Although in these sulphide processes a strongly reducing agent is present, its effect in preventing oxidation is more than outweighed by the weakening of the hydrolytic action of the soda, both directly by its combination with sulphur, and indirectly by the complication which it induces by combination with the soluble bye-products. Further, as regards the final product, they offer no advantage over the caustic alkali processes. There is, however, a considerable advantage in point of economy, which should lead to their adoption in districts where the production of malodorous gases is permitted. {69} Acid Processes.—We now come to consider the processes which are based upon the hydrolytic action of acids as a primary condition. We have seen that in the water process this condition obtains as a secondary result, and that while it aids in resolving the wood, it also determines the limit of the action, in consequence of its promoting secondary combination amongst the soluble products. The use of powerful oxidising acids, such as nitric and nitro-hydrochloric, induces an action which is sufficiently drastic to cause a complete resolution of the non-cellulose constituents of the wood with the formation of soluble products. The use of these acids has been made the subject of numerous patents. The process of Barre and Blondel consisted in digesting the wood in the cold for twenty-four hours in 50 per cent. nitric acid, by which it was converted into a soft fibrous mass. This was boiled for some hours in water, afterwards in a solution of sodium carbonate, and finally bleached in the ordinary way. Many other patents have been taken out in this direction, but none have met with practical success, owing doubtless, to the high cost of nitric acid, and the difficulty of recovery. A process has lately been patented by Young and Pettigrew (No. 14,988, 1884) in which they claim the use of either nitric or nitrous acids; the acid fumes which are evolved being condensed and reconverted into nitric acid. The process has not yet, however, been tried on a practical scale. The resolution of wood by the hydrolytic action of non-oxidising acids, is for reasons already stated, very imperfect. An important feature, however, of this action is the production of glucose as a bye-product, and a process having the double object of producing this, together with a brown pulp, was patented by Bachet and Machard in 1864, and worked for some time in Switzerland. The process consisted in boiling the wood for twelve hours in dilute hydrochloric acid; the solution, which contained glucose to the amount of 20 per cent. of the weight of the wood, was drawn off, neutralised with chalk, and fermented by the addition of {70} yeast. Alcohol was separated from the fermented liquor in the usual way. The residual pulp, after being ground with stones, was made into coarse packing paper. The process failed commercially.