To make pulp from wood, a chemical pulping process separates lignin from cellulose fibres. The kraft process is the dominant chemical pulping method, with the sulfite process second. Acidic pulping processes shorten the cellulose chains. With almost twice the yield as chemical pulping, mechanical pulps is often cheaper. The main byproducts of kraft pulping are crude sulfate turpentine and tall oil soap. These fibers are two orders of magnitude thinner than cellulose fibers produced by pulping wood. Methanethiol (MeSH) is released as a by-product of kraft pulping in pulp mills. The pulping liquor is easily recovered by distillation. Another example of evaporation is in the recovery of sodium hydroxide in kraft pulping. The kraft pulping reaction in particular releases foul-smelling compounds. Spruces are commonly used in mechanical pulping as they are easily bleached. Caustic soda is added to increase the pH in the pulping process of fibers. Historically soda pulping was the first successful chemical pulping method. This could have major environmental benefits in reducing the pollution associated with chemical pulping. No pages were fabricated using the pulping method (from either rags or wood).