CHAPTER V.

HISTORICAL SKETCH OF ALKALI MANUFACTURE.

THE manufacture which will be next described is that of 'salt-cake,' or sulphate of sodium, and as the production of this is the first stage in the manufacture of alkali, it is thought best to preface it with a historical sketch of the alkalies, their uses, etc.

art.

The word Lixivium, used by the ancient Romans, is evidently derived from Lix, signifying a lye made with ashes. Lixa, another Latin term, signifies a worker in ashes, and this in itself is a proof of the antiquity of the Marcus Terentius Varro, the Roman general, writing in the first century, tells us that the inhabitants upon the Rhine, wanting sea-salt, used a substitute procured from wood. In the excavations of the city of Pompeii, a complete soap-boiler's shop was discovered, with soap in it, which had evidently been made from oil and alkali, and the soap, though 1,700 years had elapsed, was still perfect. Several ancient writers describe nitrum, and in the ninth century Geber the Arabian describes soda distinctly, and actually distinguishes it from potash. Pliny relates that the Germans of his day used potash for soap-making. The word 'alkali' is of Arabian origin, being derived from kali (a species of vegetable); the particle al, according to Albertus Magnus, having been

added to signify the importance of the substance over that of the plant from which it is derived 1

Mr. Rodwell, in his 'Birth of Chemistry,' tells us that nitrum was a term applied to sodic carbonate by the ancients, who used it for glass-making. In fact, glass is supposed by Pliny to have been first discovered by some Phoenician merchants who were returning from Egypt with a cargo of natron (carbonate of soda), and who landed on the sandy banks of the river Belus. In order to support the vessels they used for cooking their food over the fire, they used some large lumps of natron, and the fire was sufficiently strong to fuse it with the fine sand of the river. Hence resulted the first glass.'2 Mr. Rodwell shows that, whatever may be the worth of the story detailed by Pliny, the ancients were proficient in glass-making, and that the composition of the Egyptian glass was nearly identical with that of our crown glass, in the manufacture of which alkali is necessarily consumed.

Soda in various forms occurs in nature very widely and abundantly. As sesquicarbonate, 2Na,O,3CO2+3Aq, it forms the deposits known as 'Trona' and 'Urao,' left by the drying up of soda lakes. As a mineral, in combination with carbonate of calcium, it constitutes Gay-Lussite, Na,CO2+CaCO3+5H2O. Its occurrence as chloride (salt) will be further alluded to presently. But it was from marine plants that our early supply was derived; such plants as salsola, triglochia, salicornia, atriplex, all yield sodium carbonate on incineration. Sea plants, as a rule, however, compared with land plants, contain less soda and more potash. Sea weeds contain 2 Birth of Chemistry,' p. 48.

1 Parkes' 'Chemical Essays.'

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or yield from 9 to 25 per cent. of ash calculated on the weed dry at 100° C., and in this ash the potash ranges from 4 to 24 per cent. and the soda from 2 to 24 per cent. The following information, as likewise some which has gone before, is taken from Richardson and Watts' 'Technology:'

Previous to the year 1793, soda was obtained exclusively from the ashes of marine plants, the chief quantities being derived from Alicante in Spain, Sicily, Teneriffe, and the coasts of Great Britain. Russian and American potashes were also largely imported. In fact, so large had grown this importation, that during our dispute with America a considerable quantity of saltpetre was consumed in Great Britain to furnish alkali, by heating it with charcoal or other carbonaceous matter.1 The pearlashes were prepared from potashes by calcination, whereby sulphur and carbon were burnt away, the product being employed for the nicer purposes. These potashes were prepared from the ashes of burnt wood. In the middle of the last century the Russian product was far superior to the American.

The plants described above, furnished the soda of Alicante and Carthagena, or (as it was commonly known) Barilla,' and were sown as seeds in the end of the year and gathered in the following September. So highly was the product valued, and the importance of the trade

1 Parkes'' Chemical Essays.'

regarded, that by the laws of Spain the exportation of the seed was an offence punishable by death. The plants were mowed down, sun-dried, and burnt on iron bars placed over pits 3 feet deep by 4 feet square. The ashes fell into the pit, on the floor of which they formed a semivitrified mass, which was allowed to cool, then broken into pieces, and in this state it formed the commercial barilla, the best qualities of which contained about 40 per cent. carbonate of soda.

'Kelp' was another commercial form of soda, and its manufacture on our shores (Wales and Scotland) was introduced from Ireland, by MacLeod in 1730, to the Highlands of Scotland. It is said that Lord Macdonald of the Isles realised 10,000l. a-year from his kelp shores alone. British kelp was inferior to the Spanish barilla, seeing it contained more potash, neutral salts, and carbonaceous matter. These rough alkalies were bruised and mixed with quicklime and lixiviated, to furnish the lyes used by soap-makers. They also furnished the supply for the manufacture of glass. According to Richardson and Watt's 'Technology,' kelp is still produced for making iodine and potash salts, while the mother liquors are boiled down to dryness, and yield 'kelp salts' containing from 7 to 14 per cent. of alkali, which are sold to the soda makers. In 1834 there were imported 12,000 tons of barilla; in 1850 there were imported 34,880 cwt. of barilla; in 1856 there were imported 54,608 cwt. of barilla. Scotland alone produced at one time 25,000 tons of kelp annually, so that we did not depend on the Spanish product so much as other countries.

The French Revolution of 1793 stopped the importation of soda into France, whereupon the Convention made

an appeal to the nation, and appointed a committee to discover the means of supply from native resources. Out of thirteen processes which were reported upon, that of Le Blanc was approved. Mr. Gossage has shown that the process was not an outcome of this appeal, but that Le Blanc had not only devised it previously, but had also worked it on a considerable scale. We have alluded elsewhere to the terrible privations which attended the life of this great man, and the sad story of his death. Sundry works were erected in France to carry out his process, but it was not till some years later that it was introduced into England.

At first, when introduced into England, the trade did not develope as might have been expected, because of the duties which then existed on salt, the substance from which the soda was derived by this process. The abolition of these duties in 1823 was in no small measure due to Mr. Parkes, and he ultimately received the congratulations of the Commons for his efforts. So great an effect had the abolition of the duties on the price of salt, that it rapidly fell, even in London, from 35l. to 27. 10s. per ton. When once fairly introduced into England, the manufacture of soda assumed such a rapid development that in a few years it formed the most important chemical industry of the kingdom-important, as Richardson and Watts point out, on account of the capital employed, the labour employed, and the uses of the manufactured products.

This process of Le Blanc has three stages:-(1) The decomposition of common salt by sulphuric acid; (2) the decomposition of the salt-cake' so formed by chalk and carbon; and (3) the separation of the carbonated alkali