398 



NATURE 



{Sept. 9, 1875 



actions," it may possibly be the author's intention to 

 append them to a future communication to the Royal 

 Society, in continuation of Other important papers aheady 

 published in the "Transactions," — a place which the Tables 

 will advantageously occupy. They give with sun's longi- 

 tude as argument, the inclination of the solar axis to the 

 circle of decHnation, reckoned positive when the axis is 

 west of the north point of the sun's disc, and assuming 

 the inclination of his equator to the ecliptic to be 7° i5''o, 

 and the longitude of its ascending node 74°-i' ; and with 

 argument, sun's longitude + v, the " Heliographical lati- 

 tude of the earth " and " Reduction of longitude." The 

 obliquity of the ecliptic is taken, 23° 27'-5, but to correct 

 the angle between the circle of declination and the sun's 

 axis, for difference of true and assumed obliquity, a sup- 

 plementary table is provided. 



The Tables have been calculated by Mr. Marth, and it 

 will be obvious to anyone initiated in such work, that 

 considerable trouble has been taken to ensure their accu- 

 rate production. 



MiRA Ceti. — A minimum of this variable star is set 

 down in Schonfeld's ephemeris for September 30. The 

 minima have not been properly observed nearly so often 

 as the maxima, though equally important in the inves- 

 tigation of the laws which regulate the fluctuations of 

 light, and which, according to Argelander's researches, 

 involve a more complicated formula than has yet been 

 deduced for any other variable. The circumstances of 

 the approaching minimum are very favourable for obser- 

 vation. 



SCIENCE IN GERMANY 

 {Frojn a German Correspondent^ 



ONLY for a small number of elements and their com- 

 pounds is the relatively low temperature of the non- 

 luminous gas flame sufficient to produce spectra which 

 can be of use in analytical researches ; by far the 

 larger number turn into vapour at such degrees of tem- 

 perature as we can obtain solely by the electric spark. 

 We are therefore confined to spark spectra for such 

 bodies which do not give spectra in the flame, and these 

 spark spectra can all the less be dispensed with in 

 those cases where new elements are sought for, or where 

 it is a question of proving beyond all doubt the presence 

 of certain bodies, which in their chemical properties are 

 so much alike that ordinary reagents do not suffice for 

 their discovery or separation. 



But there are difficulties in the way of practically using 

 spark spectra, which have been the reason why these 

 important means of reaction have not yet found their 

 entry into all chemical laboratories. First of all, a 

 simple method has been wanting by which spark 

 spectra can be obtained at any time. Whoever has 

 been obliged to use currents of great intensity with tem- 

 porary interruptions of days, weeks, or months, knows 

 how much unpleasantness is caused by fitting, taking 

 to pieces, and cleaning the ordinary constant batteries 

 used hitherto. Another difficulty hes in the fact that 

 spectrum tables are still wanting which would be of suffi- 

 cient service for all practical purposes. It is true that a 

 large quantity of measurements have been pubUshed, and 

 doubtless some of them are extremely accurate, but with 

 the greatest part of them the purity of the substances 

 experimented with is not in the least guaranteed, and 

 very often it can be proved not to have been attended to 

 at all. If it is attempted to reduce to a universal scale 

 all the spectrum drawings at hand which have been ob- 

 tained by different observers, with different refractive 

 media, with different widths of the slit, some at a higher, 

 and some at a lower temperature, tables are obtained 

 which are completely and utterly useless in the laboratory. 

 Lately Prof. Bunsen,of Heidelberg, has tried to remove 



all these difficulties. In a very important treatise, the 

 first part of which has just been published, he first de- 

 scribes a new battery and a new spark apparatus, by 

 means of which spark spectra can at any time be obtained 

 with the same ease and facility as ordinary flame spectra. 

 The battery is the charcoal-zinc battery without clay cells. 

 The exciting liquid is a mixture of bichromate of potash 

 and sulphuric acid. In order to prepare 10 litres of this 

 liquid. Prof. Bunsen gives the following instructions : — 

 0765 kilogrammes of commercial powdered bichromate 

 of potash, which as a rule contains about 3 per cent, of 

 impurities, are mixed with o'832 litres of sulphuric acid in 

 a stone jar while the mass is being constantly stirred ; 

 when the salt is changed to sulphate of potash and 

 chromic acid, 9*2 litres of water are added, the stirring 

 being kept up and the water allowed to flow from a spout 

 about \ inch wide ; the crystal meal, which already is 

 very warm, thus gets warmer and warmer and eventually 

 dissolves completely. The exciters for this liquid are : a 

 rod of the densest gas coal, 4 cm. broad, i '3 cm. thick, 

 and immersed 1 2 cm. deep into the liquid, and a rolled plate 

 of zinc 4 cm. broad, o"S cm. thick, and immersed to the 

 same depth as the coal ; the zinc plate is entirely coated 

 with a layer of wax (which is put on whilst hot), except 

 that plane which is turned towards the coal and which is 

 amalgamated. The distance between coal and zinc is 

 entirely optional ; in the spectral and analytical researches 

 of Prof. Bunsen it varied according t© circumstances 

 between 3 and 10 millimetres. The results with this bat- 

 tery are, however, not very satisfactory with regard to 

 duration and constancy of current, if the cell containing 

 the exciting liquid is made of the same size and shape as 

 those in the ordinary Grove or Bunsen battery. The 

 reason of this lies in the circumstance that in the 

 nitric acid of those batteries there is far more oxygen 

 contained, which is employed for depolarisation, than in 

 an equal weight of the chromate liquid, and that there- 

 fore a comparatively much larger quantity of the latter is 

 used up to obtain the same effect. The chromic acid 

 battery therefore, compared to Grove's battery, requires 

 cells of at least three to four times more capacity. The 

 best shape for these cells is that of narrow, high cyUnders. 

 The column of liquid, of about i'6 litres, has a diameter 

 of about o'o88 metres, and stands o'28 metres high in the 

 cylinder, which bears a mark at that height. The zinc- 

 coal pair is only immersed up to half its height into the 

 liquid column, and has an active zinc surface of about 

 forty-eight square cm. 



With regard to the constants of this chromic acid bat- 

 tery without clay cells, it considerably surpasses in elec- 

 tromotive force all other apparatus with clay cells hitherto 

 used. It possesses an electromotive force which is about 

 13 per cent, larger than the ordinary charcoal-zinc or 

 Grove battery. Its essential conduction resistance is 

 about 12 per cent, smaller than that of Grove's battery 

 with clay cells. In order to be able to judge the econo- 

 mical effect of the chromic acid battery, we will consider 

 a little more in detail the chemical processes taking place 

 in this battery. In unconnected freshly filled Grove bat- 

 teries the consumption of zinc is very small, only when 

 after prolonged use an electrolytic and endosmotic ex- 

 change has taken place between the two exciting liquids, 

 a consumption of zinc, independent of the generation 

 of the current, becomes apparent. In the unconnected 

 chromic acid battery, however, the consumption of zinc 

 at the very beginning is entirely the same as that which 

 is observed in connected batteries during the genera- 

 tion of the current. This circumstance makes it indis- 

 pensable to arrange the chromic acid battery in such a 

 manner as to make it easy, at every interruption of the 

 current, to bring the exciting plates out of contact with 

 the liquid. This is attained by a simple hand lever 

 arrangement by which the plates can be dipped into or 

 raised out of the liquid. It is of particular interest, not 



