When we derive the equation for capillary rise we condsider only the surface tension(cohesive) pulling the miniscus up,but why do neglect the adhesive forces acting on the miniscus?

In any liquid, intermolecular forces cause the liquid molecules to be attracted to each other. These forces that pull liquid molecules towards each other are known as "cohesive" forces. In the body of a liquid, a molecule is surrounded by other molecules in all directions, so the attractive forces cancel and the molecule feels no overall force . On the surface of the liquid/air interface, however, a molecule of the liquid feels the attractive forces of the other molecules from within the liquid, but none from the outside. This causes the outer layer of the liquid to act like a stretched membrane and minimize the surface area. We call this elastic membrane-like behavior surface tension.
[Two images: (left) Side-view photo of a meniscus in a graduated burette of colored water. (right) A sketch mimics the photo to show the concave curve of a meniscus and identify its contact angle as θ.]
The adhesive forces between the water and the glass cause water molecules to cling to the glass walls and create the well-known shape of the meniscus.

Besides cohesive forces, "adhesive" forces also exist; they cause water molecules to try to "stick," or "adhere,” to solid surfaces. The most common example of the effect of adhesive forces is the meniscus that is commonly seen when using graduated cylinders. The water molecules respond to an attractive "adhesive" force pulling them towards the glass walls. Near the walls of the cylinder, the adhesive force pulling the water towards the glass walls is stronger than the cohesive force pulling the water molecules together. This attractive force pulls the water up the sides of the glass tube against the downwards pull of gravity
[Two images: (left) Photo shows a vial of mercury with an inverted (convex) meniscus. (right) A sketch mimics the photo to show the convex curve and identify its contact angle as θ.