A theoretical and practical treatise on the manufacture of sulphuric acid and alkali, with the collateral branches

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CHAPTER I. Page QwsTKRAi* Notes ok Sodium Sulphate 3

Historical^ 3 ; chemical properties, 3 ; hydrates of sodiam sulphate, 5 ; solubility, 6 ; acid sulphates, 10 ; sulphate (saltcake) of trade, 11 ; analysis, 12 ; natural occurrence, 15.

CHAPTER II. EirUlfEEATIOK OF THE PbOCESSES FOB OBTAINISa SULPHATB 18

Sulphate as a by-product in manufacturiDg muriatic acid, 19; in manufacturing nitric acid, 19 ; in other cases, 20 ; from mother-liquors of salt-works, 20 ; from pan-scale, 21 ; from kelp, 22 ; from kieserite, 22.

Sulphate from common salt, 25 ; by heating with metallic sulphides (Longmaid's process), 26 ; by Epsom salt, 30 ; by calcium sulphate, 31 ; by the sulphates of ammonium, aluminium, iron, 33 ; of copper, zinc, manganese, lead, 35.

Chapter III

Sulphate avjd Htdbochlobic Acid from Coumon Salt ajsh Sulphubio Acid 37

Historical, 87 ; stages of manufacture, 38 ; process where HCl is the

principal product, 40.

Raw materials : common salt, 40 ; sulphuric acid, 42^

VI CONTENTS.

Page

Mannf acinire in glass retorts, 43 ; in cast-iron cylinders, 46 ; in furnaces, 50 ; regard for the condensation of acid, 50 ; for turning out large quantities, economy of fuel, purity of the sulphate, 51.

Oldest furnaces with open roasters and lead pans, 52; modification^, 55 ; Belgian furnace with open roaster, 56 ; with blind roaster and lead pans, 60 ; iron pans, 64 ; shape, 65 ; material, 68 ; treatment, 69 ; supply of acid, 70 ; furnace with one pan and two open roasters, 71 ; with one open roaster, 73 ; heating by coke or coals, 78 ; blind roasters, 78 ; the same without a separate pan-fire,' 84 ; comparison of blind and open roasters (advantages and drawbacks of each kind), 87. Gas furnaces : Wigg's, 94 ; Gamble's, 95.

Mechanical furnaces : Jones and Walsh's, 97 (Goodman's constniction, 99 ; condensation of acid, 102 ; objections raised, 103 ; improvements and latest results for acid, 106) ; Black and HiU's, 107 ; Cammack and Walker's, 110.

Process of decomposing in the pans, 115 ; charging with salt, 115 ; the sulphuric acid, 116 ; nitre-cake, 118 ; further treatment, 118 ; vapour-hoods, 119 ; tools, 121 ; finishing in the calcining furnace, 122 ; drawing the charge, 123 ; control of work, 124 ; yield of sulphate, 125 ; labour, 126 ; fuel, 126.

CHAPTER IV. The MAnuFAOiTBE of Sulphate by the Habobeaves Pbocess 128

First attempts, 128 ; preparing the salt, 131 ; generation of sulphurous acid, 137 ; reactions, 137 ; description of plant and process, 138 ; connexions, 142; heating, 146; pyrites-burners, 147; superheating the steam, 149 ; aspiration by Boot's blower, 150 ; fuel consumed, 153 ; utilization of space, 154 ; of sulphur, 155 ; condensation of hydrochloric acid, 156 ; quality of sulphate, 157 ; cost of plant, 158; advantages and drawbacks, 158; present state of the process, 159.

CHAPTER V. Costs, PuBiPioATio»r, akd Application of Sulphate 161

Costs, 161 ; refined sulphate, 166 ; Glauber's salt, 168; applications of sulphate, 169.

CONTENTS. VU

Page

Chapter VI

Historical, 171 ; chemical properties, 171 ; preparation firoxn calciuin and magnesimn chloride, 172 ; properties of dry HG, 173 ; solubility in water, 174 ; table of specific gravities, 176 ; correction for temperature, 177.

Examination, 179 ; impurities, 179 ; estimation, 181.

CHAPTER Vn.

The Condensation of Htdboohlobic Acid. 182

Historical, 182 ; noxious effect of acid vapours, 182 ; first attempts at condensation, 186 ; nuisance, 187 ; legislation in Belgium, 188 ; in England (Alkali Act), 188 ; results of the same, 189 ; principle of cooling the gas, 190 ; Schloesing's process, 191.

Different requirements in condensing HCl, 192 ; special examples, 194.

Stone tanks : French, 196 ; English, 197 ; with bevel joints, 198 ; with grooved joints, 199 ; boiling in tar, 203 ; Newall and Bowman's waterHspray, 203.

Woulfe's bottles (receivers), 205.

Coke-towers, 213 ; general construction, 214 ; defects, 215 ; previous cooling of the gases, 216 ; combination* with tanks, 217 ; description of special plant, 219 ; gas-pipes, 220 ; brick flues, 223 ; metal pipes, 223 ; stone flues, 224.

DetaDs of coke-towers, 226 : foundation, 22Q ; frame, 227 ; stone towers, 228 ; brick towers, 232 ; grating (dome), 233 ; packing, 234; cover and water-supply, 235; acid-cisterns, 237; Gateshead condensers, 238 ; condensers made of earthenware pipes, 238.

Schaffiier's condensing system (Woulfe's bottles and towers combined), 242.

Dimensions of coke-towers, 245.

Coke-towers for open roasters, 251 ; mechanical means for condensation, 251 ; Clapham's system, 251.

Acid-pumps, 255 (Doulton's, 256; Bazlehurst's, 256; Schlotters's^ 258) ; connexion of acid-pipes, 259.

• ••

VUl CONTENTS.

Page

CHAPTER Vm.

COJSTTKYAKCB OF HtDBOOHLOBIC AcID 260

Strong aoid, 260 ; weak acid, employment of, 260 ; stxength as indioated by the hydrometer, 261 ; testing for escape, 262 ; details of condensation, 265 ; results, 267.

Purification, 268 ; applications, 271 ; conveyance, 272.

THIBD BOOK— SODA.

CHAPTER I. Historical, 276

Anhydrous sodium carbonate, 276 ; hydrates, 276 ; solubility, 279 ;

sesquicarbonate, 282 ; bicarbonate, 283.

Natural occurrence of sodium carbonates, 284 ; salt lakes &c., 284. Soda from the ashes of plants, 291 ; barilla, 293.

CHAPTER n.

HiBTOBiOAL Notes on the Manupactube op Abtificial Soda 296

Dearth of potash, 296 ; prices of soda, 297 ; M alherbe's and other contemporary processes, 298 ; Leblanc's invention, 300 ; his subsequent fate, 302 ; Higgins's patent, 304 ; development of Leblanc's process, 305 ; introduction into England, 306 ; drawbacks of the process, 307.

CHAPTER III. Synopsis op the vabious Plans pboposed pob mandpactttbikg Soda . . 309

I. Soda dibect pbom coickon salt : by potash, 309 ; by lime, 310 ; by lead oxide, 310 ; by sdnc oxide, 312 ; by lead or zinc pyrophosphate, 313 ; by sodium phosphate, 313 ; by magnesia, 314 ;

CONTENTS. IX

Pag© by oxalic acid, 314; by magnesinm oxalate, 315; by hydrofluoric and bydrofluosilicic acid, 316; by alumina, 317; by alumina and Epsom salt, 319 ; by aluminium chloride, 319 ; by silica and steam, 319 ; by chromium oxide, 322 ; by carbonic acid, 323 ; by boric acid, 323 ; by ammonium carbonate, 324 ; by calcium sulphide, 324 ; by steam only, 324 ; by the galvanic current, 325.

II. Soda fbom Si7LPha.ie. A. WitTioui converting it into sulphide : by lime, 325 ; by baryta, 326 ; by strontia, 327 ; by calcium, strontium, or barium carbonate, 328 ; by calcium or lead acetate, 331 ; by barium acetate, 332 ; by potassium carbonate, ammonium carbonates, alumina, ferric oxide, 332 ; bauxite, 333 ; by silica, galena, blende, hydrofluoric acid, 335 ; by aluminium phosphate, 337 ; by calcium bisulphite, 339.

B. Soda from sodium sulphide : by coal, 339 ; by acetic acid, 339 ; by calcium or barium carbonate, 340 ; by ferric oxide with heat, 340 ; by carbonic acid, 345 ; (special plans for preparing sodium sulphide, 347 ; Weldon's process, 348 ;) by sodium bicarbonate, 352; by alumina, 353; by ammonium carbonate, magnesia, copper, zinc, lead oxide, 354 ; by ferric or manganic oxide in the wet way, 356 ; by native iron carbonate, 356 ; by sodium silicofluoride, 357.

m. Soda fbox Cbtoute, 357.

Y. Soda pbox Fblbpab, 360.

CHAPTER IV. The Mawtjpactube op Soda by the JjEBLaso Pbocess ; Raw Mate- BIALS

Sulphate, 361; calcium carbonate, 363; chalk, 363; chalk-mills, 364 ; limestone, 365 ; lime-mud, 366 ; soda- waste, 366 ; mixing-coals, 366 (bituminous substance, 367 ; ashes, 367 ; iron, 368 ; substitutes for coal, 368 ; lignite, 371 ; nitrogen as a source of cyanogen compounds, 371 ; analyses of mixing-coals, 372 ; employment of duff, 374).

Mixing the materials, 375 ; proportions, 376,

CONTENTS.

CHAPTER Y.

Page

The BljlcK'ASR FuRNkCEs 380

French fhmaces, 380 ; work in these, 382 ; yarions other furnaces, 383.

Lancashire furnace, 384 ; Tyneside furnace, 386 ; boiling-down pans attached to them, 389 ; drainers, 392 ; liquor-pump, 392.

Work in the black-ash furnace, 392 ; temperature, 394 ; tools, 395 ; reaction of the ingredients, 396 ; finishing, 398 ; turning over, 398 ; size of batches, 400 ; modifications of the ordinary process, 400 ; draught, 400 ; ball-bogies, 401 ; consumption of fuel, 402.

Revolving furnaces, 403; Pattinson's, 404; Elliott and Russell's, 404 ; Stevenson and Williamson's, 404 ; construction by Oarrick and Wardale, 406 ; pans and drainers, 412 ; railway and pots, 413; gas-furnace (Daglish's), 413; method of working, 416; Black and Hill's process, 418 ; Mactear's process, 419 ; Pechiney and Weldon's process, 421 ; other processes for avoiding the formation of cyanides, 425.

Chapter VI

Th£obt of the Soda. Pboosss acgobbiko to Lebliitc 427

Difficulties, 427 ; views of Dumas, 428 ; Unger, 429 ; Brown, 429 ; Xynaston, 430 ; Gossage, 430 ; Scheurer-Kestner, 431 ; £opp, 433 ; P. W. Hoftnann, 434 ; Kolb, 435 ; reply of Scheurer- Kestner, 438 ; formation of carbon monoxide, 440.

CHAPTER yn.

Black Ash and Taitk-liquob 442

Examination of the black-ash by weight, 442 ; by appearance, 443 ; overheating, 444 ; soft balls, 446 ; revolver-balls, 446 ; chemical testing, 446 (for sulphide, 447 ; for sulphate, 448).

Composition of black ash, 449.

CONTENTS. Xi

Page

Behaviour of black aah in the air, 453 ; action of water on black ash, 456.

Liziyiation of black ash, 460 ; general principles, 460 ; porosity of black ash, 461 ; requirements of liziviation, 462 ; oldest apparatus, 463 ; Gl^ment-Desormes^s terrace apparatus, 468.

Modem system of liziyiating^tanks, (Shanks's or Bnff-Dnnlop's), 465 ; invention, 465 ; principle, 467 ; oonstmction, 469 ; lixiviating process, 476.

Tank-waste, 479 ; insoluble soda, 479.

Treatment of revolver-balls, 480.

Other lixiviating-apparatus, 480.

Settling of the tank-liquor, 481 ; analysis of the liquor, 482 ; testing for cyanides, 485 ; iron in tank-liquors, 486 ; as ferro-sodium sulphide, 487 ; as ferrocyanide, 489.

CHAPTER ym.

Pans heated from the top, 491; collecting the black salt, 493; Stevenson's pan, 493 ; draining off the red liquor, 494 ; fishing pans, 495.

Marseilles furnaces for caustic ash, 496.

Pans heated from underneath, 500; German pans, 500; Thelen's mechanical fishing pan, 502 ; boat pans, 502.

Caustic ash, 509 ; systematic separation of the salts, 509.

Gossage's pans, 512 ; Dale's pans, 514 ; Stevenson and Williamson's pans, 514.

Carbonating and oxidizing the liquor, 516 ; Gossage's coke tower, 516; Hargreaves's apparatus, 517 ; treatment with air and CO, together, 518 ; Ludwigshafen process, 519 ; carbonating with fire-gases, 520 ; Ungerer's tower, 522 ; desulphurizing the liquor by Pauli's process, 522 ; b^ Pamell's process, 523.

Finishing the soda ash, 523 ; difficulties, 523 ; operation with caustic salt, 524 ; carbonating furnace, 525 ; Aussig gas ^nace, 527 ; work in the carbonating furnace, 528 ; mechanical carbonators, 535 ; Mactear's, 536.

XU CONTENTS.

Page CHAPTER IX.

CoioosBCiAL Soda. Ash 643

Appearance of good ash, 543 ; impurities, 543 ; sampling, 544 ; testing, 644; commercial degrees in England, Germany, France, 546 ; table of comparison, 549.

Composition of soda ash, 550.

Grinding ash, 553 ; packing in casks, 554 ; reducing strength, 554 ; kelp-salt, 554.

CHAPTER X.

The PuBiriCATioN op Soda Ash 556

Refined alkali, 556 ; dissolving, 556 ; settling, 561 ; boiling down, 562 ; calcining, 563 ; properties, 563.

Crystal soda, 563 ; reasons for making it, 563 ; quality of soda ash^ 565 ; dissolving, 565 ; coolers (cones) — English, 566, French, 568 ; mother-alkali, 569 ; yield, adulterations, 570.

*

CHAPTER XI.

BlCAEBOlTATB OP SoDA 571

Manufacture on the small scale, 571 ; sources of carbonic acid, 571 ;

apparatus, 572 ; process, 573 ; examination, '574 ; applications,

575.

Manufacture of precipitated sulphate of lime (pearl hardening), 576.

CHAPTER XII. '

Yields, 578 ; causes of loss, 530 ; cost accounts, 584.

CHAPTER XIII.

Caustic Soda 588

Properties, 588 ; solubility, 588 ; chemically pure caustic, 590 ; manufacture of sodium, 590 ; caustic liquor, 591.

CONTENTS. Xlli

Page

Maofactare of solid caustic, historical, 592 ; black-ash miztares for caustio, 595 ; causticizing, 595 ; filtering, 598 ; lime mud, 600 ; composition of liquors, 601 ; desulphurizing, 602 ; concentration of the liquor, 603 ; in steam-boilers, 603 ; in boat pans, 604 ; fished salts, 605 ; addition of nitrate, 607 ; other methods of concentrating, 609; finishing in the pots, 611; nitreing and blowing, 616 ; economizing nitre, 618 ; sampling, 618 ; settling, 619 ; packing, 620 ; bottoms, ^22; Ifatrona patent saponifier, 623 ; analyses, 623.

Grystallixed caustic, 625.

Cream caustic, 626 ; factitious potash, 628.

Costs, 628 ; applications, 631.

CHAPTER XIV.

Taot-wastb 632

Composition, 632 ; change in the air, 632 ; treatment with air and MnO,, 633.

Heaps of tank-waste, 633 ; yellow liquors, 636 ; abatement of nuisance from them, 637 ; removal of tank-waste, 637 ; applications of the same, 638.

Utilization of the sulphur of tank-waste, 639 ; factitious pyrites, 640.

Utilization of sulphuretted hydrogen, 641 ; by burning, 641 ; by mixing with SO,,, by ferric oxide, &c., 648.

Various plans for utilizing the sulphur, 650.

Becoyery of the sulphur, 652 ; historical, 652.

Schaffner's process, 653 ; oxidation of tank-waste, 654 ; residue from Hxiyiation, employment as cement, 656 ; processes of oxidation, 657 ; Eraushaar's process, 658 ; sulphur-liquors, 659 ; decomposition by hydrochloric acid in Schaffiier's apparatus, 660 ; melting the sulphur precipitate in Schaffiier's apparatus, 665 ; purification by injection of air, 667.

Mond's process, 667 ; system of tanks, 668 ; composition of liquors, 673 ; acid for decomposing, 675 ; process of same, 680 ; melting the sulphur, 683 ; yield, 684 ; combination with Schaffiier's process, 685.

Hoftnann's process, 685.

Schaffner andHelbig's process for recovering all the sulphur and lime.

XIY CONTENTS*

Page

689 ; operations, 689 ; apparatus, 689 ; apparatus, 692 ; details of process, 694 ; Aarland's modification, 695, Treatment of drainage from old tank-heaps, 696; Mactear's process, 696 ; Dr. Snuth's process, 698.

CHAPTER XV.

Htposulphize oj Sojoa 700

Properties, 700 ; (^lability, 701 ; examination, 702 ; action as antichlorine, 703 ; manufacture, 703 ; from tank-waste^ 705. Calcium hyposulphite, 707* Applications, 707.

SECOND BOOK.

SULPHATE OF SODA

AND

HTDBOCHLOEIC ACID.

VOL. II. B

Chapter I. General Notes On Sodium Sulphate

'^ Sulphate ^' and '' saltcake '^ are the teclinical names for neutral sodium sulphate (calcined Glauber's salt) . Two thirds or perhaps three fourths of all the sulphuric acid made are employed for making sulphate ; and a certain (but not comparatively very large) quantity of this substance is also produced in other ways. Not very much sulphate is sent into the trade as such^ most of it being converted into alkali at the alkali-works ; but a not inconsider* able number of manufacturers do not go beyond sulphate^ with^ of course, muriatic acid, bleaching-powder, &c. as by-products. These sell their sulphate to glass-makers, alkali-makers, and so forth.

Historical notes (comp. Kopp, ^ Geschichte der Chemie,^ iv. p. 40) . — Sodium sulphate was first described by Glauber, in his treatise 'DeNatura Salium' (1658). He made it from the residue remaining after the preparation of hydrochloric acid from common salt and sulphuric acid, and gave it the name sal mirabile, recommending it urgently for internal and external use ; later on it was called after himself, sal mirabile Glauberi. Kui^l, however, in his ' Laboratorium Chymicum ' (1716), asserts tfi^ Glauber's salt had been known as an arcanum to the Electoral house of Saxony 100 years before Glauber. On a large scale it was first produced from salt-brine at Friedrichshall in Hildburghausen, and has been known since 1767 as sal aperitivum FHdericianum or Friedrichssalz.

Properties of Sodium Sulphate.

The anhydrovs salt is obtained in a pure state by dehydrating crystallized sulphate of soda, or by evaporating the aqueous solu-

b2 tion at temperatures above 33° C.*; from strongly alkaline solutions anhydrous salt crystallizes out even at ordinary temperatures. In an impure state it forms the " sulphate '' or saltcake of the factories. It crystallizes in the rhombic system^ with an octahedral habit ; its specific gravity is 2*655 (at the fusing-point^ 2*104). It melts to a thin liquid at a strong red heat; Camelly (Journ. Chem. Soc. 1878, ii. p. 280) states that the melting-point is 861^. At a white heat it volatizes ; at the heat of melting iron it begins to boil and evaporates rapidly. The residue of incomplete evaporation has an alkaline reaction. On being ignited with coal it is reduced to hepar, according to the following equation : —

Carbon monoxide is not given off in this reaction ; on the other hand, carbon monoxide does not reduce sodium sulphate at all, or only very slightly. A current of hydrochloric acid gas at a red heat converts sodium sulphate entirely into sodium chloride, sulphuric acid being set free (Boussingault) ; according to Hensgen (Dentsch. chem. Ges. Ber. ix. 1672), with anhydrous salt a pretty high temperature is required for this reaction ; but crystallized sodium sulphate is completely decomposed even at ordinary temperatures. {This matter will be treated at greater length in Chapter VI.) When sodium sulphate is ignited with calcium carbonate there is no decomposition (Scheurer-Kestner and Kolb), which is of importance for the theory of the soda-process. A mixture of Na8S04 with AI3O3 is not changed even at a prolonged red heat ; but this takes place in the presence of water, and with especial facility in the presence of coal — sodium aluminate being formed. Fused with silica and coal, it yields silicate of soda ; on fusion with iron and caustic soda, Fe304 and the sulphate of iron and sodium are formed. Its solution is decomposed very incompletely by milk of lime, into calcium sulphate and caustic soda; but according to Tessie du Motay (Deutsch. chem. Ges. Ber. v. p. 741), at a pressure of 2 to 20 atmospheres 75 to 80 per cent, of the sodium sulphate are causticized by lime.

* According to Thomsen (Beutsch. chem. Ges. Ber. zi. p. 2042) this is not anhydrous, but the monohydrated salt, SO^Na^ H,0.

Composition of sodium sulphate.

AnhydroUB. With 7 H,0. With 10 H.O.

The anhydrous sodium sulphate attracts moisture eveD in the air, but more so in its mother liquor, in which it soon passes oyer into the salt with 7HgO, It dissolves in water at +21''-5 C. and higher temperatures with evolution of heat, hut at +3° with ab- Borption of heat. From its solution, at temperatures above 33°, again anhydrous salt crystallizes; but below SS'', either the salt with 7 or that with lOHgO — the latter under most conditions, the former, for instance, &om hot solutions when they cool while kept from contact with air by means of alcohol. The solutions show the phenomenon of aupersatiiration in the highest degree. According to Coppet (Compt. Rend. Ixxviii. p, 194), two isomeric modifications of anhydrous sodium sulphate exist : — «, formed by crystallized salt efflorescing at ordinary temperatures ; |3, by heating above 33°. Only the a modification causes by contact the crystallization of supersaturated solutions.

The tali with 7 H,0 (for composition and preparation see above) forms quadrilateral prisms, with two inclin^ end fiioes (fig. 1), transparent and much harder than Fig. 1.

the decahydrated salt. The crystals in the air become dull and even rough ; also under their mother-liquor they become dull from the forma* tion of the decahydrated salt.

7^ »ali with 10 Hg 0 (for composition see above) is the crystallized Glauber's »aU proper, which separates &om its solutions by evaporation in the open aSx or by cooling below 33°, with considerable evolution of heat. It forms very large, transparent crystals of the monoclinic system, often with many faces and, by the development of the vertical faces, assuming a long prismatic form (fig. 2). Sp.'gr. 1-471. It baa a cooling, afterwards hitter taate, and neutral reaction. It efilorescea in the »r, falling into a whit« powder, and loses the whole of its water, supposing the air to be pretty dry — for instance, in air of 14"-5 C. whose dew-point is at 9°-5. At 33° it melts in its water of crystallization with separation of one portion as anhydrons salt. In water it dissolves, with absorption of heat; for

SULPHATE OF SODA AND HYDROCHLORIC ACID.

Fig.2.

instance^ on mixing 20 parts of crystals with 100 water at 12°*5 the temperature falls to 5°*7 (Riidorff) ; on mixing 240 grams of crystals with an equal quantity of water at 18°^ the temperature falls to 7° or 8° (Hanamann) .

The solubility of the decahydrated salt in water rises from 0° to 84° C. with the temperature. At 34° and above, the solution only contains anhydrous salt, whose solubility, inversely, rises continuously on cooling from 103°*17 (the boiling-point of the saturated solution) down to 18° or 17°. Below the latter temperature the anhydrous salt cannot exist in the presence of water, but, if protected from the air, is changed into heptahydrated, with access of air or in contact with crystals into decahydrated salt. The salt with 7 HgO dissolves from 0° to 26° in increasing quantity, to the greatest extent at the latter temperature, and already at 27^ is transformed into anhydrous salt. Thus sodium sulphate for temperatures from OP to 18° presents a doubly, from 18° to 26° a triply, from 26° to 34° again a doubly different, and above 34° always the same solubility, as proved by many experiments^ of Loewel's (Ann. Chim. Phys. [3] 49, p. 32). Loewel states that the boiling-point of the saturated solution =103°*1 7; Mulder, = 103°'5; Kremers, =105°; Gerlach, ±=100^-8. The freezing-point is for each gram S04Na5 in 100 cub. centims. water lowered by 0°*297 C. (Riidorff) . Supersaturated solutions solidify by themselves at — 8° C, or at the ordinary temperature on contact with a crystal, with a glass rod, &c.

According to Gay-Lussac, 100 parts of water dissolve at the following temperatures : —

GENERAL NOTES ON SODIUM SULPHATE.

o

SO^Na,.

SO^Na^+lOHjO.

5*02 parts.

12-17 parte

11-67

10-12

26-38 „

13-30

11-74

31-33 „

17-91

16-73

48-28 „

25-05

28-11

99-48 „

28-76

87-35

161-53 „

30-75

215-77 „

31-84

47-37

270-22 „

32-73

50-65

32212 „

33-88

312-11 „

40-15

48-78

291-44 „

45-04

47-81

276-91 „

50-40

46-82

262-35 „

59-79

45-42

70-61

44-35

84-42

42-96

103-17

42-65

Solubiliiy of the three Modifications of Sodium Sulphate according

to Loewel.

Temperature.

Anhydrous salt.

Salt with 10 HjO.

Salt with 7 HjO.

100 parts water contain in the saturated state

100 parts water contain in the saturated state

100 parts water contain in the saturated state

BO^Naj.

Calculated as SO.Na.

H-IOH^O.

Calculated as SO^Naj.

SO.Na. +10HaO.

Calculated as SO^Naj.

SOJTaa +76^0.

Calculated as SO.Na. +IOH2O.

12-16

85-96

48-41

58 35

98-48

109-81

184-09

32313

412-22

SULPHATB OF SODA AND HTDROCHLORIC ACID.

Specific Gravity of the Solutions of Sulphate of Soda at different Degrees of concentration at 15® C, according to Gerlach.

FwMnt.

SO.Na^

so«y«j+iOH,o

10091

10182

10274

10363

10457

10530

10641.

10737

10832

10927

1-040

11023

104*

1-060

1-064

1-069

1-073

1-077

SO

1-066

1-090

1*094

1-098

1-103

1-111

1-116

1-120

SO

GBNKBAI. NOTES ON 80DIUU SULPHATE.

At 19°, according to Schiff (Ann. Chem. Pharm. ex. p. 70)

Speo. gnr.

Per cent.

N»,SO<+10H,O.

Per cent.

0-882

1-323

1-764

2-205

2-640

3-087

3-528

3-969

4-410

4^851

5-292

5-783

7^497

10143

10^584

11025

11466

11-907

12348

12789

13-230

Sodium sulphate is almost insoluble in absolute alcohol at ordi« nary temperatures, a little more so in alcohol acidulated with sulphuric acid. Therefore alcohol precipitates sodium sulphate from a saturated cold solution. In dilute alcohol it is more soluble; the saturated solution, according to Schi£P (Ann. Chem. Pharm. cxviii. p. 365) contains at 15° C. : —

10 SULPHA.TS OF SODA AND HYDROCHLORIC ACID.

Alcohol of spec, gray,

Per cent C^Kfi by weight.

0 10

Per oent. of SO«Nij+10H,O.

25-6 14-35

0-972

5-6

0-939

1-3

It is soluble in glycerine^ less so in strong acetic acid^ soluble in hydrochloric acid with strong evolution of heat, but with decomposition (see above) . In some saline solutions it is more easily soluble than in pure water — for instance, in solutions of potassium sulphate, magnesium sulphate, potassium chloride, potassium nitrate, in which cases of course all the bases in the solution must be regarded as combined or combinable with all the acids. On pounding together sal-ammoniac and Glauber's salt, the dry mixture becomes damp, the temperature being lowered at the same time, and a mixture of ammonium sulphate, sodium chloride, and water being formed, of which the latter previously existed in the crystals.

The other sodium sulphates, except the neutral one, have no technical importance by themselves, and only serve as transition stages in the manufacture of the neutral sulphate ; we will now describe them very briefly.

1. Three-quarterS'Saturated sulphate, If 9i^{^0^^, observed by Thomson and Mitscherlich, crystallizes first on recrystaUizing the semisaturated sulphate. Brilliant, often needle-shaped crystals of the monoclinic system, with many faces, stable in the air.

2. Hydrosodic sulphate {acid sodium sulphate, sodium bisuU

ONa phate). S04NaH=S0a<(^TT • Formed by heating common salt

with two equivalents (=one molecule) of sulphuric acid, or of neutral sulphate with more sulphuric acid ; on dissolving it in hot water and evaporating it above 50° C, anhydrous crystals, and by cooling hydrated crystals are separated.

a. The anhydrous crystals are transparent. Fig. 4.

long, quadrilateral prisms with oblique end faces (fig. 4), very brilliant also on drying; in the air they quickly become dull, without deliquescing. Sp. gr. 1-8. They melt at 14SP (Thomson), or above 816° C. (Graham), without any decomposition, and only at a higher

OXNSRAIi NOTES ON BODIITIC SULPHATE .

remoius behind temperature give out sulphuric acid. According to Kraut one portion splits up into sulphuric hydrate and neutral salt^ another into water and pyrosulphate : 2S04NaH=Na8Sj07+H20. Water decomposes the salt into neutral sulphate and free sulphuric acid; in moist air^ lying on blotting-paper^ the crystals (as also those of 6) leave effloresced neutral salt behind. Alcohol deprives the powdered salt of all free acid.

b, Hydrated saU, S04NaH, H^O, often forms very large^ transparent crystals of the monoclinic system (figs. 5 & 6) which mostly have a prismatic appearance. They attract water in moist air.

3. Quarter-saturated sulphate, S04NaH^ S04Hs^ crystallizes on cooling a solution of 1 S04Nas in not quite 7 SO4H3. It fuses at about 100^. Long^ colourless, brilliant prisms.

SOj-ONa

4. Sodium pyrosulphate , SsOjNass ^O ^

SOj-ONa on heating sodium chloride with sulphuric anhydride

(2 NaQ + 4 S08=Na,S,07 + SaOjCla, Bosenstiehl) and on igniting the acid sulphate (compare No. 2); it is also separated along with the latter from a solution of sulphate in fuming oil of vitriol j it can also be precipitated from the fuming oil of vitriol of trade (in which it always occurs) by boiling nitric acid, aqua regia, chlorine, ether, or alcohol. It probably also occurs in ordinary fomaced saltcake. Exposed to a bright red heat it splits up into neutral sulphate and sulphuric anhydride, according to the equation SsOrNa^ = S04Na, + SO^; this is the cause, at least partly, of the thick white vapours which calcined saltcake emits on being drawn out of the furnace.

The sulphate or saltcake of trade is a more or less finely granulate mass, often containing larger lumps of melted substance ; the latter are always to be suspected of containing a high percentage of sodium chloride, and often entirely consist of this internally. The finer grain a sulphate possesses, the better it is on the whole. Its colour when hot, as it is drawn out of the furnace, is a bright Jemon-yellow — if very rich in free acid, even brownish — ^if much iron is present, brownish red. In the cold it is yellowish or greenish white, often pure white. A dirty grey colour and a granular fritted consistence show that the decomposition of the common salt is incomplete.

The analyses given on p. 13 show the composition of commercial sulphate.

The following analyses by Theilkuhl (from Enapp, ii. p. 396) show the " free acid ^' as acid sulphate : —

From p From Prom

Nienburg. Liineburg. Oker.

(That from Oker is eyidently nitre-oake.)

Analysis of Sulphate.

Pure sulphate IS quite white^ forms a clear solution in water^ has a neutral reaction^ shows no trace of chlorine when treated with silver nitrate^ does not throw down any precipitates under the action of sulphuretted hydrogen^ ammonium sulphide^ sodium or ammonium carbonate^ or potassium ferrocyanide. The sulphate of trade is tested in the following way : — Mostly only the foreign constituents are estimated^ and the pure S04Nas calculated from the difPerence. If one only wants to test the sulphate for one^s own use (for alkali-making) j where it is only a check on the manufacture^ the following simple process is sufficient : 10 grms. of sulphate are weighed, dis* solved in 200 cub. centims. warm water, 20 cub. centims. (==1 grm.) taken out with a pipette, and, after litmus has been added, neutralized with standard caustic; by this the free acid is found. A second sample of 20 cub. centims. is neutralized by the same quantity of caustic as was required in the first test ; and a few drops of potassium chromate are added, and the NaCl titrated by silver solution. If, on the other hand, an analysis is to be made /or sale, a somewhat more accurate process must be employed. 10 grms. are calcined in a porcelain dish with the addition of a little ammonium carbonate, and weighed again, by which operation the moisture and the free acid are found. The latter is estimated by itself in a fresh uncalcined sample in the same way as described above. The calcined sulphate is dissolved in water and filtered^ the