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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 sulphurić 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 zinc : 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 sort. 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 dia§ram at t, fig. 23, and to the other end of the same slip of deal *y pan-like contrivance for the suspension of a counterpoise " ; next, support the slip by a fulcrum f (an upright board,
terminating above in a sharp edge, will do). These preliminaries being arranged, place under the suspended and inverted tumbler the tobacco-pipe stem delivering hydrogen gas. If
the apparatus be sufficiently delicate, the tumbler t will be raised, thus proving, the levity of hydrogen gas. There are Imany 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
petent for the operator to have mixed it with oxygen previous to combustion; and this is what the chemist Cavendish did, Having effected a mixture of oxygen and hydrogen, and filled with this mixture a thick glass vessel, as represented in the accompanying diagram, fig. 25, and since known as Cavendish's
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 becamebedeved 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 on 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 & 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 to 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,
although not very correct in its results. The second taethod 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 theingenuity of Dr. Priestley. In my sketch, fig. 26, Ihave represented
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.
* * ~ * -------- : ~~~~ LESSONS IN ENGLISH. * = * * * 79
the shape of a cone, the apex of which is truncated; n CO%2C67% 2- . * ~ *
a notch in the i wer or base edge of the cone, and the : In aread: * he ran to bear the sad tidings. The use of it will be evident from an examination of The words printed in italics form an adverbial phrase. Adverbial
made. the diagram, fig. 28. The notch admits the gas deliveri tube, the truncated apex delivers the gas into .#bottle .# rests supported on the sides. 3. 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 contriyances, 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, 1. Of time: ; On arriving home I hastened to bed. 2. Of place: He slew his foe in the dell. 3. Of manner: The father begged his life with many supplications.
An object, then, may be not only single or compound,
near or remote ; as,
Near : He sold his desk;
but also adverbial, and that of three kinds,--of time, of place, of Polannels.
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 mem. bers. These members may be two or more; they may also each form a separate sentence:
Compound Sentences of two Members. 1. 2
He will perish who loves unrighteousness.
The laking his matins and sank ai. his nest. The first sentence is equivalent to these two propositions 1. Some one will perish. 2. The lover of unrighteousness will perish. The second sentence is equivalent to these two statements “T
1. The lark sang his matins. 2. The lark sank into his nest.
Compound Sentences of three Members.
l 2 3 when the Queen arrived, the fleet had weighed anchor and sailed. 1. The Queen arrived. 2. Before then the fleet had weighed anchor. 3. Before then the fleet had sailed.
Thus what in the compound sentence stands as three members, becomes in the analysis three individual sentençës. It is easy to see that the members may be increased almost at pleasure :The sick and all but dying man drinks water and revives. Compound sentences have members of two kinds, the principal and the accessary. The principal member is that which enunciates the leading thought, the accessary member is that which enunciates the subordinate thought Principal Member. The man drinks (and) The accessary member (or members) may * * namely, interposed or appended. An accessary member is inter; posed when it appears in the body of a sentence, being introduced by a relative pronoun, a relative adverb, or a conjunction 3 °. 8-2
Access ARY MEMBER: is refreshed.
be of two kinds,
Principal. ACCESSARY Principal. INTERPOSED. Re. Pron. : The man who drinks is refreshed Rel. Ad, The man when he drinks is refreshed Conjunc.: The man if hedrinks is refreshed
Appended members are added by means of conjunctions, adverbs, and pronouns:
But the quality of an act may bé assignéd by an adverbial phrase as well as by a simple adverb; e. g.,
ACCESSARY Principal. APPENDED Conjunc.. The man drinks . . and is refreshed. Adv, ; The man is refreshed when he drinks,