Impurities of natural water -- Hardness -- Soap test -- Temporary hardness -- Clark’s softening process -- Archbutt and Deeley’s softening apparatus -- Other appliances -- Effect of temporary hardness in tanning and dyeing -- Permanent hardness -- Boiler scale -- Mud -- Iron -- Alumina -- Soda -- Copper, lead, etc. -- Sulphuric acid -- Nitrates and Nitrites -- Chlorine -- Carbonic acid -- Silicic acid -- Effect of hardness on plumping -- Peaty waters PAGE 93 CHAPTER XI. _SOAKING AND SOFTENING OF HIDES AND SKINS._ Washing of fresh hides -- Danger of putrefaction -- Soaking of salted hides and skins -- Soaking and softening of dry and dry-salted hides -- American wash-wheel -- Chemical methods -- Difficulty of softening hides dried at high temperature PAGE 108 CHAPTER XII. _DEPILATION._ Methods of depilation -- Sweating process -- Liming -- Sources of lime -- Quicklime -- Slaking of lime -- Solubility of lime in water -- Analysis of lime -- “Available” lime -- Action of lime on hide -- Liming in pits -- Suspension limes -- Effect of warming limes -- Quantity of lime required -- The Buffalo method -- Action of old limes -- Solution of hide substance by limes -- Sodium and potassium hydrates -- Payne and Pullman’s process -- Alkaline carbonates -- Alkaline sulphides -- Sodium sulphide -- Calcium Sulphydrate -- Gas-lime -- Tank-waste -- Lufkin’s liming preparation -- Barium sulphydrate -- Realgar, or red sulphide of arsenic -- “Inoffensive” unhairing solution -- Earp’s patent -- Unhairing on the beam -- Unhairing machines -- Vaughn machine -- Leidgen machine -- Unhairing in stocks and wash-wheel -- Jones machine -- Fleshing -- Vaughn fleshing machine -- Rounding PAGE 119 CHAPTER XIII. _DELIMING, BATING, PUERING AND DRENCHING._ Methods of removing lime and reducing swelling -- Use of acids -- Lactic, acetic and formic acids -- Boral -- Sodium bisulphate -- Boric (boracic) acid -- Borax -- “Pulling down” process -- Use of ammonium chloride and sulphate -- Pickling solutions -- Drenching with lactic acid -- Metabisulphite of soda -- Washing out lime, French process -- Nesbitt’s process -- Use of carbonic acid -- Carbolic acid -- Cresotinic acid -- Oxynaphthoic acid -- “Anticalcium” -- “Acrilene bating acid” -- “C.T. Bate” -- Use of sulphides and polysulphides -- Babool pods -- Bran-drenching -- Bating and puering -- Causes of bating effect -- Pepsin -- Trypsin, or Pancreatin -- Wood’s researches -- Erodin -- Palmer’s experiments -- Other artificial bates -- Relative effect of dog- and pigeon-dung bates -- Analysis of dungs -- “Scudding,” or “fine hairing” -- Preservation and use of dung PAGE 152 CHAPTER XIV. _ALUM TANNAGE, OR TAWING._