A compound, chemical formula Na2S, that is the primary ingredient in the sulfate process of chemical pulping in papermaking. The advantages of sodium sulfide pulping (yet to be named the "sulfide process," perhaps because of its phonetic similarity to the sulfite process) include a stronger pulp (the alternate name for the sulfate process, the kraft process, means "strength" in German and Swedish), the ability to effectively pulp nearly every species of tree, and its adaptability to efficient and cost-effective chemical-recovery systems. (See also Chemical Pulping.)