A sharp crack follows the passage of the spark, and the tube is instantly coated throughout its entire length with a black deposit consisting of carbon and sulphide of mercury. It is supposed by some that this decomposition of the disulphide of carbon is caused by the actual shock produced by the detonation of the fulminate; that, in other words, the particular vibration set up by the explosion is the cause of the rupture of the molecules of the disulphide. It is quite conceivable, however, that the chemical affinity between the mercury, which is evolved from the exploding fulminate in a state of vapour at a high temperature, and the sulphur in the disulphide is in a measure concerned in effecting the decomposition, if, indeed, it 'is not the chief cause; it is significant that other explosives which do not contain a metal with which the sulphur could combine appear quite incapable of bringing about the same result. Mercuric fulminate is most readily made in the following way-10 grams of mercury are dissolved in 80 cubic centimetres of strong nitric acid (sp. gr. 1·42) with gentle warming. When the whole is dissolved 80 cubic centimetres of water are added and the solution cooled; 100 cubic centimetres of methylated spirit are added to the solution, and the mixture gently warmed in a flask of about 1 litre capacity. A brisk action soon sets up, which, however, with these proportions, never becomes uncontrollable, and the fulminate of mercury separates out as a greyish-white crystalline substance. The liquid is decanted off and the crystals washed and drained. The dry fulminate should be kept in bottles containing only a small quantity in each, and the bottles should be closed with corks and not with glass stoppers. ARSENIC 599. The element may be prepared on a small scale by reducing arsenious oxide. A mixture of arsenious oxide, sodium carbonate, and powdered charcoal is introduced into a piece of combustion tube closed at one end, and heated by means of a Bunsen flame; the arsenic sublimes, and condenses as a black lustrous deposit upon the tube. Care should be taken to thoroughly dry the charcoal and the sodium carbonate before using them for this experiment, as the moisture they contain, condensing upon the tube, is liable to run back and cause its fracture, and also to prevent the formation of a good mirror. 600. The volatilisation of arsenic in a current of hydrogen may be shown by gently heating a fragment of the element in a piece of rather wide combustion tube, through which a slow stream of hydrogen is passed; the issuing gas should be allowed to escape into a suitable draught flue. As the piece of arsenic is heated it will be seen to vaporise without melting, and to sublime along the tube as a lustrous mirror. That portion of the deposit which is nearest to the flame will be seen to be distinctly crystalline, and to have a steel-grey colour, while that which is more remote from the heated part is amorphous in character, almost black in colour, and of a vitreous lustre. 601. To show the combustion of arsenic in oxygen. FIG. 191. From 3 to 4 grams of arsenic are placed in a piece of combustion tube, about 30 centimetres long, at a short distance from the end, and a gentle stream of oxygen passed over it; on heating the arsenic at a point nearest to the incoming oxygen the element ignites, and burns with a brilliant bluish-white light. The product of the combustion may be passed through an empty cylinder, where a large quantity of the arsenious oxide condenses, and then delivered into a draught flue. 602. The combustion of arsenic in chlorine. This may be shown in the same manner as described for the combustion of antimony in chlorine, Experiment 156. 603. The combustion of arsenic in bromine. See Antimony in Bromine, Experiment 211. ARSENIURETTED HYDROGEN. AsH, 604. Preparation by the action of nascent hydrogen upon arsenious oxide. Hydrogen is generated in a small Woulf's bottle from granulated zinc and dilute sulphuric acid. The exit tube should be about 7 millimetres in the bore, and the end within the bottle should be cut diagonally, in order to prevent any liquid collecting at the end, and so preventing the flame from burning steadily. Attached to the exit tube is a piece of FIG. 192. hard glass drawn out in the manner shown in the figure. When the air is expelled, the hydrogen is ignited at the end of the tube, and a few drops of a solution of arsenious oxide in hydrochloric acid are introduced As soon as the acid solution rapidity of the evolution of by means of the thistle funnel. of arsenic enters the vessel the hydrogen is greatly increased, so that care must be taken that the gas is only being quite slowly evolved at first, or the reaction may become rather tumultuous, and the liquid in the bottle froth over. . As soon as the arseniuretted hydrogen finds its way into the flame, the latter at once assumes a characteristic pale lilac colour. The apparatus should be so arranged that the products of combustion can be led into a draught flue. 605. If a cold porcelain dish be depressed upon the flame a deposition of arsenic at once takes place, as a brownish-black shining spot. 606. To show the action of heat upon arseniuretted hydrogen. The hard glass tube is strongly heated at a point where it is constricted. The arseniuretted hydrogen is decomposed into its elements, the arsenic being deposited as a mirror upon the sides of the tube. If the current of gas be not too rapid the whole of the arsenic will be so deposited, and the flame will no longer produce a stain upon porcelain. It will be seen that the arsenic deposit in the tube is entirely formed upon one side of the flame-namely, on that side farthest from the generating apparatus. ANTIMONY 607. The amorphous variety of antimony is prepared by the electrolysis of a solution of tartar emetic in antimonious chloride. 250 grams of tartar emetic are dissolved in one kilo of crude antimonious chloride, and the solution placed in a beaker, which it about two-thirds fills. The positive electrode should be as large a lump of metallic antimony as will conveniently hang in the beaker and still leave room for the negative pole-a piece of the metal weighing about two kilos will be convenient; a copper wire is soldered to one end of the lump, which must be suspended in the liquid to such a depth that the solder is not immersed. By using so large a positive electrode the solution does not become weakened, and the deposition of the antimony is therefore much more rapid. The negative electrode upon which the antimony is to be deposited may be a stout and clean piece of copper wire. The current for the electrolysis is best derived from two Smee's elements, which should be suspended in large beakers holding about one or one and a half litres of dilute acid, so that the experiment may be allowed to go on uninterruptedly for several days. So arranged, in four days the rod of amorphous antimony will be about the thickness of a finger; it may then be removed from the beaker, rinsed in distilled water, and either hung up to dry, or carefully laid upon blotting-paper. When struck or scratched, the amorphous antimony undergoes a molecular change, which spreads quickly throughout the entire length of the rod. This change is attended by a considerable evolution of heat, the temperature rising to 250°C., and dense fumes of antimonious chloride are evolved. If a piece of gun-cotton be tied round one end of the bar, before it is struck at the other end with the edge of a spatula, the gun-cotton will be inflamed by the heat generated by the change. 608. To show the combustion of antimony in oxygen. A fragment of antimony is placed upon a piece of charcoal, having a shallow hollow scooped out of it, and a spirit-lamp flame directed upon it by means of a jet of oxygen. The metal almost immediately melts and begins to burn; the lamp is then removed, and the metal will continue to burn brilliantly in the stream of oxygen gas. If while in a state of combustion the globule be thrown upon a large sheet of cartridge paper, the edges of which have been folded up in the form of a shallow tray, the globule breaks up into a number of smaller ones, which run about over the paper, |