The Lift and Force Pump.-This pump raises water both by suction and by pressure, that is, both by atmospheric pressure and by mechanical pressure. It has a solid piston, and at the bottom of the barrel on the top of the suction-pipe, a valve s opening upwards, fig. 114. Another valve o, also opening received, reacts on the water and raises it in the tube D, until the piston re-descends; and in this manner, the jet continues without intermittance. is raised to the required height, the force necessary to raise it by pressure on the piston continually increasing until it reaches that height, and is discharged from the ascension-tube. In another form of the forcing-pump, there is no use made The Load of the Piston.-In the pump just described, after of the pressure of the atmosphere. The suction-tube, of course, the water has filled the suction-pipe and the barrel up to the is dispensed with, and the pump-barrel is itself immersed in mouth of the jet, the force necessary to raise the piston is equal the reservoir of water to be raised. The continuity of the jet to the weight of a column of water having for its base the of water from the ascension-pipe is obtained by the action of horizontal section of the piston, and for its height the vertical a vessel or reservoir of air, which we shall explain in the follow-distance of the orifice of the jet from the level of the water in ing description of the pump called the lift and force pump, and the reservoir from which it is drawn. Thus let н be the pressometimes the suction and forcing pump, which differs but little sure of the atmosphere, the height of the water above the from that just described, except in the application of the air- piston, and h' the height of the column of water which fills the vessel to produce continuity in the flow. This object is also suction-pipe and the lower part of the barrel. The pressure accomplished by the operation of two pumps acting alternately, above the piston is evidently H+, and that below the piston as in the construction of the common fire-engine. H-h', since the weight of the column h' tends to balance the pressure of the atmosphere. Now, the pressure H- tends to raise the piston; the effective resistance, therefore, is the excess of H+h, above H-h'; that s, h+h', which was to be proved. Practical Application of Pumps.-In practice, the following rules are observed in the construction of pumps. The velocity of the piston is calculated to vary from six to nine inches per second. The area of the aperture covered by the valves is about half that of the barrel of the pump. The diameter of the suction-pipe, and of the ascension or discharge-pipe, is about two-thirds of that of the barrel of the pump. The stroke of the piston in large pumps varies from three and a half to five feet. In good pumps the loss occasioned by the time required for shutting the valves reduces the effect to about four-fifths of that produced by the piston. The following figures present different models of pistons and valves employed in the construction of pumps. Fig. 115, a piston packed with leather; fig. 116, a piston packed with hemp; fig. 117, a piston furnished with a single clack-va've; fig. 118, a piston with a double-clack or butterfly valve; fig. 119, interior of the barrel of a pump, in the bottom of which a single clack-valve works; fig. 120, separate view of a single clack-valve; fig. 121, a conical valve. Fig. 114. Fig. 118, Fig. 120. upwards, closes the aperture of a bent pipe, which, passing under the metal plate a, connects the valve s with the air-vessel M. From this vessel or reservoir of air, proceeds the ascension pipe D, which is employed to raise the water to any given height. At every ascent of the piston B, the water rises in the suction-pipe A and enters the barrel. When the piston descends again, the valve s is shut, and the compressed water raises the valve o in order to enter the reservoir M, and thence pass into the ascension-pipe D, in which the height attained by the water is only limited by the force of the moving power which keeps the pump in operation. If the pipe D were only the continuation of the pipe J, the flow or jet of water would be intermittent, taking place only when the piston descended, and stopping as soon as it ascended. But the continuity of these tubes is interrupted by the air-vessel M, by means of which a continued jet is maintained. The water thrown into this vessel is divided into two parts, of which the one raised in the tube D compresses the water in the reservoir M; while the other, in consequence of this pressure, is raised in the reservoir above the lower orifice of the pipe D, by the compression of the air which is above it. Consequently, when the piston re-ascends and no longer acts so as to compress the water, the air of the reservoir M, by the excess of pressure which it has explanation of this invention: but as it is connected with the Fg. 121. Bramah's Hydrostatic Press. We have already given an explanation of the forcing-pump, we repeat it here under another form, its importance demanding additional elucidation. The hydrostatic press is a beautiful application of a principle previously known for nearly two centuries, and commonly called the hydrostatic paradox; viz., that any quantity of water, however small, may be made to balance any quantity however great. The practical effect of this principle is, that when water enclosed in a vessel quite full of the liquid, is pressed by a piston at any aperture with a given force, this pressure is at once communicated to every part of the vessel of the same size as the aperture, with the same force. Mr. Bramah, by an ingenious application of the forcing-pump to an apparatus constructed on this principle, produced one of the most powerful and useful machines used in the present day. It is represented in fig. 122, where s is the piston which moves in the cylindrical succession; and let us suppose that the lower extremity of the tube g is placed between the two ajutages b and c. 1st. If we open first the ajutage b, the water runs out, its level is lowered in the tube g, and as soon as this level reaches that of b, the run of water is stopped. This phenomenon is explained by the fact of the excess of inward pressure which took place first at b; an excess which disappears when the level of the water in the tube g is brought down to b. For, before the water issued from 6, the pressure on all points of the horizontal stratum be was not the same. At e, it was composed of the pressure of the atmosphere and the weight of the column of water ge, whilst at b, the pressure was that of the atmosphere only. But as soon as the level of the water is the same at e and at b, there is an equilibrium, because that in the bottle and in the tube the pressure is then the same on all points if Fig. 188. tube ƒ, or small barrel of the pump; p is the piston which moves in the cylinder ce', or large barrel of the pump; and at bu is the tube of communication between the two barrels of the pump. A lever of the second kind raises the piston s, and the water in the reservoir b' is drawn into the barrel of the pump f. When the lever is pressed downward, a valve shuts, and prevents the water from returning into the reservoir b', and forces it along the tube tbu, in order to act upon the lower extremity of the piston p, to which is attached the plate p'; ef is another plate, against which the objects to be compressed by the machine are pushed by the former. In consequence of the quaquaversal pressure of the water forced into the large barrel of the pump from the small one, the pressure of one pound on every square inch of the surface of the liquid in the latter will be communicated to every square inch of the surface of the liquid in the former. Hence, if the diameter of the piston s be one inch, and that of the piston & be ten inches, the pressure of one pound on the former will be 100 lbs. on the latter. A noble specimen of this press was exhibited in the Crystal Palace by the Bank Quay Foundry Company, Warrington; viz., that which was used for raising the Britannia Tubular Bridge. The greatest weight lifted by this press was 1,144 tons, and the quantity of water used for every lift of six feet, was 81 gallons. The internal diameter of the great cylinder was twenty-two inches, and that of the ram or piston twenty inches. all directions in the interior of the bottle, according to the Mariotte's Bottle.-The bottle of Mariotte is an apparatus principle of Pascal formerly explained, and the upper side k which exhibits some remarkable examples of the pressure of resists an upward pressure equal to н-ko; for the weight of the atmosphere, and by means of which we may obtain a con- the column of water ko partially counteracts the pressure stant flow. The neck of this bottle is closed by a cork, through which is transmitted to k. Now, according to the mechanical which a glass tube passes, open at both ends; in the side of principle, that reaction is always equal and contrary to action, the the bottle there are three apertures furnished with ajutages, pressure H-ko is urged downward by the side k on the stratum a, b, c, at right angles to the side and closed by wooden pegs. be; so that the particle of water at o, supports in reality two When the bottle and the tube are quite full of water, let us pressures, the one equal to the weight of the column of water consider the effect of opening one of the ajutages, a, b, c, inko; the other, the pressure н-ko, resulting from the reaction of the side k. The real pressure, therefore, which the particle | remembered that inasmuch as our desire is not merely to at o supports is ko+n-ko, that is, н the pressure of the atmosphere; which it was proposed to demonstrate. 2nd. If we shut the ajutage b, and open the ajutage a, there will be no run of water; on the contrary, the air will enter the bottle by the aperture a, and the water will rise in the tube g to the level a d, when the equilibrium will be restored. For it is easy to perceive by reasoning, as in the preceding case, that the pressure is then the same at all points of the horizontal stratum a d. 3rd. Let the apertures a and b be closed, and the aperture e be open. In this case, there will be a run of water with a constant velocity so long as the level of the water in the bottle does not fall below the level of the lower orifice / of the tube: for then the air would enter this orifice and fill the upper part of the bottle, where it would take the place of the water run off. In order to demonstrate that the flow of water at e is constant, it is necessary to show that the pressure on the horizontal stratum c h is always equal to the pressure of the atmophere increased by that of the column hl. Suppose, then, that in the bottle the level of the water is lowered to the stratum ad. The air which has entered the bottle supports a pressure equal to H-pn. In consequence of its elasticity, the air transmits this pressure to the stratum eh. Now, this stratum supports besides this, the weight of the column of water pm. Therefore, the pressure transmitted to m is in reality, pm+H -pn, or H+mn, that is, +h. In the same manner, it would be demonstrated that this pressure is the same, when the level is lowered to eb; and so on, so long as the level is above the orifice ; the pressure on the stratum c h is therefore constant, and so is the velocity of the flow. But as soon as the level falls below the point, this pressure decreases, and consequently the velocity of the flow diminishes. Thus, we see that the bottle of Mariotte is a means of obtaining a constant flow; namely, by filling it with water and opening the ajutage or aperture placed below the orifice of the tube. The velocity is then proportional to the square root of the height 1h, as shown in a former lesson. LESSONS IN CHEMISTRY.-No. XXII. In the course of any chemical examination, and more especially of metals, we find certain compounds demanding our especial attention. Amongst all the combinations of mercury, perhaps the bichloride, or corrosive sublimate, is that which claims our prominent notice. It is a terrible poison: its discovery and identification, when mixed with animal fluids, involve many points of chemical interest, and the manipulative processes employed in its extraction are of great beauty and delicacy. I must premise by directing the student's attention to the fact of there being two chlorides of mercury-one the protochloride, ordinarily known as calomel; the other, bichloride, ordinarily known as corrosive sublimate: the respective compositions of which are as follow: discover a certain metal, but a given compound of a certain metal, we shall require not merely a test for mercury, but for that which is combined with the mercury and holds it in solution. Let us begin with a very characteristic test for soluble persalts of mercury generally-a solution of iodide of potas sium. The effects of this test are most remarkable, as will be seen. Having poured a weak solution of bichloride of mer cury into a test-tube or a conical glass, add to it, drop by drop, another solution of iodide of potassium, and remark the beau tiful play of colours which result, also the disappearance of all colour, all precipitate, and the resumption of perfect transparency in certain states of dilution; that is to say, so soon as a certain amount of test liquor has been added. It is useless to expatiate on changes which can be seen very much better than they can be described, but I may remark that by reversing the order of experiment in testing, and adding the bichlo ride solution to the iodide of potassium solution, instead of adding the latter to the former, the chromatic effects will vary. Now the peculiar effects here detailed are characteristic of a persalt of mercury; and the only persalt of mercury at all likely to come under one's notice in a case of poisoning is the perchloride of mercury; however, any doubt can be at once cleared up by the addition of the test for chlorine. Now what is the test for chlorine? You remember, I presume, that it is nitrate of silver-the reaction of that substance having already, under the head of "Silver," come before us. Add, then, a little nitrate of silver solution, and a white precipitate results. But there are thousands of white precipitates; how shall we know what this one is? Simply by adding hartshorn (liquor ammonie) to it, the white precipitate dissolves. It has been produced, therefore, by chlorine. We have already determined the presence of mercury, therefore our substance must be a chloride of mercury. But as there are two chlorides of mercury, which is this? It cannot be the proto-chloride of mercury because that substance is insoluble; it must, therefore, be the per- or bichloride of mercury. Thus, at length, we arrive at the demonstration. The next test we shall employ is ether; a liquid which, by the way, is rather to be considered as a separator than a test in the ordinary acceptation of the term. Having poured a little bichloride solution into a narrow test-tube, add to it about an equal volume of rectified ether always mean sulphuric ether), then closing the tube with (when the term "ether," without prefix, is used, chemists the thumb, agitate the tube. Proceeding thus, the ether and the bichloride solution will become intimately mixed. This mixture being effected, cork the tube (to prevent evaporation of the ether) and allow it to stand for the space of a few minutes at rest. Presently two distinct fluid layers will be recognisable; so well marked, so thoroughly individualised, that one may be readily separated from the other. The best 8, by the use of a little glass instrument termed a pipette. means of effecting the separation is, as represented below, fig. Fig. 8. Hence the ratio of chlorine in these two chlorides is as one to two. Calomel may be generated in various ways. The student has already generated it by the addition of common-salt solution to proto-nitrate of mercury, and he will not fail to see, by reference to the preceding tabular exposition, that if by any process we can succeed in taking from a given weight of sublimate half the chlorine it contains, the result will be calomel; and if we can succeed in removing the whole of its chlorine, the result will be metallic mercury. Chemical investigation of Bichloride of Mercury in simple and complex fluids.-Taking a portion of the solution of bichloride of mercury already prepared, let us master the appearances it The student, however, who does not possess the instrument affords with tests in simple solution. And here it will be may accomplish his result perfectly well by means of a glass Well, having separated the supernatant layer of fluid, deposit it on a watch-glass, and allow evaporation to take place. Ether is a fluid so exceedingly volatile in its nature, that the application of a very slight amount of heat is necessary to effect this volatilisation. It suffices for this purpose to hold the watch-glass in the palm of the hand. Evaporation having ceased, that is to say, all the ether having been removed, the watch-glass will be found to contain a portion of white solid material. If the white solid material be viewed through a lens it will be seen to be crystalline. What is it? Nothing more nor less than solid bichloride of mercury, which happens to possess the quality of being more soluble in ether than in water; hence ether removes it from water as we have seen. This is a very elegant test, and most useful under certain conditions. It is not, however, a good quantitative test; that is to say, the operator can never depend on removing by its agency the whole of the bichloride actually existing in a liquid. This fact was first demonstrated by the French chemist Devergie. Nevertheless we must not underrate the value of the test. poisoning cases it is a great point to make out the existence of a poison in any quantity, seeing that the law does not propound to the analytical chemist the question-"Have you extracted all the poison?" but, "Have you extracted a sufficiency to account for death?" Again, the ether test has the rare advantage of acting equally well in animal and vegetable fluids as in pure water. In The next test we will employ is the white of egg. For this purpose it will be well to beat up the substance, white of egg, with water, and strain through muslin; by proceeding thus we shall get rid of much animal membrane that would be embarrassing to the result. Having prepared the test as described, add a portion of it to the bichloride solution, and remark the white curdy deposit which results. At one time this precipitate was imagined to be calomel,-the action of the white of egg being assumed to accomplish the removal of one half of the chlorine. It is not thus: the precipitate is an actual chemical compound of white of egg (albumen) and the bichloride. At any rate it is almost, if not quite, insoluble in water and the gastric fluids; hence it is innocuous, and this is the great point to be remembered in practice. Under the head of "Tin" (during the investigation of which metal we had occasion to employ bichloride of mercury as a test), I stated that white of egg was the antidote to bichloride of mercury. You will now clearly see why, for what reason, in virtue of what chemical reactions, it is an antidote. In our next lesson we will consider the best means of extracting bichloride of mercury from complex animal and vegetable solutions, You thus see that the root of the form is Av. This is called the root because it remains permanent under all the changes. Thus you find it in λυσω, in λυσόμενος, ελύθην, &c. By prefixing certain letters to Av, and by adding certain letters to Au, you make all the varieties of form and signification. Thus, if you want to say I loose, you add w as λv-w; if you want to say they loosed, you prefix and add cav, thus, e-Av-oav. The prefixes and suffixes, by whose aid the root is thus modified, may be termed formative syllables. A knowledge of these formative syllables, combined with a knowledge of the several roots, will make you proficient in the grammar of the verbs. You will do well to make a distinction between the root of a verb and the stem. The root of a verb is the verb reduced to its ultimate or most simple form. It agrees with the stem in being generally the stem of the present tense, active voice. But it differs from the stem, inasmuch as it is one primitive form; and there are several etems-the stem of the present, the stem of the imperfect, the stem of the perfect, &c. The stem of a tense is that form which remains when the personal endings and the mood characteristics are taken away. I present the stems of the root, and of several tenses of TUπTW, I strike. Personal-endings. TUTT ETUTT ει he strikes ε thou, &c. E he struck ες he has struck ας Ε he has struck ας εις. τετυφ ετετυφ ε he had struck Imperfect Stem First Aorist Stem erv↓· Perfect Stem Pluperfect Stem That is to say, if to the present stem I add el, I get TUTTEL, which means he strikes; if to the pluperfect stem I add eg, İ get ETETUDES, which means thou hadst struck. So, if from rerupas I take away aç, I get the perfect stem rerup. If I want to make the perfect stem into the pluperfect stem, I prefix the augment ε, and make ererup. If, again, I wish to resolve TETUP into the root, I cut off the augment TE, and change the aspirate into the corresponding soft, and so obtain TUT. This the root I may raise into the present stem by affixing 7, thus-TUTT. And TUTT I may change into the imperfect stem by prefixing the augment of that tense, namely, ɛ. THE AUGMENT. After these general explanations, you are, I presume, prepared to enter into particulars. First, then, let us consider the augment or temporal prefix. I call the augment temporal, because its function is to denote past time; and I call it a prefix, because it is put at the beginning of the root or stem. The augment is of two kinds; first, syllabic; second, temporal. It is syllabic when it adds a syllable to the verb; it is temporal when it lengthens the initial vowel of the verb. The syllabic augment is of two kinds, it is simple or reduplicative; for instance, it is simple when it merely prefixes a vowel, as in λumov, I was leaving; it is reduplicative when it doubles the initial consonant, as λɛλvka; here is called the simple syllabic augment, and Xe the reduplicative. The syllabic augment is employed when the verb begins with a consonant. If the verb begins with a vowel, the temporal augment is used, the vowels a and being changed into n or εt, and i and (iota short and upsilon short) being changed into and ; o is changed into . The simple syllabic augment is found in only the indicative mood; the reduplicative extends through all the moods. The simple syllabic augment is used with the imperfect tense and with the aorist. The reduplicative augment is used with the perfect tense, the pluperfect tense, and the third future, sometimes called the paulo-postfuture. If, however, the verb begins with a vowel, the perfect and the pluperfect have, instead of the reduplicative, merely the temporal augment. The pluperfect has a double augment, inasmuch as it prefixes the simple augment ɛ to the reduplicative re, &c.; for instance, &TETVOEL. Fuller details will be given hereafter. My object in these general remarks is to afford you assistance to understand and commit to memory a general paradigm of the verb. CHARACTERISTIC LETTERS. I have previously used the terms pure verbs. This is one class into which verbs are divided. Verbs are divided generally into classes, according to the characteristic letters of the present tense, or the stem of the present tense. The letter which stands immediately before the w of the present tense is called the verbal characteristic; thus, in Avo, the v is the characteristic of the verb; and in TUTTш the 7 is the characteristic T The personal endings are the terminations by which the variations of person are indicated. They are closely connected with the mood-signs, which are the vowels that indicate the several moods. For example:1Per.Sin. Ind. Pres. M. Bovλev-o-μai Subj. βουλευ-ω-μαι of the verb; and in TAA, the A is the characteristic of the 3 Pers. Sing. Ind. Fut. Bovλev-v-E-raι Opt. Bovλev-o-01-70 verb. If the characteristic is a vowel, the verb is called pure, 1 Pers. Plur, Ind. Pres. Bovλev-o-pela Subj. Bovλev-w-peda e.g. Avw; if the characteristic is a consonant, the verb is called 2 Pers. Plur. Ind. Pres. ẞovλev-e-oØ£ Subj. βουλευ-η-σθε mute, e.g.runTw; if the characteristic is a liquid, the verb is 1Pers. Sin. Ind. Aor. I sẞovλev-σ-a-μnv Subj. Bovdev-o-w-pai called liquid, e. g. σTEλλw, I send. Thus there are three kinds 3 Pers. Sin. Ind. Aor. 1 eBovλev-o-a-ro Opt. Bovλev-6-a-ro of verbs. Pure. Tiμaw, I honour. Mute. τριβω, Ι ναό. FLEXIONAL TERminations. Liquid. φαίνω, I show. In these instances Bovλev is the root, and eßovlevo is the stem of the first aorist, while Bouλevo is the stem of the future. The personal endings are pat, rat, pela, ro, &c. And the moodsigns are the vowels o, w; e, n a, ai. Mark how readily the one permanent form Bovλev takes to itself other forms, to suit modifications in the sense. Mark, also, that the short vowels represent the indicative, and that these short vowels are changed into their corresponding long ones for the subjune Another kind of characteristic letters or syllables are the inflexions, which mark the time (tense), the manner (mood), and the persons of the verb. Look at Avropar, I will loose my-tive. You may also note that enters as an essential into the self. Analyse it, and you will find the parts stand thus:: optative forms, as in βουλευτοιτο and βουλευσαιτο. These two tenses are, you see, very near in form, differing in this only, that the latter has an a where the former has an o. The personal endings join on immediately to the mood-signs, and may appear as one; e. g., Boulevo-ps, instead of Boulevʊand unite so closely with them that they are blended together, η-ις, and βουλευ- instead of βουλευ-ε-αι. The distinction between the principal tenses and the historical tenses is important. The principal tenses, that is, the present, the perfect, and the future, form the second and the third person of the dual with the same ending; that is, ov, 25 βουλευ-ε-τον, βουλευ-ε-τον, βουλευ-ε-σθον, βουλευ-ε-σθον ; while the historical tenses form the second person of the dual in ov, but the third in ην; as, εβουλευ-ε-τον, εβουλευ-ε-την, εβου λευ-ε-σθον, εβουλευεσθην. Further, the principal tenses form the third person plural, active voice, with the termination which before a vowel becomes ou (abbreviated from vi, voi), and the third person plural middle with rai; but the historical or secondary tenses have in the active v, and in the middle vтo; as βουλευ-ο-νσι = βουλευ-ουσι(ν) ε-βουλευον ε-βουλευ-οντο. |