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nected at bottom; so that the water always stands perpendicular D Е. If two other pipes, as F at the same height in both. The central cylin- and G, be fixed into the side of the vessel, at der is furnished with a dish or scale for holding equal distances above and below the pipe D, the the goods to be weighed, 'the pressure of which perpendiculars FH and G I, from these pipes to causes it to sink. The water being thus dis- the semi-circle, will be equal; and the jets placed in the larger vessel is raised in the small spouting from them will each go to the horitube in an equal proportion, and the exact zontal distance N K, which is double the length weight of the goods will be indicated by the of either of the perpendiculars FH or GI. scale attached to the tube. This ingenious con The reader will easily perceive that the curve trivance is well adapted for small weights; and, described by the spouting fluid, in all the difif mercury be substituted for the water recom- ferent situations, will be that of a parabola; mended by Mr. Hawkins, the range of the in- being acted upon by the combined forces of the strument may be extended, without its accuracy lateral pressure of the fluid in the vessel, and the being affected by its evaporation.
force of gravity: If a hole be made in the side of a vessel, the When a solid body is plunged in any liquid, water will spout forth in a curvilinear path be- it must displace a quantity of that liquid exactly cause fluids press equally in all directions. equal to its own bulk. Hence, by measuring
The velocity with which water spouts out, at a the bulk of the liquid so displaced, we can ashole in the side or bottom of a vessel, is as the certain precisely the bulk of the body; for the square root of the depth or distance of the hole liquid can be put into any shape, as that of below the surface of the water: for, in order to cubical feet or inches, by being poured into a make double the quantity of a fluid run through vessel of that shape, divided into equal parts, or one hole as through another of the same size, it will the vessel in which the body is plunged may be require four times the pressure of the other, and of that shape, and so divided. If the width of therefore the aperture must be four tinies the the vessel is four inches by three, or twelve depth of the other below the surface of the square inches, and divided on the upright side water; and, for the same reason, three times the into twelfths of an inch, when a body of any quantity, running in an equal time through the irregular shape, as a bit of rough gold or silver, same sort of hole, must run with three times is plunged in it, every division that the water the velocity, which will require nine times the rises will show that one-twelfth of twelve cubic pressure, and consequently the hole must be inches, or one cubic inch of water, has been disa nine times as deep below the surface of the placed; so that, if it rises two divisions, the body fluid, and so on.
contains exactly two solid inches of metal. And To prove this by experiment, let two pipes of this is by far the easiest way of measuring the equal sized bores be fixed into the side of a solid contents of irregular bodies. vessel, one pipe being four times as deep below When a body is so plunged it will remain inthe surface of the water in the vessel as the other whatever part of the fluid it is put in, if it he of is : and, whilst the pipes run, let water be poured the same weight with the fluid; that is, if the constantly into the vessel, so as to keep it always bulk of the body weighs as inuch as the same full. Then if a cup that holds a pint be so bulk of the fluid; for in this case it will be the placed as to receive the water tnat spouts from same thing as if the fluid were not displaced, the upper pipe, and at the same moment a cup and as an equal quantity of the fluid would have that holds a quart be placed to receive the water remained at rest there, being equally pressed on from the low pipe, both cups will be filled at all sides, so will the solid body: it will be the same time by their respective pipes. pressed from below with the same weight of
The horizontal distance to which a fluid will fuid as from above. But if the body be heavier spout from a horizontal pipe in any part of the than the Auid, bulk for bulk, this balance will side of an upright vessel, below the surface of be destroyed, and the weight of the fluid pressing the fluid, is equal to twice the length of a perpen- from above will he greater than that pressing dicular to the side of the vessel, drawn from the from below, by the weight of the solid body, mouth of the pipe to a semicircle described upon which will therefore sink to the bottom. So, if it the altitude of the fluid: and therefore the spout be lighter than an equal bulk of the fluid, it will will be to the greatest distance possible from a rise through the fluid to the surface. But if a solid pipe whose mouth is at the centre of the semi- heavier than the fluid he plunged to a depth as circle; because a perpendicular to its diameter many times greater than its thickness, as the solid (supposed parallel to the side of the vessel), is heavier than the fluid, and there protected by drawn from that point, is the longest that can any means from the pressure of the Auid above, possibly be drawn from any part of the diameter it will float notwithstanding its weight, because to the circumference of the semicircle.
the pressure from below, being in proportion to Thus if the vessel AB, plate I. fig. 8, be full the depth, will counter-balance the weight of the of water, the horizontal pipe D be in the middle body, and there will be no pressure from above, of its side, and the semi-circle NEC he described except the weight of the body. Thus, lead is upon D, as a centre, with the radius, or semi- somewhat above eleven times heavier than water. diameter DC, or DN, the perpendicular DE If a cube of lead be placed so as to press closely to the diameter CDN is the longest that can be against the bottom of a wooden pipe one foot drawn from any part of the diameter to the cir- square, closed at the top, and plunged twelve cumference: and, if the vessel be kept full, the feet deep, and held upright, it will there swim ; jet will spout from the pipe D to the horizontal the water pressing it upwards with a force distance M M, which is double the length of the greater than its weight, and there being no pres
sure fron. the water downwards. So if a body quires 7+ grains to be put in the scale over it, in lighter than water, as cork, be placed at the boi- order to restore the equilibrium; we thus find that tom of a vessel, and so smoothly cut that no a quantity of water, of equal bulk with the guinea water gets between its lower surface and the weighs 71 grains, or 7-25; by which divide 129, surface of the bottom, it will not rise but remain the weight of the guinea in air, and the quotient, fixed there, because it is pressed downwards by or 17.793, shows that the guinea is so many the water from above, and there is no pressure times heavier than its bulk of waier. Whence from below to counter-balance that from above. if any piece of gold be tried, by weighing it
It follows from these principles, that if any first in air, then in water, and if upon dividing body be weighed in the air, and then weighed the weight in air by the loss in water, the quo in any liquid, it will seem to lose as much as an tient is 17.793, the gold is good ; if the quotient equal bulk of the liquid weighs. Not that the is 18, or between 18 and 19, the gold is very hody really loses its weight, but that it is pressed fine; but, if it be less than 17}, the gold is too upwards by a force equal to the weight of the much alloyed with other metal. If silver be liquid, the place of which it fills. Thus, if a tried in this manner, and found to be eleven piece of lead weigh an ounce before being times heavier than water, it is very fine: if it be plunged in water, that is, require an ounce 104 times heavier, it is standard: but, if it be weight on the opposite scale to balance it; if any less weight compared with water, it is mixed you hang it by a thread from its own scale, and with some lighter metal, such as tin. let it be plunged so that the water in a full jar When substances are lighter than water, a covers it, a quantity of water equal to the bulk different mode of treatment to that which has of the lead will run over the sides of the jar, and been described must be adopted for obtaining a number of grains equal to the weight of this their specific gravities; for now some force is quantity of water must be taken out of the oppo- necessary for producing their submersion :-To site scale to restore the balance: for the lead is effect this a small pulley moving with little now pressed downwards in the water with a friction may be attached to the bottom of the force not equal to its own weight, but to the dif- water jar, or to a weight sufficiently heavy to ference between its own weight and that of an cause it to remain steadily there; and the hair equal bulk of the water. And in this manner attached to the substance, must in this case pass we can determine the relative weights of all bo- downwards under the pulley, and rise again so dies, or the proportion which they bear to each that its opposite end may fix to the hook of one other in weight; which is called their specific of the scale pans. The substance is first to be gravity ; that is, their weight in kind, and some- weighed in the scale in the ordinary manner, and times their relative gravity, that is, their weight afterwards placed in the jar; water must then be compared with the weight of other bodies. By added, until the substance, by floating, draws the weighing a known bulk, as a cubic foot or a scale beam into an horizontal position; after cubic inch of any two substances, we can find which weights must be placed in the opposite their specific gravity; or their gravity as com- scale until the substance is drawn under the pared with each other : if, for instance, we found water. a cubic inch of iron weighed 1948 grains, and a Mr. Ritchie's hydrostatic balance is cheap and cubic inch of lead 2858, we should say, that the delicate; it is constructed as follows :- Let a specific gravities of the two substances were in slender beam of wood be procured, about eighthe proportion of 3 to 4f nearly; and so we teen or twenty-four inches long, and tapering a might find the specific gravity of a solid sub- little from the middle to each end. Let a fulstance, as compared with that of a liquid, by crum of tempered steel, resembling the blade of weighing an equal bulk of each. But this ope- a pen-knife, be made to pass through the middle ration is extremely difficult, because it requires of the beam, a little above the centre of gravity. the substances compared to be formed accu- Similar steel blades are also made to pass through rately into the same shape and size ; and, when the ends of the beam for suspending the scales. we are not allowed to change their figure, the The fulcrum rests on two small portions of thercomparison cannot be made at all. Thus we mometer tubes, fixed horizontally on the upright could not ascertain the specific gravity of pre- support E F, fig. 9, plate I. The support has a cious stones, crystals, metallic ores, or animal slit passing along the middle, to allow the needle and vegetable substances, without in effect de- at E F to play between the sides. A small stroying them. But the hydrostatic balance, scale made of card, and divided into any numupon the principles now explained, affords a ber of equal parts, is placed at F, for the purperfectly easy and most accurate method of com- pose of ascertaining the point at which the paring all substances solid and fluid. We have needle remains stationary. This balance posonly to weigh any substance first in air, and sesses extreme delicacy. It may even be made then in water; the difference of the weights is more sensible than that belonging to the Royal the weight of a bulk of water equal to the bulk Society of London. of the substance; and by comparing any other To ascertain the weight of any body, place substance with water, in like manner, we ascer- it in one of the scales, and bring the needle to tain its specific gravity, as compared with that of any point by means of small shot placed in the the first substance.
other scale; observe the point opposite to which Let us now take an example of the use of the the needle rests, or the middle between its exhydrostatic balance. If a guinea suspended in treme point of oscillation ; remove the body, air he counterbalanced by 129 grains in the oppo- and put into the scale as many known weights site scale, and upon being immersed in water re as will bring the needle to the same division as
before. These weights will evidently be equal or artificial vacuities, so as not to harbour any air; to the weight of the body, whether the arms of for otherwise its specific gravity cannot be ascer, the balance bc equal or not. This method of tained by weighing in water, &c. Thus a piece weighing is due to Borda.
of silver, which is much heavier than water, may In the use of the hydrostatical balance gene be formed into a hollow sphere, which will aprally, ii will be proper to observe the following pear to be much lighter than water; for, if this general precautions. The water in which the sphere were immersed in water, it would displace solid is to be weighed, besides its being either a quantity of water which is equal not only to distilled or rain water, must be quite clean. Its the silver, but also to the space which is contemperature, as well as that of the solid, must be tained in the sphere. It is for this reason that as near as possible to 62° of Fahrenheit's ther- a ship might be made of iron, or of copper, or, mometer; for which purpose the ball of the ther- in short, of any substance whose specific gravity mometer Tust be placed in the water, and the far exceeds that of water; and yet it would float temperature is adjusted by the addition of hot or as well as a ship which is made of wood in the cold water. If the solid body be soluble in usual way. water, or if it be porous enough to absorb any In order to determine the specific gravity of water, then it must be varnished, or coated living men, Mr. Robertson prepared a cistern with some oily or greasy substance; but in seventy-eight inches long, thirty inches wide, and that case some allowance is to be made on ac- thirty inches deep; and, having procured ter count of the varnish, &c. When the solid i: men for his purpose, the height of each was weighed ja water, its upper part ought to be a taken, and his weight, and afterwards they little way below the surface of the water; for plunged successively into the cistern. A ruler, instance, about an inch ; and it must by no graduated to inches ard decimal parts of an inch, means be suffered to touch the sides or bottom was fized to one end of the cistern, and the of the jar. Care must be taken that no bubbles height of the water nuted before each man went of air adhere tv the solid under water; for they in, and to what height it rose when he immersed would partly buoy it up. These may be easily himself under its surface. removed by means of a feather. The solid must The following Table contains the several rebe of a compact form, and free from accidental sults of his experiments:
One of the reasons, Mr. Robertson says, that loses 253 grains whe'r weighed in water, and induced him to make these experiments, was a only 209 grains when weighed in rectified desire to know what quantity of fir or oak tim- spirits; therefore a cubic inch of rectified spirit ber would be sufficient to keep a man afloat in weighs 209 grains, an equal bulk of water weigh- river or sea water, thinking that must men were ing 253; and so the specific gravity of the water specifically heavier than river or common fresh is about a fourth greater than that of the spirit. water; but the contrary appears from the trials Upon this principle the hydrometer is conbefore recited; for, except the first and last, structed. There are various kinds of hydromeevery man was lighter than his equal bulk of ters. One is a glass or copper ball with a stem, fresh water, and much more so than his equal on which is marked a scale of equal parts or debulk of sea water: consequently, if persons who grees. The point to which the stem sinks in fall into the water could preserve their presence any liquid being ascertained, and marked on this of mind, many might be preserved from drown- scale, we can tell how many degrees any other ing, and a piece of wood, not larger than an oar, liquid is heavier or lighter, by observing the would buoy a man partly above water as long point to which the stem sinks in it. Another as he could adhere to it.
and a very simple hydrometer is formed by preIt is evident also that a reference to the same paring a number of hollow glass beads of different general principle will enable us to ascertain the weights, but the proportions of which are known, specitic gravities of different fluids. For, if the and the beads marked accordingly; they are same substance be weighed in two fluids, the then successively dropped in the fluid to be exweignt which it loses in each is as the specific amined, until one is found which neither sinks gravity of that fluid. Thus a cubic inch of lead nor comes up to the surface, but remains at risk,
wherever it is placed in the liquid. You thus four ounces, and plunged in water, there is a fall. ascertain that the liquid is of the same specific or rise of above half an inch for every on th gravity with this bead. If the same head be part of the water displaced ; so that the diffedropped into another liquid, and sink, that rer.ce of todou th part is easily perceived. liquid must be lighter than the first; if the bead Fahrenheit's hydrometer, like the common one, come to the top, the second liquid is heavier consists of a hollow ball, with a counterpoise c, than the first; and by trying the liquid with the fig. 11, but the stem B is very slender, and terother beads, until one is found which neither minates in a small dish A. Round the middle sinks nor floats, you ascertain the relative weight of the stem is drawn a fine line; and there are of the liquid by the number of the bead. no divisions on the stem, which is always im.
A hydrometer of great delicacy and peculiarly mersed in the fluid to be tried, up to the mark, useful for measuring the specific gravity of diffe- by placing as much weight as may be required rent waters, and thereby ascertaining their de- in the small dish A. Hence, is the part immersed grees of purity, consists of a ball of glass three is constantly of the same magnitude, and the inches diameter, with another joining it, and whole weight of the hydrometer is known, this opening into it, of one inch diameter, B and C, last weight, added to the weight in the dish, will plate I. fig. 10, and a brass neck d, into which is be equal to the weight of Auid displaced by the screwed a wire u o, about ten inches long, and instrument. one-fortieth of an inch diameter, divided into Mr. Clarke's hydrometer is made of copper, inches, and tenths of an inch. The whole weight because ivory imbibes spirituous liquors, and of this instrument is 4000 grs. when loaded with glass is apt to break. It consists of a brass wire shot in the lower ball. It is found that, when about one-fourth of an inch thick, passing through plunged into water in the jar, a grain laid upon and soldered into the copper ball Bb, fig 12, the top a makes it sink one inch; therefore a plate 1. The upper part of the wire is filed flat tenth of a grain sinks it a tenth of an inch. Now on one side of the stem of the hydrometer, and it will stand in one kind of water a tenth of an marked at m, to which division it exactly sinks in inch lower than in another, which shows that a proof spirits. There are two other marks, A and bulk of one kind of water equal to the bulk of B; the one showing that the liquor is one-tenth the instrument weighs one-tenth of a grain less above proof, when this instrument sinks to A, than an equal bulk of the other kind of water; and the other indicating one-tenth under proof so that a difference in specific gravity of one when it emerges to B; a brass weight, as C, part in 40,000 is thus detected. This weight having been previously screwed on to the bottom of 4000 grs. is convenient for comparing water; at c. There is a great variety of weights of difbut the quantity of shot in the lower ball may ferent sizes, as K, &c., adapted to liquors that be varied, so as to make it lighter or heavier, differ more than one-tenth from proof, and for and so adapt it to measure the specific gravities determining the specific gravities of all such of lighter or heavier liquids. It will always be liquors as occur in trade, as well as for showan accurate and very delicate meastire for liquids ing the specific gravities of all fluids down of nearly the same weight. Indeed its delicacy is to common water. The round part of the so great, that an impurity too slight to be detected wire above the ball may be marked across, by the taste, will be discovered by this in- so that with the weight C, which fits the strument.
instrument for the trial of river water, in which The areometer invented by M. De Parcieux, it sinks to RW, it may serve for wines or of Paris, is more simple, and affords a very ac- other waters : thus in spring water it will sink curate comparison of different liquids. It is only to SP; in mineral water to M I; in sea-water to a different form of the instrument just described. SE; and in the water of salt springs to SA: A glass phial, about two inches or two inches and and the marks br, ra, po, me, denote the divia half in diameter, and seven or eight long, with a sions to which the instrument descends in Bristol plane or round bottom, is corked tight, and into water, rain water, port wine, and mountain wine, the cork is fixed a perfectly straight wire of about respectively. one-twelfth of an inch diaineter, and thirty inches This hydrometer is inferior to Fahrenheit's in long. The phial is loaded with shot, so as to two respects. In the first place, either a bubble make it sink in the heaviest liquid to be examined, of air, or a portion of the fluid, will be hid in leaving the wire just below the surface. There that part of the cavity of the ballast weight which is a cylinder of glass, about three or three and a is not filled by the screw; and it is of very difhalf inches diameter, and three or four feet long, ferent consequence which of the two is there. with a scale of equal parts on the side. The And secondly, the weights acting on the instruliquor to be tried is put into this; and the scale ment, by their residual gravity, will pot be conmarks the point to which the top of the wire stant; or, ir, other words, an additional weight sinks. This instrument is so sensible, that if it will be accompanied by an addition to the bulk stands at any point in water of the common tem of the immersed part of the instrument; and in perature, and the sun's rays fall upon the water, the case where the specific gravity of the liquid the wire will sink several inches, from the slight is not given, but required, it will not be easy to increase of heat causing an increase of bulk, and determine how much the operation of the one is consequently a diminution of relative weight in counteracted by the other However, though the water; and it will rise again when carried this last consideration evinces that the instruinto the shade. A pinch of salt or sugar throwr. ment is not fit for general use, yet it is accurate in makes it rise some inches, and a little spirits for the trial of ardent spirits, or any other partipoured in make it sink. With one of these in- cula- liquid, when the weights are adjusted by struments, weighing somewhat less than twer.ly- experiment to the intended use.
Şikes's hydrometer is now generally employed, liquors leave variable proportions of water, especially since its adoption by the commis- when thus burned in a graduated vessel. sioners of his inajesty's customs. This instru There is the greatest difficulty in ascertaining ment has but nine shifting weights, applicable what is meant by the terms proof spirit. Dr. upon the upper part of the stem, and is used Thomson, quoting the act of parliament of with a set of tables, or a sliding rule sold with 1762, states, that at the temperature of 60°, the it, for computing compensation for different tem- specific gravity of proof spirit should be 0.916; peratures. The scale is divided into ten principal and he also observes, that proof spirit usually divisions, each of which is subdivided into five means a mixture of equal bulks of alcohol and parts, and by the separate application of the water; but the specific gravity of such a mixweights in succession completes the range of ture will, of course, depend upon that of the strength from pure alcohol to water, each weight standard alcohol, which is not specified. It being equivalent to ten principal divisions. This appears from Gilpin's Tables that spirit of the hydrometer, with the weight marked 60, screwed specific gravity :916, at 60°, consists, by weight, on to the lower stem, is so adjusted as to sink to of 100 parts of alcohol, specific gravity •825, at the line mark P on the scale of the instrument 60°, and 75 of water; and, by measure, of 100 when placed in proof spirit, of the temperature parts of the same alcohol, and 61.87 of water. of 510 Fahrenheit, and, by the addition of the One of the most accurate and convenient mesquare weight on the top of the stem, it sinks to thods of obtaining the specific gravity of fluids the same point in distilled water of the same is by what is called a thousand grain bottle. temperature. This weight being just one-twelfth This is sold by most of the philosophical inpart of the entire weight of the whole hydro- strument makers, together with a weight, which ineter, together with its bottom weight No. 60, is an exact counterpoise for the bottle when causes the scale to show the difference between filled with distilled water; its magnitude being water and proof spirit, which, the act states, adjusted by grinding down the length of its shall weigh exactly twelve-thirteenth parts of an neck, until it holds exactly 1000 grains of water equal bulk of distilled water.
at 60° of Fahrenheit. This instrument conseMr. Meikle's hydrometer consists of a glass quently requires no computation, but is simply lube, open at both ends, and bent into a kind of to be filled with fluid, and placed in one scale double syphon, having four parallel legs; so of a balance, while its counterpoise is placed that the open ends are pointed in the same direc- in the other. If the fluid put into it is lighter tion or upwards, as shown in fig. 13, plate I. than water, it will appear deficient in weight, The manner of using it is very simple. Let one and as many grains must be added to the scale of the ends be stopped with a finger or cork, that contains it as will restore the balance. This and water be poured into the other. This fluid at once shows that the specific gravity of the will only rise a small way into the second leg, fluid under examination is negative, or less than because of the included air. Next stop the other the standard, and consequently must be a fracorifice, and open the one first closed; and, hav- tional number; but, should the Auid be heavier ing poured into the latter the liquid whose spe- than water, the bottle will preponderate, and cific gravity is to be tried, open the top of the weights must be put into the opposite scale, water tube; then, the instrument being held up- when their amount will be positive, and must be right, the two liquids will arrange themselves so added to the amount of the standard. For exas to press equally on the included air. This ample: if the bottle were filled with sulphuric pressure will be measured by the difference in ether, it would require 739 grains to be placed the heights of the two columns of either liquid, in the same scale to restore the balance, consemultiplied by its specific gravity, so that, by quently its specific gravity would be thus exdividing the difference of the two columns of pressed 0.739. Had it been filled with seawater by the difference of those of the other water, which is rather denser than that which is liquid, we obtain the specific gravity of the lat. distilled, twenty-six-hundredths, or rather better; that of water being unity. The difference ter than one-fourth of a grain must have been between the columns may be measured by added in the opposite scale, and these, as already applying any scale of small equal parts, or the explained, must be added to the standard 1.000 glass may be attached to a graduated plate fur- to express the specific gravity of such water, nished with verniers, &c. The longer the which would be thus written 1.026. Sulphuric columns of liquids employed, the more accurate acid again, being still heavier, would, in like the process. The expansion of the glass, or its manner require 875 grains, and would accordcapillary action, cannot affect the result, nor is ingly be expresscd 1.875. it influenced by the expansion of the scale; the A bottle, however, holding 1000 grains is often only correction required will be to reduce the inconveniently large, and a small and thin globobservations to one temperature,
ular phial, with a piece of thermometer tube There are other methods of judging of the ground into it by way of stopper, will be found strength of spirituous liquors, which though more useful · such a phial should not weigh useful are not accurate, such as the taste, the more than from 'fifty to sixty grains, and may size and appearance of the bubbles when shaken, contain between 400 and 500 grains of water. the sinking or floating of olive oil in it, and the To use it it should be accurately counterbalanced appearances that it exhibits when burned ; if it in a delicate pair of scales, and then filled with burns away perfectly to dryness, and inflames distilled water, and the stopper thrust in, the gunpowder, or a piece of coiton immersed in it, capillary opening in which allows a little to ooze it is cousidered as alcohol; the different spirituous out, and prevents the likelihood of bursting the