The English Mechanic

AND

WORLD OF SCIENCE AND ART.

FRIDAY, OCTOBER 13, 1882.

ELECTRICAL MEASUREMENTS.
By JOHN T. SPRAGUE ("SIGMA ").
HE early measures of the different rela-

the earth; at the Equator it is 978.10, at In all measurements it is necessary to latitude 45° it is 980-61, at the Poles 983:11, have a separate starting point or "unit" for these being velocities in centimetres. Taking each order of things or conceptions, though the value in England as 981, the force of these units may be derivable from the few gravity equals 981 dynes, or C.G.S. units of fundamental units-thus, from the unit force. The actual force of gravity at any length, 1 centimetre (or metre, or foot, as part of the earth is ascertained by the follow-may be), we derive unit area, the square ing formula:-g=980·60562-5028 cosine centimetre, &c., and from this again, unit 21.000003h, in which A denotes the lati- volume, the cubic centimetre, &c. In like tude and h the height in centimetres of the manner, each separate conception or order place above sea-level. of facts in electricity requires to have The erg may, therefore, be compared with a unit of its own, and the system is the common mechanical unit of work, the similar to that of the mechanical units foot-pound, because the ft.-lb. is the same which have so far engaged attention. Here, thing as 138 25 gramme metres, or expressed also, we start from a "force" generatin C.G.S. system as 13825 centigramme ing a velocity. We can now replace the metres; then, if we take gravity g as equal attraction of gravitation by two distinct upon the common agencies used in connec- ordinary ft.-lb. is equal to 13,564,325 ergs. exerted by an electric "charge," from which tion therewith, and were of necessity arbi- Such a figure shows at once that this system is derived an electro-static system of units; trary and unconnected with each other; is really adapted only to minute measure- and we have the attractions exerted by an but as the study of electrical phenomena ments. To get rid of the numerous figures electric "current" upon a magnetic pole, or grew into a science, and its applications involved, a simple system of writing is upon another current: this furnishes the became of practical importance, the various adopted, and the above figures would be electro-magnetic system of units. The startmeasures have been systematised so as to written as 1356 x 10 or 1356 × 10', and ing point or unit of electricity in the electroadapt them to mathematical treatment. For most of the calculations involved are thus static system is: "That quantity of eleethis purpose they are based upon "absolute" reduced to the alteration of the index tricity which will repel an equal quantity measures-that is to say, upon measures figures. (or attract an equal opposite quantity) at which are common to all kinds of operations; This system is becoming so increasingly the distance of one centimetre with a force upon the fundamental elements, time, length, common in electrical and scientific works of one dyne"; that is to say, would, acting mass, &c., which enter in to all physical opera- generally, that it may be well to explain it. for the second, generate a velocity of one tions. The actual measures employed or The index, as in logarithms, may be positive, centimetre per second. The unit of the suggested have been various, but the neces- signifying the " power"-that is, the num-magnetic system is based on the unit magsity of the case limits us to some form of the ber of tens by which the figure is to be netic pole, which is one which repels a similar "metric" system, which must inevitably multiplied, or negative, signifying the num- pole, one centimetre distant, with a force of supersede in time all other systems of ber of tens by which it is to be divided; one dyne. The unit electric current is that measurement, even though these latter may thus the negative index written with a dash which, in an arc of one centimetre length of be proved to have points of superiority. In represents a decimal fraction. Thus we a circle of one centimetre radius, will repel a science, at all events, all these are vanishing, haveunit pole at its centre with a force of one though the foot-pound and some others will dyne. The unit current would also, in a long be employed for ordinary purposes. length of one centimetre, repel a similar current at a distance of one centimetre with a force of one dyne. Perhaps the easiest method of forming a concrete idea of these forces is to conceive a spring balance adjusted to carry a weight of 1-981 of a gramme. Any force whatever which strains the spring to that point is exerting unit force. Thus, if a magnet-pole, fixed at one centimetre from another magnet-pole, required the spring to be stretched to that point to resist motionthat is, to maintain the centimetre distance -a force of one dyne would be exerted; or, what comes to the same thing, if the balance were graduated to successive increments of that value, it would indicate the number of "dynes" exerted by any force. The ultimate idea of force is pressure or tension, attraction or repulsion really in unit degrees, but for purposes of calculation expressed in relation to mass.

electricity were naturally have the

a thousand

1 × 10^
= 1,000,000 a million
1 × 103
= 1,000
1 x 10 = 100
1 x 10-2 = '01
1 × 10- =

a hundred

a hundredth ·000,001 a millionth

Before entering on the electric measures, it is necessary to understand the general system of which they are a branch. The fundamental elements of which units of In fact, the positive index, as in logarithms, measures are required are Length, Time, is one less than the figures representing the and Mass; of the first, two units are employed, the metre and the centimetre. The first has many advantages, but the second has been more fully worked out, and is more generally employed, and therefore, it is the one which will be used here, and we have as

units

L Length. 1 centimetre.
T Time
I second.

M Mass.

1 gramme.

number; but the negative index, unlike the
logarithmic, is the number of figures repre-
senting the decimal when written out.

In speaking or naming these values, we are burdened with a barbarous nomenclature; thus, a million ergs is called an ergsix, and so on, adding the index number to the name of the unit. Furthermore, in electricity, we have the generally adopted prefixes of mega, signifying a million, as the From these are derived the general me-mega-volt or meg-ohm; and micro signifychanical units; of motion, which is length ing a millionth, as the micro-farad, besides traversed in unit time; velocity, which is the ordinary prefixes of the metric system of motion in unit time; momentum, which is measures. mass having unit velocity; force, which is It is undeniable that the peculiar fancifula general expression for the cause which ness of some of our leading mathematicians, The two systems of units are related to generates velocity, but for systematic pur- which has led them to adopt the centi- each other in ratio which is a velocity, and poses is defined as the cause of "momen-gramme instead of the gramme as the basis expressed in the formulæ as v. The actual tum"; and work, which is the energy due to of the unitary system, is a very serious incon- value is not exactly known; but is the action of the force. Gravitation is the venience. English men of science have interesting for two reasons. It has been only absolute natural force, and as it is con- gradually submitted themselves to the experimentally determined by several emistant in its operation, it generates not only a universally-adopted metric system, and nent electricians by different processes. velocity," but also "acceleration," that is students begin to understand what is meant to say, the moving body, retaining at each by a metre gramme as the unit of work, and instant its acquired velocity, adds to this the the calory as the unit of heat, and now they new velocity due to the force; but in dealing are being puzzled afresh by a new system, with the energy involved, the actual velocity the sole reason for which is that a gramme only is considered; regarded as a force in weight is based upon the cubic centimetre the abstract, gravity, g, imparts a velocity of of water. But, as our writers are chiefly 32-2ft., or 981 centimetres per second. these mathematicians, they have it in their Regarded as a unit force, it generates this power to force people to submit. It would velocity in a mass of one gramme. Hence be of little consequence if (as many at firstwe have the following units :sight suppose) it only meant the adding of Unit value. 100 to all values as the result of using the centimetre (or one hundredth of metre) in place of the familiar metre itself. But this Dyne. is not the case, as energy or work varies as the square of the force; therefore, unit W Work Erg. force or velocity on the metre gramme second system means 100 times the unitTo understand these values it will be well force on the centimetre-gramme second to compare them with the familiar terms (C.G.S.) system; but unit energy is, conbased on gravity. The force of gravitation sequently, in the metre system, 1002, that is, (upon the earth) varies according to the 10,000-fold in value the unit energy of the distance from the centre of the " mass" of C.G.S. system.

L

1 centimetre

V. Velocity

T

per second.

Average 2-9445 x 1010 c.m.

These variations, though not large, show (like the different values found for the ohm) that while mathematicians work out their formula to the extremest nicety, the data are by no means settled.

The other point of interest is that this ratio, which, as stated, is really a velocity, is apparently identical with the velocity of light; the various determinations of which range over much the same values as the above.

Having obtained the unit of force, which represents the different expressions--potential, difference of potential, tension, and electro-motive force, the rest are derived

from considerations classed under the name
of "dimensions"; derivations in fact form
the unit length L, mass M, and time T;
which dimensions, therefore, are alike appli-
cable to any actual values given to those
units in any system.
Magnetic units:-

=

Strength of magnetic pole m = L MAT
Moment of a magnet m
L MI
Intensity of a magnetic field H= L-MIT-1
Electric Units:-

E. Static.

Force LI MI T-1 LMT-2 L-1T =

Resistance L-IT

..

LT-I

L-2T=

1

Current L3 MT-2 LIMIT-1 LT-1 = V
Quantity L MT-1 M LI

Capacity... L

L-IT

LT-1

L-IT

V

sulted, and A A represents the line of eccen- strong, because it has to bear the weight of tricity produced by the slide of an ordinary the chuck and work, and to stand the usual eccentric chuck, and BB the curved line of shocks and strains of eccentric turning. It eccentricity of the present one, a point, D, would be a great mistake to attempt to make on the curve at a given distance from the this chuck of sheet brass, as castings are so mandrel centre, although it is a point in the cheap and so far superior for anything of the curved line, is practically similar to C, a kind, and in. is the least thickness that point at the same distance from the mandrel would be likely to serve as the substance of centre upon A A. Both are, in fact, lines the two plates. I did, indeed, once see a upon a diameter: A A, in one case, and slide-rest of sheet-brass made after the old HH in the other; and this will be so in pattern devised by Maudsley, but it was respect of any other point in the curved only for use with a little rose engine Electroline, BB. If I is the mandrel centre, of, I think, 2in. centre, made to turn Magnetic on which the chuck revolves, which has a studs, buttons, and such very light work. System. E. Magnetic. straight slide; the point C in its revolution Such a plate as the top one may be racked will pass through the position D. The two for the screw by setting a tap between cenmovements of the upper plate-rectilineal or tres and centring the plate on the tool bed of the slide-rest by the hole at the upper end, where the screw, E, will be fitted, this being the centre from which the curve to be racked is struck. But the edge must first be divided, and the divisions sawn in by a small revolving cutter, if possible-the tap or hob being used merely to finish and correct these divisions, so that the tangent-screw may work in them satisfactorily. The rotation of the bob will carry the plate round upon its centre, E, and when it has revolved till clear of the bob, it must be drawn back by the slide-rest screw and readjusted. By these means it will soon be racked to a sufficient depth; but a segment like this is more tedious to work than the complete circle, because the latter can be allowed continuous revolution, and will not need constant readjustment, except to advance it slightly as the cut proceeds. The pin upon which the division-wheel A revolves ought to be slightly conical and stout. It is drilled at the upper end and tapped for a small screw, under which is placed a steel washer. The chuck-screw and the wheel A will be cast as one, and can be turned up on a mandrel, upon which it can be also held while the wheel is being divided and cut into cogs. Even here, however, if dividing and cutting the wheel is considered a difficulty, it would be easy to press into service one already cut, if such be at hand. J. L.

V, in round numbers, closely approximating value as above is 3 x 10 centimeters per second.

The units thus ascertained represent each its own idea, thing, or action; but the system is so related that we may actually treat them as though they were all one absolute unit, representing all forms of force and energy, cause, agency, and effect; we may multiply and divide them by each other as though they were abstract numbers merely, instead of concrete things; this is, in fact, the great advantage of the use of an absolute unit, and it results from the fundamental principle of the system-viz., that a unit force, acting in unit time and unit space, will produce a unit effect or operation, and expend and produce unit energy in some of its manifestations. Therefore, the ratios or actual values of the units themselves are fixed by this necessity. Starting from any two, the rest follow, of course, E E R

from Ohm's formula = C or R.

=

This relation, in fact, involves that unit current C must pass through the unit conductor (miscalled resistance) R in unit time, under the influence of unit force E; and in doing so shall expend unit energy or work, and be capable of being stored in a receiver of unit capacity, and of exerting unit force upon a unit pole or current. Hence, all being alike represented by 1, and being all inter-related, there follows the fact mentioned, that we can treat them as simple numbers without regard to their actual

natures.

But these absolute units are inconvenient for most practical uses, and, therefore, while it was necessary to base the explanation of electric measurement on this foundation, in another paper will be explained the practical system as it is now developed and accepted by all electricians.

ON THE PRODUCTION OF LOOPED
FIGURES BY GEARING.

B

A NOVEL SENSITISING SOLUTION. NOVEL sensitising solution has been recently patented by Mr. R. T. Wall, of Longfleet, Poole, the active ingredient of which seems to be white pepper, but in what way the pepper acts is not stated. The patent is for improvements in photography, and, apparently, covers several processes. The improvements consist in making a new sensitising solution from white pepper and its analogues macerated with, and in, ether, turpentine, alcohol, naphtha, chloroform, &c., or by essential and volatile oils, acetic, carbolic, or other acids, or with diluted mastic, crystal, copal, sandrac, photographic, spirit, or other varnishes. A ready way is to take one pound weight of freshly-ground white pepper and macerate it in one to two pints of ether or alcohol for some days, then press the tincture through one or more filtering media: also, in using, a little mastic varnish or oil of turpentine is added to the resultant solution if ether is used, a little spirit varnish is used when

I fitted ex Fig. 8 I have represented the eccentric curved according to the chuck used-are not, alcohol is used, and the resultant solution is radial plate and click-wheel to the chuck- first be supposed. If the experiment is posed in the usual way; and in the use of powdered pigments, cold or warm, brushed or screw. The pointer E must be shaped like D, made, it will be found easy to cut the same dusted over the surface for the purpose of deand admit the tangent-screw below, if it pattern with either chuck if the wheel A is veloping the image. The improvements also is added at all. If the tangent-screw is added, but not otherwise. With the geared consist in the manufacture of transparent sheets used, the tightening screw, C, will be less rose engine so much can be done by using this of collodion and collodion emulsions and elastic needed as an adjustable one, and may be re- chuck without such wheel that many will media for printing on uneven or other surfaces. placed by one with mushroom head, screwed probaby prefer to avoid the extra difficulties For making a clear transparent sheet of collodion in permanently from above, and merely so incurred in so making it. These difficulties, a thick preparation of collodion is made consisttight as to prevent the upper plate from however, are not nearly equal to those in- ing of acetic acid or formic acid, gun-cotton, and rising in the least from the base-plate. If curred in getting up the fittings of a chuck castor oil-canada balsam may be used also. C is used, the slot should be bevelled, so with the usual steel guide-bars and V-slides. This composition is poured upon waxed glass, that it lies in it as a countersunk-screw. The upper plate of this chuck may be edged with strips of paper by means of glue so as to form a dish, and is placed in a box, the lid This chuck is not at all a bad one, although lightened somewhat by hollowing out the being closed and then left a day or two to dry; inferior to the modern one, and is given edges more than here represented; but care On this layer a film of gelatine emulsion or rapid because so easily constructed. In effect, the must be taken not to run to extremes in this collodion emulsion is poured, and the negative line of eccentricity is dotted, being curved direction, as it should have a good bearing or transparent picture taken thereon suitably instead of straight. But if Fig. 9 is con- on the lower plate, and be very stiff and varnished and protected, when the whole may be

stripped from the glass together. If the patentee's extra rapid collodion emulsion is used, the above collodion sheet must contain gelatine or gum or indiarubber coating before the application of the emulsion. The following description will show how this emulsion is prepared. The collodion is thus made:-Ammonia bromide, 27 grains; distilled water, as little as possible; when dissolved add two or three drops of gelatined hydro-bromic acid; alcohol, 24oz.; pyroxline, 32 grains; and ether, 24oz. The emulsion with silver is formed by adding 120 grains of silver nitrate which has been dissolved in a little distilled water and then oz. of alcohol. It is poured out into a dish of sufficient capacity in order for the solvent to evaporate, and in a day and night it is ready for further treatment. This consists in breaking up the mass into pieces with a piece of glass or a bone spoon and covering it with water for some time, and pouring the whole into a calico bag which has previously been washed in carbonate of soda and then well rinsed and dried; the bag and its contents is put into an enamelled saucepan or in a stone jar covered with gelatine solution (20 grain No. 1 gelatine in one ounce of water), when the whole is boiled for 30 minutes and then taken out and put into clean warm water, twisting and washing several times till all traces of acid are removed, which can be tested by litmus-paper. When all water is wrung out the emulsion is dried on a hot-water bath or spread out in a warm room on blotting-paper. The product is mixed in 24oz. of alcohol and 24oz. ether.

The patentee also makes a collodion emulsion as follows:-Bromide of ammonia, 27 grains; distilled water as little as possible, and when dissolved add two or three drops of hydro-bromic acid containing gelatine, and then blend; glacial acetic acid, 3oz.; pyroxline, 32 or 35 grains. The emulsion with silver is formed by adding the silver nitrate solution prepared as before, but, instead of evaporating, pour the whole into a large jar filled with clean water and then into a calico bag and wring; then put it into gelatine solution and boil for 30 minutes, dry as before, dissolve in 4oz. of equal parts of ether and alcohol.

the instrument as 1,000, the unit volume adopted being 1-300 cubic centimetre. The top line of the graduation may mark a capacity of 3.1 cubic centimetres, and be figured accordingly 930, this being the smallest volume to which the inclosed air is likely to be reduced by low temperature and high atmospheric pressure. The maximum volume to which the inclosed air is likely to be expanded may be taken as 3.8 cubic centimetres, and the lowest line of graduation will be marked accordingly 1,140.

To use the instrument, the pressure on the reservoir is increased or relaxed until the level of the mercury is the same in both tubes. A reading is then made on the graduated stem, and represents the volume occupied at the actual atmospheric pressure and temperature by a mass of air which, under standard conditions, occupics a volume of 1,000. Any volume of gas measured in a holder, or registered by a meter under the same conditions, may be corrected to its true volume under standard conditions by multiplying by 1,000 and dividing by the figures read upon the instrument. Thus, if the rate at which the gas is passing through an experimental meter is 47 cubic feet per hour, and the reading of the aerorthometer (as it is proposed to name the new instrument) is 980, the corrected rate is. 4,700 or 4.8 cubic feet per hour. If the uncorrected illuminating power of a sample of gas is 15 8 candles, the acrorthometer reading being 1,050, the corrected illuminating power (which varies inversely with the volume consumed) is 15.8 × 1050, or 16-6 candles. Since the standard conditions commonly adopted in chemical and physical laboratories are a temperature of 0° Centigrade, and a pressure of 760 millimetres, and a gas under ordinary conditions is more expanded than under these conditions, it is convenient in an instrument to be used for correction to this standard to make the capacity of the bulb nearly 3 cubic centimetres, so that the 1,000 graduation may come near the top of the stem. If an instrument is required for the correction of the measurement of a dry gas, the air and mercury with which it is charged must be carefully dried.

900

QUICK ACTING ADAPTER FOR
MICROSCOPICAL OBJECTIVES.

September ult. Mr.

The patentee finds it convenient to use a box for regulating the evaporation, having both sides covered with several pieces of calico, holland, or linen, which must be soaked in alumised gelatine, The base of the instrument consists of a box with whipped and then dried, or fine perforated zinc a removable cover, and a backboard standing up T the last meeting of the Quckett Microsheet, fine horsehair or fine wire gauze may be from the hollow base. To the face of this backused. This box will keep down the too-rapid board two tubes of glass of equal calibre, CD, E. M. Nelson exhibited and described an evaporation and prevent honeycombs and other are attached, the same being set vertically side arrangement for rapidly attaching and detaching irregular markings. An elastic medium for by side. The tube C is open at top, and may the obje ives of a microscope, in lieu of double printing on uneven surfaces is made of gelatine, conveniently be contracted and bent over, to pre-nose-pices; and similar contrivances. The sugar, glycerine, chromealum, spirit, thymol, or vent the admission of dust. The tube D ter- method was suggested to him by that employed boracic acid, or any preservative agent. A glass minates at top in a bulb whose capacity is about by the French to close the breech-pieces of their plate is prepared by gluing a strip of paper four and a half times that of the tube. These ordnance. Three equal segments (each one-sixth) around the edge of the plate so as to form it into tubes extend into the hollow base, and are con- of the screw-thread of the nose-piece and of the a dish. The mixture is poured into this dish nected by means of flexible tubes, with a reser- objective are filed away-the objective can then and left to set; a negative tissue is put over it, voir, E, containing mercury. This reservoir has be at once inserted for the full length of the and it is placed on a dried pepper sensitised sur- a loose leathern top, and is intended to be con- screw, and one-eighth of a turn to the right face, the developing being effected with the tracted by the application of pressure in order makes it perfectly secure. By a similar turn to following solution:-Water 4oz., sugar 1oz., that a column of mercury may be driven into the the left, it can be detached with equal facility. gelatine loz., glycerine 6oz., thymol some drops, vertical tubes. F is a milled-headed screw pass-The best position for insertion should be alcohol oz., saturated chrome alum some drops.ing through a tapped hole in the cover of the marked, as in the other two positions more Hand drawings may be utilised for the process box and furnished at its inner end with a loose than one-eighth of a turn will be required by using the collodion sheet, coated with matted button which overlies the flexible portion of the to fix or release the objective. The liability varnish, then draw any picture on the matted mercury reservoir. By turning this screw, the of the objective to become loose and sheet with soft lead pencil, charcoal, or chalk, button may be caused to press upon the flexible fall out is so remote as to be practically imand print. cover, thereby contracting the capacity of the possible with the most ordinary care. Among reservoir. The stem of the tube D is graduated the advantages of this arrangement may be menand the backboard figured to correspond there- tioned the rapidity with which any number of with, so as to mark the capacity of the bulb and objectives can be interchanged without the necesstem down to each line of graduation. In order sity of employing a contrivance, such as the that the instrument may bear accidental inversion double, triple, or quadrupal nose-piece, which, during carriage without injury, each flexible tube with the attached objectives, adds so greatly to is embraced by a U-shaped loop of wire, the ends the weight, and can very rarely be well-centred. of which are made fast to a plate. This plate is There is no interference with any of the usual furnished with a threaded hole to receive a pres-arrangements, as the altered objectives can be sure screw, carrying on its inner end a pressure screwed into unaltered nose-pieces, and vice-versa. plate. By turning the screw the plate attached The centring of the objectives is not interfered to it may be used to compress the flexible tube with; and it is very convenient, when using between itself and the loop of wire, and thus water or oil immersion objectives, as fluid can be prevent the loss of any mercury except the very readily added or replaced. small portion remaining in the open tube.

A

VERNON-HARCOURT'S AER-
ORTHOMETER.

NOVEL apparatus to be used in ascertaining the volume which gas, measured under any ordinary conditions, would occupy under standard conditions, has been recently patented by Mr. A. G. Vernon-Harcourt, of Oxford, the object being to dispense with the use of the thermometer, barometer, and the tables, a simple arithmetical calculation being all that is necessary with the new apparatus.

In measuring gas the volume is commonly taken at the actual temperature and pressure of the surrounding air, and the measurement is then A convenient size for the instrument is to make corrected to obtain the volume which the gas the capacity of the bulb a little less than 31 would have under certain standard conditions. cubic centimetres (if the standard temperature This correction has hitherto been effected by adopted is 60° Fahrenheit) and that of the taking readings from a barometer and ther- graduated portion of the stem 0.7 cubic centimometer, by referring (in the ordinary case of a metres. The bulb and stem are to be charged gas measured over water) to a table giving the with a volume of moist air or other permanent tension of aqueous vapour at different tempera- gas occupying under standard conditions 3.3 tures, and by a calculation based upon these cubic centimetres, the stem below this level being readings and the laws of gaseous volume. The filled with mercury. This volume is marked on

Messrs. Powell and Lealand have, at Mr. Nelson's request, mude a pair of standard gauges, to be kept by the Quckett Microscopical Club for reference, and copies of it will soon be obtainable.

Since Mr. Nelson made his communication, he has ascertained that the same plan was suggested by Mr. James Vogan, and communicated by him to Science Gossip, Jan 1, 1869, p. 18, as “A Substitute for Nose-Pieces"; the only difference being the cutting away of two segments of one

fourth, instead of three of one-sixth. It is a matter of regret that so useful a suggestion should so long have remained unnoticed, and it is hoped that it will soon be generally adopted.

PRACTICAL NOTES ON PLUMBING.-
XLVI.*

By P. J. DAVIES, H.M.A.S.P., &c.

(Continued from page 105.)

OW we come to the soiling and shaving;

NOW

but before we do this, I will describe another method of lining cisterns. Suppose it is required to line a cistern in three pieces, that is, the side and end in one piece, and the bottom dropped in.

Proceed as follows:-Having the right sizes, line the lead and set it up, and boss up the angle I, Fig. 259, as also illustrated at TSB, JI, K B, Figs. 258 and 260. T is the return lead for nailing, as is also A; turn the lead to

round the lead, next boss up the four corners, sharpened, for a dull shave-hook makes dull then bulge it in the middle. This will shorten work. The shave-hook being all right, and in it each way, and will allow it to drop easily into proper order, proceed to apply the part Q into the bottom. You can now put it into its best the angle of the cistern, and with the point S position, and, with a piece of board laid upon gauge the shaving line, by holding the back part the lead, jump upon it, and so cause the bulged of the hook firmly to the angle of the lead, and

Take the compasses, set 5in. or 6in. open, and from the angles scribe all round the sides and bottom of the cistern, as shown at H, M, G, N, S, Y, &c., Fig. 257, and with the same radius strike the quadrant J N, &c., as shown; this is most useful, for the bottom especially, when wiping upright corners, as it keeps the solder off from the naked lead, and also gives a sort of finish to the work. Next soil the parts within the marks, and dry it with shavings, hot irons, or, as best you can, or, if time will allow, let it dry gradually. Next is the cutting off of the return edge or salvage Q, Fig. 261; here you

FIC 250.

with a good long stroke or sweep draw the hook down, and so shave to the desired width. If too wide, the hook, of course, must be made narrower.

Proceed with this, and clean out the bottom corners with a round-nosed spoon hook. Touch it over as you go on shaving, and all will be now ready for soldering. Some plumbers, after they have shaved their work, get a punch similar to carpenter's nail punch, and so punch the cut off edge of the lead into the back lead all up the angle; this holds it in position when not properly chase-wedged up. Never use a straight-edge for shaving a cistern. Such work is only done by those who are not proficient in their trade.

Soldering. For a cistern the size of that described at Fig. 250-namely, about 1ft. 6in. deep and 2ft. square, one large iron will do the work, and a pot of solder, say, 10lb. For large cisterns more irons will be required. I have watched will comfortably do from 8 to 10ft. of flat my own working, and find that a large iron wiping, and from 3 to 7ft. of upright wiping. I have done 9ft. of upright work with one iron, but this is a feat. For large cisterns it will be

FIC.265

as

see

Shaving.

require a good straight-edge and sharp chipping-
with the sharp chase wedge, take the chipping-
knife. Assuming it to be properly worked home
knife and small hammer, beginning at the top found much the best method to reckon enough:
near J, and cut off the salvage edge within one-31b. to the foot. This allows for getting up the
eighth of an inch, or less, of the angle; cut this heat, &c., though for small ones a lb. will be
straight, and from top to bottom, also round the ample, unless the water acts upon the tin; in
bottom, then take the sharp chase wedge, and a this last case 1 to 21b. will be required. Having
lead into the angle, which will wedge itself as with warm cloth, splash-stick, &c., ready, take
good-sized hammer, and well drive the in. of your solder-irons hot, and everything right,
touch it after cutting off the salvage with the shown, in the bottom to catch the solder, and to
tight as is required. Some plumbers do not
a piece of board B, Fig. 263, and lay it, as
chipping-knife.
prevent it getting on to the shaved part, S and
W, of the bottom. Next take another piece of
board about lin. thick, cut to fit the outer
angle as shown at A B, Fig. 263, and, with two
nails driven into the ends and into the sides of
the cistern, fix it, as shown. This will catch
the metal while the top part of the joint is being
made; or, if the cistern runs against the wall, push
be nearly the same as that illustrated at S QG, some paper, &c., between, so as to prevent waste
Fig. 262. This is about the right size, or, if of solder. Everything is now ready. Give the
anything, rather too large; from Q to S should mate orders to bring it" (the metal) and a
be in. This will shave about 1 in. wide. Some piece of board, or, if the cistern is in a closo
plumbers use a triangular cistern hook, similar place, a piece of lead or iron to stand the metal-
to that shown at ABD, Fig. 262. The circles pot on. Take the ladle full of solder in the left
F and E show the stem of the hook. When hand, and with the splash-stick in the right,
using these hooks, see that they are well commence splashing the metal on at the top

Figs. 258 and 260: this will shorten the lead
between KJ, Fig. 258, and will allow it to go
easily into its place. Next place this in,
you did the first piece, and nail it
there; that it fits properly. Now fix
the other side and end; do not use any nails
up the angles, and fix the lead by driving it
home with a chase wedge, having its point fin.
or so thick across the face, or to finish with a
in. narrower will do; well drive it home, but
do not split your lead or drive the side of the
cistern out. To prevent this, the cistern should
always be made as illustrated. The next thing
to do is to prepare the bottom, which is done as
follows:-Having measured round the bottom This is of more importance than many suppose.
and allowed for the substance of the lead sides, You cannot be too particular. In the first place,
mark out the exact size of the bottom, less in. you require a small, sharp, shave-hook, the blade
for the thickness of the turn-up lead, then with to be no larger than will shave the exact width
the chalk line, line out the lead; never scratch you require the solder to be when finished. For
it with a scriber. Now kneel upon the quarter- my part, I like the size and shape of the blade to
ing, and with the point of the chipping knife
passed under the edge of the lead, answering as
a lever, pull it up against the quartering, and
with the end of the dresser knock the lead well
up to the quartering, and so get it to stand up
square to the bottom. Having done this all
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