Obtaining a Winsor Type III microemulsion of SDS (sodium dodecyl sulfate), water, and crude oil by changing salinity involves carefully adjusting the composition and conditions to reach the desired phase behavior. Here's a general approach:

1. **Components:** Prepare the following components:

- SDS solution: Prepare a solution of SDS in water at a specific concentration.

- Crude oil: Use the crude oil you intend to use for the microemulsion.

- Saline solutions: Prepare different saline solutions at varying concentrations. You'll need solutions with higher and lower salinities than the SDS solution.

2. **Phase Behavior Screening:**

- Mix the SDS solution and the crude oil at a specific volume ratio. This will create an initial mixture.

- Gradually add small amounts of the low-salinity solution to the mixture and observe changes in the appearance (transparency) of the mixture.

- Continue to add more of the low-salinity solution until you start to see the formation of a clear Winsor Type III microemulsion phase. This phase is characterized by the formation of a transparent middle layer between the oil and water phases.

3. **Salinity Adjustment:**

- If the microemulsion forms with a low-salinity solution, you can further adjust the salinity by adding more of the high-salinity solution incrementally.

- Continue to add high-salinity solution while monitoring the microemulsion formation. Adjust until you achieve the desired phase behavior.

4. **Characterization:**

- Once you've achieved the Winsor Type III microemulsion phase, you should characterize its properties. This may involve determining the size and morphology of the microemulsion droplets using techniques like dynamic light scattering (DLS) or microscopy.

Remember that the exact composition and conditions required to achieve the Winsor Type III microemulsion can vary depending on the specific properties of the crude oil, the surfactant (SDS), and the salinity solutions used. The process may require experimentation to find the optimal conditions for microemulsion formation. Additionally, the thermodynamic stability of the microemulsion should be considered for long-term storage or use.

Always ensure safety precautions are followed when working with chemicals, and consult literature or experts in the field for guidance specific to your crude oil and surfactant system.