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The photographic news
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- 35.1891
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- 1891
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1720, August 21, 1891
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August 21, 1891.] 597 ♦ The “free” chlorine is not necessarily present entirely as such, but may exist partly in the form of oxygen acids of chlorine. + This only represents a portion of the oxygen formed, as the amount of gas dissolved in the water was not determined. had been frequently observed that the volume of liquid present exercised a considerable influence on the rate at which the substance darkened ; this point was, therefore, further investigated. The exposure of the chloride was made in tubes closed at one end, and so arranged that any gas which might be evolved would expel a portion of the water by an exit tube terminating in a bulb, in which it was collected. Four tubes of this form, havinga capacity varying from 57 c.c. to 350 c.c., were filled completely with water containing equal quantities (5 grams) of silver chloride in suspension. After half an hour’s exposure to bright sunlight, bubbles of gas collected in the tube, and continued to be evolved till the end of the experiment. The gas was measured after eight days’ exposure (April 10-17), and the liquid was examined for free* chlorine by the addition of potassium iodide and titration with N/10 sodium thiosulphate in the usual way. The total chlorine was also estimated, the combined chlorine being found by difference. In determining the total chlorine, the method adopted in all cases was to add sulphur dioxide to a known volume of the liquid, the excess being removed by potassium chromate ; sodium hydrate was next added, and the solution boiled ; the precipitated chromic hydrate was filtered off, and the liquid and washings made up to known volume ; the chlorine was then estimated with N/10 silver nitrate solution, the liquid having been previously acidified with dilute nitric acid, and neutralised with sodium carbonate. This method was found to give good results provided the reagents used were free from chlorine. The results are given in the following table : — Table I. 1. H,o. 2. O at 0° and 760 mm. 3. Total Cl. 4. Combined Cl. Free Cl. 6. HCl in 100 parts of solution. c c. c.c. gram pram gram gram 57 4-02 0-097 0-092 0-005 0-162 121 5-74 0-124 0-122 0.0017 0-101 152 5'94 0’127 0-126 0-0010 0-083 356 6-61 0-142 0-142 0-0000 0-039 It will be seen that the effect of an increasing volume of water is to increase the total quantity of chlorine in solu tion, and therefore the amount of silver chloride decom posed ; also to increase the total amount of hydrochloric acid formed and of oxygen liberated ;t there is, however, a diminution in the amount of free chlorine present. Further, it is seen, on calculating the strength of acid per 100 parts of water (Column G), that the strongest acid is found in the tube containing the smallest quantity of water, and it is here also that the largest quantity of free chlorine is present. The strength of acid and the amount of free chlorine therefore decrease as the volume of water increases. As the decomposition of silver chloride by light is to a large extent dependent on the proportion of free chlorine present, the conditions which regulate its conversion into hydrochloric acid in the solution were studied. (To be continued.) The Royal Cornwall Polytechnic’s exhibition opens on Tuesday next at Falmouth, lasting four days. LUNAR AND TERRESTRIAL VOLCANOES. The following article by the Rev. H. N. Hutchinson, B.A., F.G.S., appears in the current number of our con temporary Knowledge. It will be interesting to our readers because the writer’s conclusions are drawn from photo graphs of the moon. Excellent collographic reproduc tions of the original photographs appeared in a former number: — Readers of Knowledge will not have forgotten the Editor’s interesting paper in the May number of last year on ‘ ‘ The Great, Bright Streaks which Radiate from some of the larger Lunar Craters.” It has been suggested to me that the question of the origin of these remarkable streaks might be discussed from the geological point of view, and that I should present some facts with regard to the lines of fracture and displacement among the stratified rocks of the earth’s crust which are known amongst geologists as “faults.” Geological science has received valuable aid from astronomers, and possibly there are questions in astronomy on which geologists might throw some light; at all events, it is a good thing occasionally that students of one science should endeavour to throw light on another. I only regret that the subject is not handled by one more deeply versed in lunar questions. In my previous paper on “The Cause of Volcanic Action,” I mentioned the connection between volcanoes, mountain-chains, and lines of weakness in the earth’s crust, which are closely connected with lines of fracture ; and this would seem a fitting opportunity for turning our thoughts to those remarkable outbursts of volcanic action on a prodigious scale of which the moon’s numerous craters stand as silent yet speaking witnesses, and to inquire how far the cracks radiating from some of them may be compared with terrestrial cracks. In Mr. Ranyard’s paper we find a summary of the opinions put forward by different authorities on the subject of lunar streaks. “ There are certainly seven such ray systems,” he says, “all with craters at their centres, namely: Tycho, Copernicus, Kepler, Byrgius, Anaxagoras, Aristarchus, and Olbers.” Of these, Tycho is the most conspicuous example ; its radiating streaks come out well in lunar photographs. The radiating streaks from Copernicus are well seen in the second photo in the December number of 1890. Two of the longest from Tycho extend to a distance of over one thousand miles from the crater. Nichol thought, as Mr. Ranyard tells us, that they were composed of matter shot up from the interior of the moon ; and compares them to mineral veins or to “trap-dykes” (of basalt or other igneous rock), such as are known to pierce the sedimentary strata upon earth. Nasmyth’s opinion was that the radiations “ are cracks divergent from a central region of explosion, and filled up with molten matter from beneath.” His experiment with a glass globe to illustrate this is described in the above paper (p. 130), also in Nasmyth and Carpenter’s book on the moon (1874, p. 134). “Proctor seems to have favoured the trap-dyke theory. Neison, after carefully setting out the observed facts, refrains from advancing any theory.” Young hesitates between this theory and the idea that they may be mere surface markings. Mr. Ranyard himself thinks “ that they correspond to a series of radiating cracks, or faults, from which comparatively warm air issues charged with aqueous vapour, which is deposited as hoar-frost on either side of the vent.”
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