In 1850-51, Mr. Spence made about 20 tons of alum per week. The quantity now made by him amounts to 110 tons, of which 70 tons are produced in this district. Fully half of the total quantity manufactured in England (300 tons per week) is made by his process.

XIV. PROTOSULPHATE OF IRON.

This salt is manufactured in large quantities in this district, principally for the use of dyers, the amount being about 80 tons per week. The process of manufacture pursued here is as follows:-Iron pyrites, derived from the coalmeasures, and commonly called here coal brasses, is piled up in heaps, watered and exposed to the atmosphere. A process of slow oxidation takes place. Sulphate of iron with an excess of sulphuric acid is formed. The latter is removed by means of scrap iron. The salt is obtained by evaporation of the liquor, and is tolerably pure. An inferior quality is procured from the mother-liquor, which contains alumina.

XV. COMPOUNDS OF TIN.

Chlorides of Tin.-The quantity of these compounds (estimated as crystallized protochloride of tin) manufactured in this district amounts to about 16 tons per week.

Stannate of Soda.-This compound has for some time been extensively used for the purpose of preparing calicoes which are intended to be printed with so-called steam colours. It is usually obtained by fusing metallic tin or finely powdered tin ore with nitrate of soda. It has been found that the addition of 5 per cent. of arseniate of soda causes a saving in tin, by rendering, as it seems, the oxide of tin less soluble in the sulphuric acid, through which the goods are subsequently passed.

Stannate of soda is also prepared from scrap tin by Mr. Higgin's process. Various attempts, with more or less success, have been made at various times to separate the tin and the iron of scrap tin, or waste tinned iron, and so utilize the former metal. Mr. Higgin acts on the scrap with a mixture of muriatic acid and a little nitrate of soda. When muriatic acid is used alone, the iron dissolves more rapidly than the tin, but when nitrate of soda is added, the tin is acted on in preference. The whole of the nitrate of soda disappears, and the resulting products are bichloride of tin, chloride of ammonium, and chloride of sodium, in accordance with the following equation:

6

4

4 Sn +10 Cl H + Na NO,=4 Sn Cl2+NH, Cl + Na Cl +6 HO. The bichloride of tin is then converted, by the excess of tin present, into protochloride. A little iron dissolves at the same time and is separated by means of chalk, which precipitates the protoxide of tin, leaving the iron in solution. The former is then converted, by fusion with nitrate of soda and caustic soda, into stannate of soda, with evolution of ammonia. The iron stripped of the tin is employed for the precipitation of copper.

XVI. COPPER Ores.

Mr. William Henderson has introduced into this district a mode of dealing with very weak copper ores, which has been found extremely successful at Alderley, where the sandstone contains only 14 per cent. of copper, in the form of carbonate and arseniate. The sand containing the copper is put into wooden vats with muriatic acid, and fresh sand added until the amount of copper is sufficient for saturation. The solution is then drawn off, and the copper precipitated by waste or scrap iron. In this way ores otherwise useless have become valuable.

Another mode of attaining this object, and one in many cases to be preferred, is by using sulphuric acid and boiling down the solution of sulphate of copper so as to obtain crystals, or still further, viz. to dryness. This is then heated in a furnace having a plate, or floor, of brickwork or tiles, the fire being applied beneath, and not passing over the salt of copper: the sulphate is decomposed, and sulphuric acid passes off. But the decomposition is more effectual when carbon is added; in this way sulphurous acid is driven off, and it is then led into a chamber, and being treated with nitrous fumes in the usual way, sulphuric acid is formed, which is again used for the solution of the copper in the ore. If the ore contains suboxide of copper, it is previously roasted for oxidation. Phosphates, arseniates, carbonates, and oxides may be treated by this process.

For sulphides of copper Mr. Henderson roasts with common salt, having previously reduced the ore to fine powder. The chloride of copper is volatilized and condensed in a Gossage coke tower. The sulphate of soda remaining may be washed out of the non-volatile portion, and the copper precipitated from the solution flowing from the tower. He separates by this means the metals whose chlorides have a different rate of volatilization: chlorides such as chloride of silver are obtained in the flue close to the fur

nace.

We do not allude to the other inventions contained in Mr. Henderson's patents, as we are not aware of any being in use in this district.

XVII. NITRIC ACID.

About 48 tons of nitrate of soda per week are used in this district for making nitric acid. The salt yields its own weight of acid of sp. gr. 1·40. Nitric acid is used here for making the nitrates of copper, lead, alumina, and iron, for oxidizing tin, for etching, and also for making aniline from benzole.

XVIII. OXALIC ACID.

One of the most important and most interesting of the new manufacturing processes which we have to describe in this Report is one for the preparation of oxalic acid, invented and patented by Messrs. Roberts, Dale and Co., gentlemen to whom we owe a number of highly ingenious and useful practical processes. The method of preparing oxalic acid hitherto employed consists, as is well known, in acting on organic substances, such as sugar or starch, with nitric acid. This process has now been superseded by that of Messrs. Roberts, Dale and Co., which depends on the action exerted by caustic alkalies on various organic substances at a high temperature. That oxalic acid is one of the products formed by this action is a fact well known to chemists, but one that has not until recently been turned to any practical use. In the year 1829, Gay-Lussac published a short memoir*, in which he announced that he had succeeded in obtaining oxalic acid by heating cotton, sawdust, sugar, starch, gum, tartaric acid, and other organic acids with caustic potash in a platinum crucible. Since that time the subject has not been attended to either by scientific chemists or by practical men, so far as we know. Messrs. Roberts, Dale and Co. are, we believe, the first persons who have succeeded in carrying out the process in practice on a large scale. In their attempt to do so they were met by a number of serious obstacles, chiefly of a practical nature. These, however, they have, by dint of uncommon ingenuity, and by the application of an amount of perseverance of which, perhaps, but few men are capable, succeeded in

* Annales de Chim. et de Phys. t. xli. p. 398.

overcoming, and the process is now in full and successful operation at their works at Warrington. With a most praiseworthy liberality, these gentlemen have furnished us with full particulars regarding their process. They have also allowed us to see it in operation, and we are therefore able to lay before the Section all the details necessary for becoming acquainted with its principal features.

The only practical suggestion contained in Gay-Lussac's memoir, consists in his proposal to convert cream of tartar by this method into oxalate of potash. At that time tartaric acid was cheaper than oxalic acid, and the suggestion might therefore, under the circumstances of the time, have proved of some practical value. It was evident, however, that for the purpose of ensuring success a cheaper material had to be chosen. Messrs. Roberts, Dale and Co. found woody fibre in the shape of sawdust to answer perfectly. GayLussac states, as the result of his experiments, that potash may be replaced by caustic soda. Mr. Dale found, however, that woody fibre produces hardly any oxalic acid with caustic soda. On the other hand, when potash is used alone, the process is not remunerative. This difficulty was overcome by employing a mixture of soda and potash, in the proportion of two equivalents of the former to one of the latter, which produces the desired effect quite as well as potash alone. In what manner the soda acts in this case can only be conjectured whether in conjunction with the potash it takes the place of the latter, or whether it merely promotes the fusibility of the mixture, is merely a matter for speculation. The solution of the mixed alkalies having been evaporated to about 1.35 sp. gr., sawdust is introduced, so as to form a thick paste. This paste is then placed on iron plates in thin layers and gradually heated, the mass being kept constantly stirred. During the heating-process, water is in the first instance given off. The mass then swells up and disengages a quantity of inflammable gas, consisting of hydrogen and carburetted hydrogen. A peculiar aromatic odour is at the same time evolved. After the temperature has been maintained at 400° Fahr. for one or two hours, this part of the process may be considered as complete. The whole of the woody fibre is now decomposed, and the mass, which has a darkbrown colour, is entirely soluble in water. It contains, however, only from 1-4 per cent. of oxalic acid, and about 0.5 per cent. of formic, but no acetic acid. What the nature of the principal product intermediate between the woody fibre and the oxalic acid is has not yet been determined; it seems well worthy of further investigation. The mass is now exposed still longer to the same temperature, care being taken to avoid any charring, which would cause a loss of oxalic acid. When perfectly dry, it contains the maximum quantity of oxalic acid, viz. from 28-30 per cent. (C2 O2+3 HO), but still no acetic acid, and very little more formic acid than before. The absence of acetic acid is surprising, as it is generally supposed to be an essential product of this process of decomposition. It is possible that the acetates may be converted into oxalates as they are formed; but, on the other hand Gay-Lussac states that acetates when heated with caustic alkalies yield chiefly carbonates, and but a trifling proportion of oxalates-a conclusion to which Mr. Dale has also been led from direct experiments with acetates*.

2

The product of the heating-process, which is a grey powder, is in the next place treated with water heated to about 60° Fahr. In this the whole dissolves, with the exception of the oxalate of soda which is either contained in it, or is formed by double decomposition on the addition of water, and which, on account of its slight degree of solubility, falls to the bottom. The use of the

It may be mentioned that the process of decomposition takes place equally well in close vessels. It must therefore be accompanied by a decomposition of water.

soda in this part of the process is sufficiently apparent. The supernatant liquid is drawn off and evaporated to dryness, and the residual mass is heated in furnaces in order to destroy the organic matter and recover the alkalies which it contains, and which are employed again after being causticized for acting on fresh sawdust. In consequence of the elimination of soda, the relative proportion of the two alkalies recovered from the liquor is, of course, different to what it was at the commencement; and before being used again the quantity of each alkali contained in the mixture must be ascertained.

The oxalate of soda, after being washed, is decomposed by boiling with hydrate of lime. Oxalate of lime falls to the bottom, and caustic soda passes into solution, and may be employed again for any purpose to which it is applicable. The resulting oxalate of lime is decomposed by means of sulphuric acid, the proportions employed being three equivalents of acid to one of the oxalate; and the liquor decanted from the sulphate of lime is evaporated to crystallization in leaden vessels. The crystals of oxalic acid, which are slightly coloured by organic matter, are purified by recrystallization.

From about 2 lbs. of sawdust 1 lb. of crystallized oxalic acid may be obtained. There is no loss of oxalic acid. The only loss experienced is in alkalies. The quantity of acid at present manufactured by Messrs. Roberts, Dale and Co. amounts to 9 tons per week; and their works are capable of being extended so as to produce 15 tons, which is supposed to be the total quantity consumed throughout the world. Their plant is extensive and costly, and bears evidence of an uncommon spirit of enterprise on the part of the proprietors.

In order to give an idea of the effect which the introduction of this process has had on the market, it may be mentioned that the selling price of the aeid at this time is 8d. to 9d. per lb., whereas in 1851 it was 15d. to 16d. per lb.

Oxalic acid is used extensively in calico-printing, woollen-dyeing, woollenprinting, silk-dyeing with wood colours, in straw-bleaching, and for making binoxalate of potash, the so-called "salt of lemons."

XIX. PYROLIGNEOUS ACID.

The only improvement introduced into the manufacture of this acid during the last few years consists in the use of sawdust instead of wood in the process of destructive distillation. The sawdust is introduced into the front of the retort through a hopper, and is gradually moved to the other end by means of an endless screw, worked by machinery. During its transit it becomes completely carbonized, the gaseous and liquid products escape through a pipe, while the charcoal is allowed to fall into a vessel of water. The latter precaution is necessary, since the carbon is obtained in such a minute state of division that no cooling in the air or in closed vessels would be sufficient to stop the combustion. In other respects the process does not differ essentially from that with wood. No more acid is obtained than with wood, and less naphtha. The quantity of the former varies, however, with the temperature employed. The usual temperature is that of a dull red heat. From 1 ton of sawdust 100-120 gallons of liquid, containing 4 per cent. of glacial acid and 15 gallons of tar, are obtained, and 100 parts of the crude distillate yield 3 of naphtha. The advantage consists in the cheapness of the material employed; but, on the other hand, one of the resulting products, viz. the finely divided charcoal, is comparatively worthless.

This invention forms the subject of Mr. Halliday's patent, which was taken out in the year 1848-49. Quite recently Mr. Bowers has patented another

plan, which consists in passing the sawdust into the retorts by means of an inclined plane, and a series of scrapers.

Quantity of acid manufactured weekly in Manchester:-12,000 gallons, containing about 4 per cent. of glacial acid.

The value of the acid is £3 per ton, whilst that of the tar is from £4 to £4 10s.

The quantities of red liquor (acetate of alumina) and iron liquor (protacetate of iron) made may be stated here, as they are always made by means of pyroligneous acid, and generally by the same parties who manufacture the acid. Red liquor, 12,000 gallons. Iron liquor, 6000 gallons.

XX. STARCH AND ARTIFICIAL GUMS.

About 20 tons of starch and 34 tons of gum-substitutes, made by roasting farina and other kinds of starch, are produced in this district per week. No change has taken place in the process of manufacturing starch from flour. The old process of fermentation is still adhered to.

XXI. PURIFICATION OF RESIN.

Several very interesting and successful processes have lately been patented by Messrs. Hunt and Pochin of Salford, for the purification of resin. The aim of these gentlemen, who have devoted a large amount of time and attention to this subject, is to produce a bright, nearly colourless, solid and brittle resin from the common dark and impure commercial article. This end they attain by distilling the resin in an atmosphere of steam at about 10 lbs. pressure. The several resinous acids which on distillation by themselves split up into gaseous products and volatile oils of very variable composition, are mechanically carried over, it would appear, in presence of steam, as is well known to be the case with stearic and the other higher fatty acids; and a solid product, which cannot be distinguished from the finest resin, is obtained from a very impure material. In their patent of 1858, Messrs. Hunt and Pochin specify the formation of three distinct solid products during different stages of the process; these they distinguish as a, ß, and y resin. These three several substances present the characteristics of resins, but clarified and to a great extent deprived of colour. They are either separately or in combination applicable to and useful in the manufacture of several important articles, such as soap, size, candles, paper-size, varnish, and japan; and they may be used for distilling to produce resin-oils.

About 60 tons per week of this purified resin are now manufactured in this district under this patent.

XXII. ORGANIC COLOURING-Matters.

There are few substances of more importance to the manufacturers of this district than those which are employed in imparting colour to the various fabrics, especially those of cotton, produced here. Of these substances the majority are derived from the animal or vegetable kingdom. Indeed, with the exception of oxide of iron and chromate of lead, very few mineral substances are at the present time made use of alone by the dyer or printer. The greater intensity, beauty, and variety of the dyes which are wholly or in part composed of organic matters causes them to be preferred; and the increase of skill and knowledge of scientific principles on the part of dyers and printers has also led to their more exclusive employment. When it is stated that the quantity of dye-woods (logwood, peachwood, sapanwood, barwood, fustic, quercitron bark) consumed weekly by the dyers of this