The uric acid derived from this process is carefully washed with cold water to remove all adher ing acid—a point essential to success—and is then boiled with pure plumbic peroxide. This salt is generally more expensive than the similar salt of manganese, but it works a rapid change on the acid while the effects of peroxide of manganese are very slowly manifested. When plumbic peroxide is used the boiling is conducted as follows. A measured quantity of uric acid is placed in a cylin drical vessel made of iron, open at the top, of such dimensions as to be able to hold two gallons of water for every llb. of the acid and adapted to boiling by steam. To this water is added, or a clear saturated solution of lime water, and as soon as this is boiling briskly the dark puce-coloured lead salt is applied in gradual portions as long as the boiling liquor decolorises it, but great care must be exercised that no excess of plumbic peroxide be introduced, and that it be in a state of impalpable powder and absolutely free from acid and chlorine. In the case of pure materials, 240 lb. of the lead salt will be whitened by 168 lb. of the acid, so that when the quantity of lead added approxi mates to the maximum quantity that can be bleached by the acid, future portions should be inserted with great caution, and any slight excess created must be counteracted by the introduction of just sufficient uric acid to attain that aim. The white powder produced is oxalate of lead.
The liquid is then drawn off for future treatment, and the powder is washed with clean water.
The cleaned powder is now put into a leaden vessel and boiled with hydrochloric acid diluted with its own weight of water ; 200 lb. of acid at 1179 sp. gr. being the correct proportion for every 240 lb. of peroxide of lead that have been converted into oxalate of lead. The liquid will now contain oxalic acid, and should be treated with dilute sulphuric acid, carefully and gradually applied, as long as a precipitate forms. The oxalic acid is obtained as a solid by evaporation and crystallization, while the insoluble precipitate, consisting of chloride of lead, is collected and washed to be reconverted into the peroxide.
The liquid that had been drawn off (in which the uric acid had been Lolled with peroxide of lend) contains urea and allautoin. On evaporating this liquid by means of heat until a film com mences to form on its surface, and then allowing it to cool, the major punier' of the allantoin crys tallizes out. What remains is obtained by further evaporation of the mother liquor, which finally forms a thick syrupy liquid, composed of urea. The allantoin is now introduced with any caustic alkali or alkaline earth solution into a vessel where it may be subji et...1 to ebullition, when the allantoin is decomposed in oxalic acid and ammonia, the acid uniting with the alkali while the ammonia passes over and may be recovered. If potash has been the alkali used, the oxalic acid generated may be collected as oxalate of potash ; or if a solution of baryta has been employed, oxalic acid may be recovered from the oxalate formed by decomposition with sulphuric acid.
The syrup of urea is useful for the manufacture of ammonia, or of compounds of eyanogen. Lr the former case it is boiled with milk of lime, when it decomposes into ammonia, which is caught as it peseta off, and carbonic acid, which unites with the lime. With the latter object in view, it
must be thoroughly desiccated inn water bath, and may then be mixed with coal tar, or the dry urea may be heated up to 120° in a retort. At this heat the urea di composes into ammonia, which passes into a suitable receptacle, and oyanuric acid, which remains in the retort in a solid etate. By adding the latter to fused potassium carbonate charged with carbonaceous matter, it forms potassium cyanide. Success can attend the process only if the precautions indicated be rigidly observed. To ensure the uric acid being free from foreign acid, it may be advisable to decompose the urato of soda by hydrochloric acid, and then to subject the uric acid to a steam heat until it is thoroughly dry.
But oxalic acid also exists in guano, in combination with lime and ammonia. The ammonia oxalate is extracted by the cold water with which the guano is first treated, and may be precipitated from it by any baric or calcic salt. It is, however, considered a better plan to treat the guano with a weak solution of calcium chloride in the cold, by which insoluble calcium oxalate is left with the other insoluble portions of the guano, and on being boiled with a dilute solution of sodium carbonate forme bath mate and oxalate of soda. By allowing the whole to cool before drawing off the liquid, the greater portion of tho urate of soda will be deposited, after which the solution is evaporated, the urato of soda being first deposited, and afterwards the oxalate also. The oxalate thus produced may bo clarified by washing with cold carbonate of soda and allowing it to crystallize, and the pure acid may be extracted from it by precipitating with barium sulphide and using sulphuric acid as a decomposer.
In order to reconvert the sulphate or chloride of lead to peroxide for repeated use in the manu facture, the following method has been proposed. The apparatus required will consist of an ordinary chlorine still attached to a Woulfe's apparatus, composed of at least two vessels, each of eufficient capacity to hold 20 gallons of water for every pound of chloride of lead to be treated, and provided with a rouser, or arraugement for stirring up the mass. Each vessel is charged with a milk of lime easefully prepared in the proportion of 1 of lime to 40 of water, and the chloride of lead to be operated upon in the proportion of 1 of lime to 2 of chloride. The chlorine still is now charged, and the chlorine generated passes into the first Woulfe's vessel, and is quickly absorbed by the milk of lime and chloride of lend, which should be kept from forming a sediment at the bottom of the vessel by meana of the stirring arrangement. The chlorine should be geuerated continuously until it is found to pass through tbo first vessel without further absorption, which indicates that tbo process in that vessel is completed. The contents are then removed, and their place is filled with a new charge of lime and chloride, while the chlorine gas is introduced anew, but passed first into the second Woulfe's vessel so that they are worked off alternately.