a. Borate solution, Na2B4O7.10H2O: In a 1-L volumetric flask dissolve 38.0 g Na2B4O7.10H2O and 3.0 g sodium hydroxide, NaOH, in approximately 900 mL water, using a magnetic stirring bar. Gentle heating will speed dissolution. Adjust to pH 9.0 with NaOH or conc hydrochloric acid (HCl) . Dilute to mark and invert too mix.