DERIVAMOS UNA ECUACIÓN DE AMPLITUD PARA LA INESTABILIDAD ESTACIONARIA DEL SISTEMA ISOTÉRMICO DOBLE DIFUSIVO CON DIFUSIÓN CRUZADA. SE CALCULA UN TÉRMINO A QUINTO ORDEN EN TÉRMINOS DE LAS CONSTANTES RE-ESCALADAS DE DIFUSIÓN CRUZADA. ESTE TÉRMINO ES ESTABILIZADOR EN LA VECINDAD DEL PUNTO TRICRÍTICO. LA EXISTENCIA DE UN PUNTO TRICRÍTICO INDICA LA PRESENCIA DE UN CICLO DE HISTÉRESIS, CUYOS PARÁMETROS SE PRESENTAN EN ESTA CARTA.AbstractWE DERIVE AN AMPLITUDE EQUATION FOR THE STATIONARY INSTABILITY FOR THE ISOTHERMAL DOUBLE DIFFUSIVE SYSTEM WITH CROSS DIFFUSION. A QUINTIC TERM IS COMPUTED IN TERMS OF RESCALED CROSS-DIFFUSION CONSTANTS. THIS QUINTIC TERM IS STABILIZING IN THE VICINITY OF THE TRICRITICAL POINT. THE EXISTENCE OF A TRICRITICAL POINT INDICATES THE PRESENCE OF A HYSTERESIS LOOP WHOSE PARAMETERS ARE ALSO PRESENTED.WE DERIVE AN AMPLITUDE EQUATION FOR THE STATIONARY INSTABILITY FOR THE ISOTHERMAL DOUBLE DIFFUSIVE SYSTEM WITH CROSS DIFFUSION. A QUINTIC TERM IS COMPUTED IN TERMS OF RESCALED CROSS-DIFFUSION CONSTANTS. THIS QUINTIC TERM IS STABILIZING IN THE VICINITY OF THE TRICRITICAL POINT. THE EXISTENCE OF A TRICRITICAL POINT INDICATES THE PRESENCE OF A HYSTERESIS LOOP WHOSE PARAMETERS ARE ALSO PRESENTED.