Electrical instrument making for amateurs ; a practical handbook

Preface

THE amateur, especially if he be young, inexperienced, and unblest with " filthy lucre," must ever command our sympathy and respect He, withput. any hope of reward, except that gratification which follows the acquirement of knowledge, works on, under the greatest difficulties, to the attainment of his end — an end which, in nine cases out of ten, tends directly to the benefit of his fellow-creatures.

Nearly all the really useful inventions and discoveries, which have rendered the igth century so remarkable as a season of progress, must be attributed to amateurs. For this reason, if for no other, we should render every assistance in our power to the 'bond-fide amateur, and for this reason, along with another, have I attempted, in the following pages, to guide the tyro in his attempts at the construction of the more useful pieces of electrical apparatus. The other reason is that " a fellow-feeling makes us wondrous kind," and as I myself felt acutely the need of assistance at the beginning of my amateurscientific career, so I am pleased to suggest when

PREFACE.

and how much trouble may be saved, and expense spared by the adoption of certain simple modes of procedure.

In the following pages no attempt has been made to describe the production of such highly finished " brass and glass " instruments as those which adorn the windows of our opticians' shops. Such a high degree of finish requires a technical knowledge of French polishing, lacquering, burnishing, etc., as is not usually possessed by the amateur. The tools used, also, are supposed to be of the simplest description, such as may be found in every home, however humble. Not one of the instruments described necessitates the employment of a lathe or other expensive tool in its manufacture ; though, of course, much truer and finished circular work can be done on the lathe than in any other manner. But the instruments produced as described in this book, may be relied upon to act efficiently ; and this is, after all, the end for which every instrument is 'constructed. It must be borne in mind that this work does not profess to teach the science of electricity : and no attempt is made to enter upon the domain of scientific speculation,

Index To Sections

SECTION PACK

SECTION PAGE

i Tools ....

I

72 Dynamos, Rules for

2 Materials ... •

Winding . . . 108

3 Soldering . .

72 Ring Armature, Paci-

5 „ with Flame .

6 Pivots ....

72 Wires, Resistances of . 112

7 Glass threads . .

ii

73 Resistance of Wire

8 Straws ....

ii

9 Pith Balls .

ii

73 Wires, Carrying power •

10 „ Electroscope .

ii Gold Leaf „ .

74 Dynamos, Winding . 115

12 Coulomb's Torsion

Balance

75 Ampere, What it is .116

15 Electrophorus

79 Ammeter, To Grade . 119

17 Bertsch's Machine.

80 Voltmeter . . .121

1 8 Mounting a Glass Plate.

20 „ „ without drilling .

25 Carre's Dielectric

91 Tangents and Arcs, "

Machine .

Table of . . .136

29 Holtz's Machine .

93 Thermopile . . . 139

34 Wimhurst „

95 Batteries . ; . 146

42 Plate „

95 Porous Cells . . 147

43 Condensers .

95 Binding Screws, and

44 Leyden Jar .

Substitutes . . 148

45 Franklin Plate

95 Amalgamation . .148

45 Fulminating Panes

47 Fizeau's Condenser

97 Graphite Plates and

48 Microfarad „ .

Rods to Mount. . 150

49 Medical Coils

98 Batteries, Single Fluid. 151

49 Shocking Coil . .

98 Battery, Agitating

56 Induction Coils . .

Fluid in . . .151

58 Magneto Machine.

99 Batteries, Double Fluid 153

59 „ Shocking „

99 „ Table of

65 „ Uni-direction

Machine .

lob Telephone . . .156

72 Dynamos

72 „ Gramme.

1 08

72 „ Manchester

1 08

104 The Microphone. . 180

ELECTRICAL INSTRUMENT MAKING FOR AMATEURS.

§ I. TOOLS. — The true amateur, as a rule, has not a large assortment of tools. Little by little he gets together, or constructs those which are necessary for his purpose ; but he seldom aspires to the complete paraphernalia of a workshop. Still there are certain tooto that are indispensable, of which the following is a lJs>t In order of utility : —

i Large pocket-knife.

I Fine penknife.

I Archimedean drill and bits.

Pair of cutting pliers.

Pair of large scissors for metal.

Pair of small scissors.

Several files, large and smalL '

I Hammer.

I Mallet.

Bradawl, gimlet, pincers.

Small bench vice.

Small tenon saw.

Soldering iron.

Spirit lamp.

I Wheel glass cutter or diamond

Pair of compasses

aft. rule, s

B

^ELECTRICAL INSTRUMENT MAKING FOR AMATEURS.

I should like to have put a lathe at the heacl of this list, for that is really the king of tools ; but I would not deter the student from making electrical apparatus because he has not a lathe, as most may be made well without, though better with one.

Besides tools, the materials mentioned below will be found useful. They need not be procured all at once, but as occasion demands. If the amateur adopts the plan of keeping up a little stock of his materials and tools, as they are worn out or consumed, and more especially if he remembers that, " Order is Nature's first law," and that there chould be " a place for everything, and everything in its place," he will turn out better work, keep his temper, and v/ork better than if he allows himself to degenerate into a slipshod style of doing things. Let him never say " that'll do " to anything capable of improvement.

\ 2. MATERIALS. — The following will be found useful in carrying out the instructions given in "the ensuing pages :—

Glass rods from J to \ in. in diameter.

Ebonite rods from Jto \ in. in diameter.

Glass tubes from J to i in! in diameter.

Guttapercha.

Glass bottles, preferably green glass.

Sheets of glass ; every piece is useful.

Bottoms of broken wine-glasses as stands, &c.

Tinfoil

Sheet zinc and sheets of tinned iron.*

* Clean beef tins, sardine tins, &c., may be worked up very well and econouvically,

MATERIALS. $

Sheet copper.

Sheet brass, and brass rod, iin. diameter*

Solder.

Chloride of zinc..

Rosin.

Needles.

Watch springs.

MVhite hard varnish.

Red lead.

Benzoline.

Burnt umber.

Copper wire of various sizes.*

Prout's elastic glue.

Methylated spirits of wine.

Having these materials at hand, the amateur will find several operations are required so frequently as to render a certain amount of technical skill absolutely necessary if the work is to look neat and act satisfactorily. Among the first of the -amateur's requirements must be placed the power of soldering.

§ 3. SOLDERING. — For small work, an iron, shaped as shown at Fig. i, will be found extremely useful. The

FIG. i.

amateur can easily construct this for himself by boring a tff hole in a copper wedge 2in. long by Jin. thick, and £in. wide on the base. An iron rod, 15in. long, is straightened out for the handle, and the end of this rod

. Thia had better tie procured ^s required.

is heated in the fire and hammered up until it can be thrust through the hole in the copper wedge; what projects is then hammered down so as to form a kind of boss or rivet head, to prevent the copper bit from moving. The other end of the rod may then be filed or hammered'to a point and driven into a wooden handle. Five inches of broomhandle will answer the purpose, if nothing better can be got at

In order to solder successfully, four things are essential. Firstly, the portions to be soldered must be made scrupulously clean, either by scraping with a p\ece of sharp knife blade (kept specially for this purpose), or by sandpapering, or by filing, whichever is most convenient. Secondly the portions that are to be soldered must be raised nearly to the temperature of the melted solder. For this reason the amateur would surely fail were he to attempt to make a good joint, say, Between two sad irons, with an ordinary bit, unless he previously heated the irons to nearly the melting point of solder. In ordinary small work, where wires are soldered to wires, sheets to sheets, &c., the heat of the soldering iron itself is generally sufficient, not only to melt the solder, but also to raise the temperature of the surrounding portions to be joined to the requisite point Thirdly, the nose of the soldering iron must be perfectly clean, and covered with melted solder, or, as it is technically called " tinned."

To insure this result the soldering iron must be placed in a clear red fire until nearly red-hot (if allowed to get too hot it will not take up the solder at all), then quickly

SOLDERING. 5

and lightly filed on one face, and at once plunged into a rod of soft solder, on which a little powdered rosin has been placed The heat of the soldering iron will cause the solder to melt, and run into globules. If one of these be allowed to run into the lid of a milk tin, or other convenient tinned iron receptacle in which a little powdered rosin is also placed, and the filed face of the soldering iron rubbed briskly over the melted solder, the surface of the copper bit will be found to have taken a coating of solder as brilliant as a looking-glass. Should this not be the case, the iron must again be heated and filed and rubbed over the solder until a perfect coating has been obtained.

When once the nose of the copper bit is well "tinned," it is sufficient after each heating (provided it has not been overheated so as to burn off the solder) to rub the iron briskly on a piece of old carpet, kept especially for this purpose, just before touching the solder. Fourthly, the surfaces to be united must be kept perfectly clean, and unoxidised during the application of the heat necessary for soldering, by the application of some substance which prevents the access of air, &c., to the heated surfaces.

These substances' are various, and some are more adapted to one metal than to another. Thus rosin is excellent for tinned iron and for copper. Hydrochloric acid (spirits of salt) is perhaps the best for zinc. Chloride of zinc (killed spirits of salt), again, is excellent for iron, for copper, and for brass, where the surfaces can afterwards be well washed.

A lump of sal-ammoniac (chloride of ammonia) is also very useful for removing the oxidation from the copper tint by rubbing it against the lump for a few seconds after heating.

§ 4. As an example of the mode of proceeding, let us suppose we wish to solder a wire to the copper plate of a Daniell battery. We begin by cleaning the copper plate at the spot to which we wish to attach the wire, by rubbing it with a piece of glass or sandpaper until the surface is as brilliant as a mirror. In like manner we polish and clean the end of the copper wire. Laying the copper plate flat on the board which we keep expressly for soldering on, we place the copper wire on the desired spot.

We now put the soldering iron into the fire* (it having been previously tinned as described), and watch it until it shows by the melting of the solder on the surface that it is hot enough. We then remove it from the fire, give a rub on the sal-ammoniac or piece of carpet, then take up a globule of solder by touching one with the" cleaned nose of the bit, and, lastly, having quickly touched the surfaces both of the copper plate and wire with a feather dipped into the chloride of zinc solution, rub the surface of the plate and wire simultaneously with the soldering iron. As soon as the surfaces become sufficiently heated, the solder will be seen to flow over them. The wire must then be pressed into its desired place, the melted solder rubbed well over the point of

Care must be taken that the fire is emitting no sulphurous smoke, otherwise the mm will surely not take up the solder.

SOLDERING WITH A FLAME. 7

junction, the iron removed, while the wire is held motionless in its position, until a sudden dulling of the surface of the solder shows that it has set and is solid enough to hold the parts together. After soldering with chloride of zinc (" killed spirits," " soldering fluid "), always wash in plenty of water to prevent rusting.

§ 5. SOLDERING WITH A FLAME.— In many instances a better joint and neater-looking work can be made over the flame of a spirit or other lamp than with the soldering iron. Thte is more especially the case in small Work, such as joining wires, soldering pivots, &c As an example, let us suppose we desire to make a poised magnetic needle out of two similar pieces of needle, joining them together by means of a short tinned-iron junction, in which the pivot is inserted. (It is evident that a pivot could not well be attached to an ordinary^ sewing needle were the needle in one piece.)

The needles (of which two are required) are broken off of the desired length by means of a pair of nippers. The heads may be the portions rejected, if a very light needle is. required ; the points, if a heavier needle be net objectionable. Care should be taken that the pieces be of the same weight, to insure a well-balanced needle. 'A small piece of sheet tinned iron (" tin-plate ") about 1 in. square should now be procured and flattened out. With a screw-drill, or small punch, a clean central hole is made a trifle smaller than the largest external diameter of the pivot (See § 6 for pivots.) The piece js now cut into the shape of a small lozenge, as shov/i* at Fig. 2, A, and again flattened out by a light blow with a flat-faced hammer. The needles are now to be lightly sandpapered at the ends which r are to be soldered to the lozenge, then these extremities immersed

Fio. a.

in the chloride of zinc soldering fluid. The soldering; iron is then to be heated, and a little globule of solder caused to adhere to the prepared extremity of each needle by its aid. The needles should now present the

SOLDERING . WITH A FLAME. $

appearance shown in Fig. 2, B. The spirit lamp is now to be brought into requisition. The flame should not be too high for such work, so that the wick need not be raised much. Taking up the lozenge-shaped piece in the left hand, with a pair of tweezers (or longish piece of wire bent to a tweezer shape), and allowing one half to project, we apply with a feather a little soldering fluid to the projecting point The needle , with its adhering solder is now taken up in the right hand (a small piece of paper being wrapped round it, to prevent the fingers being burnt), and both the needle and the lozenge are held for a few seconds over the flame of the spirit lamp,1 in the position they are desired to remain (See Fig/ 2, c). The solder will soon be seen to flow. As soon as this is the case the pieces must be pressed firmly together,3 and both hands removed from over the flame of the lamp, care being taken to keep the parts constantly pressed together 4in til a sudden dulling shows that the solder is set. In 'like? manner the other needle is soldered to the other point of the lozenge. The needle may then be magnetised, and after magnetisation balanced on' its pivot, as will be described further on. Fig. 2,"D, shows the needle ready for pivoting.

§ 6.- PIVOTS. — These are* in ! constant requisition; consequently, it is well to be able to make them of all sizes. The amateur will need only, two kinds — viz, in brass and in glass. Brass pivots are very easily made from stout, hard, brass wire. The most useful size is about Ath in. in diameter. A short length of this is placed in the jaws of a vice, with Jts_circular section uppermost A bit, capable of cutting a i*«th hole, is placed in the screw-drill, and after being oiled, the drill is worked over the brass rod, the bit resting quite centrally, until the shoulders of the bit just touch the outside of the wire. This produces a good deep and evenly conical hole. The wire can now be removed from the vice, and the outside of the pivot also made conical by filing, while still on the brass rod ; when the desired shape has £>een secured, it cam be cut off with a fret-saw or file.

Glass pivots are extremely useful in all electrical experiments. The best way to make these is to soften a glass tube over a spirit lamp, and gradually but steadily pull it asunder. By so doing, two conical pieces are the result If the extreme hair-like points of these are held over the lamp, they fuse up into a round globule, thus closing up the hole. The pivots thus produced can easily be cut off (when the glass is cold.) by making a mark round the tube with a sharp triangular file, at the point where it is desired to break it off. On applying a little pressure between the finger and thumb of both hands, the pivot easily breaks away from the remainder of the tube. The pivots may be made very long and thin, by allowing the glass to soften well, before beginning to pull asunder, and such long thin pivots are very useful for astatic galvanometers, or other cases in which two objects have to be poised on one pivot Short pivots can be made by pulling asunder as soon as the glass softens in the flame. Fig. 2, C, shows how the glass tube should be held in the hands to soften, over the flame. Fig. 2, E, gives the appearance of the tube after pulling

CLASS THREADS. SI

asunder. Fig. 2, F, indicates how the hair-like extremity should be melted into a bead over the lamp, so as to close the capillary aperture, and Fig. 2, G, shows finished pivots.

§ 7. GLASS THREAD^ — These are extremely useful as insulators in small work, such as electroscopes, carriers, torsion balances, &c. They are easily made from rather thin glass rod, by heating it carefully over a clear flame (spirit-lamp, or Bunsen burner) until soft, and then pulling asunder rapidly if a very fine thread be desired ; more slowly, if a coarser filament be required. Similar threads may be made from shellac ; and these, though somewhat more brittle, are even better insulators.

§ 8. STRAWS. — The straws of various grasses, more especially the fine, straight, hair-like terminals of such grasses as Agrostis spicavzntit Alopecnrus pratensis, Phalaris arundinacca, and Aira cristata, if gathered soon after the flowers are fully matured, cut to the length of about 6 inches, dried, and then boiled in melted paraffin wax, make excellent insulating supports, far stronger than the glass or shellac ones mentioned above. The same straws, not paraffined, are, from their lightness, well adapted as pointers for such galvanometers as tangents and others, which require a separate indicator.

§ 9. PlTH-BALLS. — These are much used in experiments with frictional electricity. The best piths for ordinary purposes are those of the elder, Sambucus nigra. and of the Jerusalem artichoke, Helianthus tuberosust Before being shaped into balls or other figures, the pith should be thoroughly, dried. With a penknife, reduced to a razor-like sharpness, the pith can be cut to any desired figure, and is easily rounded to an approximate sphere. When a number of equal size have been made, the final rounding may be given by lightly rolling them with a smooth, flat board, on a level table. Care must be taken not to press too heavily, otherwise the balls will be flattened. Having now got together the few things necessary for starting work, we may try our constructive abilities on the simpler forms of electroscopes.

Electroscopes are instruments employed for the detection of the presence (and sometimes of the nature) of electricity ; not for its measurement

$ 10. PITH-BALL ELECTROSCOPES.— These are of two

FJG. 3.

kinds— viz., those in which the balls are suspended by a filament, and those in which the suspension consists of a horizontal rod, pivoted at the centre. Fig. 3, A, shows, the former ; B, the latter form.

PITH-BALL ELECTROSCOPES. 13

To make the former, a glass rod about Sin. long by Jin. thick, should have one extremity heated over a spirit lamp, and when quite soft, touched with another piece, so as to enable the operator to draw out a filament, which must be bent into the shape of a recurved hook. The rod must then be heated at a point about 2in. from this end, and, when sufficiently softened, bent neatly (not too hurriedly) at right angles. The bent rod must be allowed to cool gradually without touching anything, otherwise it will be liable to fly to pieces. When quite cold it may be fastened to the foot of a broken wineglass by means of a turn or two of stout brown paper, previously brushed over with good Russian glue, as shown at C. When this is quite dry it should receive (at this joint only) a coating of red varnish, made by mixing a few grains of red lead with a teaspoonful of white hard varnish. (The white hard varnish may be procured at any oilman's.) A single filament of cocoon silk is now to be procured, and a fine needle threaded with it The needle is passed through the centre of a pith-ball, the end of silk fibre moistened with a drop of glue, and the needle pulled until the ball reaches the glued portion of the silk. This will serve to fasten it to the b ilL The other end of the fibre may be tied or glued to the little hook of the bent glass arm. Two balls may be thus suspended, if it is required to show the repulsive effects of similarly charged bodies. To construct the horizontally-pivoted form, it is only necessary to split a straight paraffined straw (§ 8) at its centre, with a sharp penknife, insert a small glass pivot in the split, and fasten it thereto by means of a single drop of hot glue. When quite cold, a pith-ball must be attached to each end of the straw, a small hole being made in each ball with a pin, and the end of the straw (previously touched with glue) inserted in the hole* Care must be taken at this point that the balls balance one another. They may be made to do this by sliding alo'ng the straw, until when placed on a needle-point the arms of the electroscope remain perfectly level. Half of an ordinary sewingcotton reel maybe used as the foot of this electroscope. After sawing in half, the upper portion should be filed, rounded, and smoothed, a short length (say4in.) of cane, glued, and thrust in the central hole ; a needle (point upwards) forced into the upper extremity of the cane ; and, lastly, the whole wooden portion neatly varnished with the red varnish as described.

§ ii. GOLD LEAF ELECTROSCOPE.— This is a most useful instrument for the detection of minute charges of electricity. If well made, it also serves admirably to show the phenomena of induction. The requisites are a tall wide glass jar, a sheet of gold leaf, a couple of strips of tinfoil, a short piece of brass rod, about i-inch in diameter, a couple of beef tin bottoms, or similar pieces of tinned iron, and an empty cigar box.

For the glass jar, we may either use the straight glass chimneys (about 3 inches in diameter by 7 inches in height), that are used for large gas or paraffin burners, and which may be obtained at any respectable ironmongers for a few pence (see Fig. 4, A), or the bell-

GOLD LEAF ELECTROSCOPE. jj

shaped chimneys (see Fig. 4, B). Whichever shape be selected, the diameter should not be less than 3 inches

FIG. 4.

nor more than 4 inches. Preference should be given to the bell form, when procurable^ as the " cap " is more tf ELECTRICAL INSTRUMENT MAKING FOR AMATEURS.

easily fitted to the narrow neck. Having procured a glass jar, the next step is to fit a cover to both extremities. If Fig. R be chosen, the wider extremity which Is 'destined to form the bottom, should be fitted with* a tinned-iron cover. If the bottom of the glass be 3 inches diameter, it will be fitted exactly by the bottom of a Swiss milk tin. The bottom must not fit too tightly, if fitted in winter, or else the slightest increase in temperature will expand the glass and cause it to crack. If a tin " bottom " is not at hand to fit, it may readily be made, by striking out on a piece of thin tinned-iron, a circle of the same size as the outside of the glass jar. Keeping about £-inch outside this line, the circle is cut out, and then the edge turned up square by hammering lightly on the edge of an ordinary iron. The tin disc should now show ^he appearance sketched at Fig. 4, C. This bottom must not be fastened in until after the gold leaves have been adjusted. The next operation consists in making the cover to fit the other end of the jar or cylinder. If A has been chosen, two circular discs must be cut out of the cigar box wood ; one that will just drop into the jar, the other precisely the diameter of the outside of the^ar. The two circles had better be measured, struck out with the compasses, and sawn with a fret or band-saw. The two discs,, after being well smoothed, should be glued together, as shown in Fig. 4, D. If B is our choice, half a sewing-machine cotton reel will Be found to. fit with a trifling adjustment.' All that will be necessary in this case -will be to cut of? the narrow portion, leaving one of the coned heads, the

COLD LEAF ELECTROSCOPE. 17

rim of whicli can' be trimmed with a rasp, until it just fits the small mouth of the chimney. Whichever form be adopted, this wooden cover must have in it two perforations, one central, about J inch in diameter, wherein will pass the brass rod from which depend the gold leaves ; the other near the circumference, which will serve as an exit for moist air. Fig. 4, E shows the glass chimney fitted with its lower " tray " and upper " cap." At exactly opposite diameters of the glass jar, two strips of tinfoil, about | inch wide by 4 inches long, are -to be pasted itisidt the jar, reaching from a little above the middle downwards to the metal. tray. The object of these is twofold ; they increase the sensibility of the instrument by heightening the apparent repulsive effect of a charge ; and they serve to discharge the gold leaves without tearing, if by inadvertence an overcharge be given. This being done, the brass rod may be fitted to its table. Maruy operators use a brass ball at the top of the gold leaf electroscope ; for general purposes, a metallic table will be found more sensitive and more convenient. Having cut a tinned-iron or thin brass disc 3^ inches in diameter, let the edges be turned in by hammering. To the centre of this metal disc, and perpendicular to it, should be soldered about 6 inches of brass rod, having a small hole drilled in it at half its length — say iinch in diameter. Care must be taken that this rod is quite straight and smooth. The under portion of the disc, as well as the rod to within \ inch of its extremity, should now be varnished with red varnish (see § io),and set aside to dry. While this is drying, iS ELECTRICAL INSTRUMENT MAKING FOR AMATEURS.

the upper wooden cap of the cylinder may be immersed in melted paraffin wax, and allowed to remain therein until thoroughly permeated with paraffin. The -brass rod may now be passed into the central orifice of the "cap," and tightly fitted thereto by means of a roll or two of paraffined brown paper. (N.B. — When paraffin is mentioned in this work, paraffin wax is understood, not paraffin oil.} The rod must be pushed down in the orifice until the J-inch hole is just level with the top of the cap. A short brad, or similar piece of wire, pushed forcibly into this hole, will effectually prevent the rod sinking through, if. any weight be afterwards placed on the table above. A small, flat .piecet of brass, about \ inch long by £ inch square section, must now be soldered to the lower end of the rod, transversely to it, so as to form a letter JL- It is to this transverse piece that the gold leaves are to be attached. The gold leaves should be about £ ineh wide by about 2 inches long. To cut them neatly is not an 'easy job for the tyro ; still, it may be managed in the following manner : — >