Part 34

Very different optical effects, however, follow if the rays from the various-coloured flames are made to pass through a prism. As is well known, if a ray of ordinary white light is made to traverse a prism, when it issues from the prism it has become decomposed or dissected into seven luminous rays of as many different colours, the coloured image thus produced being called a prismatic spectrum, or simply a spectrum.

This phenomenon is owing to the prism refracting or bending out of its course the beam of light sent through it, and to each coloured ray of which the beam is made up being differently refracted.

"If, however, instead of the white flame coloured flames are examined by means of a prism, the light being allowed to fall through a narrow slit upon the prism, it is at once seen that the light thus refracted differs essentially from white light, inasmuch as it consists of only a particular set of rays, each flame giving a spectrum containing a few bright bands. Thus, the spectrum of the yellow soda flame contains only one fine bright yellow line, whilst the purple potash flame exhibits a spectrum in which there are two bright lines, one lying at the extreme red, and the other at the extreme violet end. These peculiar lines are always produced by the same chemical element, and by no other known substance; and the position of these lines always remains unaltered. When the spectrum of a flame tinted by a mixture of sodium and potassium salts is examined, the yellow ray of sodium is found to be confined to its own position, whilst the potassium red and purple lines are as plainly seen as they would have been had no sodium been present."[57]

[Footnote 57: Roscoe.]

Equally characteristic and well-defined spectra, the bands in which have each an invariable and fixed position in the spectrum, are also produced when the coloured flames arising from heating to the requisite point the remaining salts of the alkalies and alkaline earths are examined by the prism. On the opposite page the first spectrum shows some of the fixed dark lines that are always observed when a solar beam is examined by the spectroscope. These lines are compared with the position of some of the more important bright lines furnished by the spectra of the metals of the alkalies and alkaline earths, when their chlorides are heated upon a loop of platinum wire introduced into the flame of a Bunsen gas-burner. The characteristic bright lines given by each metal are denoted by the letters of the Greek alphabet, the earliest letter indicating the most strongly marked lines.

In the potassium spectrum the most characteristic bright lines are the red line K [Greek: a], and violet line K [Greek: b]. In the case of sodium nearly the whole of the light is concentrated on the intense yellow double line Na [Greek: a]. In the lithium spectrum a crimson band, Li [Greek: a], is the prominent line; Li [Greek: b] is seldom visible, but at the elevated temperature of the voltaic arc an additional blue line becomes very intense. In the spectrum of cæsium two lines in the blue, Cs [Greek: a] and Cs [Greek: b], are strongly marked. In rubidium the lines Rb [Greek: a] and Rb [Greek: b] in the blue, and Rb [Greek: g] in the red are almost equally specific. Thallium is recognised by the intense green line Il [Greek: a]. The spectra of the metals of the alkaline earths are equally definite, though more complicated.

By means of the spectroscope quantities so inconceivably minute as the 33,000th of a grain of chloride of rubidium, the 170,000th of a grain of chloride of cæsium, the 2,500,000th of a grain of sodium, and the 6,000,000th of a grain of lithium, have been detected, and have revealed themselves to the sight by their characteristic bands in the spectrum. Hence it is that in making use of this branch of analysis the chemist has been enabled to show the universality of many elements hitherto regarded as being very sparingly distributed throughout the globe.

Thus lithium, which until lately was supposed to be one of the rare elements, has been found as a constituent of tea, tobacco, milk, blood, and in almost all spring waters. Furthermore, the prodigiously sensitive reactions afforded by the spectroscope have not only revealed the presence of infinitesimal quantities of known elements, but have led to the discovery of new ones which had escaped detection by the older and less delicate processes of analysis. It was by means of spectrum analysis that the two alkali metals, cæsium and rubidium, were discovered by Bunsen and Kirchkoff in 1860 in a mineral water at Durkheim, and that Mr Crookes in 1861 discovered the metal thallium in the deposit found in the flue of a pyrites furnace; whilst still more recently Messrs Reich and Richter, in a spectrum examination of a zinc ore from Freiberg, discovered the metal indium.

The most brilliant spectra are given by those salts which are the most easily volatilised, such as the chlorides, iodides, and bromides of the different metals. But it is only the metals of the alkalies and alkaline earths that give spectra that are characteristic. When it is desired to obtain the spectra of the other metals, they may be raised to the requisite temperature by means of the electric spark, which in passing through the two points of the metal operated upon volatilises a minute quantity of it, and thus enables it to emit its particular light. The electric sparks are best obtained by means of Ruhmkorff's coil. Thus each metal may be made to yield a spectrum which specially belongs to it, and to it alone. When the electric discharge is sent through a compound gas or vapour, owing to the intense temperature generated separation of its constituents must take place, since the spectra produced are those of the elementary components of the gas. The permanent gases give each their peculiar spectrum when they are strongly heated, by which they may be recognised; thus the spectrum of hydrogen is composed of three bands, one being bright red, one green, and the other blue. Nitrogen gives a very complicated spectrum.

The accompanying figure exhibits a very complete form of the spectroscope adapted to a single prism.

P represents a flint-glass prism supported on the cast-iron tripod F, and retained in its place by the spring _c_. At the end of the tube A nearest the prism is a lens, placed at the distance of its focus for parallel rays from a vertical slit at the other end of the tube. The width of the slit can be regulated by means of the screw _e_. One half of this slit is covered by a small rectangular prism designed to reflect the rays proceeding from the source of light D, down the axis of the tube, whilst the rays from the source of light E pass directly down the tube. By this arrangement the observer stationed at the end of the telescope B is able to compare the spectra of both lights, which are seen one above the other, and he can at once decide whether their lines coincide or differ. _a_ and _b_ are screws for adjusting the axis of the telescope so as to bring any part of the slit at _e_ into the centre of the field of vision.

The telescope as well as the tube C is moveable in a horizontal plane around the axis of the tripod. The tube C contains a lens at the end next to the prism, and at the other end is a scale formed by transparent lines on an opaque ground; it is provided with a levelling screw, _d_. When the telescope has been properly adjusted to the examination of the spectrum, the tube C is moved until it is placed at such an angle with the telescope and the face of the prism, that when a light is transmitted through the scale the image of this scale is reflected into the telescope from the face of the prism nearest the observer. This image is rendered perfectly distinct by pushing in the tube which holds the scale nearer to the lens in C, or withdrawing it to a greater distance, as may be required. The reflected lines of the scale can then be employed for reading off the position of the dark or bright lines of the spectrum, as both will appear simultaneously overlapping each other in the field of the telescope.

By turning the tube C round upon the axis of the tripod any particular line of the scale can be brought to coincidence with any desired line of the spectrum. Stray light is excluded by covering the stand, the prism, and the ends of the tube adjoining it with a loose black cloth. The dispersive power upon the spectrum may be much increased by using several prisms instead of one. Kirchkoff used four prisms in his experiments upon the solar spectrum. Great care must be observed in placing the prisms; the refracting edge of each prism must be exactly vertical, and the position of minimum deviation for the rays to be observed must be obtained.

The preceding remarks have reference to the spectra produced when the vapours of certain elements are evolved in flame derived from artificial sources. When, however, solar light is examined by the spectroscope, results entirely the reverse follow.

If a beam of sunlight be sent through the slit of the spectroscope, the prismatic image is seen to be intersected by a number of fine black lines, varying in thickness and intensity, and invariably occupying the same relative position in the solar spectrum. These lines were first noticed so far back as 1815 by a German optician, Frauenhofer, after whom they were named Frauenhofer's lines; but it was not until the invention of the spectroscope that the origin of these lines could be accounted for. By so arranging the instrument as to cause the spectrum from a solar beam, and that from a metallic element, to fall upon the field of the telescope, so that the solar spectrum shall be above the other, both being perfectly parallel; the bright bands or lines of the metal are all seen to be continued in the dark solar lines, for, as may be seen by consulting the plate of the different spectra, several lines are sometimes produced by one element alone. If, for instance, the sodium and solar spectra are thus compared, the bright yellow sodium line will be found to agree exactly not only in position, but also in intensity and breadth, with one of the dark solar ones. And the same thing occurs when the comparison is made with many of the other metals, the bright lines in the respective spectra furnished by them are each coincident with a particular dark line in the solar spectrum, and from every dark line in the latter a corresponding bright one can be found amongst the spectra of the metals. From what has just been stated, the inference seems irresistible that this coincidence between the dark solar lines and the bright lines of the metals cannot be accidental, but must be due to some intimate connection between them, and that this is the case can be proved beyond refutation by a simple experiment, in which the bright metallic lines can be changed into dark ones, corresponding in every particular with those of the solar spectrum. Thus the bright yellow soda lines coincident with Frauenhofer's lines can be converted into dark ones by allowing the rays from a strong source of white light to pass through a flame coloured with sodium, and then making them fall upon the slit of the spectroscope. If we examine the spectrum obtained by this means, instead of seeing the usual bright double band upon a black ground, there will be presented to our sight a double dark line, corresponding exactly with the position and width of the sodium line, and instead of the black ground there will be a continuous spectrum of white light, as in the solar spectrum.

The explanation of this remarkable phenomenon is due to Kirchkoff, and is as follows:--When any substance is heated sufficiently to render it luminous, rays of a certain and definite degree of refrangibility are given out by it; whilst the same substance has also the power of absorbing rays of this identical refrangibility. In the above experiment, therefore, the yellow flame absorbed the same kind of light as it gave out, a corresponding decrease of intensity in its own particular position in the spectrum occurred, and a dark line showed itself in consequence.

In the same manner and under similar conditions the spectra of many other substances have been reversed.

Reasoning on these facts, Kirchkoff has been able to account for the presence in the solar spectrum of Frauenhofer's dark lines. He supposes that in the luminous atmosphere surrounding the sun the vapours of various metals are present, each of which would give its characteristic system of bright lines; but behind this incandescent atmosphere containing metallic vapour is the still more intensely heated solid or liquid nucleus of the sun, which emits a brilliant continuous spectrum, containing rays of all degrees of refrangibility.

When the light of this intensely heated nucleus is transmitted through the incandescent photosphere of the sun, the bright lines which would be produced by the photosphere are reversed, and Frauenhofer's dark lines are only the reversed bright lines which would be visible if the intensely heated nucleus were no longer there.

The correctness of this theory has been rigorously tested by Kirchkoff himself, who submitted the solar spectrum to a most minute and searching examination.

As a result of the knowledge thus obtained, the presence of certain metals in the sun's atmosphere was an inevitable deduction. The metals hitherto detected in the solar photosphere are--iron, sodium, magnesium, calcium, chromium, nickel, barium, copper, zinc, strontium, cadmium, cobalt, manganese, aluminium, and titanium. Hydrogen also exists in large quantity as an incandescent gas, and gives rise to the red protuberances that may be observed during a total eclipse.

During the total eclipse of 1869, M. Janssen, a French astronomer, was enabled to obtain and figure the specimen of these red protuberances, which, taken exclusively from that source of light, gave not dark lines, but bright ones, corresponding in position with those of hydrogen, magnesium, and sodium.

The fixed stars, unlike the moon and planets, which shine only by reflected light, are not merely illuminated by self luminous bodies, and yield spectra, which show them to contain many elements known to us; their spectra are crossed by dark lines similar to, but not identical with those given by the sun's light. The spectrum yielded by the star Aldebaran shows it to contain hydrogen, sodium, magnesium, calcium, iron, tellurium, antimony, bismuth, and mercury; in the spectrum of Sirius only sodium, magnesium, and hydrogen have been found; whilst in that of Orionis there is an absence of hydrogen. Most of the nebulæ and comets give spectra in which there are only bright lines. It is hence inferred that these celestial bodies are composed of masses of glowing gas, and, unlike the sun and stars, do not consist of a solid or liquid mass surrounded by a gaseous atmosphere. In the nebulæ hydrogen and nitrogen only have been found; and in comets, principally carbon.

=ANANAS HEMP= (_Ananassa sativa_, _S. Brumelia ananas_, as well as other species). This hemp comes from the West Indies and Central and South America, where the common ananas is cultivated. It is rather inferior to some varieties for spinning.

=ANASTATIC PRINTING.= See PRINTING and ZINCOGRAPHY.

=ANATHERIN BALSAM.= The following formula is published by the Netherlands Society:--Tincture of myrrh, 160 grms.; tincture of catechu, 80 grms.; tincture of guaiacum, 40 grms.; tincture of rhatany, 40 grms.; tincture of cloves, 30 grms.; spirit of cochlearia, 20 grms.; oil of cassia, 20 drops; otto of roses, 1 drop; proof spirit, 630 grms.

=ANATHERIN BALSAM= (J. G. Popp, Vienna). A mouth-wash. Red sandal wood, 20 parts; guaiacum wood, 10 parts; myrrh, 25 parts; cloves, 15 parts; cinnamon, 5 parts; oils of cloves and cinnamon, of each, 2/3 part; spirit, 90 per cent., 1450 parts; rose water, 725 parts. Digest and filter.

Dr Hager, who gives the above, says that on the expiration of the patent the following formula was published, but that a preparation made from that process had only a distant resemblance to the actual compound. Myrrh, 1 part; guaiacum wood, 4 parts; saltpetre, 1 part; to be macerated for a night with corn brandy, 120 parts; spirit of cochlearia, 180 parts. Then distil of this 240 parts, in which are to be digested for 14 days garden rue, cochlearia, rose leaves, black mustard, horseradish, pellitory root, cinchona bark, club-moss, sage-vetiver, and alkanet root, of each 1 part. Strain and filter, and to each 120 parts of the filtrate add 1 part of spirit of nitrous ether. (Hager.)

=ANATOM'ICAL.= _Syn._ ANATOM'ICUS, L.; ANATOMIQUE, Fr.; ANATOMISCH, Ger. Belonging to anatomy or dissection.

=Anatomical Prepara'tions.= Objects of interest in both surgical and pathological anatomy, and specimens in natural history, preserved by subjecting them to antiseptic processes, to which is also frequently added injection with coloured fluids (which subsequently harden), amalgams, or fusible metal, in order to display more fully the minute vessels, or the microscopic anatomy of the several parts. See FUSIBLE ALLOY, INJECTIONS, PREPARATIONS, PUTREFACTION, SKELETONS, SOLUTIONS, &c.

=ANCH'OVY= (-ch[=o]'-). _Syn._ ANCHOIS, Fr.; ANCHOVE, ANSCHOVE, Ger.; ACCIUGHE, ANCHIOVE. It.; ANCHOVA, Port., Sp. The _clu'pea encrasic'olus_ (Linn.), a small fish of the herring tribe, closely resembling the English sprat. It is common in the Mediterranean, and occurs in the greatest abundance and of the finest quality about the island of Gorgona, near Leghorn. It is taken in the night, during May, June, and July.

Anchovies are prepared for sale or exportation by salting or pickling them--the heads, intestines and pectoral fins having been first removed, but not the scales, and afterwards packing them, along with rock-salt, in the small kegs in which they are imported into this country. The small fish are valued more than the larger ones. For the table they are often fried to a pale amber colour, in oil or butter; having previously been scraped clean, soaked for an hour or two in water, wiped dry, opened (without dividing the fish), and had the back-bones removed. Before being put into the pan they are usually highly seasoned with cayenne; and after being again closed, are dipped into a rich light batter. They are also divided into fillets, and served as sandwiches, or in curried toasts. Anchovies are also extensively potted (POTTED ANCHOVIES), and made into butter (A.-BUTTER), and into sauce (A.-SAUCE), particularly the last.

The anchovy has a fine and peculiar flavour, and is eaten as a delicacy all over Europe. It was known to the Greeks and Romans, who prepared from it a kind of garum for the table. It is said to be aperitive, stimulant, and stomachic.

The high price of genuine Gorgona anchovies has led the fraudulent dealer to either substitute for them, or mix with them, fish of a less expensive kind. The most frequent SUBSTITUTIONS are Dutch, French, and Sicilian fish of allied species or varieties, sardines and even the common sprat. The genuine Gorgona fish is about the length of one's finger; and may be known by its silvery appearance; by the greater thickness of its head, which is sharp-pointed, with the upper jaw considerably the longest, and the mouth deeply divided; the dusky brown colour of its back,[58] and the pink salmon colour of its flesh. When only 3 months old, its flesh is pale; when of 6 months, rather pink; when of 10 to 12 months (or in its prime), a beautiful deep pink colour; and when much older, darker, but less lively. The fin-rays, varying in number with the age of the fish, are--

Yarrell. Hassall.[59] Dorsal 14, 16 (?). Pectoral 15, -- Ventral 7, -- Anal 18, 19 (?). Caudal 19, 26 (?).

These fins are delicate in structure and greenish-white; and the membranes connecting the rays almost transparent. "The length of the head, compared with the length of the body alone, is as 1 to 3; the depth of the body but 2-3rds of the length of the head, and compared to the length of the whole fish is as 1 to 7;" the tail is deeply forked, the gill covers are elongated, and the scales of the body large and deciduous." "The breadth of the eye is 1-5th of the length of the whole head."[60] Dutch fish may be generally known by being deprived of the scales, and the French fish by their larger size; and both by the paler or whiter colour of their flesh; and sardines and sprats by the flesh being white. The genuine fish may also be known by the pickle, after repose or filtration, being of a clear pinkish colour, without any red sediment; whilst that from spurious kinds is turbid and red only when agitated, and deposits a heavy red sediment (Armenian bole, Venetian red, or red ochre) on repose. See BUTTER, POTTING, POWDERS, SAUCES, &c.

[Footnote 58: The colour of the top of the head and back is, in the recent fish, blue, with a tinge of green. (Yarrell.)]

[Footnote 59: Counted, by Dr A. H. Hassall, in fish in the preserved state.]

[Footnote 60: Yarrell's 'British Fishes'.]

=Anchovies, Brit'ish.= See SPRATS.

=ANCHU'SIC ACID= (-k[=u]'z[)i]k). See ANCHUSINE.

=ANCHU'SINE.= (-k[=u]'z[)i]n). [Eng., Fr.] _Syn._ ANCHU'SIC ACID*, PSEU'DO-ALKANN'INE*, PSEUDO-ALKA''NIUM*; ANCHUSI'NA, L. The resinoid constituting the colouring matter of alkanet-root (which _see_).

=ANCHYLO'SIS= ([)a]ngk-e-). [L.; prim. Gr.] _Syn._ ANKYLO'SIS, ANCYLO'SIS ([)a]n-se-), L.; ANKYLOSE, Fr., Ger. In _pathology_, stiffness or immobility of a joint naturally moveable. Anchylosis is either true or complete, as when the extremities of the bones forming a joint are reunited and immovable; or false, or incomplete, where the affection depends upon a contraction of the tendons and ligaments surrounding the joints, which nevertheless admit of a small degree of motion. For the first there is no available remedy; for the second gentle and progressive flexion and extension of the part daily (carefully avoiding violence), friction with oleaginous and stimulating liniments, and the use of the hot bath, vapour bath, or hot-air or Turkish bath, and electricity, have been strongly recommended, and have frequently proved successful.

=ANCYLO'SIS.= See ANCHYLOSIS.

=ANDITROPFEN= (Kirchner and Menge Arolsen), for weak digestion. Senna, 20 parts; rhubarb, 3 parts; jalap, 6 parts; zedoary root, 2 parts; ginger, 2 parts; galangal, 3 parts; soda, bicarbonate, 5 parts; sugar, 15 parts; water, 300 parts; spirit, 65 parts. After digestion this is to be strained and mixed with an infusion of 30 parts of yarrow (with the flowers) in 300 parts of hot water. After standing some time filter. (Hager.)

=ANDROGRAPHIS PANICULATA.= (Ind. Ph.) _Syn._ KARIYÁT. _Habitat._ Commonly in shady places all over India.--_Officinal part._ The dried stalks and root (Andrographis Caules et Radix, Kariyat, Creyat). The stem, which is usually met with, with the root attached, occurs in pieces of about a foot or more in length, quadrangular, of a lightish-brown colour, and persistent bitter taste.--_Properties._ Bitter tonic and stomachic, very analogous to quassia in its action.--_Therapeutic uses._ In general debility, in convalescence after fevers, and in the advanced stages of dysentery.

_Preparations_:--

=Compound Infusion of Kariyát= (Infusum Andrographis compositum). Take of Kariyát, bruised, 1/2 an ounce; orange-peel and coriander fruit, bruised, of each, 60 grains; boiling water, 10 fluid ounces. Infuse in a covered vessel for an hour and strain.--_Dose._ From 1-1/2 to 2 fluid ounces, twice or thrice daily.