May 



1901] 



NA TURE 



II 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither ean he utiderlakc 

 ,',' return, or to (oi respond with the writers of, rejcr el 

 .H'lmistripts intended for this or any other part of NATURE. 

 ^\"c> notiiC is tal'en of anonvnwits iom»ttt>tiiations.'\ 

 On a Form of Artificial Submarine Cable. 



In order to illustrate the effect which capacity has on the 

 sending of arbitrary electrical disturbances along a conductor, 

 Mr. C. F. Varley, about the year i860, devised an artificial 

 submarine cable equivalent in its action to a real cable long 

 enough to teach Irom England to Australia. For obvious 

 reasons such a device would be a most instructive piece of 

 lecture-table apparatus. 



The so-called "K.R. Law" of Lord Kelvin states that the 

 time-lag in signalling over a cable is proportional to the capacity 

 of the dielectric sheathing per unit length, to the resistance 

 (also per unit length), and to the square of the length. 



Thus in order that the time-lag of an artificial cable shall be 

 great, both the resistance and capacity must be great. The 

 first of these two conditions is, of course, easily fulfilled, but if 

 the ordinary tin-foil type of condenser is used as the capacity, 

 both the bulk and cost of the apparatus is very considerable. 



For this reason very few artificial cables have been made 

 after Varley's plan. I have recently made an artificial cable, 

 giving about six seconds time-lag, which is entirely free from 

 the disadvantages just mentioned, and for this reason I trust 

 that it may commend itself to teachers of physics as a piece of 

 demonstration apparatus. 



In an actual cable the capacity is distributed uniformly along 

 the length of the line, but in an artificial cable of great equi- 

 valent length the capacity must be distributed non-uniformly in 

 some such way as that shown in the accompanying figure. 



In it B is the battery, K a double key so connected as to put 

 (he cable either to the ungrounded pole of the battery or to 



-^SI 





G 



earth, /'rare a number of high resistances which play the part of 

 the conducting core of the cable, and c c are the capacities which 

 play the part of the insulating sheath of the cable. G is the galvano- 

 meter, one side of which is connected to earth, and forms the 

 receiving end of the apparatus. 



This is substantially the arrangement which Varley used, the 

 only difference between his artificial cable and mine being that 

 I have substituted light, easily made electrolytic capacities for 

 the bulky, expensive commercial capacities used by him. 



As is well known, the polarisation capacity of platinum 

 electrodes in dilute sulphuric acid is very great. Unlike true 

 dielectric capacity, it isnot independent of the charging potential, 

 its value increasing with the charging potential and reaching a 

 value as high as 500 micto-farads per square inch of electrode 

 surface. 



Even though the capacity of such a cell is not a fi.xed quantity 

 we may make use of its great value in constructing an artificial 

 cable, though, of course, we are then obliged to use a battery at 

 the sending end having an E.M.F. less than the maximum 

 polarisation of the electrolytic cell. 



The capacities I used were made by fusing platinum wire into 

 the ends of little cells. made of glass tubing. These were filled 

 with water and a piece of platinum foil was corked into each so 

 as to dip a few millimetres into the water. 



I made thirty-six such cells and mounted them on a board in 

 which holes were drilled to allow the platinum wires to project 

 through so that they might dip into a trough filled with mercury 

 which was connected to earth. These thirty-six cells were divided 

 into twelve sets of three cells in parallel, and each of the twelve 

 sets were connected in the positions c ■: of the figure. The re- 

 sistances r r aggregated about a million ohm?. 

 NO. 1647, VOL. 64] 



The advantage of mounting the cells on the board as described 

 is that the action of the cable when the platinum wires are in the 

 mercury (and hence the capacities in, as shown in the figure) can 

 be rapidly compared with the action when the capacities are out. 

 In the latter case the apparatus represents an overhead line of 

 resistance equal to that of the cable. 



With the apparatus as described the galvanometer responds 

 as soon as the key is closed in case the capacities are out, but if 

 they are in there is a time-lag of about six seconds. 



A. Trowbridc-.e. 

 Physical Laboratory of the University of Wisconsin, U.S.A. 



Electro- Chemistry. 



My attention has lately been directed to your review of my 

 book on " Practical Electrochemistry " (April iS, p. 5S2). I 

 desire to thank you for noticing a modest effort at length. Vour 

 reviewer is in error in supposing that the series system of copper 

 refining is now of any commercial importance. The process 

 was founded on a delusion and is dead. The working up of 

 anode sludge, mentioned by your reviewer, is a purely chemical 

 question and does not fall within the scope of the book. I note 

 with interest that a method has been devised for refining tin, but I 

 do not anticipate its general adoption ; gold and silver being absent 

 from crude tin it is hardly to be expected that the anode sludge 

 obtained in the process of refining will be worth exploitation. 

 The electrolysis of chlorides to produce chlorates is an important 

 branch of electro-chemical industry, and omissions of details in 

 my book, quite fairly remarked by your reviewer, are due less to 

 indolence on my part than to the impossibility of obtaining 

 authentic information. Manufacturers, even in the United States, 

 where a liberal spirit prevails, are chary of allowing entry to their 

 works. A somewhat persevering inquiry at Niagara convinced 

 me of this reluctance. But in spite of this difficulty I am well 

 assured that the competent chemist, equipped with a sound 

 knowledge of the principles of electrolysis, need not fear to 

 engage in the practice of this the latest and most promising of 

 industries. Bertram Blount. 



Westminster. 



With reference to Mr. Blount's letter — if the "series system" 

 of copper refining was " founded on a delusion " it appears to 

 have been a fairly successful delusion. If Mr. Blount consults 

 "The Mineral Industry" for 1S99 he will see that the Baltimore 

 Copper Smelting and Rolling Co., which uses this system, turned 

 out between 60 and 70 million pounds of refined copper in 1898. 

 The Nichols Chemical Co., N.V., whose daily output of refined 

 copper amounts to 60 tons, also employs this method (or did in 

 November 1899). 



Mr. Blount further states that gold and silver are absent from 

 tin and therefore " it is not to be expected that the anode sludge 

 obtained in the process will be worth exploitation." Mr. Blount 

 is probably thinking of Cornish tin, but Mr. Clauses process has 

 been devised for purifying South American tin, some of which 

 contains considerable quantities of gold and silver, e g. an anode 

 sludge analysed for Mr. Claus contained 69S ozs. silver and i oz. 

 gold per ton (i ton oi anode sludge would be obtained from about 

 10 tons of crude metal). In another analysis the crude anode 

 gave 7 ozs. silver and i oz. gold per ton. 



I am still of the opinion that Mr. Blount would have con- 

 siderably added to the value of his book had he described in 

 detail the working up of a "typical" anode sludge. The 

 successful treatment of the sludge is extremely important to the 

 practical electro-chemist, and if a description of it is outside the 

 scope of a book devoted to electro-chemistry, I fail to see in 

 what book it should be described. 



In the third place I did not accuse Mr. Blount of being "in- 

 dolent " ; if he were so he would not sit down and write a book 

 of nearly 400 pages. An author must of necessity use his own 

 judgment, as to what he will include and what he will reject, 

 in writing a book. It does not, however, follow that the reviewer 

 will agree with him. F. MoLLWO Perkin. 



Specimens of " Aecidium berberidis." 

 There is a barberry bush near where I live which usually 

 bears on its leaves a number of cluster cups (^«t7i//««fe'-*«vc/«V). 

 They are just appearing. 



Perhaps some of your readers might care for a few speci- 

 mens. If so, and if they would communicate with me, I should 

 be pleased to send them a supply. J. Lewton Brain. 



Swanton Morley, Dereham, May 20. 



