460 



NATURE 



{SepL 15, 1887 



observations had been committed to me by the Swedish Academy 

 of Sciences. Those measurements having been made by the 

 same instrume.Us ^ and the same method as the Upsala observa- 

 tions, it will perhaps interest you to see some of the results. 

 The measurements will sooa appear in extenso in the publication 

 of the works of the Expedition. 



Mean, greatest, and least heights of clouds at Cap Thorelsen 

 (above the mean level of the sea). 



For want of time the number of observations was rather small, 

 but nevertheless the heights agree tolerably well with those 

 obtained afterwards at Upsala. The mean error of a single 

 determination of lower clouds (below 3500 metres), I have found 

 to be 3 '4 per cent, of the height of the cloud, that of a higher 

 cloud (above 4700 metres) to be i6'6 per cent. We had two 

 bases, but the longer one was not more than 572'6 m., as I 

 could not, for that purpose, dispose of a greater length of wire 

 for the telephonic line. This explains the great mean error 

 found for the higher clouds. The greatest velocity observed for 

 higher clouds was 27 m. per sec. at a height of 7300 m. The 

 calculations are made by the method worked out by M. Hag- 

 strom and myself in the summer of 1884, and fully described in 

 our first paper on the subject ("Mesures des Hauteurs et des 

 Mouvements des 'Nm.ge?,^' in Nova Acta Keg. Soc. Sc. Ups., 



ser. iii., Upsala, 1885). 

 Upsala, August 24. 



Nils Ekholm. 



Occurrence of Apatite in Slag. 



I SHOULD like to be permitted to ask whether any minera- 

 logical readers of Nature have themselves come across, or have 

 anywhere seen mentioned, the occurrence of crystallized apatite 

 in a metallurgical slag or other artificially-formed silicate ? 



Having recently observed such an occurrence, I have been 

 looking into the authorities I have at hand here to see whether 

 any similar formation is previously recorded. The result is 

 negative, and indeed Rosenbusch (" Mikroscopische Physio- 

 graphic der petrographisch wichtigen Mineralien," 1885), after 

 enumerating the various artificial preparations of the mineral, 

 distinctly states that " the formation of apatite from fused silicate 

 magmas has not yet succeeded." My former teacher. Prof. 

 Weisbach, of Freiberg, who takes special interest in artificial 

 formations of minerals, and carefully records all cases coming to 

 his knowledge, writes to me that he is not aware of any instance 

 of the occurrence of apatite crystals in a slag except in the case 

 of the "Thomas slags" of the basic Bessemer process. 

 These can, of course, not be classed as "silicate magmas," 

 containing as they do so large a proportion of phosphoric acid, 

 and a relatively small amount of silica ; nor do they bear any 

 analogy whatever to the silicate rocks in which we are accus- 

 tomed to observe the occurrence of apatite in Nature. 



The slag in which I have observed the formation of apatite is 

 produced during the smelting of lead ores in a blast-furnace. It is 

 a basic silicate of lime and ferrous oxide, containing about 30 per 

 cent, of silica. The principal "flux" used in the reduction of 

 the ore is " tap cinder" from the puddling furnaces, and it is 

 mainly fr-im this source that phosphoric acid is introduced into 

 the slag. The slag itself, in bulk, is dark brown to nearly 

 black in colour. It flows into slag-pots of about 3 cwts. capacity, 

 and cools slowly. 



I recently prepared some thin sections of this slag for micro- 

 scopic examination. The greater portion consists of a mass of 

 crystals of olivine, surprisingly colourless and transparent con- 

 sidering how much iron is present. The spaces between the 

 crystals are occupied by deep-brown and yellow amorphous slag, 

 and black sulphides of iron, &c. 



Bolh olivine crystals and dark amorphous matter are pene- 

 trated through and through by great numbers of apatite crystals 

 in long needles. It is a most beautiful occurrence, analogous in 

 every way to what one sees in rocks. 



' The altazi.Tiuths employed were constructed by Prof. H. Mohn in 

 Chriuiaiia for the use of the Norwegian, Swediih, and Danish Polar 

 Expeditions. 



Nearly all the apatite crystals have taken up and inclosed 

 more or less of the amorphous dark material, which forms in the 

 majority of cases a rod running down the centre, but there are 

 also many cases of symmetrical arrangement of dark matter 

 parallel to the sides of the hexagon. 



The apatite does not only occur in the mass of the slag as 

 above described ; it is formed also in free crystals, lining 

 cavities which are formed in the centre of the lumps of the slag 

 owing to gases carried over from the furnace and liberated during 

 cooling. Some of these cavities are of considerable size, and 

 are often lined entiiely with a thick growth of apatite needles, 

 some as thin as the finest hair, others of much larger dimensions. 

 I have taken out crystals over a quarter of an inch long for 

 microscopic and chemical examination. Most of them contain a 

 good deal of the amorphous slag, &c., inclosed, as in the case of 

 those in the mass of the slag. 



Sometimes in such cavities very beautiful little crystals of 

 volatilized sulphides are seen among and on the apatites. I 

 have seen galena crystals in this manner, but it is very difficult 

 to remove them from the cavities without damage or loss. 



It appears to me strange that while we have here so plentiful 

 a formation of apatite going on constantly, in many tons of slag 

 daily, it should still be on record that experiments purposely 

 conducted with a view to obtaining the mineral in a silicate 

 magma have not succeeded. W. M. HUTCHINGS. 



Eversley Park, Chester, September 3. 



I 



Electricity of Contact of Gases with Liquids. 



May I be allowed to reply to Dr. Lodge (Nature, Sept. i, 

 412) ? That the escaping gas was charged was proved (l) by col- 

 lecting it in an insulated vessel ; (2) by gencj-ating and collecting 

 it in insulated apparatus. Electrification resulted in the first case, 

 but not in the second. Details of these experiments I intend to 

 publish later. 



With all possible respect for Dr. Lodge I cannot accept his 

 explanation of the electrifications I have described. I fail to 

 see any analogy between Armstrong's machine and the experi- 

 ments with zinc and hydrochloric acid which I have made, 

 except, indeed, that, as I hold, they are all cases of contact 

 electricity. Sir W. Armstrong directs a jet of steam against 

 solid wood grooved and shaped to increase the surface of contact. 

 In my experiment, on the contrary, I find that the effect is dis- 

 tinctly lessened when the hydrogen passes through narrow tubes 

 or openings, and accordingly the strongest deflections are ob- 

 tained when a large open dish is used. I take an evaporating 

 dishy 8 or 10 inches in diameter, and put a small quantity of a 

 10 or 16 per cent, solution of HCl into it. The acid is at every 

 point at least 4 or 5 inches distant from the edge of the dish. 

 When a small fragment of zinc is thrown in a gentle eflfervesence 

 is set up, the hydrogen shooting straight up through the middle 

 of the liquid into the air. I submit that in this experiment what- 

 ever electrification results is due to gas and liquid, and not to 

 gas and solid. Moreover, after a lapse of a few minutes when a 

 sufficient quantity of ZnCl., gets into solution, the charge on the 

 dish changes its sign. Is Armstrong's machine also in the habit 

 of reversing itself? On this reversal of the electrification I base 

 my case. The dish does not vary, but the liquid does, and its 

 variation is accompanied by a change in the sign of the charge. 



With regard to the atomic charges I do ttot hold that the 

 charge on the hydrogen has anything to do with them. It is 

 true that at first I set out to inquire as to the equality of these 

 charge-;, but when I found that the charges on the evolved gas 

 and the generator were of opposite sign, I was constrained to 

 admit that the electrifications were not connected with the 

 atomic charges as I had, during the earlier experiments, supposed. 

 Had I found things the other way — that is to say, that the charge 

 of the gas had been of the same sign as the charge on the gener- 

 ator — I should not have thought it at all improbable that the 

 electrifications were due in some way to atomic charges. In 

 fact, at the outset this is exactly what I thought I might possibly 

 fall upon. However, the unexpected occurred. 



' ' But that a gas should be thus electrified strikes one as im- 

 probable." Can this be so ? Surely the distinguished champion 

 of the "air effect," who has so stoutly maintained that the 

 contact of copper or zinc with gas gives rise to a difference of 

 potential, cannot consider it very improbable that the contact of 

 a gas and a liquid should produce a similar eflfect. Perhaps k 

 is well to remember that the hydrogen in these experiments is in 

 the nascent state. J. Enright. 



