Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 260

The annexed plate, which is half the actual size of Bell's articulating telephone, represents that instrument in section.

[Ill.u.s.tration]

_m m_ is a permanent bar-magnet, to the upper end of which is attached a soft iron core, which becomes magnetised by the permanent magnet.

Surrounding the iron core is a coil of very fine insulated copper wire (_b_), the two ends of which are carried to the terminals (_t t_), by means of which one is connected with the line wire, and the other with the earth, _d_ is a disc of thin iron plate, either tinned or j.a.panned, about the size of a crown piece, and _c_ is the cavity or mouth-piece. Upon applying the lips to this and speaking into it, the iron disc (_d_) vibrates towards the soft iron core, the result being that a current of induced electricity is set up in the coil (_b_), Which, being in connection by means of the telegraph wire with a precisely similar arrangement at the other end of the line, reproduces there the spoken words by means of a corresponding disc. The magnet with its attachments are enclosed in a wooden case (_a a_, _a a_, _a a_); _n n_ are screws which secure the iron disk (_b_); _s_ is a screw for adjusting the distance between the polo of the magnet and the disk (_b_).

The extreme simplicity of Professor Bell's telephone was the outcome of several antecedent experiments, worked out by forms of apparatus gradually diminishing in complexity.

The German physicist Helmholtz had previously shown that by the agency of a current of intermittent electricity pa.s.sed through a tuning-fork, he could produce simultaneous vibrations in a number of other forks connected with the first by a wire, and that by varying the loudness of these vibrations by means of resonators, so as to combine the musical notes in different proportions, the resulting sound was an imitation of certain vowel sounds, or a copy of the _timbre_ of sound.

Professor Bell's first telephone was an extension of Helmholtz's device for producing vowel or composite sounds. A number of steel wires of different pitch were made into a harp, and connected by a powerful permanent magnet, the same arrangement being repeated at the other end of the circuit. In the magnetic field of the permanent magnet was an electro-magnet. When a permanent magnet is vibrated in the neighbourhood of an electro-magnet, this latter will have a current of electricity generated in it, the intensity of which will vary with the velocity of the vibrations in the permanent magnet, whilst it will be either positive or negative according to the direction of these same vibrations. So that a vowel sound, if produced by causing a number of the rods of the harp to vibrate at the same time, can be transmitted by a current of electricity, and will be reproduced by the harp at the other end of the connecting wire. If a piano were sung into whilst the pedal was down, not only would the pitch of the voice be echoed back, but an approach to the quality of the vowel would also be obtained. And theory teaches that if the piano had a very much larger number of strings to the octave, we should get not only an approximation to, but an exact vocal reproduction of the vowel. If, therefore, in the harp there were a large number of steel rods to the octave, and you were to speak in the neighbourhood of such a harp, the rods would be thrown into vibration with different degrees of amplitude, producing currents of electricity, and would throw into vibration the rods at the other end with the same relative amplitude, and the _timbre_ of the voice would be reproduced.

The effect when you vibrate more than one of these rods simultaneously is to change the shape of the electrical undulation, and a similar effect is produced when a battery is included in the circuit. In this case the battery current is thrown into waves by the action of the permanent magnets. Hence you will see that the resultant effect on the current of a number of musical-tones, is to produce a vibration which corresponds in every degree to the moving velocity of the air. Suppose, for instance, you vibrate two rods in the harp, you have two musical notes produced, but of course if you pay attention to a particle of air, it is impossible that any particle of air can vibrate in two directions at the same time; it follows the resultant form of vibration. One curve would show the vibration of a particle of air for one musical tone, the next one for another, and the third the resulting motion of a particle of air when both musical tones are sounded simultaneously. You have by the harp apparatus the resultant effect produced by a current of electricity, but the same resultant effect could be produced in the air. There is an instrument called the phonantograph. It consists of a cone which, when spoken into, condenses the air from the voice. At the small end of the cone there is a stretched membrane which vibrates when a sound is produced, and in the course of its vibration it controls the movement of a long style of wood, about one foot in length. If a piece of gla.s.s with a smoked surface is rapidly drawn before the style during its movement, a series of curves will be drawn upon the gla.s.s. I myself uttered the vowels _e_, _ay_, _eh_, _ah_, _aah_. These vowels were sung at the same pitch and the same force, but each is characterised on the gla.s.s by a shape of vibration of its own.

In fact, when you come to examine the motion of a particle of air, there can be no doubt that every sound is characterised by a particular motion.

It struck me that if, instead of using that complicated harp, and vibrating a number of rods tuned to different pitches, and thus creating on the line of wire a resultant effect, we were at once to vibrate a piece of iron, to give to that piece of iron not the vibration of a musical tone, but to give it the resultant vibration of a vowel sound, we could have an undulatory current produced directly, not indirectly, which would correspond to the motion of the air in the production of a sound.

The difficulty, however, was how to vibrate a piece of iron in the way required.

The following apparatus gave me the clue to the solution of the problem in the attempt to improve the phonantograph. I attempted to construct one modelled as nearly as possible on the mechanism of the human ear, but on going to a friend in Boston, Dr Clarence J. Blake, an aurist, he suggested the novel idea of using the human ear itself as a phonantograph, and this apparatus we constructed together. It is a human ear. The interior mechanism is exposed, and to a part of it is attached a long style of hay.

Upon moistening the membrane and the little bones with a mixture of glycerin and water, the mobility of the parts was restored, and on speaking into the external artificial ear a vibration was observed, and after many experiments we were enabled to obtain tracings of the vibration on a sheet of smoked gla.s.s drawn rapidly along. This apparatus gave me the clue to the present form of the telephone. What I wanted was an apparatus that should be able to move a piece of iron in the way that a particle of air is moved by the voice.[227]

[Footnote 227: From Professor Bell's lecture at the Society of Arts, Nov.

28th, 1877, published in the Journal of the Society, vol. 26, p. 17.]

We need not follow Professor Bell through the various stages by which he arrived at his most successful solution of this problem further than to state that the simplicity of construction exhibited in the present form of instrument did not characterise the earlier articulatory telephones.

Amongst the causes contributing to this simplicity may be mentioned the abandonment of an animal membrane attached to the iron plate, the diminution of the coil of insulated wire, and the subst.i.tution for the galvanic battery which formerly formed part of the circuit, of the permanent magnet.

Professor Bell records the curious fact that hardly any difference is observable in the results by varying the size, thickness, and force of the permanent magnet, and that beyond a remarkable effect in the quality of the voice, distinct articulations might be obtained from iron plates of from 1 inch to 2 feet in diameter and from 1/64th to 1/4th inch in thickness. With plates of uniform thickness, but of varying diameter, he obtained the following results. With a plate of small diameter the articulation was perfectly distinct, but the sound emitted was as if a person were speaking through the nose. By gradually enlarging the diameter of the plate this nasal effect as gradually disappeared, until when a certain diameter was attained a very good quality of voice manifested itself.

By continuing to enlarge the diameter, a coa.r.s.e, hollow, drum-like effect was produced, until when the diameter became very large, the sound resembled that one hears when the head is inside a barrel, and was accompanied with a reverberating sound. By reversing the above conditions--that is, by keeping the diameter constant, and varying the thickness--it was found that with a very thin plate the drum-like sound was produced; by gradually increasing the thickness this effect pa.s.sed off; then followed distinct articulation, until at a certain increase of thickness the peculiar nasal quality again developed itself.

In practice it has been found desirable, in establishing speaking communication between two distant places, to employ two telephones instead of a single one; one being applied to the mouth and the other to the ear during a conversation.

With one telephone it was no unusual occurrence for confusion to arise in consequence of the two speakers talking or listening at the same time.

So faithful is the transmission by the telephone of every variety of sound, that Mr Preece states, when in telephonic communication with Prof.

Bell, through a quarter of a mile he has heard him "laugh, sneeze, cough, and, in fact, make any sound the human voice can produce." It must be borne in mind, however, that the transmitted speech can only be distinctly heard in the immediate vicinity of the receiving apparatus; the keenest hearing fails to detect it at the distance of little more than a foot away. Hence, when a message is expected, the recipient has to place his ear to the mouthpiece of the instrument, and use it as an ear-trumpet.

A circ.u.mstance tending to impair the satisfactory working of Bell's telephone is, that the line wire to which the ends of the coil are attached becomes inductively affected by the currents of electricity pa.s.sing through the parallel and contiguous telegraph wires, the effect, on a line where there is an active transmission of telegraphic messages, being that the telephone "emits sounds that are very like the pattering of hail against a window, and which are so loud as to overpower the effects of the human voice."[228]

[Footnote 228: Preece.]

This inconvenience can, however, it is stated, be remedied.

If all the arrangements of the instrument were perfect, there should be no limits to the distance through which speech could be conveyed by the telephone. Professor Bell says that in laboratory experiments "no difficulty has been found in using an apparatus of this construction through a circuit of 6000 miles;" and that he had found it act efficiently between New York and Boston, a distance of 258 miles, subject to the condition that the neighbouring telegraph wires were not in action.

Mr Preece has carried on conversations between Dublin and Holyhead, a distance of 100 miles.

Two useful applications of the telephone are recorded by Professor Bell, the one its employment in connection with the diving bell; the other as a means of communication between those above and below ground in mines. It has been largely adopted in extensive factories and in commercial houses both in America and in this country, supplementing, because of its much greater simplicity and easy application, the electric telegraphs previously in use in such establishments.

We extract the following from the 'Journal of the Society of Arts,'[229]

[Footnote 229: Vol. 26, p. 887.]

"THE TELEPHONE AND THE TORPEDO.

"A novel application of the Bell telephone is one which has been made in connection with torpedoes by Captain C. A. M'Evoy, of 18, Adam Street, Adelphi. The torpedoes to which the telephone has been applied are those of the buoyant contact cla.s.s--that is, floating torpedoes, which are used for the protection of rivers and harbours. These torpedoes are held in position beneath the surface of the water by mooring lines and anchors, and it is necessary to ascertain from time to time that these deadly agents are in active working order. They are, of course, connected to the sh.o.r.e by electric wires by which they may be exploded. They are also arranged so that they may be exploded electrically by contact with pa.s.sing vessels. For this latter purpose they are fitted with what is known as a circuit closer, which is placed in the middle of the charge within the torpedo. The testing is ordinarily performed by sending a current of electricity through the torpedo and fuse; but, in order that the fuse may not be fired, and the torpedo consequently exploded during the process of testing, an extremely weak current has to be used in connection with a sensitive galvanometer. The consequence is that the indications received are so very delicate that they are not always to be relied on. Now, what Captain M'Evoy does is to supplement the electrical test by the test of sounds, and to this end he encloses an ordinary Bell telephone in each torpedo. The telephone is so placed that the vibrating diaphragm is in a horizontal plane, and upon it are laid a few shot or particles of metal, and these are boxed in. Every motion of the torpedo causes the shot to shift their position upon the face of the diaphragm and to cause a slight noise, which is distinctly heard in the receiving telephone on sh.o.r.e. Thus each torpedo two or three miles away, in the restless waters of a channel, is continually telling the operator on sh.o.r.e of its own condition in language sometimes excited, according to the state of calmness or agitation of the water at the time. Should the torpedoes be sunk, they would lie motionless on the bottom, and the silence of the telephone would indicate the fact of their inoperativeness. The telephones are connected to the ordinary electric wires of the torpedoes, but this does not prevent them from being tested in the usual way from the battery on sh.o.r.e."

=TELLU'RIUM.= A rare greyish-white elementary substance, found only in small quant.i.ties, a.s.sociated with gold, silver, lead, and bis.m.u.th, in the gold mines of Transylvania. It has often been described as a metal, but is now commonly cla.s.sed with the non-metals.

1. Tellurium may be obtained from the bis.m.u.th ore (the telluride of bis.m.u.th) by strongly heating the ore with a mixture of carbonate of potash and charcoal. A pota.s.sium telluride is formed which dissolves in water, forming a solution of a purplish-red colour, from which the tellurium deposits on exposure of the liquid to the atmosphere.

2. Schrotter gives the following method for the obtainment of metallic tellurium:--The raw material is treated with dilute hydrochloric acid as long as carbon dioxide is evolved, then with strong acid until all sulphuretted hydrogen is driven off.

The liquid is decanted from the residue, which is washed with hydrochloric acid and hot water, then boiled with aqua regia until the insoluble matter is white. From the aqua regia solution any gold that may be present is precipitated by means of ferrous sulphate, and afterwards zinc is added to precipitate the tellurium. The precipitate on the zinc is washed, dried, and heated to redness, treated with sulphuric acid to remove any silver, and the remaining tellurium is then collected.

Tellurium bears a great resemblance to bis.m.u.th in appearance, having a pinkish metallic l.u.s.tre; it further resembles bis.m.u.th in being crystalline and brittle.

Below a red heat it enters into a state of fusion; at a high temperature it becomes converted into a yellow vapour. It burns in air, when strongly heated, with a blue flame having a green rim, and giving off white fumes that have a peculiar odour. When taken internally, even in very minute quant.i.ties, tellurium imparts to the breath an offensively powerful odour of garlic. Tellurium dissolves in cold concentrated sulphuric acid, to which it imparts a rich purple-red colour. If the acid solution be diluted with water the tellurium precipitates unchanged. There are two oxides of tellurium: the dioxide (TeO_{2}) and the trioxide (TeO_{3}), the first of which corresponds to sulphurous, and the second to sulphuric anhydride.

_Tellurous acid_ (H_{2}TeO_{3}) is obtained by pouring a solution of tellurium on nitric acid of 125 into water, when the tellurous acid is precipitated as a bulky hydrate. This hydrate is slightly soluble in water and reddens litmus. It forms salts called tellurites.

_Telluric acid_ (H_{2}TeO_{4}). When tellurium or tellurous acid is gently heated with nitre a pota.s.sic tellurate is formed, this being decomposed by a salt of barium, whilst the resulting barium tellurate is in its turn decomposed, and the telluric acid separated by sulphuric acid. The telluric acid occurs in hexagonal prismatic crystals, which, when heated usually to redness, becoming converted into telluric anhydride, which then a.s.sumes an orange-yellow colour. This telluric anhydride (TeO_{3}) is entirely insoluble in water, nitric and hydrochloric acids, and alkaline solutions. Although it has but a feeble attraction for bases, telluric acid forms salts which are called tellurates. There are two chlorides of tellurium: the dichloride (TeCl_{2}) and the tetrachloride (TeCl_{4}).

They may both be obtained by the direct action of chlorine on tellurium.

_Telluretted hydrogen, or dihydric telluride_. (H_{2}Te). This compound presents a striking a.n.a.logy to seleniuretted and sulphuretted hydrogen.

Like both of these it is gaseous, but resembles the latter in smell more than the former. It burns with a blue flame, reddens litmus, and when fused into water forms a colourless solution, which becomes brown by exposure to the air, owing to the oxidation of hydrogen and the deposition of tellurmin. The salts of most of the metals are decomposed when a current of telluretted hydrogen is pa.s.sed through these solutions, from which the metals are then thrown down as tellurides. These tellurides present a close resemblance to the corresponding sulphides. The tellurides of the alkali metals, like the sulphides, are soluble in water.

_Tests._ The most distinctive character of tellurium compounds is the reddish-purple solution of pota.s.sium telluride they furnish when fused with pota.s.sic carbonate and charcoal and treated with water.

=TEM'PERATURE.= In English pharmacy it is customary to measure the degree of heat by Fahrenheit's thermometer. When a boiling heat is directed, 212 is meant. A gentle heat is that which is denoted by any degree between 90 and 100 Fahr.

Whenever specific gravity is mentioned, the substance spoken of is supposed to be of the temperature of 62 Fahr. (Ph. L.)

In the B. P., Ph. E., & D., and in chemical works in this country generally, the specific gravities of bodies are taken at, or referred to, the temperature of 60 Fahr. See THERMOMETERS.

The following data may be of use to the pharmacist:

_Degree of Fahr._ 2786 Cast iron melts (Daniell).

2016 Gold melts (Daniell).

1996 Copper melts (Daniell).

1873 Silver melts (Daniell).

1750 Bra.s.s (containing 25% of zinc) melts (Daniell).

1000 Iron, bright cherry red (Poillet).

980 Red heat, visible in daylight (Daniell).

941 Zinc begins to burn (Daniell).

773 Zinc melts (Daniell).

644 Mercury boils (Daniell), 662 (Graham).

640 Sulphuric acid boils (Marignac), 620 (Graham).