ELECTRICITY. 



Practical 



Electricity. 



Elcctn.- 



employed 

 in the con- 

 struction of 

 rl -ctrilying 

 machines. 



Rubber and 



cushion* 



PLATE 



The electrics which have been generally employed in 

 the construction of electrifying machines, are glass, sul- 

 phur, rosin, gum lac, dried wood, pasteboard impregnated 

 with amber varnish, cloth, and catskin. The most use- 

 ful and generally employed of all these substances, is 

 glass, which, independent of its other qualities, is superior 

 to all others, both in durability and in elegance. It has 

 been employed sometimes in a rough state, but almost 

 always in a polished state; sometimes it has been 

 fashioned into the shape of a globe, at other times into a 

 cylindrical form, and sometimes into a flat circular plate. 

 When the glass is used in the form of a globe or cylinder, 

 it has sometimes been found advantageous to line the 

 inside of it to the thickness of a sixpence with a resi- 

 nous composition, consisting of four parts of Venice tur- 

 pentine, one part of rosin, and one of bees wax. This 

 must be introduced in sufficient quantity into the inside 

 of the globe or cylinder, and when the glass' is brought 

 gradually to an equal degree of heat throughout, the 

 melted substance is allowed to spread itself over the in- 

 terior surface, by turning the globe or cylinder about its 

 axis. A coating is almost never used in modern elec- 

 trifying machines, but it has been found of great use in 

 improving bad ones. 



The human hand was the only rubber which was em- 

 ployed by electricians, till a cushion was introduced by 

 Professor Winkler of Leipsic. The rubber consists of 

 three parts ; the cushion, the flap, and the stand. The 

 cushion is commonly made of soft leather, generally 

 basil skin, stuffed with flannel or hair, so as to be as 

 hard as the bottom of a chair, and sufficiently soft to ac- 

 commodate itself w ithout much pressure to the surface of 

 the globe or cylinder to which it is applied. In order 

 to effect this, a spring is formed either upon the stand 

 ;? XLV ' K which supports the rubber, as in Plate CCXLV II. Figs. 



34*5 io '' ^' ^' *' 5 ' or a s P" n S * placed within the rubber, as 

 in Fig. 10. which represents the rubber contrived by 

 Mr Jon.es. A piece of flexible iron or brass cd, is pla- 

 ced within the rubber AB, and keeps the surface A of 

 the rubber in a state of uniform contact with the con- 

 tiguous surface of the glass. The length of the cushion 

 should be about 8 or 10 inches, and its breadth between 

 1 J to 1 J inches wide. The flap, which was introduced 

 by Dr Nooth, is a piece of thin oiled silk, of the same 

 breadth as the length of the cushion, and nearly equal in 

 lengthtothesemicircumferenceof the cylinder. It should 

 be sewed on the surface of the cushion about a quarter 

 of an inch from its upper edge, so that the junction of 

 the silk with the cushion may form a straight line rising 

 a little above its surface. The flap should reach to with- 

 in an inch of a row of metallic points at the extremity 

 of the prime conductor, which we shall afterwards de- 

 scribe. This flap is not used when a globe of glass is 

 employed. The rubber should be insulated upon a 

 stand of glass, or baked wood. 



The amalgam, which was first recommended by Can- 

 ton, consisted of tin and mercury. Dr Higgins re- 

 commended an amalgam of four parts of mercury and 

 one of zinc. The common amalgam, however, which 

 was for a long time used in England and on the conti- 

 nent., consisted of five parts of mercury and one of zinc, 

 reduced to the consistency of butter, cither by fusion 

 or trituration, and mixed with a little chalk, or Spanish 

 white, perfectly dry. The amalgam invented by Ba- 

 ron Kienmayer, consisted of mercury two parts, purified 

 /inc one part, and pure tin one part. When the tin 

 and zinc are intimately mixed by fusion, the mercury 

 is added before they are cold, and the whole is shaken 

 together in a wooden box. It is then poured out on a 



Different 



Higgu^'s. 



layer'.'. 



table of marble, and reduced to a fine powder in a mor- Praetk-a! 

 tar. Kienmayer found, that with the common amal- 

 gam he could charge a Leyden phial having ly square 

 feet of coated surface only with 10 revolutions, whereas 

 with the preceding amalgam he required only 6. A bat- 

 tery, consisting of 53 square feet of coated surface, re- 

 quired 250 revolutions with the commonamalgam, where- 

 as with the new amalgam it required only 150 revolu- 

 tions of the machine. In laying the amalgam on the 

 cushion, he mixed it with a little hog's lard. Nevet's Ncvet's. 

 amalgam consists of equal parts of tin and mercury. 

 Cuthbertson employed mercury with tin filings and a Cut j hbert - 

 little oil. Cavallo recommended for the tin amalgam two so 

 parts of mercury and one of tinfoil, with a little pow- Cavallo's. 

 dered chalk ; and for the zinc amalgam, four or five 

 parts of mercury and one of zinc. When the zinc is 

 melted, the mercury, heated to above the temperature 

 of boiling water, must be added to it, and shaken in 

 a wooden box. It must then be triturated with a little 

 tallow, and a very little powdered whitening ; and one- 

 fourth of the amalgam must be afterwards added. Mr 

 Singer melts together one ounce of tin and two ounces Singer's. 

 of zinc, and when they are fluid he adds six ounces of 

 mercury, and agitates the mixture in an iron or thick 

 wooden box till it is cold. It is then triturated in a 

 mortar, and formed into a paste by hog's lard. Mr 

 Singer is of opinion, that when amalgams have a large 

 proportion of mercury, their action is variable and tran- 

 sient. 



The friction of the electric is produced by turning Mechanism 

 it about its axis either with a simple winch, as in employed. 

 Fig. 1. PlateCCXLVII. or by a multiplying wheel, as in 

 Fig. 2. For this purpose, the ends of the cylinder 

 must be cemented into two pieces of well baked wood, 

 which rest upon two vertical supports, and serve also Mechanism 

 for the pivots round which the cylinder is turned. The 

 axis of the pivots must coincide exactly with the axis 

 of the cylinder, so that the pressure of the rubber 

 against the cylinder or globe may be uniform. The 

 most common way of putting the cylinder in motion is _ 



by a simple winch or handle, as in Fig. 1. When a V 

 multiplying wheel is used, as in Fie. 2. the string is al- lg$ ' ' 

 ways becoming loose ; and, though more electricity is 

 produced in a shorter time, the labour of the operator 

 is increased. When a glass globe is used, it is fixed 

 only at one end, and is supported on a single stand, as 

 in Fig. 4. The best electrical cement for attaching 

 the cylinder to its pivots, is made by mixing five pounds * *" 

 of rosin, one pound of bees' wax, one pound of red B st electri- 

 ochre, and two table spoonfuls of plaster of Paris. The ^ cemcntt 

 ochre and plaster of Paris should be well dried, and 

 then added to and alternately mixed with the other in- 

 gredients, when they are in a state of fusion. This ce- 

 ment is recommended by Mr Singer. 



The prime conductor, or the positive conductor as it is Prime con- 

 sometimes called, was first applied by Professor Boze ductor. 

 of Wittenberg-. It is a cylindrical tube of thin sheet 

 brass, or copper, or tin, or of pasteboard covered with 

 gold-leaf or tinfoil, terminating in both ends with he- 

 mispherical caps, which can be taken off at pleasure. 

 The conductor may be made solid as well as hollow ; 

 but this is altogether unnecessary, as we have already 

 seen from Coulomb's experiments, that the electricity 

 is merely distributed over the surface of conductors, 

 and never penetrates the solid mass. Conductors are 

 often made of solid wood, covered with tinfoil. The 

 greatest care must be taken in the formation of the 

 conductor, that its surface be entirely free of all points 

 and asperities ; and the holes which are made in it, of 



