neutral, with leather glue, a compound of tannic acid and glue is formed. which coagulates on storing and becomes highly viscid. If, then, the colourless and clear top liquor be decomposed with sulphate of alumina another gummy precipitate is formed. Both precipitates are soluble in alkalies or weak ammonia, and may be obtained, dried, and powdered. If then the clear liquor be neutralised with chalk or lime, a precipitate, and clarification, ensues, and the top liquor is free from smell and has lost about 25 per cent. to 30 per cent. of the total organic constituents-and those the most easily decomposable.

Dr W. Buddeus is quoted by Messrs Griffin and Little in The Chemistry of Paper-making as follows, concerning the laboratory treatment of sulphite liquors :

"The waste liquor was neutralised by ammonia, the lime was precipitated by ammonium carbonate, and the carbonate of lime thus formed was separated by filtration. The dark brown filtrate was evaporated, and the dried residue distilled. The residue contained 7.2 per cent. ammonia as salts. Water and a yellow coloured oil were obtained in the condenser, and finally a crystalline sublimate appeared on the walls of the tube. The gases escaping were caught in the gasometer. The oil, at first, had an odour like mercaptan, but this disappeared on heating slightly. This odour was, without doubt, due to organic sulphur compounds which were present in traces. The oil and water were, after this heating, distilled with The distillate was shaken out with ether, then dried, and the ether evaporated over calcium chloride. A brown oil remained, which boiled at 130° C., and which coloured a fine chip, moistened with hydrochloric acid, a strong carmine, and which was therefore believed to be pyrrol. Pyro-catechin was also obtained in the distillate, as was proved by colour-tests with iron salts, and its reduction of Fehling's solution.

steam.

"The gases were carbon monoxide, hydrogen, marsh gas, and sulphuretted hydrogen. 400 grammes of the residue yielded 180 grammes of coke, 30 litres of gas, and 200 grammes of distillate.

"Mucic and saccharic acid could not have been present as such in the liquor, because they are formed by the oxidation of carbohydrates, and the action of the liquor is a reducing one. Pyrrol is formed by the distillation of ammonium salts of these two acids. The only way of accounting for the pyrrol is the presence of succinic acid, which is very probably present, owing to the occurrence of resins in wood. Ammonium succinate changes readily by splitting off of water into ammonia succinamide, which by heating with reducing agents gives pyrrol.

"The presence of pyro-catechin is due to that of dioxybenzoic acid (1, 3, 4), which is in the liquor as dipyrocatechuic acid. The decomposition of this by distillation with ammonia is a source of tannic acid and Papier Zeitung, March 1891.

*

pyro-catechin. There is, according to Dr Buddeus, no tannic acid present in the liquor, which will give a blue-black colour with ferric chloride, because the tannin in wood is reduced by digesting with sulphurous acid.

"The reduction is probably due to dipyrocatechuic acid, but by treating with ammonia and distilling, tannic acid is eventually formed. Sulphites are oxidised to sulphates when the tannin is reduced. It may be, therefore, that the difficulty of pulping wood rich in tannin by the sulphite process is due to the action of the tannin, which renders the sulphurous acid ineffective."

F. B. Ahrens, E. Klingenstein, and P. Schubert* state that many German wood pulp mills have been compelled to close because it was found impossible to comply with the requirements of rivers pollution officials. Concerning the examination of a sample of waste sulphite liquors they state it was of a strongly acid reaction, specific gravity 1.0465, and optically inactive. The dry residue was 9.4 per cent., whereof 1·11 per cent. was ash and 8.29 per cent. organic matter-not strictly accurate determinations.

The liquors were, on coming from the digesters, nearly neutralised with lime and afterwards completely neutralised by passing over limestone. The hot lye was mixed with a known quantity of fresh lime water once boiled, filtered, and the filtrate neutralised with carbonic acid gas as mentioned before.

The liquors were then taken cold and the following results obtained :

*Zeitschr. f. angew. Chemie, 1895, page 41.

† Organic matter rendered soluble again by boiling.

:

Aluminate of soda was then tried as a precipitant, but the results were less satisfactory, and no special osmotic action was discovered on investigation.

The precipitated and neutralised liquors were then treated electrically. A current of 5 ampères and only sufficient potential was passed through the liquid from platinum electrodes, but no diminution in either mineral or organic matter was observed after 120 minutes. A high tension current was then tried, 106 volts, but the results were equally ineffective after a trial of the same duration.

It is evident, therefore, that the objectionable organic matters, if recoverable at all, call for some process hitherto undiscovered.

The author tried, unsuccessfully, treating this waste bacterially after neutralisation on the lines of his patent. It was found absolutely sterile to begin with, and the amount of bacterial filtration required for its decomposition was altogether impracticable.

A. G. Brookes (Patent Specification 8088, 1901) suggests the following

treatment:

Evaporation until only 20 per cent. of water is present.

The sulphur compounds are then said to be decomposed, yielding sulphurous acid and volatile compounds of sulphur, which are recovered.

Organic substances such as carbohydrates and albuminoids are then added to prevent the formation of a skin, and the dry residue is used as a fuel, pitch, glue, resin, or size.

CHAPTER IX.

GENERAL CHEMICAL TRADES.

Distillation of Ammoniacal Liquors.

THE gas liquor fresh from the works 'scrubbers' contains:

in addition to the constituents of the water supplied for scrubbing purposes and variable tarry or oily substances. On adding a considerable quantity of lime to the liquor, and heating, the ammonia is displaced by it, and the acids of the above salts are left combined with the lime base.

As the residual liquor leaves the stills it is generally a thick brown liquid, supersaturated, at atmospheric temperatures, with lime or lime salts, covered with an oily film, and containing much lime in suspension.

Its objectionable constituents are the tarry matters, ferrocyanides, sulphides, suspended lime, and the free lime in solution.

A sample after settlement and filtration through sand filters contained the following:

Ferrocyanides, ferricyanides, and sulphocyanides were also present. It is evident, therefore, that simple settlement and filtration is insufficient. The first important step is, of course, the settlement of the suspended lime, and this is easily accomplished by means of ordinary precipitation tanks.

The free lime might also be neutralised and eliminated in the same tanks by means of precipitants such as copperas, aluminium sulphate, etc., but the quantity of lime present is so great that the copperas required for neutralisation is enormous and the sludge in proportion.

Dr Lunge, in his "Coal Tar and Ammonia,"* describes the purification plant in use at the workmen's colonies in connection with Messrs Krupps' works, Essen, from particulars supplied by Dr Solomon, the chemist there. The clarifying plant is shown in fig. 105.

"The liquid first runs into the catchpool A, where the heavier substances suspended in the water and those floating on the top are retained. From there it flows into one or other of the feeding-vessels, B B; two of these are provided, so that one may be always in operation. They contain a small over-shot waterwheel, the prolonged axle of which carries on either side a cross with baling-buckets and a stirrer for each of the tanks, separately holding milk of lime and solution of copperas. This water-wheel is turned by the inflowing waste liquor itself, and will, of course, turn more or less

* "Coal Tar and Ammonia," by George Lunge, Ph.D., Professor of Technical Chemistry in the Federal Polytechnicum, Zurich. London: Gurney & Jackson.