . CaHo 2 PbO + 2N0 2 Ho = n 2pbo " + OH 2 . /N0 2 Bi 2 3 + 6N0 2 Ho = 2[ N0 2 Bio'" + 3OH 2 . \N0 2 -- 1 In the calcium and lead salts two molecules of nitric acid are united by the dyad compound radicals Cao", Pbo", in the bismuth salt three molecules of acid are held together by the triad compound radical Bio" f . These salts are represented graphically thus : O=~N Ca N=0 0=X Bi - 0N=0 Experiment 112. Heat a small quantity of dry plumbic nitrate (powdered) in a retort of hard glass. Connect the neck of the retort with a TJ-tube sur- rounded with cold water, or better still with a freezing mixture of ice and salt. The lead salt melts and decomposes. Ruddy fumes of nitric peroxide come off, which condense in the U-tube. Oxygen escapes through the open drawn-out end of the tube. Test the gas with a glowing chip of wood ; the wood is rekindled. Collect a little over water by attaching a delivery-tube to the U-tube. A dark-brown powder is left in the retort, turning orange-yellow on cooling. It consists of plumbic oxide, TbO. The decomposition may be expressed by the equation This experiment proves 1. That plumbic nitrate is Converted by heat into plumbic oxide. 2. That nitric anhydride, N 2 5 , is given off, but that it breaks up immediately into oxygen, and a gas of a ruddy colour, 3Sr 2 O 4 or nitric peroxide, which can be condensed to a liquid. Quantitative measurement of the oxygen evolved from a given quantity of plumbic nitrate has proved that it forms exactly of the total oxygen contained in nitric anhydride, and the breaking up of the molecule must therefore take place according to the equation W V 2 5 = N 2 4 + ; * The action of nitric acid upon metals will be explained below. NITROUS ACID. 113 and as the N 2 in nitric peroxide forms a chemical compound with O 4 , it is obvious that the nitrogen atom could no longer be penta- valentic, as four atoms of dyad oxygen cannot satisfy the combining powers of two atoms of pentad nitrogen. It is also apparent that if nitrogen acted as a tetrad element in nitric peroxide there would be no connection between the two atoms of nitrogen, thus : 0=^=0 It is therefore probable that the connection between the two nitrogen atoms still exists, even without the intervening oxygen atom, and that nitrogen retains its pentad nature, thus : 0=N=0. The fact that the atom of oxygen which linked together the two groups of N0 2 in N 2 5 is so easily driven out by heat, shows 3. That a marked difference exists between the chemical affinity which the two atoms of nitrogen in nitric anhydride exhibit for the different atoms of oxygen. The yellow liquid collected in the U-tube boils at 22 C., and solidifies to a mass of colourless crystals at 13 C. The crystals dissolve at first to a colourless liquid, which turns yellow as the temperature rises, and becomes at last red. Blue litmus-paper is turned red by the puffs of ruddy vapour expelled from the liquid ; and the compound N 2 04 was therefore thought to be an acid body, and was called hyponitric acid. This reddening of the litmus is, however, due to the water in the paper, with which nitric peroxide undergoes a decomposition, and the name hyponitric acid is quite in- appropriate. A most interesting change takes place when the ruddy vapour is passed into a solution of potassic hydrate. Complete absorption of the gas takes place, and the liquid loses its alkaline properties. On examining the products thus formed, we find two different salts, potassic nitrate, W0 2 Ko, and potassic nitrite, of the composition WOKo. The acid corresponding to this latter salt contains one atom of oxygen less than nitric acid. It is called nitrous acid, NOHD. The change may be expressed by the equation 2 2 + 2KHo = N0 2 Ko + NOKo + OH 2 . Nitrous acid, on combining with bases, forms well characterised salts, called nitrites. In the free state, however, it is extremely unstable. It cannot be preserved at the ordinary temperature, without undergoing decomposition, according to the equation : 3NOHo = N0 2 Ho + W 2 2 + OH 2 114 NITRITES. NITROUS ANHYDRIDE. Experiment 113. If instead of potassic hydrate (or, as we may also view it, potassic water) a solution of peroxide of hydrogen, or some other metallic peroxide, be added to nitric peroxide, we obtain at once nitric acid, or a cor- responding metallic nitrate, according to the equation N 2 4 + Ba0 2 The following considerations render it probable that three atoms of oxygen in nitric anhydride are held less firmly by the nitrogen atoms than the other two atoms of oxygen. In the molecule of nitric anhydride represented graphically by the formula the oxygen atom in the dotted square is the first to go out, leaving the molecule < mrr? (nitric peroxide). 0=N=0. In both formulae nitrogen acts the part of a pentad element. Nitric peroxide would appear to contain an atom of oxygen less firmly united with the nitrogen atom, such as the oxygen atom which has been placed within a dotted square 0=N=O In the molecule of nitrous anhydride, W'^Oa, nitrogen is a triad element, two of its bonds becoming latent, thus : O=N N=0. It is evident from a glance at this formula that the oxygen atoms of nitric peroxide must rearrange themselves, for we have again an atom of oxygen linking together the two nitrogen atoms, as in nitric anhydride. In consequence of the unstable nature of free nitrous acid, it can be employed for purposes either of oxidation or reduction. Nitric peroxide breaks up according to the equation W 2 4 + OH 2 = N0 2 Ho + NOHo ; and nitrous acid according to the equation SWOHo = N0 2 Ho + W 2 2 + OH 2 , PREPARATION OF NITRIC OXIDE. 115 leaving as the ultimate products of decomposition of nitric peroxide only nitric acid and a colourless gas called nitric oxide, N^Oa. Experiment 114. In order to illustrate experimentally the reducing and oxidizing action of nitrous acid (or of a nitrite mixed with a dilute acid, even acetic acid), a little nitrous anhydride may be prepared by acting with nitric acid upon lumps of arsenious anhydride, heated in a small flask, according to the equa- tion : As'" 2 O3 + 2NO 2 Ho + 2O H 2 = 2As v OHo 3 + N 2 O 3 . The gas may be collected by displacement, or over mercury. Experiment 115. Add a few c.c.'s of a slightly acidulated solution of ferrous chloride to a cylinder full of nitrous anhydride, and shake up. The light green solution becomes dark brown, owing to the absorption of N 2 O 2 , by a portion of the unoxidized ferrous salt, which forms with this latter an evanescent mole- cular compound. On the application of heat to the brown liquid, nitric oxide is evolved, and the solution of the salt becomes light yellow. The reaction may be expressed thus : 2PeCl 2 + 2HC1 + N 2 O 3 = Fe 2 Cl 6 + N 2 O 2 + OH 2 . Organic colouring matters, such as magenta or indigo solutions, reduce nitrous anhydride likewise to a lower oxide, to nitric oxide. Experiment 116. Add a slightly acidulated (sulphuric acid) solution of potassic permanganate to another cylinder of the gas. The colour of the per- manganate is immediately destroyed. The N 2 O 3 is oxidized into nitric acid by the more powerful oxidizing agent, potassic permanganate. These two experiments may equally well be performed by employ- ing a solution of potassic nitrite in the place of the nitrous anhy- dride. Experiment 111. Introduce some copper turnings or clippings into a two- necked Woulfe's bottle, provided with a funnel and delivery-tube (Fig. 63). Nitric acid, diluted with about half its bulk of water, is then poured through the funnel into the bottle, which may be placed in a basin of cold water. The evolution of red fumes soon be- gins, and the air is gradually displaced by the gas. The red fumes within the bottle disap- pear (a sign that the air has been displaced) , and at last the gas which comes off appears quite colourless. As soon as the gas which issues from the delivery-tube comes in contact with the air, it turns reddish brown. The fumes of this red- dish brown gas are injurious when inhaled ; the experiment must therefore be conducted in the open air or in a closet with sliding win- dows, and in a good draught. A glass cylinder is now filled with water, ren- dered slightly alkaline by means of a few drops of sodic hydrate (in order to absorb any fumes of nitric acid that may be carried over) and inverted over the shelf of the pneumatic trough, and the gas collected in the usual manner by the displacement of the water in the cylinder. A perfectly colourless gas is thus i 2 FlG. 63. PREPARATION OF NITRIC OXIDE. 116 PROPERTIES OF NITRIC OXIDE. obtained. The cylinder, when full, is closed under water by means of a glass plate, and then removed with its gaseous contents. On introducing several folds of litmus- paper moistened with water which has been rendered slightly alkaline by means of a few drops of sodic hydrate, the gas turns instantaneously reddish-brown at the mouth of the cylinder, where it comes in contact with the air. The blue litmus is seen to turn red as rapidly as the ruddy*fumes form. When the cylinder has been filled half way down with these fumes, the glass plate is replaced, and the lower part of the folds of litmus-paper is seen to remain blue in the colourless portion of the gas, whilst the upper part turns intensely red. This experiment proves that the colourless gas, obtained by the action of copper upon nitric acid is not an acid body, and that by mere contact with air it is converted into reddish-brown acid fumes, which are absorbed by water or by sodic hydrate. Since the oxygen and moisture of the air convert the colourless gas into an acid with which we have already become acquainted (viz., into nitrous acid), it is reasonable to suppose that the colourless gas is likewise an oxide of nitrogen, containing, however, less oxygen than nitrous acid : and since it does not react acid, it can only be one of the two remaining oxides, i.e., it must be either W 2 2 or ON 2 . Now quantitative ex- periments have shown that the gas is composed of two atoms of nitrogen and two atoms of oxygen. It is written symbolically and graphically rwo an atom of nitrogen being linked to another atom of nitrogen, leaving two more bonds free in each, which are satisfied by an atom of dyad oxygen. The reaction* which took place when copper was treated with nitric acid must, therefore, be expressed by the following equa- tion : 3Cu -j- 8IT0 2 Ho = ^ivm C/no' ~f~ ^^20 2 -1- 4OH 2) and the deoxidation of a molecule of N > 2 5 , which we have previously seen accomplished, step by step, first to W 2 C>4, then to W^Oa, and lastly to N 2 2 , is in this reaction attained at one leap. Nitric oxide is remarkable for its great affinity for oxygen, and may be employed in testing for that gas. Experiment 118. Collect some of the gas in a glass cylinder over warm water, rendered very slightly alkaline with soda, and coloured blue with litmus. The blue solution remains unchanged. Now pass a few bubbles of oxygen or air from a gas-holder up into the nitric oxide ; deep ruddy fumes will be imme- diately formed, which are, however, quickly dissolved by the alkaline water, and the blue solution becomes red. If both the oxygen and the nitric oxide are per- fectly pure, it is possible to effect a complete oxidation of the nitric oxide into nitrous and nitric acid, and to cause a perfect absorption of the two gases. Experiment 119. Plunge a burning taper into a jar of nitric oxide gas. The * There is invariably some ammonia (NH 3 ) formed in this and other similar reactions, and it would appear, therefore, that water, under favourable circum- stances, takes part in the change. ACTION OP NITRIC ACID UPON METALS. 117 taper is immediately extinguished.* This shows that nitric oxide does not support combustion. The same happens if feebly burning phosphorus is plunged into the gas. Intensely burning phosphorus, however, decomposes nitric oxide, and burns in it almost as brilliantly as in oxygen itself. The cause for its burning less brilliantly is evidently the presence of the inert nitrogen, which fixes much of the heat produced by the combination of the phosphorus with the oxygen. This nitrogen acts as a heat diluent. Temperature as well as pressure influences the amount of light given off by burning bodies. Nitric oxide has never been liquefied. Its vapour density is anomalous, since its molecule occupies four volumes instead of two. This is known to be the case with a few other bodies alike irregular in their vapour density. One volume of this gas dissolves in about twenty of water at 15 C. Its specific gravity compared with air is 1-039. Other metals, e.g., lead and mercury, are acted upon by nitric acid in like manner, i.e, they are converted into nitrates. 3Pb + 8N0 2 Ho = 3 *Fbo" + W 2 2 + 4OH 2 . 3Hg + 8N0 2 Ho = so'Hgo" + 3ST 2 2 + 4OH 2 . Others again, deoxidize nitric acid to a less extent, such as tin and silver 5Sn + SONOsHo = Sn 5 5 Ho 10 + 10N 2 4 + 5OH 2 . Metastannic Nitric acid. peroxide. 4Ag + 6N0 2 Ho = 4W0 2 Ago + W 2 3 + 3OH a Nitrous anhydride. 4Zn + 10N0 2 Ho = 4 2 Zno" + ON 2 + 5OH 2 , WtJ 2 Nitrous oxide. In this latter reaction, however, the colourless gas ON 2 , called nitrous oxide (also known as laughing gas), is never free from ihe higher oxides, W 2 2 , W 2 3 , W 2 4 ; and the reaction is not nearly so perfect as that which took place when copper was acted upon by nitric acid. We may then sum up by saying, that ruddy vapours result from the action of nitric acid upon metals. Nitric acid oxidizes likewise most of the metalloids with evolu- tion of red fumes. Powdered charcoal, when treated with nitric acid at a high temperature, decomposes it entirely with formation of carbonic anhydride and nitrogen. A mixture of finely powdered nitre and charcoal deflagrates violently (small quantities only should be mixed), potassic carbonate being left. Sulphur is gradually oxi- * Nitric oxide prepared from copper and nitric acid sometimes contains so much nitrous oxide, that a taper burns in it brilliantly. 118 COMPOUNDS OP NITROGEN AND OXYGEN. 6N0 2 Ho L = 2OH 2 + 2N 2 3 + N 2 4 . dized into sulphuric acid ; metallic sulphides into sulphates. Phos- phorus is oxidized into phosphoric acid. Dilute nitric acid (sp. gr. 1*20) should be employed, and small pieces of phosphorus only should be introduced into the hot acid at a time. By employing amorphous or red phosphorus, the danger of an explosion is avoided. Iodine is oxidized by strong boiling nitric acid into iodic acid, ac- cording to the equation : OI OHo Iodic acid. Wood, wool, horn, skin, silk, are stained yellow by dilute acid, and are converted by concentrated nitric acid into compounds of great practical importance, such as oxalic acid, gun-cotton, etc. The five compounds which nitrogen is capable of forming with oxygen illustrate very well the law of constant combining propor- tions, according to weight and volume, as will be seen from the following table : By volume. 2 vols. of N, and 1 vol. of O 2 vols. of N, and 2 vols. of O 2 vols. of N, and 3 vols. of 2 vols. of N, and 4 vols. of 2 vols. of N, and 5 vols. of O By weight. Nitrous oxide . . . . ON 2 Nitric oxide W 2 2 Nitrous anhydride N 2 3 Nitric peroxide . . N^O*, Nitric anhydride. . IffoOg 28 + 28 + 28 + 28 + 28 + 16 = 32 = 48 = 64 = 80 = 44. 60. 76. 92. 108. We must content ourselves with merely referring in a tabular form to the molecular composition of these five bodies ; remarking that nitric oxide and nitric peroxide show anomalous molecular volumes Specific gravity Molecular Molecular referred to weight. volume. hydrogen. Nitrous oxide ON 2 44 2 vols [ ~~| 22 criths. Nitric oxide N 2 2 60 4 vols. 15 Nitrous anhydride . N 2 O 3 76* 2 vols.* I 1 1 38 Nitric pe^de .. { K ^ 2 46 {? T 4 ti:^l00'C.} QH 23 to 46 criths. Nitric anhydride. . . N 2 O 5 108* 2 vols.* I I [ 54 criths. * These molecular combinations have not been determined with absolute certainty, and the above figures represent merely their probable composition. AQUA REGIA. 119 All the preceding experiments have shown that we possess in nitric acid (sometimes called aqua fortis} a powerful solvent for metals. This is owing to the mobile nature of three out of the five oxygen atoms contained in each molecule ; hence the slight resist- ance which the acid offers to the deoxidizing action of the elements, especially metals, whereby the nitric acid is partially or entirely deprived of its oxygen. Gold and platinum are not affected, i.e., not oxidized either by nitric or hydrochloric acid when in an unal- loyed condition. Aluminium strongly resists the action of nitric acid, even at a boiling heat. Tin and antimony are converted into oxides, insoluble in nitric acid. Concentrated nitric acid does not act upon iron and tin at the ordinary temperature, though it dissolves them rapidly when diluted. When iron is immersed in concentrated nitric acid (sp. gr. 1'45), it remains unacted upon ; and when subsequently placed in dilute acid, without first being wiped, it cannot be dissolved ; it is said to assume the passive state. The cause of this peculiar action has not yet been satisfactorily explained. Comparatively few of the nitrates are commonly met with ; the most important are Potassic nitrate (nitre, saltpetre) ................ NO 2 Ko. Sodic nitrate (cubic nitre, or Chili saltpetre) ...... NO 2 Nao. Baric nitrate .................................. Strontic nitrate Cobaltous nitrate . . ..... .................. Srt 2c "- Plumbic nitrate N0 2 - " Bismuthous nitrate ............................ NO 2 Bio'". N0 2 _ , Argentic nitrate (lunar caustic) .................. NO 2 Ago. Mercuric nitrate ............... ............... J^Q 2 Hgo". A mixture of six molecules of hydrochloric, and two molecules of nitric acid, is called aqua regia or nitro-hydrochloric acid 2N0 2 Ho + 6HC1 = N 2 2 C1 4 + 4OH 3 + C1 2 . The compound K 2 2 Cl4 chloronitric gas, graphic formula Cl Cl N=0 ClN=O J. 120 CHLORONITRIC GAS. may be viewed as nitric peroxide, in which two atoms of dyad oxygen are replaced by four atoms of monad chlorine. W 2 2 C1 4 is of a still more unstable nature than the compound W 2 4 . It forms a readily available source of chlorine, and is employed for dissolving gold and platinum, since chlorine acts in the nascent state on these metals, and forms with them soluble chlorides W 2 2 C1 4 + Pt = N 2 2 + Pt iv Cl 4 . Platinic chloride. 3W 2 2 C1 4 + 4Au = 3N 2 2 + 4Au'"Cl 3 . Auric chloride. Nitric oxide on escaping into the air, gives rise to the well-known ruddy fumes ; and aqua regia ought to be used only where there is a good draught to carry off these fumes. The gas which results from the action of nitric acid or aqua regia npon metals, escapes and partially recovers from the air the oxygen which the nitric acid gave up to the metals. Its tendency is to com- bine with two atoms of oxygen, and no more ; and this oxygen it yields up again quite as readily to other bodies that have a stronger affinity for that element than either nitrous anhydride or nitric peroxide possesses. Upon this remarkable property of nitric oxide is based one of the most beautiful chemical processes, viz., the manufacture of oil of vitriol or sulphuric acid. We have seen that sulphur when burned in air combines never with more than two atoms of oxygen to form sulphurous anhydride. Here, then, is a body that wants one more atom of oxygen in order to be converted into sulphuric anhydride, S0 3 : and in the W 2 4 we have a body that can readily part with one or two atoms of oxygen. Hence sul- phuric anhydride results from the reaction of these two bodies, according to the equations (1) S0 2 + W 2 4 = S0 3 + N 2 3 . (2) S0 2 + WT 2 3 = S0 3 + W 2 2 . If we add to these two conditions two others, viz., a well regu- lated supply of steam (to form sulphuric hydrate) and atmospheric air, or some other source of oxygen (to reoxidize the N 2 2 as fast as it is formed), the conversion of sulphurous into sulphuric acid becomes a continuous process. A peculiar white compound which is first formed is only a transitory product, and has little interest attached to it 2S0 2 + N 2 4 + White crystalline compound. The water or steam decomposes it in its turn I PREPARATION OF SULPHURIC ACID. S0 2 (N V 2 ) O + 2OH 3 = 2S0 2 Ho 2 + 121 Nitrous anhydride we have already seen, cannot exist in the presence of water. It is at once broken tip into nitric oxide and nitric acid 3N 2 3 OH 3 = 2N0 2 Ho + 2N 2 2 . Nitric oxide, in the presence of air, is converted into nitric per- oxide. The nitric acid and nitric peroxide thus formed, can, in their turn, oxidize fresh quantities of sulphurous anhydride. By the proper supply of sulphurous anhydride, steam, air, and nitric oxide, which acts as a carrier of oxygen, a continuous process of manu- facture of this important substance sulphuric acid can be readily secured. These interesting reactions may also be studied on an experi- mental scale. Experiment 12O. Fig. 64 represents a tall wide glass cylinder fitted with an india-rubber cork and five glass tubes, and connected with apparatus for generating steam, sulphurous anhydride, oxy- gen, and MT 2 O 2 . The two latter gases may also be stored up and conveyed to the cylinder directly from gas-holders. The unappropri- ated tube communicates with the air. As soon as the first few bubbles of nitric oxide are admitted into the cylinder dense ruddy fumes of N 2 O4 are seen, which disappear on the ad- mission of the sulphurous anhydride. The contents of the globe become colourless, and the white crystals described above make their appearance on the sides of the glass. If a slow current of oxygen be now admitted the red fumes reappear immediately, only to be decolourised again, however, according as the current of sulphurous anhydride is regulated. The white crystals which have become more numerous disappear as soon as steam is ad- mitted to the cylinder. By properly regulat- ing the admission of JX^Ofr oxygen, SO 2 , and steam, the process becomes continuous. Now substitute for the glass cylin- der the ordinary lead chambers used by the manufacturer of sulphuric acid, and for the oxygen air ; generate the sulphurous anhydride either by burn- ing sulphur, or, as is done more fre- quently now, by roasting iron pyrites, Pe iv S 2 , in a current of air, and decompose sodic nitrate or Chili saltpetre by means of oil of vitriol, and we have the outlines of the manufacturing process as it is now carried on. The sulphuric acid thus obtained so-called chamber acid, of sp. gr. 1-6, containing 70 p. c. of oil of vitriol, is quite strong FlG. 64. PREPARATION OF SULPHURIC ACID. 122 TABLE OF METALLIC SULPHATES. enough to be used for decomposing sodic chloride into sodic sulphate, preparatory to the conversion of the latter into sodic car- bonate. Evaporation in leaden pans brings the specific gravity up to 1'72, and the acid contains then about 80 p. c. of oil of vitriol. It is technically known a8 brown acid, and is largely used for making superphosphates, etc. Further concentration and puri- fication of this acid is carried on in glass vessels, or more frequently now in platinum stills. The specific gravity of the concentrated acid is 1*842. It is free from odour, and forms an oily highly cor- rosive liquid, which boils at about 338, and solidifies when cooled to 10*8. It attracts moisture from the air, and may therefore be used for drying gases which are not acted upon by the acid, e.g., N, O, H, 01, etc. The following is a list of some of the most important metallic sulphates : Potassic sulphate ...................... S0 2 Ko 2 . Sodic sulphate (Glaubers salt) .......... SO 2 Nao 2 + 10OH 2 . Hydric potassic sulphate .............. SO 2 HoKo. Ammonic sulphate .................... SO 2 Amo2. Baric sulphate (heavy spar) ............ SO 2 Bao". Strontic sulphate (celestine) . . ........ SO 2 Sro". Calcic sulphate (gypsum) .............. SHo 4 Cao". (anhydrite) ............ SO 2 Cao". Magnesic sulphate (Epsom salts) ........ SO 2 Mgo" + 7OH 2 . so 2 =n Aluminic sulphate .................... SO 2 = Al 2 o vl . SO 2 _ l| SO 2 Ko-, Potash alum .......................... S 2 Al 2 o vi -4- 24OH 2 . - Chrome alum ........................ So!^T 2 Vi SO 2 Ko-J Ferrous sulphate (green vitriol) ........ SO 2 Feo" + 7OH 2 . S0 2 =]l Ferric sulphate ....................... SO 2 = Fe 2 o vi + 9OH&. S0 2= J] Cobaltous sulphate .................... SO 2 Coo". Nickelous (sulphate) ............... .... SO 2 Nio" + 7OH 2 . Manganous sulphate .................. SO 2 Mno" + 5OK 2 . Zincic sulphate (white vitriol) .......... SO 2 Zno" + 7OH 2 . Plumbic sulphate ........ ............ SO 2 Pbo". Cupric sulphate (blue vitriol, or blue stone) SO 2 Cuo" + 5OH 2 . Mercuric sulphate ...... . .............. SO 2 Hgo". Basic mercuric sulphate (turpeth mineral). SHgo'^Hgo". Argentic sulphate ......... ........... SO 2 Ago 2 . 123 QUESTIONS AND EXERCISES. 1. Mention some natural saline compounds in which nitrogen occurs. 2. Describe a process for preparing small quantities of nitric acid by the direct combination of nitrogen and oxygen. 3. Explain the formation of saltpetre in tropical countries. 4. You have given to you Chili saltpetre and sulphuric acid. Describe how you would prepare nitric acid from these materials. Express the chemical change by an equation. 5. Calculate how much nitric acid (NO 2 Ho) by weight can be obtained from 20 grms. of potash nitre ; and how much sulphuric acid (SO 2 Ho 2 ) by weight is required in order to have only dipotassic sulphate left in the retort. 6. Show why you write NOoHo, and not NO 3 H. 7. Give symbolic and graphic formulae for nitric anhydride and nitric acid. 8. State how metallic nitrates are prepared. Give equations. 9. You have given to you a few iron nails, some pure tin foil, copper filings, and a little granulated zinc, with concentrated nitric acid and distilled water. State what chemical changes you can produce with these materials, and express the changes by equations. 10. Explain what takes place when cupric or bismuthous nitrate is heated in a retort. 11. What takes place when the vapour of Mr 2 O 4 is passed into a solution of baric hydrate ? Express the changes by equations. 12. How is nitrous anhydride prepared ? 13. Explain the reducing and oxidizing action of nitrous anhydride, or of nitrites, in the presence of an acid. 14. Give symbolic and graphic formulse for nitric peroxide, nitrous anhydride, nitrous oxide, argentic nitrite. 15. Describe the properties of nitric oxide gas. 16. Explain the action of concentrated nitric acid upon mercury and silver, sul- phur, phosphorus, and iodine. Express the changes by equations. 17. Commit to memory the list of all the oxides of nitrogen, together with their atomic and volume weights. 18. Explain the terms aquafortis, aqua regia, cubic nitre, lunar caustic, chamber acid, ignition point. 19. Explain the action of aqua regia upon gold and platinum. 20. Explain the important use of some of the nitrogen oxides in the manufacture of oil of vitriol. 21. Calculate the percentage composition of potassic nitrate. 22. How much argentic nitrate can be prepared from ten ounces of metallic silver ? 23. What evidence have you to adduce that nitrogen occurs as a pentad, as a triad, and as a monad element ? 24. Practise writing out the graphic formulse of some of the most important nitrates and sulphates. 124 AMMONIA. CHAPTER XVII. AMMONIA. FREE hydrogen and nitrogen possess very little affinity for one another, so that they cannot be united directly. A terhydride of nitrogen (three atoms of hydrogen and one atom of nitrogen) called ammonia, ITHs, is known. This is for the most part derived from the nitrogen contained in nitrogenous organic substances, such as coal, hair, horn (whence its ordinary name of spirit of hartshorn), skin, sinews, etc. The greater part of the animal body (fat excepted) consists of organic substances rich in nitrogen ; and they all yield, under certain conditions (dry distillation, putrefaction, etc.), the pungent gas called ammonia. Experiment 121. Rub together in a mortar a mixture of pulverized unslaked lime and caustic soda (called soda-lime) with some animal substance, such as glue, white of egg, horn shavings ; then introduce the mixture into a test-tube, and apply heat. A pungent gas is given off, which turns red litmus- paper blue, and yields white fumes when a glass rod moistened with dilute hydro- chloric acid is held in the gas. Experiment 122. Treat a little zinc with dilute sulphuric acid ; hydrogen gas is evolved Zn + S0 2 Ho 2 = S0 2 Zno" + H 2 . Add now, drop by drop, dilute nitric acid. The evolution of gas ceases, but the zinc nevertheless disappears. The hydrogen combines with the elements of nitric acid to form water and ammonia, which latter immediately enters into combination with the acids : (1) 4H 2 + NO 2 Ho = NH 3 + 3OH 2 . (2) NH 3 + NO 2 Ho = NO 2 (NH 4 O). (3) 2NH 3 + S0 2 Ho 2 = S0 2 (NH 4 0) 2 . A similar reaction takes place when zinc is dissolved in moderately dilute nitric acid. Owing to a secondary reaction, hydrogen and nitrogen combine to form ammonia, and zincic and ammonic nitrates are left (1) 4Zn + 8N0 2 Ho = ^Zno" + 4H 2 . (2) 4H 2 + N0 2 Ho = WHa + 3OH 2 . (3) NH 3 + N0 2 Ho = N0 2 (NH 4 0). The action of nitric acid upon zinc is invariably accompanied by the formation of lower oxides of nitrogen, ON" 2 , N" 2 O 2 , etc., which offer little resistance to the action of the hydrogen, and yield under favourable circumstances nitrogen and water. Nitrogen and hydro- gen, when together in the nascent state, i.e., at the very moment* of their liberation, combine and form ammonia, BTH 3 . The solution contains a considerable amount of ammonic nitrate, which may be proved by heating some of it with a little soda-lime. * The elements may be supposed to exist for a moment in the uncorubined state. PREPARATION AND PROPERTIES OF NITROUS OXIDE. 125 Experiment 123. Prepare some ammonic nitrate by neutralizing a solu- tion of ammonia or ammonic carbonate with dilute nitric acid (comp. Exp. 44). Evaporate the solution of the salt to dryness and fuse the crystals gently in a por- celain dish on a sand-bath. Pour out the fused mass on an iron plate, and reduce it when cold to a coarse powder. Experiment 124. Heat some of the coarsely powdered ammonic nitrate in a Florence flask, pro- vided with a delivery-tube, or in a small retort (Fig. 65) . The salt melts, boils, and gradually breaks up into ni- trous oxide (or laughing gas), ON 2 , and steam. The gas FlG 65 ._p EEPAEATION OF NITROUS OXIDE. may be collected over water. The decomposition of ammonic nitrate takes place, according to the equation : Hr0 2 (NH 4 0) = ON 2 + 2OH 2 , Nitrons oxide is a colourless gas, with a slight smell and a sweetish taste. Its specific gravity, compared with air, is 1'527 ; its volume weight (H = 1) is 22. One litre of nitrous oxide weighs 22 X '0896 grm. = T9712 grm. Nitrous oxide, when mixed with air, undergoes no change. Water absorbs it to a certain extent (1*3 of its volume at C.). This solubility distinguishes the gas readily from oxygen. A glowing piece of charcoal, when intro- duced into the gas, burns almost as brilliantly as we saw carbon burn in oxygen (comp. Exp. 24). A glowing splinter of wood bursts into flame, and burns brilliantly in the gas. A piece of sulphur placed in a deflagrating spoon and introduced into the gas immediately after kindling and whilst it burns only feebly, is extin- guished. Introduce it when burning briskly and it will burn with increased brilliancy almost as if in oxygen itself, with a pale rose- coloured flame. Atmospheric air, we know, sustains respiration. Certain animals are able to breathe nitrous oxide (which we may view as an air considerably richer in oxygen 36*4 p. c.) with impunity for several hours. When inhaled by man, it produces a characteristic kind of exhilarating intoxication, which is sometimes accompanied by immoderate laughter ; hence its name laughing gas. Pure gas only should be employed for purposes of inhalation. Nitrous oxide has of late been recommended as an ancesthetic, or agent for suspending the mental and sensorial functions during dental and surgical operations. Ammonic nitrite heated in like manner yields nitrogen and water, according to the equation HT'"0(NH 4 0) = N 2 4- 2OH 2 . 126 PREPARATION OF SAL-AMMONIAC. Experiment 125. Heat gently a concentrated aqueous solution of potassic nitrite and ammonic chloride in a retort (comp. Fig. 65). The nitrite decom- poses at about 50 C. into nitrogen gas, which can be collected over water, potassic chloride, and water, according to the equations NOKo +. AmCl = MO(NH 4 O) + KOI, and NO(NH 4 0) - N 2 +"2OH 2 . Test the gas with a burning taper. The light is immediately extinguished. Experiment 126. Fill a glass cylinder with ammonia gas, by rinsing it out with a few drops of strong solution of ammonia (the liquor ammonia of the shops) ; coyer it with a glass plate. Another cylinder or bottle is filled with hydrochloric acid gas. The two bottles or cylinders are then placed together (as seen in Fig. 43) , and the glass plates withdrawn, so that the mouth of the inverted vessel containing the hydrochloric acid gas rests almost air-tight on the mouth of the lower vessel. Both gases are seen to mix, and to combine, producing clouds of white fumes. These clouds are deposited on the sides of the glass vessels as a white salt, called ammonic chloride (sal- ammoniac), a compound of the ammonia and hydrochloric acid gas N'"H 8 + HOI = N V H 4 C1. The nitrogen atom in WH 3 is combined only with three atoms of hydrogen, and is therefore triadic ; but it is also clear from the avidity with which NH 3 combines with HOI, that two more affinities remain latent, one of which can become satisfied by hydrogen, the other by chlorine, thus : H H H N H H N H Experiment 127. Heat gently in a test-tube a concentrated solution of ammonic chloride in water, with sodic or potassic hydrate. Colourless ammonia gas is evolved, according to the equation NH 4 C1 + NaHo = HH 3 + NaCl + OH 2 , and is readily recognised, 1st, by its characteristic pungent odour ; 2nd, by its action upon red litmus -paper or turmeric-paper (changed from red to blue, and from yellow to brown) ; and 3rd, by the white clouds which it produces when a glass rod, moistened with dilute hydrochloric, sulphuric, or nitric acid is held at the mouth of the test-tube. Ammonia forms with these acids the respective salts NH 3 + HC1 = NHiCl (Ammonic chloride). 2KH 3 + S0 2 Ho 2 = S0 2 (NH 4 0) 2 (Ammonic sulphate). KTH 3 + N0 2 Ho = NO 2 (NH 4 O) (Ammonic nitrate). The compound NH 4 appears to be capable of existing only as an amalgam. It is obtained by mixing sodium- amalgam (Hg n Na m ) with a concentrated solution of ammonic chloride AMMONIUM. AMMONOXYL. 127 Hg n Na ta + mlfH 4 Cl = Hg n (NH 4 ) m + mNaCl. Sodium exerts its well known affinity for chlorine, forming with it sodic chloride ; the amalgam breaks up very rapidly into 2nHg, 2mN'H3, and mH 2 , which is evolved. On account of its salts possessing a marked similarity to potassic and sodic salts, the existence of a hypothetical metal ammonium, NH 4 , has been enter- tained by chemists. Ammonium is affected like the alkali metals, potassium and sodium. Its haloid salts, M"H 4 C1, N"H 4 I, WH 4 Br, which are well defined salts, can therefore also be viewed as derived from NH 3 + HC1 = NH 4 C1, NH 2 + HI = NH 4 I (Ammonic iodide), NH 3 + HBr = NHJBr (Ammonic bromide), by assuming that the atom hydrogen attacks the molecule JSTH 3 first, forming with it NH 4 , or the hypothetical metal called in accordance with the terminology adopted by chemists Ammonium. Since this metal combines with one atom of chlorine, it must be viewed as a monad, like potassium or sodium; and as it consists of one atom of nitrogen, and four atoms of hydrogen, and yet acts the part of an element, it is called a compound radical. It is usually written Am, instead of NH 4 , forming ammonoxyl, Amo, analogous to the radicals Ho, Ko, etc. Ammonic hydrate formed, according to the equation NH 3 + OH 2 = WH 4 Ho, appears likewise to have only a hypothetical existence, as no chemical combination seems to take place between the water and the ammonia ; for the gas gradually escapes on exposing the solution to the air, and no definite compound of ammonia and water has been observed. The escape of the gas from the solution is marked by the production of intense cold: i.e., much heat becomes latent, when ammonia passes from the liquid to the gaseous state. This property has found a practical application for refrigerating purposes, and for pro- ducing ice artificially. Ammonic chloride, sulphate, or nitrate, are best obtained by the action of the respective acids upon the ammonic hydrate : AmHo + HC1 = AmCl + OH 2 . 2AmHo + S0 2 H0 2 = S0 2 Amo 2 + 2OH 2 . AmHo + W0 2 Ho = K"0 2 Amo + OH 2 . Experiment 128. Heat a little sal-ammoniac in an iron spoon, or on platinum foil. White fumes are given off. When the salt is heated in a test-tub?, the fumes condense in the upper or colder part of the tube ; the salt sublimes unchanged. Most salts of ammonium volatilize upon the application of heat. This property renders ammonic salts of great value in chemical analysis. 128 PREPARATION OF AMMONIC HYDRATE. A solution of ammonia gas in water is indispensable in the laboratory. It is therefore important to study its preparation and properties. Experiment 129. Ammonia gas is very soluble in water. This may be shown by heating a little strong ammonia, in a small flask (Fig. 66) and passing the evolved gas over freshly burnt lump^of lime,* placed in a wide tl-tube. Any moisture which the ammonia gas carries with it is retained by the h'me. From the dry- ing tube the gas is passed into an inverted long-necked glass globe, which should be well dried first, and is col- lected by upward displace- ment. When full, the globe is closed with the thumb, and is plunged, with its mouth downw r arJs, into a bowl of water, reddened with a solution of litmus and a few drops of sulphuric acid. By cautiously withdrawing the thumb under water, the latter rushes in most eagerly, and fills the whole globe almost instantaneously. The liquid which is left in the flask reacts alkaline, for the solution is turned blue. Water absorbs about 700 times its bulk of the gas. Experiment ISO. A concentrated solution of ammonia is obtained by dis- tilling in a flask a mixture of sal-ammoniac and calcic hydrate. The gas is made to pass through a wash-bottle, containing a little water, and from thence through one or more Woulfe's bottles, filled about three-fourths with water (as shown in Fig. 47) . No funnel-tube is, however, required. The delivery-tubes must reach nearly to the bottom, as aqueous ammonia is lighter than water. The specific gravity of the solution diminishes, therefore, in proportion as the water becomes saturated with the gas. The liquid also increases in bulk, and when saturated at 15 C., it contains more than a third of its weight of the alkali. Dry ammonia gas may be collected by displacement (imperfectly), or over mercury. Experiment 131. Collect some ammonia gas by displacement, and plunge a lighted taper into the inverted cylinder (comp. Fig. 8). The flame becomes first slightly enlarged and then extinguished. The enlargement is due to a very slight and evanescent combustion of the gas. During its combustion, the hydrogen combines with the atmospheric oxygen, and is converted into water, and the nitrogen is set free. The igniting point of ammonia, like that of nitrogen, being higher than the temperature produced by its combustion, the flame becomes extinguished. Experiment 132. Pass a cxirrent of ammonia gas through a porcelain- tube placed in a Hofmann's combustion furnace, and fitted with a delivery-tube FlG. 66. COLLECTION OF DRY AMMONIA GAS AND ABSORPTION BY WATER. * Calcic chloride cannot be used, because it absorbs a considerable quantity of the gas ; nor oil of vitriol, because ammonia combines with the acid with explo- sive violence. DECOMPOSITION OF AMMONIA BY SODIUM. 129 drawn out to a fine jet. Apply a light to the gas as it issues from the jet. The gas will not burn readily, but a pale greenish flame will play over the top of the light. By gradually heating the tube in the gas furnace, and thus raising the initial temperature of the gas, it may be made to burn. On slowly cooling the tube by turning off the gas, the flame will go out again. By substituting, however, oxygen for air, by mixing the two gases in a Hemming's jet nsed for the combustion of hydrogen and oxygen the so-called oxy-hydrogen blowpipe the gas may be made to burn readily with a greenish yellow flame. Experiment 133. Heat the porcelain-tube usedinExp. 132 red hot. The issuing gas burns now readily in the air, but is no longer ammonia ; the heat has decomposed it into hydrogen, which burns, and nitrogen. This may be shown by passing the gas into water acidulated with a little acid, in order to absorb any undecomposed ammonia, and collecting over a pneumatic trough. The gas so collected consists of a mixture of 1 vol. of nitrogen and 3 vols. of hydrogen. Experiment 134. Pass some well-dried ammonia-gas over some small pieces of potassium (sodium) placed in a bulb-tube made of hard glass (Fig. 67), FlG. 67. DECOMPOSITION OF AMMONIA BY SODIUM. and heat the bulb gently by means of a small gas flame. The metal potassium displaces a part of the hydrogen, and forms a compound having the com- position MTKH 2 (potassamine) . The issuing gas burns readily ; it has all the properties of hydrogen. The composition by volume and by weight of ammonia gas has been carefully determined. Its volumetrical composition cannot, however, be demonstrated so readily, as, for instance, that of steam or hydrochloric acid gas. Ammonia is decomposed by bringing it into contact with chlorine ; and for every three volumes of chlorine so employed, one volume of nitrogen is left. The hydrochloric acid, resulting from the combination of hydrogen and chlorine, combines with the excess of ammonia, and forms the solid salt, NH 4 C1. This reaction is sometimes employed for preparing pure nitrogen. Great 130 AMMONIUM COMPOUNDS. caution is, however, necessary, on account of the possible formation of highly explosive chloride of nitrogen. The ammonia solution used should be concentrated, and always in large excess, and the delivery-tube should be wide, on account of the formation of solid ammonic chloride. By passing electric sparks fort some time through dry ammonia gas, placed in a eudiometer-tube over mercury, the gas is slowly decomposed into its component elements, hydrogen and nitrogen. The gas volume is seen to increase gradually, till the original volume has been doubled. The four volumes of mixed' gases are found on analysis to consist of three volumes of hydrogen and one volume of nitrogen ; and one volume of ammonia gas is derived from 1-J volumes of hydrogen and -J of nitrogen, weighing respectively 1036 and '4856, total = '5892 (sp. gr. of H = '0691, and of N = 9712, when compared with air). Direct estimation of the specific gravity of ammonia gas (com- pared with air) gave the number '597, from which the above differs but little. The percentage composition is readily found by rule of three calculation, viz. : Hydrogen 17'61 Nitrogen 82'39 The molecular weight of PTH 3 is 17. The specific gravity of ammonia gas compared with hydrogen is therefore 8'5, and one litre of ammonia gas weighs - 1 J- = 8*5 X '0896 grm. = '7616 grm. Gaseous ammonia can be liquefied by cooling it down to 40 C., or by a pressure of 7 atmospheres at 15 C. It may even be frozen by exposing the dry gas to a pressure of 20 atmospheres, and to a cold of 75 C. It forms then a white, transparent, crystalline body. Ammonia neutralizes the most powerful acids, forming with them salts which are readily volatilized by heat, unless they contain non- volatile acids, when the ammonia only is driven off'. A few compounds of ammonia briefly claim our attention, as they constitute some of our most important reagents. Experiment 135. Measure out two equal portions of a solution of ammonia or ammonic hydrate, also called simply ammonia. Pass through one portion a brisk current of sulphuretted hydrogen gas, as long as the gas continues to be absorbed. (The apparatus described for the preparation of chlorine water answers admirably.) Then add the second portion to it, and a solution of ammonic sulphide, SAm 2 is obtained. By completely saturating a solution of ammonia with sulphu- retted hydrogen, we obtain a solution of hydric ammonic sulphide, AmHs, in which the compound radical hydrosulphyl, Hs, has taken the place of the hydroxyl, thus : AmHo + SH 2 = AmHs + OH*. On then adding AmHo to this solution, ammonic sulphide is obtained, thus : AmHs + AmHo = SArn 2 + OH OXIDES OF CHLORINE. 131 Experiment 136. Fill a cylinder with dry carbonic anhydride gas, and another cylinder of double the size with dry ammonia gas. On bringing the mouths of the two cylinders towards each other, the two gases rush together, and form the compound 2NH 3 ,CO 2 . This body attracts moisture rapidly, and dissolves to a salt having the composition COAmoa, ammonic carbonate. Experiment 137. Pass a current of CO 2 through a concentrated solution of ammonia as long as any gas is absorbed. On setting the solution aside for crystallisation beautiful colourless rhombic prisms are obtained, which have the composition COHoAmo (hydric ammoiiic carbonate). Notice the smell of the crystals. Solutions of both these ammonium compounds are employed in the laboratory. QUESTIONS AND EXEKCISES. 1. Which are the chief sources whence ammonia and its compounds are derived ? 2. You have given to you some glue and soda-lime. Show how you would prepare NH 3 from these materials. 3. Explain the formation of ammonia by the aid of dilute sulphuric acid, metallic zinc, and dilute nitric acid. Express the changes by equations. 4. How would you prepare, 1st, ammonic nitrate, and 2nd, nitrous oxide gas? 5. What are the properties of nitrous oxide? 6. You have given to you 25 grms. of pure ammonic nitrate. How much laughing-gas, by weight and by volume, can you prepare from it ? 7. Write out the symbolic and graphic formulae for ammonia, ammonic bromide, carbonate, hydric ammonic sulphide, ammonic nitrate, and nitrite. 8. Explain the terms nascent state, sal-ammoniac, spirit of hartshorn. 9. Describe the formation of ammonium-amalgam, and give reasons why the group of elements, NH 4 , is considered to be a metal. 10. Why are NH 4 and AmHo considered hypothetical compounds ? 11. How would you show experimentally that most ammonium compounds can be volatilized and sublimed ? 12. What space will 5 '324 grms. of ammonia gas occupy at 15 C., and 745 mm. barometric pressure ? 13. How are neutral ammonic sulphide and hydric ammonic carbonate pre- pared ? 14. How would you prepare and collect dry ammonia gas ? 15. How is a concentrated solution of ammonia in water (liquor ammonia) pre- pared ? 16. Describe several methods of preparing pure nitrogen. Give equations. 17- Explain the decomposition of NH 3 by heat and by sodium. Give equa- tions. CHAPTER XVIII. OXIDES OF CHLORINE. CHLORATES. HYPO- CHLORITES. CHLORINE has but little affinity for oxygen. No method is known by which it can be made to unite directly with this element, and the compounds which can be formed by indirect means are mostly of a very unstable nature. Heat alone breaks them up readily, often with explosive violence. Only two of the oxygen compounds K 2 132 CHLORATES. HYPOCHLORITES. of chlorine, viz., the salts known as chlorates and JiypocJilorites, are of practical importance. Experiment 138. Pass a current of chlorine gas slowly into a solution of potassic hydrate, KHo. If the solution be dilute and kept cool by a current of cold water, the reaction takes, place according to the equation : C1 2 + 2KHo = KC1 + CIKo + OH 2 . Potassic Potassic chloride, hypochlorite. If concentrated (one of KHO to three of water) and kept at boiling-water temperature, chlorine is rapidly absorbed, and the change which takes place is expressed by the equation : 3C1 2 + 6KHo = 5KC1 + j + 3OH 2 Potassic Potassic chloride, chlorate. The two salts are readily separated by crystallisation : potassic chlorate, being sparingly soluble, crystallises out in plates, which can be obtained pure by re- crystallisation. We have seen that chlorine breaks up water under the influence of sunlight (Exp. 62), or steam under that of heat (Exp. 63). If instead of water we employ potassic hydrate, i.e., water in which one atom of hydrogen has been replaced by the metal potassium, the oxygen instead of being given off, attaches itself to a portion of the potassic chloride which is formed ; the quantity of oxygen which is thus fixed varies with the temperature at which the chemi- cal change takes place. In the first reaction a liquid is obtained containing the salt called potassic hypochlorite, which possesses powerful bleaching and disinfecting properties. It yields its oxygen again readily. Dilute hydrochloric acid evolves chlorine, both from the hypochlorite and from the acid itself, thus : CIKo + 2HC1 = C1 2 -f KC1 + OH 2 . The chlorine by decomposing water liberates oxygen, thus : C1 2 + OH 2 = 2HC1 + 0, or by combining with the hydrogen of organic substances and taking the place of this element, acts directly or indirectly as a bleaching agent. The best known hypochlorite is the so-called bleaching powder or chloride of lime. It is prepared on a very large scale for the pur- poses of bleaching cotton goods, by passing chlorine gas over layers of slaked lime placed in large chambers, the so-called chlorine chambers. The reaction appears to take place according to the equation CaHo 2 + C1 2 = Ca(001)Cl -f OH 2 . Calcic chloro-hypochlorite, or " bleaching powder." HYPOCHLOROUS AND CHLORIC ACIDS. 133 Bleaching powder undergoes a slow decomposition even at the ordinary temperature, giving off oxygen and leaving calcic chloride. Instances are known of glass bottles having been shattered to pieces by the accumulated oxygen ; when brought in contact with bodies which have an affinity for oxygen, hypochlorites part readily with oxygen and act thus as powerful oxidizing agents. Experiment 139. Shake up some bleaching powder with a little water and filter. Add some of the solution to a solution of a salt of manganese (lUnClo), or lead (sugar of lead) . A brown precipitate of manganic, or plumbic dioxide is obtained. The bleaching powder parts with its oxygen which combines with the IttnO, or PbO, to form mn iv O 2 , or Pb iv O 2 , calcic chloride being left in solution. Experiment 14O. Add to a solution of bleaching powder placed in a capacious flask, a few drops of cobaltous chloride, CoCL, and heat gently. Oxygen is disengaged in large quantities. The cobaltous salt (like the manganous or lead salts in Exp. 139) is immediately oxidized by the bleaching powder, and is con- verted into cobaltic oxide, Co iv 2 O 3 , and probably into an unstable cobaltic anhy- dride, Co vi O 3 , which, under the influence of heat, forthwith breaks up into Co iv 2 O 3 + O 3 , oxygen being given off freely. The cobaltic oxide remains behind when the evolution of oxygen has ceased, and appears to act merely as a carrier of oxygen. Ferric and manganic hydrates produce a similar effect. These two metals are capable of forming acid oxides, Pe^Os and lHCn yi O 3 , which part readily with their oxygen. Cupric oxide also acts in an analogous manner, owing- probably to the formation of a cupric peroxide, Cll iv O 2 . Experiment 141. Shake up a solution of bleaching powder (1 in 10 parts of water) with a solution of sodic carbonate (washing-soda) and syphon off or filter. The filtrate contains the sodic hypochlorite, formed by double decom- position, thus: Ca(OCl)Cl + CONao 2 = COCao" + CINao + NaCl, also known by the name of Eau de Javelle, and used as a disinfecting fluid, or as a laboratory reagent for purposes of oxidation. Experiment 142. Hypochlorous acid, ClHo, can be prepared by passing chlorine gas into water, holding in suspension certain metallic oxides, hydrates, carbonates, etc. Precipitated mercuric oxide or calcic carbonate is practically found to be the most advantageous, thus : 2HS-O + OH 2 -h 2C1 2 = Hg- 2 OCl2 + 2ClHo. Mercuric Hypochlorous oxychloride. acid. The product of the reaction is rectified by distillation. Aqueous hypochlorous acid has a yellowish colour, an acrid taste, and a characteristic sweet, chlorine-like smell. The strong acid decomposes rapidly, even when kept in ice. The dilute acid is more stable. It is, like free chlorine, a powerful oxidizing agent. The corresponding anhydride, OC1 2 , can be prepared by passing the chlorine over dry mercuric oxide, kept cool by ice, or by depriv- ing the hypochlorous acid of its water. It is a yellow gas, which condenses to a blood-red liquid at 20 C. It speedily decom- poses and explodes from very slight causes, and should not be pre- pared by beginners, except by taking every possible precaution. The gas may be collected by downward displacement. When passed into water it forms hypochlorous acid : OC1 2 + OH 2 = 2ClHo. Chloric acid, { A^r , which enters into the composition of chlorates, is prepared by acting upon baric chlorate by dilute sulphuric acid. 134 CHLOROUS ANHYDRIDE. CHLORIC PEROXIDE. S0 2 Ho 2 = 2 o + S0 2 Bao". ' Chloric acid is a colourless, syrupy liquid, having a strong acid reaction. When warmed it gives off a strong, chlorine-like odour. It is somewhat unstable at ordinary temperatures, and undergoes rapid decomposition when heated, being converted into perchloric acid, water, chlorine, and oxygen. It is a very powerful oxidizing and bleaching agent. Dilute acids decompose it with liberation of chlorine. Unlike the hypochlorites and chlorites, the chlorates do not bleach until after the liberation of the acid. Chloric anhydride is not known. Two intermediate oxides exist, viz., chlorous anhydride, 3 C1 2 , and chloric peroxide, O 4 C1 2 . The former is prepared by acting upon potassic chlorate with nitric acid in the presence of a reducing agent, such as arsenious acid. It is a yellowish- green gas, which is not condensed to a liquid by a cold of 20 C. It explodes when heated to 57, also when brought in contact with sulphur, phosphorus, or arsenic. It should on no account be prepared by beginners. The gas is soluble in |-th its volume of water, forming chlorous acid, OClHo. This acid combines slowly with bases, forming chlorites, which are very unstable, and break up easily into chlorates and chlorides. Chloric peroxide or chlorine tetroxide is obtained by the action of sulphuric acid upon potassic chlorate at a low temperature. Experiment 143. Powder a few crystals of potassic chlorate very finely, and mix with a glass spatula, on a sheet of white paper, with an equal quantity of finely-powdered cane-sugar. Transfer to a brick or tile, and touch it with a glass rod, previously dipped in concentrated sulphuric acid. Chloric peroxide, which is thus set free, causes a vivid combustion of the entire mass. Experiment 144. Place a few crystals of potassic chlorate at the bottom of a conically shaped glass, filled with water. Add a small piece of phosphorus, and then introduce by means of a pipette drawn out to a fine point, a little con- centrated sulphuric acid. As soon as the acid is allowed to come in contact with the salt, chloric peroxide is evolved, wliich ignites the phosphorus, and gives rise to a vivid combustion. Experiment 145. Put a few crystals of potassic chlorate into a test-tube, and allow a little concentrated sulphuric acid to run down along the sides of the tube. Hold the tube away, with its mouth turned outward, for as soon as the acid comes in contact with the salt, chloric peroxide is given off, and an explosion takes place, which is frequently violent enough to eject some of the contents. By adding the acid to the salt, so as to keep the contents of the tube at a low tempera- ture, a dark greenish gas may be collected by displacement, which, in a diluted form, has a sweetish aromatic odour, and is a powerful oxidizing agent. At 20 it condenses to an orange-red liquid. On introducing a hot wire into a test-tube containing chloric peroxide, an explosion takes place. The gas explodes with great violence above 60, often spontaneously. No corresponding hydrate is known. There exist still higher oxygenized compounds of chlorine and oxygen, viz., perchloric acid and perchlorates. The starting point PERCHLORIC ACID. PERCHLORATES. 135 for these bodies is potassic chlorate, a salt which is now largely manufactured and used by lucifer manufacturers, also for detonating powders, pyrotechnical displays, and medicinal purposes. Experiment 146. Pass a rapid current of chlorine through boiling milk of- lime, when calcic chlorate and chloride are formed, analogous to the reaction which takes place when chlorine is passed through a concentrated solution of potassic hydrate. On adding potassic chloride to the solution containing the calcic chlorate, the latter is transformed into potassic chlorate and calcic chloride, thus : JOC1 to rocl Cao" + 2KC1 = 2 \ JJ^ + CaCl 2 . r IOK loci The potassic chlorate can be more readily separated by recrystallisation from the calcic chloride than from the potassic chloride, owing to the greater solubility of the calcic salt. When potassic chlorate is heated gradually till about one-third of its oxygen has been evolved, it becomes pasty, and ceases after a time to evolve oxygen. It consists then of a mixture of potassic perchlorate and chloride, thus : OC1 O + KC1 + O 2 . .OKo Potassic Potassic perchlorate. chloride. The two salts are separated by crystallisation, potassic per- chlorate being even less soluble than potassic chlorate. Perchloric acid, C10 3 Ho (no anhydride exists), is obtained from the potassic perchlorate by distilling with about three times its weight of sulphuric acid. A colourless fuming liquid condenses in the receiver, having a specific gravity of 178. It does not solidify at 35. This acid is a most powerful oxidizing agent; it instantaneously ignites wood or paper, when thrown upon it, and is decomposed with explosion by charcoal. It is the most stable of the chlorine acids. It does not bleach. 136 TABLE OF CHLORINE COMPOUNDS. TABLE SHOWING THE COMPOUNDS WHICH CHLOEINE FORMS WITH OXYGEN, AND WITH OXYGEN AND HYDROXYL. Volume weight, or Names of Constitutional Atomic Molecular Molecular specific compounds. formulae. weight. weight. volume. gravity referred to hydrogen. Hypochlorous "} anhydride . J OC1 2 87 87 CD 43 '5 criths Chlorous an- 1 hydride .. J roci 1 Loci 119 119 nzn (anomalous) 39 -7 roci Chloric per- "1 oxide . . . . J Jo 1 135 135 ? Loci Hypochlorous ~l acid J OC1H or ClHo 52-5 52'5 ? Chlorous acid . . OClHoorjg^ 68-5 68-5 Chloric acid . . {O>{H 84-5 84-5 p Perchloric "1 acid j roci r cl 1 or i o [OHo [ H 100-5 100-5 ' QUESTIONS AND EXERCISES. 1. Explain the changes which take place when chlorine is passed through a solu- tion of potassic hydrate, 1st, through a dilute solution in the cold j 2nd, through a boiling and concentrated solution. 2. How is bleaching powder manufactured ? Express the change by an equation. 3. Qrwe illustrations of the oxidizing action produced by bleaching powder. 4. Under what conditions does calcic chloro-hypochlorite give off oxygen gas ? 5. How is " Eau de Javelle " prepared, and what are its uses ? 6. How are chlorous acid and chlorous anhydride prepared ? Describe their pro- perties. 7. Give symbolic and graphic formtilee for sodic hypochlorite, bleaching powder, chlorous anhydride, chloric peroxide, and potassic perchlorate. 8. What changes does potassic chlorate undergo by heat ? 9. Describe the method of preparing potassic chlorate on a manufacturing scale. PHOSPHORUS. 137 CHAPTEE XIX. THE OXIDES OP PHOSPHORUS AND ARSENIC. PHOSPHORUS, when pure, is a wax-like, faintly yellow, semi-opaque, solid body. It is generally sold in the form of sticks. It melts readily at 44 C., and becomes then of a yellowish syrupy con- sistency. It can be distilled, its boiling-point being 288 C. Phosphorus volatilizes, however, far below its boiling-point. Its great inflammability constitutes its most characteristic property. Friction may set it on fire. Dry phosphorus when exposed to the air, combines slowly with oxygen, and its temperature is often raised so considerably by this slow combustion that it melts and inflames spontaneously, especially in warm weather. It has therefore to be preserved in cold water, in which it is quite insoluble. We have already seen (comp. Exp. 23) that phosphoric anhydride results from the combination of phosphorus with oxy- gen. Experiment 147- Small quantities of this body may be prepared by burning some phos- phorus placed in a little porcelain capsule under a good-sized bell-jar resting on a plate as seen in Fig. 68. The phosphorus should be well dried, and the bell-jar wiped quite dry. A snow-white flaky substance is deposited on the sides of the jar, which may be scraped together with a glass spatula, and kept in a well-stoppered bottle. This white body has a great affinity for water, with which it combines with a hissing noise. On account of its great attraction for water it is often used as a dehydrating agent. Analysis has proved that this white body consists of two atoms of pentad phosphorus, and five atoms of oxygen ; hence we write its symbolic formula formula : O II P=0. Phosphoric anhydride combines with water to form the hydrated acid, thus : P 2 5 + 3OH 2 = 2POHo 3 . Phosphoric Phosphoric anhydride. acid. There exist three phosphoric hydrates, differing markedly in their properties when in combination with bases. FlG. 68. COMBUSTION OF PHOS- PHORUS. and its graphic 138 PHOSPHOKIC ACIDS. If a solution of phosphoric acid be evaporated in a platinum vessel till it has acquired a syrupy consistency, hard transparent crystals of trihydric acid are obtained. At a higher temperature (160 to 210) water is, given off slowly, and the tetrahydric acid is left, called pyrophosphoric acid (fooin -rrvp, fire), on account of its being produced from the trihydric acid by the application of heat according to the equation : 2POHo 3 = P 2 3 Ho 4 + OH 2 . , Pyropho sphoric acid. At a red heat the pyrophosphoric acid loses a molecule of water, leaving two molecules of the monohydric or metaphosphoric acid, thus : P 2 3 Ho 4 = 2P0 2 Ho + OH 2 . Metaphosphoric acid. The trihydric acid is also called ortlwpho sphoric acid (from o/?0o, right), and common phosphoric acid, because it occurs in the phos- phates most commonly employed in the arts. It contains three atoms of the compound radical hydroxyl, and is capable of forming with the monad radicals potassoxyl or sodoxyl, by the partial or total displacement of the hydroxyl in the acid, three different kinds of salts called orthophosphates, viz. : PONao 3 , Trisodic phosphate. POHoISTao;,, Common, or hydric disodic phosphate. POHo 2 Nao, Dihydric sodic phosphate. When phosphoric hydrate, or phosphoric acid, is neutralized with sodic hydrate and then evaporated to crystallisation, the second salt is obtained in large transparent, oblique rhombic prisms, which effloresce rapidly in the air. These crystals contain water of crys- tallisation, and the salt has the composition POHoNao 2 + 12Aq. (Aq., abbreviation for aqua, water, standing for water of crystallisa- tion.) A solution of this phosphate gives, with a solution of argentic nitrate, a yellow precipitate of triargentic phosphate, Ago (argent- oxyl) replacing the hydroxyl and sodoxyl, thus : POHoNao, + 3N0 2 Ago = POAgo 3 + 2N"O 2 Nao + W0 2 Ho, the liquid being acid. Experiment 148. Heat gently a small quantity of the ordinary hydric disodic phosphate in a porcelain dish on a water-bath (Fig. 69). The salt fuses first in its water of crystallisation, then swells up, and gives off puffs of steam, the water escaping from underneath the crust of the solidified salt. Cease heating when no'more water escapes, and the liquid salt becomes once more solid. On dissolving a small portion of the white mass in water, and adding a solution of argentic nitrate, the same yellow precipitate will be obtained which the salt gave before being heated. It has not been changed beyond losing its 12 molecules of FIG. 69. water of crystallisation. On dissolving in hot water, ORTHO- PYRO- AND METAPHOSPHATES. 139 and allowing to crystallise, the original rhombic prisms are obtained once more. Heat some of the dry salt in an iron spoon, or, better, in a platinum vessel, to a strong red heat over a gas flame. Water is again expelled the water which formed part of the salt, so called water of constitution and on dissolving a little of the white saline residue in water, and adding a solution of argentic nitrate, a white precipitate is now obtained, and the solution is neutral, an indication that the salt has undergone a change. On dissolving some of the ignited mass in hot water, and setting it aside to crystallise, the solution no longer deposits crystals of the original salt, but of a salt which, on analysis, is found to consist of " (sodic pyrophosphate). Its formation is expressed by the equation : 2POHo]$rao 2 = P 2 3 :N~ao4 + OH 2 . This salt contains no longer trihydric, but tetrahydric phosphoric acid, P 2 3 Ho4, called pyrophosphoric acid. Experiment 149. We are acquainted with a characteristic salt of ordinary or orthophosphoric acid, called microcosmic salt, or hydric ammonic sodic phos- phate (POHoAmoNao + 8 Aq). This salt may be readily prepared by dis- solving 6 to 7 parts of the common sodic phosphate of commerce, and 1 part of ammonic chloride in 2 parts of boiling water, and allowing the liquid to crystallise in a cool place. On heating the salt in the same manner as was done in the previous experiment, a clear transparent mass is left, which, if slowly cooled, becomes crystalline ; it now deliquesces in air, and dissolves very readily in water. The aqueous solution when almost neutral, gives with argentic nitrate a white precipitate. The supernatant liquid is neutral. Water of crystallisation and ammonia are given off, and the salt, PO 2 Nao (sodic metaphosphate), is left, which contains no longer trihydric, but monohydric phosphoric acid. The change may be expressed by the equation : POHoAmoNao = P0 2 ao + NH 3 + OH 2 . Sodic metaphosphate. We have thus become acquainted with three modifications of phosphoric acid, not to speak of other forms, viz. : 1. Common or orthophosphoric acid, POHo 3 (trihydric or tribasic). 2. Pyrophosphoric acid, P 2 3 Ho4 (tetrahydric or tetrabasic). 3. Metaphosphoric acid, P0 2 Ho (monohydric or monobasic). Pentad phosphorus being invariably the grouping element, these acids are written symbolically and graphically, thus : O II POHo 3 H O P O H A 140 PHOSPHOROUS ANHYDRIDE. H O II II O P P H H P0 2 HO H =P H. A lower oxide, formed by slow and imperfect oxidation of phosphorus (as when it is exposed to dry air at the ordinary tem- perature), viz., phosphorous anhydride, consisting of two atoms of phosphorus and three atoms of oxygen, is obtained in the form of a white powder possessing the odour of garlic. Its symbolic formula is !P"' 2 O 3 , its graphic formula : 0=P P=O, the P being in the triad condition, with two bonds left dormant in each atom. Phosphorous anhydride is of interest in so far only as it acts as a powerful reducing agent ; i.e., owing to its latent bonds it can deprive other oxides of part of their oxygen. Of the many reactions illustrative of this property, we will only cite the action of P 2 3 on silver oxide, thus : 2OAg 2 + P 2 O 3 = 2Ag 2 + P 2 5 . Phosphorus is capable of combining also with hydrogen. Experiment 15O. Introduce into a small retort (Fig. 70) some concen- trated solution of potassic or sodic hydrate, and a few small pieces of phosphorus. On heating a gaseous body is evolved, which ignites spontaneously as soon as it FlG. 70. PREPARATION OF PHOSPHORETTED HYDROGEN. issues from the water of the pneumatic trough. Each gas bubble rises through the air with a peculiar circular wreath of white smoke, which enlarges as it ascends in the air. In order to avoid every risk of an explosion, a current of PHOSPHORETTED HYDROGEN. ARSENIDES. 141 hydrogen or coal-gas may be passed for some time through the retort previous to applying heat. Phosphorus alone does not decompose water. It requires the powerful base potassa or soda to induce it to form with the oxygen of the water an oxy-acid, and with the hydrogen an inflammable gas, called phosphor etted hydrogen, thus : 3OKH + P 4 + 3OH 2 = 3POH 2 Ko + PH 3 . Potassic Phosphoretted hypophosphite. hydrogen. Bodies which appertain to the metals rather than to the non- metals, such as arsenic (As), antimony (Sb), bismuth (Bi), but which form compounds analogous with the compounds of phos- phorus, must be briefly glanced at here. These elements are like phosphorus, of a pentad nature. Arsenic, moreover, occurs in nature, closely associated with phosphorus. This close resemblance extends also to the oxides of arsenic and their salts, the arsenites and arseniates. Two oxides deserve our attention, arsenious, A.s'" 2 O 3 , and arsenic anhydride, A.S V 2 5 , written graphically : As As II II A O O O I II s As I In the lower oxide each atom of arsenic has two bonds left unsatis- fied ; and very interesting reactions, based upon the deoxidation of various higher oxides, by means of arsenious anhydride, result from this property. Arsenic is sometimes found native, but more frequently in com- bination with metals, such as iron, nickel, cobalt, etc. When arsenic is combined with metals it forms with them arsenides, from which the arsenic can be removed by roasting (in a reverberatory furnace), in the form of a volatile oxide, which is condensed in brick flues, and purified by sublimation. Experiment 151. Heat a small quantity of some finely powdered arsenide, such as arsenical pyrites, or mispicJcel, in a piece of hard glass tube (combustion-tube) , holding the tube in a slightly inclined position, so as to cause a current of air to pass oyer the ignited powder. The sulphur and arsenic combine with oxygen to form volatile compounds, viz., sul- phurous anhydride, SO 2 , and ar- senious anhydride, ASgOa, leaving the iron as oxide. The As 2 O 3 condenses in the cold part of the tube, and SO 2 passes off. The change takes place according to the equation : As 4 + 30 2 = 2AS20 3 . ~Fk 71. 142 OXIDES OF ARSENIC. Experiment 152. By heating a little of the arsenious anhydride or white arsenic so obtained on charcoal, before the blowpipe (Fig. 71), a strong garlic odour becomes at once perceptible, and white fumes ascend into the air, which are highly poisonous. The experiment should therefore be made with a very small quantity of the substance only, and in a place with a good draught. The charcoal deprives the arsenious anhydride of its oxygen, forming CO 2 and As. The metaUic arsenic being readily vjakitilized, on passing through the outer or oxidizing cone of the blowpipe flame, is partially reconverted into oxide, thus : (1) 2As 2 O 3 + 30 = As 4 + 3CO 2 . (2) As 4 + 3O 2 = 2As 2 O 3 . Arsenious differs from phosphorous anhydride by possessing but little affinity for oxygen. It requires, in fact, powerful oxidizing agents, such as nitric acid, to convert it into arsenic acid, AsOHo 3 . Experiment 153. Dissolve a little powdered white arsenic in a small flask, in hot hydrochloric acid (as it is but slightly soluble in water), and oxidize by means of concentrated nitric acid, as long as ruddy fumes of N 2 O 3 are evolved. The liquid is then cautiously evaporated to complete dryness, and a little water added to a small portion. The mass dissolves completely, showing a strongly acid reaction to test-paper. The reaction takes place according to the equation : As 2 3 + 2N0 2 Ho + 2OH 2 = 2AsOHo 3 + N 2 3 . Arsenic acid. Arsenic anhydride has, like phosphoric anhydride, a great attraction for water. It absorbs moisture from the air, and gradually deli- quesces. The solution contains trihydric or tribasic arsenic acid, precisely analogous to orthophosphoric acid, forming salts which are identical in shape (isomorphous) with the corresponding phos- phates. A sodic arseniate, AsOHoNao 2 -f 12 Aq., is obtained, when arsenic acid is neutralized with sodic hydrate or sodic carbonate, which cannot be distinguished in appearance from the common sodic phosphate. Like phosphoric acid it can form three different kinds of salts, viz. : Trisodic arseniate, AsOHoNao 2 , Common arseniate, or hydric disodic arseniate, AsOHo 2 Nao, Dihydric sodic arseniate, and is capable of retaining one or two parts of unreplaced hydroxyl, or of replacing two parts of hydroxyl by Mgo", or some other oxyl- radical of a dyad metal, as in AsOAmoMgo", ammonic magnesic arseniate. Salts are also derived from the acid in which the analogy between arsenic and phosphoric acid is still further borne out. We know salts containing As0 2 Ho, and As a 3 Ho 4 , Metarsenic acid. Pyrarsenic acid. ARSENITES AND ARSENIATES. 143 Corresponding to P0 2 Ho, and P 2 3 Ho 4 . Metapliosphoric Pyrophosphoric acid. acid. Arsenious acid forms likewise a definite series of salts, called arsenites, closely analogous to phosphites, of which the alkaline arsenites pos- sess again the greatest interest. The power of forming salts with different bases which this acid possesses is, however, not so well defined as that of arsenic acid. The compounds which arsenic and antimony are capable of forming with hydrogen, analogous to phosphoretted hydrogen, X?H 3 , viz., arsenietted hydrogen, AsH 3 , and antimonietted hydrogen, SbH 3 , will be described in the second Part of this work, under the respective metals. QUESTIONS AND EXEECISES. 1. Describe the most important properties of phosphorus. 2. How would you prepare small quantities of phosphoric anhydride ? 3. Explain how orthophosphoric, pyrophosphoric, and metaphosphoric acids are obtained. Give equations. 4. You have given to you a solution of orthophosphoric acid, and a solution of potassic hydrate. State what salts you can form with these materials. 5. Grive symbolic and graphic formulae for common sodic phosphate, magnesic pyrophosphate, sodic metaphosphate, and phosphorous anhydride. 6. How would you distinguish between a soluble orthophosphate and pyrophos- phate ? 7. Explain the terms, ortJio- and pyrophosphoric acid, microcosmic salt, ar- senide. , 8. Describe the changes which microcosmic salt and the common hydric disodic phosphate undergo, when exposed to a gradually increasing heat. Give equations. 9. How is phosphorous anhydride prepared, and what is its most characteristic property ? 10. Trace the analogy which exists between phosphorus and arsenic compounds. 11. What changes do metallic arsenides undergo when heated in a tube of hard glass, open at both ends ? Give equations. 12. How is white arsenic affected when heated on charcoal before the blowpipe flame ? Give equations. 13. In what respect does phosphorous anhydride differ from arsenious anhy- dride ? 14. "What is the action of nitric acid upon arsenious anhydride ? Give an equa- tion. 15. Write out the symbolic formulae of a few arsenites and arseniates. 16. How is phosphoretted hydrogen prepared, and what are its most striking properties ? Give an equation. 17. Calculate how much NH 3 by weight can be obtained upon ignition from 2'350 grms. of POAmoMgo". 18. Calculate the percentage composition of microcosmic salt. 144 BORIC ANHYDRIDE. CHAPTER XX. OXIDE OF BORON. ~ THE element boron occurs in nature always in combination with oxygen, as boric acid, either in the free state or combined with metals. The most important of its salts is borax, a compound of the base soda, with boric acid. Experiment 154. Dissolve a small quantity of powdered borax the ordinary prismatic crystals of B^OsNaOjj in four times its weight of boiling water, and add to the filtered solution concentratad hydrochloric acid, till litmus- paper is freely reddened. Orthoboric acid, or boric hydrate separates on cooling in thin translucent pearly plates, which can be obtained in a sufficiently pure state, by pouring off the liquid, washing with a little water, spreading the crystals on filter-paper on a warm tile, and drying at a gentle heat. They are soluble in boiling water, to which they impart only a slight acid taste ; and the solution of the acid gives to blue litmus-paper merely a wine-red tint similar to that which carbonic acid produces. When treated with concentrated hydrochloric acid the sodoxyl radical, it may be assumed, is first acted upon with formation of sodic chloride and Ho 2 . The five molecules of water (which may be viewed as hydride of hydroxyl, HHo), by attacking five atoms of oxygen, form five molecules of Ho 2 , and the hydrated acid separates, thus : 2HC1 + 5OH 2 = 4BHo 3 + 2Na01. The trihydric or tribasic acid, BHo 3 , so obtained, is converted into the metaboric acid, BOHo, by heating up to 100 C., thus : BHo 3 = BOHo + OH 2 . By exposing the acid to the strongest red heat we obtain boric anhydride. This cannot be done without incurring loss from volatilisation. The acid merely fuses and forms, on cooling, a glassy hard ringing mass. The 'composition of the anhydride is B'" 2 3 , boron being a triad element. Its graphic formula is written 0=B B=O. Experiment 155. Dissolve a few crystals of boric acid in a small porcelain dish by means of a little alcohol, and set fire to the spirit. It burns with a green flame, which becomes especially visible on stirring up with a glass rod. A similar green flame is produced if a few crystals of borax are decomposed by the addition of a little sulphuric acid and alcohol, and set fire to as before. This reaction constitutes a characteristic test for boric acid. Boric acid is principally derived from a mineral called tincal, an abnormal sodic borate, having the composition Bj0 6 Nao 2 , 10OH 2 , which may be viewed as a compound of two molecules of sodic metaborate and one molecule of boric anhydride 2BONao + B 2 3 = B 4 5 Nao 2 . ORTHOBORIC AND METABORIC ACIDS. BORATES. 145 Its graphic formula, as expressed by Dr. Frankland, is Na B B B B ISTa v v This view is borne out by the facility with which a dilute aqueous solution of borax is decomposed. On adding tincture of litmus to a concentrated borax solution, the liquid acquires a slightly reddish tint, which, on the addition of more water, turns distinctly blue, i.e., on dilution the borax solution acts like a weak solution of a free alkali mixed with boric acid. Boric acid combines with bases in the state of metallic hydrates, oxides, or carbonates, in many different proportions, both in the wet and dry way. Its salts are called borates. At high temperatures it behaves like a strong acid, displacing not only carbonic anhydride, but sulphuric and phosphoric anhydrides, from their salts. In solution, however, boric acid is but a weak acid, although it is capable of combining with free bases, and of decomposing, when in concentrated solutions the metallic carbonates, with evolution of carbonic anhydride, especially on boiling. Its feeble acid character is also manifested in borates containing excess of acid so-called acid salts which react strongly alkaline, and in which the feeble acid cannot overcome the alkaline nature of such strong bases as soda or potassa. Experiment 156. Mix intimately in a mortar some of the boric acid obtained in Exp. 154 with somewhat less than its own weight of sodic chloride, and heat the mixture in a porcelain or platinum crucible over a good gas flame. The mass fuses and a vapour is given off. Remove the lamp for a moment, and hold an inverted bell-jar over the crucible. Strips of blue litmus paper, moistened with water, are made to adhere to the inside of the jar. As soon as the vapour comes in contact with the paper the blue colour changes to red. The vapour consisted of hydrochloric acid. This may be proved by rinsing the jar with a few drops of ammonia, before inverting it over the crucible, when white fumes of ammonic chloride are formed. The change takes place according to the equation NaCl + BHo 3 = BOXao + HOI + OH 2 . Here, then, is another instance of a curious reciprocal affinity. Exp. 154 proved that boric acid is liberated from borax by con- centrated hydrochloric acid. The preceding experiment showed that boric acid drives out hydrochloric acid. It is obvious, then, that the affinity of boric acid for soda is greater at a high tempera- ture than that of hydrochloric acid ; the different action of the two acids is evidently owing to the fixed character of the one, and to the volatile nature of the other acid hydrochloric acid being volatile at the ordinary temperature. The tendency in the latter to volatilize at a high heat assisted its escape, whilst the fixedness of the boric acid was actually increased at a melting heat. Most borates fuse to transparent glasses. Alkaline borates, when fused with metallic oxides, take up and dissolve many of the L 146 CONSTRUCTION OF THE BLOWPIPE. latter, forming double borates of the alkali base and the metallic oxide, which are frequently marked by characteristic colours. Hence borax is of great use as a flux in metallurgical experiments, or on a small scale, in blowpipe reactions. QUESTIONS AND EXEECISES. 1. What is our chief source of boric acid ? 2. How is orthoboric acid obtained from borax ? Give an equation. 3. Explain the action of heat upon orthoboric acid. 4. Give symbolic and graphic formulae for orthoboric and metaboric acid, boric anhydride, borax. 5. What action takes place when orthoboric acid and sodic chloride, or potassic carbonate, are fused together ? 6. What is the percentage of boric anhydride in borax ? 7. Describe a characteristic test for boric acid. CHAPTER XXI. ON THE BLOWPIPE AND ITS USE. A useful blowpipe is represented in Fig. 72. It consists of three parts of a straight tube made of brass or German silver, a b (sometimes fitted, for greater convenience, with a horn or ivory mouth-piece) ; of an air-chamber, c d, which arrests any condensed moisture ; and of a branch tube, / g, which fits into the longer tube, a 6, at a right angle. The tube, / g, is provided with a nozzle, h, ending in a platinum jet, which fits somewhat conically over the tube, / 0, as is shown on a larger scale in Fig. 72, b. The most convenient form of mouth-piece is the trumpet- shaped, whereby blow- ing is rendered less fatiguing. Other simpler forms of blowpipes have been devised ; they require, however, no special description to be readily understood. The blowpipe is used for con- veying a continuous blast of air from the lungs into the flame of a spirit-, gas-, or oil-lamp, or into a candle flame. In any ordinary conical flame we are able to distin- guish three different parts, as repre- sented in Fig. 73 ; 1st, in the middle a dark kernel, a ; 2nd, a bright cone, efg, surrounding the dark kernel a ; and 3rd, a feebly luminous outer cone, bed, surrounding the bright F IQ . 72. FIG. 73. cone. The dark part of the flame con- NATURE OF A CANDLE FLAME. 147 sists of vapours principally of compounds of carbon and hydrogen which burn at the expense of the oxygen of the air. The luminous zone of the candle flame does not get a sufficient supply of oxygen ; it is, therefore, the hydrogen which barns chiefly, whilst the hydro- carbon vapour becomes highly heated, and is rendered luminous. In the outer or feebly luminous zone nothing impedes the free access of, and contact with, the atmospheric air ; complete combustion takes place ; both carbon and hydrogen are converted into their final pro- ducts of oxidation, ' into carbonic anhydride and water (steam). This portion of the flame is very hot, the greatest heat being con- centrated in the point c. If we hold a body, which is capable of taking up oxygen into this outer part of the flame, it becomes rapidly oxidized, since all the conditions are favourable to such a change, viz., a high temperature, and an unlimited supply of air. The outer zone of the flame forms, therefore, the oxidizing flame. If, on the other hand, we introduce a body which is capable of parting with oxygen, into the luminous part of the flame, we should expect to see it become deprived of its oxygen by the hydrocarbon vapours. The body is deoxidized or reduced in the luminous zone of the flame ; hence this section is called the reducing flame. Now, by introducing a current of air into the interior of a flame, the appearance of the flame changes immediately ; it becomes shorter and more pointed in the direction of the current of air. The luminous portion of the flame disappears altogether, and the heat is considerably increased. Two zones of combustion are, in fact, formed, by supplying air to the hydrocarbon vapours; from the inside, as well as from the outside. To produce either an oxidizing or reducing flame, the blast delivered from the blowpipe requires to be properly directed, and must be constant and regular. While blowing, the trumpet-shaped mouth-piece is pressed against the lips, and breathing is effected through the nostrils ; the epiglottis is used as a valve. The air must be forced through the blowpipe by the action of the muscles of the cheeks only. " Beginners, when first practising with the blowpipe, usually commit the fault of not closing the passage between the windpipe and the mouth at the right moment, but of blowing for a longer or shorter period from the lungs alone. This mode of blowing, if per- severed in, is undoubtedly prejudicial to health ; and it is, there- fore, advisable that the beginner should practise himself in breath- ing regularly and audibly through the nose, keeping up a con- tinuous blast by the muscles of the cheeks. This practice should be continued till he is able to do so without any perceptible exertion. In attempting this he will probably not be immediately successful, but a little practice will soon enable him to master this initial diffi- culty." (Plattner on the Bloivpipe.) Success in blowpipe operations depends to a great extent upon the lamp we use. In a laboratory which has a supply of coal-gas, a Bunsen burner of the construction shown in Fig. 74 will be found to answer extremely well. The burner rests on a foot of cast-iron, a 6, into L 2 148 CONSTRUCTION OF A BUNSEN GAS LAMP. h which a square (or round) block, c d, of brass or cast-iron is screwed. This has a cylindrical hole for conveying the air, drawn in through four holes into the brass tube, e /, which screws either into or over the cylindrical hole. A branch tube, &, whicn can be connected by means of india-rubber tubing with the gas sup- ply, conveys gas to a thin tube with a fine slit, or a couple of fine holes at its upper end, and is screwed into the cylindrical hole. The gas and air mix in the tube, e /, and burn at/ with an almost non-luminous flame. The in- draught of cold air keeps the tube cool enough to prevent the flame strik- ing back and burning at the small aperture below. By introducing, for blowpipe pur- poses, a narrower tube, g h, flattened at the top, into the tube, e /, the gas is conveyed from the thin gas delivery- tube below without becoming mixed with air, and burns with its usual lu- minous flame. On directing a blow- pipe jet into the gas flame, the latter is diverted, and we are enabled to pro- duce either a reducing or an oxidizing flame. In order to obtain a reducing flame, the nozzle (Fig. 75) of the blowpipe is held inclined, almost parallel with the surface of the flattened top of tube, g h, so as just to touch the exterior part of the flame. A more or less yellow flame will be thus pro- duced of the form shown in Fig. 75. An oxidizing flame is ob- ...--" "' tained by keeping the nozzle of FIG. 75. the blowpipe at the same incli- nation as before, but introduc- ing it somewhat further into the flame (Fig. 76), so as to obtain a clear unbroken jet. A somewhat stronger blast is also sent into the flame, so as to produce a longer and more pointed jet of flame, of a pale blue colour, and almost invisible by daylight. If a small frag- ment of an oxidizable substance be held just beyond the point of this flame, it becomes intensely heated, and rapidly absorbs oxygen from the surrounding atmosphere, or, if the blast from the blowpipe be very strong, from the air which passed unconsumed through the centre of the flame. When a substance is submitted to the action of the reducing flame, it should be held so as to be entirely surrounded by the Fio. 74. CHARCOAL SUPPORTS. 149 yellow flame, and protected from the oxidizing action of the atmo- sphere, but as near as possible to the point of the flame, in order to utilize the greater heat of that part of the jet. f FIG. 76. Far superior to a Bunsen gas-jet is Hera/path's blowpipe lamp (Fig. 77), constructed on the principle of a Bunsen burner. The gas and air issue from the mouth of the brass jet well mixed, and burn, when lighted, with a blue flame. The flame can readily be rendered a reducing one, either by increasing the supply of gas, or by diminishing the blast ; or an oxidizing one, by decreasing the gas and increasing the blast of air. By attaching the brass tube by means of flexible india-rubber tubing to a gas supply pipe, and connecting the air-tube with a short piece of tubing ending in an ivory or glass mouth-piece, the lamp becomes a highly serviceable piece of chemical apparatus. Supports. Charcoal is mostly used as a support in reduction experiments. The best charcoal is that from the wood of the pine, lime, or willow ; closely grained, free from knots, and well burnt. The pieces are best cut by a small-toothed saw into regular prisms of about six inches in length, and from one to two inches in breadth, having a flat smooth surface at right angles to the lines of growth, because the fluxes spread out on the charcoal on the other surfaces (Berzelius). A good piece of charcoal may be made to serve for many experiments, by simply filing off the used surface and ex- posing a new one after each operation. What renders charcoal so valuable as a support in blowpipe experiments is, 1st, its infusibility ; 2nd, its weak power for con- ducting heat ; 3rd, its porosity, which enables it to absorb within its pores readily fusible fluxes, such as borax, microcosmic salt, sodic carbonate, potassic cyanide, leaving the infusible substance under examination behind ; and, lastly, its power of assisting in the re- duction of oxidized substances in the inner blowpipe flame, on account of the carbonic oxide atmosphere which the charcoal furnishes by the partial combustion of its carbon. The substance to be subjected to the blowpipe flame (which if a powder should be previously moistened with a little water to 150 PLATINUM SUPPORTS. make it cohere) is placed in a shallow cavity, scraped out near the end of the charcoal, and the latter is so held that the flame impinges upon the substance at a slight angle, as seen in Fig. 71. Platinum wire, frequently also platinum foil, or a small platinum spoon, is employed for Oxidation experiments, or for the diffusion of insoluble bodies in fluxes, in order to observe the coloured glasses which they produce. Thin platinum wire is chosen, which may be used in the form of a coil, with the ends unrolled, or in pieces about half a foot in length (Fig. 78). These are fused for convenience, sake into a piece of glass tubing drawn out to a point, with the end turned into a hook or loop, to hold the borax or microcosmic salt which is to be fused into a bead. (Care must be taken that no substance, such as sulphur, lead, etc., which acts upon platinum, be fused upon the wire.) Platinum foil is employed as a support for substances which are not to be exposed to the reducing action of char- coal. The foil may be placed on a piece of charcoal, or held in the flame by a pair of forceps. Platinum Spoon. This should be of the size and form shown in Fig. 79. It may either be fixed into a wooden handle or into a cork. (The lid of a small platinum cru- cible, supported on a platinum triangle (Fig. 80), answers equally well.) It is used for fusing certain substances with Q alkaline carbonates, hydric potassic sulphate (SO 2 HoKo), FIG. 78. or nitre (NC^Ko). FIG. 79. FIG. A pair of Brass Forceps with Platinum Tips. These are con- structed as shown in Fig. 81. A fragment of the mineral or other sub- stance is held between the platinum points, a, which are opened by pressing on the knobs, fe b, and close again by FIG. si. their own elasticity. These forceps are used for holding splinters of minerals, etc., which are to be heated in the outer or hottest part of the blowpipe flame, to ascertain their fusi- bility and the colour they impart to the blowpipe flame. BLOWPIPE REACTIONS. 151 Experiment 151. Heat on a charcoal support a little litharge (plumbic oxide, PbO) in the reducing flame of the blowpipe. G-lobules of metallic lead are left, and a yellow incrustation forms on that part of the charcoal over which the flame passes. This arises from the deposition of yellow plumbic oxide on the cooler parts of the charcoal. Some of the metal is, in fact, vola- tilized, and on passing through the outer flame of the blowpipe is oxidized. The same occurs in the case of other metals ; hence the different and often characteristic incrustations, observed when metallic oxides are heated on charcoal in the reducing flame, fre- quently help to distinguish such metallic bodies in a very ready manner. Experiment 158. Heat a small piece of metallic antimony in the cavity of the charcoal in the oxidizing flame of the blowpipe. The metal melts readily, and gives off white fumes, and a white deposit of antimonious oxide, Sb 2 O 3 , covers the charcoal all round the metallic antimony, which by continued heat may be entirely volatilized. Most metals (with the exception of gold and platinum) are capable of being converted into oxides, when heated in the outer flame of the blowpipe. Experiment 159. Melt some borax on the loop of the platinum wire to a clear pearl of borax glass. The bead should be perfectly colourless, both in the hot and cold state. While the glass is still hot and fluid, it is brought in contact with a small quantity of black cupric oxide, and the outer flame of the blowpipe applied a second time. The black oxide dissolves in the liquid glass, and pro- duces a deep dark colour. If introduced in small quantities the glass is green whilst hot, and blue on cooling ; if in large quantities the green colour is so intense as to appear black ; when cool this becomes paler, and changes to a greenish-blue. When heated in the reducing flame the copper glass becomes nearly colourless, but immediately on solidifying assumes a red colour, and becomes opaque from the separation of metallic copper. By long continued blowing on charcoal the oxide is reduced, and the metal separates in the form of a small metallic bead, leaving the glass colourless. The change which takes place will be readily understood after what has been stated in Chapter XX with regard to the action of borax at high temperatures. The molecule B 3 3 forms with the CuO a cupric metaborate, thus B 2 3 + CuO = B 2 2 Cuo". In performing this experiment, and experiments of a similar nature, care must be taken not to dissolve, in the first instance, too large an amount of the oxide, or other substance under examination. If a small quantity affords no distinct reaction, more may be easily added. If, however, the colour of the bead be too intense to be clearly distinguishable, the bead may be jerked off from the wire, and the portion which still adheres fused up with a fresh quantity of borax, in which manner a more dilute bead will be obtained. We possess in microcosmic salt another most valuable flux, as it leaves, on ignition, sodic metaphosphate, a readily fusible salt. The action of this salt is analogous to that of borax ; but as ex- perience has proved that the beads which it forms with many 152 SILICA. substances are more characteristic, and the colours better denned than those produced by borax glass, it is frequently preferred to the latter as a flux. Microcosmic salt, when fusing at first in its eight molecules of water of crystallisation, is so flujd that it readily drops from the platinum loop. It is, therefore, advisable to fuse it on charcoal or platinum foil, when the water and ammonia are driven off, and a viscid residue is left. Some of the glass thus formed can readily be taken up on the platinum wire (the loop may be made somewhat smaller), and the powdered mineral or oxide fused with it in the same way as with borax. Experiment 16 O. Dissolve a little uranic oxide, TT 2 O 3 , in a bead of microcosmic salt. It dissolves to a clear yellow glass in the outer flame, and becomes yellowish -green on cooling. Heated in the reducing flame the glass assumes a beautiful green colour, which becomes more brilliant as the bead cools. The action of the sodic metaphosphate consists in taking up metallic oxides, and forming with them tribasic phosphates, con- taining more than one base. The blowpipe is of great assistance in chemical analysis, because it individualizes the body under examination, by pro- ducing distinctive changes, which are peculiar for the most part to each of the metals. Although the presence of other bodies may interfere to some extent with the special reactions of the body for which we search, and thus render the search doubtful or in some cases nugatory, it cannot be too strongly impressed upon the chemical student to gain a complete mastery over the blowpipe reactions, as being by far the most easy and readily available means of qualitative analysis. QUESTIONS AND EXEECISES. 1. Describe the construction of the mouth blowpipe. 2. Describe the nature of a candle flame. 3. Describe the construction of a Itunsen gas-burner. 4. Explain the oxidizing and reducing action of the blowpipe flame. Give examples. 5. Explain the use of borax and microcosmic salt in blowpipe reactions. CHAPTEE XXII. ON SILICA AND SILICATES. Silica is one of the most widely diffused substances in nature, and constitutes, together with the compounds which it forms with metallic bases, viz., the silicates, the greater part of the solid crust of our earth. It is found either in the free or combined state. White and yellow sand, quartz, agate, flint, rock-crystal, opal, chalcedony, are more or less pure silica. SILICIC ANHYDRIDE. 153 Experiment 161. Add dilute hydrochloric, nitric, or sulphuric acid to a solution of so-called water glass (sodic silicate). Gelatinous silicic hydrate separates, which may be thrown on a filter and washed with water, in which medium it is but slightly soluble. Dry the precipitate by placing the funnel on a hot sand-bath over a filter drier (Fig. 82). The gelatinous mass shrinks together considerably. It loses its water and becomes anhy- drous, even at the temperature of boiling water. Remove the precipitate, when dry, from the filter, and heat it strongly in a porcelain or platinum crucible. A fine white amorphous powder is left, perfectly insoluble in water. Analysis has proved that this white powder consists of one atom of the element silicon and two atoms of oxygen ; it is called silica, or silicic anhydride, Si0 2 . Silicon being combined with two atoms of oxygen must be a tetrad element, and silica is written graphically 0=Si=0. Experiment 162. Mix some finely powdered* quartz intimately with about four times its weight of fusion mixture (CONao 2 and COKo 2 mixed in molecular quantities) and heat in a covered platinum crucible over the flame of a Bunsen lamp. The mixture fuses, if sufficient heat be applied, and gives off bubbles of carbonic anhydride. Heat as long as any gas comes off, and keep the contents of the platinum crucible from ten minutes to a quarter of an hour in a state of quiet fusion ; allow to cool, and remove the solidified mass from the crucible by digesting for some time with hot water in a porcelain dish. The whole of it dissolves. This proves that the quartz was completely fused. (A suc- cessful fusion can only be effected by powdering the quartz in the first instance very finely.) Acidulate the solution now with dilute hydrochloric acid ; carbonic anhydride is evolved, owing to the decomposition of the excess of the alkaline carbonates, and gelatinous silica separates. Evaporate to complete dryness on a water-bath. Stir the gelatinous mass which is left with a stout glass rod, and break up the lumps. Transfer the dish for a short time to a hot sand-bath, and apply a somewhat stronger heat. Set it aside to cool, and treat with a few drops of concentrated hydrochloric acid. Allow the acid to soak for some time, and then add hot water. Filter the insoluble residue, wash well, dry, and ignite gently in a porcelain or platinum crucible. A dazzling white powder of silicic anhydride will be left. The changes may be expressed symbolically by the following equations : (1) 2Si0 2 + 2(CONao 2 ,COKo 2 ) = SiNao 4 ,SiKo 4 + 4CO 2 . Fusion mixture. (2) SiKo 4 + 4HC1 = SiHo 4 + 4KC1. SiNao* + 4HC1 = SiHo 4 + 4NaCl. Silicic hydrate. (3) SiHo 4 = Si0 2 + 2OH 2 . Silicic anhydride. Silicic acid (also called orthosilicic acid) is a tetrdbasic acid, being combined with four atoms of Ho. It is written graphically * Hard substances, such as quartz, should be powdered in an agate mortar. 154 ORTHOSILICIC ACID. H H Si H I i A dibasic acid is said to be produced by the evaporation in vacua at 16 C., of a solution of the tetrabasic acid in water SiHo 4 = SiOHo 2 + OH 2 . This acid is of little interest. Silicic acid is an extremely indifferent body; it is inodorous and tasteless, and has scarcely any action upon vegetable colours (litmus). It combines with bases in the wet way with great diffi- culty, and forms amorphous salts. Like boric acid it is affected quite differently at a high temperature. Experiment 163. Heat a mixture of powdered nitre (NO 2 Ko) with finely powdered quartz in a platinum crucible over a good gas flame ; ruddy fumes are seen to escape. The nitric anhydride is displaced by the silicic anhydride, and breaks up as soon as it is liberated from the nitre into NaO 4 and O. Silicic anhydride, therefore, liberates nitric anhydride from its salts. A similar action takes place when sodic chloride is employed instead of nitre. SiO 2 can even drive out SO 3 (e.g., from S0 2 Nao 2 ), especially when heated with it in the presence of charcoal ; and yet in Exp. 161 it has been shown that silicic hydrate can be separated from sodic silicate by dilute hydrochloric acid. Silica in this respect resembles boric acid. It exhibits at different temperatures the same curious reciprocal affinity, for it can be displaced from its saline combinations by hydrochloric acid, etc., or may itself displace at a high temperature, owing to its fixed character, volatile acids, such as carbonic, nitric, hydrochloric,* sulphuric acid. On passing carbonic anhydride through a solution of sodic silicate, gelatinous silicic acid separates in flakes. The reaction takes place according to the equation SiNao 4 + 4C0 2 + 4OH 2 = SiHo 4 + 4COHoNao. Hydric sodic carbonate. It is, no doubt, owing to this action of carbonic anhydride upon silicates, that many spring waters contain small quantities of silicic acid in solution. Different kinds of glass, colourless or coloured, may be made on a small scale by fusing before the blowpipe flame a small quantity * By heating the mixture of SiO 2 and NaCl in a current of steam, GENERAL PROPERTIES OP SALTS. 155 of sodic carbonate, together with some white sand, and by dipping the clear bead into various metallic oxides, and heating once more. Porcelain fire-clay, bricks, tiles, stone- ware, pottery, etc., consist mainly of aluminic silicate. A great many minerals consist of silica and earthy and metallic bases in varying proportions. QUESTIONS AND EXEECISES. 1. How does silica occur in nature ? 2. How can silicic anhydride be prepared from a solution of water-glass ? 3. How is wliite sand converted into potassic silicate ? 4. Give symbolic and graphic formulae for silicic anhydride and silicic acid. 5. How would you show experimentally that silica can displace Vt^O & or SO 3 from their respective sodic salts ? 6. Explain the action of COg upon a weak solution of sodic silicate. 7. What substances enter chiefly into the composition of porcelain, fire-clay, stone-ware ? 8. How much SiO 2 , and how much CONao 2 are required to manufacture 100 Ib. of water-glass ? 9. 1-235 grm. of fire-clay yielded 793 grm. of S1O 2 ; what is the percentage of silica in the clay ? CHAPTER XXIII. GENERAL PROPERTIES OP SALTS. THE solubility of different salts in water varies very much. Some salts, such as calcic chloride, CaCl 2 , magnesic chloride, lYIgCl 2 , cannot be left exposed to the air even, without attracting moisture very rapidly ; they are deliquescent. Others, such as calcic carbo- nate, COCao", have no attraction for water. Certain salts dissolve in water, others are insoluble. Almost all salts which are soluble in water dissolve more freely and more extensively in boiling than in cold water. A solution is said to be saturated in the cold, when no more of the salt dissolves in it ; a hot saturated solution, when boiling water has dissolved as much of a salt as will dissolve. Experiment 164. Dissolve some common salt in hot water in a porcelain dish, and raise the temperature at last to boiling. Plunge a thermometer into the liquid. The mercury rises rapidly above 100 C. the temperature of boiling water. A saturated boiling solution of sodic chloride indicates in fact a tem- perature of 108 109 C. The boiling-point of saturated solutions, and the percentage of solubility of a few well known salts, are here annexed 156 SOLUBILITY OF SALTS. Parts by weight of salt dissolved Boiling point Name of salt. in 100 parts of saturated of water. solution. Potassic chlorate 61'5 104'2 C. Baric chloride 60* 1 1044 Sodic carbonate 48'5 104'6 Potassic chloride 59'4 108'3 Sodic chloride 41'2 108'4 Ammonic chloride 88'9 114' 2 Potassic nitrate 335'1 115-9 Strontic chloride 117'5 117'8 Sodic nitrate 224'8 121-0 Potassic carbonate 205'0 135 Calcic nitrate 362'0 151-0 Calcic chloride 325'0 179'5 It appears that in most instances the boiling-point is directly proportionate to the solubility of a salt. On allowing a saturated boiling solution to cool, some of the salt crystallises out, and the crystals will be all the more perfect the slower the solution cools. In order to get good crystals, saline solutions are set aside for spontaneous evaporation. The solution should, of course, be well protected from dust, by being kept care- fully covered with filter-paper. In consequence of the constantly increasing concentration of the saline solution by slow evaporation in the air, the crystals have plenty of time to form regularly, and to grow slowly, till at last nearly the whole of the salt has been withdrawn from the solution. The remaining liquid may then be poured off from the crystals; it is called the mother-liquor. Grow- ing crystals may actually be fed with a fresh portion of the saline solution, till they have acquired a considerable size. Experiment 165. Make a hot saturated solution of the well known salt alum. Allow it to cool. Then pour off from the crystals the still warm mother- liquor into a previously warmed porcelain dish, and set aside for crystallisation. When cold, pour off the mother-liquor, and pick out a few of the best crystals. They are octahedral in shape. One or more of these octahedra are then put into the cold saturated mother-liquor, and the crystal turned over on a fresh side every day, till after eight days it has rested on every one of the eight sides. It grows during this time, and attains considerable size, whilst the form of crystalli- sation remains the same. If the crystal were not turned, it would likewise grow, but not regularly j for no deposit of saline matter can take place on the side on which it lies, nor on the side diametrically opposite to it. It would acquire what is called the truncated octahedral form. Instead of turning the crystals over, day after day, they may be allowed to form on a piece of fine string, from which they are conveniently suspended in the mother liquor, and left to grow slowly. Crystallisation furnishes as with the means of purifying soluble salts from foreign substances. It is easy to purify salts soluble with difficulty from salts which dissolve freely in water, such as potassic carbonate, calcic chloride. Smaller crystals, as a rule, are purer than large crystals, because some of the mother- liquor is apt to be locked up within the interstices of the latter. Thus com- CRYSTALLISATION. 157 mercial nitre or saltpetre contains small quantities of potassic chloride and sulphate, which can only with difficulty be removed by repeated recrystallisation : but they are readily eliminated by con- stantly stirring a hot solution of the impure salt whilst it cools, as long as a fine powder (called saltpetre flour) of potassic nitrate falls out. The impurities are left in the mother-liquor. Many salts combine chemically, the moment they crystallise, with a certain quantity of water, called water of crystallisation. This appears to be essential to their existence in a crystalline con- dition, and materially influences their structure ; for on expelling the water by heat, the crystals crumble down to a powder. The anhydrous powder attracts water again very eagerly, and such dehy- drated salts are frequently employed to deprive certain liquids, such as spirits of wine, etc., of water. A great number of salts unite with the same amount of water of crystallisation under identical conditions of temperature and satu- ration : and the molecular units of water of crystallisation are reducible to simple constant proportions, and follow the law of con- stant chemical combining proportions, as much as compounds of two or more elements. Experiment 166. Heat a few grammes of Hue vitriol, or cupric sulphate (SOIIo 2 Cuo",4aq.) cautiously in a porcelain dish. The salt fuses in its water of crystallisation, or it undergoes what is called the aqueous fusion. It is dihydric at about 100 C. Keep stirring with a glass rod, till the water of crystallisation has been driven off, and till the blue salt has nearly turned white. On adding a little water to a portion of the powder, and stirring, it acquires its blue colour again. Much heat is given off at the same time. Experiment 167. To another portion of the white powder add a little alcohol (methylated spirit). The blue colour is likewise restored. The alcohol must have become deprived of its water. In this manner weak alcohol may be rendered almost absolute, i.e., free from water. The evolution of heat which accompanied the combination of the white powder with water, points to an actual chemical combination between the water of crystallisation and the salt. On exposing the white powder to a stronger heat (about 200 C.), another molecule of water is given off, which is evidently combined differently from the four molecules of water of crystallisation. It is termed water of constitution. The water of crystallisation of a salt, obtained from one and the same saturated solution, frequently varies with the temperature, e.g., sodic sulphate (S0 2 Nao 3 ) when allowed to crystallise from its solu- tion at a temperature of 33 C., retains ten molecules of water, and yields anhydrous crystals above that temperature. Manganous sulphate (S0 2 Mno") crystallises from its aqueous solution with six molecules of water of crystallisation at 15 C. It has the composition SOHo 2 Mno" + 6 aq. Between 15 C. and 30 C. it crystallises with five, and between 30 C. and 40 C. with four molecules of water of crystallisation. The crystals belong respec- tively to the rhombic, triclinohedric, and monoclinohedric systems. It follows that the molecules of water of crystallisation are capable of modifying the character of salts as much as their other constituent 158 COLOUR AND TASTE OF SALTS. elements. The last molecule of water the water of constitution is only driven off at 200 C. Experiment 168. Expose a few crystals of wasTiing-soda (CONao 2 + 10 aq.), for some time to the air. They become opaque, and crumble at last to pieces. The salt loses its water of crystallisation, even at the common tem- perature, but more rapidly when gently heated. The same is observed when green vitriol (SOHo 2 Feo" 4- 6 aq.), hydric disodic phosphate (TOHoN"ao 2 + 12 aq.), sodic sulphate (S0 2 Nao 2 -h 10 aq.), and other similarly constituted salts are exposed to the air. These salts are said to be efflorescent, Salts which have been allowed to crystallise from water at the ordinary temperature, and have consequently taken up as much water of crystallisation as they possibly can, produce cold, when their crystals are redissolved, either at the same or at a higher temperature ; because they absorb heat from the water on passing from the solid to the liquid state. Heat must, therefore, have become transferred, in the one instance, from the dehydrated salt to the water (which has already as much heat as it can bind), and heat is therefore given off : in the other instance from the water to the crystalline salt, the latter depriving the water of heat. On mixing some salts or a mixture of certain salts in definite proportions with water, a considerable degree of cold may be produced. Mixtures of this kind are called freezing mixtures. Experiment 169. Mix one part by weight of crystallised sodic carbonate with one part by weight of water at 10 C,, and ascertain by the aid of a ther- mometer that the temperature of the water is lowered from 10 C. to 14 C. Numerous other salts may be employed with like effect. Colour of Salts. Most salts are solid bodies at. an ordinary tem- perature. Salts obtained by the action of a colourless acid upon a colourless base are likewise colourless. Coloured bases produce for the most part coloured salts on combining with colourless acids ; and the crystalline salts mostly resemble the original base in colour. Salts formed by the combination of a colourless base with a coloured acid generally exhibit the colour of the acid from which they are derived. Taste of Soluble Salts. The taste which various salts exhibit is for the most part dependent upon the constituent base. Thus, sodic salts possess a purely saline taste, not unlike that of common salt ; potassic salts possess a saline, and somewhat bitter taste. Magnesic salts have a nauseous bitterness ; aluminic salts an astringent sweet taste, etc. The taste is also influenced by the acid which the salts contain, as in sulphites and salts of metallic acids. QUESTIONS AND EXEECISES. 1. G-ive instances of deliquescent salts. 2. How would you prepare a saturated solution of a salt ? 3. What general relation is there traceable between the solubility of salts and the boiling points of their saturated solutions ? GHye instances. 4. How are salts soluble in water purified ? REACTION OF SALTS. 159 5. Explain the terms mother-liquor, aqueous fusion, water of constitution, efflorescent, freezing mixture. 6. How would you prepare octohedral crystals of alum ? 7. How is saltpetre freed from potassic chloride and sulphate ? 8. CHve the symbolic formulae of blue vitriol, green vitriol, crystallised man- ganous sulphate. 9. Explain what takes place when blue vitriol is heated 1st, to 100 C. ; 2nd, to200C. 10. What is the action of dehydrated cupric sulphate upon ordinary proof spirits (containing 50 per cent, of alcohol) ? 11. On what considerations would you select the materials for making a freezing mixture ? 12. Explain the cause of the colour which various salts exhibit. 13. What influences the taste of salts ? 14. How would you determine experimentally the percentage of water of crystal- lisation in a salt ? 15. Three grms. of washing-soda lost T888 grm. of water on drying and ignition : what is the percentage of wat r of crystallisation, and how would you calculate the formula of the crystalline salt from these numbers ? CHAPTER XXIV. REACTION OP SALTS. NORMAL, ACID and BASIC SALTS. DOUBLE SALTS. ON adding a solution of potassic hydrate to sulphuric acid (comp. Exp. 44), we obtained a salt which was neutral to litmus paper,* i.e., it did not turn blue litmus red nor red litmus blue. Now, potassic hydrate has a strongly alkaline, and sulphuric acid a strongly acid reaction : and it would, therefore, appear as if one of the most characteristic signs of the saline nature of a body consisted in its neutral reaction. This applies, however, only to a very limited number of salts, such as potassic nitrate (NC^Ko), sodic nitrate (W0 2 lSrao),sodic sulphate (SO 2 N"ao 2 ),magnesic sulphate (S0 2 Mgo"), calcic sulphate (S0 2 Cao"), baric nitrate ((N0 2 ) 2 Bao"). By far the greater number of salts, in fact most soluble sulphates and nitrates, have the power of reddening blue litmus, e.g., ferrous sulphate (S0 2 Feo"), zincic sulphate (S0 2 Zno"), manganous sulphate * Litmus is a vegetable colouring matter consisting of a true salt of a mineral base and a vegetable acid. On adding to a solution of litmus in water a mineral acid, the organic salt is decomposed, and the organic acid liberated. This acid possesses great tinctorial power, and is of a light red colour. A weak acid deprives the blue salt only of one-half of its base ; leaving a salt, containing excess of the organic acid, and imparting to the solution a peculiar wine-coloured tint. On the addition of a soluble base, the red solution turns blue again, because the base combines with the acid to form a blue salt. A sensitive litmus solution should not, therefore, contain any free base, because acids would first neutralize this latter before they could liberate the acid contained in litmus. A solution of red litmus is obtained by adding very dilute sulphuric acid, by means of a glass rod, till the blue of the litmus is changed to a distinct red. Such a solution is turned blue on coming in contact with the least trace of a soluble base. 160 DEFINITION OF A SALT. NORMAL SALTS. (S0 2 Mno"), cupric sulphate (S0 2 Cuo"). Others, again, turn red litmus-paper blue ; e.g., sodic and potassic carbonates, borax, etc. Hence there are salts which react neutral ; others which react add or alkaline, and in which the acid reaction does not arise from any free or uncombined acid in the salt, nor the alkaline reaction from any free alkali, but in which the Reaction is due rather to the relative strength of the acid and basic constituents which enter into the saline body. The powerful sulphuric acid, for instance, can only just neutralize the strong alkali, potassa ; and when in combination with weaker bases, such as the oxides of the metals proper (which, as we have seen repeatedly are without reaction on litmus-paper), it impresses its acid character upon the salts. The same applies to the salts which nitric and other mineral acids form. Weak acids, such as carbonic, boric, and silicic acid, on the other hand, are not capable of entirely neutralizing strong alkaline bases, such as potassa and soda: their saline compounds react alkaline. It is impossible, therefore, to infer the preponderance of acid or base in a salt from the reaction, if any, which it possesses ; for in solu- tions of salts, such as* S0 2 Nao 2 , and S0 2 Cuo", Sodic sulphate Cupric sulphate (neutral). (acid). salts which exhibit neutral and acid reactions, and which are formed by the displacement of the hydrogen of the sulphuric acid by atomic amounts of the metals sodium and copper, the same amount of acid causes the one salt to become neutral, the other acid. If we take a salt* to be the product of the mutual action of an acid and a metal or base upon each other, normal salts are obtained by exchanging the whole of the replaceable hydrogen of the acid for f an equivalent amount of a metal, or of a positive compound radical, such as ammonium, NH 4 . Instances of normal salts : Acid from which Salts. the salt is derived. WT0 2 Ko, neutral reaction WO 2 Ho. SO 2 Nao 2 , S0 2 Ho 2 . SO s Cao", S0 2 Ho 2 . (N0 2 ) 2 Coo", acid reaction NO 2 Ho. WOKo, alkaline reaction WOHo. S0 2 Zno", acid reaction S0 2 Ho 2 . 3?ONao 3 , alkaline reaction POHo 3 . (PO) 2 Cao" 3 (insol. in water) POHo 3 . BNao 3 , alkaline reaction BHo 3 . SiHo 4 . * Frankland : Lecture Notes, page 12. ACID AND BASIC SALTS. 161 An acid salt is obtained when two or more atoms of replaceable hydrogen are only partially exchanged for the metal or positive compound radical. The following are illustrations of acid salts Salt. Acid. S0 2 HoKo, acid reaction ............ S0 2 Ho 2 . COHoKo, alkaline reaction ........ (COHo 2 ) ? !POHoJS"ao 2 , alkaline reaction ........ !POHo 3 . AsOHoKo 2 , alkaline reaction ...... AsOHo 3 . SOHoNao, acid reaction ............ SOHo 2 . Monobasic acids form normal salts. Di-, tri-, and tetra-basic acids only can form acid salts. Djad elements replacing H 2 in dibasic acids exclude the possibility of acid salts, unless two mole- cules of acid enter into the reaction. The reaction with litmus is obviously no criterion of the normal or acid constitution of a salt. " When the number of bonds of the metal or compound positive radical in a salt exceeds the number of atoms of displaceable hydrogen in the acid, the compound is usually termed a basic salt," ex. gr. Symbolic formulce. Ordinary 1 CHoPbo" white lead. } CHoPbo" P / Grap hie formulae, , H H 9/R o-Fb-O-T Pb \/ \/ O Cu C Cu Malachite, "| Dicupric carbonate >CO(OCu"Ho) 2 O O dihydrate. H H H O I l-O-Bi O O N0 2 (OBi'"Ho 2 ) Double Salts. There exists a class of salts called double salts, containing one acid only, but two different bases, and quite dis- tinct from the acid salts just explained. The base ammonia is especially remarkable for its tendency to form double salts. 162 DOUBLE SALTS. Chemists are compelled to admit in these double salts, and in salts containing water of crystallisation, a mere molecular union or 'molecular combination. This, in chemical notation, is distinguished from atomic, combinations by the use of the comma. In all cases molecular combination seems to b of a much more feeble character than atomic union. The following are instances of double salts, in which a mere molecular combination is traceable : AmCl, MgCl 2 + 60H 2 . 2AmCl, Fe 2 Cl 6 + 3OH 2 . 2AmCl, SnCl 2 + OH 2 . 2KC1, ZnCl 2 . Other double salts are formulated atomically, thus Symbolically. Graphically. O S0 2 Amo Feo "' 60H2 ' Am S Fe O S Am. o o In like manner an important group of double salts is formed by the combination of the sulphates of the metals aluminium, chro- mium, iron, manganese, with the alkaline sulphates. They have received the name of alums from the resemblance which they have to common alum, a salt known long before the others were prepared. Examples of alums we have in S0 2 Amo i Common ammonium alum (Diam- S0 2 = A v ^ monic aluminic tetrasulphate). S0 2 -= ' S0 2 Amo 1 Graphic formula. O O v S O O Am S Al Al S Am \/ S o o DEFINITION OF CHEMISTRY. 163 S0 2 Ko 1 Potassium Iron Alum (Dipotassic 802= vi ferric tetrasulphate). S0 2 = 62 > SO a Ko_i S0 2 Ko i Potassium Chrome Alum (Dipo- S J 2 = p vi tassic chromic tetrasulphate). S 0~ 2 = 2 ' S0 2 Ko i These double salts are remarkable for the facility with which they crystallise and for the size and beauty of their crystals. QUESTIONS AND EXERCISES. 1. Give instances of salts which react neutral, acid, or alkaline with litmus- paper ; and assign reasons for the reaction which different salts give. 2. Define normal, acid, and basic salts ; give instances of each class of salts. 3. Why can litmus not be employed in order to ascertain whether a salt is a normal or acid salt ? 4. What is a double salt ? 5. Give instances of double salts in which only a molecular combination can be traced. 6. Enumerate some double salts in which an atomic union is apparent. 7. What is an alum ? Give names, as well as symbolic and graphic formulae of different alums. 8. Write out the symbolic and graphic formulae for hydric sodic sulphite, white lead, and malachite. 9. Explain in what combination water of crystallisation is considered to exist in salts. 10. You have given to you hydric potassic sulphate and saltpetre. Explain how you would demonstrate experimentally that one of these salts is an acid salt. CHAPTER XXY. DEFINITION OP CHEMISTRY. MODES OP CHEMICAL ACTION. CHEMISTRY has been defined "as the science which treats of the com- position of all kinds of matter, and of those changes in composition which result from the action either of different kinds of matter upon each other, or of external forces upon one and the same kind of matter."* Chemical changes depend upon the affinities with which every kind of matter has been endowed by nature: they are modified more or less by the temperature, and by the state of aggregation solid, liquid, or gaseous of the simple or compound bodies. * Frankland : Lecture Notes, page 1. M 2 164 CHEMICAL CHANGES. Matter undergoes a chemical change* I. When an element combines with another element in simple or multiple proportions to form a compound body : . B 4 O 5 Nao 2 + 2HC1 + 5OH 2 = 4BHo 3 + 2NaCl (Exp. 154). or by a reciprocal change : NaCl + BHo 3 = BONao + HC1 + OH 2 (Exp. 156). e. A precipitate is produced, owing to the insolubility of one of the groups of elements (produced by a mutual exchange between salt and acid), e.g. : BaCl 2 + SO 2 Ho 2 = SO 2 Bao" + 2HC1 (Exp. 97). Insoluble in water and acids. NO 2 Ago + HC1 = AgCl + NO 2 Ho (p. 69). SO 2 Ago 2 + 2HC1 = 2AgCl + SO 2 Ho 2 . (N0 2 ) 2 Pbo" + S0 2 Ho 2 = SOaPbo" + 2NO 2 Ho (p. 100). A similar exchange of elements frequently takes place when a solution of one salt is added to a solution of another salt, e.g. : BaCl 2 + SO 2 Amo 2 = SO 2 Bao" + 2AmCl (Exp. 97). NO 2 Ago + NaCl = AgCl + *TO 2 ]Nao. (KO^Pbo" + CONao 2 = COPbo" + 2NO 2 Nao. SO^ao'' + CONao 2 = COBao x/ * + SO 2 L\ T ao 2 . Ca(OCl)Cl + CONao 2 = COCao^ + CINao + NaCl (Exp. 141). The mutual exchange of elements between two salts need not necessarily be accompanied by the precipitation of a group of elements, e.g. : (ClO 2 ) 2 Cao" + 2KC1 = 2ClO 2 E:o + CaCl 2 (Exp. 146). It suffices frequently if the new compound be rendered less soluble, than either of the two salts which were mixed together, e.g., A solution of KC1 and NO 2 !N"ao, when evaporated at a low temperature, yields the two salts unchanged ; KC1 crystallises out first. But on boiling the solution of the two salts, NaCl crystallises out, and NO 2 Ko remains in solu- tion, being more soluble than NaCl (comp. Chap. XXIII). On drawing off the boiling solution from the crystallised NaCl, potassic nitrate crystallises out on cooling. Then, again, on mixing solutions of NaCl and SO 2 Mgo", it is impossible to say how the acids and bases remain combined. They may exist, 1st, as NaCl and SO 2 Mgo", 2nd, as Mg-Cla and SO 2 Nao 2 , 3rd, as NaCl, IttgfClg, SO 2 Nao 2 , SO 2 Mgo" ; * By fusion with fusion -mixture, or by long-continued boiling with alkaline carbonates. CHEMICAL CHANGES. 171 but on evaporating the solution above 15 C., NaCl crystallises out first (being the least soluble of the above salts at this temperature), and SO 2 Mgo" next, mixed with a little NaCl. When evaporated at a lower temperature, e.g., at C., SO 2 Nao 2 (being the least soluble at this low temperature) crystallises out first, and leaves J^IgfC^ in solution. Heat promotes the exchange of elements between two salts of different acids and bases, e.g., 2AmCl + COCao" = CaCl 2 + COAmo 2 . The change is owing to the volatile nature of ammonic carbonate, SO 2 Ko 2 + 2AmCl = SO 2 Amo 2 + 2KC1. These decompositions are frequently the reverse of the reactions which take place in the cold, between the solutions of two salts, e.g., CaCl 2 + COAmoo = COCao" + 2AmCl. owing to the insolubility of the calcic carbonate. Heat promotes likewise the formation of double silicates and borates, fluorides and chlorides. These compounds are frequently broken up again on being dissolved in water, the original salts being produced. In a few instances double decomposition is accompanied by resolu- tion, e.g. : Pb 3 4 + 4N0 2 Ho = 2N 2 4 Pbo" + Pb iv O 2 + 2OH 2 (Exp. 76). NH 4 C1 + NaHo = NaCl + NH 3 + OH 2 (Exp. 127). ln iv O 2 +4HCl = HInCl 2 + C1 2 + OH 2 (Exp. 59). For purposes of reference, the four different changes just enume- rated may be indicated by employing the bracketed letters (C) standing for Change I, i.e., Combination. (R) II, i.e., Resolution. (D) ,, III, i.e., Displacement. (DD) IV, -i.e., Double Decomposition. APPENDIX. THE METRIC SYSTEM. Millimetre Measures of Length. . O'OOl of a metre 0*0394 inch. Centimetre ...... O'Ol 0-3937 Decimetre O'l 3 '9370 inches. Metre 1 metre 39*37 Decametre . 10 metres 393-7 100 328-09 feet. Kilometre 1000 . 3280-9 . . . 10000 G'2138 miles. 1550 square inches. Centiare . . Measures of Surface. Are 119*6 square yards. 10000 2*471 acres. Millilitre, or cub centimetre Measures of Capacity. ic | O'OOl of a litre 0-061 cubic inch. 0-61 0'176 imperial pint. 1-76 2-2 gaUons. 22-009 220-096 er 0'01543 grains avoir. 0-15432 1-54323 15-43235 02204 Ib. avoir. 22046 , 2-20462 , 22-04621 , 220-46 2204-6 o-oi Decilitre . . o-i Litre ... 1 cubic decimetre . . 10 100 Kilolitre (stere) . . . 1000 Milligramme .... Centigramme .... Decigramme .... Weights. O'OOl wt. 1 cu. m.m. wat o-oi 10 O'l O'l c.m. 1 1 c.c. 10 10 100 1 decilitre - 1000 1 litre 10000 10 litres 100000 1 hectolitre 1000000 1 cub. metre,, Decagramme .... Hectogramme . . Kilogramme .... Myriagramme . . Quintal Tonneau . . INDEX. A. PAGE Absolute alcohol .... .... 157 Atomicity . 77 Acid, arsenic .... .... .... 141 boric .... ,. v . .... 144 chlorhydric .... .... 94 chloric 133 chlorous .... .... .... 134 hydriodic .... .... .... 67 hydrobromic .... .,.. 67 hydrochloric .... 68, 93 hydrofluoric 67 hydrosulphuric .... .... 58 hypochlorous .... .... 132 metaboric.... .... .... 144 metaphosphoric .... .... 138 metarsenic .... .... 142 metastannic .... .... 117 muriatic .... .... .... 94 nitric 110 nitrous .... .... .... 113 orthoboric .... .... 144 orthophosphoric .... .... 138 oxalic ; .... 106 phosphoric .... .... 137 phosphorous .... k ... 140 pyrarsenic .... .*.. 142 pyrophosphoric .... .... 138 siljcic 153 sulphuric 88, 99, 120 sulphurous .... .... 96 Acid salts, definition of.... .... 161 Acids, dibasic, constitution of .... Ill formation from anhydrides 87 monobasic, constitution of 161 Action, chemical, modes of .... 164 Active atomicities .... .... 81 bonds 81 Affinities, reciprocal 29 Affinity, chemical .... .... 26 definition of .... 26 Air, atmospheric .... .... 6 composition of 8 Alkalies 48 neutralized by acids .... 49 Allotropism 53, 103 PAGE Alum, common .... .... 59, 162 potassium chrome .... 163 iron ... 163 Aluminoxyl .... 89 Ammonia ..>. .... .... 124 absorption by water .... 128 combination with acids 126 composition of .... 129 decomposition by heat 129 by potas- sium.... 129 formation from nitric acid 124 Ammonia gas, preparation of .... 126 properties of .... .... 130 >, sources of .... .... 124 Ammonic bromide .... .... 127 carbonate .... .... 131 hydric .... 131 chloride .... .... 126 hydrate 127 iodide 127 magnesic arseniate .... 142 nitrate, preparation of 125 decomposed by heat .... 125 nitrite, decomposed by heat 125 salts 126, 127 volatility of .... 127 sulphate 12<5 sulphide 130 hydric .... 130 Ammonium .... .... .... 127 alum, common .... 162 amalgam 127 Ammonoxyl .... .... .... 127 Anaesthetic, use of nitrous oxide as an .... .... .... .... 125 Analysis, etymology of .... .... 37 Anhydride .... 9 arsenic arsenious boric carbonic definition of.... 141 141 144 15 88 174 INDEX. PAGE Anhydride, etymology of .... 88 nitric .... 114, 118 nitrous .... 114, 118 phosphoric .;.. 15, 13J7 phosphorous.... .... 140 silicic 153 sulphuric .... 99, 120 sulphurous .... 15, 88, 96 Anhydrides, conversion into acids by water and hydroxyl 87, 88, 137 Animal charcoal .... .... 103 a decolourizing agent 103 Antimonietted hydrogen .... 143 Antimonoxyl .... .... ..-.. 89 Aq., water of crystallisation .... 138 Aqua fortis 119 Aqua regia .... .... .... 119 Aqueous fusion .... .... .... 157 Argeutoxyl .... .... .... 138 Arseniates .... .... .... 141 Arsenic.... .... .... .... 141 acid 142 anhydride .... .... 142 Arsenical pyrites .... .... 141 Arsenides . .... .... .... 141 Arsenietted hydrogen .... .... 143 Arsenious anhydride .... .... 142 Arsenites .... .... .... 141 Artiads, definition of .... .... 78 etymology of 78 Atmosphere, composition of .... 8 Atom, definition of .... .... 38 Atomicities, classification of elements by .... .... .... 81 Atomicity .... .... ... 77 absolute .... .... 81 active 81 latent 81 marks.... .... 79, 80 Atomic theory .... .... .... 38 weight .... .... .... 38 weights of elements, Table of 40 B. Baric carbonate, preparation of, from carbonic anhydride and baric hydrate.... 106 Baric carbonate, soluble in car- bonic acid .... .... .... 106 Baroxyl 89 Base, definition of 19 PAGE Binary compound, construction of names of 22 Binary compound, definition of 22 Bismuthous nitrate dihydrate .... 161 Bismuthoxyl 89 Bleaching powder .... .... 132 Blowpipe, description of .... 146 flame 147 reduction of metallic oxides by .... .... 151 Blue vitriol 59, 122, 157 Bonds, active .... .... .... 81 latent 81 Borates 145 Borax 144 Boric acid .... .... .... 144 crystals .... .... 144 tribasic .... .... 144 anhydride .... .... 144 hydrate .... .... .... 144 Boron .... .... .... .... 144 Boyle and Marriotte's law .... 42 Bracket, use of, explained .... 90 Brimstone .... .... .... 51 Bromides, formation of.... .... 95 Bromine .... .... .... 67 etymology of .... .... 67 Burner, Bunsen's .... .... 147 c. Calcic carbonate .... 103, 104 chloro-hypochlorite .... 132 fluoride 67, 96 Carbides 108 Carbon, a reducing agent .... 168 allotropy of 103 atomicity of 105 combustion in oxygen .... 15 oxides of ....15, 103, 106 Carbonates 105 acid or hydric .... 106 alkaline 106 decomposed by dilute acids ." .... 105 Carbonates, normal .... .... 106 solubility of .... 106 Carbonic anhydride .... 15, 103 ;, action on lime-water 17, 103 Carbonic anhydride, absorption by water .... .... .... 17 Carbonic anhydride, decomposed by sodium .... .... .... 29 INDEX. 175 PAGE Carbonic anhydride, molecular weight of 104 Carbonic anhydride, preparation of 104 Carbonic anhydride, properties of 104, 105 Carbonic anhydride, volume weight of 105 Carbonic oxide .... .... .... 106 action on heated metallic oxides .... .... 168 Carbonic oxide, preparation from carbonic anhydride .... .... 106 Carbonic oxide, preparation from oxalic acid .... .... .... 106 Carbonic oxide, preparation from potassic ferrocyanide.... .... 107 Carbonic oxide, properties of .... 108 Chalcedony 152 Chalk 103 Charcoal 103 Chemical action, modes of .... 164 affinity, definition of.... 26 change distinguished from physical change.... .... 22 Chemical reactions (combinations and decompositions) .... .... 22 Chemical solution, explanation of term 95 Chemistry, definition of.... .... 163 Chili saltpetre 109 Chlorates 132 action of sulphuric acid upon .... .... .... .... 134 Chlorhydric acid .... .... 94 Chloric acid 133 peroxide.... .... .... 134 Chloride of lime 132 constitution of 132 Chlorides, nature of metallic .... 66 preparation of 94, 105 table of metallic .... 70 Chlorine 62 action on metals .... 66 water .... 64 sulphuretted hydrogen 64 Chlorine and hydrogen 67 exploded by sunlight 69 Chlorine, bleaching by 63 combustion of taper in 65 compounds of, with oxygen .... .... .... 131 Chlorine, table of 136 Chlorine, etymology of.... .... 62 PAGE Chlorine, manufactured from ox- ides of manganese .... .... 62 Chlorine, molecular and volume weight of .... .... .... 63 Chlorine, preparation of .... 62 properties of .... ....62, 63 water.... .... .... 63 Chlorites 134 Chloronitric gas.... .... .... 119 Chrome alum .... .... .... 121 Cinnabar .... .... .... 56 Classification of elements accord- ing to their atomicity .... 81 Cold saturated solution.... .... 155 Combination by volume.... .... 35 Combining proportions .... .... 37 weight, relative .... 38 Combustion .... .... .... 16 Common, or hydric disodic arseniate 142 Common, or hydric disodic phos- phate.... 138 Common phosphoric acid .... 138 salt ..., 66 Compound radical, definition of.... 89 Constant chemical combining proportions .... .... .... 71 Constitution of salts .... .... 159 water of 139 Copper, action of ammonia and oxygen on .... .... 165 action of nitric acid on 115 action of sulphuric acid on 97 displaced by iron .... 167 heated in air .... .... 11 Crith 42 Crystallisation .... .... .... 156 water of.... 139, 157 Crystals, growth of .... .... 156 Cubic nitre .... .... .... 109 Cupric metaborate .... .... 151 nitrate .... .... .... 116 oxide 10 sulphate 59, 97 preparation of crystals of .... 97 sulphide .... ....55, 59 preparation of, in dry way .... 55 preparation of, in wet way .... 59 D. Dehydrating agents .... 137 176 INDEX. PAGE Deliquescence .... .... .... 91 Density, or specific- gravity .... 20 Dicupric carbonate dihydrate .... 161 Dihydric calcic sulphate (gyp- sum) .... 91 Dihydric sodic phosphate .... 138 arseniate .... 142 Displacement, chemical change by 167 Displacement, collection of gas by 62 Distillate 46 Distillation 45 Distilled sulphur 52 water .... .... .... 45 Divalentic, explanation of term.... 78 Double salts 161 Dyad elements ..,, .... ....77, 81 list of 81 Dyads 77 E. Eau de Javelle 133 Efflorescent salts 158 Electrolysis of hydrochloric acid 68 * water 32, 33 Element, definition of 23 Elements, classified according to their atomicity .... .... 81 Elements, table of 24, 25 Eprouvette .... .... .... 57 Epsom salts .... .... .... 59 Eudiometer 33 etymology of .... 33 Evaporation, definition of .... 60 Expansion of gases by heat .... 42 Explosion of hydrogen and air .... 4 Explosion of hydrogen and oxygen .... .... .... 17 F. Ferrosoxyl 89 Ferrous hydrate, oxidation of .... 165 sulphate .... .... 59 sulphide 55, 59 preparation of 56 Filter dryer 153 Flame 147 oxidizing.... .... .... 147 reducing .... .... .... 147 structure of .... .... 147 Flint 152 PAGE Fluorides 95 preparation of .... .... 95 solubility of 96 Fluorine.... .... .... .... 67 Fluor-spar 67, 96 Flux 151 Forceps.... .... .... .... 150 Formulae, molecular .... .... 42 Freezing mixtures .... .... 158 Fusion, aqueous .... .... 157 mixture 153 G. Galena 51, 55 Gas-holder 3 jars 13 Gases, correction of for tempera- ture and pressure .... .... 43 Gases, expansion by heat .... 42 Glauber's salt 122 Gold dissolved by aqua regia .... 120 Granulated zinc.... .... .... 2 Graphic notation .... ....79, 80 Graphite 103 Green copperas .... .... .... 59 vitriol .... .... .... 59 Grouping elements .... .... 82 Gypsum.... .... .... .... 91 H. Halogen, etymology of .... .... 67 Halogens .... .... .... 67 Haloid salts 102 Hartshorn, spirit of .... .... 123 Heavy metals .... .... .... 40 Herapath's blowpipe lamp .... 149 Hexad elements.... .... .... 81 Hexavalentic, explanation of term .... .... .... .... 78 Hydrates 83 metallic action of acids on 95, 101, 112 Hydric bromide.... .... .... 67 chloride 68,92 fluoride 67 iodide' .... .... .... 67 peroxide, or hydroxyl .... 85 Hydriodic acid .... .... .... 67 Hydro-acids .... .... .... 69 Hydrobromic acid .... .... 67 Hydrocarbons .... .... .... 108 INDEX. 177 PAGE Hydrochloric acid 68, 92 absorption by water 68,93 Hydrochloric acid, action on metallic oxides .... .... 93 Hydrochloric acid, action on metals 69, 95 Hydrochloric acid, action on nitric acid .... .... .... 119 Hydrochloric acid, composition by volume 68 Hydrochloric acid, electrolysis of 68 Hydrochloric acid gas, prepara- tion of .... .... .... 92 Hydrochloric acid, liquid .... 94 Hydrochloric acid, molecular formula .... .... .... 68 Hydrochloric acid, properties of 68 solution and preparation of .... .... 92 Hydrochloric acid, synthesis of 68 volumetrical composition of .... .... 76 Hydrochloric acid gas, dry, pre- paration of 76, 93 Hydrochloric acid gas, dry, action of sodium-amalgam upon .... 76 Hydrofluoric acid .... .... 67 Hydrogen .... .... .... 1 antimonietted .... 143 arsenietted .... .... 143 displacement by so- dium 1, 76, 126, 167 Hydrogen, etymology of .... 6 flame .... .... 3 phosphoretted .... 140 preparation of .... 2 properties of .... 3 proportion of, in water 32 sulphuretted.... .... 56 the unity of atomicity 78 Hydrosulphuric acid .... .... 58 action on metallic chlorides .... .... 169 Hydrosulphuric acid, action on metallic oxides .... .... 169 Hydrosulphuric acid, action on solutions of metals .... .... 59 Hydrosulphuric acid, action on sulphurous acid .... .... 58 Hydrosulphuric acid, atomic com- position of .... .... .... 58 Hydrosulphuric acid, molecular formula of .... .... .... 58 Hydrosulphuric acid, preparation of 56 PAGE Hydrosulphuric acid, properties of 57 Hydrosulphuric acid, solution of 58 Hydrosulphuric acid, volume weight of 59 Hydrosulphyl .... .... .... 90 Hydroxyl * 85 preparation of .... 85 as a hairwash, &c 85 its reactions.... .... 86 its oxidizing power .... 87 its action on anhy- drides 88,114 Hypochlorites .... .... .... 132 as bleaching agents 133 as disinfectants .... 133 Hypochlorous acid 133 Ignition point .... .... .... 109 Iodides, preparation of .... .... 95 Iodides, solubility of 96 Iodine .... .... .... .... 67 etymology of 67 Iron, action of hydrochloric acid on 2 Iron, black oxide .... .... 10 passive state of .... .... 119 potassium alum .... .... 163 pyrites .... .... .... 56 sulphide, preparation of .... 56 J. Javelle, eau de 133 K. Kalium L. Latent atomicity .... .... 81 Laughing gas .... .... 117, 124 preparation of .... 124 properties of .... 125 Law of multiple proportions .... 44 volumes .... .... 44 Lichens, colouring matter from.... 9 178 INDEX. PAGE Lime, chloride of 132 slaked 84 water . v .... 17 Liquor ammonia .... .... 125 List of dyads 81 hexads .... .... .... 81 monads.... .... .... 81 pentads .... .... .... 81 tetrads 81 triads .... .... .... 81 Litmus .... .... .... .... 9 paper 9 Lunar caustic . 119 M. Magnesia .... .... .... 10 Magnesium, action on water .... 1 burning in air .... 10 burning in oxygen.... 16 Magnesoxyl .... .... .... 89 Manganic dioxide, combination with sulphurous anhydride .... 88 Marks of atomicity 80 Marriotte and Boyle's law .... 42 Martial pyrites or mundic .... 60 Massicot.... .... .... .... 84 Mechanical mixture .... .... 21 Mercuric oxide, preparation of from oxygen .... .... .... 7 Mercuric sulphide (cinnabar) .... 56 Mercury and sulphur .... .... 56 oxidation of .... .... 6 Metaboric acid ... .... .... 144 Metal, definition of 18 Metallic hydrates, action of sul- phuric acid on .... .... 101 Metallic oxides 48 action of hydro- chloric acid upon .... .... 95 Metallic oxides, action of moist atmosphere upon .... .... 165 Metallic oxides, action of sul- phuric acid on .... .... 101 Metallic oxides, reduction of by carbon 168 Metallic oxides, reduction of by hydrogen .... .... .... 168 Metallic oxides, table of .... 50 solubility of .... 49 Metalloids, classification of .... 40 distinction of from metals 18 Metalloxyls 89 PAGE Metals, action of hydrochloric acid on 94, 95 Metals, action of nitric acid on.... 117 sulphuric acid on 100 Metals, classification of into light and heavy .... .... 40 Metals, classification of, according to their power of combining with oxygen, and decomposing water 166 Metallic chlorides, table of .... 70 solubility of.... 69 sulphides, table of .... 60 solubility of.... 59 Metaphosphoric acid .... .... 138 Metarsenic acid .... .... .... 142 Metastannic acid .... .... 117 Microcosrnic salt .... .... 139 as a flux .... 151 Minium .... .... .... .... 84 Mispickel 141 Modes of chemical action .... 164 Molecular combination or union, how expressed in chemical no- tation 162 Molecular formula .... .... 42 of oxides of chlorine 136 Molecular formulae of oxides of nitrogen .... .... .... 118 Molecular volumes .... .... 42 weight .... .... 42 Molecule, definition of 38 of water .... .... 41 Monad compound radicals .... 89 elements, list of 78, 81 Monads 78 Monatomic elements .... .... 78 Monovalentic, explanation of term 78 Mother liquor 67,156 Multiple proportions .... .... 43 law of .... 44 Mundic 60 Muriatic acid .... .... .... 94 N. Nascent state 124 Natrium .... .... 9 Negative electrode .... .... 31 elements .... .... 40 Neutralization, explanation of term . 49 INDEX. 179 PAGE Nitrates, list of 119 decomposition of some by heat 112,125 Nitrates, occurrence in nature .... 109 Nitre 109 cubic 109 Nitric acid 119 action on carbon .... 117 hydrochloric acid 119 Nitric acid, action on iodine .... 118 metallic sulphides 118 Nitric acid, action on metals .... 117 organic matter .... .... .... 118 Nitric acid, action on phospho- rus 118 Nitric acid, action on sulphur .... 117 properties of .... Ill Nitric and nitrous acids, cause of colour .... .... .... Ill Nitric acids and nitrous, decom- posed by heat Ill Nitric and nitrous acids, mole- cular formula of .... 110, 113 Nitric and nitrous acids, prepara- tion of, on a small scale 110, 113 Nitric anhydride volume Nitric oxide composition by a "carrier" of oxy- gen 110 118 115 121 120 Nitric oxide, action of air on composition of, by volume and by weight .... 118 Nitric oxide, pure, preparation of 115 Nitric peroxide 112 composition of, by volume and by weight .... 118 Nitrites ,.. 113 Nitrogen .... .,.. .... 8 etymology of .... .... 8 function in air .... 19 preparation of, from air 7 properties of .... .... 11 table of its oxides .... 118 Nitro-hydrochloric acid 119 Nitrous acid .... .... .... 113 Nitrous acid, oxidizing and reduc- ing action of .... .... .... 115 Nitrous anhydride .... .... 115 composition of, by volume and by weight .... 118 PAGE Nitrous oxide .... .... .... ] 15 composition of, by volume and by weight .... 118 Nitrous oxide, preparation and properties of 125 Noble metals 12, 166 Non-metallic elements, list of Non-metals or metalloids, dis tinction of, from metals Notation, chemical graphic , symbolic Normal salts, definition of 0. Oil of vitriol Opal Orthoboric acid.... Orthophosphoric acid of etymology Oxalic acid, action of sulphuric acid on Oxidation, by potassic perman- ganate Oxidation of mercury in air by nitrous acid Oxide, carbonic .... its properties .... its preparation.... Oxide, nitric nitrous .... Oxides, definition of of chlorine, table of .... of nitrogen, table of .... as oxidizing agents Oxides, metallic, action of hydro- chloric acid on Oxides, metallic, action of hydro- sulphuric acid on Oxides, metallic, action of sul- phuric acid on .... .... Oxides, reduction of by hydro- gen by carbon Oxides, salifiable table of Oxygen combustion in .... etymology of .... preparation of from air.... from mercuric oxide preparation of from potas- sic chlorate . 40 18 40 79 78 160 91 152 144 138 138 107 115 6 115 106 108 107 115 115 22 136 118 119 95 59 101 168 50 50 6 7, 13 8 6, 7 7 13 180 INDEX. PAGE Oxygen, properties of .... .... 7 proportion of in water .... 32 Oxy-salts, nomenclature of, 102 Ozone, an allotropic form of oxygen 36^ preparation of .... .... 35 properties of .... .... 36 its activity 35 P. Passive state of iron Pentad elements Pentads.... Pentathionic acid 119 81 78 58 Pentavalentic, explanation of term .... .... .... .... 78 Perchlorate, potassic 135 Perissads, etymology of.... .... 78 Permanganate, potassic, powerful oxidizing agent .... .... 115 Peroxide of hydrogen (hydroxyl) 85 Peroxides 84 Phosphoretted hydrogen 140 Phosphoric acid, common .... 138 meta- or mono- basic monohydrated .... .... 138 Phosphoric acid, pyro (tetrahydric or tetrabasic).... 139 Phosphoric acid, trihydric or tri- basic 137 Phosphoric anhydride .... 15, 137 Phosphorous anhydride.... .... 140 as a reduc- ing agent .... .... .... 140 Phosphorus 137 action of potash on 140 combustion in oxygen and air 15, 137 Phosphorus, properties of .... 137 Pipette 49 Platinum black, or spongy plati- num .... .... .... .... 98 Platinum spoon and wire .... 150 Plumbago 103 Plumbic dioxide .... .... 85 combination of with sulphurous anhydride .... 88 Plumbic nitrate, decomposition of by heat 112 Plumbic oxide 84, 112 sulphide .... 51, 55, 59 Plumboxyl 89 Pneumatic trough .... .... 2 Pole, negative, positive.... .... 31 PAGE Potassamine 129 Potassic chlorate, preparation of 132 ferrocyanide, carbonic oxide prepared from .... .... 107 Potassic hypochlorite 132 hypophosphite.... .... 141 nitrate, decomposed by silicic anhydride .... .... 154 Potassic nitrate, solubility of .... 156 perchlorate 135 permanganate .... .... 115 peroxide .... .... 89 sulphate 122 hydric 111, 122 Potassium chrome alum .... 163 iron alum .... .... 163 Potassoxyl 89 Precipitant .... .... .... 60 Precipitation .... .... .... 60 Purification of salts by crystalli- sation 156 Pyrarsenic acid .... .... .... 142 Pyrites, arsenical .... .... 141 Pyrites, capillary .... .... 60 Pyrophoric iron .... .... 164 Pyrophosphoric acid .... .... 139 Quintavalence of elements .... 75 Quartz 152 E. Radicals, compound, definition of 89 Reactions, or chemical changes.... 23 in the dry way, ex- planation of term .... .... 83 Reactions in the wet way, ex- planation of term .... .... 83 Reactions, reciprocal .... .... 30 Reagents, definition of .... .... 23 Reciprocal affinities .... .... 30 Red precipitate..., .... .... 8 Reducing flame.... .... .... 147 agent, sulphurous acid as a 98 agent, nitrous acid as a 1]5 Reduction of gases to standard temperature and pressure .... 43 Reduction by means of electricity (electrolysis) 31 Reductions 26, 168 INDEX. 181 PAGE Relative combining weights .... 38 Resolution 166 Rock crystal 152 S. Sal-ammoniac .... .... .... 126 Salt, common 66, 70 definition of 160 Saltpetre 109,119 Chili 109, 119 flour 157 impurities in .... .... 157 purification of .... 157 Salts, acid Ill definition of, instances of.... 160 acid to litmus .... .... 159 alkaline to litmus.... .... 159 basic, definition of, instances of 161 Salts, colour of 158 double, constitution of, instances of .... .... .... 161 Salts, double, general properties of 161 Salts, haloid 102 neutral to litmus.... .... 159 normal, instances of .... 160 oxy, nomenclature of .... 102 percentage solubility of .... 156 purification of, by recrys- tallisation .... .... .... 157 Salts, taste of soluble 158 Sand 152 Saturated solutions .... .... 155 boiling points of various 156 Selenium 53 Separation of metals from their solutions by sulphuretted hy- drogen .... .... .... 59 Silica 152 gelatinous, preparation of 153 Silicates 154 soluble 153 Silicic acid 153 dibasic .... .... 154 tetrabasic 153 anhydride .... .... 153 hydrate 153 Silicon, a tetratomic element .... 153 Silver displaced by copper or zinc 167 Silver glance .... .... .... 60 Simple solution.... .... .... 60 Slaked lime 84 PAGE Sodic, arseniate.... .... .... 142 biborate 144 carbonate, preparation from carbonic anhydride .... 105 Sodic chloride .... .... 66, 70 decomposed by boric anhydride 145 Sodic chloride, decomposed by silicic anhydride .... .... 153 Sodic chloride, distribution of .... 67 hydrate 47 hypochlorite .... .... 133 metaphosphate .... .... 139 nitrate, or cubic nitre 109, 119 phosphate, tri- 138 hydric ammonic 139 di- .... 138 pyrophosphate 139 silicate 153 sulphate, acid or hydric 92, 122 decomposed by silicic anhydride 153 Sodic sulphate, or Glauber's salt 122 sulphite 100 acid or hydric .... 100 Sodium, action on hydrochloric acid gas .... .... ... 76 Sodium, action on water .... 1 amalgam, preparation of 77 atomicity or quantiva- lence of 77 Solution 60 Solvent 60 Specific gravity .... .... .... 20 Spirit of hartshorn .... .... 124 of salt 94 Stannic sulphide, preparation of 55 Steam, composition by volume .... 41 Sublimation .... .... .... 52 Sugar of lead 59 Sulphates, preparation from car- bonates .... .... .... 105 Sulphates, preparation from sul- phurous anhydride and metallic peroxides .... .... .... 88 Sulphates, solubility of 100 Table of metallic .... 122 Sulphides .... .... .... 55 Table of metallic .... 60 native 60 solubility of 59 Sulphites 101 acid or hydric .... 101 Sulphur.... .... .... .... 51 allotropic forms of .... 53 182 INDEX. PAGE Sulphur and copper 55 hydrogen .... .... 56 iron .... .... 55 mercury .... .... 56- oxygen .... 15, 54 tin 55 changes on heating .... 52 distillation of.... .... 52 extraction from iron pyrites .... .... .... 56 Sulphur, flowers of .... .... 51 occurrence of, in nature 51 properties of .... .... 51 roll ' .... 51 Sulphuretted hydrogen, molecular formula 58 Sulphuretted hydrogen, molecular weight .... .... .... 58 Sulphuretted hydrogen, prepara- tion of 56 Sulphuretted hydrogen, proper- ties of 58 Sulphuretted hydrogen, solution of 58 Sulphuric acid .... .... .... 120 action on metallic hydrates 101 Sulphuric acid, action on metallic oxides 101 Sulphuric acid, action on metals 100 preparation on small scale 121 Sulphuric acid, tetrahydric .... 91 viewed as a com- pound of sulphurous anhydride and hydric peroxide .... .... 88 Sulphuric acid viewed as a com- pound of sulphuric anhydride and water .... .... .... 87 Sulphuric anhydride .... 87, 120 synthesis of 99 Sulphurous acid.... .... .... 97 a reducing agent 98 action on hydric peroxide .... .... .... 88 Sulphurous acid, action on hydro- sulphuric acid .... .... 58 Sulphurous acid, action on nitric peroxide 120 Sulphurous acid, formed by pass- ing sulphurous anhydride into water.... .... .... .... 97 Sulphurous anhydride .... 15, 54, 97 combination with metallic peroxides .... 88 PAGE Sulphurous anhydride, molecular formula .... .... .... 54 Sulphurous anhydride, prepara- tion of 15, 97 Sulphurous anhydride, properties of 98 Sulphurous anhydride, synthesis of .... t 54 Supports, used in blowpipe ex- periments 149 Symbolic formulae .... .... 71 of oxides of chlorine 136 Synthesis, etymology of.... .... 37 of water 33 T. Table of names, atomic weights, and symbols of elements .... 40 Table of chemical elements and symbols 24, 25 Table of metallic chlorides .... 70 elements .... 40 n elements classi- fied 81 Table of metallic nitrates .... 119 ,, oxides .... 50 ,, sulphides .... 60 sulphates .... 122 rnetalloxyls .... .... 89 non-metallic elements.... 40 oxides of chlorine .... 136 nitrogen .... 118 solubility of salts .... 156 Tetrad or Tetratomic elements.... 78, 81 Tetravalentic, explanation of term .... .... .... .... 78 Theory, atomic .... .... .... 38 Thick type, use of 82 Tin, action of sulphur on .... 55 action of nitric acid on .... 117 pyrites (bell-metal ore) .... 60 stone .... .... .... 50 Tincal 144 Triad elements 78, 81 Triargentic phosphate 138 Tribasic phosphates (orthophos- phates) 138 Tribasic phosphoric acid .... 139 Trisodic arseniate .... .... 142 phosphate .... .... 138 Trivalentic, explanation of term 78 INDEX. 183 U. PAGE 42 82 Use of the crith.... thick type .... V. Vitriol, oil of 91 Volume of gas, calculation of .... 43 Volumes, combining .... .... 34 Volumetrical composition of hydrochloric acid .... .... 76 Volumetrical composition of steam.... ....33, 41 w. 166 Water, action upon metals composition of, by volume .... .... ....33, 41 Water, composition of, by weight 34 decomposed by voltaic action.... Water, distilled electrolysis of .... of constitution ... crystallisation Water, synthesis of Waters, acidulous .... 31 .... 45 .... 31 .... 153 138, 157 138, 157 ....33, 45 47 PAGE Waters, chalybeate 47 mineral.... .... .... 47 organic matter in natural 47 rain 46 46 47 spring ^ .... sulphurous or hepatic .... Wet way, reactions in the, ex- planation of term .... .... 83 White arsenic 142 crystalline compound of sulphuric acid chambers .... 120 White vitriol 59 Y. Yellow prussiate of potash, its decomposition by sulphuric acid , .... 107 z. Zinc, action of nitric acid on .... 124 blende 51, 60 burning of, in air .... .... 10 granulated ... .... .... 2 in oxygen .... .... .... 14 its action on alkaline hy- drates 83 Zincoxyl.... .... .... .... 89 HABBIeON AND SONS, PBINTEES IN OROINABY TO HEB MAJESTY, ST. MABTIN'S LANE. i LONDON, NEW BURLINGTON STREET, OCTOBER, 1872 A LIST OF MESSRS CHURCHILL'S WORKS CHEMISTRY, MATERIA M E D I C A, PHARMACY, BOTANY, THE MICROSCOPE, AND OTHER BRANCHES OF SCIENCE . INDEX Beasley's Pocket Formulary Do. Druggist's Receipt Book ... Do. Book of Prescriptions Bentley's Manual of Botany Bernays' Syllabus of Chemistry Bloxam's Chemistry Do. Laboratory Teaching Bowman's Practical Chemistry Do. Medical do. Brooke's Natural Philosophy Brown's Analytical Tables Carpenter's Microscope and its Revelations Cooley's Cyclopaedia of Receipts Fayrer's Poisonous Snakes of India... Fownes' Manual of Chemistry Fresenius' Chemical Analysis Galloway's First Step in Chemistry ... Do. Second do. do. Do. Qualitative Analysis Do. Chemical Tables Greene's Tables of Zoology Griffiths' Chemistry of Four Seasons Huxley's Anatomy of Vertebrates .. Do. Classification of Animals . . . Kay-Shuttleworth's Modern Chemistry Martin's Microscopic Mounting Mayne's Lexicon of Scientific Terms Do. Medical Vocabulary Microscopical Journal (Quarterly) ... Nevins' Analysis of Pharmacopoeia ... Noad on the Inductorium Ord's Comparative Anatomy Pereira's Selecta e Pnescriptis Pharmaceutical Journal and Transactions Prescriber's Pharmacopoeia Price's Photographic Manipulation ... Royle's Materia Medica... Shea's Animal Physiology Smith's Pharmaceutical Guide Squire's Companion to Pharmacopoeia Do. Hospital Pharmacopoeias ... Steggall's First Lines for Chemists ... Stowe's Toxicological Chart Sutton's Volumetric Analysis Tuson's Veterinary Pharmacopoeia ... Valentin's Practical Chemistry Vestiges of Creation Wagner's Chemical Technology Wahltuch's Dictionary of Materia Medica Wittstein's Pharmaceutical Chemistry, by Darby Year Book of Pharmacy PAGE x X X xii iv iii iii iv iv xv iv xii vi xiii v v v V V v xiii vi xiii xiii vi xii xiv xiv xii ix xv xiii ix xi xi xv viii xiv ix viii viii ix x vi xi vii xiv vii viii xi xi %* 71ic Works advertised in this Catalogue may be obtained through any Bookseller in the United Kingdom, or direct of the Publishers on Remittance being made. A LIST OF Messrs CHURCHILL'S WORKS, &c C. . Bloxam CHEMISTRY, INORGANIC and ORGANIC : With Experiments. By CHARLES L. BLOXAM, Pro- fessor of Chemistry in King's College, London ; Pro- fessor of Chemistry in the Department for Artillery Studies, Woolwich. Second Edition. With 295 En- gravings on Wood 8vo, i6s. %* It has been the author's endeavour to produce a Treatise on Chemistry sufficiently comprehensive for those studying the science as a branch of general education, and one which a student may peruse with advantage before commencing his chemical studies at one of the colleges or medical schools, where he will abandon it for the more advanced work placed in^his hands by the professor. The special attention devoted to Metallurgy and some other branches of Applied Chemistry renders the work especially useful to those who are being educated for employment in manufacture. " Professor Bloxam has given I scientific men. . . It is as- us a most excellent and useful | tonishing how much information practical treatise. His 666 pages j he often conveys in a few para- are crowded with facts and expe- graphs. We might quote fifty riments, nearly all well chosen, and many quite new, even to instances of this." Chemical News. By the same Author LABORATORY TEACHING: Or, Progressive Exercises in Practical Chemistry, with Analytical Tables Second Edition. With 89 Engravings. Crown 8vo, 53. 6d. * '** This work is intended for use in the chemical laboratory by those who are commencing the study of practical chemistry. It does not presuppose any knowledge of chemistry on the part of the pupil, and does not enter into any theoretical speculations. It dispenses with the use of all costly apparatus and chemicals, and is divided into separate exercises or lessons, with examples for practice, to faci- litate the instruction of large classes. The method of instruction here followed has been adopted by ihe author, after twenty-three years' experience as a teacher in the laboratory. iv MESSRS CHURCHILL'S WORKS John E. Bowman and C. L. Bloxam PRACTICAL CHEMISTRY, Including Analy- sis. By JOHN E. BOWMAN and C. L. BLOXAM. Sixth Edition. With 98 Engravings on Wood. [Fcap. 8vo, 6s. 6d. %* The intention of this work is to furnish to the beginner a text-book of the practical minut'ut of the laboratory. The various processes employed in analysis, or which have been devised for the illustration of the principles of the science, are explained in language as simple as possible. This edition has been embellished with a large number of additional wood engravings from sketches made in the laboratory. Also MEDICAL CHEMISTRY. Fourth Edition, with 82 Engravings on Wood. . . Fcap. 8vo, 6s. 6d. %* This work gives instructions for the examination and analysis of urine, blood, and a few other of the more important animal pro- ducts, both healthy and morbid. It comprises also directions for the detection of poisons in organic mixtures and in the tissues. Albert J. Bernays NOTES FOR STUDENTS IN CHEMISTRY : Being a Syllabus of Chemistry and Practical Chemistry. By ALBERT J. BERNAYS, Professor of Chemistry at St. Thomas's Hospital. Fifth Edition, Revised. [Fcap. 8vo, 35. 6d. ** A new feature is an Appendix giving the doses of the chief chemical preparations of the "Materia Medica." ' ' The new notation and no- menclature are now exclusively used. We notice additional notes in apparently every paragraph in the book, and a close revision of the whole." Scientific Opinion. y. Campbell Brown ANALYTICAL TABLES for STUDENTS of Practical Chemistry. By J. CAMPBELL BROWN, D.Sc. Lond., F.C.S. . . . 8vo, 2s. 6d. MESSRS CHURCHILL'S WORKS G. Foivnes A MANUAL OF ELEMENTARY CHE- MISTRY, Theoretical and Practical. BY G. FOWNES, F.R.S. Edited by H. Bence Jones, M.D., F.R.S., and Henry Watts, B.A., F.R.S. Tenth Edition. With 193 Wood Engravings .... Fcap. 8vo, 145. Rcmigius Freseuius QUALITATIVE ANALYSIS. By C. REMIGIUS FRESENIUS. Edited by Arthur Vacher. Eighth Edition, with Coloured Plate of Spectra and Wood Engravings. . . . 8vo, 123. 6d. By the same Author QUANTITATIVE ANALYSIS. Edited by Arthur Vacher. Fifth Edition, with Wood Engravings 8vo, 125. 6d. Robert Galloway THE FIRST STEP IN CHEMISTRY: A New Method for Teaching the Elements of the Science. By ROBERT GALLOWAY, Professor of Applied Chemistry in the Royal College of Science for Ireland. Fourth Edition, with Engravings. Fcap. 8vo, 6s. 6d. By the same Author THE SECOND STEP IN CHEMISTRY: Or the Student's Guide to the Higher Branches of the Science. With Engravings . . Fcap. 8vo, 105. Also A MANUAL OF QUALITATIVE ANALY- SIS. Fifth Edition, with Engravings. Post 8vo, 8s. 6d. Also CHEMICAL TABLES. On Five Large Sheets, for School and Lecture Rooms. Second Edition, the Set 45. 6d. "We can always give praise to Mr. Galloway's educational works. They are invariably writ- ten on a system and founded on experience, and the teaching is clear, and in general complete." Chemical Neii's. " Mr. Galloway has done much to simplify the study of chemistry by the instructive manner in which he places the principal details of the science before his readers." British Aledical Joiirnal. VI MESSRS CHURCHILL'S WORKS T. Griffiths CHEMISTRY OF THE FOUR SEASONS: Spring, Summer, Autumn, Winter. By T. GRIFFITHS. Second Edition, with Engravings. Fcap^ Svo, 75. 6d. U. J. Kay-Shuttleworth PRINCIPLES OF MODERN By FIRST MISTRY. By U. J, Second Edition . " We can recommend the book. "- Athenmim. CHE- KAY-SHUTTLEWORTH, M.P. Crown Svo, 45. 6d. "Deserving warmest commen- dation." Popular Science Rev. Francis Sutton HANDBOOK OF VOLUMETRIC ANALYSIS, or, the Quantitative Estimation of Chemical Substances by Measure applied to Liquids, Solids, and Gases. By FRANCIS SUTTON, F.C.S., Norwich. Second Edition. With Engravings. . . . . Svo, 125. %* This work is adapted to the requirements of pure Chemical Research, Pathological Chemistry, Pharmacy, Metallurgy, Manu- facturing Chemistry, Photography, c., and for the Valuation of Substances used in Commerce, Agriculture, and the Arts. "Mr. Sutton has rendered an essential service by the compilation of his work.' ; CJiemical JVeivs. Arnold J. Coo Icy and R. V. Tuson A CYCLOPEDIA OF PRACTICAL RECEIPTS, PROCESSES, AND COLLATERAL INFORMATION IN THE ARTS, MANUFAC- TURES, PROFESSIONS, AND TRADES : Includ- ing Pharmacy and Domestic Economy and Hygiene. Designed as a Comprehensive Supplement to the Phar- macopoeias and General Book of Reference for the Manufacturer, Tradesman, Amateur, and Heads of Families. By ARNOLD J. COOLEY. Fifth Edition, with Engravings. . . . . . Svo, 285. NAMES OF THOSE WHO HAVE CONTRIBUTED TO, OR ASSISTED IN THE REVISION OF, THIS EDITION JOHN ATTFIELD, Ph.D.,F.C.S. J. WORTLEY AXE LLOYD BULLOCK, F.C.S. E. L. BARRET, B.Sc., F.C.S. E. CANTON, F.R.C.S. SPENCER COBBOLD, M.D., F.R.S. STEPHEN DARBY, F.C.S. Dr. DE VRIJ, of the Hague WILLIAM HARKNESS,F.R.M.S. C. W. HE.VTON, F.C.S. EDMUND NEISON, F.C.S. GEORGE PHILLIPS, F.C.S. WILLIAM PRITCHARD A. E. SANSOM, M.D. Lond., M.R.C.P.S. J. B. SlMONDS JOHN SPILLER, F.C.S. JOHN STENHOUSE, LL.D., F.R.S. RICHARD V. TUSON, F.C.S. (Editor). MESSRS CHURCHILL'S WORKS vii W. G, Valentin TEXT-BOOK of PRACTICAL CHEMISTRY : A Guide to the Course of Practical Instruction given in the Laboratories of the Royal College of Chemistry. By WM. G. VALENTIN, F.C.S. With 90 Engravings. o [8vo, los. 6d. R. Wagner and W. Crookcs HANDBOOK OF CHEMICAL TECHNO- LOGY. By RUDOLF WAGNER, Ph.D., Professor of Chemical Technology at the University of Wurtz- burg. Translated and Edited from the Eighth German Edition, with Extensive Additions, by WILLIAM CROOKES, F.R.S [8vo, 255= ** Under the head of Metallurgical Chemistry, the latest methods of preparing Iron, Cobalt, Nickel, Copper, Copper Salts, Lead and Tin and their Salts, Bismuth, Zinc, Zinc Salts, Cadmium, Antimony, Arsenic, Mercury, Platinum, Silver, Gold, Manga- nates, Aluminium, and Magnesium are described. The various applications of the Voltaic Current to Electro-Metallurgy iollo\v under this division. The Preparation of Potash and Soda Salts, the Manufacture of Sulphuric Acid, and the Recovery of Sulphur from Soda-waste, of course occupy prominent places in the consi- deration of Chemical Manufactures. It is difficult to over-estimate the mercantile value of Le Mond's process, as well as the many new and [important applications of Bisulphide of Carbon. The Manu- facture of Soap will be found to include much detail. The Tech- nology of Glass, Stoneware, Limes, and Mortars, will present much of interest to the builder and engineer. The Technology of Vege- table Fibres has been considered to include the Preparation of Flax, Hemp, Cotton, as well as Paper Making ; while the applications of Vegetable Products will be found to include Sugar-boiling, Wine and Beer Brewing, the Distillation of Spirits, the Baking of Bread, the Preparation of Vinegar, the Preservation of Wood, &c. Dr. WAGNER gives much information in reference to the production of Potash from Sugar residues. The use of Baryta Salts is also fully described, as well as the Preparation of Sugar from Beet-roots. Tanning, the Preservation of Meat, Milk, &c., the Preparation of Phosphorus and Animal Charcoal, are considered as belonging to the Technology of Animal Products. The Preparation of the Materials for dyeing has necessarily required much space ; while the final sections of the book have been devoted to the Technology of Heating and Illumination. Vlll MESSRS CHURCHILL'S WORKS J. Forbes Royle anfcF. W. Headland A MANUAL OF MATERIA MEDICA. By J. FORBES ROYLE, M.D., F.R.S., and F. W. HEAD- LAND, M.D., F.L.S. Fifth Edition, with Engravings on Wood Fcap'Svo, 123. 6d. \* This edition has been remodelled throughout on the basis of the present edition of the British Pharmacopoeia. The medicines of the British Pharmacopoeia will be found arranged in natural order, the preparations described at length, and the formulse explained. Other medicines and preparations, mentioned only in the London Pharmacopoeia of 1851, are separately described and included in brackets. All remedies of value, whether officinal or not, are noticed in their place in this Manual. ' ' This Manual is, to our minds, unrivalled in any language for condensation, accuracy, and com- pleteness of information." Bri- tish Medical Journal. Adolphc Wahltuch A DICTIONARY OF MATERIA MEDICA AND THERAPEUTICS. By ADOLPHE WAHLTUCH, M.D. Svo, 155. * # * The purpose of this work is to give a tabular arrangement of all drugs specified in the British Pharmacopoeia of 1867. Every table is divided into six parts : (l) The Name and Synonyms ; (2) Character and Properties or Composition ; (3) Physiological Effect's and Therapeutics ; (4) Form and Doses ; (5) Preparations ; (6) Prescriptions. Other matter elucidatory of the Pharmacopoeia is added to the work. " A very handy book." Lancet. Peter Squire COMPANION TO THE BRITISH PHAR- MACOPCEIA. With Practical Hints on Prescribing; including a Tabular Arrangement of Materia Medica for Students, and a Concise Account of the Principal Spas of Europe. By PETER SQUIRE, Chemist in Ordinary to the Queen and the Prince of Wales ; late President of the Pharmaceutical Society. Eighth Edit. Svo, ros. 6d. By the same Author THE HOSPITAL PHARMACOPOEIAS OF LONDON arranged in Groups for Easy Reference and Comparison. Second Edition. . Fcap Svo, 55. LIST OF THE HOSPITALS Charing Cross Consumption Diseases of the Chest Fever Guy's King's College London London Ophthalmic Middlesex St. Bartholomew's St. George's St. Mary's St. Thomas's Skin University College Westminster Westminster Ophthalmic. MESSRS CHURCHILL'S WORKS J. B. Smith PHARMACEUTICAL GUIDE. By JOHN BARKER SMITH. . Crown 8vo, 6s. 6d. FIRST AND SECOND EXAMINATIONS LATIN GRAMMAR FRACTIONS METRIC SYSTEM MATERIA MEDICA BOTANY PHARMACY CHEMISTRY PRE- SCRIPTIONS. John Steggall FIRST LINES FOR CHEMISTS AND DRUGGISTS preparing for Examination at the Phar- maceutical Society. By JOHN STEGGALL, M.D. Third Edition i8mo, 35. 6d. CONTENTS Notes on the British Pharma- copoeia, the Substances ar- ranged alphabetically. Table of Preparations, contain- ing Opium, Antimony, Mer- cury, and Arsenic. Classification of Plants. Thermometers. Specific Gravity. Weights and Measures. Questions on Pharmaceutical Chemistry and Materia Me- dica. J. Btrkbeck Nevins THE PRESCRIBER'S ANALYSIS OF THE BRITISH PHARMACOPOEIA OF 1867. By J. BIRKBECK NEVINS, M.D. Lond., Lecturer on Materia Medica in the Liverpool Royal Infirmary Medical School. Third Edition, Revised and Enlarged. [Royal 32mo, 35. 6d. Jonathan Pereira SELECTA E PR^ESCRIPTIS : Containing Lists of the Terms, Phrases, Contractions, and Abbreviations used in Prescriptions, with Explana- tory Notes ; the Grammatical Construction of Prescrip- tions ; Rules for the Pronunciation of Pharmaceutical Terms ; a Prosodiacal Vocabulary of the Names of Drugs, &c. ; and a Series of Abbreviated Prescriptions illustrating the use of the preceding terms. To which is added a Key, containing the Prescriptions in an Unab- breviated Form, with a Literal Translation for the Use of Medical and Pharmaceutical Students. By JONATHAN PEREIRA, M.D., F.R.S. Fifteenth Edition. [321110, 55. MESSRS CHURCHILL'S WORKS Hcjiry Bcasley THE POCKET FORMULARY AND SYNOPSIS OF THE BRITISH AND FOREIGN PHARMACOPCEIAS : Comprising Standard and ap- proved Formulas for the Preparations and Compounds employed in Medical Practice. By HENRY BEASLEY. Ninth Edition i8mo, 6s, By the same Author THE DRUGGIST'S GENERAL RECEIPT- BOOK : Comprising a Copious Veterinary Formulary and Table of Veterinary Materia Medica ; Patent and Proprietary Medicines, Druggists' Nostrums, &c. ; Per- fumery, Skin Cosmetics, Hair Cosmetics, and Teeth Cosmetics ; Beverages, Dietetic Articles and Condi- ments ; Trade Chemicals, Miscellaneous Preparations and Compounds used in the Arts, &c. ; with useful Memoranda and Tables. Seventh Edition. [i8mo, 6s. Also THE BOOK OF PRESCRIPTIONS: Containing 3,000 Prescriptions collected from the Prac- tice of the most eminent Physicians and Surgeons, English and Foreign. Fourth Edition. [i8mo, 6s. " Mr. Beasley's ' Pocket For- mulary,' 'Druggist's Receipt- Book,' and ' Book of Prescrip- tions,' form a compact library of reference admirably suited for the dispensing desk." Chemist and Druggist. William Stoive TOXICOLOGICAL CHART, Exhibiting at one view the Symptoms, Treatment, and Mode of Detecting the Various Poisons, Mineral, Vege- table, and Animal. To which are added concise Direc- tions for the Treatment of Suspended Animation. By WILLIAM STOWE, M.R.C.S.E. Thirteenth Edition. [Sheet, 2s. ; Roller, 55. MESSRS CHURCHILL'S WORKS xi G. C Wittstcm PRACTICAL PHARMACEUTICAL CHE- MISTRY : an Explanation of Chemical and Pharma- ceutical Processes ; with the Methods of Testing the Purity of the Preparations, deduced from Original Ex- periments. By Dr. G. C. WITTSTEIN. Translated from the Second German Edition by STEPHEN DARBY. [iSmo, 6s. " It would be impossible too strongly to recommend this work to the beginner, for the completeness of its explanations, by following which he will become well grounded in practical chemistry," From the Introduction by Dr. Biichner. THE PRESCRIBER'S PHARMACOPCEIA : The Medicines arranged in Classes according to their Action, with their Composition and Doses. By A PRACTISING PHYSICIAN. Fifth Edition. [Fcap i6mo, cloth, 2s. 6d.; roan tuck, 35. 6d, R. V. Tuson A PHARMACOPCEIA, INCLUDING THE OUTLINES OF MATERIA MEDICA AND THERAPEUTICS, for the Use of Practitioners and Students of Veterinary Medicine. By RICHARD V. TUSON, F.C.S., Professor of Chemistry and Materia Medica at the Royal Veterinary College. Second Edition [In preparation. "Not only practitioners and students of veterinary medicine, but chemists and druggists will find that this book supplies a want in veterinary literature." Chemist and Druggist. THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. Published weekly . . Price 4d. THE YEAR-BOOK OF PHARMACY: Containing the Proceedings at the Yearly Meeting of the British Pharmaceutical Conference, and a Report on the Progress of Pharmacy, which includes notices of all Pharmaceutical Papers, new Processes, Preparations, and Formulas published throughout the world. Pub- lished annually. . . . . [8vo, 73. 6d. xii MESSRS CHURCHILL'S WORKS Robert Smiley A MANUAL OF BOTANY: Including the Structure, Functions, Classifications, Pro- perties, and uses of Plants. By ROBERT BENTLEY, F.L.S., Professor of Botany, King's College, and to the Pharmaceutical Society. Second Edition, with 1,127 Wood Engravings . . . Fcap. 8vo, I2S. 6d. "As the standard manual of botany its position is undisputed," -Chemist and Druggist. W. B. Carpenter THE MICROSCOPE AND ITS REVELA- TIONS. By W.B. CARPENTER, M.D., F.R.S. Fourth Edition, with more than 500 Wood Engravings. [Fcap. 8vo, I2s. 6d. %* The author has aimed to combine within a moderate compass that information in regard to the use of his instrument and its appliances, which is most essential to the working microscopist, with such an account of the objects best fitted for his study as may qualify him to comprehend what he observes, and thus prepare him to benefit science, whilst expanding and refreshing his own mind. ~o J. H. Martin A MANUAL OF MICROSCOPIC MOUNT- ING; with Notes on the Collection and Examination of Objects. By JOHN H. MARTIN, author of " Microscopic Objects." With upwards of 100 Engravings. [8vo, 75. 6d. *.** The aim of this work is to supply the student with a concise manual of the principles of microscopic mounting, and to assist his progress in the manual dexterity, as far as illustrations and words render it possible, necessary in their application. o THE QUARTERLY JOURNAL OF MICRO- SCOPICAL SCIENCE. (Established in 1852.) Edited by Dr. J. F. PAYNE, Demonstrator of Morbid Anatomy at St. Thomas's Hospital, and Mr. E. RAY LANKESTER, Natural Science Fellow of Exeter College, Oxford. [Annual Subscription, i6s. ; Single Numbers, 45. *** The Memoirs are, when needful, illustrated by Lithographic Plates, many of which are Coloured. The Journal contains, in addition, Notes and Memoranda, Reviews of Books, Quarterly Chronicle, and Proceedings of Societies. MESSRS CHURCHILL'S WORKS xiii y, Fayrcr THE THANATOPHIDIA OF INDIA; being a Description of the Venomous Snakes of the Indian Peninsula. With an Account of the Influence of their Poison on Life, and a Series of Experiments. By J. FAYRER, M.D., C.S.I., Honorary Physician to the Queen ; late President of the Asiatic Society of Bengal. With 3 1 Plates (28 Coloured) . . Folio, jl. ;s. J. Reay Greene TABLES OF ZOOLOGY : indicating the Tribes, Sub-Orders, Orders, and Higher Groups of the Animal Kingdom, for Students, Lecturers, and others. By J. REAY GREENE, M.D., Professor of Natural History in the Queen's University in Ireland. Three large sheets, 75. 6d. the set ; or, mounted on canvas, with roller and varnished , iSs. %* These Tables have been carefully prepared in accordance with the present state of science, and with a view to remove the difficul- ties which arise from the various opinions held by different zoologists. T. H. Huxley A MANUAL OF THE ANATOMY OF VERTEBRATED ANIMALS. By Prof. HUXLEY, LL.D., F.R.S. With numerous Engravings. [Fcap. Svo, I2s. By the same Author INTRODUCTION to the CLASSIFICATION of ANIMALS. With Engravings . . Svo, 6s. W. M. Orel NOTES ON COMPARATIVE ANATOMY: a Syllabus of a Course of Lectures delivered at St. Thomas's Hospital. By WILLIAM MILLER ORD, M.B. Lond., M.R.C.P., Assistant-Physician to the Hospital, and Lecturer in its Medical School. . Crown Svo, 53. "Compact, lucid, and well "We have gone through it arranged. These Notes will, if well used, be valuable to learn- ers, perhaps still more so to te ichers. " Nature. carefully, and we are thoroughly satisfied with the manner in which the author has discharged his task." Pop. Science Review. xiv MESSRS CHURCHILL'S WORKS Johri'Shea MANUAL OF ANIMAL PHYSIOLOGY. With Appendix of Examination Questions. By JOHN SHEA, M.D., B.A. Loud. With numerous* Engravings. [Fcap. 8vo, 55. 6d. VESTIGES of the NATURAL HISTORY OF CREATION. With 100 Engravings on Wood. Eleventh Edition .... Post 8vo, 75. 6d. R. G. May tie AN EXPOSITORY LEXICON OF 50,000 SCIENTIFIC TERMS, Ancient and Modern. By R. G. MAYNE, M.D., LL.D. . . 8vo, 2 10 \* This Lexicon is suited to the requirements of every educated gentleman. It embraces the correct Pronunciation, Derivation, Definition, and Application of the Names, Analogues, Synonymes, and Phrases (in English, Latin, Greek, French, and German) con- nected with Medicine and employed in Anatomy, Animal Pathology, Astronomy, Botany, Chemistry, Comparative Anatomy, Concho- logy, Crystallography, Entomology, Geology, Geography, Geometry, Ichthyology, Materia Medica, Medical Jurisprudence, Medicine, Microscopy, Mineralogy, Natural History, Natural Philosophy, Nosology, Obstetrics, Ornithology, Pathological Anatomy, Patho- logy, Pharmacy, Phrenology, Physiology, Surgery, Trigonometry, and Zoology. By the same Author MEDICAL VOCABULARY : An Explanation of all Names, Synonymes, Terms, and Phrases used in Medicine and the Relative Branches of Medical Science, giving their correct Derivation, Meaning, Application, and Pronunciation. Intended specially as a Book of Reference for the Young Student. Third Edition. [Fcap 8vo, 8s. 6d. "We have referred to this ! Botanical, and Pharmaceutical work hundreds of times, and have J Terms are to be found on almost always obtained the information i every page." Chemist and we required. . . Chemical, ; Druggist. MESSRS CHURCHILL'S WORKS xv Lake Price A MANUAL OF PHOTOGRAPHIC MANI- PULATION. By LAKE PRICE. Second Edition, Revised and Enlarged, with numerous Engravings. [Crown 8vo, 6s. 6d. %* Amongst the Contents are the Practical Treatment of Por- traits] Groups in the Studio Landscapes Groups in Open Air Instantaneous Pictures Animals Architecture Marine Sub- jectsStill Life Copying of Pictures, Prints, Drawings, Manu- scripts, Interiors Stereoscopy in Micro photography, &c., and Xotices of the last Inventions and Improvements in Lenses, Appa- ratus, &c. Photographer ; and to those who desire to enter on this path, Mr. LAKE PRICE, in the volume before us, proves himself to be ' a guide, philosopher, and " In these days, when nearly every intelligent person can, after a few weeks, master the manipu- latory details of our art-science, attention to the artistic treat- ment of subjects is a matter for the serious consideration of the friend." The British Journal of PJiotography . C. Brooke THE ELEMENTS OF NATURAL PHILO- SOPHY. By CHARLES BROOKE, M.B., M.A., F.R.S. Based on the Work of the late Dr. GOLDING BIRD. Sixth Edition, with 700 Engravings on Wood. [Fcap 8vo, I2s. 6d. CONTENTS I, Elementary Laws and Properties of Matter : Internal or Molecular Forces 2, Properties of Masses of Matter : External Forces 3, Statics 4, The Mechanical Powers, or Simple Machines 5, Principles of Mechanism 6, Dynamics 7, Hydrostatics 8, Hydrodynamics 9, Pneumatics 10, Acoustics II, Magnetism; Diamagnetism 12, Franklinic Electricity 13, Voltaic Electricity 14, Electro-Dynamics 15, Electro-Telegraphy 1 6, Thermo- Electricity 17, Organic Electricity 18, Catoptrics and Dioptrics 19, Chromatics 20, Optical Instruments 21, Polarised Light 22, Chemical Action of Light : Photography 23, Thermics 24, Radiant Heat. H. M. Noad THE INDUCTORIUM, OR INDUCTION COIL : Being a Popular Explanation of the Electrical Principles on which it is constructed. By HENRY M. NOAD, Ph.D., F.R.S., Lecturer on Chemistry at St. George's Hospital Medical School. Third Edition, with Engravings Fcap Svo, 35. xvi MESSRS CHURCHILL'S WORKS The following CATALOGUES issued by Messrs CHURCHILL will be forwarded post free on application : 1. Messrs Churchill's General List of 400 ivorks on Medicine, Surgery, Midivifery, Matcria Medica, Hygiene, Anatomy, Physiology^ CJieniistry, &c., &c. 2. Selection from Messrs Churchills General List, comprising all recent works published by them on the Art and Science of Medicine. 3. A descriptive List of Messrs ChurchilVs works on Chemistry, Pharmacy, Botany, PJiotography, and other branches of Science. 4. Messrs ChurchiWs Red-Letter List, giving the Titles of forthcoming New Works and New Editions. [Published every October.] 5. The Medical Intelligencer, an Annual List of New Works and New Editions published by Messrs J. & A. Churchill, together with Particulars of the Periodicals issued from their House. [Sent in January of each year to every Medical lVac..ui Jiicr in the United Kingdom whose name and address can be ascertained. A large number are also sent to the United States of America, Continental Europe, India, and the Colonies.] MESSRS CHURCHILL have concluded a special arrange- ment with MESSRS LINDSAY & BLAKISTON, OF PHILADELPHIA, in accordance with which that Firm will act as their Agents for the United States of America, either keeping in Stock most of Messrs CHURCHILL'S Books, or reprinting them on Terms advantageous to Authors. Many of the Works in this Catalogue may therefore be easily obtained in America. -Gtrivan & Danks, Storm Printers, G:\af II indiniil Mrcst, 1 fey market. A.N J. A* ***" FAILURE TO r*c-'~ OVERDUE. fiT 25 1935 171936 EC IC'D LD L D 21-100w-8, 1 34