LESSONS IN CHEMISTR Y.-No. V. ON HYDROGEN. THE student will remember that in the first lesson he was told to prepare a certain combination of tobacco-pipes, corks, and large-mouthed bottles. They have not been employed hitherto, and the learner may consequently think I have forgotten all about them: not so. It has been my especial object to arrange these lessons in such a manner that manipulative details, or the directions for conducting the mechanical part of operations (and chemistry is full of such), may be interspersed with a due proportion of thinking philosophy. I shall continue to hold this object in view, and therefore shall not set off the manipulative part of chemistry by itself, but describe the manufacture of every instrument when wanted. Perhaps the operative student may have observed at any rate, he ought to have observed, for no phenomenon occurring during the performance of a chemical operation and appertaining to it should remain unnoticed,-I say he may have observed, that during the act of solution of the zinc in dilute sulphuric acid a certain gas was evolved. Now this gas is termed hydrogen; it is the lightest ponderable body in nature, and the common method of procuring it is really that which the student has already followed, namely, by the operation of dilute sulphuric acid upon the metal zine: iron will answer nearly as well. Perhaps, moreover, the student may have observed that the hydrogen gas thus developed had a peculiar smell; this, however, is a casualty-pure hydrogen is almost devoid of smell. I need not describe on what the smell depends just at this time, further than stating that the cause is a sort of oil generated during the process of dissolving zinc in dilute sulphuric acid. Let us now learn a few properties of this gas by experiment, generalising these properties hereafter. For this purpose, repeat the act of solution,-using zinc and dilute sulphuric acid as before, only let the solution be performed in the bottle instead of an open dish, and stop its mouth with the perforated cork, armed with its tobacco-pipe shank, immediately after the zinc and dilute acid have been poured into it. It is scarcely necessary to intimate that the mixture of sulphuric acid with the predetermined quantity of water can scarcely, with safety, be attempted in the bottle itself, on account of the heat developed. It requires to be effected in an earthenware basin, jug, cup, or something of that sórt. Having generated hydrogen in this way, we shall soon learn one of its most prominent qualities: causing a flame to approach the end of the tobacco-pipe shank, the hydrogen which escapes will immediately take fire, proving that it is combustible. In performing this experiment, it will be well for the operator to place himself at some little distance from the apparatus, because if the light be caused to approach the extremity of the tobacco-pipe shank before the generated hydrogen has forced out all the atmospheric air which the bottle originally contained, an explosion will be the result: not dangerous in itself, but it may be destructive to the clothes by the diffusion of the dilute acid in spray. Every phenomenon, as I have before remarked, occurring, during the performance of a chemical experiment is important, and should never be passed unchallenged. In the present case, we do not stipulate for an explosion; we will effect that purposely, and by a convenient process, hereafter. Nevertheless, should an explosion occur, it would only serve to anticipate a communication of the fact, that hydrogen gas forms an explosive mixture when mingled with air in certain proportions. If an explosion occur, replace the stopper, and wait this time before applying the flame until all the atmospheric air has been expelled. This period may be readily guessed at, or may be insured, by giving the operation a little more time. Applying now the flame, the jet of hydrogen will burn tranquilly. The next experiment we will perform shall have reference to the extreme lightness of hydrogen. It is this:-Attach to one end of a thin slip of deal, a drinking-tumbler, or other similar vessel, as indicated in the accompanying diagram at t, fig. 23, and to the other end of the same slip of deal any pan-like contrivance for the suspension of a counterpoise w; next, support the slip by a fulcrum f (an upright board, VOL. IV the apparatus be sufficiently delicate, the tumbler t will be raised, thus proving the levity of hydrogen gas. There are many processes of demonstration more elegant than this : several will be mentioned hereafter. There are none, however, of equal simplicity, as they require the use of apparatus not yet described. The next experiment to be mentioned shall have reference to the products of the combustion of hydrogen gas. For this purpose, ignite a jet of such gas as it emerges from the shank of the tobacco-pipe, and hold over the flame a widemouthed bottle or tumbler, as represented in the following diagram, fig. 24: After the lapse of a few seconds, the vessel, previously dry, will be bedewed with moisture. Where does the student believe the moisture comes from? His first idea, perhaps, might be, that it comes from little particles blown out, as it were, from the liquid in the bottle. În our rough experiment, probably a little is attributable to that source; but if every care be taken to dry the gas, still its combustion yields water-nothing but water. Hence hydrogen derives its name from vdwp, water, and yevvaw, I form; hydrogen, then, means the water-former. If, instead of a tumbler, the student uses a large-mouthed bottle (a soda-water bottle answers remarkably well), he will generally succeed in eliciting a roaring or singing noise, attributable to vibrations set up in the contained air by means of the burning hydrogen. The chemistry of gases is very delicate; I shall, therefore, when describing these bodies (the term sounds oddly to an unchemical ear, though it is correct) frequently require to mention instruments that the student neither has nor requires to have, a mere description of their form and mode of operation being sufficiently instructive. Of this kind is Cavendish's Eudiometer, the instrument by which the truth that hydrogen by combustion with oxygen (for that is essential) yields water, nothing but water, was first determined. In the experiment which we have performed, the hydrogen supplied itself with oxygen from the atmospheric air; but it would have been com« 84 although not very correct in its results. The second method is by exhaustion, as we have seen in the instance of Cavendish's Eudiometer. The third method, now to be described, is by far the most usual and most important,-collection by the pneumatic trough. If a bottle be taken, filled with water, and held thus inverted over water, I need hardly say the water which it contains will not escape; but if a jet of gas be liberated under the mouth of the bottle, it follows, from a consideration of some ordinary laws of hydrostatics, that gas being lighter than water, the former will ascend and the latter will descend, until ultimately the bottle becomes quite filled with gas, but empty of water. For this elegant contrivance we are indebted to the ingenuity of Dr. Priestley. In my sketch, fig. 26, I have represented m a common basin as the vessel in which the bottle is inverted, and I have represented the bottle as supported by the hand. I need not say this way of proceding is inconvenient; to give full effect to the operation one requires that the bottle shall stand without support, and that the vessel shall be large-one, in fact rather like a tub than a basin; a vessel thus modified becomes the pneumatic trough. As relates to the bottle or jar in which the gas is to be collected, it will stand quite well without any support provided its mouth be sufficiently wide; if circumstances of any kind require the use of a narrow-mouthed bottle, it may be supported in dozens of ways, readily occurring to the operator. The student need not expend one penny in the purchase of a pneumatic trough, except he has to deliver public lectures, and requires display. The first wash-bowl, kitchen-tub, foot-pan, or slop-basin he can lay hands on will answer sufficiently well; and as for the support, I will now just mention one that in many cases answers even better than a shelf. It is this. Fig. 27. Eudiometer, he then caused an electric discharge to traverse a pair of wires a b, penetrating the glass stopper s, so that an electric spark should pass through the space s': by this elegant contrivance the gas was ignited, and the sides of the vessel became bedewed with moisture, which on being examined was found to be water. As the experiment adverted to will scarcely be performed by any chemical novice, it would be a waste of time to describe in detail the construction and use of this beautiful instrument. I shall merely content myself, therefore, with observing that the stopper is screwed tightly down by means of a contrivance indicated in our diagram; and the foot m of brass is not permanent, but admits of being acrewed off at m', and the instrument attached to this point of junction to the receiver of an air-pump. The student will easily understand, that the air originally contained in the vessel being pumped out, a vacuum will ensue, and the stop-cock e being screwed on to a vessel containing gas, the latter will rush in. The method here described is not the usual one by which vessels are filled with gas; chemists accomplish the object far more readily by what is called the pneumatic trough, to be described presently. In the experiment of Cavendish, however, water would have been inadmissible as the filling agent, and mercury scarcely more eligible. Methods of Collecting Gas.-Two methods of collecting gases have already come under our notice. Firstly, we collected hydrogen by simply inverting a tumbler over a jet, through which the gas was escaping. This method is usually called that of a displacement, and is sometimes had recourse to, In great concern he ran to bear the sad tidings. the shape of a cone, the apex of which is truncated; next cut a notch in the lower or base edge of the cone, and the stand is The words printed in italics form an adverbial phrase. Adverbial made. The use of it will be evident from an examination of the diagram, fig. 28. The notch admits the gas delivering tube, the truncated apex delivers the gas into the bottle, which rests supported on the sides. If the student were not told of these contrivances he might think me remiss; but I want to create a feeling of independence in his mind, to impress him with the conviction, that in the majority of chemical operations involving the use of mechanical contrivances, many different methods admit of being followed, each equally good. The support just described is useful, and not inelegant, but I shall not quarrel with a student who tells me that two bricks set edgeways in a pan of water, fig, 29, furnish a support which is nearly as good. phrases involve what may be called an adverbial object; thus, in great concern is an adverbial object. Adverbial objects may be various; as, manner. A simple sentence is a sentence which has one subject and one affirmation or predicate; and a compound sentence is a sentence that has more than one subject and more than one predicate. The component parts of a compound sentence are called its members. These members may be two or more; they may also each form a separate sentence: 1 Compound Sentences of two Members. He will perish who loves unrighteousness. 1 The great fault of most books which treat of chemical manipulations is this:-they represent the apparatus which is not intrinsically best for gaining any particular result, but the apparatus which makes the prettiest engraving. This, in my The first sentence is equivalent to these two propositions :~~ opinion, is but a questionable benefit to the pictorial art, and a vast disadvantage to the student of chemistry. LESSONS IN ENGLISH.-No. LXXII. By JOHN R. BEARD, D.D. 1. Some one will perish. 2. The lover of unrighteousness will perish. The second sentence is equivalent to these two statements : 1. The lark sang his matins. 1 2 3 WE have already learnt that a subject may comprise a noun or When the Queen arrived, the fleet had weighed anchor and sailed. nouns standing in apposition to the principal noun; as, Principal Nour. Queen of England, conquered Burmah. This appositional clause or member proves when analysed to be a Thus what in the compound sentence stands as three members, sentence of itself; e. g., The essential quality of the adverb is to declare the quality of adverbs, and pronouns:an affirmation, thus: He writes well. Principal. ACCESSARY and is refreshed. The man is refreshed But the quality of an act may be assigned by an adverbial phrase Conjunc.. The man drinks when he drinks, "Oxford makes by much the best outward appearance of any city I have seen, being visible for several miles round on all sides. in a most delightful plain; and adorned with the steeples of the several colleges and churches, which make a glorious show." Here I must premise that the form "the best outward appearance of any city," &c., is incorrect, and should have been the best outward appearance of all the cities I," &c. This compound sentence may be reduced into these simple sentences :— 1. Oxford makes a very good appearance. 2. Oxford makes an appearance better than many cities. 3. I have never seen a city with a better appearance than Oxford. 4. Oxford is visible for several miles round. 5. Oxford is visible from all sides. 6. Oxford stands in a most delightful plain. 7. Oxford is adorned with the steeples of several colleges. 8. Oxford is adorned with the steeples of several churches. 9. The architectural decorations of Oxford make a glorious show. The resolution of this long sentence into the several distinct propositions which it contains, has, by showing the meaning of the several parts, prepared the way for our exhibiting the logical relations which those parts sustain to each other, thus : 1. Oxford In number one, who is of the first person, because I is of the first person; who is of the singular number, because I is of the singular number. The effect of the relative on the verb is more clearly seen in the second instance, where an s is added to the verb, which accordingly appears as reflects. As the language is now written and spoken by the best authorities, the relative who has one change of form in the nominative, namely, in which; which is commonly applied to things. Who, however, has a genitive and an objective, as well as a nominative case, and may be declined or inflected thus : Singular and Plural. SINGULAR AND PLURAL. WHO DECLINED. Neuter 3. the best outward appearance the object to 2 4. of any city 5. that I have seen 6. being visible 7. for several miles round 8. on all sides 9. in a most delightful plain 10. and adorned 11. with the steeples, &c. adverbial object to 2 appended accessary to 2 accessary to the subject 1 adverbial object to 6 second accessary to 1 adverbial object to 10 appended accessary to 10 Number six presents a case of explanatory apposition, since being visible is subjoined to the subject Oxford in order to state some additional facts respecting it; number ten stands to number one in the same relation. Number twelve presents an appended relative accessary sentence of which these are the components; namely, which, a relative pronoun agreeing with its antecedent steeples; make, a verb in the indicative mood, third person, plural number, agreeing with its subject which; a, the indefinite article limiting show; glorious, an whose of which (whose) adjective qualifying show; show, a common, noun dependent on or the object to the verb make. Viewed structurally, this appendage stands thus: Instead of whose and which we sometimes find whereof. which The word as is also used with the force of a relative after such, after you have resolved each into the simple propositions of which to many, the same; c. g., it consists, and explain by grammatical analysis (that is, "parse”) |