1.General: 

(1) In solution of PH1.2 ~ 1.3,  the soluble silicon and ammonium molybdate react to generate silicon molybdenum yellow, which is the reduced by with stannous chloride to generate silicon molybdenum blue, the blue color of which is associated with the soluble silicon content in water samples. The interference of phosphate on this method can be eliminated by means of adjusting the silicate degree or with this method are available to adjust the acidity and adding the acidity or tartaric acid. 

(2) When the soluble silicon in water sample is less than 0.5 mg/LSiO2, the silicon molybdenum blue color is very shallow, it can be extracted and concentrated with  organic solvent of n-butyl alcohol in order to strengthen the chromaticity and to be convenient for color comparison. (3)This method is only used for site control. 

2. Instrument:  The colorimetric tube(ml) with ground- stopper. 

3. Reagent:  

(1) 5% ammonium molybdate solution weight/volume). 

(2) 1% of stannous chloride solution. 

(3) 5 mol/L sulfuric acid solution; Slowly add 280mm concentrated sulfuric acid in 720ml reagent. 

(4) Silica working liquid: stock solution (0.1 mg/LSiO2), the working fluid. 

① 0.05 mg/LSiO2 working fluid; Take 0.1 mg/LSiO2 stock solution and dilute it with ultrapure water for one times. 

② 0.02 mg/LSiO2 working fluid; Take 0.1 mg/LSiO2 reserve liquid and dilute it with ultrapure water accurately to five times. 

③ 1 ug/mlSiO2 working fluid; Take 0.1 mg/LSiO2 reserve liquid and dilute it with ultrapure water accurately to 100 times. All above reagents shall be stored in plastic bottles. 

(5) n-butyl alcohol.

4. Measuring method: 

(1) When the soluble silica content in water sample is greater than 0.5 mg/L SiO2, the measuring methods are as follows. 

① Inject silicon dioxide (0.02 mg/LSiO2) 0.25, 0.5, 1.0, 1.5,...Ml in a group of colorimetric tube respectively, the demineralized water is diluted to 10 ml. 

② Inject proper amount of water into a colorimetric tube and supplement the solution with demineralized water of 10 ml. 

③ Add 0.2 ml5mol/L sulfuric acid solution to the colorimetric tubes respectively and shake them well. 

④ Add 1 ml ammonium molybdate solution to the pipettes respectively and shake them well.  

⑤After the solution has been static for 5 minutes, add  5 ml 5mol/L sulfuric acid solution with the pipettes respectively and shake them well. 

⑥ Add 2 drops of stannous chloride solution respectively and then shake the pipette again. 

⑦  After the solution has been static for 5 minutes, compare color. 

(2) When the soluble silicon in water is less than 0.5 mg/LSiO2, the measurement methods are as follows: 

① Inject silica working liquid (1 ug/ml, SiO2) 0.1, 0.2, 0.3, 0.4,...Ml, into a group of colorimetric tube respectively, dilute the liquid with ultrpure water to 10 ml. (

② Take 10 ml water sample into another colorimetric tube.  

③ Add 0.2 ml5mol/L sulfuric acid solution and 1 ml of molybdenum acid amine solution into the above colorimetric tubes respectively and shake them well.  

④ After the solution has become static for 5 minutes, add 5 ml5mol/L sulfuric acid solution respectively, shake the tubes well. 

⑤ After 1 minute, add 2 drops of stannous chloride solution respectively and shake the tubes well. 

⑥ After 5 minutes, accurately add 3 ml n-butyl alcohol,  and shake sharply the tube for 20 ~ 25 times, After the solution is static and in layered, compare the clour. 

(3) The soluble silica content (SiO2) inwater sample is calculated according to the following formula: 

For the first method, SiO2 = c.a. / V x 1000 mg/L.

For the second method:  SiO2 = C.a. / V x 1000 ug/L. 

Where: C - The working solution concentration for matching the standard color, mg/l or micrograms/l. 

a - Adding amount to the working liquid of silica standard clour with the equivalent clour as water sample, ml. 

V -  The volume of water sample, mL.