Which of the following method is not employed for the purification of colloids ?

Options

A. Electrodialysis
B. Dialysis
C. Ultracentrifugation
D. Peptisation

Answer

To determine which method is not employed for the purification of colloids, we need to analyze the given options and understand the processes involved in colloid purification.

### Step-by-Step Solution:

1. **Understanding Colloids**:
- Colloids are mixtures where tiny particles of one substance are dispersed in another substance. They are heterogeneous mixtures, meaning they do not have a uniform composition.

2. **Identifying Impurities**:
- A colloidal solution is considered impure if it contains unwanted particles or excess electrolytes. Purification methods aim to remove these impurities.

3. **Common Purification Methods**:
- **Dialysis**: This method uses a semi-permeable membrane to separate small impurities from the colloidal particles. The impurities pass through the membrane while the larger colloidal particles remain.
- **Electrodialysis**: Similar to dialysis, but it uses an electric field to enhance the movement of ions and impurities through the membrane.
- **Ultrafiltration**: This technique uses a filter with very small pores to separate colloidal particles from smaller impurities.

4. **Analyzing the Given Methods**:
- The methods mentioned above (dialysis, electrodialysis, and ultrafiltration) are all valid techniques for purifying colloids.
- However, one of the options is **peptization**.

5. **Understanding Peptization**:
- Peptization is the process of converting a precipitate into a colloidal solution by shaking it with a dispersion medium and often involves adding an electrolyte.
- This process does not purify the colloid; instead, it creates a colloidal solution from a solid precipitate.

6. **Conclusion**:
- Since peptization is not a method for purifying colloids but rather a method for forming colloids from precipitates, it is the correct answer to the question.

### Final Answer:
The method that is not employed for the purification of colloids is **peptization**.