Halogen

“ Again, dried chloride sealed up in dry hydrogen discolours, owing to the combination of the chlorine with the hydrogen. Poitevin and H. W. Vogel first enunciated the law that for the reduction by light of the haloid salts of silver halogen absorbents were necessary, and it was by following out this law that the present rapidity in obtaining camera images has been rendered possible. To put it briefly, then, the visible action of light is a reducing action, which is aided by or entirely due to the fact that other bodies are present which will absorb the halogens. ”

“ Luckily sorlus is the most plentiful of the halogen groups; we have far more of it than of chlorine, bromine or iodine.”
“Sorlus? I do not know of it—it must be one of the other [Pg. 114] elements that we do not have on Earth. What are its properties?”
“It, too, is much like iodine, but heavier. It is a black solid melting at 570 degrees; it is a metallic looking element, will conduct electricity somewhat, oxidizes in air to form an acidic oxide, and forms strong oxygen acids. It is far less active than iodine, except toward oxygen. ”

“ The abnormal specific heats of the halogen elements may be due to a loosening of the atoms, a preliminary to the dissociation into monatomic molecules which occurs at high temperatures. In the more complex gases the specific heat varies considerably with temperature ”

“ It is a hard, dark-grey solid, and is a very good conductor of electricity. When heated in oxygen or nitrogen, it reacts readily, forming the oxide and nitride respectively; halogens attack it at quite low temperatures (250°-400°) , forming the halide compounds, which are indeed best prepared in this way. Strong mineral acids, with the exception of hydrochloric acid, attack it, and fused alkalies dissolve it readily. ”

“ There is another action which seems to occur almost simultaneously when exposure takes place in the absence of an active halogen absorbent, as is the case when the exposure is given in the air, that is, an oxidizing action occurs. ”

“ It liberates halogens from the halogen acids, and oxidises manganese salts to permanganates, but does not completely oxidise ferrous or stannous salts, losing instead a part of its oxygen in the gaseous form. The dioxide cannot be obtained in the wet way. ”

“ An inspection of our maps will show that the radical of a body is represented by certain well-marked bands, some differing in position according as it is bonded with hydrogen, or a halogen, or with carbon, oxygen or nitrogen. There seem to be characteristic bands, however, of any one series of radicals between 1000 and about 1100, which would indicate what may be called the central hydrocarbon group, to which other radicals may be bonded. ”

“ And as not only their oxygen compounds, but also their hydrogen compounds, have acid properties, the halogens are elements of an exclusively acid character. Such metals as sodium, potassium, barium only give basic oxides. In the case of nitrogen, although it forms acid oxides, still in ammonia we find that capacity to give an alkali with hydrogen which indicates a less distinctly acid character than in the halogens. In no other elements is the acid-giving property so strongly developed as in the halogens. ”

“ Hydrogen and oxygen may also be produced electrolytically as gases, and their respective reducing and oxidizing powers at the moment of deposition on the electrode are frequently used in the laboratory, and to some extent industrially, chiefly in the field of organic chemistry. Similarly, the formation of organic halogen products may be effected by electrolytic chlorine, as, for example, in the production of chloral by the gradual introduction of alcohol into an anode cell in which the electrolyte is a strong solution of potassium chloride. ”

“ The hydrogen in the hydroxyl group cannot be substituted, excepting it be the entire group as such; this is proved by the action of the halogens, in their phosphorus compounds, upon water, when the halogen takes the place of the hydroxyl group, but never that of the hydrogen.
Now as to some logical deductions from the foregoing considerations. Hydrogen is by many looked upon as a true metal. This theory cannot be directly proved by the above, but it is certainly greatly strengthened thereby. To compare. Hydrogen is a powerful reducing agent ”

“ All the barium-radium compounds are spontaneously luminous. The dry anhydrous halogen salts emit a particularly intense light. This illumination cannot be seen in broad daylight, but it is easily visible in the twilight or by gas-light. The light emitted may be strong enough to read by in the dark. The light emitted emanates from the entire body of the product, whilst in the case of a common phosphorescent body, the light emanates specially from the portion of the surface illuminated. ”

“ All four of the halogens unite with hydrogen, but the affinity for hydrogen decreases as the atomic weight increases, hydrogen and fluorine uniting explosively at very low temperatures and in the dark, whilst hydrogen and iodine unite only at high temperatures, and even then the resulting compound is very readily decomposed by heat. ”

“ We may say that the organic iron developers require less restraining in their action than do the alkaline developers.
In Major Russell’s process the plate was prepared by immersion in a strong solution of silver nitrate and then washed and a preservative applied. The last-named agent executes two functions, one being to absorb the halogen liberated by the action of light and the other to preserve the film from atmospheric action. Tannin, which Major Russell employed, if we mistake not, is a good absorbent of the halogens, and acts as a varnish to the film. ”

“ The hydrides of the halogens are all colourless, strongly fuming gases, readily soluble in water and possessing a strong acid reaction; they react readily with basic oxides, forming in most cases well defined crystalline salts which resemble one another very strongly. ”

“ In ammonia, and in water, chlorine and sodium are able to bring about a direct replacement. According to the law of substitution, the formation of sodium chloride, NaCl, at once shows the equivalence of the atoms of the alkali metals and the halogens. The halogens and hydrogen and the alkali metals combine with such elements as oxygen, and it is easily proved that in such compounds one atom of oxygen is able to retain two atoms of the halogens, of hydrogen, and of the alkali metals. ”

“ The platinum is maintained at a bright red heat, either by a gas flame or by an electric furnace, and the vapour is passed over it by leading in a current of oxygen. If nitrogen be present, a boat containing dry lead peroxide and heated to 320° is inserted, the oxide decomposing any nitrogen peroxide which may be formed. The same absorbent quantitatively takes up any halogen and sulphur which may be present. The process is therefore adapted to the simultaneous estimation of carbon, hydrogen, the halogens and sulphur. ”

“ The nature therefore of any gas which is possibly a constituent of that which we now consider to be a universal atmosphere, becomes invested with an importance to us far beyond what we could even conceive of a short time since.
Lastly, in regard to the question as to the nature of our elements, it appears a very noteworthy circumstance that, by combining cyanogen with sulphur, which is also an analogue of oxygen, we obtain a compound analogous to the halogens I have referred to. ”

“ Nickel occludes hydrogen readily, is attacked by the halogen elements, and oxidizes easily when heated in air. In the massive state it is unacted upon by dry air, but if moistened with acidified water, oxidation takes place slowly. ”

“ Of the metals, only a very few combine with hydrogen (for example, sodium) , and give substances which are easily decomposed. Of the non-metals, the halogens (fluorine, chlorine, bromine, and iodine) most easily form hydrogen compounds; of these the hydrogen compound of chlorine, and still more that of fluorine, is stable, whilst those of bromine and iodine are easily decomposed, especially the latter. The other non-metals—for instance, sulphur, carbon, and phosphorus—give hydrogen compounds of different composition and properties, but they are all less stable than water. ”

“ Fluorine.—F, Cl, Br, I, are called halogens or haloids, and exist in compounds—salts—in sea water. F is the most active of all elements, combining with every element except O. Until recently it has never been isolated, for as soon as set free from one compound it attacks the nearest substance, and seems to be as much averse to combining with itself, or to existing in the elementary state, as to uniting with O. It is supposed to be a gas, and, as is claimed, has lately been isolated by electrolysis from HF in a Pt U-tube. ”

“ The space a must allow for the inclusion of a copper spiral if the substance contains nitrogen, and a silver spiral if halogens be present, for otherwise nitrogen oxides and the halogens may be condensed in the absorption apparatus; b contains copper oxide; c is a space for the insertion of a porcelain or platinum boat containing a weighed quantity of the substance; d is a copper spiral. The end d is connected to an air or oxygen supply with an intermediate drying apparatus. ”

“ In the first place we may notice a tendency of several aliphatic compounds, e.g. methane, tetrachlormethane, &c., to yield aromatic compounds when subjected to a high temperature, the so-called pyrogenetic reactions (from Greek πῦρ, fire, and γεννάω, I produce) ; the predominance of benzenoid, and related compounds—naphthalene, anthracene, phenanthrene, &c.—in coal-tar is probably to be associated with similar pyrocondensations. Long-continued treatment with halogens may, in some cases, result in the formation of aromatic compounds ”

“ When heated in air it burns brilliantly with the formation of the oxide. It combines directly with the halogens, and dissolves in cold dilute sulphuric acid, in hot strong hydrochloric acid and in aqua regia, but less readily in nitric acid. ”

“ It dissolves readily in strong nitric acid, and the helium contained is thus liberated. The gas contains a certain amount of hydrogen and oxides of carbon, also traces of nitrogen. In order to get rid of hydrogen, some oxygen is added to the helium, and the mixture exploded by an electric spark. All remaining impurities, including the excess of oxygen, can then be taken out of the gas by Sir James Dewar’s ingenious method of absorption with charcoal cooled in liquid air. Helium alone refuses to be absorbed, and it can be pumped off from the charcoal in a state of absolute purity. ”

“ Hydrogen with carbon is a constituent of all combustible vegetable substances, among others, it is also an essential constituent of the gas which is used for lighting our streets and rooms; in the free state it is also a gas, the lightest of all, and burns when ignited with a feebly luminous blue flame. In this combustion—that is, in the chemical combination of hydrogen with oxygen, a very considerable quantity of heat is produced; for a given weight of hydrogen, four times as much heat as in the combustion of the same weight of carbon. ”

“ If we consider the matter rather roughly and more or less as Gassendi did, we can explain the concept of valence by assuming that the atoms possess hooks; thus hydrogen and chlorine are each furnished with one [Pg 19] hook, oxygen and zinc with two hooks, nitrogen with three hooks, etc. When a hydrogen atom and a chlorine atom are hooked together, there are no free hooks left, and consequently the compound is said to be saturated. When one hydrogen atom is hooked into each of the hooks of an oxygen or carbon atom the saturation is also complete (see Fig. 3, A, B, C) . ”

“ Such experiments show the inactive nature of the argon group of gases towards an electro-negative element, oxygen. The gases are absolutely incombustible. No other elements can withstand such treatment, save platinum and its congeners, and gold. But even these metals combine with fluorine or chlorine, when heated in a current of one or other gas. Argon, however, is wholly unaffected when electric sparks are passed through its mixture with chlorine or fluorine, the two other most electro-negative elements. To them, too, it shows itself completely indifferent. ”

“ Unlike oxygen, which is a supporter of combustion, and will not burn, hydrogen itself is combustible. There is a jar full of it; and if I carry it along in this manner, and put a light to it, I think you will see it take fire, not with a bright light—you will at all events hear it, if you do not see it. Now, that is a body entirely different from oxygen: it is extremely light; for although yesterday you saw twice as much of this hydrogen produced on the one side as on the other, by the voltaic battery, it was only one-eighth the weight of the oxygen. ”

“ To take another example, if silver is dissolved in nitric acid, one atom of silver is exchanged for one atom of hydrogen. Silver, therefore, is monovalent, and we should expect that one atom of oxygen would unite with two atoms of silver. Some elements are trivalent, as, for example, nitrogen, which combines with hydrogen to form ammonia, NH3; others, [Pg 18] again, are tetravalent, such as carbon, which unites with hydrogen to form marsh gas CH4, and with oxygen to form carbon dioxide CO2. A valence greater than seven or eight has not been found in any element. ”

“ Her smile was encouraging.
“He said—and I quote”—Mike’s voice assumed a gloomy, but stilted tone—“normal hydrogen gas consists of diatomic [188] molecules. The nuclear, or proton, spin of these atoms—ah—that is, of the two atoms that compose the molecule—may be oriented in the same direction or in opposite directions.”
He held a finger in the air as if to make a deep philosophical point. “If,” he said pontifically, “they are oriented in the same direction, we refer to the substance as orthohydrogen. If they are oriented in opposite directions, it is parahydrogen. ”