Left: the color map shows the N(HCO⁺)/N(CO) ratio as a function of and S/H. Black contours correspond to N(HCO⁺)/N(CO) = 5.8 × 10⁻⁵ and 1.2 × 10⁻⁴. Red contours indicate X(CS) = 1 × 10⁻⁸ and 4 × 10⁻⁸, which is the range of CS abundances derived in the translucent part. Center: the color map shows the N(CS)/N(SO) ratio as a functionof and S/H. Contours are N(CS)/N(SO) = 4, 5.8 and 8. Red contours are the same as in the left panel. Right: gas ionization fraction, X(e⁻) = n(e⁻)/n_H, as a functionof and S/H. According with our data, the blue region marks the range of values expected in the translucent part of TMC 1. Bottom panels: observed values in the translucent cloud. Dashed red lines are: 5.8 × 10⁻⁵ and 2.7 × 10⁻⁴ in the N(HCO⁺)/N(CO) panel; 4 and 8 in the N(CS)/N(SO) panel and 7 × 10⁻⁹ and 4 × 10⁻⁸ in the X(CS) panel.