In 1872, Dale patented a process for using woody fibre, from which nearly all the impure matters had previously been removed, leaving only the pure cellulose, instead of employing the uncleaned fibre as is commonly done, and he claims to obtain very great advantage by this plan. The method of obtaining the pure woody fibre, or celluloae, with the view of aubsequently using them in the manufacture of soda and potaah oxalates, that receives most favour with the patentee, conaists in submitting the sawdust to the influence of an aqueoua solution of caustic alkali at a high temperature, either in the open air or under preasure. By this means the impuritiea are removed from the sawdust, and a product is obtained, which yielda, on treatment with a mixed aolution of caustic soda and caustic potash, in the proportions of about two parta of the former to one of the latter, a crude soda oxalate containing a much greater percentage of oxalic acid than that prepared by the ordinary methoda in use. If it be desirable to produce potash oxalate, then caustic potash alone must be used instead of the mixture of the two caustic alkalies.
It is hardly necessary to repeat that when oxalic acid is manufactured by the action of caustic alkalies on woody fibre, the renewed alkalies need to be subjected to a high temperature in a furnace, in order to render them again fit for use. The patentee finds, that before burniug these recovered alkalies they are eminently suited for treating the aawdust as described above, and thua a special advantage is derived from the use of these recovered alkalies before they are calcined.
5. From ,Vadden—A natural consequence of the conversion of madder into garancine, ia that the oxalate of lime present in the madder is decomposed by the sulphuric acid. The thus liberated oxalic acid is commonly lost in the wash liquors ; but Pernod conducts these watera into auitably constructed tanks, where they are saturated with lime hydrate, which causes the formation of a large precipitate of oxalate of lime. This salt is collected and decomposed by the aid of sulphuric
acid added carefully, and in quantity juat sufficient for the perfect combination of the mineral acid with the lime. The sulphate of lime deposit is separated by filtration through flannel, and the aolution of oxalic acid is evaporated in leaden pans, re-crystallized, and is then fit for the market. The quantity of acid thus obtained will vary somewhat, in accordance with the quality and kind of madder employed, and it ia also worthy of remark, that the Avignon madder used by Pernod, naturally contains a large proportion of lime, a baae which greatly influences the formation of acida —and especially oxalic planta generally.
6. Other Sourees.—Many other methods of preparing oxalic acid on an industrial scale have been proposed and patented, but, owing to the cheapness of sugar, and the excellence of the new method introduced by Messrs. Roberts, Dale, and Company, it is not probable that they will ever become of commercial value. Of theae, the beat is, perhaps, a method patented some years ago by Jullion, of converting formic acid into oxalic acid. It has also been ascertained that when a mixture of sesquichloride of carbon and pulverized hydrate of potash-8 equivalents of the former to 1 of the latter—is heated for some daya in an oil-batb of 210° (410° F.), the result is a mixture of oxalate and chloride of potaasium. And also that when 1 equivalent of protochloride of carbon is heated for SOMEi time to 200° (392° F.) with at least 6 equivalents of pulverized hydrate of potash, oxalate of potash is again formed, with evolutions of hydrogen gas.