COOH  → COO- + H+ ...................(a)In nature H+ is replaced by another positive charged ion e.g. Na+ or K+, and H+ bonds with oxygen to form water. Thus, surface of an unstained bacterial cell could be represented as shown in Fig. Basic dyes are commonly used for the monochrome staining. These dyes are available as a salt of acids, for example, methylene blue chloride. When methylene blue rehydrates, it ionizes as shown in equation-(b) to methylene blue and chloride ions. The positively charged ions have the colouring property.
MB. CI Methylene blue chloride  → MB+ Methylene Blue+ Cl-chloride ...(b)
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