Transparent Color Slider not Showing Up

So, Earlier in the week I made a texture for a copper sword that sometimes spawns lightning on hit, and it has this transparent electricity aura-like thing around it. Now, when I go into the texture editor, the transparency bar that I used is gone. 

Can someone help?

 Also, I can still use to color picker on the color and have it give the the transparent version, but I cannot modify it at all or the transparency goes away.