376 



- KNOWLEDGE ♦ 



[Dec 21, 188?. 



quence. Whetlitr, however, it is sufficient to warrant 

 structural alterutions in the battery room or not is, per- 

 haps, all open question. It will answer ujany purposes to 

 which the amateur wishes to apply his battery, more par- 

 ticularly in those cases where a powerful and approximately 

 steady current is required. 



M. Trouve has also tried to increase the constancy or 

 steadiness of the current from a single fluid bichromate. 

 He turned his attention to the solution, which is prepared 

 by dissolving three ounces of bichromate of potash in twenty 

 ounces of builiug water, and, after cooling, adding gradually 

 nine ounces of sulphuric acid, stirring the solution as the 

 acid is iutroduced. A stronger solution is in this way 

 prepared, and, according to M. Hospitalier, the current is 

 steadily maintained for five hours if the zincs are gradually 

 immersed deeper arid deeper in the solution. No sane man 

 would, however, maintain that such an arrangement could 

 be regarded as a practical one — one, that is to say, which 

 could be called upon at a few minutes' notice to do work 

 either on a small or on an extensive scale. The inten.sity 

 of the current is but two volts per cell ; less, that is, than 

 can be obtained from another form, to which we shall now 

 turn. 



When Gerritt Smith arrived in England for the purpose 

 of trying the American system of quadruplex telegraphy, it 

 was found that the Daniell cell — which till then had 

 enjoyed almost exclusive tenancy of the Postoifice battery- 

 rooms — would not, unless subjected to very extensive 

 modifications in .size, yield a current such as would work 

 the system efliciently. The form of cell used in America 

 was unsuited to English ideas. The result was that resort 

 was made to a cell offered by Mr. Fuller, and which bears 

 his name. Several thousand fuller cells are in use through- 

 out the country, there being no fewer than seven thousand 

 in the Central Telegraph Office alone. Fig. 1 illustrates 



>i5?r\^^ 



the construction of the cell, which consists of a zinc rod 

 of peculiar shape, cast on to a thick copj)er wire, placed 

 in the poious ))0t, and a small carbon plate capped 

 with lead and fitted with a binding screw in the outer 

 or containing earthenware jar. The shape given to the 

 zinc is to compensate for unequal consumption, and 

 to facilitate its amalgamation, which is brought about 

 automatically. The comparatively large size of the outer 

 vessel, which is generally G inches high and 4.', inclies in 

 diameter, while the carbon is only '2 inches, is to allow a 

 large quantity of bichromate solution to be employed, and 

 so to save time in renewing or recharging, and to mini- 

 mise polarisation. The cell is charged by placing in the 

 porous pot dilute sulphuric acid in the ptojiortion of nine 



of water to one of acid, and in the outer jar a strong solu- 

 tion of bichromate of potash, with about 10 per cent, of 

 sulphuric acid added. Great as is the stii' made when we 

 are told that certain batteries are constant fur four, five, or 

 six hours, the Fuller cells are frequently called upon for 

 longer periods. In quadiuplex telegraphy a current is 

 always on the line- — that is to say, so loug as the circuit 

 is being worked ; and thus it i>> that the cells are giving a 

 practically uninterrupted current from 7 a.m. till 6 p.m., or 

 perhaps later, day after day for weeks, without requiring 

 any serious attention. It is, of course, only fair to point 

 out that the resistance offered by a telegraph circuit is as 

 a rule much higher than in experimental circuits, a 

 fact which operates very materially in favour of the battery, 

 because with a circuit of very low resistance — say half a mile 

 of copper wire of about the same thickness as a common pin 

 — the current is proportionately larger, or capable of pro- 

 ducing greater thermal effects, and the battery, as a 

 consequence, is more speedily exhausted. 



Where delicate apparatus is employed, or where the 

 battery circuit is frequently broken and re-made, con- 

 siderable danger results from the use of batteries of low 

 resistance. For example, it frequently happens that 40, 

 CO, and even SO cells are used on a circuit, the resistance 

 of which is, perhaps, 5,000 Ohms, or more. Supposing, 

 now, that the wire suddenly breaks and falls to the ground, 

 or that some other of the many ills that an aerial telegraph 

 line is heir to takes place, then the battery, if the fault 

 happens to be close up, will be practically shortcircuited, 

 the current immensely increased, and the platinum contacts 

 in the instruments fused ; or, if any coils happen to be in 

 the circuits, as is the case in some systems, they stand a 

 good chance of being fused, and so rendered useless. To 

 prevent this as far as possible, the porous pots used in the 

 telegraph service are painted with a very thin coating of 

 an insulating material, so as to raise the internal resistance 

 of the cell to 2 Ohms. 



We should have said something concerning the latest of 

 the many proposals to use bichromate batteries for electrie- 

 lighting, but this we must defer till another opportunity 

 presents itself. 



SUN VIEWS OF THE EARTH. 



View of the British Isles, France, &c., as seen foreshortened frou-. 

 the Sun in Winter. 



National Health Society. — At a meeting of tht- 

 society on the 11th inst. it was decided to assist, as far as 

 possible, the useful work now carried on by the Sanitary 

 Aid Committee. These are being started in several parts 

 of London in connection with the local committee of the 

 fJharity Organisation Society. The National Health 

 Society will issue shortly a handbook for the use of 

 sanitary-aid visitors, explaining in simple terms the 

 existing laws between tenants and landlords, and the 

 leaflets and pamphlets already published by the society 

 will also be of great service. 



