Colorimetry method is based on the color reaction to form colored compound, it is measured by comparing the colored substance solution or color depth to determine the content of the component. Colorimetry is an analysis of the color reaction of the basic requirements: the reaction should have a high sensitivity and selectivity, consisting of colored compound produced by the reaction that is constant and stable, it is the larger color difference and color agents. Selecting the appropriate color reaction and controlling the appropriate reaction conditions, which is the key to colorimetry analysis.

There are two commonly colorimetry: visual colorimetry and photoelectric colorimetry, visual colorimetry method is a commonly standard method, which uses different amounts of analyte standard solution in the exact same set of colorimetry tube. The sample solution is also the color under identical conditions, and the standard color gamut is visually identified, the amount of the standard solution can be contained, calculating and determining the content of the sample analytes.

The high levels of tungsten trioxide is determined generally by the use of photoelectric colorimetry, according to the situation of tungsten concentrate, which is based on selecting the visual colorimetry, and acidity, potassium thiocyanate, etc. The test of amount of titanium trichloride conditions is that weighing accurately 0.500 g sample of 2 g of sodium hydroxide flux of iron crucible, placing in a muffle furnace, the temperature is gradually raised to 85 ℃, heating it 25 to 30 minutes, removing to a pre-melted into a 300 ml beaker , heating the water to about 100 ml, which is immediately placed on a hot plate 2 a boil for 5 minutes, removing ,cooling, and washing out the iron orange vortex. The solution can be transferred into a 250-mL volumetric flask diluting the mark.

Hydrothermal method is the scope of liquid chemical method. It means in chemical reaction, a sealed pressure vessel with water as a solvent, carried out at high temperature and pressure conditions. Hydrothermal reaction depends on the type of reaction that can be divided into hydrothermal oxidation, water and heat reduction, hydrothermal precipitation, hydrothermal synthesis, water hot solution, hydrothermal crystallization. So the hydrothermal method is the most popular method in crystallization.

Experimental Procedure
The polished clean tungsten sheet was placed in distilled water and ultrasonic cleaning in ethanol were 10min, after drying and controlling the temperature in a muffle furnace at 450 ℃, the tungsten trioxide layer is formed in the calcinations of 30min. Hydrothermal reaction solution of polyethylene glycol (300) 10% is prepared by volume of 0.02mol / L sodium tungstate solution, the solution was adjusted pH2.0 with 3mol / L hydrochloric acid. 25ml of the solution is placed in the Teflon reactor and the tungsten sheet vertically was placed in a pre-oxidized, the reaction temperature is controlled at 180 ℃ 6h. The reaction product was removed with distilled water soak about 10min, and repeating it three times to remove the product surface residue, and then the preparation of tungsten trioxide photoanode is completed after drying calcining at 550 ℃ 180min.

Conclusions
1. Hydrothermal preparation method can generate highly ordered nano-strip structure of tungsten surface, it can reach 1.5V 1.8mA / cm2in the photoanode of current;
2. a curve is made from oxidation of the tungsten film, corresponding to WO₃ cubic phase in the oxidation process of 450 ℃ , the oxide layer will be formed on the surface of the tungsten sheet;
3. b curve is hydrothermal reaction product that is not calcined WO₃, corresponding to the orthorhombic WO₃;
4. c curve is the calcined WO₃, corresponding to the monoclinic WO₃, which shows three distinct peaks, the highest peak meter bar is vertically grown on the substrate, the height can reach 6.91 microns, which in shows excellent orientation role of tungsten oxide layer of the substrate with polyethylene glycol in the hydrothermal reaction of crystal growth.