to in all glass manipulations), at the point where the closing is to be effected, it is softened at about a quarter of an inch on each side of this point, by means of a coarse blowpipe flame, produced by the mouth-blowpipe, or by one of those especially devoted to glassblowing. The glass must be slowly turned round in the flame, as well as moved from side to side, so that it may be uniformly heated; when it is pretty soft, it is very gently drawn out in the flame by slowly separating the hands, the tube being still rotated, until the end is drawn off; at the end of the tube thus formed, there will be a little knob of fused glass, termed a bleb, which is removed by means of a piece of glass rod, first gently heated in the flame, so that the bleb may adhere to it. Hitherto, the tube has been held in the left hand; it is now shifted to the right, without removing it from the flame, and so turned that the whole of the closed extremity may be uniformly softened; when this is the case, the tube is quickly removed from the flame, and blown into with a steadily increasing pressure, which will have the effect of regularly expanding those portions of the glass which have been thickened in the flame, and thus, of equalizing its thickness. If great pressure be suddenly exerted upon the soft glass, it will be blown out into a very large thin bulb, which will immediately burst. The sealing of tubes required to bear considerable pressure, is effected much in the same manner as the simple closure just described; but, in drawing off the end, it is retained in the blowpipe flame until it has acquired the necessary thickness, and no attempt need be made to take off the bleb. In the manufacture of glass bulbs, the latter may be required at the extremity of the tube (as in thermometers), or in the middle (as in the tubes employed in reducing metallic oxides by hydrogen); for the former case, a piece of tube of the proper thickness having been selected (of course, the thicker the walls of the tube, the larger the bulb may be made), it is closed at one end, in the manner above described, and the bleb removed; the closed extremity is then well and uniformly softened in the flame, and retained there until the glass has acquired a thickness proportionate to the size of the required bulb; the tube is then rapidly removed from the flame, and a steadily increasing pressure applied by the mouth till the bulb is of the proper size; if this is not the case after a first attempt, the bulb must be uniformly reheated (which will cause it to collapse), and again expanded. If the bulb is required on the body of the tube, one end of the latter, if not closed, must be stopped by a cork, the tube well softened regularly for about an inch, and then steadily expanded, as in the other cases; if the tube is rather thin, that portion upon which the bulb is required may be thickened, by gently pressing the tube, as it were, upon itself, when soft. Tubes of moderate width, drawn out to a long open point, are often required in testing for arsenic. These are made by well softening about an inch and a half of the tube (German glass), then removing it from the flame, and rapidly but steadily drawing the ends apart, till the narrow tube thus produced is of about twice the required length, so that two arsenic-tubes may be obtained by one operation; they are then separated by a sharp file. It is almost impossible to describe the manipulation requisite in drawing out the combustion-tubes for organic analysis, and none would be able to effect it after merely reading even the minutest description. The tube required is to be (of German glass) drawn out to a closed broad point, forming with the main tube an angle of about 45°, in such a manner that the section of the point in any part may be perfectly round, not flattened or elliptical; this is the result of a really difficult manipulation, which will be found to consist in forcibly drawing out the softened tube, with a peculiar turn of the wrist, which at once gives the proper angle, and preserves the roundness of the point. ELEMENTARY CHEMISTRY. § 68. AN element may be familiarly defined as a substance which cannot be resolved into anything further. Our present elements are only the boundaries to which chemical research has hitherto penetrated; we have no evidence that some of these may not ultimately be shown to be compounds. The number of elements at present discovered is sixty-four, of which only thirty-seven are ordinarily met with, the remainder being of comparatively rare occurrence, and, generally speaking, of little practical importance. These sixty-four elements are divided into two classes; the metals and nonmetallic substances, which latter are often improperly termed metalloids. The distinctive features of these two classes are, in many cases, not very decidedly marked, and some chemists therefore place amongst the non-metallic bodies certain substances which others rank with the metals. A division like this, founded, in some cases, rather upon opinions than upon facts, may be looked upon as useful in affording assistance to the memory, but should not be considered one of the important features of the science. We will state the chief points upon which this classification of the elements depends. A metal usually possesses a peculiar power of reflecting light, which is denoted by the term metallic lustre, and it is a better conductor of heat and electricity than are non-metallic substances. These are the chief physical differences; but it is in their chemical relations that the difference between these two classes of elements is most clearly perceived. The metals possess, generally, a great affinity for oxygen and the saltradicals (chlorine, bromine, &c.), with which they combine to form, respectively, bases and salts; in fact, this property of forming a base by combination with oxygen, may be almost regarded as a sine quâ non in the definition of a metal, for there are few metals which do not exhibit it; whilst none of the nonmetallic bodies are capable of forming basic oxides, and these latter are generally characterized by a tendency to form powerful acids by combination with oxygen. It may then be generally asserted that all elements which possess a metallic lustre, which are pretty good conductors of heat and electricity, and which are capable of forming basic oxides, are metals, and that those elements which are not thus distinguished, are non-metallic substances. The metals include by far the greater number of the elements, the nonmetallic bodies numbering, according to the usual division, only thirteen; but of these twelve are of considerable importance, whilst twenty-five only of the metals receive any application worthy of notice in this work. In the following list, the elements are enumerated, with their symbols and equivalents. To these metals we must now add DONARIUM, which was discovered in the present year by Bergemann, in certain Norwegian minerals. Another new metal, NORIUM, also claims a place in the list. Of the non-metallic elements, three, oxygen, hydrogen, and nitrogen, are permanent gases; and four, viz., chlorine, bromine, iodine, and fluorine, are known as the elementary salt-radicals. From the mineral wolfram. NON-METALLIC BODIES. OXYGEN.1 Sym. O. Eq. 8. Sp. Gr. 1.1057. § 69. OXYGEN was discovered by Priestley, in August, 1774, and one year later by Scheele, who was then unaware of Priestley's discovery. Eighty-nine per cent. (by weight) of water consists of oxygen; atmospheric air also contains twenty-three per cent. of the same element, which likewise exists in combination with most of the other elements in various proportions. Preparation. The most important methods of preparing oxygen are: I. By heating binoxide of manganese to redness in an iron retort (§ 23):— 3MnO, Mn,O,+0, = II. By heating moderately in a flask, retort, or hard glass tube, a mixture of powdered chlorate of potassa with about one-fifth its weight of binoxide of manganese. (The latter is not altered at the temperature employed, but by its presence considerably promotes the decomposition of the salt. Sand and sesquioxide of iron act in a similar manner, but with less energy.) The decomposition which chlorate of potassa undergoes, is shown by the following equation: KO.CIO,=KC1+0,2 The oxygen prepared from chlorate of potassa and binoxide of manganese, almost always contains small quantities of chlorine, of carbonic acid, and of aqueous vapor. If required perfectly pure, it may be passed, first through a tube containing fragments of hydrate of potassa, which removes the two former impurities, and afterwards through a long bent tube containing pumice-stone, moistened with oil of vitriol, to remove the moisture (§ 28). III. By heating the red oxide of mercury: HgO=Hg+0. IV. By heating together four parts of strong sulphuric acid, and three parts of bichromate of potassa : KO.2CrO,+4(HO.SO,)=KO.SO,+Cr,O,380,+4H0+0, § 70. Properties.-Oxygen is a colorless, inodorous, and tasteless gas, which From us, acid, and yvás, I produce. In heating chlorate of potassa by itself, if the process be arrested as soon as the evolution of gas begins to slacken, the salt will have undergone the decomposition represented by the following equation: 2KO.C10,=KO.CLO,+KC1+0. When the heat is again continued, the evolution is renewed with increased violence, and the whole of the oxygen is evolved. 3 Boussingault has recently described a method of obtaining oxygen directly from the atmosphere, by passing a current of moist air over heated baryta (BaO), which is thus converted into binoxide of barium (BaO,); by exposing the latter, in the same apparatus, to an elevated temperature, the second equivalent of oxygen is again evolved, and may be collected as usual. This process has the advantage of being continuous, since the same amount of baryta may be made alternately to absorb and evolve an equivalent of oxygen. has never yet been condensed to the solid or liquid form. It is very sparingly soluble in water. It supports combustion; any substance having considerable affinity for oxygen, on being introduced into it while undergoing combustion, burns with greatly increased brilliancy and rapidity. If a piece of charcoal be attached to a copper wire, heated in the blowpipeflame, and plunged with one point redhot into a jar of oxygen, it burns rapidly away, being converted into carbonic acid. Sulphur and phosphorus, kindled, and introduced into oxygen, also burn with great brilliancy (§ 33). A chip of wood which has been kindled and blown out so as to leave a spark on the extremity, immediately bursts out into flame when immersed in a vessel of oxygen, thus affording a rough test of the quality of the gas. Some substances (e. g. steel or iron wire), which only undergo gradual oxidation when exposed to the air, burn rapidly and brilliantly if introduced into oxygen, while in contact with some inflamed substance (§ 33). Oxygen is indispensably necessary for supporting respiration; animal heat and life being dependent upon a gradual combustion (a slow combination of combustible substances with the oxygen inspired) in the system. This combustion would, however, proceed too rapidly, if pure oxygen were inhaled (arterial action being increased to an enormous degree). The atmosphere contains this element in a proper state of dilution for respiration. Oxygen combines with all the elements (excepting fluorine); with many of them it unites in several proportions. Most of its combinations with metals have basic properties; those which it forms with metalloids are termed acids (§ 10). Some few metallic oxides, consisting of three equivalents of oxygen to one of metal (teroxides), and others containing still more oxygen, possess feeble acid properties (e. g. antimonious and antimonic acids, SbO, & SbO,; manganic and permanganic acids, MnO, & Mn,O,). The name of oxygen was given by Lavoisier to this element, because at that time all known acids were believed to contain oxygen. At the present time we are well acquainted with a number of acids that contain no oxygen, and many circumstances tend to favor the view that hydrogen is the real acidifying principle.1 § 71. Uses of Oxygen.-Oxygen is sometimes used to accelerate combustion, thereby much augmenting the heat and light of certain flames: it has been applied to this purpose in the Bude light, in which the flame of the Argand lamp is supplied with oxygen. Substances which are with difficulty oxidizable are frequently submitted to the action of pure oxygen at a high temperature; this is especially the case in the incineration of certain organic substances. § 72. OZONE. This remarkable body was first discovered by Schönbein. He detected it in the atmosphere (by means of tests to be presently described), and found it to be formed in almost every instance of electric discharge into the air; also, when water is electrolyzed, and when phosphorus is allowed to act upon moist air at ordinary temperatures. Preparation.-Ozone is best obtained by placing a piece of recently scraped phosphorus, about half an inch in length, into a clean bottle (of about two quarts capacity), in the bottom of which is as much water as will half cover the phosphorus; the mouth should then be closed slightly (to prevent any mischief ensuing if inflammation of the phosphorus should take place), and the bottle set aside. Ozone is almost immediately produced, its formation being indicated by the ascent of a column of vapor from the piece of phosphorus, and the luminosity 1 Some interesting experiments recently made by Faraday have shown that oxygen is possessed of decided magnetic properties. 2w, to smell. |