In the context of washing powders, both sodium sulphate and sodium silicate serve specific roles. Sodium sulphate is used as a filler in the detergent, its primary function being to keep the washing powder dry by absorbing moisture. This helps in the preservation of the detergent and prevents it from clumping together, making statement 1 correct.

On the other hand, sodium silicate serves to maintain the alkalinity of the washing powder. A higher level of alkalinity helps the detergent in breaking down the oils and dirt on the clothes, thereby improving the washing performance. This makes statement 2 also correct.

Thus, both statements 1 and 2 accurately describe the role of these two substances in washing powder, making option 3, "Both 1 and 2", the correct answer.