Hair is softened by treatment with an aqueous solution of a salt of a mercapto-butane sulphonic acid.  The solution may be weakly acidic or rendered alkaline by means of sodium hydroxide, ammonia, tri-sodium phosphate, borax, meta borate or soda.  It may also contain alcohols such as methyl, ethyl or propyl alcohol, wetting or emulsifying agents or reducing agents, e.g. hydroxylamine, to prevent premature oxidation of the mercapto compounds.  Alkali-metal and ammonium salts of 3- and 4-mercapto-butane-1 sulphonic acids and 4-mercapto butane-2 sulphonic acid are mentioned.  The action of the mercapto sulphonates may be terminated by means of a suitable oxidizing agent, e.g. hydrogen peroxide, its derivatives, e.g. per-compounds, or its addition compounds, e.g. with urea or by means of a compound capable of reacting with a mercapto group e.g. aldehydes such as formaldehyde and glyoxal.  The reactions are described with reference to the permanent waving or smoothing of hair (see Group IV (c)). Specification 589,956 is referred to.  The Specification as open to inspection under Sect. 91 relates to the softening or dissolving of sulphur-containing sclero proteins in general by means of solutions of salts of any mercapto sulphonic acid.  Wool, feathers and nails are further examples of proteins and 3-mercapto-propane-1-sulphonates and 2-hydroxy-3-mercapto-propane-1 sulphonates are mentioned.  In the after-treatment of the proteins there may be used alkylene halides in place of the oxidizing agents and aldehydes.  The use of the solutions in depilatories is described (see Group VI).ALSO:In the permanent waving of hair or smoothing of curly hair, an aqueous solution of a salt of a mercapto-butane sulphonic acid is applied to the hair to convert the disulphide-like linkages in the protein of the hair into mercapto groups.  The waving or smoothing of the thus softened hair is subsequently rendered permanent by terminating the action of the mercapto compound by means of an oxidizing agent which does not degrade hair, e.g. hydrogen peroxide, its derivatives such as per-compounds, and its addition p  compounds, e.g. with urea, and bromates, or by means of a compound capable of reaction with a mercapto group, e.g. aldehydes such as formaldehyde and glyoxal. Suitable sulphonic acids are 3- and 4-mercapto-butane sulphonic acids-1 and 4-mercapto-butane sulphonic acid-2, used in the form of their alkali metal or ammonium salts.  The aqueous solutions are normally used in concentrations of about 5 to 25 per cent and at 25 DEG  to 40 DEG  C. for 1/2 to 2 hours; the solution may be slightly acidic but is preferably made alkaline by addition of caustic alkalies such as caustic soda, ammonia or alkaline reacting salts such as tri-sodium phosphate, borax, meta-borate or soda.  An alcohol such as methyl, ethyl or propyl alcohol may be present, as well as scented substances, wetting or emulsifying agents and reducing agents to prevent premature oxidation of the mercapto compound. In an example, hair is permanently waved by means of an aqueous solution of the sodium salts of 4-mercapto butane-1 and -2 sulphonic acids, caustic soda, hydroxylamine sulphate and an ethylene oxide-sec. fatty alcohols condensate, followed by a treatment with dilute hydrogen peroxide solution.  Specification 589,956 is referred to.  The Specification as open to inspection under Sect. 91 refers to the use of solutions of salts of mercapto sulphonic acids generally, in particular the lower aliphatic acids in the treatment of wool as well as hair and gives as additional examples, salts of 3-mercapto butane sulphonie acid - 1 and 2 - hydroxy - 3 - mercapto propane sulphonic acid-1.  It is stated that in the after-treatment, alkylene dihalides, e.g. the dibromides or other alkylating agents, may replace the oxidizing agents and aldehydes.  This subject-matter does not appear in the Specification as accepted.ALSO:The Specification as open to inspection under Sect. 91, relates to depilatories comprising a solution of a salt of a mercapto-sulphonic acid, e.g., the alkali metal and ammonium salts of 3-mercapto-propane sulphonic acid-1, 2-hydroxy 3-mercapto-propane sulphonic acid-1, 3- and 4-mercapto-butane sulphonic acid-1 and 4-mercapto-butane sulphonic acid-2.  The solutions may be aqueous and contain an alcohol such as methyl, ethyl or propyl alcohol.  They may be used slightly acidic but preferably are rendered alkaline by means of ammonia, caustic alkalies such as caustic soda or alkaline reacting salts such as tri-sodium phosphate, borax, metaborate, or soda.  There may also be present scented substances, wetting or emulsifying agents and reducing agents such as hydroxylamine to prevent premature oxidation of the mercapto compounds.  Example 2 describes a depilatory cream consisting of sodium 2-hydroxy 3-mercapto propane-1 sulphonate in an aqueous emulsion of wax alcohols, the emulsifier being the triethanolamine salt of fatty alcohol sulphonates, precipitated calcium carbonate and an alkali resistant perfume.  This subject-matter does not appear in the Specification as accepted.