What is a common method used in boiler water treatment?

The correct answer focuses on the practice of adding sodium hydroxide and sodium phosphate in boiler water treatment. This method is commonly employed to maintain proper pH levels and prevent corrosion within the boiler system.

Sodium hydroxide is used to elevate the water's pH, making it alkaline, which helps to prevent corrosion of the boiler materials. An alkaline environment is conducive to reducing the solubility of iron and other metal oxides that can lead to corrosion. Sodium phosphate, on the other hand, serves multiple purposes: it aids in controlling the formation of scale and assists in maintaining the proper chemical balance in the boiler water.

In contrast, the other options provided do not effectively address the complexities of boiler water treatment. Some methods, such as using distilled water exclusively, may not contain the necessary chemical additives to control pH or manage scaling properly. Regularly introducing chlorine is more associated with cooling water treatment to manage microbial growth rather than with boiler systems. Finally, the mention of "Parkinson's solution" does not have a recognized application in standard boiler water treatment practices, making it less relevant in this context.

Thus, the practice of adding sodium hydroxide and sodium phosphate stands out as a foundational method for ensuring the longevity and efficient operation of boiler systems