Hugo Müller

IV. Experimental researches on the electric discharge with the chloride of silver battery

Tube-potential. During the course of the experiments described in Part II. it could not fail to be noticed that the potential necessary to produce a discharge in partially exhausted tubes diminished with the pressure until a certain minimum-pressure had been attained; and that after this minimum had been reached, the potential had to be increased as the rarefaction was carried on, until at last 11,000 cells could no longer produce a discharge. Although Part II. contains many measurements from which it would be possible to calculate the tube-potential (the potential necessary to produce a discharge in a tube) for certain pressures, yet as they would not form a continuous series it was deemed desirable to make a special set of experiments with a constant number of cells, 11,000. This we have done in the case of hydrogen with a new tube, 162, 33 inches long and 2 inches in diameter, the distance between the ring and straight-wire terminals being 29·75 inches. In commencing each set of experiments the deflection of a tangent-galvanometer was observed when the battery was short-circuited; by a table previously calculated, the value of the deflection in ohms of resistance per cell could be read off: this multiplied by 11,000 gave the total resistance of the battery; the tube was then connected with the terminals and the galvanometer again observed, this gave a less deflection and indicated a greater resistance, which, multiplied by 11,000, gave the total resistance of the tube and battery; by subtracting the resistance of the battery the resistance of the tube was ascertained. Calling the total resistance R, the tube-resistance r, the tube-potential V, V= r × 11,000/R. Thus in the first experiment cited, the battery, short-circuited, gave a deflection of 61°, indicating a total battery-resistance of 230,000 ohms; when the tube was connected a deflection of 7°, indicating a total resistance, tube and battery, of 3,383,000 ohms = R, 3,383,000—230,000=3,153,000=r the tube resistance, 3,153,000 x 11,000/3,383,000= 10,250=V. The deflection observed was found to be different when the ring was made positive and negative respectively; the following results were obtained in each particular case:— Observations July 3rd, 1878. — 11,000 cells, short-circuit, deflection 61°, total battery-resistance = 230,000 ohms; deflections afterwards taken with the tube connected, the ring being positive.

Chemical Examination of Burmese Naphtha, or Rangoon Tar

In several localities of the kingdom of Burmah, there emanates from the soil in considerable quantity a peculiar oleaginous substance, which is employed for a variety of purposes, but chiefly as a lamp-fuel and as an unguent, by the natives, and exported in moderate quantities under the name of Burmese naphtha, or Rangoon tar. It is obtained by sinking wells of about 60 feet in depth, in which the liquid is collected by the miner as it oozes from the soil.

IV. On the height of the aurora borealis

Our experiments on the electric discharge, which have been already published in the “Phil. Trans.” and the “Proceedings of the Royal Society,” enable us to state with some degree of probability the height of the Aurora Borealis, when its display is of maximum brilliancy, and also the height at which this phenomenon could not occur on account of the great tenuity of the atmosphere. In Part III of our electric researches, “Phil. Trans.,” p. 159, vol. 171, we have shown that the least resistance to the discharge in hydrogen is at a pressure of 0·642 millim., 845 M; after this degree of exhaustion has been reached, a further reduction of pressure rapidly increases the resistance. When the exhaustion has reached 0·002 millim., 3 M, the discharge only just passes with a potential of 11,000 chloride of silver cells (11,330 volts) ; at the highest exhaust we have been able to obtain (and which we believe has not been surpassed), namely, 0·000055 millim., 0·066 M, not only did 11,000 cells fail to produce a discharge, but even a 1-inch spark from an induction coil could not do so.

I. On terephthalic acid and its derivatives

Whilst pursuing our investigation of Burmese naphtha, an abstract of which we have already communicated to the Society, we noticed, among the products of the action of nitric acid on certain liquid hydrocarbons contained in Rangoon tar, an acid of peculiar properties. A very lengthened investigation of this acid and its derivatives we are about bringing to a close; but as the drawing up of this account will necessarily occupy a considerable time, we have thought it desirable to send a short abstract of the chief results we have obtained, with the view of its appearing in the ‘Proceedings’ of the Society. M. Caillot, about fifteen years ago, obtained a peculiar acid among the products of the action of dilute nitric acid on oil of turpentine, to which he gave the name of Terephthalic acid, on account of its generation from oil of turpentine and its isomerism with phthalic acid.

The Kekulé Memorial

THE death of August Kekule on February 13, 1897, terminated a career rich in scientific achievement. In him we have lost an investigator who has exerted a profound influence on the development of chemistry.

The Chemistry of Paints and Painting.

CONSIDERING the widespread interest which attaches to all matters connected with pictures and painting, it is perhaps somewhat surprising that up to within quite recent times no attempt has been made to discuss and review in a comprehensive and efficient manner the materials and methods of painting from a strictly chemical point of view. It will, however, be readily conceded that the field is an extensive one, and it is, moreover, obvious that an intimate acquaintance with the technique of painting will be found only very rarely associated in the same individual with a thorough knowledge of chemistry. Neither a mere chemist nor a mere artist could undertake the task with a fair prospect of success.The Chemistry of Paints and Painting.By A. H. Church (London: Seeley and Co., 1890.)

III. Experimental researches on the electric discharge with the chloride of silver battery

Striking Distance. In a postscript to Part IV of our researches, we stated that, with 14,400 cells, partly of the rod form, partly of the chloride-in-pow der form, the length of the spark between paraboloidal points was 0.7 inch (17.8 millims.), and between a point and disk 0.62 inch (15.7 millims.), and that it does not appear, therefore, that the law of the spark being as the square of the number of cells holds good beyond a certain number. These results were obtained at the Royal Institution; since the removal of the battery to our laboratory we had not, at the date of the postscript to Part IV of our researches, charged up the whole of it. Recently, however, we have put the battery in thorough order, by scraping the zinc rods of the cells already charged up and added newly made up cells to bring up the total to 15,000 cells, all of the rod form.

VII. On the electric discharge with the chloride of silver battery

In anticipation of a paper to be shortly communicated tot he Society, we wish to state that we have found that the pressure of least resistance for a given gas is not a constant, but that it varies with the diameter, shape, and dimensions of the vessel employed. Moreover, that the dark space near the negative in electric discharge in vacuum tubes is dark only by comparison.

The Inevitable Test for Aurora

IN NATURE, vol. xxii. p. 33, is an implication, if not also a declaration, that the limits of height in the atmosphere, at which the Aurora Borealis both can, and cannot, appear, have been ascertained by those world-respected scientists, Messrs. Warren De La Rue and Hugo W. Müller, F.R.S.S. both. The skill of their experiments, the sufficiency of their exhausting apparatus, and the power of their unequalled chloride of silver battery are beyond all question; and they did, without doubt, ascertain in a very complete manner at what particular degrees of rarefaction of certain glass vessels, their electric discharges therein, took such and such appearances.

Experimental Researches on the Electric Discharge with the Chloride of Silver Battery. Part II. The Discharge in Exhausted Tubes.

We cannot flatter ourselves that we have done more during our three and a half years’ work than contribute a few facts towards the data necessary for the solution of the problem of the cause of stratification produced by the electric discharge in vacuum tubes. We refrain for the present from suggesting any hypothesis to account for this beautiful phenomenon, in the hope of being able to confirm, experimentally, certain views which we entertain concerning it. The paper we have now the honour of laying before the Society consists mainly of a record of the various appearances presented by the discharge in residual gases at various pressures and with various currents.