presence of arsenic is harmless, it is not probable that the purification of sulphuric acid by the removal of arsenic will ever be practiced in this country. CONCENTRATION OF SULPHURIC ACID. The strength of the acid from the chambers generally does not exceed 50° B., or about 62 per cent. H,SO,. Such acid is strong enough for the manufacture of fertilizers, ammonium sulphate, and even for the salt-cake process. For petroleum refining, making nitric acid, and especially in the manufacture of nitrobenzene and nitroglycerine, stronger acid is needed. Acid from the Glover tower may reach a strength of 62° B, or about 82 per cent. pure acid, but beyond this strength the concentration must be carried on in platinum or glass stills. Acid from the Glover tower can not generally be concentrated in platinum, because it usually contains a large amount of sulphate of iron (ferric sulphate), caused by the action of the acid in the tower on the pyrites dust swept in with the burner-gas; this impurity would cause the formation of crusts on the bottom of the pan, and bring about its rapid destruction. When platinum stills are used, therefore, chamber acid is first concentrated in lead pans by the waste heat of the platinum stills or burners, to about 60° B., and then run into the stills. The great drawback in the use of platinum is its rapid corrosion, which is especially marked in the case of acid containing nitrogen compounds or large quantities of arsenic. Nitrogen compounds are removed by addition of ammonium sulphate, as already stated. According to Mr. W. H. Adams,* platinum stills would last almost indefinitely for the concentration of acid free from arsenic up to a strength of 65° B., or about 90 per cent. pure. This is strong enough for petroleum refining, but for the manufacture of nitro-compounds further concentration is necessary. Beyond this point, lead, iron, and other substances are rapidly precipitated and adhere to the bottom of the pan, and the chief injury to the apparatus takes place in the removal of the last portions of water. Within the last few years cast-iron retorts have been successfully used in the United States for final concentration, and are now employed on a large scale at extensive works near New York. Final concentration in iron retorts is also practiced in France at the Établissement Malétra, Rouen. The question of the corrosion of the platinum stills has been carefully investigated by Mr. Scheurer-Kestner, who has determined the comparative loss of platinum per ton of acid distilled: Acid of 98 per cent., 6 to 7 grammes per ton; and acid of 99.5 per cent., 9 grammes per ton. In the case of acids containing considerable quantities of *Twenty years' Progress in the Manufacture of Sulphuric Acid, Proc. Amer. Inst. Mining Engineers, 1887. +Comptes Rendus, April 29, 1878. oxides of nitrogen, the corrosion was found to be over three times as great as the amount just stated. Platinum containing 30 per cent. of iridium sustains only about one-third as much loss as pure platinum. This alloy has been introduced for making stills, but proved to be too brittle for good service, and has been abandoned. PLATINUM APPARATUS FOR CONCENTRATION. Johnson, Matthey & Co., of London, made a very remarkable exhibit of platinum and platinum ware in the English section. In the case was displayed a pair of platinum retorts on the Delplace system, for the concentration of sulphuric acid. The retorts are of oblong shape, low and flat, with dome-shaped roof and central outlet pipe for vapors. Each retort is 1.5 metres long (or about 60 inches). One retort is placed on a slightly higher level than the other, and the two are connected by a tube in such a manner that the acid may flow continuously through both vessels. Acid of 60° B. flows into the first, and finally issues from the second at a strength of 66 B., containing then 97 per cent. H,SO,, corresponding to 79 per cent. anhydride. The condensed vapors from the first retort show a strength of 5° to 15° B.; those from the second reach a strength of 62° to 63° B. This form of concentrating apparatus is now chiefly used in the leading European works, and is also in use to some extent in the United States. One pair of retorts like those exhibited weighs about 2,000 ounces, costing about $17,500, and will concentrate 10 tons of acid daily to 76 per cent. of anhydride, or 5 tons to 79 per cent. The exhibit of Johnson, Matthey & Co. included also a great variety of articles in platinum; bars of platinum containing 10 per cent. of iridium, of X-shaped section, made for the use of the International Commission of Weights and Measures in the construction of standard metres." At the laboratory of the commission, at Breteuil, near Paris, thirty such bars, costing $2,000 each, are now undergoing comparison and adjustment. Beautiful specimens of the rarer metals contained in small quantity in native platinum, were also displayed, including about 3 pounds of granulated osmium, which can not be fused into a compact mass, and a fused ingot of iridium, weighing 54.4 ounces. Blocks of the three lighter metals, rhodium, palladium, and ruthenium, each of several pounds' weight and almost fabulous value, were also exhibited. It was stated that the stock of platinum ware carried by the firm often represents a value of £250,000 sterling. F. Desmontis, Lemaire et Cie., Paris, also made a fine exhibit of platinum concentrating apparatus. The form of still chiefly made at present is circular in shape, and provided with a number of concentric partitions so arranged upon the bottom of the still that the acid traverses the whole series of compartments before making its exit. This company owns also the patents for stills on the Faure & Kessler system, which consists of a pan of platinum surmounted by a dome of lead cooled by a water jacket. This form of apparatus is much lower in first cost than that consisting entirely of platinum. In Europe platinum stills are chiefly used, while in the United States the Faure & Kessler apparatus seems to be preferred. The following firms in this country are said to be using stills made by Desmontis, Lemaire et Cie: The Bergenport Chemical Company (Charles Pratt), New York. James Morgan & Co., New York. G. H. Nichols & Co., New York. The Putnam Company Chemical Works, New York. The Frankford Chemical Company, Philadelphia. Harrison Brothers & Co., Philadelphia. Chas. Lennig & Co., Philadelphia. The Pennsylvania Salt Manufacturing Company, Philadelphia. A. Cochrane & Co., Boston. The Merrimac Chemical Company, Boston. The Smith & Leyden Company, Atlanta. The Clifton Chemical Works, Atlanta. The Grasselli Chemical Company, Cleveland. The Star Glass Company (W. C. De Pauw), New Albany. James Irwin & Co., Pittsburg. Malha & Chappell, Chicago. The Marsh & Harwood Chemical Company, Cincinnati. The Matthiessen & Hegeler Zinc Company, La Salle, Illinois. Smith & Becker, Buffalo. T. P. Shepard & Co., Providence. The Talbot Dye-Wood and Chemical Company, Lowell, Massachusetts. FUMING SULPHURIC ACID. This product, known also as Nordhausen sulphuric acid, because formerly largely made at Nordhausen, in Prussian Saxony, is now made almost exclusively by the firm of M. D. Stark, in Bohemia. The acid is made from the Przibram slates, which contain considerable quantities of coal and iron pyrites. These slates are broken and piled up in heaps, and allowed to weather, with occasional sprinkling, for 2 or 3 years. During this period the pyrites becomes oxidized to ferric sulphate, with the formation of some aluminium. sulphate. Finally, the mass is lixiviated, and the brown liquors so obtained are concentrated to a sirup; this is then run onto a floor and solidifies to "crude vitriol stone." The stone is then calcined in an open furnace to remove water and oxidize ferrous sulphate; the calcined mass consists then essentially of anhydrous ferric sulphate, This is broken up, charged into fire-clay retorts, and distilled; the fuming acid is condensed in clay receivers. The residue of ferric oxide remaining in the retorts, known as "caput mortuum," or col cothar, finds extensive use as a red pigment. It is ground under a millstone and again calcined with the addition of different quantities of salt, from 2 to 6 per cent., by which different shades of color are produced.* Winkler's process for making sulphuric anhydride has lately been perfected, and has come into extensive use. Sulphuric acid is decomposed by heat into water, sulphur dioxide, and oxygen; the water is absorbed by a strong acid, and the mixture of sulphur dioxide and oxygen caused to recombine by passing the gases over red-hot platinized asbestus. The details of the process are kept secret by the manufacturers using it. According to Lunge, (vol. III, p. 385), Dr. Majert, at the Schlebusch works near Cologne, employs this method, decomposing the sulphuric acid in upright fire-clay retorts, the joints of which are luted with melted glass. The gases pass into a condenser and drying tower, then into cast-iron retorts filled with wire gauze shelves covered with layers of platinized asbestus. Hanisch finds that the combination of the gases is greatly aided by compression during the heating. The anhydride is also manufactured on a large scale by Chapman & Messel, of London, probably by a process similar to the above.† Fuming sulphuric acid and sulphuric anhydride are largely used for dissolving indigo, sulphonating certain organic compounds in the manufacture of coal-tar colors, as eosine and alizarine, and also in the refining of ozokerite or mineralwax. The most important exhibits of sulphuric and other acids at the Exposition will be noticed under the head of alkali industry. III. ALKALI MANUFACTURE. GENERAL OUTLINE OF THE PRESENT POSITION OF THE ALKALI INDUSTRY. Probably the most striking change in the whole field of chemical industry which the past 10 years have witnessed is the rapid growth and extension of the ammonia-soda process. Up to 1863, the date of the establishment of the first Solvay works at Couillet, the whole of the world's supply of soda (with the exception of the small quantity made from sea-weed and from. cryolite) was manufactured by the Leblanc process. Soda manufactured by the ammonia process was exhibited by Solvay at the Paris Exposition of 1869, and again at the Vienna Exposition of 1873, where a diploma of honor was granted to the inventor for his services in the development and improvement of the process. At the Paris Exposition of 1878 Mr. Solvay was awarded a grand prize, having established a second factory in France at Varangeville-Dombasle, at which 40,000 tons of soda were annu * Lunge, Sulph. Acid and Alkali, vol. 1, p. 630. See the report by Watson Smith on the London Inventions Exhibition, 1885, p. 50. ally produced. The firm of Brunner, Mond & Co. had also established works to use this process at Northwich and Sandbach, in England. The annual production of ammonia-soda in 1878 was approximately as follows: At the same time there were produced by the Leblanc process 500,000 tons of soda in England, and also very large quantities in France, Germany, and Austria. Since 1878 the progress of the ammonia-soda industry has been extremely rapid, while since 1880 the production by the Leblanc process has begun to decline. Since the soda produced appears in the various forms of soda-ash, crystals, and caustic, it is difficult to compare the production of the two processes in successive years. The amount of salt decomposed by each process gives, however, a fair basis for comparison. From the reports of the English alkali inspectors the following table has been compiled, showing the relative amounts of salt decomposed by the Leblanc and ammonia-soda processes, respectively, in Great Britain and Ireland since 1878: The above table shows that about one-fourth of the soda now made in the United Kingdom is manufactured by the ammonia-soda proSimilar statistics in regard to France and Germany are not obtainable, but according to Hasenclever,* the relative advance of ammonia-soda has been far greater in those countries than in England. In 1887, of the total soda produced in Germany 75 per cent. *Chem. Industrie, 10, 290. |