SO far as we can find out, the acidimetry of hydrogen fluoride has not yet been particularly investigated, but it is well known that as a n acid it stands apart from hydrogen chloride and other stron,a mineral acids. For whilst it even surpasses sulphuric acid in the intensity of its reaction with water and many organic substances, it yet shows such mild acidic characters, that its " avidity " number places it in this relation among vegetable acids. Further, it not only decomposes the oxides of

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... some metnllojids, such as boron, silicon, phosphorus, and sulphur, forming fluorides possessing some degree of stability i n presence of water, but also gives with potash, soda, and ammonia, salts which are alkaline to litmus. T o investigate the subject, we hare experimented Kith the following common indicators of neutralisation of acids by bases ; litmus, lacmo'id, methyl-orange, phenacetolin, phenolphthaleh, rosolic acid, cochineal, brazil wood, and turmeric paper. These indicators have been prepared and used in the usual way, for the most part 5 s described in Sutton's VoZumetric AnaZysis. I n order to ascertaiii what personal difference there might be in the estimation of the particular shades of colour which iiidicat ed neutralisation, we worked .separately, and on materials all prepared by each f o r his own use. The first and last of the tables appended contain the results obtained by Haga, and the second those obtained by Osaka. -For titration in ,the experiments recorded in Tables I and 11 , clecinormal solutions, in the experiments given in Table 111 twicedecinormal solutions of potassium and sodium hydroxides and of ammonia were taken. They were almost pure, containing only the merest traces of silica and alumina, but as these, and also carbon dioxide when present in noticeable quantity, affect the indications of some of the colour reagents, we mere careful to determine for each indicator the exact titre of the alkali solutions in terms of a decinormal sulphuric acid which had been standardised by barium chloride, thus rendering ourselves independent of the effects of any impurities present.