DETAILED DESCRIPTION What is claimed is: 1. A ferroelectric liquid crystal mixture composed of at least two components, which contains as one component at least one ionophore of the general formula (I) ##STR9## in which R. sup. 1,R. sup. 2,R. sup. 3,R. sup. 4, independently of one another, are alkyl of 1 to 15 carbon atoms, in which one --CH. sub. 2 -- group can be replaced by --CCO--, or --CO-- or one --CH. sub. 2 -- not adjacent to the N-atom by --O--, cyclohexyl, phenyl or benzyl, and X is an alkylene of 2 to 9 carbon atoms, in which one or two non-adjacent --CH. sub. 2 -- groups can be replaced by --O--, in which two adjacent --CH. sub. 2 -- groups can be replaced by 1,2-phenylene or 1,2-cyclohexylene, in which two adjacent --CH. sub. 2 -- groups can be replaced by CH(CH. sub. 3)--CH(CH. sub. 3)-- and in which a hydrogen atom of a CH. sub. 2 group can be substituted by R. sup. 5 or R. sup. 6, in which R. sup. 5 is alkyl of 1 to 15 carbon atoms, R. sup. 6 is alkyl of 1 to 15 carbon atoms or CH. sub. 2 --O--CH. sub. 2 --CO--NR. sup. 1 R. sup. 2. 2. A ferroelectric liquid crystal mixture as claimed in claim 1, which contains at least one ionophore of the formula (I) in which R. sup. 1,R. sup. 2,R. sup. 3,R. sup. 4, independently of one another, are alkyl of 1 to 15 carbon atoms, in which a --CH. sub. 2 --group can be replaced by --COO--, or one --CH. sub. 2 -- not adjacent to the N-atom by --O--, cyclohexyl or phenyl, and X is an alkylene of 2 to 9 carbon atoms, in which one or two non-adjacent --CH. sub. 2 -- groups can be replaced by --O--, in which two adjacent CH. sub. 2 groups can be replaced by 1,2-phenylene or 1,2-cyclohexylene, in which two adjacent --CH. sub. 2 -- groups can be replaced by --CH(CH. sub. 3)--CH(CH. sub. 3)-- and in which a hydrogen atom of a CH. sub. 2 group can be substituted by R. sup. 5 or R. sup. 6, in which R. sup. 5, R. sup. 6, independently of one another, are alkyl of 1 to 15 carbon atoms. 3. A ferroelectric liquid crystal mixture as claimed in claim 1, which contains at least one ionophore of the general formula (I) in which R
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