The use of a solution of carbonic acid for removing lime has been patented by Nesbitt,[90] who takes advantage of the fact that calcium carbonate is soluble in excess of carbonic acid (p. 94). The gas, which he generates, as for soda water, by the action of acids on chalk, or limestone, is received in a gasholder, and forced by a compressing pump into the vessel containing the hides, which is preferably a rotating drum lined with copper, and capable of bearing a pressure of about three atmospheres. The invention excited considerable interest on its introduction, as the gas is, certainly, quite uninjurious to the hides, and it was claimed that it enabled the grease and dirt to be better removed than by the ordinary methods. Further experience has shown, however, that the removal of the lime is far from complete, since, for success, it is not only necessary to bring it into solution, but to wash it out with carbonic acid solution under pressure, as on exposure to the air, solutions of lime in excess of carbonic acid rapidly deposit calcium carbonate. At the present time, the only tannery in which to my knowledge the process is in use is that of Messrs. Mossop and Garland, of Capetown, who state that it answers very well for harness-leather when a pure lime made by calcining sea-shells is used for liming, but is not satisfactory with ordinary stone lime. It is difficult to account for this on chemical grounds. Gluestuff may be treated very satisfactorily by simply blowing carbon dioxide, or washed and cooled lime-kiln- or furnace-gases, into an open pit in which the material is kept agitated. In this case, however, there is no need for the actual removal of the lime, so long as it is carbonated and its caustic character destroyed. Carbonic acid does not decompose lime-soap, and hence sets free no fatty acids, which, together with grease, are the main cause of the turbidity of glue, and the process therefore yields a more brilliant though darker coloured glue than does treatment with sulphurous acid. [90] Eng. Pats. 7744 and 12,681, 1886. Several acids of the aromatic series have been from time to time recommended as deliming agents, and generally possess the merit of acting at the same time as powerful antiseptics. In this connection it may be well to mention the solution of 1 per cent. of phenol and 2 per cent. of boric acid used by Dr. Parker and the writer for preparing and preserving skins for colour tests (L.I.L.B., p. 133). This answers very well as a bate even when much diluted, and may be rendered cheap enough for use in practice by the employment of a good commercial carbolic acid instead of pure phenol, and the use of sulphuric acid to remove lime from the solution and render it capable of repeated employment. The carbolic acid should not be too dark in colour, and should be carefully dissolved, or “carbolic” stains will result.