602 



NATURE 



{Oct. 19, 1882 



to which there seemed every human probability he might 

 reach. At an early age he turned his attention to scientific 

 pursuits, and commenced his career as a chemist, tie 

 training for which so eminently fittel him for the active 

 part he took for the last twenty-five years in matters 

 relating to photography. When scarcely o:' age he wrote 

 his "Traite' Generate de Photogruphie," a new edition of 

 which was called for almost year by year, its popularity 

 being nearly unprecedented. Usually sound in his ideas, 

 we may take it that much of the teaching of photo 

 chemistry has been propagated through the instrumen- 

 tality of that work. Not only was Van Monckhoven an 

 ardent experimentalist in the domain of chemical physics, 

 but he also entered into all optical questions bearing on 

 photography with a zeal which those alone who had the 

 pleasure of his acquaintance can estimate. The Monck- 

 hoven solar enlarging apparatus is a standing record of 

 his great ability in this department of science. At a very 

 early period of his career he applied the spectroscope to 

 record the effects of light on different inorganic and 

 organic bodies, and his photographic researches on the 

 spectra of gases occupied no inconsiderable portion of 

 his time ; his very latest published work, presented 

 recently to the Academie des Sciences, being on the effect 

 of temperature and pressure on hydrogen. Whilst 

 Science, for herself, had charms for Van Monckhoven, 

 yet he was able to put to commercial use much of 

 the knowledge which he had acquired. For instance, 

 he entered with enthusiasm into the mysteries of carbon 

 printing, and established a factory for the production 

 of the necessary tissue. Indeed the Monckhoven's tissue 

 is the only one which enters into any sort of competition 

 with that manufactured by the Autotype Company. Again 

 to perfect the preparation of the latest photographic 

 novelty — gelatine plates— he rushed into researches with 

 all the ardour of an experimentalist, and having more or 

 less mistered its intricacy, he established a manufactory 

 for their commercial issue, and probably the Monckhoven 

 plates are better known on the Continent than any other. 

 Van Monckhoven, besides being the author of the trea- 

 tise on photography, contributed many memoirs to 

 various periodicals, amongst which we may name La 

 Lumi'ere, Le Bulletin Beige, and La Revue des deux 

 Mondes. His style was vigorous, and everything he 

 had to say was written with a terseness which many a 

 busy scientific man may envy. In reviewing Van Monck- 

 hoven's life we cannot point to any great discovery 

 or to any startling inventions he made, but he was 

 one of those men who are so useful to science, giving, as 

 it were, the decorations to the more solid building. We 

 are sure that though there may be greater names, 

 there is scarcely one which is more universally known 

 than his, and whose loss will be more universally felt. 

 There are not many who can claim to be distinguished as 

 an astronomer, a chemist, an optician, and photo-chemist, 

 Van Monckhoven could make good his claim to such dis- 

 tinction, and withal to be a busy man in the world of 

 commerce. 



Within a short time of his death he was engaged in an 

 important research on the influence of pressure and tem- 

 perature on the spectra of gases, in which he had intro- 

 duced quite a new method of attack, and one which 

 promised to be of great value. 



THE CHEMISTRY OF THE PLANTE AND 

 FAURE ACCUMULATORS 

 Part IV.— The Function p/ Sulphate of Lead 

 T N our previous communications on the chemistry of 

 *• the lead and peroxide batteries we have frequently 

 remarked on the formation of lead sulphate and its 

 importance in the history of a cell. 

 . In Part I. (Nature, vol. xxv. p. 221) we showed that 



the local action that takes place at first energetic illy 

 between the metallic lead and the peroxide is gradually 

 diminished by the formation of sulphate of lead. 



In Part II. (vol. xxv. p. 461) we stated that in the 

 original formation of a Faure cell sulphate of lead is 

 oxidated on the one plate and reduced on the other. We 

 also described an experiment in which two platinum 

 plates were covered with lead-sulphate, immersed in 

 dilute sulphuric acid, and placed in the circuit of a gal- 

 vanic current ; the result being that " the white sulphate 

 was decomposed to a large extent on each plate, the 

 positive being covered with deep chocolate-coloured 

 peroxide, the negative with grey spongy lead." 



In Part III. (vol. xxvi. p 251) we showed that on the 

 discharge of a cell, lead sulphate is the ultimate product 

 on both plates. 



It might naturally be inferred from our previous state- 

 ments that in the re-charging of a cell this lead sulphate 

 would be oxidated on the one plate and reduced on the 

 other as in the original formation. This matter, however, 

 has given rise to so ne controversy. All subsequent 

 experimenters admit the oxidation of the lead-sulphate, 

 but Dr. Oliver Lodge could not obtain any reduction 

 of it, when pure sulphate was employed. Sir William 

 Thomson also, when experimenting, with two platinum 

 plates and layers of sulphate, obtained only a doubtful 

 indication of reduced metal. The question as to whethej 

 the sulphate is reduced or not on re-charging a Faure 

 cell is one of vital importance; for if the sulphate formed 

 at each discharge accumulates on the positive plate 

 it would clog up the space, and, what is perhaps worse, 

 a fresh surface of the lead would have to be oxidated (or 

 rather, converted into sulphate) at each discharge. Thus 

 the positive plate will be continually corroded, and its life 

 will be limited. 



We have already replied to Dr. Lodge in Nature 

 (vol. xxvi. p. 342), but we thought it desirable to repeat 

 the experiment with the platinum plates, especially with a 

 view to determine whether the reduction was effected 

 slowly or with any rapidity. We fastened 20 grms. of the 

 white sulphate upon a negative plate by binding it round 

 tightly with parchment-paper, placed it vertically in the 

 sulphuric acid, and passed a continuous current of some- 

 what under an Ampere. The hydrogen was at no time 

 wholly absorbed — indeed the greater part of it certainly 

 escaped — but after the lapse of twenty-four hours, small 

 patches of grey metallic lead became distinctly visible 

 through the wet parchment-paper ; and these gradually- 

 spread in an irreguhr manner. At the end of ten days it 

 was found that the whole of the sulphate, except a few 

 small patches on the surface, was reduced to a grey 

 spongy mass. Although there could be no reasonable 

 doubt that this was metallic lead, a portion of it was 

 tested chemically, and proved to be such. 



It thus appears that the reduction of the pure sulphate 

 of lead is an absolute fact, although it does not take place 

 so easily as the oxidation. 



In an actual cell the sulphate of lead is of course mixed 

 with other bodies. Thus, in the formation of a Faure 

 battery, the minium is converted by the sulphuric acid 

 more or less completely into peroxide of lead and sul- 

 phate. We have already described an experiment in 

 which 4489 c.c. of hydrogen were absorbed on a plate, 

 the materials of which were capable of absorbing only 

 4574 c.c, if the whole sulphate as well as the peroxide was 

 reduced In our note-book we have the particulars of 

 four other experiments made in each case with the same, 

 or nearly the same, amount of material, in which 4199, 

 4575, 4216, and 4387 c.c. respectively were absorbed, 

 although perhaps in not one of these cases was the experi- 

 ment continued until the action was absolutely complete. 

 As, however, it may be objected that the amount of 

 sulphate produced upon these plates was an unknown 

 quantity, we have in a recent experiment treated the 



