In order for it to prevail herein it must have established at the hearing on said pleas of privilege that said instruments, in themselves, constituted a binding written contract wherein appellee, W. R. Armitage, was obligated to ship the maximum amount of lumber specified in said offer to appellant, at Houston, Texas, and that appellant was bound thereby to purchase that amount of lumber at the prices therein stated. Camp v. Screen Broadcasts Inc., Tex.Civ.App. 118 S.W.2d 398; Lopez v. Cantu, Tex.Civ.App. 130 S.W.2d 345; Quinn v. Johnston, Tex.Civ.App. 122 S.W.2d 266. Subdivision 5 of Article 1995, Vernon's Ann.Civ.Stat., provides: