THERMO-ELECTRICITY.] UNDULATORY F ORCES. ELECTRO-MET ALLURGY. 



241 



with great advantage, to such relief printing surfaces, 

 whether of copper or other soft metal ; for if they be 

 coated with iron, according to the invention, they will 

 yield almost an indefinite number of impressions, pro- 

 vided the iron surface be renewed as often as may be 

 necessary, and the printing surfaces be again recoated. 



"In carrying out the invention, I prefer to use that 

 modification of Grove's battery, known as Kunsen's ; and 

 I do so because it is desirable to have what is called an 

 intensity arrangement. The trough I use for containing 

 the solution of iron, in which the engraved printing sur- 

 face is to be immersed, in order to bo coated, is lined 

 with gutta-percha, and it is 45 inches long, 22 inches 

 wide, and 32 inches deep. In proceeding to prepare for 

 work, the trough, whether of the size above-mentioned 

 or otherwise, is filled with water in combination with 

 hydrochlorate of ammonia (sal-ammoniac), in the pro- 

 portion of one thousand Ibs. by weight of water, to one 

 hundred Ibs. of hydrochlorate of ammonia. A plate of 

 sheet iron, nearly as long, and as deep as the trough, is 

 attached to the positive pole of the battery, and immersed 

 in the solution. Another plate of sheet iron, about half 

 the size of the other, is attached to the negative pole of 

 the battery, and immersed in the solution ; and when 

 the solution has arrived at the proper condition, which 

 will require several days, the plate of iron attached to 

 the negative pole is removed, and the printing surface to 

 be coated is attached to such pole, and then immersed in 

 the bath till the required coating of iron is obtained 

 thereto. If, on immersing the copper plate in the solu- 

 it be not immediately coated with a bright coating 

 of iron all over, the bath is not in a proper condition, 

 and the copper plate is to be removed, and the iron plate 

 attached, and returned into the solution. The time 

 oxupied in ottaining a proper coating of iron to a print- 

 ing surface, varies from a variety of causes; but a work, 

 man, after some experience, and by careful attention, will 

 readily know when to remove the plato from the solution ; 

 and it is desirable to state, that a copper plate should not 

 bo allowed to remain in the bath, and attached to the 

 negative pole of the battery, after the bright coating of 

 iron begins to show a blackish appearance at the edges. 

 Immediately on taking a copper plate from the bath, 

 great care is to be observed in washing off the solution 

 from all parts ; and this I believe may be most conveni- 

 ently done by causing jets of water forcibly to strike 

 against all parts of the surface. The plate is then dried 

 and washed with spirits of turpentine, when it is ready 

 for being printed from in the ordinary manner. 



" If an engraved copper plate be prepared by this pro- 

 cess, instead of a comparatively limited number of im- 

 pressions being obtained, and the plate wearing out 

 gradually, a very large number can be printed off without 

 any sign of wear in the plate, the iron coating protecting 

 it effectually ; the operation of coating can be repeated as 

 many times as required, so that an almost unlimited 

 number of impressions can be obtained from one plate, 

 and that a copper one. 



"This process will be found extremely valuable for 

 electrotype plates, and also for photogalvanic plates, since 

 they can be so protected as to acquire the durability of 

 steel ; and more so, for a steel plate will require repairing 

 fniiii time to time ; these will not, but simply recoating, 

 whenever it is found necessary : by these means one 

 electro-copper plate has yielded more than 12,000 im- 

 prussions, and was found quite unimpaired when exam- 

 ined minutely. 



" It is easy to appreciate the importance of this inven- 

 tion, as applied to artistic or line engraving more espe- 

 cially ; for a copper plate being once engraved, if submitted 

 to the acierage process, will become a lasting property, 

 not liable to deterioration by printing, and the public 

 may expect to be supplied with the very best impres- 

 sions at a more moderate charge ; whilst, to the numerous 

 branches of commercial engraving, for the ceramic manu- 

 factures and others, as well as to the vast number of old 

 engraved copper plates existing in this country, this pro- 

 ceM is likely to confer an immense additional value. 

 " I need not say that copper in by no means the only 



VOL. I. 



metal to which the process is applicable, for the same 

 principle will be found to answer in the case of other soft 

 metals used for printing purposes ; and I shall only add, 

 in conclusion, that although the principle of electrotyp- 

 ing has been applied, up to the present date, in a variety 

 of ways since it was organised by Thomas Spencer, in 

 1837 ; this is, I believe, the first time that an attempt has 

 been successfully made to prepare an engraved copper 

 plate with harder metal, with the view of increasing its 

 printing capabilities ; and I feel happy to have been the 

 first to introduce so valuable a discovery into this, my 

 adopted country." 



THERMO-ELECTRICITY. 



WE have yet to draw attention to another source of elec- 

 trical power, which of late years has attracted considerable 

 attention from scientific men. In the previous pages, we 

 have repeatedly noticed how frequently the disturbance 

 of electrical equilibrium is attended with the production 

 of other forces, such as heat, light, &c. These and other 

 facts have led to the idea that each of the undulatory 

 forces has a common origin a theory which has already 

 been enlarged on. We must now explain the methods 

 by which electricity may be evolved by the action of 

 heat on certain metals, and describe some of the pheno- 

 mena which result therefrom. 



As we have seen, electrical effects result, in some cases, 

 chiefly from the action of intense electricity, or that which 

 has the quality of exerting its effect at a distance from 

 the source of power. To some extent, thermo-electricity 

 falls under this category, but little quantity being 

 noticed in its action. Our thermo-electric batteries, 

 however, have hitherto been on a very small scale, and 

 therefore we may yet perceive greater effects when larger 

 arrangements are made. 



A thermo-electric battery is easily constructed. It is 

 composed of a bar of two different metals, F | g- 92 _ 

 generally bismuth and antimony. The bars c 



may be united at one end, as represented 

 in Fig. 92 ; whilst the others are left free. 

 In the cut, a is supposed to represent the bar 

 of antimony, and 6 that of bismuth. Now, 

 if heat be applied at the point, c, a current 

 of electricity will be produced ; and if a 

 number of these arrangements be connected 



Fif . 93. together, as in Fig. 93, 



they will form a ther- 

 mo-electric battery ; the 

 current induced passing 

 in the direction indi- 

 cated by the arrow. 



Another method of 

 makinga thermo-electric 

 battery, is that of solder- 

 ing, end to end, b;us of 

 bismuth and antimony, and of rolling them into a bundle, 

 such as is represented in the annexed figure, in which 

 c e represent the wires proceeding respec- 

 tively from the last bar of each metal. The 

 principle is precisely the same as that de- 

 scribed already, but the arrangement is more 

 convenient for many experiments. If wires 

 be conducted from the extremities of the 

 coil, they can be then attached to apparatus just as is 

 done in some voltaic batteries, &o. 



The cause of electric disturbance, although evidently 

 dependent on heat, is not easily investigated in all its 

 details. Extremes of temperature favour the develop- 

 ment of the current ; thus, if one metal be heated whilst 

 the other is cooled by ice, a more powerful current is 

 produced than by heating alone. It has been stated 

 that difference of conducting power is partly the cause ; 

 and this is borne out, apparently, by the order in which 

 the conducting power of metals is connected with that of 

 thermo-electric production. The following table shows 

 the thermo-electric relationship of some metals in refer- 

 ence to this question ; the greater differences between 

 them in position, the more powerful is the battery 



2 I 



Fig. 01. 



