Mav 25, 1883.1 



SCIENCE. 



463 



PHYSICS. 



Electricity. 



On secondary batteries. — Professor Barker 

 gives a brief liisiory of secondary batteries from the 

 discovery of electrolytic polarization by Gautherot, 

 in ISOl. to tlie invention of the Faure cell, together 

 with the re.'sults of his own experiments upon cells of 

 this latest form. 



In chai-ging his series of thirty-four cells by means 

 of a Gramme machine, he used, in order to prevent 

 discharge by a current backward through the ma- 

 chine when the electro-motive force of the latter fell, 

 a ' cut-out,' in which an electro-magnet, through 

 which the current flows, forces the end of a metal 

 bar against a spring, pressing it down, and thus keep- 

 in? the circuit closed while the current flows in the 

 desired direction. When the current begins to fail, 

 the reaction of the spring opens the circuit. 



Using this cut-out, Prof. Barker found that the 

 secondary battery could be employed with great ad- 

 vantage in steadying the current furnished to a 

 series of Edison lamps by a Gramme machine driven 

 by a sas-engine. For this purpose he connected the 

 Gramme and the battery as if for charging, the cut- 

 out being in the circuit, and connected, also, the 

 poles of the battery with the lamps. The electro- 

 motive force of the machine was made .very nearly 

 equal to that of the battery, so that, just after each 

 explosion in the gas-engine, the machine prevailing 

 sent a current through the lamps, and also a small 

 current through the battery, slightly charging it; 

 but, before the next explosion occurred, the electro- 

 motive force of the machine had fallen to such a 

 point that the battery now sent a current to the 

 lamps. It is stated, that, although the engine gave 

 only one explosion in four strokes, the pulsations in 

 the light entirely disappeared when the above arrange- 

 ment was adopted. 



Prof. Barker states that his experiments entirely 

 confirm those of Gladstone and Tribe as to the forma- 

 tion of lead sulphate when a secondary cell remains 

 in open circuit. In several cases the acid of the cells 

 disappeared entirely in this way, and lead sulphate 

 formed the entire coating on both plates. On at- 

 tempting to re-charge such a cell, the resistance was 

 found to be very high, and torrents of gas were 

 evolved from both plates. After a time the resist- 

 ance fell to it's normal value, and the waste of gases 

 ceased, though not till a considerable quantity of 

 energy liad been lost. 



It "appears, moreover, that in the cells employed, 

 although they were intended to be all of like dimen- 

 sions a1id construction, there was great difference of 

 storing-capacity and of resistance. After an liour's 

 use on the lamp-circuit, different cells gave on a tan- 

 gent galvanometer deflections varying from 87° to 0°. 

 When the discharge was continued for a long time, 

 so as nearly to exhaust J,he battery, it was found that 

 many of the cells were reversed, so as to be now 

 opposing the action of the others. " In place of con- 

 tinuing uniform as a single cell, the electro-motive 

 force of a series of cells begins to fall when about 

 half the charge which it ought to be capable of yield- 

 ing has been drawn from it." In the Plante cell the 

 local action is far less than in the Faure, the lead 

 peroxide in the former being very much harder, so 

 that not a trace of the sulphate was found in such a 

 cell after six months of frequent use. Prof. Barker 

 appears, therefore, to consider the Plante cell more 

 promising than the Faure, in spite of the much 

 greater time required to form it. — (Proc. Amer. 

 assoc. ; Montreal meeting, 1882. ) E. H. H. [923 



CHEMISTRY. 



(^General, physical, and inorganic.) 

 Ammonio-argentic iodide. — By digesting ar- 

 gentic iodide with a solution of ammonia, A. Lougi 

 obtained the compound 'S'B. 3 Agl. — (Gaz. chim. ital, 

 1883,86.) c. F. M. [924 



Bleaching-po-wder and analogous bodies. — 

 The constitution of this substance is again reviewed 

 by Lunge and Naef. In 1882 Kraut objected to the 

 formula, CI — Ca — O — CI, first proposed by Odling 

 for the dry salt, and apparently confirmed, in 1880, 

 by Lunge and Schaeppi. Kr.aut's objections were 

 twofold. In the first place, he asserted that all 

 the chlorine in bleaching-powder was expelled by a 

 mixture of carbonic dioxide and hypochlorous acid, 

 and, secondly, that bleaching-powder was analogous 

 to the lithium salt (LiCl -|- LiOCI). In answering 

 the first objection, Lunge and Naef affirm that Kraut 

 must have started with a basic calcic chloride, which, 

 with hypochlorous acid, gave, first, bleaching-powder, 

 from which carbonic dioxide set free the chlorine, — 

 Gig'jj + HOCl = H,0 + Cag'(,j . - Cag'^j + CO, = CaCO„+ 2C1. 



They further assert that CaCl, may be decomposed by 

 hypochlorous acid (CaCl, -|- C1,,0 = CaOCl, -|- Cl,).- 

 Concerning the second point urged by Kraut, Lunge 

 and Naef find that eighty-eight per cent of lithic 

 hydrate is converted into the basic chloride, while, 

 according to Kraut, fifty per cent only should enter 

 into the reaction, if it is analogous to bleaching- 

 powder. Chlorine is not eliminated from the lithium 

 salt by carbonic dioxide at ordinary temperatures. 

 At higher temperatures the chlorate is formed, and 

 oxygen evolved. The strontium salt corresponding 

 to bleaching-powder, when treated with carbonic 

 dioxide, behaves in a manner strictly analogous to 

 the calcium salt. The authors regard these facts as 

 sufBcietit to establish the formula. CI — Ca — O — CI. 

 — (Berichte deutsch. chem. r/eseUsch.,xvi. 84.) c. F. M. 



[925 



Action of certain vegetable acids upon lead 

 and tin. — Mr. F. P. Hall tried the action of acetic, 

 tartaric, and citric acids upon lead, tin, alloys of these 

 metals, and upon cans that had been used to preserve 

 fruit. In a solution of approximately the same 

 strength as common vinegar, these acids exerted a 

 much greater corrosive action upon tin than upon 

 lead, whether acting upon the metals separately or in 

 the form of allovs. Both metals were dissolved free- 

 ly, especially from the cans. The lead probably came 

 from the solder, since it was not detected in the tin 

 of which the cans were made. In the composition of 

 tin foils, every variation was found between samples 

 that were free from lead and those which contained 

 a very high percentage of this metal, —(^iner. chem. 

 journ., iv. 440.) c. r. m. [926 



{Analytical.) 

 Direct estimation of chlorine in presence of 

 bromine or iodine, and of bromine in presence 

 of iodine. — According to the observations of G. 

 Vortmann, metallic chlorides are not affected when 

 boiled with the peroxide of lead or of manganese and 

 dilute acetic acid, and only with difficulty by the con- 

 centrated acid. Bromides are decomposed by plum- 

 bic, but not by manganic peroxide, while iodides are 

 readily decomposed by either. To determine chlorine 

 in presence of bromine, the latter may be expelled 

 by evaporating the solution to dryness with plumbic 

 peroxide and dilute acetic acid. Iodine may be ex- 

 pelled from a mixture of a chloride and an iodide by 

 either plumbic or manganic peroxide and acetic acid. 

 Manganic peroxide is also used to decompose au 



