Can't craft a slime block in Minecraft?

Hi, I play vanilla 1.7.9 minecraft on Windows, and I really want to craft a slime block for no reason because they look adorable! However i can't craft one! I have 9 slimeballs and placed them all in my crafting table, but it just didn't appear in the result. I looked at minecraft.gamepedia to check if it wasn't a mod- and it isn't a mod! So how come it's not working? Did Mojang delete it?