For analysis of sulphites and sulphurous acid solution, see L.I.L.B., pp. 16 and 37. _Boric acid_, _borax_ and other _borates_ are not very powerful disinfectants. They have no injurious action upon the skin, but to be effective require to be employed in pretty strong solutions, say 1 per cent., and their comparatively high cost unfits them for general use as antiseptics in the tannery, though boric (boracic) acid is very useful as a drenching and deliming agent (see pp. 156, 229, and L.I.L.B., p. 37). _Mercuric chloride_, corrosive sublimate, HgCl₂, is an extremely powerful antiseptic, preventing the growth of some species of bacteria in solutions so dilute as 1 in 300,000 (Koch). 1 in 14,000 is disinfectant (Miquel), but its power varies very much upon different organisms (Jörgensen states that 1 in 400 is required to kill _Penicillium glaucum_), and it is unsuited for most purposes in leather manufacture, both from its extremely poisonous character, and because it is rendered inactive by various substances present in the materials used. _Mercuric iodide_ dissolved in iodide of potassium solution was patented by Messrs. Collin and Benoist as an antiseptic in tanning, but it is ineffective for the same reasons as mercuric chloride; although under favourable circumstances it is even more powerful than the latter. _Copper sulphate_, _zinc chloride_ and _sulphate_, and many other metallic salts are powerful antiseptics, but have only a limited application in leather industries, and do not usually actually sterilise. _Arsenic_ (arsenious acid), which has been used in curing hides, is an excellent insecticide, but not particularly effective as an antiseptic; and sulphide of arsenic (realgar) when used in limes (see p. 139) seems to have but little antiseptic effect. Arsenious acid is easily soluble in alkaline solutions. _Fluorides_ have been suggested as antiseptics in the tannery, but do not seem of much practical value. The most important antiseptics at present are those derived from coal tar, and belonging to the aromatic series. Of these, the phenols (carbolic acid, cresol, etc.) are the most used.