{ Phosphate of soda 2 { Dilute nitric acid 1
{ Sulphate of soda 2 { Muriatic acid 1
The effects of most of these mixtures may be considerably increased by previously cooling the ingredients _separately_ in other freezing mixtures.
In connexion with this branch of science, and especially with chemistry, the youthful philosopher should practise the art of decanting air from one jar to another standing over water, beginning by pa.s.sing it from a small to a larger jar, then with two of equal size; and when he can accomplish the transfer without permitting even one bubble to escape, he may essay the much more difficult task of transferring the air from a large to a smaller jar.
[Ill.u.s.tration]
He should also practise using the blowpipe until he can keep up a steady and uninterrupted flame for ten minutes or a quarter of an hour, without stopping for breath. It is quite possible to replenish _wind_ in the mouth, which alone ought to be used, without interrupting the breathing for an instant, but it requires some practice.
[Ill.u.s.tration: (1) Box blowpipe, A, the stem; B, the mouthpiece; C, the box, in which is placed a piece of sponge to absorb the moisture of the breath; D, the extremity (this is moveable, and each blowpipe has several, with different apertures); E, the hollow pivot, in which the extremity and its arm turn. The box is opened by the milled ring seen at the bottom.]
SPECTRUM a.n.a.lYSIS.
If the youthful student wishes to occupy his leisure in a most amusing and instructive manner, and at the same time to acquire a ready method of testing for the presence of the various metals, he cannot do better than purchase from Mr. John Browning, of 111, Minories, the Amateur"s Spectroscope, price two guineas; or, if sufficiently ingenious, a prism and lenses may be purchased for sixteen shillings, and fitted up in paper tubes. Indeed, it is always better to buy some complete set or portion of a set of apparatus, instead of the trashy so-called "Boys"
Cabinets," which contain very much that is useless and very little for instructive experiments. The instrument enables the observer to examine the properties of metallic salts when in the state of a glowing or incandescent gas. Common light affords a continuous spectrum or band of colours, red at one end and violet at the other, the intermediate colours being orange, yellow, green, blue, and indigo. The spectra of the metals in the state of luminous vapour are not continuous, but are represented by distinct bands or lines of light.
[Ill.u.s.tration: Solar Spectrum, and Spectra of the Alkanes and Alkaline Earths. Copied from the Original Drawings of G. KIRCHHOFF and R.
BUNSEN.]
Every element, metallic or otherwise, when converted into a luminous gas, produces lines which are always found in the same part of the spectrum, and are therefore unalterable in position. The instrument (Fig. 1) is called the Spectroscope.
[Ill.u.s.tration: _Fig. 1._--THE AMATEUR"S SPECTROSCOPE.
A, Tube with knife edges; B, the prism; C, the telescope; D, the lamp, supplied with gas by pipe E; F, stand carrying the platinum wire. The wire may be held in the hand, but is more convenient when attached to a stand.]
The instrument (Fig. 2) will exhibit the dark fixed lines in the solar spectrum, and also the bright lines in the spectra of incandescent metals.
[Ill.u.s.tration: _Fig. 2._--THE HERSCHEL-BROWNING DIRECT VISION SPECTROSCOPE.]
[Ill.u.s.tration: _Fig. 3._
A, another form of gas lamp; B, the flame; C, adjusting stand to carry the platinum wire and the lamp.]
HOW TO USE THE SPECTROSCOPE.
Screw the tube carrying the knife edges at the small end into the prism bore, and the telescope into its proper ring. Now place any common bright light exactly in front of the knife edges, and while looking through the telescope arrange the knife edges until a bright and continuous spectrum is visible.
TO OBTAIN THE BRIGHT LINES IN THE SPECTRUM GIVEN BY ANY SUBSTANCE.
Remove the bright flame from the front of the knife edges, and subst.i.tute in its place the flame of a common spirit lamp or, still better, a gas-jet known as a Bunsen"s Burner. Take a piece of platinum wire about the substance of a fine sewing needle; bend the end into a small loop about the eighth of an inch in diameter; fuse a small bead of the substance, or salt, to be experimented on into the loop of the platinum wire, and attaching it to any sort of light stand or support, bring the bead into the front edge of the flame, a little below the level of the knife edges. If the flame be opposite the knife edges, on looking through the eye-piece of the telescope the fixed lines due to the substance will be plainly visible. When minute quant.i.ties have to be examined, the substance should be dissolved, and a drop of the solution, instead of a solid bead, be used on the platinum wire.
The delicacy of this method of a.n.a.lysis is very great. Swan found, in 1857 (Ed. Phil. Trans., vol. xxi. p. 411), that the lines of sodium are visible when a quant.i.ty of solution is employed which does not contain more than 1/2,500,000 of a grain of sodium.
To view Fraunhofer"s lines on the solar spectrum it is only necessary to turn the knife edges towards a white cloud, and make the slit formed by the knife edges very narrow by turning the screw at the side of them. In every instance the focus of the telescope must be adjusted in the ordinary way, by sliding the draw tube until it suits the observer"s sight, and distinct vision is obtained.
It should be noted that lines at various parts of the spectrum require a different adjustment in focussing the telescope.
The small prism turning on a joint in front of the knife edges is for the purpose of showing two spectra in the field of view at the same time. To do this it must be brought close to the front of the knife edges. Then one flame must be placed in the position in which the flame of the candle is shown in the small figure, and the other directly in front of the slit. On looking through the telescope, as before described, the spectra due to the two substances will be seen one above the other.
When the slit is turned towards a bright cloud, and a light is used in the position of the candle flame, the spectrum of any substance may be seen compared with the solar spectrum. In this manner Kirchhoff determined in the solar spectrum the presence of the lines of the greater number of the elements which are believed to exist in the sun.
PROFESSOR STOKES" ABSORPTION BANDS.
This instrument is expressly adapted to the prismatic a.n.a.lysis of organic bodies, according to the method recommended by Professor Stokes in his lecture at the Chemical Society, printed in the _Chemical News_.
To observe these bands it is only necessary to place a very dilute solution of the substance in a test-tube, then fix the test-tube in the small clip attached to a ring which slips on in front of the knife edges. Upon bringing any bright light in front of the tube, on looking through the telescope, if the instrument has been properly adjusted, a bright spectrum will be seen, interrupted by the dark bands due to the substance in solution.
One of the simplest and most interesting experiments of this kind can be made by preparing dilute solutions of madder, port wine, and blood.
In these very dilute solutions no difference can be detected by the una.s.sisted eye, but on submitting them in the manner already described to the test of spectrum a.n.a.lysis, very different appearances will be presented.
The absorption bands may, however, be most conveniently examined and accurately investigated by means of Sorby and Browning"s new Micro-Spectroscope.
TO MAP OUT ANY SPECTRUM.
Place the eye-piece with cross wires in the telescope, with the cross in the shape of an [X]. Then move the telescope so that the point where the wires cross comes successively in contact with the various lines, noting the readings of the nonius on the arc. From these readings, by the help of any mechanical scale of equal parts, a map may be easily constructed.
By the a.s.sistance of spectrum a.n.a.lysis four new metals have been discovered, viz. Caesium, Rubidium, Thallium, Norium. It is often a cause of grumbling with young beginners in chemistry that there is so much washing of gla.s.ses and slopping required to obtain proper results from tests; but here is a most refined mode of testing, which may be carried on in the drawing-room, and so delicate that a portion of sodium salt even less than 1/180,000,000th part of a grain can be easily detected.
Formerly the metal Lithium was considered to be a very rare one, but since the use of the spectroscope, quant.i.ties less than the 1/6,000,000th of a grain have been detected; it now appears that lithium is a very common metal, and exists in the human body, the sea, and may be obtained from many other common sources. Lithium has been found in the ashes of marine plants, the ashes of tobacco--in milk, coffee, tea, human blood, and in muscular tissue; it has also been found in meteoric stones.
The coloured plate is a faithful copy of Kirchhoff"s Diagram, and shows the solar spectrum, also the spectra of pota.s.sium, sodium, lithium, strontium, calcium, barium, rubidium.
PART IV.
Domestic Pets.
BEES.
CANARIES.
DOGS.
GOLD FISH.
GUINEA PIGS.
HEDGEHOGS.
JACKDAWS.
JAYS.
MAGPIES.
OWLS.