Sle føllen schreiben. Was soll das heißen? Es soll sich zugetragen haben. $ 84. You should write; you are to Chemical Characteristics of Cadmium.-By this time the student (1) The passive voice is formed by adding to the auxiliary werden, to become, through all its moods and tenses, the perfect participle of the main verb, thus : INDIC. ACTIVE. Pres. ich lobe, I praise, I have praised, Plup. ich hatte gelobt, I had praised, 1. Fut. ich werde loben, I shall praise, 2. Fut. ich werde gelobt haben, INDIC. PASSIVE. ich werde gelobt, I am praised. I have been praised. I had been praised. ich werde gelobt werden, I shall be praised. ich werde gelobt worden sein, I shall have praised, I shall have been praised, &c. (2) It will be noted, that wherever the perfect participle of the main verb (as gelobt above) is joined with the participle of the auxiliary, the latter is written worden, not geworden, whereby an offensive repetition (of the syllable ge) is avoided. Sometimes worden is altogether omitted in the past tenses, but this should be avoided. (3) The German, by confining werden with the past participle to the expression of passiveness and using fein, when the participle is to be taken as a mere adjective, has a manifest advantage over the English passive. Thus, if we wish to say, in German, he is feared, it will be, er wird gefürchtet! if the intention, howver, be merely to mark the state or character of the person as one who is feared, that is, whose character or conduct inspires fear generally, the German will be, er ist gefürchtet, he is (1) feared (man). The form of expression in English, it will be observed, is the same for both ideas: "he is feared." (4) The Germans, however, employ the passive form far less frequently than the English. They prefer other methods: thus, man fagt, one says, i.e. it is said; der Schüffel hat sich gefunden, the key has been found. LESSONS IN CHEMISTRY.—No. X. In order to obtain the solution on which future experiments are to be conducted, you may either select as a basis the metal cadmium itself, or the oxide of cadmium. Country readers may send each a letter to Messrs. Bland and Long, of Fleet-street, asking them to forward a few grains of cadmium, the expense of which will be very trifling. Cadmium is a soft white metal, in appearance very much like tin; it is frequently associated with ore of zinc, in a preparation of which metal, oxide of zinc, it was first discovered by Professor Stromeyer, in 1817. Cadmium readily dissolves in sulphuric acid (oil of vitriol), also in hydrochloric or muriatic acid (spirit of salt); perhaps the latter will best suit our purposes. Let the acid be dilute (four or five by measure of water to one of acid), and aid the solution by heat. Ascertain when the process of solution is complete that a little free acid is present, for on this acidity hinges a curious point in analysis. I need scarcely say this determination of acidity is accomplished by litmus paper in the usual manner. And now let me recall to your memory a certain fact. If hydrosulphuric acid gas be transmitted through a solution of zinc in either sulphuric or hydrochloric acid, no precipitate falls if either of the solution acids be in excess. On trying the experiment, however, with a solution of cadmium, we get a precipitate at once. This precipitate, you will remark, is yellow-so very much resembling the sulphuret of arsenic in appearance. that it is impossible by mere ocular inspection to discriminate between them. Their chemical characteristics soon point out distinctions; thus, for example, sulphuret of arsenic is soluble in ammonia, whilst sulphuret of cadmium is not; and still more conclusive is the result of heating with charcoal and carbonate of potash or soda in a tube. in the case of arsenic we get the well-known crust; in the case of cadmium we do not. The history of cadmium is very curious, and demands the attentive study of every chemist, as showing the necessity of extreme care in following out investigations. It is the custom throughout Germany for a government commission to examine druggists' shops from time to time, with the object of determining whether the drugs and chemicals are pure. In the year 1817, a certain commissioner, having examined a specimen of oxide of zinc, held by a very respectable druggist, pronounced it pearance developed on the addition of sulphuretted hydrogen. to contain arsenic. The commissioner was deceived by the apAgainst his decision the druggist appealed. Professor Stromeyer was called on to investigate the subject, and the result of his labours was the discovery of the new metal cadmium. Nothing can be more easy than the process adopted by Stromeyer for the separation of cadmium from the associated zinc. He dissolved both in hydrochloric acid, taking care that the acid remained in excess. He then transmitted a current of hydrosulphuric acid gas, and the cadmium was thrown down in the form of yellow sulphuret. The latter he collected, washed, mixed with black flux, and exposed to red heat in a crucible. The sulphuret was reduced, and metallic cadmium obtained. In other words, he pursued the exact course to obtain metallic cadmium, that you have pursued on many occasions now to obtain metallic arsenic, with the sole exception that he employed a higher temperature. The general theory of the routine for obtaining a metal from its sulphuret is pretty nearly the same; only arsenical sulphurets, however, are capable of being reduced to the metallic state, and the metal volatilized by the mere heat of a spirit-lamp flame. PERHAPS you will think we have had enough of arsenic, and that it is time to proceed to another metal. Presently we will do so, but before taking leave of arsenic altogether, we must not fail to notice a very elegant method of separating it, under certain circumstances, by the process of a German named Reinsch. Reinsch's process consists in adding to an arsenical liquid a few drops of muriatic acid, immersing a few slips of clear bright copper, and boiling in a glass or porcelain vessel. By this treatment, if any arsenic be present, it will, except under certain peculiar conditions, be thrown down upon the copper in the form of a crust. The copper tbus coated being then removed, thrown into the hydrogen generator, and the gas which escapes tested, the distinctive characteristics of arsenic will be observed. In bidding arsenic farewell, let me impress upon your memory the fact of there being no antidote to this poison. By the expression antidote, we mean Chemical Characteristics of Antimony.-The_metal antimony some body which has the property of counteracting the effects of a being one of those which, in certain states of solution, precipitate poison. For the most part, antidotes act by rendering the poison hydrosulphuric acid, yellow (we call it yellow by courtesy; its in question insoluble; for it is an axiom in medicine that che-true colour is orange), it forms a continuation of that thread we mical bodies only act on the animal system in virtue of their in-have laid hold of to conduct us through the labyrinth of chesolubility. I am aware that you will find in certain books a mistry. statement somewhat at variance with this remark of mine: you Antimony is in many respects a very peculiar metal. The will find charcoal mentioned as one antidote to the effects of learner would find it a difficult task to make a solution of this araenic, magnesia another antidote, and the hydrated peroxide of metal, therefore he will do well to procure ten or eleven grains of iron, a third. As come rns the two former, they have not the tartar emetic, a substance which contains antimony, and which slightest pretence to efficacy; the third is efficacious, but it will readily dissolves in water. Ten grains of tartar emetic, and about not keep, it must be prepared when wanted, therefore for all prac- two wine glasses full of distilled water, will form a very proper tical purposes it does not exist. We will now take up another solution for our future experiments. He must not omit, however, metal, cadmium. to make himself acquainted with the metal antimony as well. If he live in the country, he had better procure a small quantity in a bottle. Probably the village druggist will say he keeps antimony. He keeps that which is commonly sold by his trade under the name of antimony, but the substance is really a sulphuret of that metal. If the druggist chance to have real metallic antimony, he will know it by the name of Regulus of antimony. Having procured a little of the metal, observe well its general characteristics-its hardness, its steel-grey appearance, and its brittleness. Experiment 1.-Having put a fragment of the metal into a glass tube closed at one end, and surrounded the tube with a strip of stout paper in order to protect the fingers against heat, fig. 51, apply a spirit-lamp flame, and remark whether any portion of the metal be volatilised, as was the case with arsenic. You will find that antimony, although a volatile metal (as indeed all metals are, the difference being purely one of degree), is totally incapable of volatilisation by the mere flame of the spirit-lamp. Hence, whatever legal theorists may say, there can be no danger of confounding this substance with arsenic. Fig. 51. occurred in our experiments. All the metallic antimony has been rendered by this means insoluble; hence it follows that given the problem of separating antimony from an alloy, or mixture of antimony with another metal or other metals soluble in nitric acid, the separation may be effected in this simple manner. Now only one other metal exists which is rendered insoluble by nitrio acid, that metal is tin. Experiment 4.-Fuse together, in a tobacco pipe or iron spoon, equal parts of antimony and zinc. Break the mass into smal fragments by hammering, and pour upon the fragments nitric acid; wait until the action has ceased, wash the residue copiously with distilled water and you will have effected the separation of the two metals-the zinc will be obtained in solution, and the antimony will remain in the condition of white powder. Experiment 5.-I desired you a short time since to remark the orange-coloured gas which escaped on the addition of nitric acid to antimony. I shall have a great deal to state about that gas and its components hereafter; meantime I wish you to repeat the experiment with slight variations. Instead of conducting the operation in a closed vessel, use by preference a little flask, as shown in fig. 52, if you have it (a Florence flask would be too large); if not, a large test tube, i. e., a glass tube closed at one end, as in fig. 53. Experiment 2.-Lay a fragment of antimony upon a piece of charcoal, and direct upon it the blowpipe flame. Treated thus the metal is readily volatilised, but the greater portion of it deposits again on the charcoal in concentric rings. Remark the difference of effect between the inside and the outside blowpipe dame. Remember the appearance developed by the same treatment on zine,,and, if you please, repeat the experiment with that metal, in order that the results developed by it may be compared with those of antimony. Experiment 3.-Place a little powdered antimony in a watch glass, or something of that sort. Pour on it a little nitric acid faquafortis), and remark the violent action which takes place. Observe the orange fumes which are developed, and particularly Fig. 52. Having projected some roughly powdered antimony into the flask, pour upon it some nitric acid, rapidly replace the cork, and insert the delivery end of the bent glass tube under the mouth of the collecting bottle. These arrangements being made, the evolved gas will be collected. Remark, however, it is now no longer orange-coloured, but totally devoid of all colour. When the bottle becomes about half filled with the colourless gas, remove the delivery tube, or, what is still better, collect the which still comes over in a separate bottle. as Experiment 6.-Agitate, by a sort of underhanded motion, the gaseous contents, and remark that no absorption takes place. In there were absorption, the water-level of the bottle would rise. Experiment 7.-Place the half-filled bottle on the shelf of the pneumatic trough, and measure into it an amount of atmospheric air about equal to the amount of gas it already contains. Remark Specific Weight of Solids.-When solid bodies can be had only in the state of powder, their specific weight is determined in the following manner. Take a small glass bottle with a Irge mouth and a ground stopper or top exactly fitted to it; weigh the powder of the substance whose specific gravity is required, and place it in one of the scales of a balance, alongside of the glass bottle completely filled to the top with water, and carefully closed and wiped; next, put as much shot or grains n the other scale as will produce equilibrium; when this is obtained, take the glass bottle up and pour the powder into it; a certain quantity of water will now be forced out of the bottle, which must be carefully wiped and closed as before, and replaced on the scale whence it was taken. The equilibrium will no longer exist, seeing that the powder has taken the place of the water forced out of the bottle; weights must therefore be put on the scale alongside of the bottle until the equilibrium be restored; then, these weights will represent the weight of the water equal in volume to that of the powder. This being obtained, you have only to find the specific weight by a calculation exactly similar to that explained in ́our last lesson. It is necessary to observe that, in making this experiment, the air must be carefully excluded from the glass bottle, such as naturally adheres to the particles of a comminuted body, and occasions them to displace a sensible quantity of water. This exclusion of the air is effected by placing the bottle, after the powder has been poured into it, under the receiver of an air-pump, and exhausting it of the air it contains; or, by boiling the water into which the powder has been poured. It is necessary also that the powder be insoluble in water, or incapable of chemical affinity. Diamond, the heavier Specific Weights. Platinum, rolled 22.069 Platinum, hammered 20.337 Gold, hammered 19.362 Gold, melted, but not hammered 19.258 Lead, melted 11.352 Silver, mel.ed 10.474 Bismuth, melted 9.822 Copper, wire drawn 8-878 Copper, not hamnitred S.788 Sreel, tempered, but not hardened 7-816 7-788 Specific Weight of Liquids.-The specific weight of liquids may be determined, first, by the Hydrostatic Balance. Thus, to the hook of one of the scales of the balance, attach a body on which the liquid has no chemical action, as, for example, a ball of platinum. Weigh this ball successively in air, in distilled water at the maximum density, and in the given liquid, and observe the loss of weight which it suffers in water and in the given liquid; you will thus obtain two numbers, which represent the weight of equal volumes of water and of the given liquid; you have then only to divide the second weight Bodies Soluble in Water.-If a body be soluble in water, by the first, and the quotient will be the specific weight or neither of the methods of finding the specific weight of a body, specific gravity of the given liquid. Thus, let p be the weight which we have explained, will be available for this purpose. of the ball of platinum in air, p' its weight in water, and pits We must then find its specific weight relatively to a liquid in weight in the given liquid, d being put for the specific weight; which it is not soluble, as for example, alcohol. Having then, the weight of the water displaced by the ball of platinum found, by a process about to be explained, the specific weight is p-p', the weight of the given liquid displaced by the same is of alcohol relatively to water, we find the specific weight of the given substance, by multiplying its specific weight rela-2-p"; therefore, we have d—P—P". tively to alcohol by the specific weight of alcohol relatively to water. Thus, if under equal volumes, p be the weight of the p substance, p′ that of alcohol, and p" that of water; then will p' |