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Ozone : Ozone, Formula |
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Andrews and Tait (1860) filled a tube, A,
with dry oxygen, which communicated with a sulphuric acid manometer, B. Sulphuric acid is without action on ozone. After the silent discharge, a maximum contraction of one-twelfth was observed. When the tube was heated to 300°, the original volume was restored. A glass bulb of mercury broken inside the tube by means of a short length of glass rod which could be shaken on it, was converted into a black powder, and a variable volume of gas remained. A bulb of potassium iodide solution broken in the gas produced iodine, and the volume of gas remained unchanged, although it no longer expanded after heating to 300° and was therefore completely converted into oxygen. A possible explanation of the constancy of volume of the gas when the ozone is destroyed by potassium iodide is that, at the same moment as one portion of ozone reacts with the iodide, another portion changes into ordinary oxygen, the expansion due to the second change being exactly equal to the contraction due to the first. In any case, ozone is apparently denser than oxygen. Odling, in 1861, pointed out that the reactions could be explained on the assumption that the formula of ozone is O3: 2KI + O3 (1 vol.) + H2O = 2KOH + O2 (1 vol.) + I2. The formula O2+n will obviously give the same result, but O3 is the simplest, and there were no experiments pointing to a more complicated formula. Odling's formula was confirmed by Soret in 1866-68 by two sets of experiments ("Eau oxygénée et ozone," in Classiques de la Science (III), pub. A. Colin, Paris, 1913). Soret pointed out that oxidisable bodies which destroy ozone without change of volume, such as those used by Andrews and Tait, give no indication of the real density of ozone. Thus, suppose that 100 vols. of oxygen after electrisation contract to 90 vols. Assume that too vols. contain 100 O2 molecules, then the contracted gas must contain 90 molecules of (O2 + ozone). This change of volume can be explained by numerous formulae for ozone, since the only condition to be satisfied is that the 90 volumes, after heating, shall expand again to 100 volumes. This is the case with the following formulae:    In order to find the relative volume of ozone in the mixture, some solvent or absorbent is necessary which takes up the whole of the ozone without liberating oxygen (as is the case with potassium iodide). By comparing the contraction on absorption with the expansion on heating (or contraction on ozonisation) it would be possible to distinguish among the above cases. Thus, if the formula is O3, the contraction on absorption is 20, the expansion on heating 100-90 = 10. If the formula is O4, the contraction is 10 and the expansion 10; if the formula is O22, the contraction is 1 and the expansion 10. The formula O3 thus requires that the contraction on absorption shall be double the expansion on heating. Soret found that suitable absorbents for ozone were certain essential oils, such as oil of cinnamon and oil of turpentine. He took two flasks, of 250 c.c. capacity, filled with ozonised oxygen over water (Fig. 153). In one flask the ozone was absorbed by turpentine, when dense white fumes were produced; in the other it was decomposed by heating the flask by a flame. The contraction in the first flask was found to be almost exactly double the expansion (after the gas had cooled) in the second. Thus, Odling's formula, O3, was confirmed. Expt. 6. - The apparatus shown in,
devised by Newth (1896), consists of two concentric glass tubes, the inner fitted into the outer by a ground-glass joint. The inner tube contains dilute sulphuric acid, and the apparatus, previously filled with dry oxygen, is supported in a jar of water and crushed ice. Two wires from the coil dip into the liquids. By means of projections from the inner and outer tubes a thin glass tube, a, containing oil of turpentine or oil of cinnamon is held in position in the annular space. The manometer containing concentrated sulphuric acid coloured with indigo communicates with the apparatus, and the oxygen is ozonised. The contraction is read off on the gauge. The inner tube is then twisted so as to break the tube of oil of cinnamon, and after absorption has occurred the further con traction is read off. It will be found that the contraction on absorption is twice the contraction on ozonisation, i.e., double the expansion which would have occurred on decomposing the ozone by heat. In each case, before reading off the volume, an adequate time must be allowed for the gas to assume a constant temperature. |
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