SCIENCE, INVENTION, DISCOVERY. 



317 



the alternation increases, they become, not 

 more but less dangerous. In fact, Tatuin has 

 shown that their fatal effects are nearly in- 

 versely proportionate to their frequency. Thus, 

 with currents alternating about 5,000 per sec- 

 ond, the current needed to become fatal is 

 about ten times greater than at the ordinary 

 low frequency of about 120 per second. With 

 still higher frequencies used' by Tesla (up to 

 20,000 per second) the currents are incompar- 

 ably less dangerous than at low frequencies ; 

 but still altogether harmless. 



Electricity, Storage of. The storage 

 of electricity is the conversion of electricity 

 into chemical energy under such circumstances 

 that it may be readily converted back into 

 electricity. The secondary batteries, which 

 are used for storing purposes, are termed " ac- 

 cumulators." The first* battery of this kind 

 was made by Hitter about 1840, and it con- 

 sisted of a series of disks of a single metal, al- 

 ternated with cloth or card moistened in a 

 liquid by which the metal would not be af- 

 fected chemically. In 1859 Mr. Gaston Plante 

 made a secondary battery, for which he used 

 plates of lead instead of plates of platinum. 

 Passing a current through these, lead oxide 

 was deposited, and after the charging-current 

 was removed the lead and lead-oxide were 

 found to yield a very slight current. To in- 

 crease this, Plante devised the plan of first 

 charging the plates, then discharging, then 

 charging again with the battery-current re- 

 versed, and so on, until, by repeated oxida- 

 tions and subsequent reductions of the oxidized 

 material, very porous plates were made. These, j 

 by their porosity, exposed a large surface to 

 the oxidizing action of the current, so that a 

 small porous plate took up as much electricity 

 as one of large superficial area. Plante found 

 that by connecting a number of cells together, 

 and, after charging them, arranging them in 

 series that is, the positive plate of one con- 

 necting with the negative plate of another, and 

 so on he could store for use quite powerful 

 currents of electricity. In 1880 another elec- 

 trician, M. Camille Faure, devised the plan of 

 coating Plante's lead-plates with red-lead, and 

 then incasing them in flannel. The advan- 

 tage of the red-lead is that it is very quickly 

 made porous, and therefore the process of re- 

 peated charging of the plates, known as the 

 " forming " process, was reduced from weeks 

 to days, and even to hours. This discovery, 

 by reducing the time and expense of making 

 the secondary battery, gave it a commercial 

 value that it never had before, and it was ' 

 hailed as a great advantage. Since that time ; 

 a number of patents have been obtained for ! 

 storage-batteries, and they now exist in differ- \ 



ent forms, but generally modeled on the in- 

 ventions of Plante and Faure. The efforts of 

 inventors have been mainly directed toward 

 reducing the weight of the cells and to devis- 

 ing new ways of holding red-lead on the plates. 

 This last-named substance, becoming porous, 

 drops off readily, and for this reason the in- 

 casements of flannel, etc., were first devised. 

 In some of the storage-batteries a plate or 

 frame of cast lead is used, with receptacles, 

 cells, etc., which are filled with the red-lead. 



Electroplating. The first to gild the 

 baser metals by means of the galvanic current 

 was Brugnatelli, in FS03 ; but the first to make 

 the process a success was the chemist De la 

 Rive, and it has since been greatly improved 

 by later inventions. The process depends upon 

 the peculiar power which the electric current 

 possesses of separating certain compound bodies 

 into their constituent parts. For instance, if 

 a current from a galvanic battery is passed by 

 means of platinum electrodes through water to 

 which sulphuric acid has been added, this 

 chemical separation, which is called electrolysis, 

 will take place, the water being resolved into 

 its constituent gases,, oxygen and hydrogen. 

 Now, if some sulphate of copper be thrown 

 into the liquid, electrolysis will still go on, 

 with a double result : the water will be sepa- 

 rated into its elements, and the hydrogen, by 

 its stronger affinity, will form a new compound 

 with the sulphur in the sulphate, setting the 

 copper free ; and the liberated copper, being 

 electro-positive in character, will be deposited 

 on the platinum electrode, which is negative. 

 On this general principle the process of electro- 

 plating or electrotyping depends, and its art 

 consists in applying the metals thus released 

 from their solutions to artistic and useful pur- 

 poses. To carry on electroplating on a large 

 scale oblong vats are used, which hold 200 

 gallons of solution'. Silver plates connected 

 with a powerful galvanic battery are placed at 

 intervals in the vats ; they form the positive 

 electrodes and correspond in extent of surface 

 with the articles to be coated, and face them 

 on both sides. These articles act as the nega- 

 tive electrodes, and are suspended by copper 

 wire from brass rods laid lengthwise over the 

 vats and connected with the battery. The 

 articles are prepared for plating by being first 

 boiled in a solution of potash to free them 

 from all grease ; they are then quickly dipped 

 in red nitrous-acid to remove any oxide that 

 may have formed on the surface, and after this 

 are well washed in water to remove every trace 

 of the acid ; they are then dipped into a solu- 

 tion of mercury .and then washed in water 

 again. The effect of this latter operation is 

 to make the film of silver adhere more readily. 



