Make 5 ml of solution S1 alkaline, if necessary, by the addition of a measured volume of dilute sodium
hydroxide solution and dilute to 15 ml with water. To the solution, add 0,3 ml of alkaline potassium
tetraiodomercurate solution. Prepare a reference solution by adding to 10 ml of a standard ammonium
solution (containing 1 mg/l NH3) the same volume of dilute sodium hydroxide solution as for solution S1,

diluting to 15 ml with water and adding 0,3 ml of alkaline potassium tetraiodomercurate solution。Place the
solutions in test tubes and stopper the tubes.

After 30 s, any yellow colour in the test solution shall not be more intense than that in the reference solution,
which corresponds to 2 mg/l NH3 in solution S1.

关键是标红色部位的怎么翻译啊，我不太看得懂，因为这里说1mg/l的NH3，但是后面标黄色部位的说是2mg/l的NH3.我想又不是加热，怎么可能浓度会变大啊，请高手指点。