arrangement thus recalls that of a buttercup, a resemblance which extends to the fruit, which is a head of achenes or follicles. The flowers contain honey, and attract flies, short-lipped bees or other small insects by the agency of which pollination is effected. The fruit of Butomus is of interest in having the seeds borne over the inner face of the wall of the leathery pod (follicle). Damasonium derives its popular name, star-fruit, from the fruits spreading when ripe in the form of a star. It is a western FIG. 2.-Water Plantain (Alisma Plantago). Plant about 3 ft. high. I, Flower; 2, same in vertical section; 3, horizontal plan of flower; 4, mature fruit. Mediterranean plant which spreads to the south of England, where it is sometimes found in gravelly ditches and pools. The order contains about fifty species in fourteen genera, and is widely distributed in temperate and warm zones. Alisma Plantago (fig. 2), a common plant in Britain (except in the north) in ditches and edges of streams, is widely distributed in the north temperate zone, and is found in the Himalayas, on the mountains of tropical Africa and in Australia. ALISON, ARCHIBALD (1757-1839), Scottish author, son of Patrick Alison, provost of Edinburgh, was born on the 13th of November 1757 at Edinburgh. After studying at the university of Glasgow and at Balliol College, Oxford, he took orders in the Church of England, and was appointed in 1778 to the curacy of Brancepeth, near Durham. In 1784 he married Dorothea, youngest daughter of Professor Gregory of Edinburgh. The next twenty years of his life were spent in Shropshire, where he held in succession the livings of High Ercall, Roddington and Kenley. In 1800 he removed to Edinburgh, having been appointed senior incumbent of St Paul's Chapel in the Cowgate. For thirty-four years he filled this position with much ability, his preaching attracting so many hearers that a new and larger church was built for him. His last years were spent at Colinton, near Edinburgh, where he died on the 17th of May 1839. Alison published, besides a Life of Lord Woodhouselee, a volume of sermons, which passed through several editions, and a work entitled Essays on the Nature and Principles of Taste (1790), based on the principle of association (see under AESTHETICS, p. 288). His elder son, Dr William Pulteney Alison (1790-1859), was a distinguished Edinburgh medical professor. SIR ARCHIBALD ALISON, Bart. (1792-1867), the historian, was the younger son, and was born at Kenley, Shropshire, on the 29th of December 1792. He studied at the university of Edinburgh, distinguishing himself especially in Greek and mathematics. In 1814 he passed at the Scottish bar, but he did not at once practise. The close of the war had opened up the continent, and Alison set out in the autumn of 1814 'for a lengthened tour in France. It was during this period that the idea of writing his history first occurred to him. A more immediate result of the tour was his first literary work of any importance, Travels in France during the Years 1814-1815, written in collaboration with his brother and A. F. Tytler, which appeared in the latter year. On his return to Edinburgh he practised at the bar for some years with very fair success. In 1822 he became one of the four advocates-depute for Scotland. As a result of the experience gained in this office, which he held until 1830, he wrote his Principles of the Criminal Law of Scotland (1832) and Practice of the Criminal Law of Scotland (1833), which in 1834 led to his appointment by Sir Robert Peel to the office of sheriff of Lanarkshire, which ranks next to a judgeship in the supreme court. The office, though by no means a sinecure, gave him time not only to make frequent contributions to periodical literature, but also to write the long-projected History of Europe, for which he had been collecting materials for more than fifteen years. The history of the period from the beginning of the French Revolution till the restoration of the Bourbons in 1815 was completed in ten volumes in 1842, and met with a success almost unexampled in works of its class. Within a few years it ran through ten editions, and was translated into many of the languages of Europe, as well as into Arabic and Hindustani. At the time of the author's death it was stated that 108,000 volumes of the library edition and 439,000 volumes of the popular edition had been sold. A popularity so widespread must have had some basis of merit, and the good qualities of Alison's work lie upon the surface. It brought together, though not always in a well-arranged form, an immense amount of information that had before been practically inaccessible to the general public. It at least made an attempt to show the organic connexion in the policy and progress of the different nations of Europe; and its descriptions of what may be called external history of battles, sieges and state pageants-are spirited and interesting. On the other hand the faults of the work are numerous and glaring. The general style is prolix, involved and vicious; mistakes of fact and false deductions are to be found in almost every page; and the constant repetition of trite moral reflections and egotistical references seriously detracts from its dignity. A more grave defect resulted from the author's strong political partisanship, which entirely unfitted him for dealing with the problems of history in a philosophical spirit. His unbending Toryism made it impossible for him to give any satisfactory explanation of so complex a fact as the French Revolution, or accurately to estimate the forces that were to shape the Europe of the 19th century. A continuation of the History, embracing the period from 1815 to 1852, which was completed in four volumes in 1856, did not meet with the same success as the earlier work. The period being so near as to be almost contemporary, there was a stronger temptation, which he seems to have found it impossible to resist, to yield to political prejudice, while the materials necessary for a clear knowledge of the influences shaping European affairs were not as yet accessible. The book is now almost wholly out of date. In 1845 Alison was chosen rector of Marischal College, Aberdeen, and in 1851 of Glasgow University. In 1852 a baronetcy was conferred upon him, and in the following year he was made a D.C.L. of Oxford. His literary activity continued till within a short time of his ALIWAL-ALIZARIN | 673 on the west side of Mossel Bay. Both places were named in death, the chief works he published in addition to his History being the Principles of Population (1840), in answer to Malthus; honour of Sir Harry Smith, governor of Cape Colony 1847-1852, a Life of Marlborough (1847, 2nd edition greatly enlarged, 1852); Aliwal (see above) being the village in the Punjab where in 1846 and the Lives of Lord Castlereagh and Sir C. Stewart (1861.) This he gained a great victory over the Sikhs. Crossing the Orange it was a beautiful site for a town," and in the May following It was latter, based on MS. material preserved at Wynyard Park, is still River at this spot in September 1848, Sir Harry noted that of value, not only as the only available biography, but more especially because Alison's Tory sympathies enabled him to give the town was founded. In the early months of the Boer War a juster appreciation of the character and work of Castlereagh of 1899-1902 Aliwal North was held by the Boers. ALIZARIN, or 1.2 DIOXYANTHRAQUINONE, than the Liberal writers by whom for many years he was mis-reoccupied by the British in March 1900. judged and condemned (see LONDONDERRY, Robert Stewart, 2nd marquess of). Three volumes of Alison's political, historical and miscellaneous essays were reprinted in 1850. He died at Possil House, Glasgow, on the 23rd of May 1867. His autobiography, Some Account of my Life and Writings, edited by his daughterin-law, Lady Alison, was published in 1883 at Edinburgh. Sir Archibald Alison married in 1825 Elizabeth Glencairn, Both sons daughter of Colonel Tytler, by whom he had three children, Archibald, Frederick and Eliza Frances Catherine. became distinguished officers. SIR ARCHIBALD ALISON, Bart. (1826-1907), the elder of the sons, entered the 72nd Highlanders in 1846. He served at the siege of Sevastopol; and during the Indian Mutiny he was military secretary to Sir Colin Campbell and was severely wounded at the relief of Lucknow, losing an arm. From 1862 to 1873 he was assistant adjutant-general at headquarters, Portsmouth and Aldershot. He was second in command of the Ashanti expedition 1873-1874, and was made a K.C.B. For three years Alison was deputy adjutant-general in Ireland, and then, for a few months, commandant of the Staff College. He was promoted to be major-general in 1877, and was head of the intelligence branch of the war office (1878-1882). He commanded the troops at Alexandria in 1882 until the arrival of Sir Garnet Wolseley, led the Highland brigade at the battle of Tel-el-Kebir, and remained in command of the army of occupation until 1883. He commanded at Aldershot 1883-1888, was for some months adjutant-general to the forces during Lord Wolseley's absence in Egypt, was made G.C.B. in 1887, was promoted general, and became a military member of the Council of India in 1889. He retired in 1893 and died in 1907. ALIWAL, a village of British India, in the Ludhiana district of the Punjab, situated on the left bank of the Sutlej, and famous as the scene of one of the great battles of the 1st Sikh War. Late in January 1846 it was held by Ranjur Singh, who had crossed the river in force and threatened Ludhiana. On the 28th Sir Harry Smith, with a view to clearing the left or British bank, attacked him, and after a desperate struggle thrice pierced the Sikh troops with his cavalry, and pushed them into the river, where large numbers perished, leaving 67 guns to the victors. The consequence of the victory was the submission of the whole territory east of the Sutlej to the British. ALIWAL NORTH, a town of South Africa, on the south bank of the Orange River, 4300 ft. above the sea, and 282 m. by rail N.W. by N. of the port of East London. Pop. (1904) 5566, of whom 1758 were whites. The town, a trading and agricultural centre for the N.E. part of the Cape and the neighbouring regions of Basutoland and Orange Free State, presents a pleasing appearance. It contains many fine stone buildings. The streets are lined with trees, and water from the neighbouring sulphur springs flows along them in open channels. The river, here the boundary between the Cape province and Orange Free State, is crossed by a stone bridge 860 ft. long. The sulphur springs, I m. from the town, which yield over 500,000 gallons daily, are resorted to for the cure of rheumatism and skin diseases. By reason of its dry and-bracing climate, Aliwal North is also a favourite residence of sufferers from chest complaints. In the neighbourhood are stone quarries. Aliwal North is the capital of a division of the province of the same name, with an area of 1330 sq. m. and a pop. (1904) of 14,857, of whom 40% are whites. Aliwal North was so called to distinguish it from Aliwal South, now Mossel Bay, the seaport of the pastoral Grasveld district, C&H1<CO>C2H2(OH)2[1·2], a vegetable dyestuff formerly prepared from madder root (Rubia C26 H28014+2H2O=2C6H12O6+C14H8O4 In practice, the crude anthracene is purified by solution in the higher pyridine bases, after which treatment it is frequently sublimed. It is then oxidized to anthraquinone by means of sodium dichromate and sulphuric acid in leaden vats, steam heated so that the mixture can be brought to the boil. When oxidation is complete the crude anthraquinone is separated in filter presses and heated with an excess of commercial oil of vitriol to 120° C., the various impurities present in the crude material being sulphonated and rendered soluble in water, remove impurities, and dried. The anthraquinone so obtained whilst the anthraquinone is unaffected; it is then washed, to is then heated for some hours at about 150-160° C. with fuming sulphuric acid (containing about 40-50 % SO%), and by this treatment is converted into anthraquinone-8-monosulphonic acid. The solution is poured into water and sodium carbonate of the monosulphonic acid (known as silver salt) separates out. is added to neutralize the excess of acid, when the sodium salt This is filtered, washed, and then fused with caustic soda, when the sulpho-group is replaced by a hydroxyl group, and a second hydroxyl group is simultaneously formed; in order to render the formation of this second group easier, a little potassium chlorate or sodium nitrate is added to the reaction mixture. The melt is dissolved in water and the dyestuff is liberated from the sodium salt by hydrochloric or sulphuric acid, or is converted into the calcium salt by digestion with hot milk of lime, then filtered and the calcium salt decomposed by acid. The precipitated alizarin is then well washed and made into a paste with water, in which form it is put on to the market. K. Lagodzinski (Berichte, 1895, 28, p. 1427) has synthesized alizarin by condensing hemipinic acid [(CH2O)2C6H2(COOH)2] with benzene in the presence of aluminium chloride. The product on acidification gives a compound C15H12O5 H2O which is probably an oxy-methoxy-benzoyl benzoic acid. This is dissolved in cold concentrated sulphuric acid, in which it forms a yellowish red solution, but on heating to 100° C. the colour changes to red and violet, and on pouring out upon ice, the monomethyl ether of alizarin is precipitated. This compound is hydrolysed by hydriodic acid and alizarin is obtained. It can also be synthesized by heating catechol with phthalic | plants or wood (pot-ashes). Later, Martin Heinrich Klaproth, anhydride and sulphuric acid at 150° C. C.H. COO+C2H.(OH):{[1·2] = H2O+CH, COCH2(OH)2. Pure alizarin crystallizes in red prisms melting at 290° C. It is insoluble in water, and not very soluble in alcohol. It dissolves readily in caustic alkalis on account of its phenolic character, and it forms a yellow-coloured di-acetate. Its value as a dyestuff depends on its power of forming insoluble compounds (lakes) with metallic oxides. It has no affinity for vegetable fibres, and consequently cotton goods must be mordanted before dyeing with it (see DYEING). Numerous derivatives of alizarin are known. On solution in glacial acetic acid and addition of nitric acid, ẞ-nitroalizarin with sulphuric acid and glycerin is converted into alizarin blue. The trioxyanthraquinones-purpurin, anthrapurpurin, anthragallol and flavopurpurin-are also very valuable dyestuffs. These compounds may be represented by the following formulae: CO \OH COA Anthragallol. CO/ Purpurin. OH OH OH HO CO OH OH OH OH HO Anthrapurpurin. Flavopurpurin. Purpurin (1.2.4 trioxyanthraquinone) is found with alizarin in madder root; it is now prepared synthetically by oxidizing alizarin with manganese dioxide and sulphuric acid. After the separation of the silver salt (see above) obtained on sulphonating anthraquinone, the remaining acid liquid gives on treatment with calcium carbonate the calcium salt of anthraquinone 26 disulphonic acid (anthraquinone-a-disulphonic acid). This is converted into the sodium salt by means of sodium carbonate, and on alkali fusion yields flavopurpurin. In a similar manner anthra purpurin is prepared by alkali fusion of anthraquinone 2.8 disulphonic acid. Anthragallol is synthetically prepared by the condensation of benzoic and gallic acids with sulphuric acid OH finding vegetable alkali in certain minerals, such as leucite, proposed to distinguish it as potash, and at the same time assigned to the mineral alkali the name natron, which survives in the symbol, Na, now used for sodium. The word alkali supplied the symbol for potassium, K (kalium). In modern chemistry alkali is a general term used for compounds which have the property of neutralizing acids, and is applied more particularly to the highly soluble hydrates of sodium and potassium and of the three rarer "alkali metals," caesium, rubidium and lithium, also to aqueous ammonia. In a smaller degree these alkaline properties are shared by the less soluble hydrates of the "metals of the alkaline earths," calcium, barium and strontium, and by thallium hydrate. An alkali is distinguished from an acid or neutral substance by its action on litmus, turmeric and other indicators. ALKALI MANUFACTURE. The word "alkali" denotes both soda and potash, but by "alkali manufacture" we understand merely the manufacture of sodium sulphate, carbonate and hydrate. The corresponding potash compounds are not manufactured in the United Kingdom, but exclusively in Germany (from potassium chloride and from the mother-liquor of the strontia process in the manufacture of beetroot sugar) and in France (from vinasse). The term alkali is employed in a technical sense for the carbonate and hydrate (of sodium), but since in the Leblanc process the manufacture of sodium sulphate necessarily precedes that of the carbonate, we include this as well as the manufacture of hydrochloric acid which is inseparable from it. We also treat of the utilization of hydrochloric acid for the manufacture of chlorine and its derivatives, which are usually comprised within the meaning of the term " alkali manufacture.” of alkali from various materials, but none of these has become A great many processes have been proposed for the manufacture of any practical importance except those which start from sodium chloride (common salt); and among the latter again only three classes of processes are actually employed for manufacturing purposes, viz. the Leblanc, the ammonia-soda, and the electrolytic processes. I. THE LEBLANC PROCESS The Leblanc process, which was invented by Nicolas Leblanc (q.v.) about 1790, begins with the decomposition of sodium or from pyrogallol and phthalic anhydride in the presence of chloride by sulphuric acid, by which sodium sulphate and sulphuric acid or zinc chloride. A. Baeyer in 1890, by heating alizarin with fuming sulphuric acid for 24-48 hours at 35-40° C., obtained a product, which after treatment with caustic soda gave a sulphuric acid ester of quinalizarin, and this after acidification and boiling was converted into quinalizarin (Alizarin Bordeaux) or 1.2.6.9 tetra-oxyanthraquinone. Penta-oxyanthraquinones have been obtained from purpurin and anthrapurpurin, while a hexaoxyanthraquinone has been obtained from 1.5 dinitro-anthra- | quinone. ALKAHEST (a pseudo-Arabic word believed to have been invented by Paracelsus), a liquid, much sought after by the alchemists, having the power of dissolving gold and every other substance, which it was supposed would possess invaluable medicinal qualities. hydrochloric acid are produced. The sodium sulphate is afterwards fluxed with calcium carbonate and coal, and a mixture is thus obtained from which sodium carbonate can be extracted by exhausting it with water. Leblanc himself for a time carried out his process on a manufacturing scale, but he was ruined in the political troubles of the time and died by his own hand in 1806. His invention was, however, at once utilized by others in France; and in Great Britain, after a few previous attempts on a small scale, it was definitely introduced by James Muspratt (q.v.) in 1823. From that time onward the Leblanc process spread more and more, and for a considerable period nearly all the alkali of commerce was made by it. The rise of the ammonia-soda process (since 1870) gradually told upon the Leblanc process, which in consequence has been greatly restricted in Great Britain and Germany, and has become practically extinct in all other countries, except as far as its first part, the manufacture of sodium sulphate and hydrochloric acid, is concerned. ALKALI, an Arabic term originally applied to the ashes of plants, from which by lixiviation carbonate of soda was obtained in the case of sea-plants and carbonate of potash in that of landplants. The method of making these "mild" alkalis into The production of alkali in Great Britain, soon after the caustic" alkalis by treatment with lime was practised in the introduction of the Leblanc process, became the most extensive time of Pliny in connexion with the manufacture of soap, and it in the world, and outstripped that of all other countries put was also known that the ashes of shore-plants yielded a hard together. With the rise of the ammonia-soda process, for which soap and those of land-plants a soft one. But the two substances the economic conditions are nearly as favourable in other were generally confounded as "fixed alkali" (carbonate of countries, the predominance of Great Britain in that domain has ammonia being "volatile alkali "), till Duhamel du Monceau in become less, but even now that country produces more alkali 1736 established the fact that common salt and the ashes of sea- than any other single country. Most of the British alkali works plants contain the same base as is found in natural deposits of are situated in South Lancashire and the adjoining part of soda salts ("mineral alkali "), and that this body is different | Cheshire, near the mouth of the Tyne and in the West of from the vegetable alkali" obtained by incinerating land- Scotland. 66 Various industries are carried on in Leblanc alkali works, as already a good upward draught, and when circulating round the follows: 1. Manufacture of sodium sulphate. 2. Manufacture of hydrochloric acid. 3. Preparation of chlorine. 4. Employment of chlorine for the manufacture of bleachingpowder and of chlorates. 5. Manufacture of ordinary alkali from sulphate of soda. 6. Manufacture of caustic soda. 7. Manufacture of soda crystals. 8. Recovery of sulphur from alkali waste. = muffle are at a lower pressure than the gases within the muffle, so that in case of any cracks being formed, no hydrochloric acid escapes into the fire-flues, but vice versa. Since the work with ordinary hand-wrought salt-cake furnaces is disagreeable and costly, many attempts have been made to construct mechanical salt-cake furnaces. Of these J. Mactear's furnaces (fig. 3) have met with the greatest success. They consist of a horizontal pan, 17 ft. wide, which is made up of a central pan (e), and a series of concentric compartments (c), (c2), (c), and which is supported on a frame (d d), revolving i. Manufacture of Sodium Sulphate.-This is commercially round a perpendicular axis on the wheels (n n). It is covered known as salt-cake, and is made by decomposing common with an arch and heated on the top from one side (1), either salt with sulphuric acid of about 80 %, the reaction being by an ordinary coal-grate or by a gas-producer. A set of 2NaCl+H2SO4 Na2SO4+2HCl. This reaction proceeds in two I stirring blades carried in the frame (b b), and driven by gearing, stages. At first principally acid sodium sulphate, NaHSO4, is formed together with some normal sulphate; later, when the temperature has risen, the NaHSO4 acts with more NaCl so that nearly all of it is converted into Na2SO4. The gaseous hydrochloric acid evolved during all this time must be absorbed in water, unless it is directly converted into chlorine (see below, 2 and 3). The process is carried out either in hand-wrought furnaces, or mechanical furnaces, both called "decomposing or" salt-cake furnaces." In the former case, the first reaction is produced in castiron pans or "pots," very heavy castings of circular section, fired from below, either directly or by the waste heat from the mufflefurnace. The reaction is completed in a "roastingfurnace." The latter was formerly often constructed as a reverberatory furnace, which is easy to build and to work, but the hydrochloric acid given off here, being mixed with the products of the combustion of the fuel, cannot be condensed to strong acid and is partly, FIGS. I and 2.-Salt-cake Furnace. (Sectional Elevation and Plan.) if not entirely, wasted. It is, therefore, decidedly preferable to employ "muffle-furnaces" in which the heating is performed from without, the fire-gases passing first over the arch and then under the bottom of the muffle. This requires more time and fuel than the work in "open " furnaces, but in the muffles the gaseous hydrochloric acid is separated from the fire-gases, just like that evolved in the pot, and can therefore be condensed into strong hydrochloric acid, like the pot-acid. This roaster-acid is, however, of less value than the pot-acid, as it contains more impurities. It is not easy to keep the muffles permanently tight, and as soon as any leakages occur, either hydrochloric acid must escape into the fire-flue, or some fire-gases must enter into the muffle. The former is decidedly more objectionable than the latter, as it means that uncondensed hydrochloric acid is sent into the air. This drawback has been overcome by the construction of "pluspressure" " furnaces (figs. 1 and 2), where the fire-grate is placed 11 ft. below the top of the muffle. In consequence the fire-gases, when arriving there by the chimney shaft (a), have | M passes through a gap in the arch in such a manner that the gases cannot escape outwards. The salt is conveyed to the furnace by a chain of buckets running on the pulley (g), and passing into the hopper (h), and through the pipe (i) is mixed with the proper amount of acid supplied by the pipe (f). The mixture is fed in continuously to the central pan (e), whence it overflows into the compartments (c1), (c), (c) successively until it reaches the circumference, where it is discharged continously by o and p into the collecting-box (q), being now converted into salt-cake. This furnace acts very well, and has been widely introduced both in Great Britain and in other countries, but it has one great drawback, apart from its high cost, viz. that all the hydrochloric acid gas gets mixed with fire-gases, and consequently is condensed in a weaker and less pure form than from ordinary pots and muffles. This has led some factories which had introduced such furnaces to revert to hand-wrought muffle-furnaces. Much was expected at one time from the "direct salt-cake process" of Hargreaves and Robinson, in which common salt is subjected in a series of large cast-iron cylinders to the action of pyrites-burner gases and steam at a low red heat. The reaction going on here is: 2NaCl+SO2+O+H2O= Na2SO4+2HCl. This means that the previous manufacture of sulphuric acid in the vitriol-chambers is done away with, but this apparently great simplification is balanced by the great cost of the Hargreaves plant, and by the fact that the whole of the hydrochloric acid is mixed with nine or ten times its volume of inert gases. Owing to this, it is practically impossible to condense the gaseous hydrochloric acid into the commercial acid, although this acid may be obtained sufficiently strong to be worked up in the Weldon chlorine process (see below, 3). Therefore the Hargreaves process has been introduced only in a few places. Although the consumption of salt-cake for the manufacture of alkali is now much less than formerly, since the Leblanc alkali process has been greatly restricted, yet it is largely made and will continue to be made for the use of glassmakers, who use it for the ordinary description of glass in the place of soda-ash. Nor must it be overlooked that salt-cake must be made as long primary duty of preventing nuisance, but quite as much to showing manufacturers how to make the most of the acid formerly wasted in one shape or another. Not merely Great Britain but all mankind has been immensely benefited by the labours of the British alkali inspectors, which were, of course, supplemented by the work of technical men in all the countries concerned. The scientific and technical principles of the condensation of hydrochloric acid are now thoroughly well understood, and it is possible to recover nearly the whole of it in the state of strong commercial acid, containing from 32 to 36% of pure hydrochloric acid, although probably the majority of the manufacturers are still content to obtain part of the acid in a weaker state, merely to satisfy the requirements of the law prescribing the prevention of nuisance. The principles of the condensation, that is of converting the gaseous hydrochloric acid given off during the decomposition of common salt into a strong solution of this gas in water, can be summarized in a few words. The hydrochloric acid gas, which is always diluted with air, sometimes to a very great extent, must be brought into the most intimate contact possible with water, which greedily absorbs it, forming ordinary hydrochloric acid, and this process must be carried so far that scarcely any hydrochloric acid remains in the escaping gases. The maximum escape allowed by the Alkali Acts, viz. 5% of the total hydrochloric acid, is far above that which is now practically attained. For a proper utilization of the condensed acid it is nearly always imperative that it should be as strong as possible, and this forms a second important consideration in the construction of the condensing apparatus. Since the solubility of hydrochloric acid in water decreases with the increase of the temperature, it is necessary to i keep the latter down-a task which is rendered somewhat difficult both by the original heat retained by the gases on their escape from the decomposing apparatus, and by the heat given off through the reaction of hydrochloric acid upon water. FIG. 3.-Mechanical Salt-cake Furnace. (Sectional Elevation.) as there is a sale for hydrochloric acid, or a consumption of the latter for the manufacture of chlorine. 2. Manufacture of Hydrochloric Acid (commercially also known as "muriatic acid "). This unavoidable gaseous bye-product of the manufacture of salt-cake was, during the first part of the 19th century, simply sent into the air. When its deleterious effects upon vegetation, building materials, &c., became better known, and when at the same time an outlet had been found for moderate quantities of hydrochloric acid, most factories made more or less successful attempts to "condense" the gas by absorption in water. But this was hardly anywhere done to the fullest possible extent, and in those districts where a number of alkali works were located at no great distance from one another, their aggregate escapes of hydrochloric and other acids created an intolerable nuisance. This was most notably the case in South Lancashire, and it led to the passing of Lord Derby's "Alkali Act," in 1863, supplemented by further legislation in 1874, 1881 and later. There is hardly another example in the annals of legislative efforts equal to this, in respect of the real benefit conferred by it both on the general public and on the manufacturers themselves. This is principally the consequence of the exemplary way in which the duties of inspector under these acts were carried out by Dr R. Angus Smith (1817-1884) and his successors, who directed their efforts not merely to their Very different methods have been employed to effect all the above purposes. In Great Britain Gay-Lussac's coke-towers, adapted by W. Gossage to the condensation of hydrochloric acid, are still nearly everywhere in use, frequently combined with a number of stone tanks through which the gas from the furnaces travels before entering the towers, meeting on its way the acid condensed in the tower. This process is excellent for effecting a complete condensation of the hydrochloric acid as prescribed by the Alkali Acts, and for recovering the bulk of the acid in a tolerably strong state, but less so for recovering nearly the whole of it in the most concentrated state, although even this is occasionally attained. On the continent of Europe, where the last-named requirement has been for a long time more urgent than in Great Britain, another system has been generally preferred, namely, passing the gas through a long series of stoneware receivers, and ultimately through a small tower packed with stoneware or coke, making the acid flow in the opposite direction to the gas. Great success has also been obtained by "plate-towers" made of stoneware, which allow both the coke-towers and most of the stoneware receivers to be dispensed with. 3. Preparation of Chlorine.-In this place we speak only of |