Chapter V: Part III: Instructions for the Preparation of the Tests Employed (3)

Sometimes a dropping tube is employed to measure small quantities of liquid. In this case the point should be drawn off abruptly, and the scale should be marked on the shank or tube with spots of black enamel.

Pl. 2, fig. 21, represents a peculiar variety of dropping tube employed in some experiments. It is made in the same manner as the common dropping tubes, excepting that, when the tail is formed, it is sealed at the extremity, bent there into a ring, and then pierced at A.

Pl. 3, fig. 26, represents another variety of dropping tube, a description of which is unnecessary.

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FOUNTAINS.--It will readily be understood by those acquainted with the construction of hydraulic apparatus, that, by means of a judicious arrangement of glass tubes, a great variety of fountains may be produced. The following are given as examples.

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FOUNTAIN OF CIRCULATION.--Take a tube, twenty-four or thirty inches long, nearly half an inch in diameter, and with pretty thick sides; blow a bulb at one of its extremities, and bend the other into a U, after having drawn it out as indicated by pl. 3, fig. 4. Pierce the tube at B, and join there a short piece adapted to receive a cork. Then prepare a bulb of the same size as the first bulb, and solder it to the extremity of a very long and almost capillary tube, which you must bend in zig-zag, in such a manner as to make it represent a Maltese cross, a star, a rose, or any other figure that may be suggested. The side of the bulb opposite to that which is attached to this twisted tube, ought to be formed like the neck of a bottle, in order that it may receive the drawn-out part of the larger tube, which should enter the bulb until the point of the large tube nearly touches the neck of the little tube at its junction with the bulb. This disposition is shewn in the figure. Seal now the other end of the little tube to the bulb of the large tube; then, with a little cement or sealing-wax, close the space between the bulb of the little tube and the point of the large tube. The instrument being thus prepared, as much alcohol, previously coloured red, must be inserted by the neck _b_ as is sufficient to fill one of the bulbs. The neck is then closed with a cork, and a little cement or sealing-wax. Or, instead of forming this neck to the instrument, the additional piece may be drawn out to a point, which permits it to be sealed hermetically.

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FOUNTAIN OF COMPRESSION.--Introduce into a tube of large diameter a piece of capillary tube with thick sides. This must pass a little beyond the extremity of the large tube, which is to be softened and soldered to the other, so that it shall be fixed concentrically. The common point is then to be drawn out. When the tube is quite cold, and the small tube properly fixed in the centre of the large one, cut the latter at a proper distance, border it, and choke it near the end, which must be fashioned in such a manner as to be capable of being completely closed by a cork. See pl. 2, fig. 29.

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INTERMITTING FOUNTAIN.--This apparatus is represented by pl. 3, fig. 16. Solder a cylindrical reservoir to the extremity of a capillary tube, pierced at _a_, and sealed at its extremity. Draw out abruptly the point of the reservoir, and give it a very small orifice; then give to the capillary tube the form indicated by the figure. Prepare next a funnel resembling a mercury-funnel, but much larger; choke the neck of this funnel, and bend the tube into the form of a syphon.

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HERO’S FOUNTAIN.--Solder a bulb to the extremity of a tube, and transform the bulb into a funnel. Close the funnel with a cork, and solder to the other end of the tube a bulb similar to the first. Next, solder a third bulb between two tubes, of which one must be twice as long the other; solder the longer of these tubes to the bulb of the first tube, and draw out the point of the shorter tube. You have now a long tube, with a funnel at one end, a contracted point at the other, and two bulbs in its length. Give to the whole apparatus the form indicated by pl. 3, fig. 21.

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FUNNELS.--It will be seen, upon looking over the engravings, that funnels require to be made for a great variety of instruments; you ought therefore to acquire as soon as possible the art of making them well. The following are those most frequently required.

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RETORT FUNNEL.--Blow a bulb at the extremity of a tube; present the superior hemisphere of the bulb to the flame, and when it is sufficiently softened, blow strongly into the other end of the tube. The air will force its way through the bulb, making a hole which will be larger or smaller according to the extent of surface which may have been softened. The opening of the funnel being made thus, there is nothing more to do than to adjust the edges, which, in the present state, are both fragile and irregular. This it is very easy to do. The edges are softened, the most prominent parts are cut off with the scissars, and the parts which are thin are bent back on themselves, that they may become thicker. Upon turning the funnel round in the flame, the smaller irregularities give way, and the edges become rounded. See pl. 2, fig. 24.

When the funnel is desired to be very large in proportion to the size of the tube, a bulb is made from a larger tube, and afterwards soldered to the small tube, and transformed into a funnel in the manner above described.

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FUNNEL FOR INTRODUCING MERCURY INTO NARROW TUBES.--The mercury-funnel is represented by pl. 2, fig. 25. Blow a bulb between two points; cut off one of the points, and open the bulb at that place, in the manner described in the preceding article.

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HYDROSTATIC FUNNEL.--This is represented by pl. 3, fig. 31. It is an instrument of constant use in chemical experiments. Form a funnel at the extremity of a tube in the manner described above, having previously blown a bulb near the middle of the tube. When this has been done, bend the tube into the form shown by the figure.

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HOUR-GLASSES.--Blow four bulbs on a tube close to each other; open the two end bulbs like funnels, and then form them into flat supports or pedestals, according to the method described at the article _Test-glass with a foot_. Obstruct entirely the canal which separates one of these feet; choke to a certain extent the passage between the two remaining bulbs; and close the canal between the other foot and the bulbs, after introducing the quantity of sand which you have found to be necessary. See pl. 3, fig. 13.

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HYDRAULIC RAM.--This instrument is represented by pl. 4, fig. 15. Employ a tube about six feet long, with thick sides and of large diameter. Seal it at one extremity, _k_, and border it at the other; solder at _p_ an additional piece, choked so as to receive a valve. Pierce the tube at _l_; draw it out, and fix a funnel there; then twist the tube into a spiral. Form, on the other hand, a fountain of compression, _o_, and a funnel, _m_; and fix both of these pieces by means of sealing-wax, as soon as the two valves _p_ and _l_ have been put into their places.

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HYDROMETERS.--_Hydrometers_ are instruments which, on being plunged into liquids, indicate immediately their density or specific gravity. _Areometers_ differ from hydrometers sometimes in graduation, sometimes merely in name. The following are examples of hydrometers, of which a great many varieties are in use.

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BAUMÉ’S HYDROMETER.--Make a cylinder between two points, and solder it to the extremity of a tube with thin sides, and which must be very regular on the outside. Close the open part which is to form the stalk of the hydrometer with a little wax. See pl. 1, fig. 9 and 15. When the soldering, which must be well done, is complete, and the stalk well centered, choke the reservoir at a little distance from the base of the point, by drawing it out in such a manner as considerably to diminish the canal in this part. Remove then the ball of wax which closed the tube, draw off the point of the cylinder, and make the part which was pulled away from the cylinder by the choking, into a bulb, by blowing with precaution into the tube. If the reservoir is required to be spherical instead of cylindrical, it must be softened and expanded by blowing. When it is intended to ballast the instrument with mercury, the canal must be completely stopped at the point where it is choked. In this case, the part drawn away from the cylinder is expanded into a bulb by blowing through the extreme point, which is to be cut off after the instrument is completed.

In the first case, you ballast the instrument with lead shot, which you fix in the lower bulb by means of a little wax, which closes the canal at the choked part. In the second case, after having proved the ballast by putting it first into the large reservoir, it is removed into the little bulb, and the latter is immediately sealed.

One of the essential conditions of a good hydrometer is that the stalk should keep a perfectly vertical position when the instrument is plunged in water. If, therefore, on proving the ballast, you perceive the stalk to rest obliquely, you must take care, on retiring it from the water, to wipe it dry, and to present the choked part between the cylinder and the little bulb to the flame; when it is softened, it is easy, by giving it a slight bend in the direction where the stalk of the hydrometer passes from the vertical, to rectify the defect.

Finally, when the instrument is ballasted, you must seal the stalk, after having fixed in its interior the strip of paper which bears the graduated division.

This method of operation serves equally for all the areometers known under the names of _areometer of Baumé_, _pèse-sels_, _pèse-liqueurs_, _pèse-acides_, and _hydrometers_, which differ only in the scheme of their graduation. As to the _size_ and the _length_ of the stalks, they depend upon the _dimensions_ you desire to give to the degrees of the scale, and upon the _use_ to which the instruments are destined. For the areometer of Baumé, and for the _pèse-sels_, the stalks are generally thicker and shorter than for hydrometers. Pl. 4, fig. 19, 20, and 21, represent different hydrometers.

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NICHOLSON’S HYDROMETER.--Solder a bulb to the extremity of a capillary tube; open it so as to form a very wide funnel, or rather capsule; border the edges, and melt the point of junction with the tube so as to close the opening of the latter. Solder the other extremity of the tube to a cylindrical reservoir. Soften the point at the lower extremity of the cylinder, and obstruct the canal so as to convert the point into a glass rod; bend this rod into a hook. Now blow a bulb at the end of a point, as if to make a mercury funnel; but, after having softened the hemisphere of the bulb opposite to the point, and placed the latter in the mouth, instead of blowing into the bulb so as to make a funnel, strongly suck air from the bulb: by this means the softened part of the glass is drawn inwards, and you obtain a capsule with double sides, as exhibited by pl. 2, fig. 17. This capsule must have a small handle fastened across it, by which it may be hung to the hook formed at the bottom of the cylinder described above.

This hydrometer being always brought to the same level, the point to which it must be sunk in the liquid experimented with, is marked on the stalk by applying a little spot of black enamel. The instrument is represented by pl. 4, fig. 23. A variation in form is shewn by pl. 4, fig. 22.

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HYDROMETER WITH TWO BRANCHES.--To measure the relative density of two liquids which have no action on each other, you employ a simple tube, bent in the middle and widened at its two extremities. See pl. 2, fig. 11.

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HYDROMETER WITH THREE BRANCHES.--This consists of a tube bent in such a manner that the two branches become parallel. To this tube another is soldered at the point of curvature, and is bent in the direction exhibited by pl. 2, fig. 12. When the two branches are put into different liquids, and the operator sucks air from the third branch, the two liquids rise in their respective tubes to heights which are in the inverse ratio of their specific gravities.

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HYDROMETER WITH FOUR BRANCHES.--This is merely a tube bent three times, and widened at its extremities. Pl. 2, fig. 13.

To graduate hydrometers with two, three, and four branches, you have to divide their tubes into a certain number of equal parts.

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MANOMETERS.--Make choice of a tube nearly capillary, very regular in the bore, and with sides more or less thick, according to the degree of pressure which it is to support. Seal this tube at one end, blow a bulb with thick sides near the middle, and curl it in S, just as is represented by pl. 2, fig. 9. For manometers which serve to measure the elasticity of the air under the receiver of the air-pump, what is generally employed is a tube closed at one end and bent into a U. Pl. 2, fig. 10. You should take care to contract these at some distance from the sealed part, in order to avoid the breaking of the instrument on the sudden admission of air. Manometers are graduated, as will be explained in the sequel.

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MARIOTTE’S TUBE.--This is represented by pl. 2, fig. 7. It consists of a tube thirty-nine inches long, closed at one end, bordered and widened at the other, and bent into a U at the distance of eight inches from its sealed end. The graduation of this instrument will be described hereafter.

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PHOSPHORIC FIRE-BOTTLE.--This is a short piece of tube closed at one end, and widened and bordered at the other, in such a manner as to receive a cork. Pl. 3, fig. 34. It is in this little vessel that the phosphorus is enclosed. Glasses of this form can be employed in a great variety of chemical experiments.

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PULSOMETER.--This instrument consists of a tube, of which each extremity is terminated by a bulb; it is partly filled with nitric ether, and sealed at the moment when the ebullition of the ether has chased the atmospheric air wholly from the interior of the vessel. Pl. 2, fig. 16.

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PUMP.--Solder a cylinder, B (pl. 4, fig. 12), to the extremity of a small tube, C, and form their point of coincidence into a funnel, to which you will adapt a valve. Pierce the wide tube or body of the pump at D, and solder there a piece of tube bent into an elbow and widened at the other end into a funnel, which is to be furnished with a second valve, as is represented in the figure. Prepare then the fountain of compression E, and, by means of a cork and a little sealing-wax, fix it upon the branch D. To prepare the piston, A, blow a bulb at the end of a tube, flatten the end of the bulb, and choke it across the middle, in order to form a place round which tow can be twisted, to make it fit the tube air-tight. Finish the piston by twisting the other end of the tube into a ring, as at A. The valves are formed of small cones of cork, or wood, having in the centre an iron wire of sufficient size and weight to enable them to play well.

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RETORT FOR CHEMICAL EXPERIMENTS.--Plate 3, fig. 9, represents a combination of a large and a small tube, forming a retort, which can be employed with much advantage in many chemical experiments. When a gas is to be distilled by means of such a vessel, the ingredients are put into the wide tube, which is previously closed at one end, and then the other end of the tube is either drawn out or soldered to a narrow tube. Pl. 3, fig. 8 and 29, represent such vessels under different forms. Very often a sort of retort can be formed by joining a wide tube to a long bent narrow tube, by means of a cork.

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TUBULATED RETORT.--This is represented by pl. 3, fig. 6. Prepare a retort, such as is described in the preceding article, but one which is bent near the closed end; pierce it at A (fig. 6), and solder there a little piece of tube previously drawn out and sealed, such as is represented by pl. 1, fig. 11. When the soldering is finished, soften the end of the little tube, pierce it, and fashion it into a bottle neck, so that it can be closed by a cork. Finish the instrument by forming the open end according to the purpose to which it may be destined. In the figure, the end is represented as drawn out for the convenience of blowing into the retort to pierce the tubulure.

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RUMFORD’S THERMOSCOPE.--This instrument is represented by pl. 3, fig. 35. It is necessary to take a tube almost capillary, to solder a bulb at each extremity, to pierce it laterally at _b_, and to solder there a piece of tube previously drawn out, but of which you open the point for the purpose of finishing the sealing of the bulb A. After doing this, you bend the two branches, as shewn in the figure. When the liquid has been introduced into the instrument, you must seal the little piece of tube which serves as a reservoir.

This instrument can be made in another manner. Take two pieces of tube, one of them twice as long as the other; solder a bulb at one end of each of these tubes, and at about the third part of the length of the long tube, parting from the bulb, bend it at a right angle; pierce the little tube at a corresponding distance, and solder to the hole the end of the long tube. The soldering being finished, and the whole system having the form indicated by pl. 3, fig. 35, introduce, by the open end of the short tube, a small quantity of coloured acid, and then seal the end of the short tube, which serves as a reservoir.

The interior diameter of the tubes which are generally employed as thermoscopes, is one-eighth or one-twelfth of an inch. The mode of graduation is described in a subsequent chapter.

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SYPHONS.--The _simple syphon_ is a glass tube bent, at a little distance from the middle, into a form which is intermediate between those of ⋂ and ⋀, the legs being stretched apart like those of the latter, but the bend being rounded like that of the former. The tube is bent _near_ the middle, and _not exactly at_ the middle, in order that the legs may be of unequal lengths; an arrangement which is indispensable. Syphons are made of different lengths and diameters, for various purposes. They can be made of tubes so capillary that it is sufficient to put them into water to make them act: the liquid rises in them by capillary attraction, and does not require to be sucked through the tube, as it does when large syphons are employed.

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WIRTEMBERG SYPHON.--This syphon is the same as the simple syphon, excepting that the two branches are of equal length, and are bent in U at both extremities. Pl. 3, fig. 22.

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SYPHON WITH THREE BRANCHES.--This instrument is represented by pl. 2, fig. 19. Close a tube at one end and draw it out at the other; pierce it at some inches from the contracted extremity, and solder to the hole a little tube of which the other end has been closed with wax. Give the tube the bend necessary to constitute a syphon, and open the two branches. The soldering of the two tubes is facilitated by giving to the extremity of the little tube a bend which adapts it to be applied parallel to the large tube. When the syphon is desired to be well finished, the mouth-piece of the little tube must be bordered and widened, and a bulb must be blown near the mouth-piece.

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SYPHON WITH JET OF WATER.--This instrument is represented by pl. 3, fig. 1. Take a tube of a large diameter, close it at one end, and draw it out at the other. Cut the contracted part in such a manner as to be able to introduce, through the orifice, the extremity, also drawn out, of another tube, which should be almost capillary. Solder these together in such a manner that the point of the small tube shall remain fixed about an inch within the interior of the reservoir. Pierce again the latter, at B, and solder there another branch of the same diameter as the former; but fix it in such a manner that its side shall be contiguous to the side of the reservoir. Finally, give to the branches the bend represented by the figure.

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SPOONS.--Solder a bulb to the extremity of a capillary tube; open the bulb as for a funnel, but make the opening laterally. Cut with scissars the edges of the part blown open, and in such a manner as to form a spoon or a ladle, according as the bulb had the form of a sphere or an olive. This instrument is useful for taking small quantities of acids. Pl. 3, fig. 11.

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SPIRIT LEVEL.--The spirit level is represented by pl. 2, fig. 28. Choose a piece of tube very straight, and with sides precisely of the same thickness in all parts. Seal it at one end, and draw it out abruptly at the other. Fill it almost entirely with alcohol, and seal the point by the jet of a candle.

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TEST GLASS WITH A FOOT.--Take a tube drawn out at one end; choke it at an inch from the base, in such a manner as to obstruct the canal almost entirely. Pl. 1, fig. 12. Cut off the point, close the opening, and soften the whole end completely; then blow it into a bulb and burst it into a funnel. Now present the contracted part to the fire, so as totally to close the passage. Border and soften the funnel, and by pressing it against a flat plate of metal give it the form of a foot, or pedestal. Cut the tube at the length which you desire the test-glass to have, and border the edges of the opening. This is a very useful little chemical instrument. It is represented by pl. 3, fig. 10.

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THERMOMETERS.--Thermometers are instruments employed for appreciating changes of temperature, either in the atmosphere or in substances which we have occasion to examine. The following are the principal varieties now employed.

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ORDINARY THERMOMETER.--If you desire to make standard thermometers, you must have capillary tubes of perfect accuracy in the bore. You are assured of regularity in the diameter of a tube when a drop of mercury, made to pass along the canal by means of a gentle inclination, or by air blown from an Indian-rubber bottle, gives everywhere a metallic column of the same length.

For ordinary thermometers this precaution is superfluous. In all cases you employ a tube more or less capillary, at one of the extremities of which you blow or solder a spherical or cylindrical reservoir. See pl. 4, fig. 1 and 2. You fill the instrument with well-purified mercury, or alcohol, which you boil in the tube, in order to chase the air from it. As it is necessary to heat the instrument throughout its whole length, you must place it on a railing of iron wire, inclined in the manner represented by pl. 4, fig. 14, and covered with burning charcoal, or red-hot wood ashes. It is better, however, to employ a kind of muff, formed of two concentric wire grates, between which you put burning charcoal, and reserve the centre for the instrument. The tube is thus kept in a vertical position, which allows the bubbles of air to escape with more facility. An iron wire is made use of to fasten the tube precisely in the centre of the column of fire. The operation is considerably promoted by soldering a little funnel to the upper extremity of the thermometer tube; and, in order to avoid the interruption of the column of liquid by bubbles of air, it is better to give to the superior part of the reservoir the form of a cone (pl. 4, fig. 3), rather than to preserve the completely spherical form indicated by pl. 4, fig. 2.

When the ebullition has expelled all the air which was contained in the mercury, or alcohol, you immediately plunge the open extremity of the instrument into a vessel filled with one or the other of these liquids; or, instead of this, you pour the liquid into the funnel, in order that the instrument may be quite filled at the common temperature. You then cut off the funnel, if one has been used, and, by properly elevating the temperature of the reservoir, you expel so much of the liquid that the summit of the column rests at the point which you desire to make choice of for the mean temperature: this operation is termed _regulating the course of the thermometer_.

There are two methods of closing thermometers: you may either produce a vacuum above the column of mercury, or you may allow air to remain there. In the first case, after having drawn out the end of the tube, you heat the liquid until a single drop passes out of the opening; you then instantly bring the point into the jet, and seal it.

In the second case, you seal the instrument at the ordinary temperature, and having previously raised to a reddish-white heat the button of glass which is formed by the sealing, you suddenly elevate the temperature of the mercury. The liquid, on rising, compresses the enclosed air, which dilates the red-hot button at the summit of the tube, and produces a species of reservoir. This reservoir is indispensably necessary when you leave air above the column of liquid, in order to provide against the bursting of the instrument on those occasions when the temperature of the mercury comes to be considerably elevated. See pl. 4, fig. 13.

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DIAL THERMOMETER.--Terminate a piece of tube, of six-tenths of an inch in diameter, with two points, and solder to one of these points a tube one-eighth of an inch in diameter and six inches long; close the end of this small tube, and, heating a zone of the reservoir, near the base of the other point, blow a bulb there. Cut off the point by which you have blown, at a little distance from the bulb; open and border the end of the narrow tube, and bend it into a U. See pl. 4, fig. 16.

Fill the bulb and the reservoir with alcohol, and add a drop of mercury which fills a certain space in the narrow tube. This mercury bears on its surface a little iron weight, to which a thread is fastened; the other end of this thread passes over a pulley, whose axis turns a needle. The expansion or contraction of the alcohol causes the mercury to rise and fall, and consequently produces a movement of the needle or index of the dial. This thermometer is graduated like the others, by being brought into comparison with a standard thermometer.

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CHEMICAL THERMOMETER.--This instrument is merely a common thermometer, the divisions of which, graduated on paper, are enclosed in a very thin glass tube, to hinder them from being altered or destroyed when the instrument is plunged into liquids. Pl. 4, fig. 4, 5, 6, and 7, represent chemical thermometers of various kinds.

The case of the thermometer can be made in two different ways. According to the first, you take a tube of a pretty large diameter, and with very thin sides; you draw out one end and obliterate the point, which you bend into a ring, in a direction perpendicular to that of the case; you pass through this ring the stalk of the thermometer, which is thus placed parallel to the large tube. After having fixed the graduated scale in the interior of the case, by means of a small drop of sealing-wax, which has been dropped on the slip of paper, and which, being supported against the side of the case, needs only to be warmed to adhere there and fix the scale securely to its envelope, you close the upper extremity of the case by drawing it out, obliterating the canal and soldering it to the thermometer tube which has been introduced into the ring at the lower end of the case. You heat the connecting piece till it is soft, and then push the thermometer up and down until the zero marked on its tube corresponds with the zero marked on the scale within the case. See pl. 4, fig. 6 and 7.

The second method of making the case is as follows:--You take a tube with thin sides, and sufficiently large to contain the entire thermometer; you draw out the tube at one end, and choke it at some distance from the point of the contracted part. This you must do in such a manner as to form a little bulb, which is to be ballasted in the manner described at the article _Hydrometers_. After having introduced into the case a little ball of cotton, you place therein the thermometer, furnished with its scale, and in such a manner that the reservoir rests on the cotton. You terminate the upper end of the case either with a ring or by a contraction which permits the instrument to be suspended by a cord. See pl. 4, fig. 4 and 5.

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SPIRAL THERMOMETER.--Take a tube which is not capillary, but which has thin sides; close one of its ends, and bend it round by pressing it with a metallic rod; continue to bend it round till it has made several turns, all in the same plane. See pl. 1, fig. 13. The latter turns may be managed with the fingers instead of the metallic rod. When the reservoir so formed is sufficiently large, solder to the end of it a capillary tube, which you point in a direction perpendicular to that of the axis of the spiral. The instrument is represented by pl. 4, fig. 8.

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POCKET THERMOMETER.--The pocket thermometer differs in nothing from the thermometer just described, except that the capillary tube, instead of passing away from the spiral in a straight line, is turned round, so as to form a continuation of the spiral. See pl. 4, fig. 17.

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MAXIMUM THERMOMETER.--This instrument consists of an ordinary mercurial thermometer, bent at a right angle near the origin of the reservoir, and in the horizontal column of which a little steel or iron rod has been introduced: this rod, by gliding in the tube, where it experiences very little friction, serves as an index. Since this index does not permit the instrument to be sealed with the vacuum above the mercury, you must terminate the sealing by a little reservoir, as we have described at the article on the second method of closing thermometers. The instrument is represented by pl. 4, fig. 24.

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MINIMUM THERMOMETER.--This instrument is constructed pretty nearly in the same manner as the preceding. The liquid, however, must be alcohol, and the index a little rod of enamel, which ought not to be quite so large as the bore of the thermometer tube. You seal the tube by making a vacuum above the column.

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BELLANI’S MAXIMUM THERMOMETER.--This thermometer is represented by pl. 4, fig. 9. Take a tube which is very regular, and about one-eighth or one-twelfth of an inch diameter in the bore; solder a reservoir at each end, one of them much larger than the other; make a bend near the large reservoir, and then fill the instrument with alcohol to A. Above that, place the first index, which consists of a very small piece of tube closed at one end and cut off square at the other. In the interior of this tube the two ends of a hair are fixed, by means of a little rod of iron, which is pushed into the tube. Introduce a quantity of mercury above this index, make the bend B, add again mercury as far as C, then another index similar to the first. Finally, fill the rest of the tube and the half the little reservoir with alcohol, and seal the point.

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DIFFERENTIAL THERMOMETER.--This instrument is represented by pl. 3, fig. 14. Take a tube ten or twelve inches long, and one-eighth or one-twelfth of an inch internal diameter; blow a bulb at one end, and bend the tube at a right angle towards the fourth part of its length. Prepare a second tube in the same manner, and solder the bent ends together, so as to form a single tube with a bulb at each end, having previously poured into one of the bulbs a small quantity of sulphuric acid tinged red.

Instead of following the above method, you may take a single tube of twenty or twenty-four inches in length, and of the above-mentioned diameter; you solder a bulb at each end, bend the tube twice till it represents the figure, pour in the acid, and then seal the open points. The graduation of the differential thermometer, as well as of all the other thermometers, is described in a subsequent section.

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TUBE FOR CRYSTALLIZING SPERMACETI.--Take a little capillary tube; curl one of its ends into a ring, and solder the other to a cylindrical reservoir, two-thirds of the capacity of which you fill with very pure spermaceti dissolved in sulphuric ether; you then seal the point of the reservoir. See pl. 3, fig. 27.

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TUBE FOR DEMONSTRATING THE NON-CONDUCTABILITY OF HEAT BY LIQUIDS.--This is represented by pl. 2, fig. 26. It is a tube sealed at one end, bordered at the other, and bent in such a manner as conveniently to permit the upper part of a column of liquid to be exposed to heat.

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TUBE FOR ESTIMATING THE DENSITY OF VAPOURS.--Represented by pl. 2, fig. 14. It is merely a tube sealed at one end, bordered at the other, and bent as shewn by the figure.

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TUBES FOR EXPOSING SUBSTANCES TO HEAT AND GASES.--This instrument consists of a tube bent in the middle into a U. Pl. 3, fig. 3. It is much employed in chemistry, for containing substances which we wish at the same time to expose to an elevated temperature and to the action of certain gases. This tube can also be employed for cooling gases, or liquids, in distillation; the bent part being, in this case, dipped into water or a freezing mixture, or enveloped in wet paper or cloth.

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TUBES FOR THE PRESERVATION OF OBJECTS OF NATURAL HISTORY, OR OF CHEMICAL PREPARATIONS.--Take a tube of which the width and length corresponds with the object which is to be enclosed; draw it out at one end, and, after having obstructed the point, twist it into a ring. Introduce the object by the open extremity, which you must afterwards draw out; fill the tube with the liquid necessary to preserve the object, and then seal the point. See pl. 2, fig. 27.

If you desire to have the power of taking out the object at will--as, for example, when grain is preserved, or when, in chemistry, the tube is employed to contain salts and other compounds, of which small quantities are now and then required for use--you do not seal the end of the receiver, but border it in such a manner that it can be closed by a cork.

In some cases a cork is not sufficient to secure the substance from the action of air: it must then be assisted with a little cement. By melting together two parts of yellow wax, one part of turpentine, and a small quantity of Venetian red, a very useful cement for such purposes is obtained.

It is sometimes necessary to _suspend_ the objects enclosed within the tube: you then introduce a little glass hook, the tail of which you solder to the upper extremity of the tube; managing this operation at the same time that you make the external ring for the support of the instrument. By turning the hook round cautiously, which is done when the end of the tube is in a soft state, and by cooling the whole with care, you may succeed in fixing the hook in the centre of the tube. See pl. 3, fig. 20.

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TUBE FOR EMPTYING EGGS.--It is a simple tube, drawn out to a capillary point at one end, and bent there into a V. See pl. 3, fig. 23.

The application which the author has made of this instrument, and of the tube represented by pl. 3, fig. 26, has been shewn in a memoir inserted in the _Annales des Sciences Naturelles, Tom. XV. Novembre_ 1828, concerning a new method of preparing and rendering durable collections of eggs destined for cabinets of Natural History.

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VIAL OF THE FOUR ELEMENTS.--This instrument is represented by pl. 2, fig. 27. Take a tube drawn out at one end, obstruct the canal two inches from the extremity, and twist the contracted part into a ring. Draw out the other end of the tube, introduce the proper liquids, remove the point of the tube, and seal it. The liquids generally employed for filling the vial of the four elements are, 1. Mercury; 2. A very concentrated solution of carbonate of potash; 3. Oil of turpentine; 4. Alcohol. A portion of air is also allowed to remain in the tube.

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WATER HAMMER.--Pl. 2, fig. 18, is a representation of this instrument. Choose a tube of a good diameter, and with thick sides; seal it at one end and draw it out at the other. Blow a bulb at the base of the contracted part; then, having put a quantity of water in the tube, let it boil therein, to expel the atmospherical air. When you imagine that all the air has been expelled, and that nothing remains in the tube but steam and water, seal the open point.

When you have to seal a tube in this manner, you should be careful to draw out the extremity of the tube somewhat abruptly, and leave a very small opening, so that it shall be sufficient to expose the point to the jet of a candle blown by a mouth blowpipe, to have the sealing completely and suddenly effected. You can afterwards round this sealed part by turning it in the flame of the lamp, provided, however, that you have preserved a sufficient thickness of glass at the sides of the point. If you omit to take this precaution, the pressure of the atmosphere, acting with great force on the softened glass when it is unsupported by the partial vacuum within the tube, is capable of producing such a flattening, or even sinking in of the matter, as could not subsequently be rectified; except, indeed, by heating simultaneously the liquid contained in the tube and the glass to be mended, which is an operation of a very delicate description.

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WELTER’S SAFETY TUBES.--After having closed a tube at one end and drawn it out at the other, give it the curvature exhibited by plate 3, fig. 18. Pierce it then laterally, in the middle of the part _a b_, and solder there the extremity of a tube, to the other end of which a funnel has been soldered: it is necessary that the funnel be closed by a cork. The soldering being terminated, a bulb must be blown and the tube bent in S, in the manner shewn by the figure. Then open the closed end, and cut off the contracted point.

THE

ART OF GLASS-BLOWING.

V.--_Graduation of Chemical and Philosophical Instruments._

OF THE SUBSTANCES EMPLOYED IN THE PREPARATION OF THESE INSTRUMENTS.

Before proceeding to the subject of _graduation_, it is necessary to say a few words respecting the substances which are generally employed to fill a variety of instruments, particularly barometers and thermometers.

_Mercury._--It ought to be completely purified from all foreign substances. You can separate it from the dust it may contain by passing it through a piece of chamois leather; you tie a very hard knot, and by pressure oblige the mercury to pass out in a fine rain. This process is sufficient for the purification of mercury which merely contains extraneous bodies in suspension; but it is not sufficient when the mercury to be purified contains tin, lead, or other metals, in solution. It is then necessary to distil the mercury; upon which the fixed metals remain behind. The oxide of mercury produced by the distillation is removed by agitating the distilled metal with sulphuric acid, and subsequently washing it with a large quantity of water, till all the acid is removed; it is then dried as completely as possible with blotting-paper, and afterwards is moderately warmed.

_Alcohol_ ought to be very pure and well rectified. It is necessary to colour it, because, being colourless of itself, it could not be seen in capillary tubes. To colour alcohol, you infuse carmine in it, and, after some time, decant or filter the clear solution. The liquid should be perfectly transparent, and free from all extraneous substances. It is not proper to employ alcohol in the construction of standard thermometers; mercury being much preferable.

_Sulphuric Acid._--It is made use of for the differential thermometer, and the thermoscope of Rumford. It has the advantage of being lighter than mercury, and very slightly volatile: these two qualities, joined to its tendency to absorb the vapour of water, render it very proper to be employed for various instruments. It must be very concentrated, and tinged red by carmine.

_Ether._--Sulphuric and nitric ether, with which some small instruments are filled, are merely employed to shew with what facility these liquids are brought to their boiling point.

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OF GRADUATION IN GENERAL.--Graduation, generally speaking, consists in dividing lines, surfaces, and capacities, into a certain number of equal or proportional parts. It is not our intention to treat here of the methods furnished by practical geometry for effecting such divisions with mathematical accuracy; these methods are known to every body. We shall confine ourselves to describing the processes of graduation which are peculiar to the instruments constructed by the glass-blower.

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EXAMINATION OF THE BORE OF TUBES.--We have already observed, that, for standard thermometers and other instruments which require to be made very accurate, it is necessary to employ tubes which are extremely regular in the bore. When a drop of mercury, passed successively along all parts of the tube, forms everywhere a column of the same length, the examiner is assured of the goodness of the tube.

That a tube may be regular in the bore, it is not necessary that the bore be cylindrical; it is sufficiently accurate when equal lengths correspond to equal capacities. A tube with a flat canal, for example, can be perfectly accurate without at all approaching the cylindrical form. It is only necessary that a drop of mercury occupy everywhere the same length. We may observe, by,the way, that, in flat canals, the flattening should be always in the same plane.

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DIVISION OF CAPILLARY TUBES INTO PARTS OF EQUAL CAPACITY.--As it is very difficult to meet with capillary tubes which are exactly regular in the bore, it happens that the tubes which glass-blowers are obliged to employ have different capacities in parts of equal length. You commence the division of these tubes into parts of equal capacity by a process described by M. Gay-Lussac. You introduce a quantity of mercury, sufficient to fill rather more than half the tube, and make a mark at the extremity of the column. You then pass the mercury to the other end of the tube, and again mark the extremity of the column. If you so manage that the distance between the two marks is very small, you may consider the enclosed space as concentric, and a mark made in the middle of the division will divide the tube into two parts of evidently equal capacity. You divide one of these parts, by the same process, into two equal capacities, and each of these into two others; and in this manner you continue to graduate the tube until you have pushed the division as far as you judge proper.

But it is still more simple to introduce a drop of mercury into the tube, so as to form a little cylinder, and then to mark the two extremities of the cylinder. If it were possible to push the drop of mercury from one end of the tube to the other, in such a manner as to make it coincide, at every removal, with the last mark, it would be very easy to divide the tube accurately; but as it is very difficult, not to say impossible, to attain this precision of result in moving the column of mercury, you must endeavour to approach exactness as nigh as may be. You measure, every time you move the mercury, the length of the cylinder it produces, and carry this length to the last mark, presuming the small space which is found between the mark and the commencement of the column to be fairly represented by the same space after the column. You thus obtain a series of small and corresponding capacities.

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GRADUATION OF GAS JARS, TEST TUBES, &C.--If the tube is regular in the bore, close one end, either by sealing it at the lamp, or by inserting a cork, and pour into the interior two or three small and equal portions of mercury, in order to have an opportunity of observing the irregularities produced by the sealed part. Take care to mark, with a writing diamond, the height of the mercury, after the addition of each portion. When equal portions of mercury are perceived to fill equal spaces, take with the compass the length of the last portion, and mark it successively along the side of the tube, where you must previously trace a line parallel to its axis.

For tubes which are irregular in the bore, and where equal lengths indicate unequal capacities, it is necessary to continue the graduation in the same manner that you commenced it--that is to say, to fill the tubes by adding successively many small and equal portions of mercury, and marking the height of the metallic column after every addition. These divisions will of course represent parts of an ounce or of a cubic inch according to the measure which you make use of. When you have thus traced on the tube a certain number of equal parts, you can, by means of the compasses, divide each of them into two other parts of equal length. The first divisions being very close to one another, the small portion of tube between every two may be considered without much risk of error as being sensibly of equal diameter in its whole extent.

When the tube which you desire to graduate is long and has thin sides, it would be difficult to fill it with mercury without running the risk of seeing it break under the weight of the metal. In this case, you must use water instead of mercury.

Bell-glasses of large dimensions are graduated by filling them with water, placing them in an inverted position on a smooth and horizontal surface, which is slightly covered with water, and passing under them a series of equal measures of air. But it is then necessary to operate constantly at the same temperature and under the same atmospheric pressure, because air is very elastic and capable of being greatly expanded.

In all cases, tubes, bell-glasses, &c. ought to be held in a position perfectly vertical. The most convenient measure is a dropping-tube, on the stalk of which a mark has been made, or a small piece of tube, sealed at one end, and ground flat at the other; the latter can be accurately closed by a plate of glass.

The marks which are traced on tubes being generally very close to one another, you facilitate the reading of the scale by giving a greater length to those marks which represent every fifth division, and by writing the figures merely to every tenth division. See pl. 4, fig. 8. The number of divisions is somewhat arbitrary; nevertheless, 100, 120, 360, 1000, are divisions which, in practice, offer most advantages.

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GRADUATION OF HYDROMETERS.--Cut a band of paper on which the graduation of the instrument can be traced, and let fall upon it a little drop of sealing-wax; then roll the paper upon a little glass tube, and introduce it into the stalk of the hydrometer. The instrument is afterwards to be plunged into distilled water, which is carefully kept at the temperature of 40° F. above zero. Give the instrument sufficient ballast to make it sink till the point (_a_, pl. 4, fig. 20,) which you desire to make to represent the density of water, touches the surface of the water. Mark this point with much precision; it is the zero of the instrument. The other degrees are taken by plunging the hydrometer into distilled water to which you have added 1, 2, 3, 4, 5, &c. _tenths_, or 1, 2, 3, 4, 5, &c. _hundredths_, of the substance for which you wish to construct the hydrometer, according as you desire the scale to indicate tenths or hundredths.

When you have thus marked the degrees on the stalk of the instrument, transfer them to the paper with the help of the compasses. The scale being completed, replace it in the tube of the hydrometer, where it must be fixed; in so doing, take care to make the degrees on the scale coincide precisely with those marked on the stalk.

You can thus procure hydrometers for alcohol, acids, salts, &c. which are instruments that indicate the _proportion_ of alcohol, acid, salt, &c. contained in a given mass of water.