'■ • -1 ’A. - - VI ’P*'; :;ffi gj. mTOffwWiiii^iV wi Ife* 1 c * n -- I. c. s. REFERENCE LIBRARY A SERIES OF TEXTBOOKS PREPARED FOR THE STUDENTS OF THE INTERNATIONAL CORRESPONDENCE SCHOOLS AND CONTAINING IN PERMANENT FORM THE INSTRUCTION PAPERS. EXAMINATION QUESTIONS. AND KEYS USED IN THEIR VARIOUS COURSES SULPHURIC ACID ALKALIES AND HYDROCHLORIC ACID MANUFACTURE OF PAPER SCRANTON INTERNATIONAL TEXTBOOK COMPANY 199 Copyright, 1902, 1905, by International Textbook Company. Entered at Stationers’ Hall, London. Sulphuric Acid: Copyright, 1902, by International Textbook Company. Entered at Stationers’ Hall, London. Alkalies and Hydrochloric Acid, Parts 1,2,and 3: Copyright, 1902, 1909, by Inter¬ national Textbook Company. Entered at Stationers’ Hall, London. Alkalies and Hydrochloric Acid, Part 4: Copyright, 1902, by International Text¬ book Company. Entered at Stationers’ Hall, London. Manufacture of Paper: Copyright, 1902, 1910, by International Textbook Com¬ pany. Entered at Stationers’ Hall, London. All rights reserved. Press of International Textbook Company Scranton, Pa. 199 29821 THE GETTY CENTER LIBRARY PREFACE Formerly it was our practice to send to each student entitled to receive them a set of volumes printed and bound especially for the Course for which the student enrolled. In consequence of the vast increase in the enrolment, this plan became no longer practicable and we therefore con¬ cluded to issue a single set of volumes, comprising all our textbooks, under the general title of I. C. S. Reference Library. The students receive such volumes of this Library as contain the instruction to which they are entitled. Under this plan some volumes contain one or more Papers not included in the particular Course for which the student enrolled, but in no case are any subjects omitted that form a part of such Course. This plan is particularly advan¬ tageous to those students who enroll for more than one Course, since they no longer receive volumes that are, in some cases, practically duplicates of those they already have. This arrangement also renders it much easier to revise a volume and keep each subject up to date. Each volume in the Library contains, in addition to the text proper, the Examination Questions and (for those subjects in which they are issued) the Answers to the Examination Questions. In preparing these textbooks, it has been our constant endeavor to view the matter from the student’s standpoint, and try to anticipate everything that would cause him trouble. The utmost pains have been taken to avoid and correct any and all .ambiguous expressions—both those due to faulty rhetoric and those due to insufficiency of state¬ ment or explanation. As the best way to make a statement, explanation, or description clear is to give a picture or a iii IV PREFACE diagram in connection with it, illustrations have been used almost without limit. The illustrations have in all cases been adapted to the requirements of the text, and projections and sections or outline, partially shaded, or full-shaded perspectives have been used, according to which will best produce the desired results. The method of numbering pages and articles is such that each part is complete in itself; hence, in order to make the indexes intelligible, it was necessary to give each part a number. This number is placed at the top of each page, on the headline, opposite the page number; and to distinguish it from the page number, it is preceded by a section mark (§). Consequently, a reference, such as §3, page 10, can be readily found by looking along the inside edges of the headlines until § 3 is found, and then through § 3 until page 10 is found. International Correspondence Schools CONTENTS Sulphuric Acid Section Page Introduction. 1 1 Principles Governing the Manufacture of Sulphuric Acid. 1 7 The Production of Sulphur Dioxide or Burner Gas. 1 21 Furnaces and Burners for the Production of Burner Gas. 1 23 Brimstone Burners. 1 25 Pyrites Burners. 1 27 Testing the Burner Gas . 1 36 Calculation of Volume of Burner Gas ... 1 40 The Catalytic, or Contact, Process .... 1 43 The Chamber Process.2 1 Apparatus Employed in the Chamber Proc¬ ess . 2 5 Surface Condensers. 2 16 Operation of the Chamber Process .... 2 28 The Purification of Chamber Acid .... 2 42 Concentration of Dilute Acid Solutions and the Production of Sulphuric Monohy¬ drate . 2 48 Alkalies and Hydrochloric Acid Sodium Chloride. 3 1 Sodium Carbonate. 3 9 The Solvay Process. 3 11 Cryolite-Soda Process. 3 33 Salt Cake. 3 35 v VI CONTENTS Alkalies and Hydrochloric Acid— Continued Section Page Crude Materials for Salt Cake. 3 36 Apparatus and Method of Manufacture of Salt Cake. 3 33 Soda by the Le Blanc Process. 3 43 Sodium Hydrate. 4 1 Sodium Bicarbonate. 4 \ \ Hydrochloric Acid. 4 12 Chlorine. 4 25 Deacon’s Process for Chlorine. 4 39 Nitric-Acid Chlorine Process. 4 45 Potassium Chlorate. 4 54 Electrolytic Methods. 5 1 Electrolytic Preparation of * Alkali and Chlorine. 5 23 Fused Electrolyte. 5 26 Hulin’s Process. 5 26 Acker’s Process. 5 28 Dissolved Electrolyte . 5 30 Processes Using Diaphragms. 5 31 Processes Using a Mercury Cathode ... 5 39 Electrolytic Bleach . 5 44 Analytical Methods. 6 1 Ammonia Soda. 6 1 Salt-Cake Process. 6 17 Le Blanc Process. 6 20 Sodium Bicarbonate. 6 32 Caustic Soda. 6 32 Hydrochloric Acid. 6 36 Chlorine, Bleaching Compounds, Chlorates 6 41 Manufacture of Paper Development of Paper Manufacture ... 16 1 Paper-Making Materials.16 2 Manufacture of Pulp. ...16 7 Esparto Pulp.16 12 Pulp from Straw, Jute, and Other Materials 16 13 CONTENTS v ii Manufacture of Paper —Continued Section Page Wood Pulp.16 14 Mechanical Process .16 14 Soda Process.16 19 Recovery of Soda.16 34 Sulphite Process.16 42 Bleaching and Beating.17 1 Bleaching the Various Fibers.17 1 Beating.17 16 Sizing.17 21 Loading.17 27 Coloring.17 28 Manufacture of Paper from Pulp .... 17 30 Making of Paper by Hand .17 30 Making of Paper by Machine.17 31 Water and Its Purification.17 46 Filters.17 50 Analyses and Tests of Materials Used and of Finished Products.18 1 Apparatus and Chemicals.18 1 Analytical Methods.18 11 SULPHURIC ACID (PART 1) INTRODUCTION 1. General Remarks and Definitions. —Before consid¬ ering the technology of sulphuric acid ,, it is of the greatest possible importance to have a clear idea as to just what sul¬ phuric acid is and the place it occupies among the oxides and acids of sulphur. The technical processes to be described, instead of seeming complicated will then appear consequent and logical, and the bewildering chemical and commercial terminology with which the evolution of the manufacture has incrusted the subject will be cleared away, or at least will be more readily understood. 2. Hydrates and Solutions of Sulphur Trioxide'. —It was stated in Inorganic Chemistry that sulphur trioxide S0 3 when absolutely pure is a colorless, mobile liquid of 1.940 sp. gr. at 16° C., and when cooled it solidifies into long, trans¬ parent prismatic crystals. If a little water is added, a mass of opaque, white, asbestos-like crystals will result, which melt at about 50° C. If 10.11 per cent, of water is added to the pure sulphur trioxide, a transparent crystalline mass is obtained, melting at 35° C. and readily decomposing at moderate heat into H 3 SO i and S0 3 . If 18.37 per cent, of water is added to pure sulphur triox¬ ide, a limpid, colorless, oily fluid is obtained of 1.8372 sp. gr. COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL. LONDON §1 199—2 2 SULPHURIC ACID 1 at 15° C. (Lunge 1.8385), which solidifies at 0° C. into large, plate-shaped crystals and readily decomposing at moderate heat into H\0 and SO s . If 31.04 per cent, of water is added to the pure sulphur trioxide, large, clear, hexagonal, columnar crystals that melt at 8.5° C. are obtained. All these mixtures of pure sulphur trioxide and water, or solutions of sulphur trioxide in water, possess characteris¬ tics, such as crystallization, melting points, change of vol¬ ume, etc., that show them to be definite chemical compounds or hydrates of sulphur trioxide. Again, if from 14 to 18 per cent, of water is added to pure sulphur trioxide, a thick, oily liquid that throws off dense white fumes on exposure to the air is obtained. These fumes are the vapor of sulphur trioxide combining with the moisture of the air and forming a non-volatile hydrate. If 23.67 per cent, of water is added to the pure sulphur trioxide, a thick, oily liquid is obtained of 1.835 sp. gr. and stable at ordinary temperatures. This is the oil of vitriol of commerce, or 66° Baume sulphuric acid (in the United States). In the same way, water may be added in other percent¬ ages; in some cases hydrates, but nearly always simply solu¬ tions, result. 3. If these hydrates exist at low temperatures as definite crystalline compounds, and if on a rise of temperature they all decompose with more or less ease with the disengage¬ ment of either sulphur trioxide or water, and if in their ordi¬ nary form they present all the properties of simple solutions, it follows that between sulphur trioxide 5(9 3 and water H % 0 there exists a consecutive series of homogeneous liquids or solutions, among which must be distinguished definite com¬ pounds, or hydrates; therefore, it is quite justifiable to look for other definite compounds between sulphur trioxide and water, which are distinguished by the variation of proper¬ ties of any kind uniformly occurring with a solution of any uniform percentage of sulphur trioxide and water. Few of ooooooooo O') C/J O') (/) O') O') O') o>) O') 8SxSS$Si^ ,, x II II II II II II II II II S o w oq3.o35^ - h 1 CO>WCOO»H ++++++++ ooooodooo o a, 2* g ’ll II * li? m $82 ^ 888 8 ~~ •sj OOiO o p 888 0 ) lOBrH i_J* vi i~ ci l> 05 £-50 88 5J8«8fc58SgS8?SXa8SSt5*asafcS8S5»8RaSS8SSa!SeS8PS!8 :8B88S888S8S8te8aSa88SS8Si8S|S8S|8SgSSgSSSSSS OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOlD 00 CO I>-CO CO CO C 051-H rH CQ CO CO lO CO CO ^ ^ ^ ^lO l£5 lO IC5 lO IC5 lO lO CO CO CO CO CO CO CO I> « i:- ;S88888S8882382? icSSjSSjeooScSwOTeoeow-rTr' 588888888288? 5 O) »H pHlD00C3CDO ■^(NHCDOCD-^COrHCDCOCD^COrHO OQ ^ CO l> 0 > rH CO ID t> 00 O OQ Tjj CD OO O 060606000003030303030 030030303030303030303030303030 ;82SS2giSg8§383SSEk oit-oi5’rj5«s22SbSH33IS ^r^HHH'HH'TPH'H'COOjCOCOCOCCC JOCOCOOCDCOOO-COOO-'^Ot^'^rHO- > OCOI> H 0003 ID 03 CO CD O Ttl i— UO 00 4 000(0 ID CO pH o 00 O ID CO C3 O 00 O'- ID CO 5 OHCOID t> 03 rH 03 Th CD 00 O 03 CO ID C> 03 ) *--HH pH rH iH0303 03 03 03CO CO CO CO CO CO 3 0303® 0303030303 03030303030303 0303 • wMi-caxNcooH'rtWHOcaxN t- t»i- w ^ o J r—(D'-^rHC-T^rHCO^ rHOOlDrH C0LDC300 H LD00C3 CC 03 03 OOO rH ID0303 CD O CO -IDC0C3O00 0*10-^03 00310^03^- 03 3 C-® H CO Th CD 00 O 03 rtj ID 03 i-H CO ID CD h ID ID ID ID ID CD CD CD CD CD CD C> O-O-1> 0 OOOOOOCO0000000000000000000000OO 00 ssgggss D Dt-oi o D O* A ® C3 03 © J2 OC ClCi 03 O ?OCOCDr^l>00CD ^3G3COrHC^fHC3 -H!>C003COC300 X> OH C3 CO ID CD 30000000000000 8S 8g* xx $xx go 0“^ Su St . CO CD CO 2? SS88 >A ’S' Q ^ x « 3 2 p ^ J3 0 O £ <° ? 6 -~3 e r/] 'H <8 « ° b o. u 3 o +J 'C : Wi rt’S o ft « <4-4 ^ CU •g E § x .5 o 4 ) l. ^S3c J2 > O 8 ^ 58383S 1 SULPHURIC ACID 3 these variations of properties of definite solutions have been determined with sufficient accuracy. In other words, the term sulphuric acid is the generic name of a series of solutions of sulphur trioxide in water, some of which are chemical hydrates of the sulphur trioxide and most of which are merely solutions of convenient strength for use in the arts. 4. In Table I are given the principal characteristics of the various commercial solutions of sulphur trioxide in water. The best known hydrates are also shown. It will be noticed that none of the hydrates are recognized com¬ mercially. 5. Nomenclature of Solutions and Hydrates of Sul¬ phur Trioxide. — The term sulphuric acid is usually applied to the monohydrate of sulphur trioxide S0 3 ,H 3 0, and yet at the same time it covers the whole range of hydrates and solutions containing a smaller percentage of SO a than the monohydrate, and also the hydrates and solu¬ tions containing more S0 3 than the monohydrate. As the moment that moisture is added to sulphur trioxide it becomes an acid, the term sulphuric acid therefore applies to the whole range of hydrates and solutions of S0 3 in water. There is no reason why the monohydrate should monopolize the term sulphuric acid other than the fact that it marks the margin of the acids of sulphuric trioxide that are stable in liquid form at ordinary temperatures; and even this is not quite correct, as the actual monohydrate itself, even at 40° C., begins to give off fumes of sulphur trioxide, and even in a dry atmosphere becomes weaker until it con¬ tains 1.5 per cent, of water. At this point, however, it really becomes stable, so far as the separation of the sulphur trioxide is concerned, and in a dry atmosphere will remain unchanged. It is this sulphuric acid that contains not more than 98.5 per cent, of H t SO v or 80.41 per cent, of S0 3 and 19.59 per -cent, of water, that it has been possible to make by the 4 SULPHURIC ACID §1 so-called chamber process , aided by concentration (evapo¬ ration of water) and by distillation, and which has therefore been commercially available. If stronger acid were required, recourse to the fortification of this acid by sulphur trioxide made at great cost was necessary. The 80.41-per-cent. S0 3 , or 98.5-per-cent. fJ 3 S0 o or as near to it as possible, was fortified with sulphur trioxide until it became 81.63-per¬ cent. S0 3 acid (monohydrate), and if a greater strength or a so-called fuming acid were required, more sulphur trioxide was added, and the acid thus fortified considered as the mono¬ hydrate plus a certain percentage of free sulphur trioxide. 6. Nordhausen or Fuming Sulphuric Acid.—As until comparatively recently the only commercial sulphur trioxide was produced as a fuming or IVordhausen acid (i. e., an acid containing a greater percentage of sulphur trioxide than the monohydrate) and very costly to make, every effort was made to bring the chamber acid to its greatest strength (to eliminate by evaporation as much water as possible). For, as the proportion of sulphur trioxide to water in monohy¬ drate is 81.63 to 18.37, every part of water in the acid to be fortified first requires 4.444 parts of sulphur trioxide to form the monohydrate before any so-called free sulphur trioxide or H 3 S0 i ~p S0 3 is obtained. With the one exception of pyrosulpluiric acid, disulphuric acid, or solid oleum, terms applied to the hydrate H 3 S 3 0^ or 2S0 3 -f- H 3 0, there is no nomenclature that covers the whole range of acids from the monohydrate, or 81.63-per-cent, sulphur trioxide, to the sul¬ phur trioxide itself, except the terms fuming or Nordhausen acids; the first is descriptive of a characteristic of these acids and the second is the name of a town in Prussian Saxony where a warehouse for the storage of these acids was located, the factories being at Braunlage, Goslar, and other places. As, therefore, the term sulphuric acid is used not only to define the actual sulphuric monohydrate, but also to describe the whole range of hydrates and solutions of sul¬ phur trioxide, it becomes necessary for accurate expression 1 SULPHURIC ACID 5 to define the hydrate or solution referred to in terms of per¬ centage of sulphur trioxide contained in it. When acids stronger than commercial oil of vitriol (76.33 per cent, of S0 3 ) were rare and acidum sulphuricum distillatum (80.41 per cent, of S0 3 ) was the strongest commercial acid known, it was, of course, natural that the strength of all acids should be referred to the monohydrate, or nearest, hydrate. 7. Commercial Methods for [Determining the Strength of Solutions Weaker than the Monohydrate. For ascertaining the strength of those solutions weaker than the monohydrate, recourse is had to their specific gravity—a fairly accurate method up to a certain point, but uncertain just about the reference point (monohydrate), as in passing from 79.99 per cent, of S0 3 (98 per cent, of H t S0 4 ) to 81.63 per cent, of S0 3 (100 per cent, of H 3 SO 4 ) the specific grav¬ ity decreases from 1.8415 to 1.8372. The specific gravity, however, rises just so soon as the monohydrate point is passed and S0 3 is slightly in excess. In commercial acids a further cause of inaccuracy exists, owing to the effect on the specific gravity of the almost con¬ stant impurities present. Furthermore, commercial methods of observing the specific gravity are neither uniform nor accurate, even apart from the inaccuracy of the instruments themselves. 8. Specific-Gravity, or Density, Determinations.— The hydrometer used in connection with sulphuric acid is simply an instrument for determining its specific gravity, or density, in comparison with distilled water at 15° C. (or 60° F. in the United States). With commercial acids the use of the hydrometer should be limited to the solutions contain¬ ing up to 76.33 per cent, of S0 3 (93.5 per cent, of N 3 S0 4 ). Specific-gravity determinations beyond this point are unre¬ liable on account of impurities in the acid, and all deter¬ minations above this point should be made alkalimetrically. Apparently, it should be easy to make the hydrometric scale an exact basis of universal calculation, but in practice there are many different hydrometer scales. One of the 6 SULPHURIC ACID §1 difficulties is the uncertainty as to the standard of maxi¬ mum density. In Europe this is generally understood to be 1.842 sp. gr. at 15° C., or 06° Baume. As this specific gravity would correspond to a fuming acid, it is difficult to see on what this standard is based. The specific gravities of solutions of sulphur trioxide, just between 97 and 100 per cent, of d/ 3 SO t (79.19 and 81.63 per cent, of S0 3 ), are given in Table II. TABLE II SPECIFIC' GRAVITY OF SOLUTIONS OF SULPHUR TRIOXIDE HtSO* S0 3 Specific Gravity 97.00 79.19 1.8410 97.70 79.76 1.8415 98.20 80.16 1.8410 98.70 80.57 1.8405 99.20 80.98 1.8400 99.45 81.18 1.8395 99.70 81.39 1.8390 99.95 81.59 1.8385 100.00 81.63 1.8372 9. In England, the Twaddell scale starts with a maxi¬ mum specific gravity of JL.850, or 170°. Each intermediate degree represents a difference of .005 in specific gravity. In the United States, the Baume scale is also used, the 66°, however, corresponding to 93.5 per cent, of H t S0 o or 76.3265 per cent, of S0 3 , or a specific gravity of 1.835. The modulus, or formula of division, where d = specific gravity and n — the number of degrees, for the European Baume is , 144.3 ~ 144.3 and for the United States Baume is 145 i ~~ 145 — ri §1 SULPHURIC ACID 7 Throughout this work, the United States Baume is used, as it is the one universally adopted by sulphuric-acid manu- turers in this country. In addition to these scales, those of Gerlach and others are used in different parts of Europe and in different factories in the same country. All of which tends to show that the only precise and accurate way of describing the acids of sulphur trioxide is in terms of per¬ centage contents of such oxide. PRINCIPLES GOVERNING THE MANUFACTURE OF SULPHURIC ACID 10. When sulphur dioxide S0 2 and oxygen are brought together under certain conditions, they combine to form sulphur trioxide SO s . This in the presence of water vapor becomes hydrated, and these hydrates are known as sul¬ phuric acid. The conditions under which sulphur dioxide and oxygen may combine are varied. For the commercial manufacture of sulphuric acid, this combination is brought about in two ways. 1. By what is known as contact or catalytic action , the two gases are brought together in the presence of certain substances, as finely divided platinum, and other substances described farther on, that have the peculiar power to cause them to unite chemically. The dry sulphur trioxide thus formed is absorbed in the proper amount of water, to give an acid of the desired strength. 2. The two gases are brought together in the presence of steam and some of the higher oxides of nitrogen, as, for instance, The oxide of nitrogen gives up oxygen to the sulphur dioxide and forms, in the presence of water vapor, sulphuric acid. The lower oxide of nitrogen formed immediately takes up oxygen from the air present and is regenerated. The reaction is quite complicated but is continuous. A small amount of oxide of nitrogen serves to oxidize an 8 SULPHURIC ACID 1 indefinite amount of sulphur dioxide to the trioxide. This is the reaction used in the so-called chamber process. In the discussion of the two processes for the manufac¬ ture of sulphuric acid, the above-mentioned reactions will be quite fully dealt with. Before discussing these, however, the various sources of sulphur and the preparation of sul¬ phur dioxide will be taken up. 11. Raw Materials Used in the Manufacture of Sul¬ phuric Acid. —Commercial sulphuric acid is derived from the following raw materials: 1. Brimstone {a) derived from sedimentary deposits accompanied by or derived from gypsum, found in Sicily, Louisiana, etc. ; ( b ) derived to a limited extent from volcanic deposits (Solfatara). 2. Recovered sulphur {a) from alkali waste (Chance and Klaus processes); (b) from spent oxides from gas works. 3. Sulphureted hydrogen obtained as a by-product in the manufacture of ammonium sulphate, etc. 4. Iron pyrites, in which the principal value is the sulphur. 5. Iron pyrites with copper pyrites, in which the princi¬ pal value is copper (sometimes also gold and silver) and the sulphur may be considered as a metallurgical by-product. 6. Zinc blende, in which the principal value is zinc. 7. Copper-nickel pyrrhotites, in which the principal value is the metal. 8. Copperas slate ( Vitriolschicfer ), which is oxidized to ferrous and then to ferric sulphate in the Nordhausen proc¬ ess for the manufacture of fuming sulphuric acid; also other acid sulphates of the alkalies, which, upon being- heated, are first changed into pyrosulphates and then split up into neutral sulphates and sulphur trioxide. It will be noted that these raw materials divide themselves into the following classes: (a) Where the sulphur is the principal or only value, as brimstone and most iron pyrites; (£) where the sulphur is a recovered or a by-product from a 1 SULPHURIC ACID 9 previous chemical process, and, therefore, only available locally or under special conditions, as hydrogen sulphide, alkali waste, etc; (c) where the sulphur is of secondary value and is virtually a waste product in a metallurgical operation; (d) where the sulphur is derived from sources that are only suited on account of their cost for special proc¬ esses and products, as the various sulphates. 12 . The history of the manufacture of sulphuric acid commercially shows, as may be expected, that at first brim¬ stone, as being technically the simplest raw material, was exclusively used. This was, in turn, supplanted by iron pyrites. Iron pyrites are now being largely driven out by the waste gas produced in the desulphurization of copper, zinc, nickel, gold, and silver ores, and it is not difficult to see that in time the great bulk of acid will be produced as an adjunct to the various metallurgical processes. Literally, in the United States thousands of tons of sulphur are being delivered into the air as sulphurous gas every day of the year by the various metallurgical works. The capital invested in the present plants, the capital cost of making the necessary changes to render the gas available, remoteness from present markets, and other necessary costly adjust¬ ments alone prevent this sulphur from being recovered as sulphuric acid. As to the use of sulphates for the manufacture of fuming acid, this industry is practically dead, having been replaced entirely by the catalytic or contact process described far¬ ther on. 13. Preparation of the Raw Material. — Brimstone or sulphur requires little or no preparation, as it comes to the market in suitable condition to be put into the burners. Crude sulphur in the Sicilian warehouses is graded accord¬ ing to its purity and also, in a way, according to the method employed in its extraction. Grading is done by simple inspection, without sampling or assaying. Three qualities are recognized : firsts , seconds , and thirds. Light-colored sulphurs are included in the first 10 SULPHURIC ACID §1 two grades and darker varieties in the thirds. Seconds and thirds are subdivided into “vantaggiata,” “buona,” and “cor- rente.” Firsts are nearly chemically pure and of a canary- yellow color, while seconds vantaggiata are but slightly inferior. Seconds buona have a fine chrome-yellow color; seconds corrente have a dirty yellow color; and thirds are chocolate brown on the exterior, shading to greenish brown inside. 14. For the American trade, two special classes are made, seconda uso America , best seconds, which is a mixture of seconds corrente and thirds vantaggiata; and terza uso America , best thirds, a mixture of terza vantaggiata and terza buona. The chemical purity of these classes differs comparatively little. The various grades of seconds range from 99.85 to 99.70 sulphur; and of thirds, from 99.64 to 99.58 sulphur. The principal difference—namely, that of color—is due to temperature and other points connected with the fusion. 15. The spent oxides of gas works, which contain sulphur, are first treated for the recovery of the salts of ammonia, ferrocyanides, and sulphocyanides, and are then roasted as if they were the fines, or dust, of the metallic sulphides and in the same class of furnaces. 16. Sulpliureted hydrogen, when ignited in the air, burns with a blue flame, water and sulphur dioxide resulting H % S+W=H % 0 + S0 % with limited air access, or when the flame is cooled by the introduction of a cold body; only hydrogen burns and the free sulphur separates. Advantage is taken of this reaction to use the hydrogen sulphide produced in the Chance process for the utilization of alkali waste for the manufac¬ ture of sulphuric acid ; or by the Klaus process, for the lecovery of sulphur. The hydrogen-sulphide gas is simply burned in a suitable combustion chamber and the resulting passed to the lead chambers, or otherwise oxidized to S0 3 . 1 SULPHURIC ACID 11 17. The metallic sulphides, the bisulphides of iron, or iron and copper pyrites, can be roasted both in the form of small lumps or as dust, or fines, and by their own heat of combustion alone. The monosulphides, or copper- or nickel-bearing pyrrhotites and zinc blendes must be roasted as fines and with the aid of additional fuel. Many pyrites are so friable as to crumble to fines when being mined, and many pyrites carrying copper, gold, silver, and other valuable metals are in the form of concentrates, or fines; such ores are disseminated, when found, among large proportions of quartz or other gangue matter, or consist of the sulphides of several metals, which it is desirable to separate before further metallurgical treatment. If these ores occur in massive form, they must first be broken into small pieces. This is done either by hand or by rock breakers. The method used will depend on local condi¬ tions, such as cost of labor, etc., and on the mechanical condition of the ore, such as friability, etc. The ore must then be screened and sized. As a rule, except in the case of a very free-burning iron pyrite or under special conditions, such as extreme; friability of the ore and insufficient facilities for roasting the fines, the largest size produced should pass through a 3-inch ring; the next size should pass through a 2-inch ring; and so on. Too much emphasis cannot be given to the necessity for properly sizing the ore and burning one size only in the same burner. This applies not only to the lump ore but also to the smalls and fines. 18. In the first place, it is evident that fora “dead” roast, or a roast of equal efficiency, the capacity of any given furnace will be controlled by the time taken to roast the largest pieces. Therefore, to secure the efficient and eco¬ nomical use of costly apparatus, the economy of power and labor, or in other words, maximum output at minimum cost, it is necessary to have a reasonably close sizing of the charge of raw ore to any given furnace. Moreover, that serious class of troubles met with in roasting ores, called clinkering , scarring , etc., and much of the labor of breaking 12 SULPHURIC ACID 1 up and barring the bed of ore in a lump burner is the direct result of improper sizing. These scars, or clinkers, are really the formation of a fusible matte of ferrous sulphide FeS, owing to the irregular passage of air through the bed of ore on the furnace grates. If the ore is reasonably sized, air will be uniformly admitted through the bed and each piece of ore will get sufficient air for its complete oxidation. Moreover, the resulting regularity in the condition of the furnaces will tend to produce uniformity in the conditions of the burner-gas and the acid-making process. 19. Combustion of Sulphur and Its Thermochem¬ istry. —When brimstone or a metallic sulphide is heated in the air, or burned, the following reaction takes place: •S 3 -j- 2 0 3 = 2 S0 3 In this respect, the combustion of sulphur appears to form an exception to the general rule of thermochemistry— viz., that where two or more compounds are possible as the products of chemical combination, that product will be formed which produces the greatest heat in the reaction; for example, C and O can form carbon monoxide CO or carbon dioxide C0 3 , and carbon dioxide is the usual product of com¬ plete combustion; sulphur and oxygen can form sulphur dioxide SO a and sulphur trioxide SO a , yet sulphur diox¬ ide is the usual product of combustion. The reason for this is that the heat of the oxidation of sulphur to the trioxide is so great as to cause the dissociation of the trioxide into the dioxide and oxygen, or in other words, that the difference in the temperature of the production and dissociation of sulphur trioxide is so slight that unless some means are taken to carry off the heat of the reaction effectively it cannot exist. This fact becomes highly important in the considera¬ tion of the various contact processes. As a matter of fact, the gas produced by the combustion of brimstone or the metallic sulphides always contains varying proportions of sulphur trioxide, so that techni¬ cally the equation given above does not quite represent the reaction of the combustion of sulphur in air. 1 SULPHURIC ACID 13 The fact that the burner gas contains varying quantities of sulphur trioxide is shown by the formation of free sul¬ phuric acid, when such gases are washed in water or dilute sulphuric acid or passed over iron filings before being used in the manufacture of sulphite pulp. 20. Burner Gas.—Burner gas, whether derived from the combustion of brimstone or the metallic sulphides, forms the basis of the manufacture of sulphur trioxide and all its hydrates and solutions. • It consists, according to the raw material used, of a mixture of sulphur dioxide and sulphur trioxide, nitrogen, oxygen, and many impurities, such as flue dust, iron, silica, arsenious and hydrofluoric acids, and com¬ pounds of selenium, thallium, zinc, lead, etc. 21. As air consists approximately of 79 parts, by volume, of nitrogen and 21 parts, by volume, of oxygen, and as 1 volume of oxygen on combining with sulphur forms 1 vol¬ ume of sulphur dioxide, which in turn requires \ volume of oxygen to form the trioxide, it is plain that 14 per cent, of sulphur dioxide in the burner gas is the highest theoretical percentage possible; as each 14 volumes of sulphur dioxide containing 14 volumes of oxygen requires 7 volumes of oxy¬ gen to form sulphur trioxide, or 21 volumes of oxygen in all, in which case the burner gas would contain the fol¬ lowing : Volumes of oxygen as sulphur dioxide. 14 Volumes of oxygen to form sulphur trioxide. ... 7 Volumes of nitrogen. 79 Total.100 In practice, however, even if pure sulphur is used to pro¬ duce the burner gas, this percentage would not be practicable, as no matter what process is used a certain excess of oxygen is found necessary. This excess of oxygen is usually not less than 5 per cent, and the proportions therefore are about as follows: 14 SULPHURIC ACID §1 Volumes of oxygen as sulphur dioxide. 14.0 Volumes of oxygen to form sulphur trioxide. . 7.0 Volumes of oxygen excess. 5.0 Volumes of nitrogen with the sulphur trioxide 79.0 Volumes of nitrogen with the excess of oxygen 18.8 Total.123.8 From which it is evident that even when burning brim¬ stone or pure sulphur, the percentage of sulphur dioxide in the burner gas should not exceed 11 per cent. Asa matter of practice, 10 per cent, is rarely exceeded, as with less air sub¬ limation of the sulphur is likely to take place unless great care is used. 22. When the question is one of roasting the metallic sulphides, it is evident that the matter is further compli¬ cated, as oxygen (and with it nitrogen) must not only be admitted to oxidize the sulphur to the trioxide and to provide for the necessary excess, but also to oxidize the metallic contents of the ore. The calculation will, of course, be different for the various ores used, but it may be stated in general terms that the burner gas pro¬ duced when burning the metallic sulphides should range from 5 to 8 per cent, of sulphur dioxide. A less percent¬ age than 5 per cent, can only be used (on account of its dilution with inert nitrogen) at the expense of a larger and, therefore, more expensive plant; nor, with reasonably well-constructed burners, need the percentage of sulphur dioxide fall below 5 per cent, unless under very exceptional circumstances. 2,i. Available Sulphur.—As all the raw material for the production of burner gas contains varying quantities of impurities, and as it is quite impossible, at the temperatures existing in the various furnaces used in sulphuric-acid manu¬ facture, to entirely desulphurize any of these raw mate¬ rials—various percentages of sulphur remaining in the ash or cinder—it is manifestly advisable to base figures relating SULPHURIC ACID 15 O ® $ ' to the process or yield upon the amount of sulphur actually available or existing in the burner gas as oxides of sul¬ phur SO 9 or S0 r The loss in the desulphurizing process is estimated separately, and it is to this available sulphur that all calculations will refer. Certain losses of sulphur occur in the process of desulphurizing by the escape of gas during charging and discharging and the various manipulations connected with the roasting. Losses also occur by partially roasted ore passing through the furnace; this is generally due to care¬ lessness on the part of the burner men. Other quite unavoidable losses are caused by the temperature of the furnace being insufficient to convert the sulphides of cer¬ tain metals occurring with the iron pyrites into oxides, they remaining in the cinder as sulphates. O qo £ ' ^_ o iU « 10 r o_y Sa ^ • 1C 0-t T_ 1 o s S ta <0 ' O os S co N ' 8 10 N ' P a b S 03 O-i a ), (c), (V/), and (^). (a) is a side elevation, also showing vertical sections through several parts; ( b) is a plan showing horizontal sections through several different parts; (r) shows a vertical section from front to back through the center of an individual furnace; (d) and (c) will make themselves clear in the following description: 38 . At a is the grate upon which the ore is burned. The thickness of the bed of ore carried on the grates will be from 2 to 2£ feet, as shown in (c), but will vary somewhat accord¬ ing to the sizing and character of the ore. It must in any case permit a passage of the air uniformly through its mass and not in spots or against the furnace walls. The ore is shoveled into the furnace through the charging door b, and must be spread as evenly over the surface of the bed as possible, being slightly deeper against the walls of the fur¬ nace, as shown in ( 2 + 2 H a 0 = 3H,SO A + 2 NO the oxide thus formed combining directly with the sulphur dioxide, oxygen, and water to form nitrososulphuric acid. (5) 2 SO, + 2NO + 36> + Hfi = 2 (HO)(NO t )SO t which is converted into sulphuric hydrate and nitrous oxide according to equation (2). If the above reactions could be started with the exact quantities of nitrous acid, sulphur dioxide, water, and oxy¬ gen necessary, it is evident, to secure a continuous process, all that would be necessary would be to secure a continuous supply of the exact quantities of sulphur dioxide, oxygen, and water, and return to the beginning of the process the nitrous oxide accumulated at the end of the process by simply supplying any mechanical loss common to all com¬ mercial processes. 4 SULPHURIC ACID §2 This is approximately what is done in the chamber process. The nitrous oxide cannot, however, be returned direct, as the oxygen, being supplied as air, carries with it a very large proportion of inert nitrogen, which must be gotten rid of. It becomes necessary, therefore, to separate the nitrous oxide from the inert nitrogen in such a way that the iV 2 (? 3 can again be made available and the inert nitrogen wasted into the atmosphere. Advantage is taken of the power of the stronger solu¬ tions of sulphur trioxide from 60° to 66° Baume, to absorb and retain the nitrous oxide in fairly stable solution. SULPHURIC ACID 5 ( 6 ) 21/ S O + N,0 3 = 2 (HO){NO,)SO t + H % 0 In other words, nitrososulphuric acid is formed. When dis¬ solved in a large excess of the sulphuric-acid solution, the product is termed nitrous vitriol. The nitrous anhydride so absorbed can be set free, however, on dilution of the acid and especially in the presence of sulphur dioxide. When this nitrous vitriol is diluted, in the presence of sulphur dioxide at the beginning of the process, so as to set free the nitrous anhydride and complete the cycle, the reaction is represented by equation (4) above given. The diagram in Fig. 1 shows the chemical reactions that take place during a complete cycle. To read it, begin at the center and follow the direction of the arrows. APPARATUS EMPLOYED IN THE CHAMBER PROCESS 5. In the manufacture of sulphuric acid by the so-called chamber process, the first essential piece of apparatus is a sulphur or pyrites burner provided with some means of nitrating the burner gas. Any of the burners previously described may be used. 6. Nitrating Oven. —Fig. 2 (a) and (b) shows an attach¬ ment to the burners by which nitrating by potting may be accomplished. Fig. 2 (a) is a horizontal section through the niter pots d, and Fig. 2 {b) is a vertical longitudinal section through one of these niter pots. The extreme end of a bench of lump pyrites burners is shown at a. The flues b from the burners enlarge into the niter ovens c, in which are placed the cast-iron niter pots, or “pigs,” d. The cast-iron dishes e underneath the niter pots catch any acid material boiling over from the pots and prevent its penetrating the brickwork of the furnace. A cast-iron hopper, or funnel, / provides for the introduction of niter and sulphuric acid into the niter pots, the acid being,stored in the tank g and conducted by a lead pipe and cock to the §2 SULPHURIC ACID 7 hopper. The common flue and dust chamber h leads to the cast-iron flue k, through which the gas is carried to the Glover tower. When the burners are in operation, the pots d are supplied with niter and a regulated amount of sulphuric acid added. The fumes of nitric acid thus formed mix with the hot burner gas and pass to the Glover tower. The sodium sul¬ phate formed in the pots is removed through the cast-iron neck i, which is usually kept closed with a wooden plug, into the cast-iron dishes j. When cold and solid, it is broken up and removed. 7. This method of nitrating by “potting” is by no means satisfactory, because it adds another element of periodic irregularity to what should be a continuous proc¬ ess, and because, unless in the hands of careful and skilled workmen, it is a wasteful and a dirty process. It is also difficult in this way to supply the chambers with nitrous oxide just in the quantity and at the time when it is most wanted—that is, when something in the process is going wrong. Sometimes, also, on account of faulty con¬ struction, there is insufficient heat to decompose the niter rapidly enough or else the heat is too great and too direct and the sulphuric acid is evaporated before it has reacted completely with the sodium nitrate. Wherever, therefore, the size of the plant justifies the manufacture of nitric acid on a small scale or where it is in any way possible, nitration should be secured by the use of nitric acid run into the Glover tower with the nitrous vitriol. This is accomplished by means of a small glass siphon from the nitric-acid tank or carboy, fitted with a glass cock and discharging from the cock into a glass funnel with a bent neck, so as to form a seal or lute and fixed into the center of the top lead of the tower. It does not matter how weak or impure the nitric acid may be for this purpose; indeed, in some works, the spent acid from the manufacture of nitroglycerin is used, as the acid is almost instantly decom¬ posed upon entering the tower. 8 SULPHURIC ACID §« 8. Glover Tower. —The apparatus in which the sulphur dioxide, oxygen, and nitrogen of the burner gas are mixed with the nitrous oxide N t O v derived from the nitrous vitriol used in this stage of the process, water vapor and the nitrous fumes from the nitrating ovens, which after the process is once under way is only sufficient to make up for the mechanical loss, is known as the Glover tower. In this tower, the gases and vapors are not only thoroughly mixed, but the dilute sulphuric acid constantly flowing down is both denitrated and concentrated by the hot gases, ren¬ dering it strong enough to be again used for absorbing N^O % at the end of the process. 9. The heat of combustion of the sulphur to SO a in the furnaces is usually more than sufficient to concentrate the whole of the make of chamber acid if. entirely util¬ ized to 66° Baume, or to 93.5-per-cent. H^SO^. In a well- constructed plant, that is, where the heat is fAirly well utilized, the Glover tower will concentrate from one and one- half times to twice the entire make of chamber acid to 60° or 62° Baume (62- to 80-per-cent. H^SO^), or, in other words, this quantity of chamber acid can be used to dilute the nitrous vitriol and will leave the Glover tower at 60° Baume ? or over. Of course, if it is not desire^ to keep this amount of acid in circulation between the Glover and Gay-Lussac towers, the nitrous vitriol may be diluted in whole or in part with water. The temperature of the burner gas entering the Glover tower will vary, of course, with the construction and length of connections, but will average probably about 550° C. The greatest possible temperature produced by the com¬ bustion of sulphur will, of course, vary with the nature of the raw material. Mendeleeff estimates the highest possible temperature of actual sulphur burning in air to be 1,974° C. and in oxygen 7,258° C. 10. The construction of the Glover tower is clearly shown in Fig. 3. It consists of a circular brick-lined tower e §2 SULPHURIC ACID 9 covered with a lead sheathing p and lead pan o at the bot¬ tom, and is filled to near the exit pipe g with a packing f Fig. 3 consisting of broken quartz, the pieces being large at the bottom, but decrease in size towards the top. This packing 199—6 10 SULPHURIC ACID §2 §2 SULPHURIC ACID 11 rests upon the grill tiles d , which are supported by the walls b. The tank h contains dilute or chamber acid, which flows through the equalizer h x and the distributor h 3 over the top of the packing. On the other side is a similar arrangement i, zj, and z' 2 for the distribution of nitrous vit¬ riol, which is strong sulphuric acid coming from the Gay- Lussac tower, described later, and heavily charged with nitrous oxide N % O v this JV 3 0 3 being set free on dilution of the vitriol in this tower. The burner gas enters the tower at the bottom by means of the pipe a, which is surrounded next the tower by the cast-iron cooling ring q, which prevents the heat from injur¬ ing the lead sheathing next the pipe. The gas is distributed through the gas spaces c and passes through the grill tiling up through the packing, coming in intimate contact with the dilute acids from above, which are giving up N 3 0 3 , and become mixed with the latter and also with steam formed by the hot burner gas on the dilute acid. This mixture of burner gas, nitrous oxide, and steam passes on through the pipe g into the first lead chamber. As previously stated, the rapid evaporation of the moisture concentrates the down-flowing acid considerably. The deni¬ trated and concentrated acid having a strength of from 60° to 62° Baume is drawn off at j; the lead-covered cast-iron plate, or dish, n catches the acid or other leakage. The exit pipe k is for use when the tower is washed by flooding with acid in too large quantity to pass through j. The tower is sup¬ ported on the foundation walls / and the I beams in. In dimensions, the Glover tower will average about 24 feet in height and 12 feet in diameter. The construction is necessarily heavy, in order that it may withstand the high temperatures. 11 . Lead Chambers. — The thoroughly mixed gases from the Glover tower containing nitrous oxide N 3 0 3 and water vapor are allowed to pass to the chambers in which the oxidation of the sulphur dioxide to trioxide and the for¬ mation of sulphuric hydrates takes place. These chambers SULPHURIC ACID §2 SULPHURIC ACID 13 are usually three in number, of greatly varying dimen¬ sions, but average between 50 and 100 feet long by from 20 to 30 feet wide and 20 to 30 feet high. They are con¬ nected together in series, the communication between them being comparatively small. The construction of the cham¬ bers is shown in Figs. 4, 5, 6, and 7. Fig. 4 is a side elevation, showing the method of framing. The chamber building is built on posts n' upon which are the corbels-supporting the stringers The joists m! are laid on these stringers, and upon these are laid the sills a of the chambers. The posts b and the intermediate uprights c are erected upon the sills and stiffened by the braces d. The crown tree e surmounts the posts and intermediates, and on this the top joists g are laid. The floor of the chamber is covered with sheet lead, so as to form a pan whose, edge is shown at z. The edge of the lead curtain forming the inside lining of the sides is shown at j. The end wall of the cham¬ ber building is shown at o’. 1 \ In Fig. 5 (zz), ( b ), (c), and (d) is shown the method of .attaching and supporting the lead lining. Fig. 5 (zz) shows the method of cutting the lead straps for supporting the lead lining. Fig. 5 (b) shows the top joists g with the lead straps n attached, the lower ends of the straps being burned to the top lead in. Fig. 5 (c) is a plan of the top, showing the method of fitting the lead lining into the corners. The top lead in is supported from the top joists g. The crown tree is at e. A long horizontal strap k is nailed to the crown tree and supports the side lead at the top where it is attached to the top lead. The attachment of the top and side leads is best shown in Fig. 5 (z/), which is self-explana¬ tory. In Fig. 6 (a), (b), and (c), further details of the attach¬ ment of the side and pan lead are shown. Fig. 6 (a) shows a horizontal section through the posts b and the uprights c at a corner, showing the attachment of the side straps l to both posts and lead. Fig. 6 (b) is a side elevation towards the bottom of the chamber, showing the method of attaching 14 SULPHURIC ACID §2 Fig. 6 2 SULPHURIC ACID 15 Pig. 7 16 SULPHURIC ACID 2 the sides of the lead pan i by rolling the top over the strip p. Fig. 6 ( c ) is a vertical section through a side, showing the relative positions of the side lead j to the pan i. This pan is kept about two-thirds full of acid and at all times the curtains or sides should dip at least 2 inches into the acid. When it is desired to draw acid from the cham¬ bers, it is done by means of the arrangement shown in section in Fig. 7. A pipe o is burned into the bottom of the cham¬ ber; the entrance to this pipe is protected from the wash of the flowing acid and a stratum of cool acid is kept on the bottom by means of a loose lead ring /, which may be removed when it is necessary to entirely empty the chamber. The pipes from two or more adjacent chambers meet in the cylindrical lead boot q. This boot is provided with a lead plug r or valve and seat communicating with a pipe .y lead¬ ing from the chambers to a tank or wherever it can flow by gravity. The entrances t to the boot from the chambers can also be plugged, so that acid can be drawn from either chamber or both, and the level in the two chambers can be regulated as desired. SURFACE CONDENSERS 13. Immediately on the entering of the gas into the chambers, the formation of sulphuric acid commences. This acid is formed as a very fine mist. This mist gradu¬ ally and slowly settles on the sides and bottoms of the chambers. As the gas leaves the first chamber it is very advantageous to condense this mist of already formed acid that it contains, so as to leave the gas free to enter into renewed activity upon entering the second chamber. The same thing may be said of the gas leaving the second cham¬ ber and entering the third chamber. Many proposals have been made to secure condensation at these points. 14. Lunge Condenser.— Lunge has introduced what he calls plate columns for this purpose, consisting of a lead tower, or column, fitted with flat, perforated, earthenware 18 SULPHURIC ACID §3 plates in layers one above the other and about 2 inches apart. A stream of chamber acid is run over the plates. The perforations are so arranged that the acid in dropping- through the perforations of one plate splashes upon the solid part of the plate below it and is thus broken into spray, up¬ on meeting which the gas is cooled and deposits its mist of contained acid. This apparatus, therefore, may be con¬ sidered as a type of spray condenser, similar to the well- known form used in steam engineering. Fig. 8 shows the Lunge type of spray condenser. The gas is admitted at a into the lead-lined box b , whence it passes through the perforations in the plates c , c, meeting the stream of acid supplied by the distributors d and lutes e. This acid, together with the condensed mist contained in the gas, is collected in the pan f and either run back into one of the chambers or conveyed by lead pipe to storage. The gas passes on to the vent chamber i and through the col¬ lecting pipes g, g lt g v g a , and the main pipe k. 15. Gilchrist Condenser. — The Gilchrist pipe col¬ umns consist of an oblong tower, or column, of lead pierced in its smaller diameter by a series of lead pipes open to the air at each end. The lead column is surrounded by a wooden breaching and flue in such a way as to cause a cur¬ rent of air through these pipes, thus tending to keep them cool. The gas passing through this column is cooled by contact with these pipes and the acid mist is condensed on them. This apparatus may therefore be considered a type of air-cooled surface condenser. Fig. 9 shows the Gilchrist air-cooled surface condenser. The gas is admitted at a into the lead box b. This box is pierced by numerous lead pipes c, c, c, open at ; both ends. The acid mist contained in the gas is condensed on these pipes and the comparatively cool surfaces of the lead box and runs to the bottom of the box b, whence it is carried to a chamber, or storage, by a pipe d. The gas then passes through the collecting pipe e to the vent chamber. The lead box is surrounded by a wooden breaching, so that the §2 SULPHURIC ACID 19 air entering g from below is drawn through the lead pipes c , c, c into the breaching g' and thence to the draft pipe /, thus tending to keep the apparatus cool. 16. The Falding Condenser.— The Falding surface condenser consists of a series of lead pipes surrounded by water as the cooling medium. They are arranged in such a way as to secure a maximum efficiency with a minimum use of water. This apparatus may therefore be considered as a type of water-cooled surface condenser. Fig. 10 shows the Falding water-cooled surface con¬ denser. In this condenser, the entering gas is broken up into a number of small streams through lead pipes a , a , a , a. These pipes dip almost to the bottom of a series of water- cooled lead pipes d, d, of larger diameter, with closed bot¬ toms. The annular space between these pipes contains a strip of lead, which forces the gas to return in a spiral through acid to the top of the annular space, whence it 20 SULPHURIC ACID §3 SULPHURIC ACID 21 §2 passes through pipes c , c into the next chamber or into a header or manifold and thence into the next chamber. The condensed acid mist runs from the apparatus at b. 17. Other Condensers. —Many manufacturers use sim¬ ple lead towers filled with quartz, brick, or special earthen¬ ware shapes. These towers do not take sufficient account of the necessity for cooling, and while they are efficient to a certain extent, they are not sufficiently so when their cost relative to an equal amount of chamber spaces is taken into consideration. If all operations have been properly conducted, the gases coming from the last lead chamber are practically free from sulphur dioxide, and consist of inert nitrogen, the excess of oxygen, and nitrous oxide N 3 0 3 . This latter gas, if freed from the other two gases, may be used over again as an oxidizer for more sulphur dioxide. This separation depends on the fact that nitrous oxide N 3 0 3 is readily absorbed by concentrated sulphuric acid forming the so-called nitrous vitriol, while the other useless gases are unabsorbed. The apparatus in which this absorption takes place is called the Gay-Lussac tozver. 18. Gay-Lussac Tower.— This piece of apparatus is in construction very similar to the Glover tower, but dif¬ fers from it in that it is of somewhat lighter build. Its height is greater, the average height being about 50 feet, and its diameter is somewhat less, being about 8 to 10 feet. The details of the Gay-Lussac tower are shown in Fig. 11. The brick walls e are of light weight and are covered with a lead sheathing p. Under the brick bottom is the lead pan o resting in the lead-covered cast-iron dish n. The tower is supported on the I beams in by the foundation walls /. The filling f is of broken quartz, coarse at the bottom but becoming finer at the top, as in the Glover tower. The tank h contains strong, 62° Baume, sulphuric acid, which flows through the equalizer t and the distributors ^ over the top of the packing. §2 SULPHURIC ACID 23 During operation, the mixed gases from the chambers enter at the bottom through the pipe a , pass through the gas spaces c in the supporting wall b, and up through the grill d into the packing material. As the gases ascend, they come in contact with the descending concentrated sulphuric acid, which absorbs the NJD r The unabsorbed gases pass through the pipe g into the air or, more com¬ monly, into a second Gay-Lussac tower, which absorbs any N 9 0 3 that may have escaped absorption in the first tower. The nitrous vitriol is drawn oft' at the bottom of the tower at j. The exit k is for flushing purposes. The nitrous vitriol coming from the Gay-Lussac tower is pumped to the tank over the Glover tower and is used in the Glover tower, where it gives up its which again passes through the system. 19. Diagram of Chamber Process.— The disposition of the various pieces of apparatus already described and the cause of the various materials and products is indicated in the diagram shown in Fig. 12. Reference to this diagram will enable one to keep a general idea of a plant in mind and better understand the process as the details are dis¬ cussed. In the figure, A is a bench of pyrites burners, niter oven, etc. The burner gas is conducted through the pipe d to the Glover tower E, where it meets the dilute acids and oxides of nitrogen. The fan J carries the gases through the pipe i to the first chamber A", where oxidation of the sulphur dioxide takes place, thence to the second and third cham¬ bers M and N, through the flues t\ and z 9 and surface con¬ densers L and L v The acid drained from the bottom of each chamber and the condensers is collected in the tank R 2 . The pump S t of one of the styles shown in Figs. 13 and 14 delivers this acid to the tank H x , over the Glover tower, or to the storage tank U, whence it goes to the tank car V. The strong acid coming from the Glover tower is collected in tanks Q and R x and is delivered by the pump A, to the tank H t over the second Gay-Lussac tower P and to the §2 SULPHURIC ACID 25 storage tank U r The gases from the last chamber N are conducted through the pipe i 5 to the first Gay-Lussac tower O and thence to the second Gay-Lussac tower P, their flow being maintained by the fan J v The exhausted gases pass to the atmosphere at t. The nitrous vitriol from the first Gay-Lussac tower is collected in the tank R A and is delivered by the pump to the tank H over the Glover tower. The nitrous vitriol from the second Gay-Lussac tower, containing but little N 3 0 3 , is collected in the tank R 3 and is delivered by the pump S 3 to the tank H 3 over the first Gay-Lussac tower. In different works, this scheme varies somewhat in detail, but not in its essential points. 20. Acid Pumps. —In both the catalytic and chamber processes, it is necessary to transfer large volumes of acid from one part of the works to another. This is done by means of pumps of peculiar construction, some of which are designed to act automatically, so as to give a continuous flow of acid. Two styles of pumps, the Kestner automatic and Monteju's acid egg , are here described. 21. Kestner Automatic Pump. —This apparatus, shown in Fig. 13, is automatic and works continuously; it is constructed of cast iron for -strong acid, but is lead lined for weak acids. It is operated by compressed air. The acid chamber is connected by the vertical pipe b with the valve box c , which must be placed higher than the tank supplying the apparatus, so that in no case acid can rise within a foot or two of it. Acid is admitted from the supply to a by means of the pipe d and check-valve e. The float f con¬ nected with the counterbalanced compressed-air valve g by means of the rigid rod h running inside the vertical pipe b and stuffingbox i, is raised by the inflowing acid until it opens the compressed-air valve g. The compressed air from the pipe /communicating with / at j flows through the pipe b into the acid chamber a , driving the acid up through the pipe k to a receiving tank; for instance, on top of a tower. As soon as chamber a is empty the float falls, closing the air valve, and the operation is repeated. The air valve and 199—7 26 SULPHURIC ACID 2 float are so balanced that the total movement of the rod does not exceed T *g inch. The great advantage of this appa¬ ratus is that it insures a steady flow of acid (which can be accurately controlled) over the towers. 22. Monteju’s Pump With Acid Egg.— This pumping arrangement is illustrated in Fig. 14. The tankH contain¬ ing the acid communicates at e with the receptacle or “ egg ” G by means of the pipe b, the flow being controlled Fig. 14 28 SULPHURIC ACID §2 by the globe valve c. The plug valve b' is merely auxiliary, and should not be relied on, as it can only with difficulty be made to withstand the back pressure. The check-valve d is used under ordinary circumstances. This valve permits the flow of acid into the egg until the acid rises to the level of the valve, which, when the compressed air is let into the egg, immediately seats itself and prevents the air from for¬ cing the acid back into tank A. Compressed air is admitted to the egg by means of the pipe f and the valve /. The pipe h controlled by the valve i delivers the acid from the egg to the splash box j of the distributing tank P. When air is admitted to the egg, as it cannot pass valves d and c, and valve i being open, it forces the acid to a height of from 50 to 100 feet through h into the splash box j , which is a lead-lined box with two openings, through the lower of which the acid escapes into an open part of the tank, and thence through the exit in into a receiving tank on top of the towers and an upper opening of large area, whereupon the air escapes iijto the atmos¬ phere without splashing the acid over things. The exit n from j' into another receiving tank is provided in case the egg is used for pumping two kinds of acid, the plug being simply moved from n to m and a branch connection to a second supply tank being inserted at o , the flow of acid from either supply tank into the egg being then controlled by plugs b'. OPERATION' OF THE CHAMBER PROCESS 23. If the reactions involved in the chamber process have been understood, the importance of extreme regularity both as to volume and composition, of the supply of the substances entering into these reactions will appear obvious. For, although the process involving these reactions is a con¬ tinuous one, and in fact more especially on this account, if loss is to be avoided and success attained, the supply of the necessary ingredients must be as exact as if the proc¬ ess were an isolated reaction involving the complete union 2 SULPHURIC ACID 29 of carefully weighed proportions. The materials in ques¬ tion are: (1) A constant stream of burner gas of uniform volume and percentage of sulphur oxides and free oxygen. (2) A uniform supply of finely divided water or water vapor of constant tension. (3) A uniform supply or circulation of nitrous vitriol containing a constant percentage of nitrous oxide N a O a . (4) A uniform supply of nitric oxide or acid for making good the oxides of nitrogen lost in the process (mechanically or otherwise). It is only by careful watchfulness, honest work, and proper management, together with a rationally constructed plant, that a near approximation can be made to the requirements as to absolute uniformity called for. When, however, such approximation is reached, the difficulties of the chamber process disappear and the operation will proceed month after month with little, if any, variation, and with uniform results. 24. Conditions in the Glover Tower. —The burner gas, having an average temperature of about 550° C., in passing from below through the Glover tower meets a finely divided stream of nitrous vitriol -f- N a O a greatly diluted with chamber acid or with water, or both, and often carrying with it nitric acid, sufficient to supply the loss inevitable in the process ^mounting from 1.5 to 3 per cent. (The consumption of oxides of nitrogen is always given in terms of percentages of sodium nitrate NaNO % cal¬ culated on the available sulphur burned.) This stream of mixed acids enters the top of the tower at from 40° to 50° Baume, according to the degree of concentration and deni¬ tration required and the concentrating efficiency of the tower. The hot, moist, sulphurous gas drives off the nitro¬ gen oxides in the upper part of the tower, and as it descends to the lower and hot zone, the water is expelled from the dilute acid as steam. The acid is thus concen¬ trated to from 60° to 62° Baume, or in special cases to 64° Baume, or even to 66° Baume and flows from the tower, while a stream of gas containing a mixture of oxides 30 SULPHURIC ACID §2 of sulphur and nitrogen, steam, oxygen, and nitrogen, passes over to the first chambers. 25. Conditions in the Chambers.— The gas thus enter¬ ing the first chamber contains all the elements necessary for the production of the hydrate or solution of sulphur tri¬ oxide and in a condition of maximum activity. At this point, the percentage of sulphur oxides is greatest, the free oxygen is in greatest excess, and the oxides of nitrogen NO and iV 2 (9 3 are such as possess the most powerfully oxidizing effect. The temperature of the gas (80° to 100° C.) is also conducive to an active reaction. Therefore, it is at this zone of reaction that one would naturally look for a large make of acid, and such is actually the case, for between the Glover tower and the first forty feet of the first chamber, with all the elements and conditions of the process at their best, from 60 to 80 per cent, of the whole acid is made. 26. In a properly constructed plant, that is, a plant con¬ sisting of rightly proportioned Glover tower, chambers, and Gay-Lussac towers, a sufficient quantity of nitrogen oxides should be supplied to the gas by means of the Glover tower to raise the temperature of the reaction (as shown by the thermometers penetrating the sides of the chambers, say at a distance of 25 feet from the end that is nearest the Glover tower) to fiom 95° to 100° C. This, of course, does not apply to the oxides of nitrogen supplied to the system to replace the mechanical loss, but to the nitrogen oxides recovered at the end of the process and gradually accumu¬ lated as nitrous vitriol (nitrososulphuric acid dissolved in a large excess of 60° to 62° Baume sulphuric hydrate or solu¬ tion) and which is run over the Glover tower in dilute form to again utilize its contained oxides of nitrogen. The oxides of nitrogen so stored may be termed niter in circula¬ tion, and it is evident that, according to the quantity of .this nitrous vitriol of uniform percentage contents of nitro¬ gen oxides accumulated, put into circulation at the Glover and recovered at the Gay-Lussac towers, so will be the ratio §2 SULPHURIC ACID 31 of active nitrogen oxides to the sulphur oxides at this crit¬ ical initial point; i. e., the Glover tower and first part of the first chamber. 27. Provided always that the towers are properly pro¬ portioned to fulfil their functions of denitration and absorp¬ tion (or recovery), it is desirable to accumulate and put into and keep in circulation about 20 per cent, of niter (by niter is meant oxides of nitrogen calculated as nitrate of soda NaNO s on the available sulphur burned). This will secure an active process at the beginning and a rapid oxidation of the gradually lessening percentage of oxides of sulphur after the first active zone has been passed, owing to the large excess of active oxides of nitrogen in the chamber gas, and, consequently, a rapid change of these oxides of nitrogen to nitrous oxide N t O t , in which form it is capa¬ ble of being at once absorbed in the Gay-Lussac tower. This will, on the other hand, prevent the process becoming sluggish and slow, with the consequent danger of sulphur dioxide escaping into the Gay-Lussac tower unoxidized, where it will decompose and so prevent the complete absorp¬ tion of the nitrous oxide by the sulphuric acid, which takes place according to the following equations: + 2H i SO i = 2 (HO)(NO,)SO, + H,0 2(HO)(NO i )SO i + SO, + 2 H t O = 3 H t SO t + 2NO The oxide NO will not be absorbed, but passes with the inert nitrogen into the atmosphere. It will also avoid (by at once absorbing from the process) the danger of the A T t 0 3 being changed to NO, or even to nitric acid HN0 3 , when in the first case it would be lost as stated above, or in the second case it would not only be lost but would rapidly destroy the lead of the apparatus and contaminate the acid made. 28. After the first 40 or 50 feet of travel of the gas in the first chamber, the temperature indicated by the side ther. mometers will rapidly diminish. This would naturally be expected as the reactions become less intense, on account of 32 SULPHURIC ACID §2 the lesser proportion of sulphur dioxide contained in the gas, and also its greater diffusion in the chamber and its saturation with a mist of already formed sulphuric hydrate. The length of the active zone, of course, varies according to the volume of burner gas passed into a chamber of any given size, and also to the intensity of the first reactions, depend¬ ing on the proportion of nitrous vitriol kept in circulation; but sooner or later, and generally within the first 60 feet, the reactions, as indicated by the thermometers, will become sluggish and will so continue until the gases have been thor¬ oughly mixed and the various elements brought into more intimate contact by passing them through a pipe connection and in their mixed condition allowing them to again expand in a second lead chamber. For this reason, it is now usual in the United States to limit the length of the first chamber to from 50 to 75 feet. 29. Where a positive method of controlling the currents of a gas (such as the use of fans, etc.) exists, it is preferable, in the case of large volumes of burner gas being handled, to divide the gas between two or more first chambers of lim¬ ited length, so as to secure a large zone of great activity rather than an extended zone of rapidly diminishing activity or sluggish reaction. The condition of the gases at the end of the first cham¬ ber, or after the zone of great activity, is such as to call not only for a thorough mixing but also for a cooling and a con¬ densing of the mist of acid already formed. Radiation of heat from the surface of the chambers, while very consid¬ erable, is not sufficient by itself to conduct away the heat of the active zone so as to secure the best results. The tow¬ ers, surface-, air-, and water-cooled condensers and plate columns employed have already been described. These apparatus, by bringing the gases again into intimate con¬ tact, also undoubtedly start the reactions into renewed activity. 30. The second chamber in a properly proportioned set and with sufficient nitrous vitriol in circulation (in* otfyer §2 SULPHURIC ACID 33 words, with a sufficiently active process) will almost entirely oxidize the remaining sulphur dioxide, so that with or with¬ out further surface condensers between the second and the third chamber, the oxidation will be completed at once on entry into the third chamber, which then acts merely to dry and cool the gas, now consisting of inert nitrogen, the excess of oxygen, and nitrous oxide, and render it fit for absorption in the Gay-Lussac towers. For cooling and drying the gas, a long pipe connection between the last chamber and theGay- Lussac tower is of great advantage; it can, however, be replaced by a surface condenser of any of the types pre¬ viously mentioned. In this description of the passage of the gas through the sulphuric-acid plant, it must be remembered that while the gas enters the chambers containing a large proportion of water vapor derived from the concentration or evaporation of the dilute acid supplied to the Glover tower, this water is rapidly absorbed by the formation of the sulphuric hydrate and precipitated to the pans of the chambers. More water, either as finely divided spray or as steam, must be added. Steam is the usual medium employed, either low-pressure steam (20 pounds per square inch) or exhaust steam from a neighboring engine, or both. 31. Admission of Steam to the Chambers.— It is well to have sufficient points of admission for the steam, either on the top or sides of the chambers, each point being supplied with an indicating valve, so that the steam may ultimately be supplied just at such points and in such quan¬ tities as experience may show to be the best in each individ¬ ual case, and under varying conditions of conducting the process. Just as it is with the burner gas and the supply of nitrogen oxides, so must the flow of steam to the process be in every respect uniform. To secure this, the steam pipes must be well covered and trapped and the main line sup¬ plying steam to the branches must be supplied with steam gauges and an efficient reducing valve, which must be con¬ stantly watched and kept in order, The arrangement of SULPHURIC ACID 2 Fig. 15 2 SULPHURIC ACID 35 the steam-pipe connections is shown in Fig. 15. The main supply pipe u is laid between the chambers, the vertical pipe z extending from it to the top and having branches v to the chambers right and left. The lead terminal pipes x enter the chambers by means of the hydraulic lutes y, which are ordinary water seals. At in is the top lead of the cham¬ ber. The indicating valves w serve to regulate the flow of steam to the chambers. If steam is admitted to the sides of the chambers, the lead terminal pipes enter the side leads or curtains through specially constructed stuffing- boxes. With uniformity in the supply of gas, nitrogen oxides, and steam, and a draft subject to proper control once started, the chamber process becomes continuous and simply requires careful watching to maintain the regularity of the conditions. A careless burner man, by admitting too much air to the furnaces and thus reducing the percentage of sul¬ phur dioxide in the burner gas, or a careless tower man in sending an irregular flow of nitrous vitriol over his Glover, will very quickly destroy the harmony of the reactions and too quickly disarrange the process to such an extent that first the supply of nitrogen oxides in circulation and then the sulphur dioxide itself will be pouring out into the atmos¬ phere and the process will have resolved itself into the same, or almost the same, conditions, the acid maker has to confront when “starting up his chambers” or, in other words, at the beginning of everything. 32. Stai*ting tlie Chamber Process. — This part of the operation requires the exercise of care and judgment, and it will take from 24 hours, where fans are used, to three or four times as long before the process is normal. The Glover tower, with its massive packing, absorbs much heat, and it will take considerable time for it to reach a tempera¬ ture at which it will perform its double functions of denitra¬ tion and concentration in a satisfactory manner, more espe¬ cially as the acid that must be run into it from above has a constant cooling effect. At the same time, the Gay-Lussac 36 SULPHURIC ACID 2 towers become saturated with sulphur dioxide, which prevents the proper absorption of the nitrous oxide, and the formation, consequently, of a stock of nitrous vitriol for the Glover tower. These difficulties, of course, are exaggerated where no stock of 60° to 62° Baume acid or of nitrous vitriol is on hand, and where the process has to be started with a supply of chamber acid alone (or even of water), as is generally the case in an isolated chamber system. When such is the case, the chamber pans must be filled with sufficient acid of from 50° to 54° Baume to form a hydraulic lute with the curtains or side and end sheets of the chamber lead. A small quantity of acid must be run down the Glover tower until the packing is thoroughly moistened, and the Gay-Lussac towers should also be supplied with acid. Whether nitrogen oxides are to be supplied by “ potting,” or by the direct use of nitric acid on the Glover tower, arrangements must be made that will enable an abnor¬ mal amount to be used until such time as the towers are working properly and the stock of nitrous vitriol for circulation is secured. It will be advisable, at first, to supply an amount of nitrogen oxides equal to at least 8 or 10 per cent, of sodium nitrate, on the available sulphur. The burner gas is then turned into the Glover tower and the chamber system. At first and until the Glover tower is performing its functions properly, it will be necessary to supply steam to the first part of the first chamber. This, however, will have to be done with extreme caution, as too great an excess of water is likely to cause the formation of nitric acid HNO a , which will cause the rapid deterioration of the chamber lead. 33. As the Glover tower gets hotter it will concentrate the limited amount of acid with which it is supplied, to about 60° Baume, and the quantity of acid can then be gradually increased. This stronger acid is at once supplied §2 SULPHURIC ACID 37 to the Gay-Lussac towers, which will then commence to absorb a little nitrous oxide; with patience and watchful care matters will gradually assume a normal condition. A sufficient stock of nitrous vitriol having been accumulated, and the steam admission, pumping arrangements, and the flow of acid over the various towers regulated, the extra niter supply will be reduced to a point where it is just sufficient to supply the daily loss and maintain the circula¬ ting supply of nitrous vitriol intact. The acid concentrated by the Glover tower should test 62° Baume at 60° F. (66.4-per-cent. S0 3 ). Such part of it as is intended to be run over the Gay-Lussac towers should be run from the Glover tower into a cooler and cooled as thoroughly as the temperature of the cooling water will allow. It is then pumped to the supply tank on the second Gay-Lussac tower, where it meets with the gas just leaving the system and poorest in A r 2 (9 3 . It will run from this tower containing vary¬ ing percentages of nitrososulphuric acid, and is known as the first, or weak nitrous vitriol. It is then pumped to the first Gay-Lussac tower, or the tower nearest to the last chamber, where it meets the gas strongest withA^C^. Sufficient acid should be supplied to these towers to permit a nitrous vitriol containing 2.5 to 3 per cent, of A \0 3 to run from this first tower. This second, or nitrous vitriol, proper, is then passed to the stock tanks for nitrous vitriol, an exactly equal amount, both in quantity and percentage of N t O a , being taken from the stock tanks and pumped to the top of the Glover tower and run down the tower together with a suffi¬ cient stream of weak sulphuric acid to dilute it sufficiently to secure denitration and also to secure its concentration in the Glover tower to 62° Baume. 34. All well-equipped plants are now being built with two Gay-Lussac towers, both because in this way it is possible to secure sufficient cubic capacity without undue height or diameter, and because if, for any reason, the proc¬ ess becomes irregular (“goes back”) and sulphur dioxide gets into the first tower, decomposing the nitrous vitriol, 38 SULPHURIC ACID 2 then the second tower will still absorb and to a consider¬ able extent take up the work which the first tower is doing badly, the first tower, in the meantime, assuming the func¬ tions which should have been performed by the last chamber. In this way, time is secured to find out just where the trouble is and remedy it before much harm is done. If, however, the trouble is not found and remedied, the sulphur dioxide will gradually get into the second tower and the process will be “lost,” or in other words, with the excep¬ tion that the Glover tower is hot, the acid maker will have to proceed as in starting up the system. 35. It must be borne in mind, and too great emphasis cannot be given to the statement, that when the chamber process begins to go wrong, it is on account of a break'in tJie uniformity of the supply of the various elements. Either the burner gas is richer or poorer in sulphur dioxide, the nitrous vitriol is poorer in nitrous oxide on account of the acid supplied by the Glover tower being weaker than 62° Baume, or too much or too little steam or higher or lower pressure steam is being supplied. When such irregularity is noticed, the acid maker must at once increase the flow of nitrous vitriol from his stock over the Glover tower. He will then immediately test his burner gas, nitrous vitriol, steam, etc. until he finds where the irregularity is occurring. This remedied in time, the process will rapidly become normal again and the increased supply of nitrous vitriol may be cut off gradually, in the meantime more 62° Baume acid being run over the Gay-Lussac towers so as to recover as far as possible the nitrous vitriol temporarily taken from stock. As the activity of the chemical reactions going on in the chambers is proportional to the heat produced by them, it is plain that in a regular normal process the temperature at the most active and least active zones will bear a constant ratio to one another, so long as the process is regular; this fact affords a very delicate indicator of the regularity of the process. §2 SULPHURIC ACID 39 36. If a chamber thermometer, placed in the side of the first chamber about 20 feet from the entrance of the gas from the Glover tower, that is, in the zone of greatest activ¬ ity, registers 100° C., and a thermometer placed in the side of the second chamber, or a zone of lesser activity, regis¬ ters 70° C., when the process is at its best and working with absolute regularity, the difference between the two readings represents the relation between the greatest and lesser activity of that process when normal. If these tempera¬ tures vary so as to disturb this difference of 30° C. so little as 1° C., it is time for the acid maker to investigate his process and find out what is wrong. This will often enable him to save serious disturbance in his process before it has manifested itself in any other way. It must be noted that it is a disturbance of the difference or ratio, however, and not of the actual temperatures. The zones of most and least active reaction ebb and flow slightly in the cham¬ bers so that the actual readings of the thermometers may both be a degree or two higher or lower at various times of the day and especially at various seasons of the year. In addition to the temperature readings, the manometer also affords a delicate test. Manometers registering the tension of the contents of the first and last chambers will show a constant difference of pressure when the process is regular and constant; such difference once determined when the process is at its best will be maintained so long as nor¬ mal conditions prevail. As a guide, to the proper supply of steam at various zones of the process, drip pans are placed on the sides of the chambers, which enable a sample of the acid forming on the sides of the chambers to be taken and tested with the hydrom¬ eter and otherwise examined. This acid, being taken from the cool sides of the chambers, contains more water than the average of the acid being formed in the chamber. This difference is about 3° Baume. A curtain or side drip read¬ ing of 50° Baume would, therefore, represent approximately an average formation of 53° Baume acid in that portion of the chamber. 40 SULPHURIC ACID §3 3 7 . Curtain Drip.— For taking these samples the device shown in Fig. 16 is employed. To the curtain or side lead - - T ■®>) igpp illi ((mmk "a y III iH is attached an inclined lead trough a about 4 feet long. At its lower end is attached the pipe b, which passes through the fig. 16 §2 SULPHURIC ACID 41 curtain /, and is bent so as to form a lute or seal. Acid caught in the trough a runs through the pipe b and drips into the funnel h, communicating with the hydrometer jar^. This jar, together with a rack for the hydrometer, etc., stands in a lead tray d from whose bottom the drip pipe g leads to the chamber pan k. As acid is constantly dripping into h and overflowing from c, the acid in c varies according to that forming in the chamber, and hence tests of this give a fair indication of the condition of affairs in the chamber at that point. Different acid makers prefer to keep the drips of the dif¬ ferent chambers stronger or weaker. This is within cer¬ tain limits immaterial. The acid in the first chamber, in spite of the large amount of water Supplied by the Glover tower, will rarely fall below 52° Baume. The acid formed in the chambers should, however, never be allowed to get strong enough to absorb and retain more nitrous anhydride than is absolutely inevitable, especially in so far as such chambers are concerned from which acid is withdrawn from the system. This strength will also be about 52° Baume, and the tendency to absorb nitrogen oxide will increase with every degree Baume above this point. Nor, on the other hand, must the acid get so weak as to permit the formation of nitric acid in the chambers. This strength will be about 45° Baume. Therefore, the acid formed in the chambers must in no case be weaker than 44° or 45° Baume, nor should it be much, if any, stronger than 52° Baume. Although the drips are highly useful adjuncts in con¬ trolling the chamber process, samples of the bottom acid should also' be taken at intervals, and in each individual chamber the acid maker must learn in this way to compare the actual strength of the acid formed in the chambers as he finds it with the strength of the acid as shown by his drip tests. Such tests of the bottom acid are most satisfactory when taken from a tank that has been filled with acid drawn off from the chamber. 199—8 42 SULPHURIC ACID 2 THE PURIFICATION OF CHAMBER ACID 38. General Remarks. —In addition to the impurities brought into the process with the burner gas, as was previ¬ ously mentioned, some of which will not travel beyond the Glover tower, chamber acid will contain sulphates of lead derived from the slow deterioration of the lead apparatus, and also small quantities of nitrogen oxides and even nitric acid. From a commercial standpoint, the impurities that are most injurious are the arsenic and selenium compounds and even distillation will not entirely eliminate these, unless special precautions are taken. They will pass over into the products made from acid contaminated with them (for example, into muriatic acid and calcined salt cake made from salt and arsenical sulphuric hydrate). If acid con¬ taminated with arsenic or selenium is used for “ pickling ” sheet iron or wire, preparatory to galvanizing or covering the sheets with zinc, tin, or lead, the galvanic action set up in the dilute acid bath will cause the arsenic or selenium to precipitate and become deposited on the iron sheets, which will prevent the adhesion of the zinc, tin, or lead, and result in “ blistered ” sheets. 39. Most other impurities, especially lead or iron sul¬ phates, will separate in the tanks by sedimentation, or, at the worst, will produce a discoloration of the acid that does not unfit the acid for most commercial purposes. Fortu¬ nately, very few of the metallic sulphides contain selenium except in minute traces. Practically all the metallic sul¬ phides contain arsenic, and many of these best adapted otherwise for sulphuric-acid manufacture contain it in con¬ siderable quantity. Arsenic, therefore, is the principal impurity of chamber acid, and on account of its poisonous characteristics, it becomes especially necessary to eliminate it. When sulphuric hydrate is used for refining crude petroleum, or for the manufacture of mixed acid for making nitroglycerin, arsenic is not detrimental, or at least the manufacturers do not object to arsenical acids. The arsenic contained in the enormous quantities of sulphuric hydrate 2 SULPHURIC ACID 43 used in the manufacture of superphosphates and fertilizers may even be of advantage in destroying insects, etc.; but for other purposes, and especially for processes connected with the manufacture of food products, its elimination becomes absolutely necessary. If the manufacturer is not prepared to thoroughly purify his product from arsenic and intends it for the general market, or for galvanizing, food products, or other similar purposes, then he must limit his choice of raw material, often to his great disadvantage as to cost, to such raw materials as are practically free from arsenic (as brimstone, some few of the iron bisul¬ phides, etc.). If his ores contain only a little arsenic, he can sometimes obtain a fairly pure acid from the second chamber, using the acid produced in the Glover tower and first chamber for purposes less exacting of purity; this, however, is a dangerous makeshift. 40. Purification From Arsenic. —As all methods for the purification of acid from arsenic are based on its precipi¬ tation and ultimate removal by sedimentation, it is evident that this operation must take place when the acid is of least density; in other words, while it is still chamber acid (50° to 52° Baume) and before further concentration. This statement must, howexer, be qualified in regard to such manufacturers of 66° Baume and extra-concentrated acid who are equipped to manufacture such acids by distil¬ lation, as will be hereafter described. In many metallurgical plants, where the acid is a by¬ product and the principal value is in the metallic contents of the metallic sulphides, and in cases where the cheapness or other advantages outweigh the disadvantage of consider¬ able arsenical contents in the raw material, the whole output must be treated for the elimination of the arsenic. 41. Freiberg 1 Process for Removing Arsenic. —Where this is necessary, the only practical process is a modification of what is known as the Freiberg process. This process depends on the conversion of arsenious oxide into arsenious 44 SULPHURIC ACID §3 sulphide by means of sulphureted hydrogen gas, the precip¬ itation taking place according to the following equation: As 2 0 3 -f- 3 H 3 S = As 2 S 3 + 3 Hfi. As sulphureted hydrogen will decompose strong sulphuric acid as follows, 3 H t S + H^SO^ = 4 HJD -j- 2 S 3 , it is better to purify the acid as little over 50° Baume as possible. By this process it is stated that at Freiberg, acid containing as high as .14 per cent, of arsenic can be purified until it contains only .0002 per cent, of arsenious oxide As 3 0 3 . 4 : 2 . In chemical works, where sulphate of ammonia is prepared from the gas liquor of illuminating gas works, the sulphureted hydrogen is a troublesome by-product, but can be made readily available for purifying the acid in the Frei¬ berg process. It contains, however, some pyridine bases that must first be eliminated if acid of good color is required. If this source of sulphureted hydrogen is not available, then it must be prepared by treating iron sulphide with dilute sulphuric hydrate FeS + H 3 SO 4 = FeSO t -f- H 3 S. The iron sulphide may be prepared in a simple little furnace by heat¬ ing scrap iron or rails with brimstone. On the large scale, however, it can be very cheaply produced in a cupola fur¬ nace by smelting pyrites fines or inferior pyrites with sili- cious slag. The iron sulphide so produced is broken into rather large pieces and filled into a generator, where it is treated with any available dilute sulphuric acid, such as is often produced about an acid works from the washings of tanks, tank cars, etc., and too dirty for general commercial purposes. These generators are all made on the same general plan (practically that of Kipp’s apparatus, but they are con¬ structed out of lead, wood, and iron, and are often made large enough to hold a charge of iron sulphide sufficient to last several weeks. 43. Freiberg Sulphureted Hydrogen Generator. —A simple and efficient generator for sulphureted hydrogen is shown in Fig. 17. It consists of a cast-iron generator A with flanged top and manhole b and an acid reservoir c. This 2 SULPHURIC ACID 45 generator, as well as reservoir c, is lined with lead. The generator is partially filled with iron sulphide d through the manhole b and the tank with weak sulphuric acid. The acid will then flow from the reservoir c to the generator A, and on coming in contact with the iron sulphide will form sulphureted hydrogen. The valve e and pipe are for carry¬ ing away the hydrogen sulphide; when the valve e is open, the hydrogen sulphide passes constantly away; when e is Fig. n closed, the pressure in A rises until the acid is driven back into the tank r, and the evolution of hydrogen sulphide practically ceases. The weight of the acid in reservoir c being carried by the pressure in A , upon opening the valves the acid again flows into A and generation of gas recom¬ mences. A cleaning vent is provided at f, from which the iron sulphate can be removed when the acid is spent—i. e., entirely converted into iron sulphate—and g is a screen of perforated lead. 46 SULPHURIC ACID 2 4:4. Pi’ecipitation of the Arsenic. —The chamber acid is then run by gravity into a series of gas-tight lead-lined boxes or tanks. Each box in the series is provided with a perforated coil of pipe in the bottom connecting on the out¬ side with the main supply pipe for sulphureted hydrogen and a valve controlling the admission of the gas; it is also con¬ nected at the top by means of pipes and valves with every other box in the series, in such a way that the gas may be made to pass through any one of the boxes first and then consecutively through the others; and, also, that any one of the boxes may be disconnected temporarily from the series. In this way, in a series of, say, four boxes, when the acid in box 1 has had sufficient treatment by the gas, it may be cut out and boxes 2, 3, and 4 remain. When box 2 has been treated sufficiently, then boxes 1, 3, and 4 remain in operation. The box so cut out is allowed to settle as long as necessary. The precipitation of arsenic sulphide has then taken place to such an extent that the upper stratum of acid, amounting to three-quarters or even more of the whole contents, may be decanted or drawn off by a siphon in a pure state, requir¬ ing no further treatment. The rest of the acid containing the precipitated arsenious sulphide must be filtered. 45. Each series of boxes is provided with two simple gravity filters, which consist of lead-lined boxes filled with broken quartz or sand of graduated sizes. The impure acid is run by means of a pipe and valve on to one of these filter beds, from which it will emerge practically free from arsenic. When one filter becomes foul the other filter is put into commission and the foul one cleansed by the removal of the arsenious sulphide from its surface. The exit gas pipe from the last box of any one or more series of boxes enters the bottom of the tower shown in the construction. Just sufficient acid is run into this tower to prevent the escape of any sulphureted hydrogen that has not been absorbed in the boxes. The apparatus for the precipi¬ tation and filtration of the arsenic sulphide, together with all pipe connections, is illustrated in Fig. 18 («)and ( b ). §2 SULPHURIC ACID 47 The main pipe a brings sulphureted hydrogen from the generator shown in Fig. 17. The branches and valves b t , b 3 , b 3 , and b t communicate with the gas-tight, lead-lined boxes C lf C 3 , C 3 , and C v and the perforated coils d t , etc. The acid pipe line e is for filling the boxes C v C 3 , C 3 , and U 4 with chamber acid by gravity, fitted with branches and valves e v c\, e 3 , and e 4 . The return gas pipe f collects the hydrogen sulphide remaining after it has percolated through the acid in the boxes and conveys it to tower G. It is fitted with branches and valves /„/„/„ and / 4 . The tower G is packed in various ways, and a stream of weak arsenical acid runs down through it, meeting the weak hydrogen sulphide not taken up by the arsenical acid in boxes Uj, C 3 , C 3 , and C v This stream must be regulated to completely utilize the hydrogen sulphide and prevent its loss into the atmosphere. The tower is fitted with acid supply line h, tank h y , and distributor h r The filters / and f l are used alternately. A blow case or acid egg J is used for pumping the purified acid to the storage tanks. After a box is sufficiently treated with hydrogen sul¬ phide the gas valve is closed and the manhole opened. The box is then allowed to stand for from 12 to 24 hours, when the arsenic sulphide will be found to have settled to such an extent that about three-fourths of the contents of the box may be decanted off by means of a siphon and passed direct to storage. The remaining quarter is drawn through pipe k and branches k v k 3 , k 3 , and into whichever one of the filters happens to be in commission. This filter strains out the arsenic sulphide, permitting the purified acid to run through pipe l into the pumping apparatus, whence it also passes to storage. The tank is then again filled with acid and another tank cut out for treatment. 4G. Stalil Metliod for Removing Arsenic.—For the purification from arsenic of comparatively small quantities of acid, Doctor Stahl’s method is very satisfactory. The 48 SULPHURIC ACID 2 acid is diluted to 40° or 42° Baume heated to 80° C., and a solution of barium sulphide of 8.3° Baume is run in at the bottom of the vessel in such a way that no hydrogen sulphide escapes. The arsenic trisulphide is filtered off on a sand bed placed on a layer of quartz lumps, and in this way the arsenic will be reduced to .01 per cent., but as the acid on standing in the filter again takes up a little arsenic, it is treated with gaseous hydrogen sulphide and is thus reduced to .005 per cent, arsenic. Arsenic may also be precipitated as a sulphide by means of the sulphides of sodium, calcium, iron, and ammonium, and by sodium and barium thiosulphates, but for most pur¬ poses these substances are objectionable either on the ground of cost or because they leave objectionable impurities dissolved in the acid treated. CONCENTRATION OF DILUTE ACID SOLUTIONS AND THE PRODUCTION OF SULPHURIC MONOHYDRATE 47. The acid solutions resulting from the reactions of the chamber process consist (1) of chamber acid aver¬ aging about 50° Baume, rarely over 52° to 54° Baume, and often diluted for purpose of purification as low as 40° Baume; (2) of acid concentrated to 60° to 62° Baume by the heat of the burner gas in the Glover tower. The concentration of these two products varies materially and must be separately considered. 48. Concentration in Lead Pans. —The first concentra¬ tion of the dilute chamber-acid solutions, varying from 40° to 54° Baume, which come under the first class above, is always effected in shallow lead pans. Concentration in lead can only be made to 60° Baume or slightly over, as the lead pans are rapidly acted on by hot acid of greater strength. The evaporation is carried on in these pans by means of (a) waste heat; (b) direct heat applied either (r) above or ( d ) below the pans, derived from coal, coke, natural or pro¬ ducer gas, oil or petroleum, tar, or applied as steam. 2 SULPHURIC ACID 49 Practically, except in special cases, steam is not found sat¬ isfactory and the benches used are of two varieties, viz., those in which the heat is passed over and those in which the heat is passed under the pans. Pans used to be placed over the brimstone burners, utili¬ zing the heat of combustion. When pyrites began to take the place of brimstone, the pans were still placed above the burners. This practice is now almost entirely done away with, partly because of the large amount of dust involved by the use of pyrites and partly because of the trouble caused by leaks from the pans saturating the costly masonry of the furnaces with acid and of the difficulty of repairs to the pans when so placed, but principally because the intro¬ duction of the Glover tower utilizes the waste heat of the furnaces to much better advantage. Fig. 19 includes a pan bench arranged to be fired from below. The dilute solution flows continuously through the pan bench in quantity to insure its leaving the bench a uniform density of about 60° Baume. This acid must now be further concentrated, either in glass, porcelain, or platinum. After the acid reaches a strength of 64.5° Baume, it may be further and finally concentrated in iron stills or the final concentra¬ tion may be made in glass or platinum. Below this strength (64° to 65° Baume) it acts too strongly on the iron. The concentration in porcelain cannot be carried beyond about 65.5° Baume. 49. Concentration in Platinum, or Partly in Plati¬ num and Partly in Iron.— In Fig. 19 is shown a bench of platinum pans or stills i, o, and q, also the bench of lead pans e, /, and g, in which the preliminary concentration is made. Platinum stills of circular or oblong shape with rounded corners are made of many different patterns; some are provided with platinum covers; some have water-cooled leaden covers or hoods, as in Fig. 19. The principle, how¬ ever, is the same in all; they are practically evaporating kettles for continuous service, provided with an inlet and 50 §2 SULPHURIC ACID 51 exit for the stream of acid and with means for eliminating and condensing the steam or weak distillate. During the gentle evaporation of these dilute hydrates in the lead pans, little but water, in the shape of steam, is driven off; after the solution reaches a density of 60° Baume, more and more of the hydrate is driven off with the water; when the solution reaches a density of 66° Baume (93.5-per-cent. H^SOJ, the distillate will attain a density as high as 60° Baume (77.6-per¬ cent. H^SOy When the solution in the pans contains in the neighborhood of from 95- to 98-per-cent. H^SO 4 , the distil¬ late will have a density of 66° Baume (93.5-per-cent. HJSO 4 ). Much of this distillate is too weak for a reconcentration. It is sometimes run into the drain, but should be used for dilu¬ ting the nitrous vitriol on the Glover tower. The apparatus shown in Fig. 19 (a) and ( b ) is continuous in its operation. The fireplaces a, b, and c communicate with the common flue d. This flue atone end is arched over with “ pigeon¬ hole ” or open brickwork, permitting the fire gas to pass into e ', under and from end to end of a lead pan e. The heated gas returns under lead pan f through flue f, and then passes through flue g' under lead pan g to the stack. Chamber acid is run into lead pan g, whence it flows to pan f and thence to e, from which it passes by platinum pipe h to platinum dish i, covered by a lead water-cooled hood j. The steam and acid vapors escape by pipe k into water-cooled condenser / and thence into the small condens¬ ing tower M. Acid then flows from platinum dish i by platinum tube n into platinum dish o, provided with water- cooled lead hood and exit to condenser. From platinum dish o the acid passes through platinum pipe p into platinum dish q , also provided with hood and exit to condenser. As the acid leaving o will have reached a strength of from 64.5° to 65° Baume, an iron dish is often substituted for platinum dish q. The acid then runs through platinum pipe r into cooler S, and thence to storage. 50. Concentration in Iron. —Different manufacturers have different views as to the material best suited to this 52 SULPHURIC ACID 2 final concentration. Iron, if properly cast and of suitable com¬ position, is but little acted on by acid of 64.5° Baume, and it is, of course, very much cheaper than platinum. On the other hand, for the manufacture of the ex¬ tra concentrated acid, from 97- to 98-per¬ cent. H^SO^ or 79- to 80-per-cent. SO s iron is also more suitable. Hot acid stronger than 94 - per - cent. H^SO A acts strongly on plat¬ inum, but has very little action on iron. In this country final concentration in iron may be said to be the rule and the practice is rapidly gaining ground in Europe. 51. Concentration in Glass Retorts or Stills.— This practice is practically obsolete in the United States, but the following de¬ scription of the ap¬ paratus sometimes used will be of interest. In Fig. 20 (a) is shown §3 SULPHURIC ACID 53 a side view and section of the furnaces and retorts, and Fig. 20 (b) shows an end view of the same. The glass retorts c, c v and c 2 are arranged in steps as shown. The acid from the pan bench flows by gravity through the pipe a and funnel b into the highest retort c. The over¬ flow from c flows through the pipe f to c i and so on down the series; the concentrated acid from the last retort c 2 flows to the cooler //, from which it can be drawn by means of the pipe i. The weak distillate is carried through the “goosenecks” d, d 1} and d 2 to the vapor flue e. A separate fire is maintained under each retort in the fire¬ boxes j, j \, and j r At k, k ,, and k 2 are the ash-pits. The flue l carries the fire gases to the stack. In case of breakage of retorts, their contents are carried off by means of the conduit in. 52 . Concentration in Porcelain or Glass Beakers or Dishes: Systems of Negrier, Webb, Levinstein, and Others.— The principles involved in all these systems of concentration are very similar, and, generally speaking, are merely modifications in details of construction. The acid flows continuously from dish to dish or beaker to beaker. The firing is done from below and the acid vapor is carried away by a separate flue. Fig. 21 shows the Negrier §2 SULPHURIC ACID 55 apparatus and illustrates this method of concentration. All these methods, however, are open to the objection that it is very difficult to prevent the escape of acid fumes into the air. The operation of the Negrier apparatus shown in Fig. 21 is as follows: Pan acid from a flows through conduit b into the first porcelain dish c 1 and so on by means of the lip on the dishes from one dish to the others,, c„ .... c % until the strong, concentrated acid reaches the conduit d , through which it is taken to a cooler and the storage. Heat is provided by fireplace e. The products of com¬ bustion pass under the porcelain dishes until they reach the flue f and are carried to the stack. The distillates and water vapor pass through the flue g and are carried to a suitable condensing apparatus or to the stack. 5,3. Concentration by tlxe Kessler Process.— This method consists of the direct use of heated air or fire gas for evaporating the water from dilute sulphuric-acid solutions. The current of hot gas produced from a coke fire or pro¬ ducer is brought into immediate contact with the dilute acid. In this process, the following conditions must be ful¬ filled: The current of hot air or gas must be brought into contact with a sufficiently large surface of acid to imme¬ diately and considerably reduce its temperature. The air or gas must then be completely saturated with steam and acid vapor. The apparatus must not only be able to resist the action of hot acid and acid vapors, but must be so con¬ structed that the crusts and deposits formed can either be readily removed or will not interfere with the efficiency of the apparatus. Under these conditions , tJie acid can be con¬ centrated at a temperature far below its boiling point. In order to produce acid of 95-per-cent. HJSO 4 , boiling at 284° C., the temperature need not exceed 170° to 180° C.; for the most highly concentrated acid boiling at 320°, a tem¬ perature of 200° to 230° C. will suffice. 54. The Kessler still is shown in detail in Fig. 22 (a), ( b ), and (c). Apart from the coke fireplace a, the apparatus is 56 SULPHURIC ACID divided into two parts, respectively, the saturator c and the recuperator d. The hot air enters the saturator at about 300° C. to 450° C. and leaves it at 150° C. The acid mist or vapor passing out of the saturator is retained in the recu¬ perator, which acts as a dephlegmating or distilling column. Fig. 22 (a) is a longitudinal section through the whole of the apparatus. A large coke fire in the furnace a supplies the hot air that passes through the flue b to the satu¬ rator c. The saturator is constructed of lava (from the town of Volvic in France) with deflecting plates in such a way as to bring the hot gas into close and immediate contact with a large surface of acid, thus securing immediate reduction in temperature and saturation of the gas with the steam and acid vapors formed. The acid vapors contained in the gases leaving the saturator are recovered in the recuper¬ ator d. The recuperator d, shown enlarged in Fig. 22 ( c ), is a dephlegmating column, also constructed of Volvic lava. It is supplied with weak acid. In the recuperator the gas leaving the saturator at 150° C. is reduced in temperature to 85° C., at which temperature all the acid vapor contained in the gas is condensed, while the steam or water vapor passes out of the apparatus at e. The concentrated acid passes from the apparatus at /"into the cooler^. The solutions can be concentrated to 98-per-cent. H^SO i and Glover tower acid can be used. The fuel used to con¬ centrate 100 parts of 95-per-cent. H^SO 4 from 54° Baume or 68.25-per-cent. H i SO A is stated to be 8 parts of small gas coke for the hot-air producer and 3 or 4 parts of coal for power for the exhauster. No weak acid is made, and the product is clear and free from nitrogen compounds; no cooling water is required ; the apparatus takes up little room and requires little repair. 55. Concentration and Distillation, Starting With the Glover Tower. —It has already been stated that the 2 SULPHURIC ACID 57 heat produced in the desulphurizing furnaces is sufficient, if properly conserved, to concentrate the whole of the acid made in any chamber plant to 66° Baume. This can be done in the Glover tower if the tower is con¬ structed so as to stand the action of the hot, concentrated acid. There are, however, two drawbacks to this plan. The first is the impure condition of the concentrated acid, which thus contains most of the impurities of the burner gas, rendering it fit commercially for only a few purposes, and the second drawback is the danger of the Glover tow r er under these conditions not performing its denitrating function properly. The latter objection can be overcome in several ways. Two towers can be placed one above the other, the burner gas passing from the lower to the upper tower. The upper tower denitrates the nitrous vitriol and supplies a stream of hot acid from 58° to 60° Baume to the lower tower, the function of the lower tower being simply one of concentration. If two chamber systems are near to each other, as is often the case in a chemical plant, then the Glover tower of one system may be employed as a deni- trator and the Glover tower of the other as a concentrator; the burner gas from the two towers, the one intensely nitrous and the other not nitrous, being thoroughly mixed with a fan and passed on and distributed by the fan to the two-chamber systems. In this case all the nitrous vitriol is run down the ore tower and denitrated, the result¬ ing denitrated acid of 60° to 62° Baume being concentrated to 66° Baume in the concentrating tower. The drawback of impurity, however, still remains, and except when an unusually pure metallic sulphide is used as raw material, the acid is only fit for limited use. 56. A modification of this plan, however, has now been in use at several works for some years, producing a very pure acid at a very low cost. This consists in denitrating and concentrating the acid in a suitably constructed Glover tower until it has a density of 64.5° Baume, at which point, it will be remembered, hot acid attacks iron but little. 199—9 SULPHURIC ACID §3 This acid, with the full heat imparted to it by the Glover tower (170° to 200° C.), is run from the tower directly into a large cast - iron still (about 8 feet X 2 feet X 6 inches). This still has a cast-iron cover and is so set in the brickwork of the fire that the fire gas plays all around it. In this still it is rapidly concentrated to about 95-per-cent. or some degree of strength higher than 93.5-per-cent. H^ t SO i (66° Baume). The 95-per¬ cent. H^S0 4 acid is then run into a connecting iron still, also completely surrounded with the fire gases. In this still it is further concentrated to a very impure 98-per-cent. H^SO^ As nearly all the 98-per-cent. dd 2 SO t acid made in this country is made for the manufac¬ turers of nitroglycerin, who do not call for a pure acid, and as after being mixed with nitric acid to make the so-called mixed acid , in which form it is sold to manufacturers of nitroglycerin, it is usu¬ ally filtered to remove _I_ IG. 24 §2 SULPHURIC ACID 59 solid impurities, the impure condition of this acid is of little moment. The important fact is that the distillates produced by these two stills, respectively, are pure distillates of 60° Baume and 66° Baume, both of which are commercial solu¬ tions largely used in the arts in this country. Furthermore, as the acid runs hot from the Glover tower to the first iron still, means are taken to add very small quantities of ammo¬ nium-sulphate solution, .1 to .5 per cent, on the 66° Baume acid produced. This not only destroys any nitrogen com¬ pounds remaining in the strong, hot acid, but also converts the volatile arsenious acid into non-volatile arsenic acid, which therefore either remains in the stills or the 98-per-cent, concentrate and does not pass over with the distillate of 66° Baume and 60° Baume acid. The apparatus employed in this method of concentration is shown in Fig. 23 (a) and ( b ). The Glover tower A, Fig. 23 (b), is connected by the platinum pipe, or nozzle b , and the platinum box and tube c with the first iron still d. In this still the acid is concentrated to a strength higher than 93.5-per-cent. H 2 SO v generally to aboht 95-per-cent. H^SO^. The distillate from this still will average about G0° Baume. The acid from the first still d flows to the second still f through the pipe e. In this still the acid is concentrated to 97.5-per-cent. H^SO^. The distillate passing out at g averages about 66° Baume. The concentrated acid finds an outlet through the pipe h into the cooler I. A longi¬ tudinal section of one of the stills is shown in Fig. 23 ( a ). 57 . Lunge Freezing Process for the Production of Sulphuric Monohydrate. —The solution employed should contain at least 97-per-cent. H^SO v and in order to obtain a good yield of monohydrate should be stronger. The solu¬ tion is first cooled and then charged into the iron cells of an ordinary ice plant. When the solution in the cells is properly frozen, the cells are dipped in warm water to detach the frozen solution from the sides of the cells. The frozen mass is then crushed and passed to a cast-iron 60 SULPHURIC ACID 2 centrifugal separator, in which the crystallized mass of monohydrate is separated from a solution of about 94-per¬ cent. // 2 vS( 9 4 . The pure crystal monohydrate is then melted in a water-jacketed enameled pan and run into carboys or other packages. 58 . By the above methods is produced the strongest acid which it is possible to produce by the chamber process. For obtaining the monohydrate or stronger solutions of S0 3 , we have already seen that the old Nordhausen process has been replaced by the contact process. 59 . The diagram, Fig. 24, shows the various methods of manufacturing and concentrating sulphuric acid, and also the relations of the several processes of manufacture. A very useful function of the contact process is as an adjunct to an existing chamber process, where it can be used for strengthening the solutions of sulphur trioxide pro¬ duced in the lead pans or the Glover tower, thus repla¬ cing the concentrating plant or enabling a stronger acid to be produced than is possible by concentration, and at the same time increasing the capacity of the plant. ALKALIES AND HYDRO¬ CHLORIC ACID (PART 1) CHEMICAL METHODS SODIUM CHLORIDE OCCURRENCE OF SAET 1. Sodium chloride, or common salt, as the raw material from which practically all the compounds of sodium as well as hydrochloric acid, chlorine, and bleaching' powder are more or less directly made, easily stands foremost in its importance to the human race among the substances occur¬ ring in nature. Fortunately, salt occurs in large quantities in the ocean, it issues from the earth in many places as brine from salt springs, and, most important of all, it occurs in large solid beds in nearly all countries. SALT FROM SEA-WATER 2. The average amount of solid material in the Atlantic Ocean is about 34 grams per liter, of which a little more than three-fourths is salt, while the remainder consists of chlorides, bromides, iodides, and sulphates of potassium, magnesium, and calcium. The Pacific Ocean contains about COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL, LONDON 23 2 ALKALIES AND HYDROCHLORIC ACID §3 the same amount of solids of approximately the same com¬ position, while the waters of the various inland seas range from comparatively dilute to saturated solutions. Table I gives the composition of the more important large bodies of salt water. TABLE I COMPOSITION OF THE LARGE SALT-WATER BODIES Atlantic Ocean Per Cent. Pacific Ocean Per Cent. Mediterranean Sea Per Cent. Solid salts . . • 3-63 3.50 3-37 H.O . 96.37 96.50 96.63 Solid Contents: NaCl . 77-03 73.96 77.07 KCl . 3-89 2.48 CaCh .... MgCL .... 7.86 13.19 8.76 NaBr 1 1.30 I.OI •49 MgBrJ CaSO 4 .... 4-63 MgSO* .... 5-29 4.63 2.76 xr,so t .... 3.18 8-34 CaC0 3 1 MgCOj • • • 3.85 .10 Salt is obtained from sea-water either by evaporating the water by means of the heat of the sun or by freezing out the water; it would not pay to use fuel for evaporating such a dilute solution. For this purpose, a low, level shore is selected, and a series of basins are formed and lined with beaten clay, which prevents the water from soaking away. The brine is kept circulating from one of these basins to the next until the sun’s heat and hot winds have concentrated it to the crystallization point, when it is allowed to stand until about 50 per cent, of the salt has crystallized out. The remainder of the brine, which contains so much magnesium §3 ALKALIES AND HYDROCHLORIC ACID 3 salts that they would separate out with the salt, is called bittern. This is run into another vat for the separation of the potassium and magnesium salts, or it is run back into the ocean. In the United States, large quantities of salt are produced by this method at Great Salt Lake, Utah, and at a few places in California. In Europe, the principal pro¬ duction is in Southern France and Italy; in Siberia, considerable salt is obtained by freezing the water instead of evaporating it. _ ROCK SALT 3. The most important source of salt is the large, solid deposits that have been left by the partial or complete drying up of inland seas at some prehistoric period. The same process is going on today at the Dead Sea, the Great Salt Lake, and other places. In the course of time, these deposits have become covered with a layer of earth varying from a few feet to several hundred feet in depth. When this layer of earth is not too thick, the salt can be most econom¬ ically obtained by sinking shafts and mining. The most important and extensive salt mines in the world are at Stass- furt, Germany. These mines produce not only large quantities of pure salt, but also the greater part of the world’s supply of potassium salts. The Louisiana rock salt is very pure. Excellent salt is now mined in that state and also in New York and Pennsylvania. The salt from these places is used largely for manufacturing purposes, being crushed and screened to the several sizes required. SALT FROM BRINE 4. Brines may be divided into two classes: natural brines , which flow from springs or wells from a natural reservoir, and may be quite dilute; and artificial brines , which are made by running water into a rock-salt deposit. These may always be made saturated if desired. In the United States, the processes used for evaporating brines are the following, being named in the order of the number of plants using the 4 ALKALIES AND HYDROCHLORIC ACID 3 system: grainers, solar evaporation , open pan , vacuum pan , and kettle. 5 . Solar Evaporation. —The solar-evaporation method depends on the direct heat of the sun. The brine as it is pumped from the wells first goes to a settling tank, where the iron, which is usually present in the form of acid ferrous carbonate, is precipitated as ferric hydroxide by the escape of the carbon dioxide and the oxidizing action of the air. Other sedimentary material also separates out at the same time. The brine is then run into shallow wooden vats, usually from 18 to 20 feet wide, from 100 to 400 feet long, and about 8 inches deep, where it is allowed to stand until salt crystals begin to separate out, by which time most of the calcium sulphate has deposited. Finally, the concen¬ trated brine goes to the salt pans, which are similar to the vats just mentioned, but not quite so deep. Here the salt separates as crystals, and the brine is renewed from time to time until a salt layer about 3 inches thick is formed. The residue of the brine, which contains most of the chlorides of calcium and magnesium, is then run to waste, and the salt is “harvested” by scraping it together and putting it into tubs having perforated bottoms, where it is allowed to drain thoroughly. The vats are built on piles and are arranged so that the brine, after being pumped into the settling tank, can run to the other vats by gravity. In countries where very little rain falls, especially during certain seasons of the year, as in California, and various tropical or semitropical countries, the vats can stand uncovered continuously. In the eastern part of the United States, however, where rains occur fre¬ quently, it is necessary to provide the vats with movable covers that can be rolled back during fair weather. The salt obtained by this process is in large, bulky, cubical crystals that occlude considerable quantities of mother liquor, and on account of the deliquescent calcium and magnesium chlorides thus mixed with the salt, it becomes moist in damp weather. §3 ALKALIES AND HYDROCHLORIC ACID 5 6 . Kettle Evaporation.—In the kettle process, the brine is evaporated in cast-iron kettles that are about 4 feet in diameter by 2 feet deep and are heated either by direct fire or by a steam jacket. When necessary, for the removal of the iron, the brine is mixed with a little milk of lime and allowed to settle; it is then run into kettles and evaporated. The calcium sulphate, which separates out first, is removed from time to time until the salt begins to crystallize. The salt is removed from the kettle at intervals, drained into baskets, and then dumped into bins so as to dry thoroughly. When heated by direct fire, the kettles are arranged in rows of from sixteen to twenty-five over the flues; and as those at the front end are the hottest, the brine evaporates most rapidly at that point, giving the finest crystals, while the kettles at the back end produce crystals more like the solar salt. With steam-jacketed kettles, the product is much more uniform. 7 . Open-Pan Process. —The open-pan process is probably the oldest of all methods that use artificial heat, for the Romans at the time of their occupation of England used practically the same arrangement as the present, except that their pans were of lead and only about 6 feet square. The pans a, Fig. 1, now used are made of iron and are from 70 to 150 feet long, from 20 to 25 feet wide, and from 12 to 18 inches deep. They are heated by direct fire. The grates, of which there are three or four for each pan, with the doors b for charging, are situated at the front end of the pan and are connected to a chimney, which is placed at the rear end of each pan, by flues that lead under the pan. The brine, after having been purified by milk of lime and settled, is led into the back part of the pan, where it becomes slowly heated and concentrated so that it deposits its calcium sulphate as it slowly flows toward the front and hotter portion of the pan, where the greater part of the salt is deposited. At intervals the salt is scraped together and on to draining boards c by means of long-handled wooden hoes. The workmen pass between the pans on wooden walks d. The 6 ALKALIES AND HYDROCHLORIC ACID §3 roof covering the pans and furnace is cut out at the peak in order to allow steam to escape, but it is covered with a cap to keep out rain. 8. Gralners. —An important modification of the pan process is the so-called grainer. The pans are made of either iron or wood and have the same general dimensions as those in the pan process, except that they are somewhat deeper. The evaporation is caused by steam circulating through pipes that are raised about 6 inches above the bottom of the pan and are kept constantly covered with brine; in other respects, the operation is practically the same as in the pan process. 9 . Vacuum-Pan Process. —The vacuum-pan proc¬ ess leads to a very fine grade of salt, and on this account is used in several places. Since salt is about equally soluble in either hot or cold water, it is not possible to concentrate the solution in the pan and then run the solution outside to crystallize, as is done in many other cases; also, if the vacuum pan is used for anything more than bringing the brine to its saturation point, the salt must be allowed to deposit in the pan. This can, of course, be accomplished by using a simple pan that is covered over and partly exhausted, but it is then necessary to open the pan from time to time to remove the 8 ALKALIES AND HYDROCHLORIC ACID 3 salt, which is an obvious disadvantage. To do away with this difficulty, several continuous-acting vacuum pans have been proposed, the best of which is Pick’s triple-effect evaporator, which is shown in Fig. 2. In this apparatus is followed the principle of keeping each element under less pressure than in the preceding one, and evaporating its contents by means of steam taken from the preceding element. The brine enters at g, and at rs is a vertical coil of pipes, which, : in the first element, is supplied with steam through e and is sufficiently long to condense the steam so that it flows as water from the opposite end s. The heat from the steam coil evaporates the brine ac, and the steam passes through the pipe / into a similar vertical coil at b', where it condenses and boils the brine in a'c', which stands under less pressure than that in ac; the steam from a'c', in turn, evaporates the brine in a"c ", which is under still lower pressure. The salt as it separates collects in the funnels c,c',c", and can be brought into the filter chambers d, d', d" when desired by turning the valves at i, i', i". Each filter chamber has a filter in the bottom por¬ tion, from which a pipe h returns to the upper part of the element, so that the mother liquor may be returned if desired. The salt may then be washed by means of the rose x , and the wash water run off by the tap y. The salt can be with¬ drawn through an opening in the side of the filter chamber. 10. Frequently, in preparing fine table salt, the brine is first mixed with sodium carbonate to precipitate, so far as possible, the calcium as carbonate, and then with a little soap, or some similar substance, to remove the remainder of the calcium and magnesium as the insoluble soaps of these elements. 3 ALKALIES AND HYDROCHLORIC ACID 9 SODIUM CARBONATE NATURAL, AND ARTIFICIAL SODA 11. Natural Occurrence.—Sodium carbonate occurs in nature widely distributed. It is seldom found, however, as the normal carbonate, but as a partial decomposition product of sodium bicarbonate of the composition Na 2 C0 2 - NaHC0 3 -2H 2 0, commonly known as Trona or Urao. It has long been known in Egypt, where it is called Wadi Atrium , or Natrium; in Hungary it is called Szekso. Sodium carbon¬ ate is also found in Russia and other countries. Very large deposits are found in many parts of the United States, especially in Wyoming and California. In Wyoming are found lakes that contain over 2 pounds of crystallized sodium carbonate per gallon of water and only a small amount of sodium chloride. Coal is mined within 15 miles of these lakes, so that it is estimated that from 98 to 99 per cent, of pure sodium carbonate can be made for one dollar a ton. A company has been incorporated to undertake its manufacture. Sodium carbonate is also obtained from springs located at Soda Springs in the same state. The waters of these springs carry about the same quantity of sodium carbonate, and the product supplies the local demand and part of that of California, but the total tonnage available is not large. Probably the largest deposits of natural sodium carbonate in the world occurs in California. Mono Lake in that state has an area of 65 square miles and is estimated to contain 75,000,000 tons of sodium carbonate and 18,000,000 tons of sodium bicarbonate. This lake is situated high in the moun¬ tains, however, where fuel is scarce and solar evaporation is out of the question; besides, the difficulty of removing the finished product makes the working of this deposit impos¬ sible, for the present at any rate. Owens Lake, however, which has an area of about 110 square miles, contains a sodium-carbonate deposit of from 40,000,000 to 50,000,000 10 ALKALIES AND HYDROCHLORIC ACID 3 tons, and is constantly being added to at the rate of about 200,000 tons each year. The soda is here obtained by solar evaporation, and large quantities are produced. A third large deposit, which has recently been discovered in Mexico, is located about 21 miles from Adair Bay on the Gulf of California. This deposit covers an area of about 60 acres to a depth of from 1 to 3 feet, and is only covered by about 3 inches of sandy silt. The average sample of the dry soda showed 76 per cent, of sodium carbonate, 5 per cent, of sodium sulphate, 1 per cent, of sodium chloride, and about 18 per cent, of soluble matter. The source of natural soda is probably feldspar rocks that are decomposed by atmospheric conditions. The sodium carbonate formed is washed by rains into lakes, and, lacking outlets, their waters become supersaturated. Probably some sodium carbonate is also made by transforming sodium chloride to sodium sulphate by calcium or magnesium sul¬ phate, then reducing the sodium sulphate to sodium sulphide by certain algae, and converting the sulphide into the car¬ bonate by the action of carbon dioxide. Notwithstanding these large natural deposits of sodium carbonate, they are the sources of very little of the soda of commerce. Owing to the cost of solution, evaporation, purification, and transportation, the product, except at points of consumption near the deposits, can be manufactured much more cheaply from salt by processes about to be described. 12 . Until near the end of the 18th century, practically all the world’s supply of soda was obtained from these natural deposits and from the ashes of certain plants that grow in or near the sea, most of it, however, coming from the latter source. For this reason, the potassium carbonate found in the ashes of land plants was much the cheaper and more commonly used alkali at that time. The plant soda was made in Spain, where it is called barilla; in France it is called varil , or blanquette. 13 . Artificial Soda. —The artificial preparation of sodium carbonate, frequently called soda ash , dates back to §3 ALKALIES AND HYDROCHLORIC ACID 11 the latter part of the 18th century and has now become one of the largest of the chemical industries. While many proc¬ esses for the manufacture of soda have been proposed, the only ones in use on a large scale at present are Le Blanc's process , the cryolite-soda process , the am?nonia-soda, or Solvay, process , and the electrolytic process. These processes are named in the historical order in which they became impor¬ tant, but they will be treated in the order of their present importance in the production of soda ash in America. THE SOLVAY PROCESS 14 . Historical.—The fact that when solutions of sodium chloride and ammonium bicarbonate are mixed, a part of the sodium separates out as sodium bicarbonate, was probably known in the early part of the 19th century. Not until 1838, however, was it recognized as a possible method for the manufacture of sodium carbonate. In that year, H. G. Dyar and J. Hemming took out an English patent for making sodium carbonate by means of the reaction NaCl + HNH 4 C0 3 = NaHC0 3 + NH t Cl and then heating the sodium bicarbonate to drive off the carbon dioxide and water, leaving sodium carbonate. This patent covered the chemistry of the process practically as it is worked at the present time, and also many of the mechanical principles. At that time, however, the cost of ammonia was so great that they did not succeed in keeping the loss low enough to make the process profitable. About 1855, Schloesing and Rolland patented in England some improvements on the preceding process, and at a factory in France actually manufactured about 25 tons of soda a month for nearly 2 years. They did not succeed in recovering the ammonia sufficiently well, however, and abandoned the method. Various other inventors worked on the process between 1838 and 1863, and fortunes in time and money were spent to no avail. In the latter year, Ernest Solvay, a Belgian, took up the process without knowing much about 12 ALKALIES AND HYDROCHLORIC ACID §3 the other work that had been done on it. He worked on the process until 1873 before the mechanical difficulties were overcome and the method became an assured success. From 1873 until the present time, the process has been constantly growing in importance and strength, so that now more than half the world’s supply of soda is made by this method. 15 . Outline of the Process. —In brief, the Solvay process consists in preparing carbon dioxide from lime¬ stone, passing this gas into an ammonium-hydrate solution to form ammonium bicarbonate, mixing salt solution with the ammonium bicarbonate, and getting sodium bicarbonate, which precipitates, and ammonium chloride, which remains in solution. The sodium bicarbonate is then calcined to form soda ash. and the carbon dioxide, after being cooled, is let back into the process. The ammonium chloride is decomposed by milk of lime, the ammonia is set free so that it may be used over again, and the chlorine goes to form calcium chloride, which is mostly run to waste. The reactions are then CaCo 3 — CaO + C0 3 NH 4 0H+ C0 3 = HNH 4 C0 3 NaCl + HNH t C0 3 = HNaCO a + NH 24 H,0+ 48 CaO-MnO, + 24 MnCl, = 24 CaO-(MnO,), + 24 Afn(OH), + 24 CaCl, 24Mn{OH) 2 + 60, = VIMnOMnO, + 24// 2 <9 124 MnCl, + 160 Ca{OH), + 49<+ = 36 CaO-(MnO,),+ 26 Mn O ■ Mn O, + 12 ACaCl, + 160 H 2 0 From this last equation it may be noted at once that at the end of the operations there is a mixture of 3 6CaO (MnO,), and 26i MnO-MnO„ or 98 MnO, + 2>6CaO + 2 6MnO, from 124 gram molecules of manganese chloride. That is to say, 36 ALKALIES AND HYDROCHLORIC ACID 4 there is 79 per cent, of the manganese in the form of the dioxide, as against 86 per cent, of the manganese in this condition before the last addition of manganese chloride. The present condition is much better, however, for although the percentage of the manganese converted to the dioxide is somewhat smaller than before, the amount of base present is much more reduced than the active manganese. Before the second addition of manganese chloride, there are 74 gram molecules of base to 86 gram molecules of manganese diox¬ ide; that is, 53.75 per cent, of the total number of gram molecules that can react with hydrochloric acid is manganese dioxide. When the operation is completed, however, there are only 62 gram molecules of base to 98 gram molecules of the manganese dioxide, or 61.25 per cent, of the active gram molecules is manganese dioxide. It is obvious, then, that the second addition of manganese chloride and longer blowing are decided advantages. 52. Weldon Mud. —The mixture of calcium and man¬ ganese manganites obtained by the operations just mentioned is a black, shiny precipitate, which is in suspension in a solution of calcium chloride. This mixture is run from the oxidizers to the settling tanks, where it is allowed to stand for 3 or 4 hours. At the end of this time the precipitate will have settled into the lower half of the solution, and the clear calcium-chloride solution can be drawn off from the top; the shiny mass remaining is called Weldon mud. The Weldon mud finds several uses besides the prepara¬ tion of chlorine; it is used in gas purifiers, to remove iron from alum, to remove sulphides from caustic soda, and for several similar purposes. Weldon at one time recommended that this mud be used instead of chalk for neutralizing the still liquors, but later abandoned it for that purpose. At present, Weldon mud is used quite extensively in that way, for it not only saves the chalk, but also utilizes the acid of the liquor to neutralize the bases in the mud, and thus increases the efficiency of the mud as an oxidizing agent. The use of Weldon mud for neutralizing the still liquors has §4 ALKALIES AND HYDROCHLORIC ACID 37 the disadvantage that all the impurities, such as calcium sulphate, iron, and aluminum, are left in the mud. This makes it necessary occasionally to neutralize a batch with chalk and allow the impurities to settle out. When this method is used, great care is taken to keep sulphuric acid out of the hydrochloric acid. Sometimes, calcium chlorine is added to precipitate the sulphuric acid before the hydro¬ chloric acid is used. CHLORINE BY THE WELDON PROCESS 53. Weldon mud is used chiefly in the generation of chlorine, and for this purpose it is much more active than manganese ore. The stills used are similar to those already described, but the method of working is somewhat different from that when manganese ore is used. In working with Weldon mud, the hydrochloric acid is run as hot as possible directly from the condensers into the stills, and the mud is then added slowly, so as to regulate the flow of chlorine until sufficient for the acid is present. Too much must not be added, especially if the still liquors are neutralized by chalk, for in that case the manganites that are unacted upon will settle with the mud from the neutralized liquors and be lost. When the color of the liquor in the still shows that enough mud has been added, steam is blown in and the chlorine is driven off as completely as possible. In this way, it is possible to leave only from I to 1 per cent, of free hydrochloric acid in the still liquor. This is equivalent to about 3 per cent., as counted on still liquor from manganese ore, for the water in the Weldon mud makes its still liquor more dilute than that from manganese ore. From U to 3 per cent, of the manganese is lost in the cycle of operations, and this is supplied by continuously decomposing the neces¬ sary amount of manganese ore in a small still and adding its liquor to the general supply. Only about 30 per cent, of the chlorine in the hydrochloric acid is obtained in the bleaching powder. The remainder is, for the most part, run to waste as calcium chloride. 38 ALKALIES AND HYDROCHLORIC ACID §4 54. Apparatus.—The apparatus used in performing this cycle of operations is shown in Fig. 16, which represents a cross-section through part of it. Starting with the still liquor from the still A , the liquor runs into the neutralizing tank B , where it is mixed with either chalk or Weldon mud and thoroughly stirred. It is then pumped, by means of the Fig. 16 pump C, through the pipe shown, to the settling tank D. If chalk is used for neutralizing, the mud obtained is value¬ less; if Weldon mud is used, however, the mud here obtained can be used in the chlorine still. From D the neutralized liquor goes to the oxidizers E, E. Meanwhile, lime is slaked in tanks F, E, and made to the proper consistency. This lime is then pumped, by the pump and pipe shown, to the reservoir G, §4 ALKALIES AND HYDROCHLORIC ACID 39 from which place it is run in proper quantities into the oxidizers E, E. Air is forced into the mixture through the pipe /, which extends to the bottom of the oxidizers, by the blowers H. From the oxidizers, the batch is drawn off into the settling tanks K , from which the mud is again run as needed into the still A. It will be noted that nearly all the materials are moved as solutions, or slimes, so that the work is almost entirely mechanical. The solutions, or slimes, are pumped to the highest point of the plant and then allowed to flow down through the various pieces of apparatus until they once more reach the lowest point. Practically the same number of men are required for a small plant as for a large one, so that on this account, the working of a large plant is more economical. DEACON’S PROCESS FOR CHLORINE 55. In the process just described the manganese has acted simply as an oxidizing agent to remove the hydrogen from the chlorine and set the latter free. Although the steps are a little further removed, there is a direct analogy between this operation, when the Weldon manganese-recovery method is employed, and the making of sulphuric acid, where nitric oxide is used as a carrier of oxygen from the air. And, just as recently the problem of causing sulphur dioxide to com¬ bine directly with the oxygen of the air by passing a mixture of the two gases over platinized asbestos or ferric oxide has been solved in a practical manner, so, much earlier, it was found that when hydrochloric acid and air are passed over porous material saturated with salts of copper, lead, or manganese, the oxidation of the hydrogen of the hydro¬ chloric acid into water takes place direct. It was discovered and patented by Oxland, in 1845, that when a mixture of hydrochloric acid and air is passed through a tube filled with red-hot pumice, the following reaction takes place: 4 HCl + 0 % = 2H,0 + 2 Ch 40 ALKALIES AND HYDROCHLORIC ACID §4 This is a reversible reaction, however, and, under the conditions here stated, the decomposition of the hydrochloric acid is very incomplete. Ten years later, in 1855, Vogel found that when cupric chloride is heated it decomposes into cuprous chloride and chlorine, according to the reaction 2 CuCl, = 2 CuCl + Cl, Then by passing hydrochloric acid and air over the cuprous chloride, an oxychloride of the composition CuCl,'3Cu0‘3H,0 is formed, which finally goes over into cupric chloride, the final reaction being 4 CuCl + AH Cl + O, = ACuCl, + 2 H,0 In practical working, however, it was found that only about one-third of the chlorine was obtained from the cupric chloride, instead of the theoretical one-half. There was also a loss of copper salts, and on account of these and other difficulties, the process was never successful. 56 . The idea occurred to Deacon, however, to combine these two methods, and he took out his first patent to that effect in 1868. Various contact substances have been pro¬ posed and patented, but certain salts of copper are found to be the, best. In general, the process as carried out now con¬ sists in passing a suitable mixture of hydrochloric acid and air through tubes containing clay balls saturated with a cop¬ per salt. Copper sulphate is generally used to saturate the balls, but it is claimed that this is soon converted into the chloride. The reactions taking place in the tube are generally considered to be 2 CuCl, = 2 CuCl + Cl, 2 CuCl + O, = 2 CuO -f Cl, 2 CuO + AH Cl = 2 CuCl, + 2 H,0 It is held by some, however, that the copper salt only acts catalytically, and that the reaction is direct between the hydrogen of the acid and the oxygen. 4 ALKALIES AND HYDROCHLORIC ACID 41 DETAILS OF THE DEACON PROCESS 57. Hydrochloric Acid. —The acid used for the Deacon process must be as uniform in composition as possible and free from' dust, sulphuric acid, and arsenic compounds, for otherwise the contact substance will deteriorate very rapidly. Uniformity of composition is not hard to get when the acid is liberated from its solutions. When the acid goes to the decomposer direct from the salt-cake oven, however, it is not so easy to maintain uniformity, for the acid is given off rapidly at first and more slowly later. This diffi¬ culty is largely overcome,however, by connecting several fur¬ naces to each decomposer, so that by charging the salt-cake furnaces in rotation, a nearly uniform flow of acid gas is obtained. Where the acid is used direct from the salt-cake ovens, only the pan acid is used, for this acid is much purer than that from the roaster, and the acid from the latter can be condensed and sold as acid or used in the Weldon process. At the present time, the custom at many works is to condense all the hydrochloric acid produced and then liber¬ ate the gas from its solution by running it into hot, concentrated sulphuric acid, and blowing a current of air through the mixture; a very pure hydrochloric-acid gas is thus obtained. This method of purifying the hydrochloric acid was worked out by Hasenclever, and has done much to make the Deacon process a success; for this reason, the process is frequently referred to as the Deacon-Hasen- clever process. Calcium chloride has been proposed for setting hydro¬ chloric acid free from its 'solutions. It possesses no advantage over sulphuric acid for this purpose, however, and the latter is more generally used. 58. The hydrochloric acid is mixed with about an equal volume of air, which furnishes the theoretical amount of oxygen necessary to decompose it. Since, however, even in the presence of the catalytic substance, the reaction is not 42 ALKALIES AND HYDROCHLORIC ACID §4 complete, an excess of air will drive the decomposition of the hydrochloric acid further. The disadvantage, however, enters here, that the excess of air dilutes the already much diluted chlorine, so that it is better to allow a portion of the acid to escape decomposition than to produce such dilute chlorine. The mixture of air and hydrochloric acid must be as dry as possible—the drier the better—before going to the decomposer. It has been found in practical working, how¬ ever, that very satisfactory results are obtained if the mix¬ ture is cooled to 37° C. Gas saturated with moisture at that temperature works in the hot decomposer nearly as well as perfectly dry gas, and the cost of drying is saved. 59. A portion of the reactions in the decomposer absorbs heat and a part evolves heat, but the sum total of these reac¬ tions is an evolution of several calories of heat for each gram molecule of hydrochloric acid oxidized. There is not enough of this heat, however, to make up for loss through radiation and also bring the gas mixture to the best temperature for the decomposition. The gas mixture should therefore be heated to about 450° C. before it goes to the decomposer, as this temperature has proved to be the best for decomposition. 60. I he gas that issues from the decomposer consists of a mixture of hydrochloric acid, chlorine, oxygen, nitro¬ gen, and water vapor. Both the hydrochloric acid and the water vapor must be removed if the chlorine is to be used for bleach making. The gases therefore pass through a cooling arrangement to condense the water as much as possible, and with it the acid. The gas is then washed with water, and is finally passed through towers, down which sul¬ phuric acid is sprayed, to dry it completely. 61. Apparatus.—The apparatus for carrying out the Deacon process is shown in Fig 17. It consists of a cooling and condensing arrangement for the gases as they come from the salt-cake furnace or from the Hasenclever purifier. This cooling and condensing apparatus usually consists of a long, upright pipe A and a small coke, or plate, tower B. The gas mixture goes to the heater C, which consists of a 43 44 ALKALIES AND HYDROCHLORIC ACID §4 series of pipes, up and down through which the gas must pass. The pipes are enclosed and heated by the gases from a fire in the grate d. Having been heated to about 450° C., the gases pass into the decomposer E. Several forms of this piece of apparatus have been proposed, but the one here illustrated is the most satisfactory. It consists of a large circular outer chamber, into which the mixture of air and acid passes from the heater. Arranged inside of this chamber, so that the gas must pass through them, are the cylinders containing the catalytic material. The walls of these cylinders are made similar to Venetian blinds, so that the gas must take a downward course on entering, and, after traversing the filling, must take an upward course on leaving. The gases from the whole system collect- in the center, and are drawn off by a pipe to the purifying appara¬ tus. Each cylinder is arranged so that it can be cut out of action when necessary for emptying and refilling, for the catalytic material deteriorates slowly by use and must be renewed about every 12 weeks. Frequently, in the style of decomposer shown here, all the cylinders are kept in continuous action, and when it is necessary to recharge them, the fresh material is charged at the top as rapidly as the old is withdrawn at the bottom. Many methods have been proposed for cooling and washing the gas that comes from the decomposer, but the one illustrated at F is probably the most efficient and at the same time the most simple. The apparatus for this method consists of upright pipes that end in troughs of water, the pipes serving to cool the gases and the water to wash out the hydrochloric acid. Finally, the gas is completely dried by sulphuric acid in the towers G. A suitable vacuum is maintained in the whole apparatus by means of a pump placed beyond G. 62 . Comparison of the Weldon and the Deacon Processes. —It is difficult to say whether the Weldon or the Deacon process leads in the production of chlorine at the present time, and it is equally difficult to say which process is the better, as this depends on general conditions. 4 ALKALIES AND HYDROCHLORIC ACID 45 In the old manganese-dioxide method, theoretically 50 per cent, of the chlorine of the acid was obtained free, but in practice not over 30 to 33 per cent, was realized. In the Weldon process, only 40 per cent, of the chlorine of the acid is theoretically available, but about 30 to 33 per cent, is also obtained here and the manganese is recovered as well. In both cases a strong chlorine is made. In the Deacon process, 100 per cent, of the chlorine in the acid is theoretically obtainable, and in practice 50 to 80 per cent.; the rest is recovered as acid to be used over. The chlorine is much diluted, however, only averaging from 7 to 10 per cent, chlorine, so that it is not so suitable for as many pur¬ poses as the stronger gas obtained from the other methods. NITRIC-ACID CHLORINE PROCESS 63 . A number of processes have been proposed that involve the oxidation of hydrochloric acid by means of nitric acid, according to the reaction SHCl + HNO, = 2// 2 <9 -f NO Cl + Cl u but these have never been put in practice. Where chlorine is used in large quantities it is some¬ times made "on the spot, either directly from salt or from hydrochloric acid. The use of salt, however, is almost obsolete, and the carrying of the hydrochloric acid is incon¬ venient and somewhat dangerous. For this reason, it can rarely be economically made at any place far removed from alkali works. On the other hand, the chlorine gas is bulky and must be converted into some compact form for shipment. 64 . Liquid Chlorine. —Chlorine is a gas that is com¬ paratively easily liquefied, for it becomes liquid when cooled to —34° C. at the ordinary atmospheric pressure, or when subjected to a pressure of 6 atmospheres at the ordinary temperature. Liquid chlorine is such a corrosive substance, however, that until recently it was not considered possible to find pumps to work it, or tanks to hold it when it was com- ALKALIES AND HYDROCHLORIC ACID §4 4G pressed. The pumps used in compressing chlorine consist, for the most part, of a plunger that works in petroleum and forces the petroleum against a column of sulphuric acid. The chlorine collects over the acid, and when the acid is raised, the chlorine is forced into a tank and com¬ pressed. Moist chlorine acts very strongly on iron at the ordinary temperature, but when perfectly dry, it has practically no action on this metal, and iron tanks can be safely used for storing and shipping it when in the liquid form. In Germany, chlorine is transported in iron or steel tanks. These tanks hold about 5,000 pounds each, and three or four of them are fastened to a railroad car. Chlorine is also largely sold in steel cylinders that hold from 50 to 200 pounds each. One volume of liquid chlorine is equal to 400 volumes of chlorine gas at ordinary conditions of temperature and pressure. No matter from what source chlorine is derived, whether from hydrochloric acid, as previously described, or electro- lytically, as will be described later, its principal use is in the manufacture of bleaching powder, and all the methods for that purpose are the same BLEACHING POWDER 65 . When chlorine is passed over dry, slaked lime, a com¬ pound is formed that again gives up the chlorine when treated with an acid. This compound was at first supposed to be calcium hypochlorite, Ca{OCl)t , and was called chloride of lime; it is now more commonly known as bleaching powder. Bleaching powder yields only 100 volumes of chlorine for each volume of the substance, and requires acid to set it free. It is, nevertheless, a most convenient means for the transportation and storing of chlorine and is almost univer¬ sally used. 66. Lime. —The lime used for making bleaching powder should be very pure and well burned. Impurities are decidedly undesirable, for in addition to making it impossible to make a strong bleach if the lime does not contain a high 4 ALKALIES AND HYDROCHLORIC ACID 47 percentage of calcium oxide, clay and similar substances cause the bleach solutions to settle badly. Iron and man¬ ganese cause a colored bleach, which does not sell readily; besides, these substances cause a more rapid decomposition of the bleach than would otherwise occur. Thus, a limestone of as great purity as possible having been selected, it is burned in such a manner as to avoid having the ashes of the fuel mix with the lime. A reverberatory furnace is fre¬ quently used for this purpose. The carefully burned quick¬ lime is slaked by sprinkling with water; and as an excess of water cannot be used, the best plan is to let the lime lie for 2 or 3 days to allow it to slake well through before using. Perfectly dry slaked lime does not work well with chlorine, and, on the other hand, too great an excess of water must be avoided or the lime will cake together and not chlorinate through. Theoretically, calcium oxide requires 32 per cent, of its weight of water to convert it into the.hydrate, and from 2 to 4 per cent, of water in addition to this, depending on the dehydration of the chlorine, is generally used. After slaking thoroughly, the lime is sifted through a sieve having from 12 to 25 holes to the linear inch. The finer the division of the lime, the better it absorbs the chlorine. It is now ready to spread in the absorption chambers. 67 . Absorption Chambers. —The chambers for absorb¬ ing the chlorine are commonly large rooms made of brick or stone laid in asphalt cement; though they are sometimes made of lead, which is probably the best material and is not much more expensive than the others. The floors are either of asphalt or lead. The lime in the chambers must be turned over when the layer is thick, so that the chambers must be high enough for a man to stand upright while turning and removing the material. An ordinary chamber is about 100 feet long, 30 feet wide, and 62 feet high. It is usually estimated that 200 square feet of floor space is required per ton of bleach per week. The slaked lime is spread on the floor in a layer from 2 to 4 inches thick, and is furrowed by a rake to give a large absorbing surface. The gas passes 199—17 48 ALKALIES AND HYDROCHLORIC ACID §4 into the chamber at the top of one end and out of it at the top of the opposite end. The chlorine, being heavy, settles to the bottom of the chamber and is very rapidly absorbed at first and then more slowly, as the lime becomes more nearly saturated. In the case of single chambers, when the absorption becomes too slow, the gas is shut off and, after freeing the chamber of chlorine, men go in and turn and relevel the lime. In the more modern works, where three or more chambers are worked together, the turning can be avoided, for the strong gas goes into the most nearly finished chamber and then to fresher lime, so that the chlorine does not escape. When the layer of lime is not over 2 inches thick, the operation will usually be finished without turning the material; when the layer is more than 2 inches thick, the material usually has to be turned. A second passing of the gas will generally bring the available chlorine in the bleach to 36 to 38 per cent., and that is sufficient. If this percent¬ age is not obtained, the material must be turned a second time and again treated with gas. If this treatment does not bring the bleach to the desired strength, it must be packed and sold for what it will bring, for further treatment with chlorine will only result in the decomposition of the bleach already formed. 68. Chlorine. —The chlorine must be free from carbon dioxide and hydrochloric acid, and as free from water as pos¬ sible. The stronger the chlorine the better; very dilute chlorine, such as comes from the Deacon method, cannot be used in this form of apparatus. The chlorine must be intro¬ duced into the chamber very slowly, so as to avoid a rise in temperature, for if the temperature is too high, chlorates will form and the bleach will decompose, giving oxygen.. On no account should the temperature go above 40° or 45° C., while a lower temperature is better. 69 . On opening the chamber to turn or remove the bleach, the chlorine escapes into the air and thus makes the task disagreeable. This is obviated somewhat by letting the chambers stand for some time before opening, or, better. §4 ALKALIES AND HYDROCHLORIC ACID 49 by sprinkling a little fine dust of calcium hydrate in from the top. At best there is a great deal of hard, disagreeable work connected with the process, and the plant covers a large area. The attempt has been made to do away with these difficulties by stirring the lime mechanically while it is being chlorinated. By this means the lime is chlorinated rapidly and discharged into the barrels without much hand labor. This method is subject to a great disadvantage, since the rapid absorption of the chlorine causes the temperature to rise too high. This has been somewhat obviated lately by cooling the apparatus from the outside. 70 . As already mentioned, the apparatus that is suitable for strong chlorine cannot be used for the more dilute chlo¬ rine obtained in the Deacon method, for the absorption is too slow with such weak gas. Deacon avoided this difficulty by using large stone chambers in which shelves were placed close together. On the shelves, the finely powdered slaked lime was spread in layers not over f inch thick, and the chlorine passed downwards over these shelves. This arrangement works very well, but it requires very large chambers. For each ton of bleach produced in a week a shelf space of 1,373 square feet is necessary. With the dilute chlorine, the absorption is not so rapid, and a mechanical chlorinating apparatus can be used to good advantage. 71 . The best of the mechanical chlorinating devices consist of cast- or wrought-iron cylinders that are 15 to 18 inches in diameter and about 20 feet long. These cylinders are fitted with a conveyer that operates on the principle of an Archimedean screw. A carefully regulated quantity of slaked lime passes continuously into the cylinder at one end and meets the chlorine, which is moving in the opposite direction. When using very dilute chlorine, as from 4 to 6 per cent., three of these cylinders are placed so that one is over the other, the top one fitting into the one below and the second into the third, from which the bleach is allowed to flow into a drum, or cask, in which it is packed. 50 ALKALIES AND HYDROCHLORIC ACID 4 The chlorine is prevented from escaping by luting all open¬ ings with lime or bleaching powder. Bleach made in this manner rarely contains over 35 per cent, of chlorine, which is the lowest standard when freshly made. These methods are patented, although the validity of the patents is open to question. 72 . Properties of Bleaching Powder. —The chloride of lime should be either in the form of white powder or in lumps that will break easily. It is acted on by the carbon dioxide of the air, and will therefore lose strength if exposed; even when protected from the air, it gradually loses strength, especially when it is jarred, as in transportation. The bleach has a peculiar odor, which is probably due to chlorine. In order to exclude air and moisture, it is usually packed tightly in barrels, and these should be kept out of the sun as much as possible. The bleach loses about 1 per cent of chlorine in packing (probably chlorine that is held mechanically in the bleach), and then should have from 33 to 38 per cent, of available chlorine at the works. When bleach is imported into the United States, it rarely contains over 32 or 33 per cent, of available chlorine, the rest being lost in transportation. 73 . Composition of Bleaching Powder. — When bleaching powder was first made, it was considered to be calcium hypochlorite, Ca(0Cl) 2 . It was then shown that this whs improbable and that certain considerations seemed to lead to the view that the powder was a mixture of calcium chloride and hypochlorite, CaCl* + Ca(OCl) 2 . There are, however, several reasons for assuming that this formula is incorrect. Among others, it might be mentioned that if it con¬ tained calcium chloride, it should be deliquescent, but bleach is not; calcium chloride is soluble in alcohol, but it cannot be extracted from bleach by this means. Lunge has proposed the formula Ca Cl OCl for the substance, and has so well supported this view by experiment that it is generally accepted as correct. When bleach is dissolved in water, it breaks up into calcium chloride and hypochlorite. 4 ALKALIES AND HYDROCHLORIC ACID 51 74 . Valuation of Bleach.— The only constituent of value that bleaching powder contains is the chlorine that can be utilized for bleaching purposes. The amount of the available chlorine is determined by analysis, and in most countries, outside of France, the value of the bleaching powder is expressed in terms of the percentage of the avail¬ able chlorine contained, as shown by analysis. For example, a 32-per-cent, bleach means that the bleach under consider¬ ation contains 32 per cent, of chlorine that is available for bleaching purposes. In France, and to some extent outside of that country, the strength of the bleach is expressed in Gay-Lussac degrees; that is, the number of cubic centimeters of chlorine gas, reduced to the standard conditions of 0° C. temperature and 760 millimeters of mercury pressure, that 1 gram of the bleaching powder will yield. If it is remem¬ bered that 1 gram of chlorine under standard conditions occu¬ pies 314.7 cubic centimeters, it is easy to calculate the Gay-Lussac degrees from the percentage in the composition. For example, if there is 32 per cent, of available chlorine in a sample of bleach, each gram of the bleach will con¬ tain .32 gram of available chlorine and will yield 314.7 X .32 = 100.7 cubic centimeter of chlorine under standard condi¬ tions, or it is 100.7° Gay-Lussac, strong. These are some¬ times called French degrees , and the percentage of available chlorine in the bleach is frequently called English degrees . Table II shows at once the relation between the Gay-Lussac degrees and the English degrees. 52 ALKALIES AND HYDROCHLORIC ACID 4 TABLE II RELATION BETWEEN GAY-LUSSAC AND ENGLISH DEGREES Gay- Lussac Degrees English Degrees Gay- Lussac Degrees English Degrees Gay- Lussac Degrees English Degrees 63 20.02 85 27.OI 107 34.OO 64 20.34 86 27-33 108 34-32 65 20.65 87 27.65 109 34-64 66 20.97 88 27.96 I 10 34-95 67 21.29 89 28.28 111 35-27 68 21.61 90 28.60 I 12 35-59 69 21.93 9 i 28.92 11 3 35-91 70 22.24 92 29.23 114 36.22 7 1 22.56 93 29-55 n 5 36.54 72 22.88 94 29.87 116 36.86 73 23.20 95 30.19 11 7 37 .i 8 74 23-51 96 30.41 118 37-50 75 23-83 97 30.82 119 37.81. 7 6 24.15 98 3 i-i 4 120 38.13 77 24.47 99 31.46 12 1 38.45 78 24.79 100 3 I -78 122 38.77 79 25.10 101 32.09 123 39.08 80 25.42 102 32.41 124 39-40 81 25.74 103 32-73 125 39-72 82 26.06 104 33-05 126 40.04 83 26.37 105 33-36 127 40.36 84 26.69 106 33-68 128 40.67 75 . Uses. —Bleaching powder is used mostly for bleach¬ ing vegetable fibers. The fiber to be bleached is first satu¬ rated with the bleach in clear solution; it is then “soured” by passing it through dilute acid and is finally washed. Since the bleaching powder must be dissolved, it would seem that it might better be made direct in solution, as was done in the early days of the industry. The solution of bleaching powder 4 ALKALIES AND HYDROCHLORIC ACID 53 does not keep well, however, and the large amount of water makes it inconvenient and expensive to transport. Liquid bleach therefore is made only in a few cases where the bleaching establishment is near an alkali works. In making liquid bleach, the chlorine is not passed through the milk of lime, for this operation would put too much pressure on the chlorine stills, but goes over the surface of the liquid and is thus absorbed. 76. Eau de Javel. —The first bleach manufactured was prepared by passing chlorine into a solution of potassium carbonate (crude potash). As the works were situated at Javel, near Paris, the bleach took its name from that place. A little later, sodium carbonate was substituted for the potash, and the solution made from this substance became known as Eau de Labarraque. This latter substance is still sometimes made and used for certain purposes. When the chlorine is passed over a sodium-carbonate solution, the first action is to convert the carbonate into the bicarbonate and form hypochlorous acid, according to the reaction Na 2 C0 3 + CL + H,0 = NaCl + HNaCO 3 + HCIO If the chlorine is passed long enough, the bicarbonate is decomposed and the carbon dioxide is evolved. The reac¬ tion is NaHCO 3 + CL = NaCl + CO , + HCIO In this case, however, chlorate is likely to be formed. Another class of liquor, which is more stable than the prece¬ ding, is made by passing chlorine over caustic soda. The solution must be left slightly alkaline and kept cool to prevent the formation of the chlorate. The reaction then is 2 NaOH+ CL = NaCl + NaCIO + H 2 0 By this means, a fairly stable solution of bleaching material is obtained. Until recently it was not considered possible to make this bleach solution stronger than 15 per cent, of available chlorine, and that strength did not keep well. It has been found, however, that this instability is caused by the presence of sodium ferrate, which acts cata- 54 ALKALIES AND HYDROCHLORIC ACID 4 lytically and causes the solution to decompose. When the sodium hydrate is carefully purified from iron, solutions of the hypochlorite containing as high as 50 per cent, of avail¬ able chlorine can be made, and solutions with 35 percent, of available chlorine are quite stable. Solutions with 20 per cent, of available chlorine can be kept for weeks with prac¬ tically no change. The solution must be kept slightly alka¬ line, however, or the hypochlorite will change over into the chlorate. 77 . With the aid of the bleach liquors so far spoken of, acid must be used to get the bleach effect, and then it is neces¬ sary to wash thoroughly. Sometimes this is disadvantageous, and other hypochlorites are made that decompose more readily on the fiber and thus do not need acid. Practically all of these hypochlorites are made from the calcium hypo¬ chlorite. The aluminum bleach is the most important of these, and its method of preparation is typical of the method used in the preparation of all the others. The aluminum bleach consists of a solution of a mixture of aluminum chloride and hypochlorite that is made by treat¬ ing a solution of calcium bleach with aluminum sulphate; the calcium sulphate separates out, and the aluminum compounds are left in solution. The aluminum hypochlorite is very unstable and is made only as needed; it is so unstable that it decomposes on the fiber without the use of acid. The aluminum compound left is antiseptic, so that it not only does not need to be washed out, but in many cases it is a decided advantage to leave this compound on the bleached material. For example, when used to bleach paper stock, the aluminum chloride prevents fermentation when the stock is stored. POTASSIUM CHLORATE 78 . There are at present two general methods for making potassium chlorate 9 the electrolytic , which will be discussed in its proper place, and the chemical. The chemical process most generally used consists in making calcium chlorate and then converting this into potas- §4 ALKALIES AND HYDROCHLORIC ACID 55 sium chlorate by adding- potassium chloride and allowing the less soluble potassium chlorate to crystallize out. The cal¬ cium chlorate is made by absorbing chlorine in milk of lime; so that probably calcium hypochlorite is first formed and then transformed into the chlorate. The reactions taking place are doubtless 2 Ca{OH), + 2 CL = CaCL + Ca(OCl), + 2 H 2 0 and BCa{OCl), = Ca{Cl0 3 ) 2 + 2CaCl, or 6Ca(0H), + 6C/ 2 = 5 CaCL + Ca(Cl0 3 ). + 6/1,0 and Ca ( C10 3 ), + 2 KCl = CaCL + 2KCIO, A greater saving is made in this way than would be possible by starting with caustic potash instead of caustic lime. RAW MATERIALS 79 . Lime. —The lime used in this process should be the very best, and as free from impurities as possible. It is usually burned in a reverberatory furnace. The thoroughly burned lime is slaked, made into milk of lime, and strained before it goes to the absorbers. It should then be used without delay, as otherwise calcium carbonate will form and thus lead to a loss of chlorine. 80 . Chlorine. —Chlorine made by either the Weldon or the Deacon process can jbe used, and generally no attempt is made to remove the water and carbon dioxide. The hydrochloric acid is removed only when it occurs in such large quantities as in the Deacon process. Chlorine made by Weldon’s process is preferable, as it is stronger and gives better absorption. 81 . Potassium Chloride. —Nearly all the potassium chloride used is imported from Germany, and it contains from 90 to 93 per cent, of potassium chloride. The other constituents are mostly soluble and are practically harmless. The following analysis gives a fair idea of the average composition of commercial potassium chloride, so-called muriates: 56 ALKALIES AND HYDROCHLORIC ACID §4 H a O . Organic . . . . Insol. and Fe,0 3 Al 2 O a . Al t (SOt) 3 . . . JVa^SO,. . . . . CaClt . . . . MgCL . NaCl . KCl . . . . . Per Cent. . 4.50 .05 .15 .47 .20 .30 .25 .50 . 2.25 . 92.00 82. Water. —The water, especially that used for crys¬ tallization, must be pure. Suspended matter tends to pre¬ vent the formation of crystals and leaves them impure when formed. The presence of sulphides leads to the formation of lead sulphide, for there is usually lead in the final liquor from the lead crystallization pans. Sulphates are liable to be reduced by organic matter and thus lead to the presence of sulphides; they should therefore be excluded, as the lead sulphide will make the crystals dark colored and spoil their sale. Iron and carbonates are also objectionable. APPARATUS AND PROCESS 83. Absorbex*s. —In making the calcium chlorate, the chlorine must be passed over the surface of the milk of lime. The absorption of the chlorine by this material takes place in large, flat, quadrangular tanks, which are built of slabs of sandstone. Where the sandstone slabs come together, they are grooved out, and a thick rubber cord is introduced. The whole is then tightly fastened together by means of iron tie- rods that are placed around the outside. In order that the absorption may take place more readily, each tank is fitted with an agitator that stirs and splashes the milk of lime so that an intimate mixture of it and the chlorine takes place. These agitators pass into the tanks through hydraulic lutes; the manholes in the tanks are also provided with hydraulic lutes, so that the tanks are closed tightly when in operation. 4 ALKALIES AND HYDROCHLORIC ACID 57 The absorbers are usually set up in series of from three to five, so that the liquor can flow from one to the next, while the chlorine enters the absorber that is most nearly finished and leaves the one newly charged. The gas that leaves the last absorber is nearly free from chlorine, but is finally run through a tower, down which milk of lime is flowing, in order to remove the last trace of chlorine before escaping into the air. 84. In carrying out the operation, the lowest absorber is emptied when the absorption is complete, and the contents of each absorber is run into the next lower one. The upper absorber is then charged with milk of lime of 1.085 or 1.100 specific gravity (that is, about 113 grams of CaO per liter). The absorber should not be charged over two-thirds full, for there is danger that it will foam over at some stage of the absorption. Chlorine is now passed into the lowest absorber, and this operation is continued until all the lime is converted into calcium chloride and calcium chlorate. As the chlorine is absorbed, the temperature of the absorb¬ ing liquid gradually rises and must therefore be carefully watched. The temperature should not be allowed to exceed 55° C., or the yield of chlorate will decrease. The temper¬ ature can be very easily regulated by adjusting the flow of chlorine. The charge requires from 12 to 30 hours from the time it is first run in until it is finished. The time depends on the size of the absorbers and the strength of the chlorine gas and the milk of lime. Slow absorption, using weak solutions, gives the best results from a chemical point of view; but, on the other hand, more concentrated solutions and quick absorption save time and fuel, so that a balance must be struck for each locality, depending on the price of coal. The end of the reaction in the absorber is shown by the appearance of a pink color, which is due to the formation of calcium manganate from manganese in the lime or carried over with the chlorine. Another rapid test consists in filtering off a little of the solution and adding dilute hydro- 58 ALKALIES AND HYDROCHLORIC ACID 4 chloric acid to it. An effervescence, or evolution of chlorine, shows that the solution still contains calcium hypochlorite and that the operation is incomplete. 85. Settling Pans. —When the absorption is com¬ pleted, the finished liquor is run into large iron pans, where it is left for from 3 to 10 hours for the insoluble matter, such as sand, calcium carbonate, etc., to settle out. The capacity of the settling pans must at least equal the capacity of the absorbers, for, on account of the sand, etc. that settles in these pans, their actual capacity is frequently much less than their nominal. When the liquor has settled thoroughly, it is pumped by means of force pumps having gun-metal barrels to a higher level, in order that it may then run by gravity through the rest of the operations. The best suction pipe for the pump is a short, rubber hose that can be moved so as to suck the liquor close to the mud without getting part of the latter into the concentrating pots. The mud is allowed to accumulate in the pans until they are nearly half full; it is then washed two or three times. The wash water is used in making milk of lime, while the mud is thrown out. 86. Concentrating Pots.— The liquor from the settling pans is carefully gauged, and a sample is sent to the labora¬ tory for analysis. Meanwhile, the liquor goes to the con¬ centrating pans, which are best made of cast iron and are similar in size and shape to those used in making caustic soda, and is here warmed. By this time the analysis of the liquor should be made, and the amount of potassium chlo¬ ride necessary to convert the calcium chlorate into potassium chlorate is calculated. This amount, plus about 1\ per cent., is then added, and the whole is concentrated to about 1.31 specific gravity (taken hot). In winter, a slightly lower specific gravity will answer. 87. First Crystallizing Pans. —The concentrated liquor is now baled into the crystallizing pans. These are generally U-shaped, and are set into brickwork so as to be a slight distance above the floor. These pans are made §4 ALKALIES AND HYDROCHLORIC ACID 59 of iron, and should be of such a size that the contents of a pot just fills a certain number of them. The room in which these pans are set should have a cement floor that slopes toward a catch basin. The pans are allowed to stand for from 9 to 14 days, depending on the time of year, to crystal¬ lize the liquor. The crystals are filtered off by means of a centrifugal machine, thoroughly washed with water to remove the cal¬ cium chloride and iron, and then recrystallized. The mother liquor, which is mainly calcium chloride, con¬ tains from 10 to 35 grams of potassium chlorate per liter, and is cooled to —10° C. by artificial means. In this way, the amount of potassium chlorate is reduced to about 3 grams per liter. 88. Recrystallization.— The crystals obtained by the first recrystallization always contain a large amount of impurities, and are therefore placed in a large, lead-lined, iron cylinder. Water is added and steam blown in until the solution has a strength of 1.10 to 1.11 specific gravity (taken hot). This apparatus is placed high enough so that the solution can be drawn direct to the crystallizing pans through 3-inch, steam-heated, steel pipes. These operations are carried out in a separate building and with all possible clean¬ liness. The crystallizing vats are usually of iron and are lead-lined; a convenient size is 5 feet by 4 feet, and 3 feet deep. These vats should be raised a little above the cement floor, so that leaks can be detected, and the floor should slope to a catch basin, to avoid loss of the liquor accidentally spilled. From 7 to 10 days are allowed for the crystals to separate out; they are then filtered off in a centrifugal machine and washed until not over .05 per cent, of chlorides is shown by testing. The mother liquor is used for dissolving fresh crystals until it reaches a specific gravity of about 1.08; it is then too impure and is stored until enough is obtained, when it is boiled down and crystallized for crude crystals. The mother liquor from these crystals is run into the ordinary concen¬ trating pots. 60 ALKALIES AND HYDROCHLORIC ACID §4 89 . Drying the Crystals. — The thin, transparent crystals are thoroughly drained and then put on the drying table. This table is made of boiler iron, has an upturned rim, and is covered with lead. .It is heated by steam. 90 . Grinding the Crystals.— For many purposes, the dry crystals can be marketed direct; but for others, they must be ground to a fine powder. This is a very dangerous operation and must be performed with the greatest care. The engine for driving the mill is situated outside of the building, and all inflammable material is excluded so far as possible. The crystals are ground between two small stones (about 26 inches in diameter), of which only the top one revolves. The crystals are fed in at the center of the top stone through a hopper, and are best ground warm from the drying table, as in this way the mill clogs less. The ground crystals are then sifted through mechanically rocked sieves, and the fine powder is packed. OTHER CIIEORATES 91 . Sodium clilorate is more soluble than the potassium salt, and for this reason is more suitable for many purposes; it is, however, for the same reason, not so easy to make, as it cannot be readily separated from the other sub¬ stances in solution. Sodium chlorate can be made from the calcium-chlorate solution by evaporating it to 1.5 specific gravity, and then cooling to 10° or 12° C. The calcium chloride is crystallized out until there is only 1.2 molecules of calcium chloride to 1 molecule of calcium chlorate. By then adding sodium sulphate and a little sodium carbonate, all the calcium is precipitated and sodium chloride and chlorate are left in solution; then by boiling down, the salt is separated out and the chlorate alone is left in solution. The solution is then run off and cooled, when most of the sodium-chlorate crystallizes out free from salt. 92 . Hargreaves makes sodium chlorate by-the direct action of chlorine on crystalline sodium carbonate and sys- §4 ALKALIES AND HYDROCHLORIC ACID 61 tematic leaching, so as to dissolve out the soluble chlorate and leave the less soluble salt behind. He places the crys¬ tallized sodium carbonate in the-tower b, Fig. 18, which is supported on the grate cc; the chlorine enters at d and, passing upwards, is absorbed. Liquor from the tank e slowly trickles down over the charge and is run off through pipe /. From this point the liquor goes into the sieve, which holds back any solid material, and then runs through into the cistern, from which it is pumped back again to the tank e until it is saturated with sodium chlorate. The liquor is then run off into pans and crystallized. 93 . Barium chlorate as well as any other metal¬ lic chlorates can be made from sodium chlorate by mixing the chlo¬ ride of the metal whose chlorate is wanted, evapora¬ ting the mixture down, and fishing out the sodium chloride. The metallic chlorate then separates out in cooling. These chlorates may also be made in a similar manner to the methods just given for the making sodihm chlorate. of 62 ALKALIES AND HYDROCHLORIC ACID §4 94. Chlorates, especially the potassium salt, are coming into extensive use in the manufacture of explosives for tun¬ nel work, as the gases resulting from explosives of this type are less injurious than those from dynamite; they are also safer, as their constituents are transported separately and mixed on the spot. Nitrobenzal and nitrotuluol mixed with the chlorate are frequently used for this purpose. ALKALIES AND HYDRO¬ CHLORIC ACID (PART 3) ELECTROLYTIC METHODS GENERAL PRINCIPLES THE ELECTRIC CURRENT 1. Sources of Current.- —There are three sources from which a continuous flow of electricity may be obtained, namely, the voltaic cell in some one of its various forms, the dynamo , and the thermopile. Of these, the voltaic cell is too expensive to be used as a source of electricity for electrolytic work on a commercial scale, because its action depends on the dissolving of expensive materials. In the thermopile a flow of electricity is obtained by heating the junction of two metals and thus converting heat directly into electricity. This method, however, wastes heat, and is also too expen¬ sive for commercial use. The dynamo depends for its action on the rotation of a coil of wire in the field of force of a magnet, and as the coil can be rotated by means of a steam engine, or, better still, by water-power, it furnishes the most economical source of electricity at present known. The dynamo current is generally used direct from the machine, COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL, LONDON 25 199—18 2 ALKALIES AND HYDROCHLORIC ACID but it may be stored for future use by means of a special form of battery, called a storage battery. The storage battery also has the advantages that it can be transported and that it will yield a uniform current. Any voltaic cell that, after being used, can be returned to its original condition by the passage of an electric current in the opposite direction is, in the perfect sense of the word, a storage battery. Only one form of battery, however, has proved itself useful for practical purposes. This consists of a plate of lead coated on both sides with lead peroxide and a plate of spongy lead dipped in a solution of sulphuric acid. If this battery has been charged and the two lead plates are joined by a wire, the lead becomes transformed into lead sulphate and hydrogen separates at the lead-peroxide plate. Here the hydrogen is oxidized to water, and the lead per^ oxide is reduced to lead oxide, which also goes over into lead sulphate. If a current is now passed into the cell for the purpose of recharging it, the reverse operations go on, and the cell is returned to its original condition. For convenience, in this Section, the storage battery will be referred to as the source of current, although it should be borne in mind that all statements made will hold equally well for the current from any other source, at least so long as it is not an alternating current. 2. Analogies. —When two unconnected dishes of water are placed on different levels, there is a latent power in the water in the higher dish, by virtue of its position, that gives the water a tendency to flow into the lower one, which it will do if they are connected by an open tube. In a similar manner, the electric energy accumulated in the plates of the storage battery is latent so long as they are not connected; but as soon as they are joined by a wire, a current flows through the wire from the plate that corresponds to the higher dish of water into the plate that corresponds to the lower one. In the case of the water, it is said to have a “head” of a certain amount, measured by the difference of level of the two dishes; in the case of the electricity, the §5 ALKALIES AND HYDROCHLORIC ACID O term head is synonymous with difference of potential, and this is measured in a unit called a volt. This difference of poten¬ tial of the plates of a cell is called the electromotive force of the cell. The water in flowing through the tube is retarded by the friction of the tube, and therefore does not reach the lower level with as much force as would otherwise be the case. The flow of electricity is resisted by the conductor, and this resistance is measured in ohms. The quantity of electricity corresponding to the quantity of water is measured in coulombs , and its rate of flow is measured in amperes. Since electricity is a manifestation of energy, perhaps its analogy to heat is a better one than that just given. In this case, the difference of potential, or electromotive force, cor¬ responds to the difference of temperature of two points, the resistance of the conductor corresponds to the non-conduc¬ tivity of the connecting medium for heat, and the quantity of current corresponds to the quantity of heat, in calories, that passes from the point of higher to that of lower temperature. 3. Units of Measurement.—Just as in measuring dis¬ tance, a certain unit, as the foot or the meter, is arbitrarily selected to express the distance, or as in measuring differ¬ ences of temperature, some definite unit, as a degree, is selected to express the difference of temperature, so, in electrical measurements, certain units have been selected carefully to express the various values that are dealt with. The unit of resistance, the olim, is the resistance at 0° C. of a column of mercury 1 square millimeter in section and 1.0626 meters long. • The unit quantity of electricity, the coulomb, is the quantity of electricity that will deposit 1.118 milligrams of silver from the solution of a silver salt under suitable conditions. The unit of difference of potential, or electromotive force, the volt, is the difference of poten¬ tial that will send 1 coulomb per second through a resistance of 1 ohm. The unit of the rate of flow of a current, the ampere, is the rate of flow that will carry 1 coulomb past a point on the conductor each second. The unit of electrical 4 ALKALIES AND HYDROCHLORIC ACID §5 power, the watt, is the product of the volt and ampere, and is equivalent to tI? horsepower; or, in other words, 746 watts equals 1 horsepower. The unit of electrical energy, the volt coulomb, or joule, is the product of the volt and coulomb, and is equivalent to .24 calory. The current den¬ sity is measured by the number of amperes entering or leaving the solution per unit surface of the electrodes; it is usually expressed in amperes per square decimeter , although other units of surface are sometimes used, as the square meter, square foot, etc. MEASUREMENTS 4 . Resistance.—Electrical resistance may be measured by an apparatus called a Wlieatstone bridge. A bridge when completed, ready for taking measurements, consists of three main parts: (1) An adjustable resistance box con¬ taining a number of coils, the exact resistance of each coil being known; (2) a galvanometer for detecting small cur¬ rents; and (3) a battery of several cells. The coils of the resistance box are divided into three groups; two of these are called proportional , or balance , arms , and the third is known as the adjiistable arm. Each proportional arm is composed of three and sometimes four coils with resistances of 1, 10, 100, and 1,000 ohms, respectively. The adjustable arm contains a large number of coils ranging from .1 ohm to 10,000 ohms. The operation of the bridge depends on the principle of the relative differ¬ ence of potential between two points in a divided circuit of two branches. The electrical con¬ nections of the bridge are shown in Fig. 1. M represents the resistance of one of the balance arms, which, for convenience, will be Fig. 1 §5 ALKALIES AND HYDROCHLORIC ACID 5 termed the upper balance arm; N, the resistance of the other balance arm, which will be termed the lower balance arm; P, the resistance of the adjustable arm; and X, an unknown resistance, the value of which is to be determined. One terminal of the detecting galvanometer G is connected at c, the junction of the upper balance arm and the unknown resistance; the other terminal is connected at d, the junc¬ tion of the lower balance arm and the adjustable arm. One pole of the battery is connected at a, the junction of the two balance arms; the other pole at b, the junction of the adjustable resistance and the unknown resistance. The current from the battery divides at a , part of it flowing through resistances M and X , and the rest through N and P. When the resistances M, N, P, and X fulfil the proportion — = then the two points c and d will have the same potential, and no current will flow through the galva¬ nometer G. Since the resistances of M, X, and P are known, the resistance of X may be found by the funda- M mental equation X = — X P, provided the arms are so adjusted as to cause no deflection of the galvanometer. For example, suppose that the two ends of a copper wire are connected to the terminals b and c, and after adjusting the resistance in the arm so that the galvanometer shows no deflection, the resistances of the different arms read as fol¬ lows: M = 1 ohm, N = 100 ohms, and P = 112 ohms. Then, by substituting these values in the fundamental equation, X = %XP = N ~ 0 X 112 - 1.12 ohms 5. The coils of resistance can be bought already put up in boxes and standardized, so that it is frequently more con¬ venient to buy them that way than to make them. They are called resistance boxes. In these resistance boxes, as shown in Fig. 2, the ends of the wire of each spool are fastened to metal pieces a, which are so arranged that they can be connected by a metal pin b. When the pin is in place, 6 ALKALIES AND HYDROCHLORIC ACID §5 the current can flow from one plate to the next through the pin, and there is practically no resistance. When the pin is removed, however, the current must flow through the wire, and a resistance is thus introduced. Just as a certain resistance is found when an attempt is made to pass an electric current through a wire, so is a resistance met when a solution is used as a conductor. The determi¬ nation of the amount of this resist¬ ance is a matter of importance. 6. Conductivity of Solutions. Although it is customary to speak of the resistance of a wire, sometimes the conductivity is spoken of, and in the case of solutions, it is much more common to speak of the conductivity than of the resistance. The unit of conductivity, which has no special name, is the conductivity of a body that, for 1 centi¬ meter length and 1 square centimeter base, has a resist¬ ance of 1 ohm. The specific conductivity of a solution is the conductivity of a centimeter cube of the solution. The conductivity of solutions, however, is expressed as the equivalent conductivity of the solution; this is the specific conductivity multiplied by the number of equivalent weights in grams of the dissolved substance in 1 cubic centimeter of the solution. By the term equivalent weight is meant the molecular weight divided by the number of valences repre¬ sented in the metal part of the salt; or, in the case of acids, by the the number of acid-hydrogen atoms. For example, //j - SV \ HN0 3 , CHzCOOH, —etc., if the formulas 2 2 2 are expressed in terms of the atomic weights, are equivalent weights. 7. Effect of Temperature. — The conductivity of solu¬ tions increases very rapidly with a rise of temperature. The amount of the increase varies for different solutions, Fig. 2 5 ALKALIES AND HYDROCHLORIC ACID 7 but it averages about 2 per cent, of the conductivity for each •degree rise of temperature; of course, a fall of temperature gives the reverse effect. It is therefore very necessary to keep the solution at a definite temperature while making the conductivity measurements. For this reason, the vessel containing the solution is kept in a constant-temperature bath during the whole time of the measurement. 8. Constant-Temperature Bath. —A suitable con¬ stant-temperature bath for technical work may be made by wrapping a wooden pail in felt, as by this means water at nearly the same temperature as the room can be kept at a constant temperature for a long time. (Most determinations are made at either 18° or 25° C.) With an arrangement of this kind, the desired temperature can be obtained by mixing hot and cold water, the temperature being determined by a thermometer hanging in the water. When higher tempera¬ tures are to be used or several determinations are to be made at one time, more elaborate apparatus, with stirrers and auto¬ matic temperature regulators, can be arranged. 9. Conductivity Vessel. —The conductivity vessels vary in form, according to the conductivity of the solution. For solutions of low conductivity, as the organic acids, ammonia, etc., a resistance I vessel with broad electrodes placed close together is necessary; for better conduct¬ ing solutions, as inorganic acids, salts, and caustic alkalies, a small surface of elec¬ trodes with a rather long and small con¬ necting tube is more suitable. For the first class of solutions, a vessel like the one shown in Fig. 3 is the most suitable. This vessel S, which is cylin¬ drical, is made of glass and is fitted with a hard-rubber cap b having three holes. One of these holes is for a pipette, when it is necessary to introduce or remove liquid, and the other two are for the electrodes. The electrodes consist of two La. Fr«. 3 8 ALKALIES AND HYDROCHLORIC ACID §5 circular platinum disks c, c that are fastened to capillary glass tubes d, d by means of heavy platinum wire. The capillary tubes are filled with mercury, which makes a con¬ nection between the ends of the platinum wires from c, c and the copper wires that lead to the other connections. The glass tubes d, d are securely fastened into the cover b by means of sealing wax, so that the platinum disks c, c always hold their relative positions. For the better conducting solutions, a vessel of the form shown in Fig. 4 is very suitable. It consists of a glass Fig. 4 vessel a y each arm of which is provided with a hard-rubber cap b bearing a curved platinum electrode c. 10 . Platinizing the Electrodes. —The electrodes in either vessel should be coated with a good layer of platinum black. This is best obtained by introducing the clean platinum electrodes into a 3-per-cent, solution of platinum chloride containing vV per cent, of lead acetate, passing the current from four Daniell cells for 5 or 10 minutes, and then reversing the current and passing it for an equal length of time in the reverse direction. The electrodes must be thoroughly washed before they are ready for use. 11. Determination of the Conductivity of Solu¬ tions. —In determining the conductivity of solutions, 5 ALKALIES AND HYDROCHLORIC ACID 9 use is made of the apparatus described in Art. 4, except that, on account of the polarization (see Art. 26) by the passage of the current, it is not possible to use a direct current. Instead of the direct current, it is necessary to have a cur¬ rent that flows in one direction at one instant and in the opposite direction at the next instant. By this means, polar¬ ization can be largely avoided. The alternation of the cur¬ rent can be produced by means of an induction coil that is introduced between the battery B, Fig. 1, and the Wheatstone bridge. The difficulty then arises that the galvanometer cannot be used, for the rapidly alternating current will simply cause the needle of the galvanometer to vibrate. Therefore, in place of the galvanometer G, a telephone is used. This instrument gives a buzzing sound as long as a current flows through it, and thus shows when the branches of the bridge are equal. This arrangement is shown in Fig. 5. The battery B fur¬ nishes the current to the induction coil /, where it is made to alternate rapidly. The conductivity vessel is represented by c, and a known resistance by R. R and c make up two sides of the Wheatstone bridge and the wire eabd , which 10 ALKALIES AND HYDROCHLORIC ACID §5 is stretched over a graduated scale and has a sliding contact/, makes up the other two sides. In making a determination, the solution is placed in the conductivity vessel c, and this vessel is put in a constant-temperature bath. The resist¬ ance R is selected so as to be nearly equal to the unknown resistance (or conductivity). (If the resistance of the solu¬ tion in c is totally unknown, a preliminary determination will show the approximate value of c, when R can be suitably selected.) The induction coil / is then started, and the con¬ tact / is slid until the noise in the telephone T ceases. By then reading the length of a and b on the scale, the ratios - = — will be known. That is, a , b, and R are known, and since b R R X - = c, c is easily found, and the conductivity equals -. b c To get the specific conductivity, which is the conductivity of a cube of the solution with 1 centimeter edge, it is necessary to know the surface measurements of the electrodes and their distance apart. This is not easily determined, however, so that use is generally made of what is called the resistance capacity of the vessel. 12. Resistance Capacity.—In order to determine the resistance capacity, use must be made of some compound that can be obtained in a pure state, of which a -solution of definite strength can be prepared and whose specific con¬ ductivity is already known. In order, however, to obtain accurate results, the resistance capacity of the vessel in which the determination is to be made must be ascertained. Calling the specific conductivity of a certain solution /, that of the same solution in the vessel used A, and the desired resistance capacity of the vessel K , the following formula is obtained: In all further determinations with the same vessel, the value K can be used, as it represents a constant so long as the electrodes keep their relative positions. From this it §5 ALKALIES AND HYDROCHLORIC ACID 11 follows that, having determined the conductivity of any other solution in the same vessel, the specific conductivity of any such solution may be obtained by the formula l = KL 13 . Solutions for Resistance Capacity. —The follow¬ ing solutions maybe used in • determining the resistance capacity of a vessel: A sulphuric-acid solution, 30 per cent. H 2 SO t , has a specific gravity of 1.223 at 18° C. Ordinary chemically pure sul¬ phuric acid is suitable for making the solution. The specific conductivity at 18° C. is l = .7398. A ± error of .005 in the specific-gravity determination causes a ± error of .004 in the conductivity value. A magnesium-sulphate solution has a specific gravity of 1.19, at 18° C. Commercial chemically pure magnesium sul¬ phate is good enough for use. The specific conductivity at 18° C. is / = .04922. An error of .003 in the specific gravity corresponds to an error of .00001 in the specific conductivity. Other solutions are sometimes used, but these will usually meet the needs of the worker in the electro-alkali industry. 14 . Quantity of Electricity. —The quantity of elec¬ tricity is measured by determining the amount of silver deposited by the current; or, since there is a direct relation (see Art. 23 ) between the amount of silver and any other metal that may be separated, copper and, sometimes, hydro¬ gen are separated instead of silver. A suitable arrangement for carrying out this measurement consists of a copper plate or wire gauze that can be accurately weighed and two other copper plates. In measuring the quantity of electricity, the weighed plate is hung, between the other two copper plates, in a solution of 15 grams of copper sulphate, 5 grams of sul¬ phuric acid, and 5 grams of alcohol in 100 cubic centimeters of water. When the current passes, the copper is dissolved from the outside plates and deposited on the weighed one; thus, by weighing the middle plate at the end of the process, the amount of current that has passed can be readily calcu¬ lated. Each coulomb deposits .329 milligram of copper; 12 ALKALIES AND HYDROCHLORIC ACID §5 therefore, the total weight, in milligrams, of copper deposited divided by .329 gives at once the number of coulombs of electricity that has passed through the voltmeter. In another style of apparatus for this purpose, platinum electrodes are used. The current is passed through a solu¬ tion of sulphuric acid, and the gas evolved is measured. The arrangement first mentioned can also be used for measuring amperes; thus, by noting the time required for copper to deposit on the plate, all the information necessary for the calculation is obtained. The number of coulombs divided by the number of seconds required for them to pass gives the number of amperes. For example, if the volt¬ meter shows 40 coulombs in 40 seconds, then the number of amperes is 1. 15. Ammeters.—Although the preceding arrangement is the most exact for measuring the quantity of the current of electricity, there are instruments, known as ammeters, that have a sufficient degree of accuracy for most tech¬ nical work, and, on account of their great convenience in han¬ dling, they are exten¬ sively used. These instruments are made in many forms, but probably the most con¬ venient and accurate is that shown in Fig. 6, which is known as the Weston ammeter. The Weston instrument depends for its operation on the fact that if a coil, free to move, is pivoted in a magnetic field, it will swing around its axis when a current is passed through it. In these instruments, a rectangular coil is delicately pivoted between the poles of a permanent magnet, and when a current flows through the coil, it is deflected, carrying with Fig. 6 §5 ALKALIES AND HYDROCHLORIC ACID 13 it a pointer that swings over the scale shown in the figure. The movements of the coil are counterbalanced by small spiral springs; the greater the current, the greater is the deflection of the coil. The ammeter is inserted in the circuit so that all the current will pass through. 16 . Measurement of Electromotive Force. —The electromotive force is measured most exactly by using a standard cell of known electromotive force and comparing the unknown electromotive force with it. The best known standard element is Clark’s, which consists of a rod of zinc in a saturated solution of zinc and mercury sulphates, and has mercury for the other pole. Such an element, when care¬ fully made, has an electromotive force of 1.4336 volts at 15° C. This cell varies considerably with the temperature, on account of the varying solubility of the zinc sulphate with varying temperature. The high temperature coefficient is a decided disadvantage, so that the Weston cell, which has a comparatively small temperature coefficient, is gaining favor. The Weston cell consists of a cad¬ mium amalgam in a saturated solution of cadmium and mercury sulphates, with mer¬ cury for the other pole. A very suitable form of the Clark element, and one that can be conveniently made in any laboratory, is shown in Fig. 7. This element consists of a small glass cylinder a set in a wooden block b. The cylinder contains mercury c in the 14 ALKALIES AND HYDROCHLORIC ACID §5 bottom, then a layer of mercurous sulphate d, which is covered with a mixture of zinc-sulphate crystals e and a saturated zinc-sulphate solution /. A cork g is then soaked in melted paraffin, and a zinc stick h and a glass rod z, in which a platinum wire is fused, are fastened into the cork and the whole inserted in the cylinder. A layer of wax is then placed over the stopper, and wires lead from the platinum wire and the zinc stick to the binding screws k, k . 17 . It is not advisable to compare a number of cells direct with a standard element, because this operation taxes the capacity of the element too much. The capacity of a constant element can be checked up against the standard and then used for comparison. The determination depends on the fact that if a constant cell is closed with a resistance, the fall of potential will be uniform over the whole length of the resistance. Furthermore, if a cell is connected with another cell of equal but opposed electromotive force, no current will flow. The operation consists in closing the cell E, Fig. 8, with a resistance a b. The fall of potential is uniform then for each portion of a b. The wires connecting E with a and b are so large that they have practically no resistance com¬ pared with a b. From a a wire leads through the galvanom¬ eter G and the unknown cell x to the slide contact c. At intervals, to check the constancy of E, the standard cell is introduced at x, and c is moved until no current flows. Then ac represents the fraction of the electromotive force of E that is equal to the electromotive force Y of the stand¬ ard cell. The standard cell is then replaced by the one to ALKALIES AND HYDROCHLORIC ACID 15 §5 be measured, and the point c, at which no current flows, is again established. Calling this resistance ac ', then the elec¬ tromotive force of the cell that is being measured is equal to Y X a C ■ If a Clark standard cell is being used, Y = 1.4336 a c and 1.4336 X —- is the unknown electromotive force. a c A small storage battery is a very suitable cell for A, and the distance a c need only be determined twice a day. 18 . Tlie Voltmeter. —For a great many purposes, an instrument called a voltmeter is sufficiently accurate and much more convenient for measuring electromotive forces than the method just described. This instrument is really an ammeter having a high resistance and provided with a scale calibrated to read volts instead of amperes. By calling the current c, the electromotive force e, and the resistance R, then e = cR (see Art. 20). Then, if the resistance of the instrument is infinitely large compared with the resistance of the rest of the current, the instrument having been cali¬ brated to read volts can be used to read direct. A voltmeter is connected across the circuit, so that the entire current does not flow through it. 19 . Shunt Circuit.—When a wire leads continuously from one side of a battery, or other source of current, to the other side, it is called a circuit. If, however, two points of the circuit are connected by a wire, it is called a shunt circuit. For example, in Fig 9, the wire acb forms a cir¬ cuit from the battery E. When a wire is brought across from a to b, a shunt circuit, or shunt , is formed. If the wire ab has a small resistance compared with acb , then most of the current will pass across a b, and in the reverse case, the opposite is true. If the wires are of equal resistance, the current will be equally a 16 ALKALIES AND HYDROCHLORIC ACID §5 divided. If it is desired to obtain the difference of potential between the points a and b , a high-resistance voltmeter is inserted in the shunt a b and the difference of potential is read direct. 20. Ohm’s Law.—The relation existing between the current, the electromotive force, and the resistance of a system is known as Ohm’s law. According to this law, the current is directly proportional to the electromotive force and inversely proportional to the resistance, or, expressed as an equation, electromotive force current =- resistance 21. Electric Conductors. —When an electric current passes through a wire, the wire may become hot or suffer other physical changes, but it remains essentially the same as before. On the other hand, if the current passes through a solution, it decomposes the dissolved substance, and its products collect at the points where the current enters and leaves the solution. This leads to a division of electric con¬ ductors into two classes. All electric conductors that are not decomposed by the electricity passing through them are called conductors of the first class; all conductors that are decomposed by the electricity passing through them are called conductors of the second class, or electrolytic conductors. There is an indefinite number of conductors of the second class, most of which may, however, be comprehended in the general title of solutions. Comparatively few pure sub¬ stances other than the metals conduct electrolytically. Such substances as hydrochloric, nitric, and sulphuric acids, which are comparatively good conductors in water solution, do not conduct at all when in the pure, dry condition. By the pure, dry state is meant hydrochloric-acid gas condensed to a liquid; the same applies to nitric acid and sulphuric acid. Water is also a very poor conductor. Fused salts, however, conduct quite well, and some few, as lead and silver chlo¬ rides, conduct somewhat in the solid condition when not too far from their melting point. 5 ALKALIES AND HYDROCHLORIC ACID 17 ELECTROLYSIS 22. As just stated, sulphuric acid, although a non-con¬ ductor when pure and dry, is a good conductor when mixed with water, and the solution is an electrolyte. Solutions in general that conduct are called electrolytes, although the term electrolyte is frequently applied to the dissolved substance. For instance, in this case it is customary to speak of sulphuric acid as an electrolyte, meaning that its water solution is a good conductor. The current enters and leaves the solution by wires, and these, where they dip into the solution, are called elec¬ trodes. When a current is passed through a sulphuric-acid solution, oxygen separates at one electrode and hydrogen at the other. The electrode at which oxygen, or, in general, the acid radical, separates is called the positive electrode , or anode; and the one at which hydrogen, or, in general, the metallic radical, separates is the negative electrode, or cathode. Since by the passing of an electric current through an electrolyte, matter separates out at the elec¬ trodes, the electrolyte must be decomposed and matter must be carried with the current, as the concentration about the electrodes soon differs from the rest of the solution. The matter that travels with the current is called an ion. Ions are divided into two classes. The ions that travel toward the anode are called anions , and those which travel toward the cathode are called cations. The ions are per¬ fectly definite substances, but frequently they are not the substances that separate at the electrodes, because, at the instant they are set free, they may react with the solvent to form new substances. For example, the ions from sul¬ phuric acid are hydrogen and SO if the hydrogen separates as such, but the SO t breaks down and gives oxygen and sulphuric acid once more. In the electrolysis of sodium sulphate, the ions are sodium and SO it but the sodium reacts with the water to give hydrogen and sodium hydrate, and the S0 4 acts as in the preceding case, giving oxygen and sulphuric acid. 199—19 18 ALKALIES AND HYDROCHLORIC ACID §5 23. Faraday’s Law. —When a certain amount of elec¬ tricity passes through a solution of sulphuric acid, a definite amount of hydrogen is liberated. It does not matter how quickly this amount of electricity passes through the solution, because the same amount of hydrogen is sure to be liberated. Neither do the concentration of the solution and the temper¬ ature have any effect. Each gram of hydrogen liberated by an electric current requires the passage of 96,540 coulombs. It makes no difference what substance is electrolyzed to give hydrogen, so long as only hydrogen is liberated at the cathode, 1 gram will be freed when 96,540 coulombs of elec¬ tricity have passed. If, therefore, an electric current is passed successively through solutions of hydrochloric acid, sul¬ phuric acid, phosphoric acid, etc., exactly the same amount of hydrogen will be liberated. What has been stated for hydrogen holds true for other elements and combinations of elements. If, in electrolyzing a solution of sulphuric acid, the hydrogen given off at the cathode and the oxygen at the anode (having waited until secondary reactions, which appear at the beginning of the electrolysis, have stopped) are measured, it will be found that the volume of the hydrogen is twice that of the oxygen; that is, the gases are liberated in the proportions in which they combine. Equivalent weights of the substances are liberated. Furthermore, if an electric current is passed successively through solutions of sulphuric acid, copper sulphate, silver nitrate, ferrous sulphate, and ferric sulphate, provided the solutions are suitably prepared to avoid secondary actions at the electrodes, there will result, when 1 gram of hydrogen is liberated, 31.5 grams copper, 108 grams silver, 28 grams iron from the ferrous solution, and 18.7 grams iron from the ferric solution. If the atomic weights of these elements are noticed, it will be found that the values just mentioned are in each case the atomic weight of the element, expressed in grams, divided by its valence. This relation was first noticed by Faraday and is known as Faraday’s law. Briefly stated, this means that chemically equivalent quan¬ tities of substances are separated by the same amount of an §5 ALKALIES AND HYDROCHLORIC ACID 19 electric current, and for every 96,540 coulombs of current that pass, if no side reactions enter in, 1 gram equivalent each of the cation and of the anion is obtained. .24. Electrolytic Dissociation. —The way in which the current is carried in an electrolyte has long been a subject for speculation. It is now possible, however, to account for the quantitative phenomena of electrolysis by assuming that the dissolved substance is dissociated before the passage of the current. For example, when sodium chloride is dissolved in water, it is dissociated to a greater or smaller extent into sodium ions and chlorine ions, each of which bears a charge of electricity. That substances are dissociated is also made very probable by measurements of the boiling and freezing points of solutions of electrolytes. Now, when the current passes through the solution, for every 96,540 cou¬ lombs of electricity passed, a gram equivalent pf the cation and of the anion separates out, gives off its charge at the proper electrode, and becomes an ordinary substance again. Substances are usually not entirely dissociated in solution, but consist of a mixture of undissociated and dissociated molecules. In water solution, most of the salts and the stronger acids and bases are quite highly dissociated at mod¬ erate dilution, and the dissociation ranges from this to zero dissociation for non-conductors. Since the electricity is carried by the ions, its conductivity by a solution must depend on the number of free ions in solution and the speed with which they move. An increase in the concentration of a solution increases the number of free ions and its conductivity, but this conductivity is not proportional to the increase in concentration, for the more concentrated a solution is, the less is it dissociated. 25. Migration Velocity. —The speed with which the ions move, generally known as migration velocity, depends on the viscosity of the solvent and the individual kind of ion. The speed with which some ions travel at 18° C. in water solution, with a difference of potential between the electrodes of 1 volt, is given in Table I. 20 ALKALIES AND HYDROCHLORIC ACID 5 It will be seen that the velocity with which ions move through water varies considerably, hydrogen and hydroxyl far exceeding all others. Hydrogen moves about five times as rapidly as chlorine, so that in the electrolysis of hydro¬ chloric acid, there is a tendency for the concentration of the acid to decrease rapidly at the anode and to increase at the cathode. TABLE I SPEED OF IONS IN WATER SOLUTION Cations Centimeters per Hour Anions Centimeters per Hour H io.8o OH 5.60 K 2.05 Cl 2.12 NHi 1.98 I 2.19 Na 1.26 NO, I.9I Ag 1.66 C 2 H 3 0 2 I.04 26. Polarization. —When a suitable electric current is passed between copper electrodes through a zinc-sulphate solution, the copper dissolves from the anode to form copper sulphate, and the zinc is deposited at the cathode. If, after the current has been passing for some time, the source of current is cut out and the copper plates are connected by a wire, a current will flow in the opposite direction from the first one. This phenomena is known as polarization. If the electromotive force of the cell is measured, it will be found to be about 1.1 volts. That is, a Daniell cell has been formed, and the condition very soon after the direct current begins to pass is the same as if a current were running against a Daniell cell. Therefore, it will not be possible to keep up the passage of electricity through a cell of this kind unless the original current has an electromotive force greater than the electromotive force of polarization. The passage of a current through copper electrodes in a solution of copper sulphate simply dissolves copper from the anode and deposits it at the cathode, so that in this case §5 ALKALIES AND HYDROCHLORIC ACID 21 there is no polarization, and a current of the smallest electro¬ motive force will flow continuously. Nearly all cases of electrolysis give polarization, and the passage of the current can only be continued when the elec¬ tromotive force of the source of the current is greater than the electromotive force of polarization of the solution. This electromotive force of polarization can be measured directly, or it can be calculated from the heat of the reaction that would cause the polarization. 27. Calculation of tlie Electromotive Force of Polarization From tlie Heat of Reaction.— When a metal reacts in an electric cell, there is a certain amount of energy set free that may be evolved as heat or as electrical energy, as circumstances may favor the one or the other. If, therefore, the heat of the chemical reaction is known, the electromotive force of the cell can be calculated. This however, will, not give the exact value for the cell, because a temperature coefficient, which varies with the kind of cell, also enters into the calculation. Since the electromotive force of polarization is only the current tendency set up by the separated product, it can also be calculated in the same way as the direct electromotive force. If the electromotive force of polarization is called e, and the valence of the ion is represented by n, then, when 1 gram ion has separated out, or if the gram ion is formed from the electrode and going into solution, the electrical energy is ne 96,540 volt coulombs. This, in calories, is ne 96,540 X .24 = ne 23,170 calories. If the heat energy is repre¬ sented by O, then Q = ne 23,170, and e = —— volts. ~ ^ n 23,170 From this can be calculated very nearly the minimum elec¬ tromotive force necessary to electrolyze a solution, assu¬ ming that no secondary reactions enter in. For example, if a solution of hydrochloric acid is electrolyzed, hydrogen sepa¬ rates at one pole and chlorine at the other. These, from their tendency to combine, will give an electromotive force opposed to the decomposing current, which can be calculated 22 ALKALIES AND HYDROCHLORIC ACID §5 by the preceding formula. The heat of formation of a gram molecule of hydrochloric acid in dilute solution is 39,300 cal- 39 300 ories, and the valence of hydrogen is 1; therefore, e = —-v 23,1 1 u = 1.69 volts, and it will require a current of at least that electromotive force to pass continuously through such a solution. 28. Summary.—The electrolysis of a solution according to the preceding explanations may be summarized as follows: 1. Every electrolyte is, by the passage of the current, decomposed into two parts—the cation and the anion. These are in certain cases the positive and negative elements of the compounds. In other cases they are combinations of ele¬ ments, as in potassium ferrocyanide, where the cation is potassium and the anion is the ferrocyanide radical. 2. The metal of a compound usually separates at the cathode, but in certain cases, as in ferrocyanides, one metal goes to the anode. 3. Water solutions of salts of the metals that decompose water naturally do not give the metal at the cathode, because as soon as the metal is separated it decomposes the water and forms a hydrate. Very strong solutions of the hydrates may be exceptions to this; also, when a mercury cathode is used, the metal dissolves in the electrode and is protected from decomposition. 4. The liberated ion appears only at the surface of the electrode. 5. There is a certain minimum electromotive force required for the electrolysis of a solution, and this is deter¬ mined by the heat of reaction of the liberated ions. If less than this minimum electromotive force is supplied, the current will pass until enough of the ions are liberated to set up the electromotive force of polarization, when the cur¬ rent will stop. In the case of the electrolysis of a solution between electrodes of the same metal as the positive ion, there will be no polarization, and the weaker current will flow continuously. §5 ALKALIES AND HYDROCHLORIC ACID 23 6. The chemical work done is proportional to the mini¬ mum electromotive force of polarization, and if a greater electromotive force than the minimum is required, it will not appear as chemical work in separating more ions, but as heat energy. 7. Various secondary reactions may take place as: (a) The decomposition of one or both of the ions (usually the negative one, however); for example, S0 4 may decom¬ pose into S0 3 and O. ( b ) The ions may react on the elec¬ trodes, as in the electrolysis of dilute sulphuric acid between zinc electrodes, in which case the S0 4 acts on the anode, giving ZnSOt, and only hydrogen is set free. ( c ) Abnormal ions may be liberated, as the frequent formation of ozone, 0 3 , the deposition of a black porous deposit of copper, and the deposition of lead or manganese dioxide on the anode. ELECTROLYTIC PREPARATION OF ALKALI AND CHLORINE INTRODUCTION 29. Historical.— The fact that solutions are decom¬ posed by the electric current has been known since the beginning of the 19th century, and a process was patented for the electrolysis of salt solutions during the first half of that century. It was not until the dynamo was perfected, however, that the commercial electrolysis of salt solutions could even be considered. About 1880 an interest in the subject began to be shown by applications being made for patents; but even in 1888 many leading men in the alkali industry considered the electrolysis of salt in a commercial way impractical. At the present time, however, there are several processes that are considered commercially success¬ ful for the making of alkali and bleach from salt by elec¬ trolysis, and much more than half of all the chlorate of the world is made by this method. 24 ALKALIES AND HYDROCHLORIC ACID §5 30. Electrolysis of Salt. —The electrolysis of salt involves first the separating of the ions—sodium at the cathode and chlorine at the anode. Then, if fused sodium chloride is being electrolyzed, the chlorine is evolved and collected, and the sodium separates as metal; if the tempera¬ ture is kept suitably high, the sodium can be drawn off and cast into bars. This process might be used for the prepara¬ tion of metallic sodium, but the metal can be produced more cheaply and easily by the electrolysis of the fused hydrate. If a solution of salt is used for electrolysis, the chlorine will be evolved as before, but the sodium acts on the water as soon as set free and forms sodium hydrate and hydrogen. As soon as formed, the caustic-soda solution begins to conduct a portion of the current and to be decomposed, liberating oxygen at the anode and wasting the current. There is also a possibility that a portion of the chlorine will get mixed with the caustic liquor and thus form sodium hypo- chloric, which may in turn be converted into sodium chlorate, or be reduced by the hydrogen to sodium chloride. These various processes may be represented by the equations 2NaCl = Na, + Cl, Na, + 2H,0 = 2NaOH+ H, 2NaOH + Cl, = NaCl + NaCIO + H,0 Z NaCIO = 2 NaCl + NaCIO, NaCIO + H, = NaCl + H,0 In addition to the loss of alkali and chlorine by its reversion to salt, it should be remembered that, as was pointed out with the sodium hydroxide, all of these substances conduct and waste current. 31. Conditions Favoring Electrolysis. —The ideal conditions to be sought in selecting a process for the elec¬ trolysis of salt, for the formation of sodium hydrate and chlorine, may be summarized as follows: 1. The process must work at as low voltage as possible, in order to give the maximum decomposition per electrical horsepower. §5 ALKALIES AND HYDROCHLORIC ACID 25 2. The combination of the caustic soda and the chlorine to form sodium hypochlorite must be avoided, in order to prevent a loss of current and to avoid great wear and tear on the electrodes. The accumulation of the sodium hypo- 'chlorite also prevents the continuous use of the electrolyte. 3. The products of the electrolysis must not be allowed to accumulate in the decomposition cell. 4. Strong and pure solutions of sodium hydrate must be obtained, in order to avoid the expense of concentrating the solutions and that the product may be salable. 5. The apparatus must be simple and need but little attention and repairs. 32. Electrodes. —The cathodes in the electrolysis of salt solutions cause very little trouble, as it is compara¬ tively easy to find materials that are resistant to the action of caustic soda. With the anode, however, it is much dif¬ ferent, for here is set free the very active chlorine, and, by secondary actions, the still more active oxygen and oxides of chlorine. The obtaining of anodes that would be suffi¬ ciently resistant, and at the same time not too expensive, was one of the most difficult problems to solve in the early days of this work. The two conditions that a successful electrode must fulfil are that it shall be a good conductor and at the same time resistant toward the products of electrolysis. The only sub¬ stances that satisfactorily meet these conditions are carbon and the platinum metals, with their alloys. Carbon, in the form of coke, is not badly acted on by chlorine, but oxygen and the oxides of chlorine act on it considerably and cause it to disintegrate. The overcoming of this difficulty was at one time almost despaired of, and recourse was had to making the electrodes as cheaply as possible from slabs of gas coke and frequently renewing them. At the present time, however, carbon electrodes are made by mixing finely ground coke with tar and some suitable metal or metallic oxide, pressing the mixture into shape, and heating it to drive off the more volatile substances. The electrodes are 26 ALKALIES AND HYDROCHLORIC ACID §5 then subjected to the highest temperature of the electric furnace. By this means, carbides of the metal are formed; but these are immediately decomposed, liberating the metal and leaving carbon behind in a fine graphite form. Carbon electrodes made by this or a similar method are now very generally used in the production of caustic soda and chlorine by electrolysis. The other possible composition for anodes is an alloy of 90 per cent, of platinum and 10 per cent, of iridium, which is for more resistant toward the products of electrolysis than platinum alone. These electrodes are expensive, however, and are not so much used in the preparation of chlorine and caustic soda as the carbon electrodes. On the other hand, in the preparation of chlorates, the platinum-iridium alloy is almost exclusively used, as the use of carbon is practically out of the question on account of the oxidizing substances that form in large amounts. FUSED ELECTROLYTE 33. The use of fused salt as an electrolyte offers certain difficulties that do not occur with the solution, and inventors have largely turned their attention to the perfecting of those processes which use solutions of salt in water. Three of the processes that use fused salt as an electrolyte and have been patented deserve mention; they are Vautin's , Hulin’s , and Acker’s. Of these processes, Vautin’s proved impractical and has apparently been abandoned, but the other two processes are in apparently successful operation. HULIN’S PROCESS 34. Hulin’s process consists in the electrolysis of a fused mixture of sodium and lead chlorides, using a lead cathode. One difficulty that is experienced ordinarily in the electrolysis of fused salt is, that both the sodium and the chlorine rise to the top of the material and it is very hard to prevent loss by their reuniting. In this method, however, §5 ALKALIES AND HYDROCHLORIC ACID 27 the lead cathode is fused; but this occurs at the bottom of the electrolyte, so that the chloride is evolved and carried away from the top of the apparatus and the sodium remains as an alloy with the lead at the bottom. Vautin employed a similar arrangement, but, attempted to electrolyze sodium chloride alone. This led to the formation of a crust of the lead- sodium alloy on the surface of the cathode, with a subse¬ quent high electromotive force and loss of sodium. Hulin avoids this difficulty by using an electrolyte of a mixture of sodium and lead chlorides, so that lead is continuously deposited with the sodium and an alloy of the proper com¬ position is built up. By this method, the mixture of chlo¬ rides must continuously become poorer in lead chloride unless more of the substance is continuously added. This addition of lead chloride is best made, or rather the lead for the cathode is best supplied (for it consists in a simple trans¬ fer of lead from the anode to the cathode), by employing two anodes—one of carbon and the other of lead. By allowing any desired fraction of the total current to pass through the lead anode, as much of it as is needed is dissolved in the electrolyte. It is found in practice that the best results are obtained by allowing 12 per cent, of the total current to pass through the lead anode and the remainder through the carbon anode. The electrolysis takes place in cast-iron crucibles, which are surrounded by poor heat-con¬ ducting material and lined with an insulator. The heat of formation of salt from sodium and chlorine is 97,600 calories, and therefore, according to the formula (e = the \ n 23,170/ electromotive force theoretically necessary to decompose fused sodium chloride is about 4.2 volts, because this value is calculated by using the heat of formation of solid sodium chloride; that for the fused chloride will be diminished by a value equal to the heat of fusion, and its electromotive force of polarization will also be less. In practice, each crucible employs a current density of 700 amperes per square foot of electrode surface and an electromotive force of 7 volts. By the use of such high current density it is possible to get a 28 ALKALIES AND HYDROCHLORIC ACID 5 large amount-of decomposition of the electrolyte per unit of electrode surface, and thus to employ a small plant. The yield per electrical horsepower-hour is 81 grams of chlorine and 54 grams of sodium. The chlorine is converted into bleaching powder by the usual method. The lead alloy, which contains from 23 to 25 per cent, of sodium, may be sold directly for many uses where metallic sodium is required. This alloy, however, is usually treated with water, and by suitable working, a strong solution of caustic soda of a high degree of purity is obtained. This caustic requires very little fuel for its evaporation, and for this reason is much better than the more dilute caustic obtained by many processes. The lead is left by this operation as a spongy mass, and, together with considerable lead peroxide that is also formed, it makes a valuable by-product. This process was considered so promising in 1899, that a company with a capital of over $500,000 was formed, and works, that are still in successful operation, were erected at Clavaux, France, for carrying out this method. ACKER’S PROCESS 35 . The Ackei* electrolytic process, which was opera¬ ted at Niagara Falls, New York, until some years ago, when the works were destroyed by fire, differs from the Hulin proc¬ ess in that it uses fused lead as the cathode and continu¬ ously removes the sodium from the sodium-lead alloy, so that the lead can be used continuously. The appa¬ ratus for carrying out this process is shown in Fig. 10. It consists of an iron base a embedded in brick work b, which rests on brick pillars c. Sometimes, however, the apparatus rests on the ground and has places excavated for the parts projecting below the surface. The upper part consists of slabs d that are made of acid-resisting slate or of fireclay. These slabs are carefully luted into the iron shoulders, as shown, by fireclay. Through the top cover project three graphite anodes e , while at / is provided a charging hole for fresh salt. At g is molten §5 ALKALIES AND HYDROCHLORIC ACID 29 salt, and at h an alloy of molten lead and sodium. At i is a pipe for conducting away the chlorine. At j is a pipe for blow¬ ing in steam; k serves for conducting away the hydrogen; and l conducts the fused caustic soda o to the shipping tin m. The extension p serves for drawing away the fused contents of the cell, when it is necessary to empty it for repairs, and q shows the cathode connection. At s is an iron plate that serves to separate the molten salt, which is the cathode proper, from the alloy below. The top is covered with a non-con¬ ducting material /, as asbestos wool. 36. To start the operation, the interior of the cell is heated by hydro¬ gen flames until it is thoroughly hot; then molten lead and molten salt are- run in, the covers and electrodes put in place, and the current started. The chlorine is given off at the anodes, rises to the surface, and is conducted away through the pipes i. The sodium separates on the surface of the fused lead, which acts as the cathode and alloys with it. Meanwhile, superheated steam is blown in through pipe j and thus causes the lead to rise in w, over¬ flow, and circulate as shown by the arrows. As soon as the cell is in working order, the sodium alloy is decomposed in w by the steam, and the fused caustic soda rises to the surface of the lead in o and runs off through pipe l into 30 ALKALIES AND HYDROCHLORIC ACID §5 the shipping- can in. Pipe l contains a plunger valve, so that the flow of caustic can be stopped if desired. The lead flows in the direction of the arrows, displaces the sodium alloy just formed, and thus forms a system of circulation. The hydrogen, which is formed by the action of the steam on the sodium in the alloy, escapes through the pipe k , and can be collected and burned over the salt, in the form of an oxyhydrogen flame, to keep up the temperature of the cell. Since the cell is well insulated, the heat from the steam and the heat of the reaction Na + H. 2 0 = NaOH + H nearly suffice to keep the temperature of the cell at the proper point. _ DISSOLVED ELECTROLYTE 37. The so-called wet processes, or those in which the sodium chloride is in solution as an electrolyte, comprise the most important methods for obtaining the products of electrolysis. A serious difficulty is encountered in working these processes, however, because the materials formed at the electrodes tend to mix and form compounds that are not wanted. There are three methods by which the products formed about the electrode may be kept separate: (1) by a difference in the density of the liquids; (2) by diaphragms; (3) by using a mercury cathode. DIFFERENCE IN DENSITY 38. In the processes that depend on the difference between the specific gravity of the sodium hydrate formed and the rest of the solution to keep the products of the reaction separate, the anode is placed at the top of the decomposition vessel, so that the chlorine is set free without traversing more than a small portion of the liquid. On the other hand, the cathode is placed at the bottom of the cell, and the caus¬ tic solution, being heavy, stays at the bottom and can be drawn off. Theoretically, this is a good arrangement, but practically, it is almost impossible to prevent the diffusion §5 ALKALIES AND HYDROCHLORIC ACID 31 and mixing of the chlorine and caustic soda. This difficulty is also increased by the hydrogen, which is set free at the cathode, rising through the electrolyte and mixing it. The Richardso7i-and-Holland process avoids the difficulty with the hydrogen by using a copper cathode covered with a coating of copper oxide. The copper oxide oxidizes the hydrogen as rapidly as it is formed. When necessary, the electrodes are removed and the copper oxide is regen¬ erated by heating in the air. By this method a fairly good separation of the caustic soda and the chlorine can be main¬ tained; this process was tried on a manufacturing scale, but it has been abandoned. PROCESSES USING DIAPHRAGMS 39. The use of a diaphragm is a favorite method for keeping the solutions around the cathode and anode separate, but it is very difficult to find a diaphragm that will meet all the requirements. To be satisfactory, a diaphragm must resist the action of the contents of the bath, must keep the anode liquor well separated from that of the cathode, and must not offer great resistance to the passage of the current. Many diaphragms have been proposed, but none of them has proved very satisfactory until recently. Only a few of the various forms of apparatus using diaphragms for electrolysis of a salt solution, however, will be mentioned. 40. Tlie Townsend Process. —Among the large num¬ ber of diaphragm cells, the one invented by E. P. Townsend can be considered as one of the best and most efficient at the present time. A longitudinal section of this cell is shown in Fig. 11. This cell is rectangular in shape and is about 9 feet 6 inches long, 3 feet high, and the upper part is 12 inches wide, while the lower part is 18 inches wide. The founda¬ tion H is made of a good concrete and extends the whole length of the cell. To this foundation is fastened a plate D, made of either hard rubber, earthenware, hard¬ ened asbestos, or some similar non-conductive material. 32 ALKALIES AND HYDROCHLORIC ACID 5 This plate is perforated and simply serves as a support for a diaphragm. Next to this perforated plate is placed the diaphragm 5 of woyen asbestos cloth, the inequalities, or interstices, of which are filled with a paint made of ground asbestos fiber, oxide of iron, and hydrated oxide of iron in a colloidal condition. The object of this coating is to protect the asbestos cloth and to make it equally pervious to the brine. A sheet of metal or wire gauze, which acts as the cathode, is fastened as shown, so that there is first the perforated plate D, then the diaphragm S, and finally the metal or wire-gauze cathode. The reservoirs /, formed of bulging wire plates and generally known as the cathode compartments, are filled with some liquid hydrocarbon compound that is immiscible with and inert toward the cathode product, which, in this case, is sodium hydrate. The hydro¬ carbon compound best adapted for the purpose, is refined petroleum, or kerosene. On top of each of the cathode compartments is an outlet R for the escape of the liberated hydrogen, and at the bottom of each is another outlet P for the withdrawal of the cathode liquid, which is sodium-hydrate solution, as pre- A *>*1 a WitepA ■a A a £ a a A d.A.jy. Aii Fig. 11 §5 ALKALIES AND HYDROCHLORIC ACID 33 viously stated. The level at which the sodium-hydrate solution is kept is indicated at A, and above this is the column of kerosene oil, the upper level of which is marked O. At G is shown the anode, or anodes, of Acheson graphite connected with the current conductors X, and the current connection to the cathodes is shown at the side of the cathode reservoir. The upper part of the anode cham¬ ber is closed with a perforated layer C of some inert substance, such as concrete. These perforations serve to conduct ^way the chlorine gas evolved. The brine flows through the anode compartment in the center of the cell, and on its passage becomes weaker and weaker, owing to the transmission and transformation of the salt through the diaphragm and the cathode. This weakened brine, which also contains small amounts of sodium hypo¬ chlorite, sodium chlorate, caustic soda, and chlorine, is con¬ ducted to a reservoir, where it is again strengthened with salt, the hypochlorite decomposed, and the solution neutralized with a suitable amount of hydrochloric acid. The decom¬ position of the sodium hypochlorite and the neutralization of the brine are of considerable importance, owing to the fact that the accumulated hypochlorite acts on the anodes and rapidly disintegrates them. With little care, however, the formation of sodium hypochlorite can be avoided; in fact, the presence of this compound in more than comparatively minute quantities is an indication of a lack of care in the adjustment of the current and general management of the cells. 41 . The most notable feature of the Townsend cell is the use of a non-conducting liquid, such as kerosene, in the cathode chamber. When this cell is in operation, the globule of the caustic-soda solution is forced through the perforated cathode plates by hydrostatic pressure and is surrounded by the kerosene, which is not only indifferent to the action of the caustic soda, but also to that of the electric current. The globule of caustic-soda solution, being thus removed from the field of activity, drops to the bottom of the cathode com* 199—20 34 ALKALIES AND HYDROCHLORIC ACID 5 partments from which it is drawn off. By increasing or decreasing the height of the salt solution in the anode chamber, its flow through the diaphragms and cathode plates should be regulated to conform to the decomposing potenti¬ ality of the current and the decomposition of the sodium hydrate into metallic sodium and subsequent reoxidation thus avoided. At present, a saturated solution of salt is used that circulates continually into and out of the cell through passages molded in the concrete for that purpose. The brine leaving the cell contains about .02 gram of sodium hypo¬ chlorite per liter, is decidedly alkaline, and is practically saturated with chlorine. The chlorine leaving the anode chamber at C can be obtained about 97 per cent, pure, but it is considered better practice to draw it off 90 per cent, pure, owing to the fact that this gas is used in the manufacture of bleaching powder; also, in order to prevent a too rapid combination with the slaked lime employed in this process and a subse¬ quent decomposition due to the heat of formation, the chlorine gas, especially during the warm weather, would have to be diluted with air anyhow. In practice, it is found that with a current of 4.5 volts and 4,000 amperes 460 pounds of sodium chloride can be decom¬ posed in 24 hours in the Townsend cell. The efficiency of the cell is 96 per cent, of the theoretical output, and even if pressed to its highest output, it is never lower than 90 per cent., as will be seen from an average yield, which consists of 270 pounds of chlorine and 300 pounds of sodium hydrate, calculated to 100 per cent. NaOH. More economical work, but with a decreased output, may be done by reducing the voltage to 3.3. The solution of caustic soda as it leaves the cathode chamber contains about 20 per cent, of sodium hydrate, but it is more economical to reduce this percentage, at least so far as the current utilization is concerned. 42. As has been previously stated, the solution of caustic soda is saturated with salt, which is crystallized out §5 ALKALIES AND HYDROCHLORIC ACID 35 by evaporation. Triple-effect evaporators are used for this purpose, and by means of this kind of apparatus the specific gravity of the caustic-soda liquid can be brought up to 1.5, although in practice it is advisable to keep it much lower, owing to the fact that by bringing up the specific gravity as high as 1.5, too much salt is crystallized out and deposited in the vacuum chambers. After the caustic solution leaves the evaporators it is further concentrated in open iron kettles by direct heat. Finally, the solution is ladled from these open iron kettles into a finishing pot, where it is fused and then run into the usual form of sheet-iron drums. During the process of evaporation in the iron kettles, most of the salt is deposited and fished out. The finished caustic tests 76 per cent, sodium oxide, Na 2 0. Although, as has been previously stated, it would be more economical theoretically to use a voltage of 3.3 in this cell and a strength of caustic- soda solution leaving the cathode chamber of 9 per cent, sodium hydrate, in practice it is better to run the cell at the higher voltage with the stronger solution of caustic, this, of course, at the expense of the increased current. 4*3. Le Sueur Process. — The Le Sueur process is a combination of the density and diaphragm methods of separa¬ tion, for while it uses a diaphragm, the electrodes are so placed that the gravity separation will be as effective as possible. The electrolyzing vessel a, Fig. 12, is made of i-inch boiler steel, and is about 9 feet long, 5 feet wide, and li feet deep. The anode compartment is made by. building common bricks b in Portland cement to a height somewhat greater than the electrolyzing vessel and then covering the compart- 36 ALKALIES AND HYDROCHLORIC ACID §5 ment with spruce planks c. Carbon has been discarded as an anode substance in favor of the 10-per-cent, iridium-platinum alloy already referred to. The anodes are made according to a method devised by Le Sueur. This consists in rolling 4-inch pieces of the platinum-iridium wire very thin, except at one end; the unrolled ends are then bunched together and fastened in a glass tube so that they just extend into the interior, and the flat ends are spread out. When the anodes are in place through the spruce cover to the anode compartment, con¬ nection is made with the main conductor by means of a drop of mercury in each glass tube, an iron wire reaching to the top of each tube. These electrodes cost about 73 cents each, and enough to make 200 tons of bleach per month will cost about $5,000. 44 . The anode compartment is separated from the cathode compartment by an asbestos diaphragm supported on a wire gauze, which at the same time serves as the cathode. By thus bringing the diaphragm close to the cathode, the resistance of the cell is diminished; also, by making use of the gravity system, the caustic soda is kept quite well separated from the chlorine. It is nevertheless, impossible to prevent some diffusion and the formation of sodium hypo¬ chlorite, which not only causes loss of current, but also acts' on the electrodes. This is avoided in the anode compart¬ ment by keeping the solution slightly acid with hydrochloric acid, which decomposes the hypochlorite and gives chlorine. The sodium hypochlorite that collects in the cathode com¬ partment is converted into sodium chlorate and recovered. The diaphragm and cathode are arranged as shown, being sloped to one end of the cell, so that the hydrogen wfll pass to the higher parts and then out of the cell. On an average, the diaphragms last 7 weeks, but some have been known to last as long as 24 consecutive weeks. The anodes and the cell itself are practically indestructible. Instead of the theo¬ retical 2 volts, the process uses 6| volts and 1,000 amperes per cell. A solution containing from 10 to 15 per cent, of 5 ALKALIES AND HYDROCHLORIC ACID 37 sodium hydrate can be separated by this process, but it will also contain considerable salt. This liquor is concentrated under diminished pressure, the salt separated by centrifugal machines, and the evaporation completed in iron pots. The efficiency of the Le Sueur process is about 87 per cent, of the theoretical amount of chlorine and somewhat less of sodium hydrate. The process is in successful opera¬ tion on a commercial scale at Berlin Falls, New Hampshire, where the caustic is used in making wood pulp and the chlorine is used to bleach the pulp. 45 . Hargreaves-and-Bird Process. — The Har- greaves-and-Bird process can be best classed under the head of diaphragm processes, although, strictly, the diaphragm does not divide the cell. The process is distinctive in that the walls of the cell are composed of the diaphragm and the cathode. The diaphragm is composed of a layer of paper or some other suitable material, as a copper-wire gauze, covered with a layer of Portland cement, which in turn is covered with a layer of asbestos. This is impermeable to the salt solution, but allows the sodium ion to pass. The cell is put together with a copper-wire gauze, which serves as the cathode, on the outside, and the whole is set into an enclosing jacket. The carbon anodes are hung in the anode compart¬ ment, and the brine to be electrolyzed slowly flows in at the bottom of the cell and passes out at the top through the same pipes as the chlorine. During electrolysis, the sodium ions migrate to the top cathode and are there, as rapidly as set free, converted into caustic soda by blowing in steam; or into soda crystals, by steam and carbon dioxide. The diaphragm and cathodes are made 10 feet long and 5 feet high, and as one is on each side of the cell this con¬ struction gives 100 square feet of cathode surface. A cell of this size decomposes on an average 237 pounds of salt every 24 hours, and gives 365 pounds of 37-per-cent, bleach and 213 pounds of soda ash by the use of 2,300 amperes and 3.9 volts per cell. This represents an efficiency of about 97 per cent, of the electrical energy used. The brine is best 38 ALKALIES AND HYDROCHLORIC ACID §5 obtained direct from the wells; in passing through the cell, 75 per cent, of it is decomposed. The dilute brine can be returned to the well to be resaturated. The chlorine can be converted directly into bleach, and the caustic is strong and pure. In the manufacture of sodium carbonate, for which this process is well suited, the solution is so concentrated that the carbonate crystallizes out without concentration. The sodium carbonate made in this manner is very pure, averaging, when dehydrated, 97.9 per cent, of Na 3 C0 3 , 1.53 per cent, of NaCl , and .53 per cent, of Na 2 SO if etc. The sulphate is probably due to sulphur dioxide in the furnace gases that are used for carbonating. The apparatus is simple and requires very little attention. The only part that suffers great wear is the diaphragm, and that is quite cheap. This process has been running satisfac¬ torily in a small way for several years, but a large plant has been erected recently in England. 46. A considerable amount of money has been spent in recent years in the purchase of many of these cells, with the right to use them, by paper makers that consume large quantities of bleaching powder, and also by those who employ the soda-pulp process for the manufacture of wood pulp. The main reason for making bleaching powder and caustic soda at paper mills is to reduce the cost of these products. It will readily be seen that the freight on the product is often the largest single item of cost, especially where mills that use from 10 to 15 tons of bleach per day are located a great distance from the Chemical manufactory. Then, again, paper mills generally locate where water-power can be obtained, and thus have plenty of cheap power to operate the electrical apparatus. Even where soda wood pulp is not made, but where the sulphite process is in operation, a bleaching liquor is made by using the caustic soda as a base and saturating it with chlorine. This liquor is much more efficacious than bleaching powder. Then, too, owing to competition, mined salt of great purity is now sold much cheaper than lime. §5 ALKALIES AND HYDROCHLORIC ACID 39 PROCESSES USING A MERCURY CATHODE 47. Many processes for the electrolysis of salt in which a mercury cathode is used have been proposed. These have the advantage that the sodium separates with the mercury as an amalgam and can be converted into hydrate outside of the cell. By this means a solution of caustic soda of high concentration and practically free from salt can be made. The process suffers from the disadvantage that only dilute amalgams can be made, for otherwise there is a loss of cur¬ rent, and the mercury must therefore be frequently changed. There is also a chance of a large loss of mercury, because when the sodium is acted on by the water, mercury is mechan¬ ically carried away by the hydrogen; also, considerable mercury is carried off in the form of vapor, even at ordinary temperatures. 48. Castner-Kellner Process. —The Castner-Kell- ner process is the most satisfactory and successful process of this character; in fact, it has proved to be the most satis¬ factory of all processes for the electrolytic decomposition of salt. As shown in Fig. 13, the cell is divided into three com¬ partments, the center one of which contains the iron cathodes and serves for the decomposition of the sodium amalgam. The two end divisions serve as anode compartments and con- 40 ALKALIES AND HYDROCHLORIC ACID §5 tain the carbon anodes b , b. One end of the cell rests on a knife edge c, and the other is supported on an eccentric d, which revolves and thus slowly raises and lowers the end of the cell. Brine fills the two end compartments and is renewed, as necessary, by fresh brine flowing in; the exhausted brine is always resaturated. A thin layer of mercury covers the bottom of the apparatus, and is so regulated in amount that all of it practically flows alternately from the end compart¬ ments into the 'middle, as the cell rocks. Strictly speaking, the ends of the cell are not anode com¬ partments, but are alternately complete cells in which the salt is decomposed, the chlorine separating on the carbon anode and passing off, and the sodium dissolving in the mer¬ cury cathode to form an amalgam. Then, as the cell tips, the amalgam flows into the center compartment, where it forms the anode of a primary battery, and the iron electrode here becomes the cathode of this battery. This arrangement has the advantage that the hydrogen, instead of coming from the surface of the mercury and thus carrying that metal with it, comes from the iron cathode, and the sodium simply goes into solution from the mercury as caustic soda. There is also an advantage in that the current from this battery aids in the electrolysis in the end cells. Owing to the frequent removal of the sodium amalgam from the anode cell, it rarely contains over .02 per cent, of sodium, and as a consequence the cell gives a high degree of efficiency, being from 88 to 90 per cent, of the theoretical. 49. Since no caustic soda is formed in the anode com¬ partment, there is no formation of sodium hypochlorite, and therefore the anodes have practically no wear. Also, since the electrolyte contains no hypochlorite, it can be used con¬ tinuously by being conducted through a supply of salt so as to be resaturated. The resistance in the cell is very low, so that a current of 4 volts and 550 amperes per cell will decom¬ pose 562 pounds of salt every 24 hours and will yield 38i pounds of caustic soda and 34i pounds of chlorine. The caustic solution can be made of nearly any desired §5 ALKALIES AND HYDROCHLORIC ACID 41 concentration, and is practically made about 20 per cent, sodium hydrate. This solution can be concentrated by simple evaporation and yields a caustic 99i per cent. pure. The chlorine obtained is from 95 to 97 per cent, pure, and for the rest contains a small amount of hydrogen. The cells are very simple and require only little attention, the work being almost automatic. Repairs are seldom needed, but when necessary any cell can be cut out of action without disturbing the work of the others. This process has been operating successfully for several years in England, on the Continent, and in America. The English company has been able to declare 8-per-cent. annual dividends on a capital of over li million dollars, and the American company is doing much better. CONCLUSIONS 50 . From the foregoing, the following conclusions may be formed: 1. In the fusion processes, fused salt is a good conductor of electricity, and very high current densities can therefore be used, which means that a large output can be obtained from a small plant. Concentrated solutions of caustic soda, or, as in the Acker process, even fused caustic soda, can be made. On the other hand, the wear and tear on the cell, especially if heated from without, is very great, and the cost of keeping the material fused must be considered. The hot chlorine is not so easy to handle as the cold chlorine from the other processes and is also much more dilute. 2. The process using gravity for separating the products has very few good points. 3. In the diaphragm processes, the cells are cheap and the wear and tear on the cell is not great. They require very little skilled labor. They suffer, on the other hand, considerable loss of caustic soda and chlorine through their recombination and by reduction at the cathode, and have high resistance in the cell. This, however, is nearly pro¬ portional to the power of the diaphragm to stop diffusion, so that the higher the resistance, the smaller is the loss of the 42 ALKALIES AND HYDROCHLORIC ACID §5 products through mixing, and the reverse. Except in the Townsend process, the diaphragm processes furnish a low strength of caustic, the concentration and purification of which is expensive. The Hargreaves-and-Bird process cannot be included in this general statement, as it is not strictly a diaphragm process. 4. The mercury-cathode cell has very little loss through the recombination of the products of the reaction. The cells are quite free from wear and tear. A highly concentrated caustic-soda solution can be made if desired, but it is usually cheaper to concentrate the solution after it has attained a strength of about 20 per cent, than to overcome too great a resistance of the solution. The initial cost of the cells is high, and a large amount of mercury is constantly in use. About 7 tons of mercury is required for each ton of caustic soda produced in a day. The power to move the cell is small, but must be considered in estimating the cost of working the plant; it also adds to the complication of the plant. Various estimates of the cost of bleach and caustic by the electrolytic process have been made, and practically all of them show that these products cost more by this method than by the older processes. Nevertheless, the electrolytic processes are able to continue and pay dividends, so that, apparently, something is wrong with the calculations. The truth of the matter is that sodium hydrate can be made more cheaply by the ammonia-soda process than by any other, but this process cannot produce chlorine. The electrolytic process can produce chlorine more cheaply than the Le Blanc process, so that the electrolytic processes must be con¬ sidered essentially as processes for the production of chlorine, and the caustic soda as a valuable by-product. 5. It may be well to discuss here the best method to adopt for the manufacture of caustic soda and bleaching powder, whether the Le Blanc, the ammonia-soda, or the electrolytic process. In England, using Spanish pyrites, and in fact in any country where pyrites carries copper and where the utiliza- § 5 ALKALIES AND HYDROCHLORIC ACID 43 tion of the sulphur is of secondary importance, but where its oxidation products have to be condensed in order to prevent the insufferable nuisance caused by letting the sulphurous acid arising from the burning of the pyrites escape into the air, the Le Blanc process, coupled with the recovery of the sulphur, bids fair to hold its own'. These conditions, how¬ ever, do not prevail in the United States at present, and but few plants exist here where this process is practicable. With increased demand for copper and the enactment of laws compelling the condensation of sulphurous acid result¬ ing from the roasting of its ores, the number of plants employing the Le Blanc process may be increased. In the United States, the ammonia-soda process is the method principally used for the production of carbonate and caustic soda; but, unfortunately, as has been shown, the chlorine is lost in combination with calcium as calcium chloride, which finds only few large uses. In England, one use for calcium chloride is to add it to water used for sprin¬ kling the roads, and, from reports, this plan has met with good results. Where good brine can be obtained from salt wells or strata for the pumping, and where limestone is cheap and coal can be had at a low price, these advantages far outweigh the loss of the chlorine. The electrolytic processes have made great strides in late years—utilizing, as they do, both of the constituents of salt, and that directly without the intervention of complicated methods, as in the Le Blanc process—and leave nothing to be desired, provided electric power can be obtained cheaply, and, as in the Hargreaves process, carbonate can be quite easily made by introducing carbon dioxide into the cathode compartment of the cell. To illustrate, say that 1 electrical horsepower produced by means of water-power costs from $18 to $20 per annum. At the same point, using the most economical type of steam boiler and a turbine engine, it will cost from $37 to $38 per annum; with producer gas and a gas engine, $40 to $42; and with a reciprocating steam engine, $42 to $45. But it must be borne in mind that the electric power has to be paid for whether used or not. If 7,000 44 ALKALIES AND HYDROCHLORIC ACID §5 horsepower is to be contracted for, and, through the exigen¬ cies of supply and demand, the manufacturer’s production should be curtailed one-half and only 3,500 horepower used, he would still have to pay for the 7,000 horsepower. Again, there are localities where good bituminous coal can be had for from 80 cents to $1 per ton at the mines, and if works could be located advantageously in such places, it would bring the cost of electric energy very close to that derived from water-power, considering the enormous investment necessary for installing the latter. ELECTROLYTIC BLEACH 51 . One of the main things to overcome so far has been the formation of hypochlorite in solution; however, when a bleaching solution is wanted, the hypochlorites are just what are needed. As early as 1883 Hermite patented a process and advocated the use of electrolytic bleach. He proposed to electrolyze solutions of calcium chloride, magnesium chloride, or a mixture of one or both of these with salt in such a way as to obtain hypochlorites in solution. This is easily accomplished by placing the cathode over the anode, so that the chlorine in arising, must pass through the caustic formed; and if the electrolyte is kept circulating through the bleach vat, the apparatus lasts well and the process is satisfactory. 52. A very satisfactory apparatus for carrying out an electrolysis of this character has been invented by Kellner. Fig. 14 shows an apparatus of this character in vertical section and ground plan. It consists of a cell c with a cover d. The side walls, which act as insulators, carry electrode plates ) When gas is abundant and under pressure, the tube m is attached to the source, / and g are opened, and 2 or 3 liters of gas allowed to flow through the burette, thus sweeping out the air and leaving a good sample of gas. By closing / and g the gas is enclosed. (c) When the gas is abundant, but not under pressure, as happens in taking samples between the lime kilns and the pumps, it is necessary to attach an aspirator at n to draw the gas through the burette. A suitable arrangement for aspirating in this case consists of a large bottle o. This bottle is filled with water, the rubber tube p attached at n, the pinch cock r opened, and then the stop-cocks g and f opened. After 2 or 3 liters of gas have been drawn through the burette, first g and then f is closed, p is disconnected from n, and the sample is ready for analysis. Having the burette filled with the sample of gas, the cup / is filled with water to a mark that is 1 centimeter above the stop-cock /, c is then attached to n, and d and g opened. Water thus flows into the burette and compresses the gas. When the water reaches the 100-cubic-centimeter mark, ^is closed and f is turned to connect the burette with /. Gas will escape until the gas in the burette is under the atmos¬ pheric pressure, plus the pressure of 1 centimeter of water. f is then closed and the volume of gas read (it should be exactly 100 cubic centimeters). The rubber tube i of the suction flask A is then attached at n, g is opened, and, by sucking on j, the water is almost completely removed from the burette, leaving a partial vacuum; g is then closed, and i removed from n. For the determination of carbon dioxide, a small beaker containing a suitable solution of caustic potash is brought under n, and g turned so that the alkali solution rises in the burette; g is then closed. The burette is then grasped at /, loosened from the clamp k (the ends of the burette are grasped between the first and second fingers of each hand 10 ALKALIES AND HYDROCHLORIC ACID §6 beyond the stop-cocks to avoid heating the gas by the hands), and after the water is emptied from /, the burette is thoroughly shaken, so that the gas is well mixed with the caustic potash. The burette is then replaced in the clamp k, n is brought under caustic-potash solution, and g again opened. The alkali will rise in the tube, and when it has filled as much as it will, g is once more closed and the burette shaken as before. This is repeated as long as the alkali solution continues to rise in the burette. Water is then filled to the 1-centimeter mark in /, / is opened to insure equal pressure, then closed, and the volume of gas read. The difference between this reading and 100 gives the volume percentage of the carbon dioxide in the gas mixture. For the determination of oxygen, the caustic potash is removed as far as possible by means of the suction flask h, and alkaline pyrogallol allowed to rise in the burette in its place. The same operations as for carbon dioxide are per¬ formed until all the oxygen is absorbed. The volume of gas is then read. The difference between this volume and 100 gives the volume percentage of carbon dioxide and oxy¬ gen, and deducting the volume percentage of carbon diox¬ ide leaves the volume percentage of oxygen in the gas. In each of the above cases the gas is read over strongly alkaline liquids that tend to adhere to the burette and ren- dei the results inaccurate. This can be avoided by sucking out the alkaline liquid, allowing water to enter, rinsing the burette two or three times, each time sucking out the water, and then measuring the gas over nearly pure water. The carbon monoxide is determined by sucking out the alkaline pyrogallol or water after measuring the oxygen, replacing it with a hydrochloric-acid solution of cuprous chloride, and proceeding as in the preceding cases. After the carbon monoxide has been completely absorbed, as shown by the absorbing liquid no longer rising in the burette, the absorbing liquid is sucked out as completely as possible and the gas washed two or three times with water to completely remove the hydrochloric acid. This diminution in volume of the gas gives the volume percentage of carbon monoxide ALKALIES AND HYDROCHLORIC ACID 11 in the gas; the remainder of the gas is the volume percent¬ age of nitrogen in the gas. 11. Reagents for tlie Bunte Burette.— The caustic potash is made by dissolving 100 grams solid potassium hydrate in 200 cubic centimeters of water. The alkaline pyrogallol is made by dissolving 32 grams potassium hydrate in 200 cubic centimeters of water and 40 grams of pyrogallic acid in 200 cubic centimeters of water. The two solutions are thoroughly mixed and kept carefully guarded from the air in a rubber-stoppered bottle. It is even better to keep the two solutions separate and only mix them when needed for use. The cuprous-chloride solution is made by dissolving 200 grams of cupric chloride in 500 cubic centimeters of water and 500 cubic centimeters of concentrated hydrochloric acid, and allowing the solution to stand tightly stoppered in a bottle containing copper turnings or strips of sheet copper until it becomes clear and colorless. 12 . Liquor From Carbouators.— The free and com¬ bined ammonia are determined as described in Art. 7. These are the only determinations usually made. 13. Bicarbonate From the Filters. —1. Total alkali is determined by titrating 4.2 grams of the sample with normal sulphuric acid, using methyl orange as indicator. Each cubic centimeter of normal acid used corresponds to.738 per cent, of Na % 0 in the sample. 2. Sodium Bicarbonate .—The .determination of sodium bicarbonate in the presence of sodium carbonate depends on the reaction NaHCO 3 + NaOH = Na t C0 3 + Silver nitrate is used as indicator, for it gives a white pre¬ cipitate with sodium carbonate, but as soon as a single drop of caustic-soda solution is present in excess the silver car¬ bonate precipitate turns brown, owing to the formation of silver oxide. 12 ALKALIES AND HYDROCHLORIC ACID 6 Normal sodium-hydrate solution is prepared by dissolv¬ ing 50 grams of pure sodium hydrate in 1 liter of water and adding sufficient barium hydrate to more than precipitate all the carbon dioxide. The solu¬ tion is then standardized as usual by titrating with normal sul¬ phuric acid, using phenol phthal- ein as indicator, and then cor¬ rected to exactly normal 'strength This solution must after stand¬ ardization be carefully guarded from the carbon dioxide of the air. A convenient arrangement for the solution and burette is shown in Fig. 2. The burette a is closed at the top with a stopper, through which passes a glass tube connecting with a sugar funnel b , which is filled with pieces of soda lime and so removes the carbon dioxide from the air that enters the burette. At the lower end of the burette a tube is blown on which connects, by means of the glass tube d and two short pieces of rubber tube, with the bottle e containing the standard solution. The bottle e is closed with a two-holed rubber stopper, through one hole of which leads the tube d to the burette, and through the other a glass tube to the sugar funnel f that contains the soda lime. The liquid can be started first by blowing on the end of f after the stop-cock c has been opened. After the apparatus is once in operation the burette can be repeatedly filled, by merely opening the stop-cock c, without exposing the solution to the air at any point. The determination is made by weighing out in a beaker 4.2 grams of the sample, adding 100 cubic centimeters of water (not warmer than 20° C.), and running in the caustic-soda §6 ALKALIES AND HYDROCHLORIC ACID 13 solution until within about 1 cubic centimeter of the end reaction. The solution is then thoroughly stirred and the standard solution run in, at first .2, and then .1 cubic centi¬ meter at a time, until a drop taken out and brought in con¬ tact with a 25-per-cent, silver-nitrate solution on a white plate shows a brown color at once. Even before the end point, the drops turn brown on standing. If the compo¬ sition of the sample is not approximately known at first, it must be approximately determined by weighing out a por¬ tion of the sample and running in the standard caustic 2 or 3 cubic centimeters at a time and testing until the end point is passed. Then, for the final determination, some¬ what less than this amount of the standard solution is taken as above. The number of cubic centimeters of the normal alkali used multiplied by 2 gives the percentage of sodium bicarbonate in the sample. 3. The percentage of sodium carbonate in the sample is given by multiplying the difference between the number of cubic centimeters of normal acid required for the total alkali and the number of cubic centimeters of normal caustic alkali required for sodium bicarbonate by £f. For example, if it takes 39 cubic centimeters of normal acid to neutralize a sample and 35 cubic centimeters of normal alkali to convert the bicarbonate into the carbonate, then 39 X . 738 — 28.79 per cent, of NajO\ 35 X 2 = 70 per cent, of sodium bicarbonate; and (39 — 35) X £§ = 5.05 per cent, of sodium carbonate. 4. Ammonia is determined according to the volumetric method given in Quantitative Analysis. 5. Moisture is determined by weighing out 10 grams of the sample in a small platinum or porcelain evaporating dish and heating, at first carefully on a sheet of asbestos, and finally to from 300° to 400° C. The loss in weight, after deducting the carbon dioxide corresponding to the sodium bicarbonate, gives the moisture. 14. Mother Liquor. —The mother liquor from the filtra¬ tion of the liquors from the carbonators is tested for free and combined ammonia and salt. 14 ALKALIES AND HYDROCHLORIC ACID §6 1. Free and combined ammonia are determined as under Art. 7. 2. Salt is determined by evaporating 10 cubic centi¬ meters of the liquor to dryness in a platinum dish, heating the residue until the ammonium chloride is volatilized, then cooling and weighing. 15. Milk of Lime. —1. The determination of the specific gravity usually is sufficient for controlling the milk of lime. If the milk of lime is thin, it is thoroughly mixed and the reading on the hydrometer is quickly taken. If the milk of lime is thick, a rather broad cylinder is selected, the milk of lime thoroughly mixed, the hydrometer inserted, and the cylinder jarred on the table until the hydrometer will sink no lower, when it is read. A hydrometer called the Baume hydrometer , with the spindle arbitrarily divided into so-called degrees, is frequently used for this purpose. Table II shows the degrees Baume and grams per liter of calcium oxide corresponding to a considerable range of specific gravities. 2. Complete Analysis. —At intervals a complete analysis of the milk of lime is required. For this purpose the sample is thoroughly mixed, and 250 cubic centimeters measured out and filtered. The residue on the filter is taken without washing, dried at 100° C., and weighed. This weight mul¬ tiplied by 4 gives the undissolved portion per liter. The undissolved portion and the filtrate are then sepa¬ rately analyzed, exactly as under “Quicklime.” 16. Waste From Ammonia Stills. —1. Excess of lime is the constituent of this waste, concerning which it is most important for us to have information—that is, the lime that is still available for liberating ammonia from its salts. For its determination, boil 100 cubic centimeters of the waste until no more ammonia is given off, then add ammonium sulphate in excess, boil again, and collect the ammonia evolved this time in normal acid (see the volumetric determination of ammonia, Quantitative Analysis'). By titrating, the necessary information for finding the amount § G ALKALIES AND HYDROCHLORIC ACID 15 of ammonia evolved is obtained, and from this it is a simple matter to calculate the amount of free lime in the waste. Ca(OH) 2AY/ 3 (NH t ) % SO< + '-■-' = CaSO t + — + H % 0 74 34 34 : 74 = wt. NH s found : x x X 10 = the amount of available lime per liter of the waste. TABLE II Specific Gravity Degrees Baume Grams CaO in Liters Specific Gravity Degrees Baume Grams CaO in Liters i. 007 I 7-5 1. 125 16 ' x 59 1.014 2 16.5 i -134 17 170 1.022 3 26.0 1.142 18 181 1.029 4 36.0 1.152 X 9 x 93 1.037 5 46.0 x. 162 20 206 1.045 6 56.0 1.171 21 218 1.052 7 65.0 1.180 22 229 1.060 8 75 -° 1.190 2 3 242 1.067 9 84.0 1.200 24 2 55 i-o 75 10 94.0 1.210 2 5 268 1.083 11 104.0 1.220 26 281 1.091 12 115-0 1.231 2 7 2 95 1.100 13 126.0 1. 241 28 3°9 1.108 14 137.0 1.252 2 9 3 2 4 1.116 15 0 06 1.263 30 339 2. Complete Analysis .-—Determine the specific gravity, the amount of undissolved material, and analyze the insol¬ uble portion as in Art. 15. In the soluble portion: (a) Titrate 50 cubic centimeters with normal sulphuric acid, using phenol phthalein as indicator, and calculate the result as Ca(0H) o . (b) Determine the calcium in 25 cubic centimeters, as usual, by precipitating with ammonia and ammonium oxa¬ late, filtering, and titrating the precipitate with potassium 199—22 16 ALKALIES AND HYDROCHLORIC ACID §6 permanganate. Deduct the calcium corresponding to the amount of calcium hydrate found under (a) and calculate the remainder as calcium chloride in grams per liter. (c) Determine the sulphur trioxide in 50 cubic centi¬ meters by precipitating with barium chloride, and calculate the result as sodium sulphate in grams per liter. (d) Determine the chlorine in 5 cubic centimeters by Volhard’s method. Deduct the chlorine corresponding to the calcium chloride found under (b) and calculate the remainder as sodium chloride in grams per liter. TITE FINISHED PRODUCT 17. Soda Ash.—For the complete analysis of soda ash, the following determinations are usually made : 1. Sodium Carbonate. —Weigh out 2.65 grams of the dry substance, dissolve in about 150 cubic centimeters of water, and titrate with normal sulphuric acid, using methyl orange as indicator. The number of cubic centimeters of acid used multiplied by 2 gives the percentage of sodium carbonate. 2. Sodium Bicarbonate. —This substance rarely occurs in large amounts in soda ash, and its determination may usually be omitted. If there is a reason for determining it, use the method given under Art. 13. 3. Sodium Chloride. —Dissolve 5 grams of the sample in water and titrate by Volhard’s method. 4. Silica. — Dissolve 50 grams of the sample in about 150 cubic centimeters of water and acidify with concen¬ trated hydrochloric acid, evaporate to dryness on the water bath, take up with water and a little hydrochloric acid, filter, ignite, and weigh. Calculate as silica; of course it consists of everything insoluble in hydrochloric acid. 5. Ferric Oxide and Alumina. —Determine the ferric oxide and alumina in the filtrate from the silica by precipi¬ tating with ammonia as usual. 6. Calcium Carbonate. — Divide the filtrate from the above determination into two equal parts, and in one half §6 ALKALIES AND HYDROCHLORIC ACID 17 determine the calcium, as usual, with ammonia and ammo¬ nium oxalate, and calculate as calcium carbonate. 7. Magnesium Carbonate.^- Determine the magnesium in the filtrate from the calcium determination, as usual, with ammonium phosphate, and calculate as magnesium car¬ bonate. 8. Sodium Sulphate. —Determine the sulphur trioxide in the other half of the filtrate from the ferric oxide and alumina determination by means of barium chloride, as usual, and calculate as sodium sulphate. . A complete analysis of this character is necessary from time to time, usually each month, of an average of the soda ash made. For the daily control of the output, however, a determination of the sodium carbonate and the sodium chloride is generally sufficient. SALT-CAKE PROCESS CRUDE MATERIALS 18 . Salt. — The usual determinations are as follows: 1. Sodium Chloride. —Weigh out 4 grams of the sample, dis¬ solve in water, and dilute to 1,000 cubic centimeters. Take 50 cubic centimeters of this solution and titrate with T V nor¬ mal silver nitrate, using about cubic centimeter of potas¬ sium chromate as indicator. This gives the total chlorine, and when no other substances are determined, this is all calculated as sodium chloride. When magnesium and other substances present as chlorides are determined, the chlorine of these is first subtracted from the total before calculating it as sodium chloride. 2. Water. —The determination of water in salt offers some difficulties on account of its tendency to decrepitate and so fly out of the dish in which one is heating it. The most satisfactory method of making the determination is to select a tall Erlenmeyer flask of Jena glass, of about 250 cubic centimeters capacity, and weigh it with a small 18 ALKALIES AND HYDROCHLORIC ACID §6 funnel in its mouth. About 5 grams of salt are then intro¬ duced and its weight exactly established by weighing flask, funnel, and salt. The funnel is then removed and the flask is heated for 3 or 4 hours on a suitable sand bath, which has a temperature of about 150° C. The funnel is then replaced in the mouth of the flask and the whole allowed to cool and then weighed. The funnel serves the purpose of preventing the air from circulating in the flask, so it can be cooled out of a desiccator. This determination gives all the water in the salt except part of that which is chemically combined with impurities. For most purposes the combined water can be neglected, but when it is necessary to determine it, this can be done by heating the flask to 300° or 400° C. with the funnel in its mouth, cooling and weighing. 3. Sulphur Trioxide. — Dissolve 10 grams of salt in about 300 cubic centimeters of water, acidify with hydro¬ chloric acid, and digest at 70° or 80° C. for an hour to dissolve all the calcium sulphate present. Make this to 500 cubic centimeters, filter through a dry filter, and take 250 cubic centimeters for analysis. Determine the sulphur trioxide by precipitating, as usual, with barium chloride in a hot solution. Unless there are reasons for doing otherwise, the sulphur trioxide is calculated as calcium sulphate. 4. Other Determinations. — These determinations are sufficient for the daily work, unless salt happens to come in from a new source, when it must be analyzed like the aver¬ age sample below. The daily samples are save'd, however, and at the end of each month an average sample is prepared and, in addition to the above determinations, insoluble in acids, ferric oxide and alumina, calcium, and magnesium are determined. For this purpose 50 grams of the sample are dissolved in water and hydrochloric acid and the determi¬ nations are carried out as under Art. 1. The magnesium is calculated as chloride, and the calcium in excess of the sulphur trioxide is calculated as calcium chloride. Conversely, any sulphur trioxide in excess of the calcium is calculated as sodium sulphate. §6 ALKALIES AND HYDROCHLORIC ACID 19 FINISHED PRODUCT 19. Salt Cake.—The determinations usually made are as follows: 1. Free Acid .—Dissolve 20 grams of the salt cake in water and dilute to 250 cubic centimeters. Take 50 cubic centimeters and titrate with normal sodium-hydrate solu¬ tion, using methyl orange as indicator. The acidity is calculated as sulphur trioxide, although it may be due to hydrochloric acid and salts of the heavy metals, as well as acid sodium sulphate. If the salt cake contains large amounts of iron and aluminum salts, and it is desired to exclude the acidity due to these salts, the titration may be carried on without an indicator and the end point taken when flakes of the precipitate of the hydrates begin to appear. Each cubic centimeter of sodium-hydrate solution used corresponds to 1 per cent, of sulphur trioxide. 2 . Salt. —Take 50 cubic centimeters of the solution pre¬ pared as above and determine the chlorine according to Volhard’s method, using T V normal silver nitrate. Calcu¬ late all the chlorine to sodium chloride. Each cubic centi¬ meter of silver-nitrate solution used corresponds to .0731 per cent, of salt. For the daily determinations, these two substances are all that are necessary, except when the salt cake is being made especially free from iron for use in glass manufacture, when this must also be determined in each batch. For the monthly average sample and for certain cases for shipment, it is also necessary to make the following determinations: 3. Insoluble in Acids.— Determine in 50 grams of sample, as under “Silica,” Art. 17. 4. Ferric Oxide .—Weigh out 20 grams of the sample, reduce with zinc and sulphuric acid, and titrate with per¬ manganate, as directed in Quantitative Analysis. 5. Alumina .—Dissolve 20 grams of the sample in about 150 cubic centimeters of water, add hydrochloric acid, and 20 ALKALIES AND HYDROCHLORIC ACID §6 precipitate with ammonia as usual. After weighing the combined oxides, deduct the ferric oxide found above and calculate the remainder to the percentage of alumina. 6. Lime. —Determine, as usual, in the filtrate from the alumina determination. 7. Magnesia. —Determine, as usual, in the filtrate from the lime determination. 8. Sodium Sulphate .—The determination of the sodium sulphate in this case is a rather difficult matter and it is fre¬ quently taken as the difference between the total percentage of the other substances found and 100. Perhaps the most satisfactory method of procedure is to dissolve 2 grams of the sample in as little hot water as possible, make alkaline with ammonia, and precipitate so far as possible with ammonium carbonate. Filter and redissolve the precipitate in as little hydrochloric acid as possible and reprecipitate with ammonia and ammonium carbonate. Filter and unite the two filtrates in a platinum dish and evaporate to dryness, moisten the residue with sulphuric acid to be certain that the salt present is all converted into sulphate, heat to drive off the excess of acid, and weigh. Calculate the salt found by Volhard’s method to sulphate, deduct this weight from that found above, and the remainder is sodium sulphate. LE BLANC PROCESS CRUDE MATERIALS 20 . Salt cake is analyzed according to Art. 19. 21 . Limestone is analyzed according to Art. 3. 22 . Coal is analyzed according to the method given in Quantitative Analysis. In addition, determine the nitrogen by Kjeldahl’s method, which also is described in Quantita¬ tive Analysis. §6 ALKALIES AND HYDROCHLORIC ACID 21 INTERMEDIATE PRODUCTS 23. Black Ash. — The obtaining of a representative sample presents perhaps more difficulties than are usually the case, for the charges as drawn from the furnace are hard and very non-homogeneous, so that great care must be exercised in selecting the sample to get it as representative as possible, for even at best it is imperfect. After the sam¬ ple has been carefully selected, it is rapidly crushed and mixed so that 50 grams of an average of the sample can be weighed out. These 50 grams are rapidly but thoroughly ground in a mortar and then brought into a 500-cubic-centi¬ meter flask, the mortar rinsed down with water, which has been boiled to expel carbon dioxide, and then cooled to about 35° C. The rinsings of the mortar are poured into the flask and the flask filled nearly to the 500-cubic-centimeter mark with the same warm water. During the pouring of the rinsings and water on the black ash, it must be thoroughly shaken to prevent its caking together on the bottom of the flask. The flask is then allowed to stand about 2 hours with frequent shaking. A preferable arrangement, and one that saves much work, is to use one of the many stirrers that run by a turbine or an electric motor. They may be obtained from tiny dealer in chemical apparatus. After standing 2 hours the flask is filled to the mark and the solution is ready for use. 1. Free Litne. —Thoroughly mix the contents of the flask and pipette out 25 cubic centimeters of its contents' into a porcelain dish. The outside of- the pipette should be rinsed off before running out its contents and then the inside should be rinsed into the porcelain dish. Add an excess of a 10-per-cent, barium-chloride solution and titrate with normal hydrochloric acid, using phenol phthalein as indica¬ tor. Each cubic centimeter of acid solution equals 1.12 per cent, of CaO. 2. Total Lime. —Pipette out, as above, 25 cubic centi¬ meters from the supply flask into a small flask, make acid with concentrated hydrochloric acid, and boil to expel all 22 ALKALIES AND HYDROCHLORIC ACID 6 the carbon dioxide. Add a few drops of methyl orange and then sodium carbonate to exactly neutralize. Add 40 cubic centimeters of a normal sodium-carbonate solution and boil to precipitate all the calcium (together with magnesium, etc., which, however, can be neglected) as the granular carbon¬ ate. Make up to 250 cubic centimeters and filter through a dry filter. Take 125 cubic centimeters and titrate back to neutral with normal hydrochloric acid, using methyl orange as indicator. Each cubic centimeter of the sodium carbonate used in excess of the acid required to titrate back is equal to 2.24 per cent, of CaO. Neither of the above methods is very exact, but they answer for factory con¬ trol. The supply flask is now tightly stoppered and allowed to stand until the liquor has become completely clear. 3. Total alkali comprises all the sodium present as car¬ bonate, sulphide, and hydrate. Pipette out 20 cubic centi¬ meters of the clear liquid from above and titrate, as usual, with normal hydrochloric acid, using methyl orange as indi¬ cator. Each cubic centimeter of acid corresponds to 1.55 per cent, of Na^O. 4. Sodium Sulphide. —Pipette out 10 cubic centimeters of the clear liquor from the supply flask, dilute to about 200 cubic centimeters, acidify with acetic acid, and titrate with T V normal iodine solution, using starch paste as indica¬ tor. Each cubic centimeter of iodine solution used equals .39 percent, of sodium sulphide, and is equivalent to .1 cubic centimeter of normal acid. 5. Caustic Soda. —Pipette out 40 cubic centimeters of the clear liquid from the supply flask into a 100-cubic-centi¬ meter measuring flask, add 20 cubic centimeters of a 10-per¬ cent. barium-chloride solution, and fill to the mark with water. Thoroughly shake and allow to settle. Pipette out 50 cubic centimeters and titrate with normal hydrochloric acid, using methyl orange as indicator. This titration gives both sodium hydrate and sodium sulphide. To determine the hydrate alone, multiply the number of cubic centimeters of iodine solution used above by 20 and 6 ALKALIES AND HYDROCHLORIC ACID 23 subtract the product from the number of cubic centimeters of normal acid used here. The remainder gives the number of cubic centimeters of normal acid used for the caustic soda, and each cubic centimeter equals 2 per cent, of NaOH. 6. Sodium Carbonate. — Subtract the total amount of hydrochloric acid used for the sodium hydrate and the sodium sulphide above from the amount used for the total alkali, and the difference gives the number of cubic centi¬ meters of normal acid used for the sodium carbonate. Each cubic centimeter of normal acid equals 2.65 per cent, of sodium carbonate. 7. Salt. —Pipette out 10 cubic centimeters of the clear liquid from the supply flask and titrate according to Vol- hard’s method for chlorine. All the chlorine is calculated as salt, and each cubic centimeter of the y 1 ^ normal silver nitrate solution used equals .58 per cent, of salt. 8. Sodium Sulphate. —Pipette out 20 cubic centimeters of the clear liquid from the supply flask and add hydro¬ chloric acid in slight excess. Boil to expel carbon dioxide and precipitate hot, as usual, with barium chloride. The weight of barium sulphate multiplied by .3047 gives the per¬ centage of sodium sulphate. 24. Lye From Extraction of Black Ash.—The follow¬ ing determinations are made : 1. Specific Gravity. —Determine the specific gravity of the warm lye by means of the Baume hydrometer. 2. Total Alkali.— Determine the total alkali in 2 cubic centimeters of the lye, as under Art. 23 . 3. Sodium Sulphide. —Determine the sodium sulphide in 2 cubic centimeters of the lye, as under Art. 23 . 4. Caustic Soda. —Determine the caustic soda in 2 cubic centimeters of the lye, as under Art. 23 . 5. Sodium Carbonate. —Determine the sodium carbonate, as under Art. 23 . 6. Salt. —Determine the salt in 2 cubic centimeters by Volhard’s method, described in Quantitative Analysis. 24 ALKALIES AND HYDROCHLORIC ACID §6 7. Sodium Sulphate. —Determine the sodium sulphate in 5 cubic centimeters, as under Art. 23. 8. Total Sulphur. —Treat 5 cubic centimeters of the lye with an excess of bleaching powder and hydrochloric acid (the chlorine must smell strongly). Boil off the chlorine, filter from insoluble matter, and precipitate with barium chloride, as usual. 9. Sodium Ferrocyanide. —Acidify 30 cubic centimeters of the lye with hydrochloric acid and add, with constant stirring, a strong solution of bleaching powder from a burette, until a drop taken out shows no blue color with a ferric-chloride solution. The ferric chloride must be free from ferrous salts, and the end point must be quite accu¬ rately reached, although a drop or two in excess does no harm. This oxidizes the sodium ferrocyanide completely to sodium ferricyanide. Add to the oxidized solution T V nor¬ mal copper sulphate from a burette, until a drop of the solu¬ tion no longer gives a blue color with ferrous sulphate, but shows a red color. This indicates that no more sodium ferricyanide is present in the solution, and that the ferrous sulphate is reducing the yellowish copper ferricyanide to the reddish copper ferrocyanide. The first decided red color must be taken as the end point, even if it disappears after a time. The copper-sulphate solution is made by dissolving 12.457 grams of crystallized copper sulphate in 1,000 cubic centimeters of water and standardizing it against pure non- effforesced potassium ferrocyanide. 10. Silica , Ferric Oxide, and Alumina. —Acidify 100 cubic centimeters of the lye with hydrochloric acid, heat to boil¬ ing, add about 1 gram of ammonium chloride, and precipitate with ammonia. Heat until the ammonia odor is very faint, filter, ignite, and weigh as usual. 25. Carbonated Lye.— The determinations are made as above, but in addition the sodium bicarbonate is determined. 6 ALKALIES AND HYDROCHLORIC ACID 25 Sodium Bicarbonate. — The method given in Art. 13 cannot be satisfactorily used here, for the sulphide that may be present will interfere with the test. The following method, however, gives good results when carefully carried out. A standard solution of caustic soda free from carbon dioxide is required and is best prepared by dissolving 50 grams of the best caustic soda in 1 liter of water and adding barium chloride to precipitate all the carbon dioxide. The solution is then standardized by acid as usual, made to normal, and preserved as under Art. 13. For the analysis, take 50 cubic centimeters of the carbonated lye and add 30 cubic centimeters of the caustic-soda solution, then an excess of a 10-per-cent, barium-chloride solution, and finally titrate wifh normal hydrochloric acid, using phenol-phthalein solution as indicator. The difference between the amount of caustic-soda solution taken and the normal acid required gives the number of cubic centimeters of normal caustic soda required for the bicarbonate present, and each cubic centimeter equals .084 gram of sodium bicarbonate. For example, if 25 cubic centimeters of normal acid is required to titrate back, then 30 — 25 = 5 cubic centimeters of caustic soda required for the bicarbonate present. There¬ fore, .084 X 5 = .42, and .42 X 20 = 8.4 grams of sodium bicarbonate per liter of lye. 26. Red Liquors. —The red liquor may be analyzed the same as the crude lye, except that in the case of crude lye all the oxidizable sulphur compounds are assumed to be sul¬ phides. In the case of a red liquor, however, through oxida¬ tion and other changes the sulphite and thiosulphate become prominent and must be determined, especially when the red liquor is used for the manufacture of caustic soda. 1. Sodiu m Sulphide, Sulphite , Thiosulphate, and Sulphate. ( a ) Determine the total alkalinity by titrating 25 cubic centi¬ meters of the liquor with normal acid, using methyl orange as indicator. This gives sodium carbonate, sodium hydrate, sodium sulphide, and one-half of the sodium sulphite (Na a S0 3 is alkaline to methyl orange, while HNaS0 3 is neutral). 26 ALKALIES AND HYDROCHLORIC ACID 6 (b) Acidify 25 cubic centimeters of the liquor with dilute acetic acid and titrate with ^ normal iodine solution. This gives sodium sulphide, sodium sulphite, and sodium thio¬ sulphate. (c) Take 50 cubic centimeters of the liquor and pre¬ cipitate it with an alkaline-zinc solution, make to 200 cubic centimeters, and take 100 cubic centimeters. Acidify this with dilute acetic acid and titrate with y^ normal iodine solu¬ tion. This gives sodium sulphite and sodium thiosulphate. (d) Take 100 cubic centimeters of the liquor and add an excess of a 10-per-cent, barium-chloride solution to pre¬ cipitate the sulphite, make up to 200 cubic centimeters, cork tight, and allow to settle clear (or filter); then take 50-cubic-centimeter portions of the clear liquid for titration. (1) Titrate a 50-cubic-centimeter portion with normal hydro¬ chloric acid, using methyl orange as indicator. This gives sodium hydrate and sodium sulphide. (2) Acidify a second 50-cubic-centimeter portion with dilute acetic acid and titrate with yk normal iodine solution. This gives sodium sulphide and sodium thiosulphate. 2. The Calculation .— b — d (2) = A cubic centimeters tV normal iodine solution corresponding to sodium sulphite. b — c — B cubic centimeters y^ normal iodine solution corresponding to sodium sulphide. d (2) — B — Lcubic centimeters yk normal iodine solution corresponding to sodium thiosulphate. d (1) — Jy B — D cubic centimeters normal acid solution corresponding to sodium hydrate. 1 — [d (1) A] = E cubic centimeters normal acid solution corresponding to sodium carbonate. Each cubic centimeter of T V normal iodine solution equals .0039 gram of NaJS, .0063 gram of Na t SO s , or .0158 gram of Na^S^O^. Each cubic centimeter of normal acid equals .04 gram of NaOH , or .053 gram of Na t CO a . 2H, Tank Waste.—Samples are collected in wide-mouth glass-stoppered bottles and kept closed until analyzed. The § G ALKALIES AND HYDROCHLORIC ACID 27 determinations are made on the moist substance, as any attempt to dry it inevitably leads to oxidation, and so to a change of composition. 1. Alkaline Sodium Compounds .—Stir 20 grams of tank waste thoroughly together with about 175 cubic centimeters of warm water, let stand 1 hour to thoroughly settle, and pour off the clear liquid. Pass carbon dioxide for 5 minutes, and boil to about one-half of the original volume, to decom¬ pose calcium bicarbonate and precipitate calcium carbonate. Filter and titrate the filtrate with normal acid, using methyl orange as indicator. Each cubic centimeter of normal acid equals .031 gram of Na^O. 2. Total Sodium Compounds.—Cleat 17.7 grams of the waste in a porcelain dish with sulphuric acid of 50° Baume until the waste is completely decomposed, heat to drive off all the free acid, add hot water, and bring into a 250-cubic- centimeter measuring flask. Add milk of lime (made by slaking lime, shaking up with water, pouring off one portion to remove alkalies and then shaking up with water and filter¬ ing) to remove any free acid and magnesia, fill to the mark, let settle, and pipette off 50 cubic centimeters. To this 50 cubic centimeters add 10 cubic centimeters of a saturated barium-hydrate solution and filter through a dry filter. Take 50 cubic centimeters of the filtrate and precipitate all the barium by carbon dioxide and boiling. Filter and titiate the filtrate with normal hydrochloric acid, using methyl orange as indicator. When the above amount of substance is taken and allowance is made for the precipitates in the volumes, each cubic centimeter of normal acid used equals 1 per cent, of NaJJ. FINISHED PRODUCTS 28. Soda Ash. — The determination of silica, sodium sulphate, sodium chloride, ferric oxide and alumina, calcium carbonate, and magnesium carbonate is carried out asunder Art. 17, In addition to these substances, it is necessary to 28 ALKALIES AND HYDROCHLORIC ACID §6 deteimine in Le Blanc soda, total alkali, sodium carbonate, caustic soda, sodium sulphide, and sodium sulphite. 1. 1 otal Alkali. —Dissolve 3.1 grams of the soda ash in about 150 cubic centimeters of distilled water and titrate with normal sulphuric acid, using methyl orange as indi¬ cator. Each cubic'centimeter of the acid used equals 1 per cent, of Nafi. 2. Sodium Carbonate. —Calculate from determinations 3 and 4 (below) the equivalent percentages of Na.fi and deduct the sum of these results from the percentage of Nafi found in 1. The remainder is the alkali equivalent of the sodium carbonate, and this remainder multiplied by 1.71 gives the percentage of sodium carbonate in the soda ash. For example, if 58 cubic centimeters of normal acid is used in 1, .10 cubic centimeters of T V normal acid in 3, and 5 cubic centimeters of silver nitrate in 4; according to 1, we have 58 per cent, of Nafi, according to 3, .31 per cent, of Nafi as NaOH, and according to 4, .39 per cent, of Nafi as Nafi; or .31 -f- .39 = .7 per cent, of Nafi in the substance in other forms than sodium carbonate and 58 — .7 = 57.3 per cent, of Nafi as sodium carbonate. Then 57.3 x 1.71 = 97.98 per cent, of sodium carbonate in the soda ash. 3. Caustic Soda. —Dissolve 10 grams of the soda ash in about 75 cubic centimeters of water, add an excess of a 10-per-cent, barium-chloride solution, and titrate with T V nor¬ mal hydrochloric acid, using phenol phthalein as indicator. Each cubic centimeter of acid used equals .04 per cent, of NaOH and. is equivalent to .031 per cent, of Nafi. 4. Sodium Sulphide. —Dissolve 5 grams of the soda ash in about 100 cubic centimeters of water, heat nearly to boil¬ ing, and make strongly alkaline with ammonia. Titrate with an ammoniacal silver-nitrate solution until no more silver sulphide forms. Near the end it is advisable to filter off a little and test to make sure of the end point. To make the standard silver solution, dissolve 13.845 grams pure silver in pure nitric acid, add 250 cubic centimeters of strong ammonia water, and dilute to 1 liter. Each cubic §6 ALKALIES AND HYDROCHLORIC ACID 29 centimeter of the silver solution equals .1 per cent, of sodium sulphide, and is equivalent to .0795 per cent, of NaJJ. 5. Sodium Sulphite .—Dissolve 5 grams of the soda ash in about 50 cubic centimeters of water, acidify with acetic acid, and titrate with yL- normal iodine solution. Each cubic centimeter of iodine solution equals .126 per cent, of sodium sulphite. 29. Crystal Soda.—This substance is analyzed in the same manner as the above, except that on account of the large amount of water of crystallization, about double the amount must be taken for analysis. CHANCE-CLiAUS SULPHUR RECOVERY 30. Available Sulphur in Tank Waste.— In this deter¬ mination the sulphide sulphur is set free by hydrochloric acid, collected in sodium-hydrate solution, and after acidi¬ fying, titrated with iodine solution. The details of the process are as follows: Weigh out in a 500-cubic-centimeter flask 2 grams of the tank waste, insert a two-holed rubber stopper through one hole of which is passed a funnel tube with a stop-cock, and through the other a tube bent to connect, by means of a tight rubber tube, a suitable absorp¬ tion apparatus. The apparatus described for the determi¬ nation of sulphur in iron by evolution, in Quantitative Analysis , is suitable for this purpose. Two of the absorption tubes should be partially filled with sodium-hydrate solu¬ tion and connected to the evolution flask. Slowly run hydrochloric acid (1 part of acid to 1 part of water) through the funnel tube on to the waste until the decomposition is completed. Boil the flask, to drive out all the hydrogen sulphide, and when the first absorption tube has become warm on account of the steam condensed in it, open the stop-cock of the funnel tube and allow the apparatus to cool. Empty the absorption tubes into a 500-cubic-centimeter measuring flask, fill to the mark with well-boiled water, and take 50 cubic centimeters for titration. Dilute this to 30 ALKALIES AND HYDROCHLORIC ACID §6 200 cubic centimeters with well-boiled water, acidify with acetic acid, and titrate with T V normal iodine solution. Each cubic centimeter of the iodine solution, equals .0017 gram HJS or .0016 gram S. 31. Lime-Kiln Gases. — Determine carbon dioxide, oxygen, and carbon monoxide as under Art. 8. 32. Gas From tlie Gasometer. —Determine hydrogen sulphide and carbon dioxide together by absorbing them in caustic-potash solution in the same manner as carbon dioxide is determined in Art. 8. Determine hydrogen sulphide alone by fitting a flask of exactly known content (about 500 cubic centimeters) with a two-holed rubber stopper, through one hole of which passes a funnel tube with a glass stop-cock; the stem of the funnel tube should end just below the stopper. Through the other hole in the stopper passes a tube, which leads to the bottom of the flask and is fitted with a stop-cock. For making the determination, allow gas from the gasometer to pass through the apparatus until the air is completely displaced, close both stop-cocks, disconnect from the gasometer, and empty the gas from the tubes outside of the stop-cocks. Run in through the funnel tube about 25 cubic centimeters of a normal sodium-hydrate solution and shake thoroughly until all the gas is absorbed. Wash out into a 250-cubic-centimeter flask with air-free water and make to the mark on the flask. Take 50 cubic centimeters, dilute to about 250 cubic centi¬ meters with air-free water, acidify with acetic acid, and titrate with standard iodine solution. The standard iodine, solution should contain 11.43 grams of iodine per liter, when each cubic centimeter equals 1 cubic centimeter of hydrogen- sulphide gas at 0° C. and 760 millimeters of mercury pres¬ sure. To reduce the gas employed to normal conditions use the formula given for this purpose in Quantitative Analysis. If necessary to calibrate the flask, it can be done with suffi¬ cient accuracy by weighing it empty, then filling with water to the stop-cocks, and weighing again. The difference 6 ALKALIES AND HYDROCHLORIC ACID 31 between the two weights gives the weight of water in the flask, and, therefore, the volume in cubic centimeters. If greater accuracy is desired, the temperature of the water may be taken and the expansion of the water above 4° C. allowed for. Furthermore, the volume of air in the flask at its first weighing is approximately given by the weight of water; the weight of the air can be deducted from the weight of the flask plus air, thus giving the weight of the empty flask. For example, the flask plus air weighs 300 grams, the flask plus water at 18° C. weighs 795 grams; then 795 — 300 = 495 grams of water at 18° C., which equals, approximately, 495 cubic centimeters as the capacity of the flask. Correcting, 1 liter of air under standard conditions weighs 1.293 grams; and if the barometer stands at 750 millimeters of mercury pressure, the weight of 495 cubic centimeters of air can be calculated (see Quantitative Analysis). For v = 29 j" = 458 cubic centimeters at standard conditions = .458 liter. Therefore, 1.293 X .458 = .6 gram, the weight of air in the flask. The real weight of the flask is, therefore, less by this amount than the apparent weight and the weight of water becomes 495.6 grams. But 1 gram of water at 18° C. equals 1.001373 cubic centimeters, and therefore the corrected volume of the flask is 496.3 cubic centimeters. 33. Waste Gas From Claus Kiln.— The important sub¬ stances to determine in this gas are sulphur dioxide and hydrogen sulphide. These are best determined by conduct¬ ing 5 liters of the gas through a suitable absorption appar¬ atus containing caustic-soda solution. The gases are absorbed, giving sodium sulphide and sodium sulphite. The caustic solution is then made to 250 cubic centimeters with air-free water and 50 cubic centimeters taken, acidified with acetic acid, and titrated with T V normal iodine. This gives both the hydrogen sulphide and sulphur dioxide. 100 cubic centimeters of the original solution is then taken, 199—23 32 ALKALIES AND HYDROCHLORIC ACID 6 the sulphide precipitated with an alkaline-zinc solution, one-half filtered off, acidified with acetic acid, and titrated with yL normal iodine solution; this gives the sulphur dioxide. 1 cut c centimeter of y 1 ^ normal iodine solution equals .0017 g’.am of H^S or .0032 gram of SO„ and equals 1.12 cubic centimeters of either gas at 0° C. and 760 milli¬ meters of mercury pressure. SODIUM BICARBONATE 34. The crude materials for sodium bicarbonate manu¬ facture are the soda crystals from Le Blanc soda or the ammonia-soda ash, and lime-kiln gas. For the analysis of these substances, see Arts. 8, 17, and 29. FINISHED PRODUCT 35. Sodium Bicarbonate. —Analyze the same as soda ash, Art. 17. The daily tests consist in the determination of total alkali, sodium carbonate, sodium bicarbonate, and sodium chloride. CAUSTIC SODA CRUDE MATERIALS 36. The crude materials for the manufacture of caustic soda differ, depending on whether the substance is made at a Le Blanc or at an ammonia-soda works. The methods for all of them, however, will be described, and the student can select those that apply to the work that he is doing. 1. Red Liquor .—Analyze as under Art. 26. 2. Soda Ash .—Analyze as under Art. 17 or 28. 3. Milk of Lime. —Analyze as under Art. 15. §6 ALKALIES AND HYDROCHLORIC ACID 33 INTERMEDIATE PRODUCTS 37. While some of the following may be very properly considered as finished products, or otherwise classified, for the sake of simplicity they are given under this head. 38. Caustic Liquor. —The following determinations are made: 1. Specific Gravity .—The specific gravity is taken of the liquor at different stages of the evaporation, and although other substances affect the results, a fair idea of the run of the liquor can be obtained by this determination alone. Table III gives the percentage of caustic soda corresponding to the different specific gravities at 15° C. TABLE III Specific Gravity Grams of NaOH Per Liter Specific Gravity Grams of NaOH Per Liter Specific Gravity Grams of NaOH Per Liter 1.007 6 1.142 144 1.320 38 i 1.014 12 1.152 J 5 6 I- 33 2 399 1.022 21 1.162 167 i -345 420 1.029 28 1.171 177 i -357 441 1.036 35 1.180 188 1 - 37 ° 462 1.045 42 1.190 200 1-383 483 1.052 49 1.200 212 i -397 506 1.060 5 6 1.210 225 1.410 528 1.067 6 3 1.220 239 1.424 553 i -°75 70 1-231 253 1.438 575 1.083 79 1.241 266 i -453 602 1.091 87 1.252 283 1.468 629 1.100 74 1.263 299 1.483 658 1.108 104 1.274 3 l6 1.498 691 1.116 112 1.285 332 1-514 721 1.125 123 1.297 348 i- 53 ° 75 ° I-I 34 i 34 i- 3 ° 8 364 34 ALKALIES AND HYDROCHLORIC ACID 0 2. Total Alkali and Sodium Carbonate. —These two val¬ ues are determined according to Art. 23. 3. Salt. —In caustic from ammonia soda, it is frequently necessary to determine the amount of salt. Proceed accord¬ ing to Volhard’s method, described in Quantitative Analysis. 4. It is only necessary to determine sulphur compounds when the caustic is made from red liquor or crude Le Blanc soda. Sodium sulphate is sometimes determined in liquor from ammonia soda. Make the determinations according to Art. 26. 39. Fished Salts. —For analysis dissolve 25 grams of the salts in 500 cubic centimeters of water. 1. Total Alkali. —Titrate 25 cubic centimeters, as usual, with normal acid, using methyl orange as indicator. 2. Salt. —Titrate 25 cubic centimeters with silver nitrate by Volhard’s method, described in Quantitative Analysis. 3. Sodium Sulphate. —Determine in 25 cubic centimeters, by acidifying with hydrochloric acid and precipitating hot with barium chloride, as usual. 4. Oxidizable Sulphur Compounds. —Treat 25 cubic centi¬ meters of the solution with bromine water until it is colored, acidify with hydrochloric acid, boil off the excess of bro¬ mine, and precipitate as sulphate with barium chloride as usual. The difference between the amount of sulphate found here and that found above gives the oxidizable sul¬ phur. This determination is, of course, unnecessary when the caustic is made from ammonia soda. 40. Caustic Bottoms. — This sample sometimes comes to the laboratory in fairly large lumps in a stoppered bottle that has the stopper covered with sealing wax. This wax should not be broken until the sample is wanted for analy¬ sis. Then several pieces are taken, wrapped quickly in sev¬ eral thicknesses of heavy brown paper, and crushed on an anvil by means of a hammer; 20 grams are then weighed off and dissolved in water. It is necessary to work quickly § G ALKALIES AND HYDROCHLORIC ACID 35 until the caustic is weighed, to prevent its absorbing water from the air. 1. Insoluble. —When the above 20 grams are dissolved, filter, and wash thoroughly. Collect the filtrate and wash¬ ings in a 500-cubic-centimeter measuring flask, make to the mark, and save. The filter and contents are ignited and weighed. 2. Total Alkali. —Take 50 cubic centimeters of the above filtrate, add a little lacmoid for an indicator, and add nor¬ mal acid to more than neutralize. Heat to boiling, to expel the carbon dioxide, and titrate back with normal alkali. The difference between the acid and alkali used gives the acid required for neutralizing the total alkali. Each cubic centimeter of normal acid equals .031 gram of Na^O. 3. Sodium carbonate is determined according to Art. 23. 4. Salt is determined according to Art. 23. 41. Caustic Mud. — The determinations are as follows: 1. Total Alkali. —Extract 25 grams of the sample by shaking it with several small portions of hot water, finally filter, wash, and unite the filtrates and washings, pass carbon dioxide for 10 minutes, boil to decompose bicarbonates, refilter, if necessary, and titrate with normal acid, using methyl orange as indicator. Each cubic centimeter equals .031 gram of Nafi. 2. Caustic Lime. —Shake about 25 grams of the waste with a little water and titrate with normal acid and phenol phthalein. The sodium above was present as hydrate and carbonate, but a fair average will be reached if we deduct one-half of the number of cubic centimeters of acid required for total alkali, from the amount taken above, and call the remainder of the acid used by the waste, caustic lime. Each cubic centimeter of acid equals .037 gram of Ca(OH) r 3. Calcium Carbonate. —Titrate 1 gram of the sample with normal hydrochloric acid, using methyl orange as indi¬ cator, and deduct the acid required for caustic lime. Each cubic centimeter of acid equals .05 gram of CaCO r 36 ALKALIES AND HYDROCHLORIC ACID §6 FINISHED PRODUCTS 42. Caustic Soda. — The method for preparing the sample for analysis given under Art. 40 can be used to advantage here. For analysis weigh out 50 grams, dissolve in water, and make to 1,000 cubic centimeters. 1. Total Alkali. —Titrate as usual, using normal hydro¬ chloric acid and methyl orange. 2. Caustic soda is determined as under Art. 23. 3. Sodium carbonate is determined as under Art. 23. 4. Salt is determined as under Art. 23. 5. Sodium sulphate is determined as under Art. 39. 6. Other constituents are determined as under Art. 1H. HYDROCHLORIC ACID RAW MATERIAES AND INTERMEDIATE PRODUCTS 43. Hydrochloric acid is almost without exception ob¬ tained from salt by the action of sulphuric acid. For its crude materials and intermediate products, see under the heading “ Salt Cake.” The absorption of the gas in the bombonnes and towers is watched by means of specific-gravity tests. These are best made by arranging a cylinder and hydrometer in such a way that a portion of the acid is being continuously collected in the cylinder in which the hydrometer floats. By this means it is possible to see the specific gravity at a glance, and the delay and trouble of collecting the sample is avoided. Table IV gives the specific gravity and composition of solutions of hydrochloric acid at 15° C. 44. Waste Gases. — The gas that escapes from the absorption towers must not contain much hydrochloric acid, for it is injurious to vegetation. The sample is taken by 6 ALKALIES AND HYDROCHLORIC ACID 37 inserting a glass tube to the center of the chimney through which the gas passes to the outside air. To the outer end of the tube is attached a double-acting rubber suction bulb, and this, in turn, is connected to an absorption apparatus TABLE IY Specific Gravity Per Cent. HCl Grams HCl per Liter Specific Gravity Per Cent. HCl Grams HCl per Liter 1.000 . 16 1.6 1-115° 22.8 6 255 1-005 Li 5 12.0 1.1200 23.82 267 I.OIO 2.14 22.0 1 - 125 ° 24.78 278 1.015 3 - 12 32.0 1.1300 25-75 291 I. 020 4-*3 42.0 1 - 135 ° 26.70 303 1.025 5 -i 5 53 -o 1.1400 27.66 315 I.030 6.15 64.0 i-i 4 2 5 28.14 322 I -°35 7 -i 5 74 -o 1 - 145 ° 28.81 328 I.040 8.16 85.0 1-150° 29-57 34 ° 1-045 9.16 96.0 1-1520 29-95 345 I.050 10.17 107.0 1 - 155 ° 3 °- 55 353 I -°55 11.18 118.0 1.1600 3 i -52 366 I.060 12.19 129.0 1.1630 32.10 373 I.065 i 3 -19 141.0 1.1650 32-49 379 1.070 14.17 152.0 1.1700 33-46 392 O M i 5 - 16 163.0 1.1710 33- 6 5 394 1.080 16.15 174.0 1 - 175 ° 34-42 404 IT) 00 0 w i 7 -i 3 186.0 1.1800 35-39 418 1.090 18.11 197.0 1.1850 36-3 1 43 ° I -°95 19.06 209.0 1.1900 37-23 443 1.100 20.01 220.0 1-195° 38.16 456 1-105 20.97 232.0 1.2000 39-H 469 1.110 21.92 243.0 . similar to that mentioned in Art. 30. The absorption apparatus is fitted with large test tubes, or small flasks, so that two pieces will hold 150 or 200 cubic centimeters of water. It is then filled with water and is connected in 38 ALKALIES AND HYDROCHLORIC ACID 0 position. The bulb is then compressed a sufficient number of times to force the desired amount of chimney gas through the absorption apparatus. By careful work the amount of gas used can be quite accurately estimated by this method; if greater accuracy is wished, the gas after passing through the absorbing apparatus may be run into a gasometer and measured. The liquid from the absorption apparatus is washed into a flask and titrated by Volhard’s method, which is de¬ scribed in Quantitative Analysis. Another very simple and very effective form of absorption appara¬ tus that can be used has been recommended by the English alkali inspectors ; it is shown in Fig. 3. The gas enters at a, passes out through the holes at the lower end of the tube, and passes up through a number of thin ends cut from a small rubber tube, which breaks the gas into fine bubbles, then out through the holes, in the direction of the arrows, into the bottle, and finally escapes through the tube b. This tube is filled below with pieces of rubber tube and above with glass wool. By moistening the contents of b with water and adding a little indi¬ cator, as methyl orange, any failure on the part of the apparatus to absorb the acid is shown in b by the change in the indicator. FINISHED PRODUCT 45. Hydrochloric Acid. —The analysis of hydrochloric acid varies according to the purpose for which the acid is to be used. For many purposes a simple determination of the specific gravity is sufficient, while for other purposes a more §6 ALKALIES AND HYDROCHLORIC ACID 39 extended examination is necessary. In the following, the methods of analysis are given for all cases, except the so- called chemically pure acid, the examination of which is practically never required in the ordinary chemical works. 1. Sulphuric Acid .—Take 50 cubic centimeters of the acid to be tested, almost neutralize with pure sodium carbonate, heat to boiling, and precipitate with barium chloride, as usual. Each gram of barium sulphate found corresponds to .34335 gram of S0 3 . Another method, which gives quite accurate results and, on account of its rapidity, is very suitable where several determinations must be made each day, is as follows: Pre¬ pare a glass tube 6 millimeters broad and 250 millimeters long closed at the lower end, while the upper end expands into a tube 15 millimeters broad. Provide a rubber stopper for the broad tube. By mixing acids of known composition make a series of acids containing from .2 or .6 up to 3 per cent, of sulphuric acid. Take 10 cubic centimeters of the first of these acids, heat to boiling, pour into the above tube, nearly neutralize with ammonia, and precipitate with 5 cubic centimeters of a boiling hot, saturated, barium-chloride solution. Insert the rubber stopper, place in a centrifugal machine, and whirl for 5 minutes. Mark the height of the precipitate, empty, and repeat with the next stronger sam¬ ple. In this way graduate the tube and use it for the deter¬ mination in the same way, using 10 cubic centimeters of the sample, instead of the known solution, and reading off the percentage of sulphuric acid on the tube. 2. Sulphurous Acid .—Add bromine to 50 cubic centi¬ meters of the acid to color it and boil until color disappears. Proceed as for sulphuric acid. For rapid work, use 10 cubic centimeters of the sample and use the rapid method given above. In either case, deduct the barium sulphate found above from the total and each gram of barium sulphate in excess corresponds to .27468 gram of S0 3 . 3. Arsenic .—The detection and determination of arsenic in hydrochloric acid that is to be used in the preparation of 40 ALKALIES AND HYDROCHLORIC ACID §6 foodstuffs is very important. A very large number of methods for both its qualitative and quantitative determi¬ nation have been proposed and are in use. The following, however, seem to be the most convenient and exact. (a) Qualitative Tests. —Take 10 cubic centimeters of the sample in a test tube, dilute with 10 cubic centimeters of distilled water, carefully pour on the top of the acid 5 cubic centimeters of a freshly prepared hydrogen-sulphide solution, and allow to stand for 1 hour. Prepare a second tube in exactly the same manner and allow to stand for 1 hour in a water bath at from 70° to 80° C. If no precipitate, or yellow ring, appears between the two layers in either case, arsenic is absent. By this method the presence of fa milligram of arsenic in the 10 cubic centimeters of acid can be detected. For the most accurate detection of arsenic take 5 liters of the acid, add about |gram of potassium chlorate, to prevent the arsenic volatilizing as AsCl 3 during evaporation, and dilute with water until the specific gravity does not exceed 1.1. Evaporate to dryness in a well-enameled porcelain evaporator, take up the residue in a little water, and test the solution in a Marsh apparatus, which is described in Quali¬ tative Analysis. {b Quantitative Determination. —When very small amounts of arsenic are to be determined, take 5 liters of the acid, and concentrate to small bulk as above, using potas¬ sium chlorate to prevent loss of arsenic by volatilization, then proceed as follows: If fairly large amounts are known to be present or are shown by the qualitative test, take 50 cubic centimeters, partly neutralize with sodium carbonate, dilute to 150 cubic centimeters, and precipitate as sulphide, following the directions given in Quantitative Analysis. Remember here that the arsenic may be present as arsenic acid and that, under those circumstances, heat and consider¬ able time (from 12 to 20 hours) are necessary to completely precipitate all the arsenic. 4. Selenium. —Test with stannous chloride as described in Qualitative Analysis. 6 ALKALIES AND HYDROCHLORIC ACID 41 5. Hydrochloric Acid. — Take 10 cubic centimeters of the sample in an accurate pipette, dilute to 250 cubic centi¬ meters, and take 25 cubic centimeters for titration. Titrate with normal caustic-soda solution, using methyl orange as indicator. Deduct the amount of caustic corresponding to the S<9 2 already found from the total and the rest corre¬ sponds to HCl. Each cubic centimeter of alkali equals .0365 gram of HCl. For example, if 10 cubic centimeters of normal alkali is required for 1 cubic centimeter of the sample and .004 gram of S0 2 has been found in the previous determination, then .1 cubic centimeter of the alkali was used by the sulphuric acid, and the amount used by the hydrochloric acid is 9.9 cubic centimeters, which equals .36135 gram of HCl in 1 cubic centimeter of the sample, or 361.35 grams per liter. It is customary to report results of this kind in grams per liter; but if the percentage is wanted, determine the specific gravity and divide the grams per liter by 10 times the specific gravity, the result will be the percentage of HCl. When the amount of hydrochloric acid alone is to be determined in a sample, it is simpler to titrate 10 cubic cen¬ timeters of the diluted sample with T V normal silver nitrate, using Volhard’s method, which is described in Quantitative Analysis. Each cubic centimeter of the silver-nitrate solu¬ tion equals . 00365 gram of HCl. CHLORINE, BLEACHING COMPOUNDS, CHLORATES CRUDE MATERIALS 46. Manganese Ore. —The ordinary determinations are as follows: 1. Moisture. —Spread 2 grams of the finely powdered ore thinly on a watch glass and dry at 100° or 110° C. until the weight remains constant. 42 ALKALIES AND HYDROCHLORIC ACID 6 2. Available Oxygen .—For this determination are needed a 4 normal potassium-permanganate solution and a ferrous- sulphate solution made by dissolving 100 grams of ferrous sulphate and 100 grams of sulphuric acid in 1 liter of water. For the determination, weigh out 1.0875 grams of the dried ore (prefer¬ ably that used for the moisture determination) into a 200-cubic-centi¬ meter flask provided with a tube leading to the bottom of a second flask containing sodium-bicarbonate solution. The arrangement of the flasks is shown in Fig. 4. Measure exactly 75 cubic centimeters of the ferrous sulphate into the flask with the manganese ore, insert the stopper with the tube leading into the sodium-bicarbonate solution, and heat until a dark-colored residue is no more apparent. Allow the solution to cool, wash into a 500-cubic-centimeter beaker, Pig. 4 dilute to about 200 cubic centimeters, and titrate with £ nor¬ mal potassium-permanganate solution until the color stays permanent for about \ minute. The ferrous-sulphate solution must be standardized each day by measuring out 75 cubic centimeters, using the same pipette as above, and titrating it with the £ normal potas¬ sium-permanganate solution. The difference between the amount of potassium-perman¬ ganate solution used to titrate the ferrous-sulphate solution and that used with the ore gives the available oxygen, or rather the manganese present in the ore as MnO r If the above amount of ore is weighed out, each cubic centimeter of £ normal potassium-permanganate solution corresponds to 2 per cent, of MnO 2 . Another very exact and rapid method that can be used direct, or as a check on the above method, is given in Quan¬ titative Analysis, under the description of the nitrometer. 6 ALKALIES AND HYDROCHLORIC ACID 43 3. Carbon Dioxide. —Determine according to the absorp¬ tion method given in Quantitative Analysis. 4. Acid Necessary to Decompose Ore. —Bring 1 gram of the ore into a flask containing 10 cubic centimeters of the hydrochloric acid being used in the chlorine manufacture and whose titration strength has been previously determined. Insert a stopper, with a return condenser, in the flask and heat until the ore is dissolved. Allow to cool and titrate with normal caustic-soda solution until the brown flakes of iron hydrate no longer dissolve by shaking. The differ¬ ence between the caustic soda used here and that required for the titration of 10 cubic centimeters of the original acid gives the acid used in decomposing the ore. 47. Limestone. —Analyze according to Art. 3. 48. Quicklime. —Analyze according to Art. 4. 49. Slaked Lime. —Water, carbon dioxide, and calcium hydrate are usually determined. 1. Water. — Weigh out from a well-closed weighing tube 1 gram of the sample into a weighed platinum crucible and heat, at first gradually and then to the strongest tem¬ perature of the blast lamp; cool; and weigh. The loss of weight equals carbon dioxide and water. 2. Carbon Dioxide. —Determine according to the absorp¬ tion method given in Quantitative Analysis and deduct the result from the carbon dioxide and water previously deter¬ mined. 3. Milk of Lime. —See Art. 15. INTERMEDIATE PRODUCTS 50. Free Acid in Still Liquor.— Titrate 25 cubic centi¬ meters of the still liquor with normal sodium-hydrate solution until the brown flakes of ferric hydrate no longer dissolve by thorough shaking. Each cubic centimeter of caustic-soda solution used equals .0305 gram of free hydro¬ chloric acid. 44 ALKALIES AND HYDROCHLORIC ACID §6 ♦> 1 . Calcium Chloride in Clear Liquor. — Acidify 25 cubic centimeters of the clear liquor with acetic acid, add ammonium oxalate in excess, allow to stand 3 hours to insure complete precipitation of the calcium oxalate, and filter on an asbestos filter, using a Gooch crucible. Bring the cru¬ cible containing the precipitate of calcium oxalate into a 300-cubic-centimeter beaker, add 100 cubic centimeters of distilled water and 10 cubic centimeters of concentrated sul¬ phuric acid. (Use care in adding the acid, that the contents of the beaker do not spatter out.) Now titrate the oxalic acid obtained from the above operations with normal potassium-permanganate solution. Each cubic centimeter of the T V normal potassium-permanganate solution is equal to .0028 gram of calcium oxide, or .00555 gram of calcium chloride. Weldon Mud. —The following determinations are required: 1. Manganese Dioxide. —See Art. 46. 2. Total Manganese. —Weigh out 10 grams of the mud, acidify with concentrated hydrochloric acid, boil to drive off all the chlorine, and then neutralize the excess of acid with precipitated chalk. Acidify with acetic acid, add bromine, heat, and continue the addition until the solution retains the odor of bromine. Add alcohol slowly until the red color disappears and filter on a Gooch filter. Test the filtrate, to see if it turns brown, with the addition of a drop of bromine water; if so, precipitate the rest of the manganese and add it to the precipitate already obtained. All the manganese is now on the filter as manganese dioxide. Introduce filter and all into a flask and proceed to determine the manganese dioxide according to Art. 46. 3. Total Base.' —This indicates the base present that neu¬ tralizes the hydrochloric acid without producing chlorine. Dilute 25 cubic centimeters of normal oxalic-acid solution to about 100 cubic centimeters,, warm to 75° C., and add 10 grams of the mud. Shake until the precipitate is pure white, dilute to 202 cubic centimeters, filter through a §6 ALKALIES AND HYDROCHLORIC ACID 45 dry filter, take 100 cubic centimeters of the filtrate and titrate back with normal caustic-soda solution. (The extra 2 cubic centimeters is to allow for the precipitate.) If we call the caustic-soda solution used x, the oxalic acid used is 25 — 2x. Of this, part is used to neutralize the base, and part to reduce the manganese dioxide to manganese monox¬ ide and then neutralize that. We have just found the amount of manganese dioxide in 10 grams of the mud and can calculate its equivalent in oxalic acid from the equation MnO s + 2 (COOH\ = Mn{CO a ) # + 2CO, + 2 H t O Calling this amount of oxalic acid expressed in cubic cen¬ timeters of normal solution y, then the amount of normal acid used by the base is 25 — (2x -\-y) = s - Since the base consists of a mixture of lime, magnesia, manganese hydrate, and iron hydrate, it is customary to report the result here in cubic centimeters of oxalic acid used. 53. Gas From Sulphate Pan.—The hydrochloric-acid gas from the “ pan ” must be mixed with the proper amount of air as it goes to the “decomposer,” and this mixture is controlled by analysis. The analysis is carried out by sucking the gas, by means of an aspi¬ rator, through a standard solution of caustic soda containing methyl orange. The instant the color changes, the flow of the gas is stopped and the volume of gas in the aspi¬ rator is determined by measuring the amount of water that has run out of the aspirator. A suitable piece ot apparatus for this determination is shown in Fig. 5. The lower end of the tube leading into the absorption bottle is blown out and arranged with a number of small holes to 46 ALKALIES AND HYDROCHLORIC ACID 6 break up the gas into small bubbles and so assist the absorp¬ tion. By using the same amount of normal alkali each time, the amount of hydrochloric acid absorbed is constant; and by measuring the air carried through, the composition of the mixed gas can be easily calculated. As, for example, if we use 100 cubic centimeters of normal alkali that is equal to 3.65 grams hydrochloric acid, which is equal to 2.24 liters of hydrochloric-acid gas under 0° C., and 760 millimeters of mercury pressure. If the gas collected measures 3 liters after correcting for temperature and pressure, then the total gas used is 5.24 liters, of which 57.3 volume per cent, is air and the remainder hydrochloric acid. 54. Gas From Decomposer. — Arrange three absorp¬ tion bottles, similar to that shown in Fig. 5, in a series as close to the decomposer as possible, and divide 250 cubic centimeters of caustic soda of 1.075 sp. gr. between the three bottles. The aspirator is so regulated that it con¬ tinues during the working off of a pan charge. Five liters of the gas are sucked through the absorption bottles, then the contents of all three flasks are united and diluted to exactly 500 cubic centimeters. ( 2 (3) (CM CO,), Ca + 2 HCl = 2 CH 3 COM + Ca CL The amount of bleach necessary to produce a good color depends on the thoroughness of previous treatments, but may be given as from 2 to 5 pounds of bleaching powder for every 100 pounds of pulp. 6. Bleaching of Esparto.—Esparto fiber is very often bleached in the washing and beating engine, where it is subjected to an acid bleaching. The required quantity of bleach liquor is added, and after mixing for about i hour, the highly diluted acid is added (using about 6 ounces of acid to 100 pounds of fiber) and the bleaching continued until a good color is produced. The liquor used tests about 17 MANUFACTURE OF PAPER 5 4° Baume at 60° F. Esparto fiber is also bleached in large potchers made of brick and lined with cement, the agitation being accomplished by means of large revolving paddles made either of wood or iron, preferably the latter. From 10 to 15 pounds of bleaching powder is required to bring 100 pounds of esparto to a good color. 7. Bleaching of Straw. —Straw fiber is bleached by methods similar to those used for bleaching esparto. The amount of bleach required is from 8 to 12 pounds for each 100 pounds of pulp. 8. Bleaching of Jute and Manila.— Jute and manila are usually bleached in the washing engine, and chloride of lime, when used, is added in a very weak solution, which bleaches the fiber to a cream color, oxidizing it to some extent. Strong bleach should not be used, as it will chlorinate the fiber. It is better to use a weak solution of sodium hypochlorite in the bleaching of jute, as a solution of this kind will prevent the formation of the chlorinated compound. As it is difficult to bleach jute fibers to white, they are gen¬ erally used for papers that do not require a high color. From 9 to 10 pounds of bleaching powder is required for each 100 pounds of pulp. 9 . Bleaching of Ground Wood. —Owing to the fact that ground wood contains nearly all the intercellular con¬ stituents of the wood, which have to be removed by the bleach before any action takes place on the coloring matter of the fiber, it cannot be economically bleached, and is therefore used for common papers, as stated before. The color of ground wood can be considerably improved by treat¬ ing it with a dilute solution of sodium bisulphite. 10 . Bleaching of Chemical Wood Fiber.— There are many forms of bleaching potchers for bleaching chemical wood fiber made by the various chemical processes. Some potchers very much resemble a beating engine (in fact, some paper makers bleach their stock in the beaters), others are large cylindrical wooden tanks provided with an agitator, 6 MANUFACTURE OF PAPER §17 which consists of a central rod with paddles attached at different heights, while still others are large, open, tile-lined vats made of brick, having wings attached to a revolving horizontal shaft so as to keep the stock agitated during the bleaching operation. It has been found by practice that better results can be obtained by bleaching the stock in open bleachers. All forms of bleachers have a steam line running into them, by means of which the stock can be heated during the operation. The heating must be done very cautiously, as there is great danger of chlorinating the fiber if heated too highly; there is also danger of heating it too highly in one spot (where the steam enters), with the same result. Better results can be obtained by heating the stock to the required temperature before adding the bleaching liquor. It is advisable not to exceed a temperature of 115° F. If this temperature is exceeded, there will be trouble from time to time with chlorinated fiber. 11. At times, owing to insufficient treatment in previous operations, it is difficult to bring a bleacher of stock up to color. In such a case, the action can be greatly assisted by washing out the products of the bleaching action, treating with a weak solution of alkali, and washing again. After this treatment, the most refractory pulp can be brought up to color by again treating with bleaching solution. In bleaching sulphite pulp, the fact that from 14 to 22 per cent, of bleaching powder is required indicates that the powder has to perform other actions besides bleaching. The amount of bleaching powder required increases with the amount of incrusting matter left in the pulp. Using the soda solution just mentioned before bleaching will greatly reduce the expense of bleaching. 12 . In bleaching sulphite pulp, some paper makers warm the pulp in a 13-per-cent, solution of bleaching powder, and after 1 hour’s time add a 2.5-per-cent, solution of sulphuric acid. The pulp is then washed for 2j hours and rebleached with a 2-per-cent, solution of bleaching powder, finally adding a |-per-cent. solution of sulphuric acid. §17 MANUFACTURE OF PAPER 7 In bleaching soda or sulphite fiber, the strength of the bleach solution used is generally from 3i° to 4° Baumd at 60° F. (about i pound of bleaching powder to a gallon). It is advisable to keep the solution as regular as possible in order that the results obtained may be uniform. The bleaching of wood fiber requires from 12 to 25 pounds of bleaching powder for each 100 pounds of pulp, depending on the wood used, the process by w 7 hich the fiber was isolated, etc. After bleaching any fiber, it must be well washed in order to remove the excess of bleach and soluble by-products. This is done in some mills by means of a drum washer in the potchers; in others, by the same operation in the beaters; and in still others, the bleached stock is pumped with a large quantity of fresh water to large drainers, or chests, having perforated bottoms and allowed to stand until it drains down solid, after which a large amount of water is added and the stock is pumped to the beaters, mixers, or pulp-machine stuff chest. 13 . In order to get good results from bleaching, the stock should be well agitated. The question of agitation has caused considerable experimenting to be done by the management of the various paper mills, and as a result, some mills have adopted a system of continuous circulation. In this system, the stock, after the bleach has been added, is taken to a battery or a set of bleachers, through which it is made to pass, being pumped from the bottom of one bleacher to the top and opposite end of the other, and then from the bottom of the second bleacher, on the opposite side from where it entered, to the top of the third, and so on through a series of about six bleachers, all of which are furnished with agitators. As nearly all bleach solutions contain some chlorate, which is inactive as a bleaching agent, it is generally advisable to add a small quantity of sulphuric acid. This acid should be added when the available chlorine has just about been exhausted, or when the stock shows a pale-blue color with iodic starch. Also, time should be allowed for its action 8 MANUFACTURE OF PAPER §17 before sulphurous acid or bisulphide liquor used as an antichlor is applied. The sulphuric acid should be very much diluted before it is added—about 1 quart of acid to a barrel of water—and should be run in very slowly. The adding- of sulphuric acid will liberate the chlorine from the chlorate and will give the liberated chlorine an opportunity to assist in bleaching the stock. In cases where the bleaching capacity of the plant is insuf¬ ficient, it is advisable to add a little sulphuric acid to hasten the bleaching action. In this way it is possible to bleach more economically, and, in addition, the washing of good bleach solution from the stock is avoided. Great care, how¬ ever, must be exercised in thus forcing the bleaching. 14 . It is generally customary to use some form of anti¬ chlor to neutralize the last traces of bleach after the stock has come up to the required color. Sulphite and hyposul¬ phite of soda are used to a great extent for this purpose. Sulphurous acid is also used to some extent. This acid removes the slight yellow tint left in the pulp after bleaching, bringing it to a fine white. On exposure to the atmosphere for any length of time, this yellow tint will appear again, because the coloring matter that was temporarily removed by the reducing action of the sulphurous acid will again become oxidized. When treated with an antichlor, the pulp must be rewashed. 15 . Electrolytic Bleaching.—There has been consid¬ erable experimenting with methods of preparing bleach liquor by the electrolysis of common salt, and as a result of these experiments such a degree of proficiency has been gained that electrolytic bleach plants have been installed in a large number of mills in the United States and in Europe. The process of bleaching with the product of the elec¬ trolysis of an alkaline chloride was first worked on a com¬ mercial basis in 1886, when M. Hermite developed the process for the production of magnesium hypochlorite by the elec¬ trolysis of a 5-per-cent, solution of magnesium chloride. 17 MANUFACTURE OF PAPER 9 The process of electrolytic bleaching is based on certain well-known principles of electricity, a general idea of which is here given. A metallic conductor does not suffer any apparent change when a current of electricity passes through it, but various magnetic and heating effects are produced. Some liquids, as well as solids, are good insulators, while others conduct electricity, and are termed electrolytes. The latter suffer decomposition in proportion to the amount of current pass¬ ing through them. The poles are the points at which the current enters and leaves the liquid, the point at which the current enters being termed the anode , and the point at which it leaves, the cathode. The products of decomposition of the liquids are observed at the poles, and are called tons; that liberated at the anode is termed the anion , and that liberated at the cathode, the cation. In the process of decomposition of fused common salt, chlorine is given off at the anode and sodium at the cathode. When a solution of common salt is used, a secondary reaction takes place, due to the contact of the liberated ions, and there is a tendency toward the forma¬ tion of sodium hypochlorite, which remains in solution, and hydrogen, which escapes at the cathode. There is also a decomposition of the water itself into hydrogen and oxygen, and the oxygen that is liberated at the anode will attack the material of which it is made, and, in the case of carbon, destroy it in a short time. It is the aim of the inventor to procure an anode that will resist the action of the pioducts of electrolysis. Platinum is the best in this respect, but as it is very expensive, different forms of carbon have been used to a great extent. It is also advantageous to use as little water as possible; hence, nearly all inventors use a saturated brine solution. The quantity of electrolyte decomposed by the passage through it of a given quantity of electricity is always the same. The current efficiency of a cell is determined by dividing the quantity found by the theoretical amount. 16. That which causes electricity to flow from a point of high potential to a point of low potential is called the 10 MANUFACTURE OF PAPER §17 electromotive force (E. M. F.), the unit of which is the volt. The unit of quantity of current is the coulomb; the unit of rate of flow, which is 1 coulomb per second, is called the ampere; and the unit of resistance to the flow is the ohm. An electromotive force of 1 volt will send a current of 1 ampere through a resistance of 1 ohm. A current of 1 ampere, theoretically, yields 1.34 grams of chlorine and 1.51 grams of caustic soda per hour. Owing to complica¬ tions due to secondary reactions, the yield in practice is only about 1 gram of chlorine per ampere per hour. The power of a current in doing work is measured in units called watts. A current of 1 ampere, under an electromotive force of 1 volt, has an energy of 1 watt. One horsepower equals 746 watts. Two pounds of coal is converted into 1 horsepower of mechanical energy, which, as stated, is equivalent to 746 watts. This is converted through the dynamo (with customary loss) into about 650 watts, which is the efficiency of the dynamo for each horsepower. An electromotive force of from 3 to 5 volts is required between the terminals, and since the power of a circuit in watts is equal to the number of amperes flowing multiplied by the electromotive force in volts, to produce 1,000 grams of chlorine it will require (assuming the electromotive force to be 4 volts) 4,000 watts, or about 6 horsepower per hour, which means the consumption of 12 pounds of coal. A great difficulty experienced in the process thus far set forth is in getting the caustic-soda solution free from salt, as a diaphragm is required between the anode and the cathode that will furnish as little resistance as possible and at the same time prevent the passage of brine solution through it. Several different materials are in use for diaphragms, such as unglazed earthenware, asbestos, etc. 17. A great many processes have been proposed for the production of chlorine and caustic soda by electrolysis, all of which have the same fundamental principles underlying them, namely, working with a saturated brine solution, 17 MANUFACTURE OF PAPER 11 having a diaphragm between the poles, and separating the chlorine from the soda. There has, however, been consider¬ able difference in the designs of the apparatus. The dynamo generally used is one so wound as to deliver a continuous current of large volume under moderate volt¬ age, say about 1,250 amperes at 120 volts. The cells are usually arranged in multiple, and the current is conducted to them through large copper conductors. Following are descriptions of a few of the styles of cells that have been patented and are now being worked on a paying basis at many paper mills. (For description of other cells, see Alkalies and Hydrochloric Acid.) 18. The Mercer Cell. —In Fig. 1 is shown the Mercer cell, which consists of an earthenware crock that is open at the top and sides (the side openings marked /, shown in (c), are five in number) but closed at the bottom. The brine solution is poured into the cup b at the side of the cell, and passes into an inner tube c, which extends almost to the bottom of the cell, where the brine solution is discharged. This enables the cell to be kept full and prevents the gas from escaping while filling. The crock is enlarged at m so as to form a groove, as shown, into which the lid, shown in (a), will fit and thus permit the cell to be luted air-tight. The diaphragm used is asbestos, a sheet of which is wrapped around the openings in the crock. A perforated sheet-iron jacket k, shown in (e), is securely bound around the asbestos diaphragm by means of iron bands /, which are in three pieces and bolted together, as shown in (/). The anodes consist of round sticks of carbon g, shown in {d ), four of which are attached to a lead support h that has a long lead projection i extending from its center. There are small projections «, shown in ( b ) and (c ), on the inside of the crock, upon which the lead support rests. The long lead projection passes out through the lid at d, as shown in (a) and (e ), and is luted air-tight. This lead connects with the conductor from the dynamo. The chlorine gas escapes through e to the gas main. Six of these shells are placed in 17 MANUFACTURE OF PAPER 13 a long, oblong sheet-iron tank that is just wide enough to admit them. The sheet-iron jacket k touches the bottom of the tank and, together with the tank, forms the cathode. The tank is supported on pieces of glass. The soda passes through the diaphragm and unites with the water, which is continually flowing in at one end of the tank and out at the other, forming caustic-soda solution. The strength of the soda solution depends on the amount of water flowing into the tank. The solution is deep enough to cover the asbestos diaphragms. The chlorine gas passes through the gas main and into the lime tower, where it comes in contact with milk of lime. The milk of lime is mixed in a tank on the second floor, and passes down the tower to a tank below, from which it is again pumped into the tank above. This continuous circulation is kept up until the bleach solution has reached the required strength, when it is allowed to settle, the liquor run off, and the lime sludge, with the addition of more fresh lime, used again. This bleach liquor is tested from time to time for available chlo¬ rine by the usual arsenious-acid tests, in order to ascertain when it is up to the desired strength. The finished liquor should contain from 1.56 to 1.75 per cent, of'available chlo¬ rine. If there is not sufficient lime to take up all the chlorine to form hypochlorite, the excess of chlorine will cause the formation of chlorate, which results in the loss of the active bleaching agent. For this reason, the Baume test is not sufficient in testing the bleach liquor made by this process, and, as just stated, the arsenious-acid test should be resorted to. 19. Outhenin-Chalandre Cell. —In Fig. 2 is shown the Outhenin-Chalandre cell, which consists of an inner closed anode cell a containing round carbon anodes c that are connected by means of a lead support b with a terminals. A lead pipe g passing through the top carries the chlorine gas to the gas main. The sheet-iron cathode h forming part of the plate m , the top of which serves as the terminal, are contained in sloping, porous tubes. These tubes are her- 14 MANUFACTURE OF PAPER §17 metically sealed through the walls of the anode chamber, but allow free circulation of cathode liquid through them. Each tube is fastened in place by an arrangement, as shown at i. The anodes are suspended in rows of six between adjacent sets of cathode tubes. Water is admitted to the cathode chamber through the funnel /, and caustic-soda solution is drawn off at k. The anode solution is sodium chloride, and the cath¬ ode solution, sodium hydrate. The hydrogen produced at the cathode passes up to the tubes and is collected in the hood /. It is then con¬ ducted away and used for other purposes. The anode cell is filled through pipe n. It is claimed for this process that caustic soda can be made fairly con¬ centrated, and that a sample of caustic soda made in this manner contained 97.5 per cent, caustic soda (dry basis). The chief advantages of this cell are the com¬ plete separation of soda and chlorine and the collection and utilization of the hydrogen; but, on account of the diaphragm, a high electromotive force is required between the terminals. In some mills, an evaporator somewhat similar to the Yaryan is employed to remove the salt from the caustic liquor. 20. Treatment of Bleached Stock.— The bleached and washed stock, in case the washing is not done in the beaters, follows one of the following courses: It is (1) trans¬ ferred to the mixers; (2) transferred to the wet machine; (3) transferred to the pulp machine; or (4) transferred directly to the beating engine. §17 MANUFACTURE OF PAPER 15 1. The object of the mixers, which are large, cylindrical tanks provided with agitators in the center and capable of holding several bleachers of stock, is to furnish uniform stock for the beaters, in case the pulp is worked right up into paper. The stock is passing in and out of the mixers continually. 2. The wet machine, similar to the one described in Manufacture of Paper, Part 1, is used in case it is desired to transfer, or ship, the pulp in folds or to weigh the amount used in the beaters. This plan is usually followed in the treatment of the sulphite fiber, after which it contains about 65 per cent, of moisture. The pulp is transferred to the beater in folds, but is opened out before it is placed in the beater. 3. Before passing over the pulp machine, the pulp first passes through a screen similar to the one described in Manufacture of Paper , Part 1. From the floor box of this screen the pulp passes up through a number of holes into a vat where it is mixed with more water. There is a wire- covered roll revolving in this vat, by means of which the pulp is taken up and transferred to a felt, as in the wet machine, and conveyed over one or more suction boxes through a series of press rolls and over the driers (the suc¬ tion boxes, driers, and press rolls being similar to those of a paper machine, to be described later). The pulp is wound on a long reel at the end of the machine and is finally slit and rewound in rolls of a convenient size to handle (from 100 to 150 pounds each). There are usually several reels so arranged that while one is being cut another is winding, and thus the pulp is run continuously. These rolls are weighed and tied up for shipment. They contain about 7 or 8 per cent, of moisture. The rolls are either chopped up and put into the beaters in sheets or allowed to run in from a spindle. 4. The stock is pumped directly from the drainers to the beaters, where it is finally mixed for the paper machines. 199—29 16 MANUFACTURE OF PAPER §17 BEATING 21. Beating Process. —In the beating process, the material is disintegrated in order to obtain a close, even sheet of paper. The amount of beating required varies according to the nature of the stock and the class and grade of paper to be manufactured. The beating process is one of the most important steps in the operation of paper making. No amount of skill of the paper marker will remedy a mis¬ take due to carelessness or lack of skill on the part of the beaterman. 22. Beating Engine. —The beating engine, which has been referred to before, is shown in Fig. 3. This machine is made of wood or iron and is provided with a washer a , a bedplate and roll b, and a midfeather c, as in the breaking engine previously described. The washer, which is shown in Figs. 4 and 5, consist of an octagonal drum, the faces of which are made of latticework, admitting of the free 18 MANUFACTURE OF PAPER §17 passage of water to the interior, while the ends are closed in such a manner as to allow the water to pass out at the axis only. This drum is covered with a fine-mesh wire cloth, which prevents the fiber from being carried ofif with the wash water. The interior of the drum, shown in cross- section in Fig. 5, is so arranged that, in revolving, the arms a take up the water and carry it to the axis of the drum, through which it is conveyed to the trough c, shown in Fig. 4. 23. The engine roll, which is shown in Fig. 6, is pro¬ vided -with projecting steel knives that are tapered in the opposite direction to the knives in the bedplate, which are placed under the roll in the beater; thus, when the roll Fig. 6 revolves, it produces a cutting action similar to that of a pair of shears. There is a small depression in the floor of the beater, known as the sand trap , in which heavy particles of dirt, sand, etc. are caught during the beating operation. It is in this engine that the stock is prepared for the paper machine. By the beating and cutting action of the roll and the bedplate, the fibers are separated and reduced in length, the fineness being regulated by varying the distance between the roll and the bedplate. The fibers obtained from straw do not require any beating; those from esparto and wood require considerable; and those from rags, on account of their length, require excessive beating and cutting. Rag stock intended for strong, thin papers must be drawn out in the washer for at least 6 hours, and in the beater for 11 or 12 hours, using blunt plates and rolls. §17 MANUFACTURE OF PAPER 19 24. The beating is carried on by gradually lowering the roll until the required effect is produced. In order to pro¬ duce paper of the quality required, it is necessary to mix various fibers, which is usually done in the beating engine. In mixing these various fibers, such as rags with esparto, rags with wood, esparto with straw, sulphite stock with soda stock, ground wood with other fibers in preparing newspaper, etc., and, in fact, any of the fibers, the paper maker must use his best judgment, bearing in mind the different effects produced on the different fibers by the beating action,-etc. 2o. Broke Beater.—The broke beater, as its name suggests, is used in working up broke , which is partly formed paper obtained when starting the paper machine, paper damaged in passing over the drying cylinders, and imperfect or rejected paper. This engine is the same as the ordinary beating engine, except that it has a steam line by means of which the stock is highly heated. In some cases, a little caustic soda is added to the stock to assist in breaking it up again. 26. Jordan Engine.— The Jordan engine is an improved form of engine that will save from one-third to one-half the time required for beating, when done in the Fig. 7 beating engine. The working of the Jordan engine will be clearly understood by referring to Figs. 7 and 8, which show the Horne-Jordan engine set up and also the interior struc- 20 MANUFACTURE OF PAPER §17 ture. This machine consists of a cast-iron cone a, which fits into the cone b, forming the body of the engine. The cone a revolves at a speed of from 350 to 400 revolutions per minute. Both cones are fitted with angled steel knives that are held in position by hardwood wedges. The plate c is bolted on tightly, and the packing gland d is adjusted over the shaft. The arrangement shown at e is attached as shown in Fig. 7, and by means of the screw arrangement /, the cones can be adjusted to regulate the fineness of the stock. This type of Jordan is the one in most general use, although there are other types that give very good results. Among Fig. 8 these may be mentioned the Marshall perfecting engine. This engine differs from the Jordan in having rims on the end of each of the cones, set with knives, which cut at this point also. The half-beaten stock from the beating engine is pumped into a supply chest located over the Jordan. From this chest the Jordan is supplied with stock by means of a pipe, the stock entering the engine at i and the finished stock leaving the engine at o. From this point the stock is conveyed through a pipe to the stuff chest, from which it is pumped to the screens of the paper machines. §17 MANUFACTURE OF PAPER 21 SIZING, LOADING, AND COLORING SIZING 27. It is necessary that writing paper, book paper, etc. shall not readily absorb ink or water, so that when used for writing or printing the ink will not spread, but will leave good, plain characters. This property is imparted to the paper by the use of what are known as sizing agents, which are assisted to some extent by the loading agents, which will be considered later. 28. Engine Sizing. —The process known as engine sizing is carried out by precipitating rosin size with alum, or some other precipitant, upon the fiber in the beating engine. 29. Rosin Size. —There are many ways in which rosin size may be prepared, but they all accomplish the same purpose—that is, getting the rosin in such shape that it can be made into a solution, from which it is again precipitated as already suggested. There has been a great deal [of dis¬ cussion as to what the true sizing agent is, some of the authorities contending that the free rosin is the only sizing agent, others that the resinate of aluminum is the true sizing agent, and still others that it is due to both. Practical expe¬ rience inclines to favor the view that the sizing is as much due to resinate of aluminum as it is to the free rosin, as sizes in which the free rosin varied from 3 per cent, to 35 per cent, have been successfully used. When using a size containing 3 per cent, of free rosin, a larger amount of alum was required to precipitate the size, but no more rosin was required to furnish a hard-sized paper than when 35 per cent, of free rosin was used. The chief advantages of using a size containing a large amount of free rosin are the saving of considerable soda in making up the rosin soap and the 22 MANUFACTURE OF PAPER §17 saving- of an enormous amount of alum or other precipitant used. It is quite probable that some classes of paper are sized best by means of free rosin, while others are sized best by resinate of aluminum. 30. Rosin size containing any amount or percentage of free rosin desired can, of course, be made by using less soda to dissolve it. When, however, a certain limit is reached, it is difficult to dissolve or to emulsify the size without causing the separation of raw rosin in sticky lumps, or masses. One of the best methods of dissolving and emulsi¬ fying high free-rosin size consists in injecting the boiling size into boiling water with a steam injector and then diluting the milk with cold water. 31. Brown Size. —In preparing brown size, about the same method is followed in the different mills, but dif¬ ferent proportions are used. The rosin is first crushed and then shoveled into a hot solution of caustic soda in the mix¬ ing kettle. The boiling is continued cautiously until the rosin is saponified, the kettle being heated by either live steam or a steam coil. Any tendency of the size to boil over can be overcome by sprinkling a little cold water on it. The size should be well stirred during the boiling operation. The amount of caustic soda required varies from 18 to 22 pounds for each 100 pounds of rosin. Care should be taken not to use too much water, and the aim should be to keep the mixture at such a density that the size will float and the dirt will sink to the bottom. Salt is sometimes added to increase the density. Salt also causes the thick size to separate more thoroughly from the liquor. The separated black liquor is thrown away. The heavy size con¬ tains about 40 per cent, of water. The finished size should be drawn off and allowed to stand for about 1 week before it is used. When using, it is customary to dilute the size to a very thin solution containing over 85 per cent, of water. 32. White Size. —A very good method of preparing white size is the one patented by H. Hampel and Victor Zampis, of Vienna. This method has been used to some Fig. 24 MANUFACTURE OF PAPER §17 extent in the United States. The apparatus for the prepara¬ tion of white size consists of a large oblong tank, which has an agitator consisting of wings, or paddles, that revolve on a horizontal shaft. The cooking is not done under pressure. These tanks are of various sizes, but the proportions about to be given are for a tank that will hold 1 ton of rosin. The tank is covered by means of a large lid that has a small manhole in the top, which can also be covered, for introducing the ingredients. Fig. 9 shows a side view (a), two end views (b) and (c), and a top view (d) of the tank used. In the figure, a is the shaft to which the agitator paddles b are attached. The shaft is run by the cog wheel e, which, in turn, is run by the smaller cog wheel / and the pulley g. There is a small opening, or manhole, c in the large door d on the top of the tank, through which the charge is added. When the cook is ready to be dumped into the tank, the valve h is opened. The dimensions of the tank shown in the figure are 4 ft. 3 in. X 2 ft. X 2 ft. 33. In making up the heavy size, 31 gallons of water is brought to a boil, the agitator started, 60 pounds of soda ash added, and the agitation continued for several minutes, to dissolve the soda. The steam is then shut off and 400 pounds of rosin, which has previously been finely crushed, is slowly added. The steam is then turned on gradually, and 1,600 pounds of rosin is added, care being taken that there is enough steam on to keep the rosin from getting too thick. The temperature is brought up to 180° F., the steam shut off, and 160 pounds of soda ash cautiously added. After all the soda ash is in, the mixture is agitated without steam for about 4 hours and then brought almost, to a boil, being kept at this temperature for about 2 hour. The steam is then shut off, the agitator stopped, and the size dumped into the storage tank below. One cook will make about 300 gallons of heavy size. The white size is made by mixing about 60 gallons of the heavy size with 2,000 gallons of water that has been heated 17 MANUFACTURE OF PAPER 25 to about 175° F., but the steam is shut off before adding the size. This mixture is agitated for about *2 hour and allowed to cool before using. A milk-white liquid containing much free rosin in emulsion is thus procured. 34. In another method of preparing white size, rosin is boiled with alkali and water under pressure in order to pre¬ vent the escape of the volatile resins. The operation of boiling is carried on in a cylindrical vessel, at the top of which is provided a manhole for charging purposes. The vessel is also provided with a perforated plate about 2 feet from the bottom, the object of which is to prevent the rosin from forming into a hard mass at the bottom of the vessel. The carbon dioxide generated is also retained; this, it is claimed, improves the size. When the cooking is complete, the rosin size is forced to the storage tanks by means of the pressure remaining in the boiler. Before adding the size to the stock, the excessive amount of water is removed from the latter by means of the drum washers and the washer is then raised. The quantity of size required is strained into the beaters in order to keep out any dirt that would other¬ wise enter the paper through this source. After adding the size, the stock should be allowed to circulate a short time, and the required amount of alum should then be added. This precipitates the combined rosin as resinate of aluminum, with the production of sodium sulphate, 3 Na 2 R + AM SO*), = 3 Na,SO* + Al t R> In the reaction expressed by this equation, R denotes resinic acids. The alum may be added in the dry state, but it is customary to dissolve it first, and knowing the strength of the solution, the amount required can be measured. The amount of alum needed depends on the amount of size used and the proportion of free rosin in the size. 35. Animal Size, or Glue. —In order to prepare ani¬ mal size, or glue, the glue is mixed with water at a tem¬ perature of about 190° F. for from 10 to 15 hours, a little alum being generally added. The size is sometimes added to the stock in the beaters just before dumping, but it is 26 MANUFACTURE OF PAPER 17 generally added on the machines’ by a method called tub sizing , which will be described later. 36. Miscellaneous Sizes. —Starch is used to some extent as an auxiliary sizing agent, as are also sodium aluminate, sodium silicate, and casein. Casein is usually applied on the machine, and is used to give a coating or better finish to the paper; it is also used in about a 40-per¬ cent. solution in the beating engines. Starch is prepared by boiling it with water, care being taken not to boil it too hard. It is only necessary to boil the starch until the globules burst. Too much boiling causes the starch to loose some of its viscosity. Casein is the nitrogenous substance in milk, and in its original state is soluble in water. It is prepared for sizing by precipitation with magnesium sulphate o'r by heating milk to which sulphuric acid has been added. 37 . Adaptation of Various Sizes. —The principal adaptations of the various sizing agents are as follows: Rosin size is used to fill up the pores in the paper between the fibers and to make the paper waterproof, thus keeping ink from spreading to a greater or less degree, depending on the amount of size used. Animal size is used mostly as a surface size. When used with rosin size, it makes the paper still better in the property of preventing ink from spreading. Animal size also gives the paper a better surface. Casein size is of great value as a paper coating, as it gives the papei a good finish. The chief advantages claimed for casein size, however, are the production of a more elastic fiber and an increased yield of paper. Starch at the present time is used mostly as a filler, making the paper stronger. It is claimed that paper in which starch is used has a better surface and feel. The value of the use of starch is very doubtful, as it is used in small quantities. Sodium aluminate is sometimes used in place of sodium carbonate in preparing size. The size is added to the pulp in the usual manner and precipitated with either magnesium S17 MANUFACTURE OF PAPER 27 chloride or sulphate. Rosin, magnesia, and alumina are all precipitated at the same time, which is claimed to be an advantage. Sodium silicate is used when a hard paper capable of pro¬ ducing a rattling sound is desired. It is strongly caustic and can be used in place of sodium carbonate, or it may be mixed with the size in the engine. When alum is added, there is formed a bulky, gelatinous precipitate of hydrated silicic acid, similar to precipitated alumina. The use of sodium silicate will produce a good, hard writing paper. LOADING 38. In the manufacture of almost any kind of paper, except those of the very highest quality, it is customary to load the stock; that is, to add some comparatively cheap material, such as china clay, agalite, pearl hardening, etc., to the stock in the beaters, so as to give weight to the paper and also to make it less transparent and improve its surface. While, as has been stated, the appearance of a paper is greatly improved by loading, the strength of the paper is somewhat impaired, especially when a large amount of filler is used. In some mills, it is customary to mix the filling material with water and to keep the mixture agitated continually. The strength of the mixture is known and the amount required is readily measured out, but in many mills the filler is added in the dry state. 39. The material most extensively used as a filler is a fibrous variety of magnesium silicate generally known as agalite. Preference is given to this material, because from 65 to 75 per cent, of it is retained in the stock. China clay, or kaolin, which is the purest form of aluminum silicate, gives a retention of almost 50 per cent. Gypsum, or calcium sulphate, is used to some extent as a filler in high-class papers, but on account of its slight solubility, it does not give so good a retention as do the other two fillers just mentioned. Gypsum is sold as a filler, 28 MANUFACTURE OF PAPER §17 or loading- agent, under various trade names, such as pearl hardening , mineral white, wheelwright filler , etc. Gypsum is not used in the raw state, but is generally burned to remove part of its water of crystallization. The retention of this filler in paper is only from 35 to 40 per cent. Barium sulphate is sold under the name of Blanc fix , and an artificial compound of precipitated calcium sulphate and alumina is sold under the name of Salem white. Both of these compounds are used as a paper coating. COLORING 40. Coloring is effected by adding dyestuffs or pig¬ ments to the stock in the beaters. There is a great variety of coloring matter that can be mixed with the stock to pro¬ duce various shades in the finished paper. A yellow tint in the stock is neutralized by adding red or blue. The blues generally used are ultramarine, smalt, Prussian blue, and various aniline blues. The reds are usually prepared from cochineal or aniline dyes, but as the latter are affected by the use of alum, cochineal red is to be preferred. Alizarine and red ocher (oxide of iron) are also used to a great extent in producing red tints. Yellows are produced by the use of yellow ocher, lead chromate, and some of the coal-tar dyes, the principal ones being metanyl yellow and auramine. Browns are produced by the use of pigments of the iron oxides, or the Bismarck browns (salts of triamido azobenzene). Greens are usually produced by means of malachite green or Victoria green; blacks, by the use of lampblack, Frankfort black, or blue black. It is better to mix the coloring matters with water before adding them to the stock in the beater. The aniline colors should be dissolved in hot water and then diluted. Carmine should be dissolved in a little ammonia water and then diluted. Samples of the pulp treated are taken from time to time and matched against a sample of the paper that the paper maker is running, and the trained eye of the beaterman can readily determine when the desired effect is produced. §17 MANUFACTURE OF PAPER 29 In order to obtain the color desired, it is first necessary for the beaterman in charge to try to match the color and then to calculate the amount of coloring matter required in the beater. This is best accomplished by mixing a definite amount of stock containing a known quantity of air-dry fiber with a convenient amount of water at about 80° F., and then adding the dyestuff from a burette, using a 1-per-cent, solution. After this the stock is squeezed out and matched, the amount of coloring matter calculated, and the required amount added to the beater. The water from the paper machine, or back water , as it is called, should be used over again, and the amount of water on the machine should be so regulated that very little of it will go to waste. In this way, there will be a great saving in the loading and coloring matter, which would otherwise go to waste. Before attempting to size or color the stock, it should be perfectly cold; otherwise, good results cannot be obtained. When the stock has been uniformly colored and well worked up in the beaters, it is passed to the Jordan engine, where it is finally prepared for the paper machines. 41. There are three classes of dyes used in the coloring of paper, namely, acid aniline dyes, which require acid or alum to bring out their brightest and strongest effect; basic aniline dyes , which show their best effect in alkaline solutions; and s7ibstantation dyes, which are fixed without the use of a mordant. It is best to use only basic or only acid dyes whenever possible, and not some of each kind. The acid colors, as a rule, are faster to light than are the basic dyes. If both an acid and a basic color are to be used in coloring the same beater of stock, each color should be dissolved and added separately. If mixed, one will precipitate the other. 42. Following are the conditions to guard against in the coloring of paper: 1. The fading of color. This often occurs when colored paper is exposed to light or is brought into contact with 30 MANUFACTURE OF PAPER §17 certain chemical substances. Care should be taken to select a color that will not fade when the paper is put to the use for which it is intended. The greatest difficulty along this line has been experienced in the making of colored paper for soap wrappers; it seems almost impossible to produce a paper the color of which will entirely resist for any length of time the action of the caustic alkali in the soap. 2. Irregularity of color of the two sides of the paper. Fre¬ quently, when pigments are used, the side of the paper next to the wire is not colored so well as the upper side. This is due to the fact that some of the coloring matter is drawn away from the lower sides by the suction boxes. 3. Unevenness of the color. This is generally due to mixtures of various fibers that have different affinities for the coloring matter used, and is very marked when chemical wood pulp is mixed with mechanical wood pulp. MANUFACTURE OF PAPER FROM PUEP MAKING OF PAPER BY HAND 43. The pulp made by the various processes described is now in suitable condition for making into paper. For some fine grades of paper, this is done by hand, but by far the greatest amount of paper used is machine made. Both processes will be described. 44. In making paper by hand, the stock is passed from the beaters to vats. These are 5 feet square and 4 feet deep, and are provided with a steam pipe, to keep the pulp at the required temperature for working, and with an agitator, to keep the pulp and water well mixed. The stock is taken from the vat by hand in a mold. This mold consists of a frame that is covered first with heavy wire and then with a fine-mesh wire, upon which the sheet is formed. A movable frame is fitted upon the outside of the mold, which extends a little above the wire, forming a sort of wire-bottom tray. §17 MANUFACTURE OF PAPER 31 The movable frame, termed the deckle , forms the edges of the paper, and should fit snugly to the frame. The stock is taken up in the mold, which is then shaken, the deckle removed, and the mold passed to another workman, who turns the sheet on a piece of felt, while the vatman forms another sheet. Felt is laid between all the sheets, and when about 50 deep, they are removed to a press, where the water is squeezed out. The sheets are then removed from the felts and are either hung up or laid out on a board to dry. They are then sized by spreading out the sheets in a vat of animal size, after which they are dried slowly, pressed again (preferably by running through calen¬ der rolls), and passed to the finishing room, where the specks are picked out, the imperfect sheets separated, and the balance counted and packed for shipment. Water¬ marked paper can be made by having the desired mark worked in wire on the bottom of the mold. MAKING OF PAPER BY MACHINE 45. Paper Machine, or Fourdrinier.— In Fig. 10 is shown a paper machine, or fourdrinier, as it is called. The stock forms into a sheet upon a fine-mesh, endless wire cloth, the width of the sheet being regulated by means of a rubber strap, called a deckle strap , shown at a . The water from the pulp passes through the wire cloth, and the formed sheet is carried by means of a felt through press rolls and then over driers and calenders to reels. The stock coming from either the Jordans or the beaters passes into a large cylindrical tank, called the stuff chest , which is made of either wood or iron and is provided with an agitator that extends to the bottom of the tank and is kept moving at a moderate speed. The stock is pumped from the stuff chest to the regiilating box , which is a small box that is constantly kept filled by means of the inlet pipe at the bottom, the excess of stock being carried back to the stuff chest by an overflow pipe near the top. The discharge pipe leading to the screens is located near the bottom of the 199—30 32 Fig. 10 §17 MANUFACTURE OF PAPER 33 regulating box, so that there is a uniform pressure at all times. The amount of stock furnished can be regulated by means of a cock on this pipe. In some mills, the stock passes from the regulating box over a sa?id table , which is a long, shallow box with a felt-covered bottom, having strips of wood placed across the direction of flow of the pulp. The object of this table is to hold back sand, etc. that has escaped removal by previous treatment. The stock then passes to the screens. However, it is not always customary to use a sand table, the stock going directly from the regu¬ lating box to the screens. 46. The screens are similar to those described in Manu¬ facture of Paper , Part 1, and serve to remove any foreign matter, etc. that has escaped removal up to this point. After passing through the screens, the stock should be free from lumps and dirt and ready for making into paper. Frequently, considerable trouble is caused by the frothing of the stock on the screens and also on the wires. Frothing is often caused by the liberation of carbon dioxide when hard water has been used in thinning down the stock. The addi¬ tion of alum to the water before using it will usually help to prevent this occurrence; also, in some mills, a mixture con¬ sisting of li gallons of linseed oil, 1 gallon of bleach, and li gills of turpentine is successfully employed to prevent frothing. After leaving the screens, the stock usually flows into what is called the head-box , entering at the bottom, where it is mixed with more water, which is furnished by a supply pipe. This box serves to mix the stock well before it flows on the wire; this it does by overflowing the box. The head- box also serves to catch any heavy particles of matter, as they will remain at the botton and can be washed out from time to time. Between the head-box and the slicers is a heavy rubber apron that fits over the wires and extends across the full width of the wire and to within li inches of the slicers. The purpose of this apron is to prevent any water from running 34 MANUFACTURE OF PAPER §17 through the wires and to bring the stock in its proper state of dilution and in a uniform stream right up to the slicers. 47. The beaters are sometimes so full that it is not possible to add sufficient water as they are dumped into the stuff chest. In such cases, the heavy stock goes to the bottom and is drawn into the pipe leading to the screens and thence to the head-box without being sufficiently diluted. On a heavy sheet of paper as high a difference as 5 pounds per ream will be caused by this variation in the thickness of the stock. In order to overcome sudden changes of the consistency of the stock and to insure the production of a paper of uniform thickness and weight, the stock in a number of mills is passed from the stuff chest to a small box provided with a metal float. When the stock that enters this box becomes too heavy, the float rises and opens a valve, through which is supplied fresh water to thin the stock. When the stock is properly diluted, the float drops and automatically closes the valve. In order to insure a good supply of stock to the stuff pump, the pipes leading from the chests should not be less than 4 inches in diameter. This pump should be capable of pumping sufficient stock to insure a good overflow when the paper machine is working at its best. 48. The thickness of the sheet is regulated by a gate, called the slicer. This device is made of two pieces of brass that are bolted together in the middle, and it can be lengthened or shortened to suit the width of the sheet. The slicer is placed near the point where the stock is passed on the wire, and can be regulated at different heights, according to the thickness of the sheet required, by means of screws. The height must be the same all the way across, so that the sheet will be uniform in thickness. The slicer is shown at b, Fig. 10. The level of the stock behind the slicer should not be kept too high, or it will lap over the deckle strap and cause small knots to pass down on the edge. Only sufficient water should §17 MANUFACTURE OF PAPER 35 be used to close the sheet nicely, and there should be just enough shake to the wire to fill it evenly. 49. The wire , as it is called, is really an endless wire cloth, closely woven and having from 60 to 70 meshes per linear inch. The length of the wire is from 35 to 40 feet, and the width is usually from 100 to 130 inches, though some are made as wide as 160 inches. The wire passes around the lower couch roll c, Fig. 10, down under the save-all, and back to the breast roll. In its passage over the surface, the wire is supported by a large number of small brass rolls, called table rolls , and in returning to the breast roll, it passes over several small rolls. The frame has an attachment by which the wire is given a shaking motion from side to side, which serves to weave the fibers in their passage over the wire. Under the wire is situated the save-all , which is a shallow box d, Fig. 10, into which the waste water coming through the wire drops, and is used in place of fresh water for dilu¬ ting the stock in the head-box referred to previously. 50. Near the end of the wire and under it are situated the suction boxes e , four of which are shown in Fig. 10. These are long, narrow boxes, which extend across the whole width of the wire and are connected with a vacuum pump. The cover of the box, which is very smooth, is perforated, and the water is further removed from the stock by having the wire pass over it. There is a screw arrangement at the end of the box by means of which plugs may be moved for¬ wards or backwards, according to the width of the paper, so that the boxes will not lose their suction. These plugs are always kept in as far as the deckle straps. The deckle straps a, Fig. 10, are heavy, square, rubber bands that rest on the wire and are carried along with it, thus regulating the width of the sheet. 51. The dandy roll /, Fig. 10, is situated near the end of the wire, and is used for making the “water mark” in the paper. It consists of a skeleton roll covered with a wire cloth, upon which the desired design is worked- with fine wire. If the paper is required to be alike on both sides, with Fig. 11 §17 MANUFACTURE OF PAPER 37 no special design, the roll is covered only with wire cloth, the impression of which corresponds with the impression on the wire cloth. Paper made in this way is known as wove paper . Laid paper is made by the dandy having a number of equidistant trans¬ verse wires upon its upper surface. 52. The paper passes under the dandy roll and is carried by the wire cloth between the couch rolls c,c', Fig. 10, which are brass or wooden cylinders with a jacket of felt. In some machines, the top roll is made of wood and the bottom roll is made of iron covered with a layer of heavy rubber. There is a screw arrangement above the top roll by means of which the pressure can be regulated, thereby pressing the water out of the paper in its passage between the rolls. The paper is then carried, by means of felts and the assistance of the machine tender, through the press rolls proper. The number of press rolls varies on different machines, the machine shown in Fig. 11 having three sets, as shown at a, b, and c. The top roll of each set is provided with what is termed a doctor d, which keeps the roll clean by scraping off the pulp that sticks to it. The pressure on these rolls is also regulated by a screw arrangement. After passing through the last press roll, the sheet is transferred by the machine tender across an open space to the driers, or drying cylinders; this space e is wide enough for the machine tender to pass back and forth under the sheet. 53. These drying cylinders are large, hollow rolls and are heated by means of steam. The paper is carried by means of a drier felt over the series of drying cylinders, which vary in number on different machines, and can be seen in the distance in Fig. 12. 54. Tub Sizing. —After the paper has passed over a couple of the drying cylinders, it passes through a vat of liquid animal size and then between two rollers, which squeeze out the excess of size. The paper is then wound on a reel. In some mills, the paper is allowed to stand for a time and is then passed from the reels over a series of Fig. 12 passing over the driers, the sheet is transferred to the calenders. 55. Calendering:. —In the operation known as calen¬ dering, the paper is given a high finish by pressing it 38 MANUFACTURE OF PAPER §17 wooden drums furnished with fans, by means of which the paper is dried slowly. The most general custom is to pass the paper from the squeeze rolls over another series of driers, and thus keep the sheet in continual motion. After 17 MANUFACTURE OF PAPER 39 between rolls on a machine called a calender. Calenders consist of a series of highly polished, revolving, iron cyl¬ inders that have a screw arrangement at the top for regulating the pressure. The number of cylinders on different machines varies, some having as high as three sets; the machine shown in Fig. 12 has only one set a. The paper passes over these rolls, acquiring a high finish, and thence to the reels shown at b. In order to give a strong glaze to the surface of the paper, one or more of the calender rolls are kept hot by passing steam through them; and, again, in order to produce what is known as a water finish , some of these heated rolls are also kept wet. There are usually two reels in a set, and after one has been wound to the desired thickness, the paper is cut and started on the other reel. When rewinding into rolls, only one sheet is wound at a time, being passed from the reel around a smooth brass roll and through the slitters , which are small, sharp-edged, revolving wheels. The slitters are arranged so as to divide the sheet into two or more sheets of equal size. The sheets formed in this manner are rewound on cores attached to shafts c, which are clamped down and made to revolve by means of a friction clutch. When laying the paper in sheets at the end of the machine, as many as five reels are slit and cut at one time, as will be explained further on. By the use of the paper machine just described, there is a continuous sheet of paper forming, passing over the machine, and winding. 56. Supercalendering. — It is sometimes necessary to have an extra-high finish on the paper; this is done on the glazing calenders, which are generally called supercalenders. These machines are also of various types, one being a series of rolls that are alternately of highly polished iron and com¬ pressed paper, the iron rolls being hollow and heated by steam. Another type consists of a stack of highly polished, chilled-iron rolls. The rolls are bored out and can be heated by steam; also, there is an arrangement by which one or more of the rolls can be raised, according to the finish required. Fig. 13 17 MANUFACTURE OF PAPER 41 The supercalender in most common use is shown in Fig. 13. It consists of a stack of rolls that are alternately of highly polished iron and compressed paper, neither of which is heated by steam. These rolls are pressed down against each Other by turning a wheel a, which operates the large wheels b at the top of the calenders. The lower roll is made to revolve at a high speed, and by means of the friction exerted on the second roll, it revolves in the opposite direction, and in a like manner all the other rolls revolve at a high speed. Owing to the great friction on these rolls, they become very hot. The iron and paper rolls are designated by the letters i and p , respectively. The roll of paper to be calendered is transferred from a small truck to the bar d, when, by turning a crank at c, the position of the roll is changed to e. The sheet is then passed up to a machine tender, who passes it under a brass roll / and then around the rolls of the calender, finally winding it on a core placed on the rod d. It is customary to have a perforated steam pipe extending across each side of the machine, so that a little steam can strike both sides of the sheet as it starts over the calenders. The paper coming from the calenders has a very high finish, and is transferred to the slitting and rewinding machine. 57. Cutting the Paper. —Very frequently, as pre¬ viously stated, the paper is cut at the end of the paper machine, where the large reels of paper are first slit by means of small, sharp-edged wheels, under which it passes before coming to the main knife, which is a knife projecting from a revolving drum and extending across the whole width of the machine. This knife operates by passing closely against a dead knife, over which the paper passes. At every revolution of the drum, the paper that has been previously slit is cut into sheets of uniform size. These sheets drop upon traveling belts made of felt, from which they are lifted by girls or boys and placed in stacks, which operation is termed laying the paper. These stacks are removed to trucks and conveyed to the finishing room. It 42 MANUFACTURE OF PAPER §17 is customary to slit and cut several different reels at the same time, and in place of one sheet, there are two or more sheets laid at one time in the same stack. When rewinding at the end of the machine, large rolls from the machine are generally slit into smaller rolls. When making paper that is to go to the supercalendering room, it must come from the paper machines in rolls, which after supercalendering, are transferred to the cutting depart¬ ment, where they are cut into sheets and laid as just explained. 58. Slitting and Rewinding Machine. —In Fig. 14 is shown a slitting and rewinding machine that slits and rewinds one large roll into six small ones. The large roll is placed on a reel, as shown at a . This reel can be made to run easy or hard, as desired, by turning a screw arrangement b that regulates the brake c. The. end of the paper is then passed through the slitting knives, which 17 MANUFACTURE OF PAPER 43 are so arranged as to regulate the size of the smaller rolls desired, and thence to cores attached to the reels d and e, which are run by cogs and chains attached to cogs on the slitting-knife shaft. When the machine is in motion, the winding of the smaller rolls causes a continuous pull on the sheet. This unwinds the large roll, so that by tightening the brake c the smaller rolls are rolled tighter. The slitting knives are similar to those at the end of a paper machine, one pair being shown in Fig. 14 (b). The cutting surfaces are slightly hollowed out, so as to make them sharp. The knife g is held against the knife h by the spring i. The sheet of paper passing through the knives is represented by the dotted line j j. 59. Guillotine Paper Cutter. — The guillotine paper cutter, which is shown in Fig. 15, is used for trimming the edges of paper and also for cutting a large number of sheets at one time. This machine is provided with a gauge by means of which the size of the sheet cut can be regulated. The sheets of paper to be cut are placed on the bed a in packs from 3 to 4 inches thick, touching the back support b, which can be moved backwards or forwards by turning the 44 MANUFACTURE OF PAPER §17 wheel d. This support is connected by means of an upright rod / with an endless measuring tape g, and the size of the sheet is read off at the pointer in front of the tape. By giving the lever e a slight turn and pushing it to one side, it forces a friction clutch i against the pulley and sets the machine in motion. The clamp c and knife h descend, and when the clamp reaches the paper its progress is arrested, thus holding the paper tight while the knife passes on down through it. The machine is so regulated that as soon as the knife has passed through the paper, the clamp and knife return to their original position. This upward-and-down- ward motion is kept up as long as the friction is kept on; but as soon as the lever is allowed to resume its original position the machine stops. 60. Finishing the Paper. —After cutting, the paper is passed to the finishing room, where it is counted, sorted, and packed for shipment. The sheets are gone over in this room by girls, and the defective sheets are thrown to one side, to be used up as “broke” or sold as an inferior quality of paper. The sheets that pass inspection are either packed in boxes or tied up with heavy wrapping paper, a wooden frame being placed on each side of the package so as to prevent the paper from being damaged in shipment. The sheets are packed up in reams, which consist of from 480 to 516 sheets. The rolls of paper are also well done up before shipping. Papers are generally sold by weight; therefore, the weight per ream is also expressed when distinguishing between them. Thus, 26 X 40 — 80 — 500 means a ream of 500 sheets 26 in. X 40 in. and weighing 80 pounds. PASTEBOARD AND PARCHMENT PAPER 61. Pasteboard, or Cardboard. —In the manufacture of boards all kinds of waste material occurring in the mill may be used, being sorted according to the quality of the board desired. After being well beaten, the material is mixed with a suitable amount of rag pulp, clay, etc. The boards are manufactured by superposing several sheets of paper and §17 MANUFACTURE OF PAPER 45 causing them to unite (1) by a sizing mixture; (2) by superposing several wet leaves at the time of couching; (3) by molds provided with thick deckles; or (4) by machines simi¬ lar to paper machines, but having no drying cylinders, allow¬ ing the boards to dry in the open air. 62. A method employed in making cardboard with two different faces is as follows: Two pulps are mixed sepa¬ rately, and the first is run on the wire of a paper machine. When the water drains off to some extent, the second material, highly diluted with water, is run on—better, after the first pulp has passed over the first suction box—the water from the second draining off through the first. The paper is then passed over the machine in the ordinary way. A good cardboard is made from shoe linings mixed with No. 1 linen rags, the larger amount being shoe linings. Cardboard made of these materials is hard-sized and has a smooth, erasable surface. High-grade mill bristols are made of a small percentage of rag pulp, the balance being wood pulp, mostly spruce. These boards are surface-sized and allowed to dry. Card middles , which are used for making shoe boxes, are covered on one side with coated paper. They are made of ground wood on a cylinder machine. Old printed paper is also used. Tag boards are made mostly from spruce sulphite; some tag boards have ground wood mixed in. Jute is also largely used. Straw is used extensively in the manufacture of the cheaper quality of boards. 63. Parchment Paper. —In making parchment paper, white unsized paper is dipped for h a minute in strong sulphuric acid of 60° Baume and afterwards in water containing a little ammonia. The acid converts part of the cellulose into hydrocellulose, which gives the paper a gelatinous surface. Paper treated in this way becomes translucent and much stronger. In other methods, ammo- niacal-cuprous-oxide solution or zinc chloride is used instead of sulphuric acid- 46 MANUFACTURE OF PAPER §17 WATER AND ITS PURIFICATION REMOVAL OF ORGANIC IMPURITIES 64. Water is one of the most important factors in the manufacture of paper, as it is impossible to make good papers with the use of impure or dirty water. There is such a large quantity of water used around a paper mill that the problem of water purification is of great importance. Almost every paper mill has in connection with it a filter¬ ing plant, the size of which varies with the amount of water used and the condition of the water before filtering. If the water is very hard, it should undergo the usual treatment for boiler purposes; but for the manufacture of paper, the prin¬ cipal factor to be considered is the organic impurity. This causes the growth in the water of what are termed Algce , which form a kind of slime, coating the pipes and eventually causing the appearance of slime spots in the paper. 65. Filtration. —The aim of the paper maker is to remove the organic impurity from the water, which is very successfully accomplished by the use of the Warren or the Jewell type of gravity filter. In each of these systems, the water undergoes a preliminary treatment, as follows: 66. In the alum treatment , the water is first pumped into a deep box, and before passing on to the settling basin it is treated with a solution of sulphate of aluminum, as follows: The alum is mixed up strong in one tank and then run into another tank, where it is diluted to the required strength; it then passes through the pipe z, Fig. 16, and valve h to a small oblong box C, from which it is conveyed by the alum pump to the incoming water. The valve is provided with a ball floaty, which is so arranged that it will close the valve and stop the flow of the solution of alum when the box is full, thus preventing the alum from overflowing. The faster §17 MANUFACTURE OF PAPER 47 the pump works, the more alum solution flows into the box, so that it is kept at the same level all the time. The alum pump is operated by means of a turbine wheel, which is fastened to the side of the deep box previously mentioned, right over the opening from the box to the nar¬ row runway, so that all the water entering the runway must pass through the turbine wheel. There is a gearing on the rod / at the turbine that causes the rod to rotate, the speed varying with the speed of the turbine, and hence with the flow of water. The rod / has a similar gearing where it meets the gear-wheel e of the alum pump, which it causes to rotate. The pump consists of long, hollow arms a bent in the direction of the rotation. These arms when rotating pass through the alum solution, each one taking up its allotted portion of the same and conveying it to the drum b. From the drum, the solution is conveyed by six long tubes c to the bell d, where it is discharged. The bell is so arranged that it is outside of the box C, and deflects the alum solution so that it is deposited in the funnel j at the side of the box and conveyed to the incoming water. 199—31 48 MANUFACTURE OF PAPER §17 67. After treatment with the solution of alum, the water, when using the Warren system, passes through a long settling basin so arranged that it moves slowly out to the end of the basin, passes around a partition that extends down to the center of the basin, and returns on the other side. The size of this settling basin varies with the con¬ dition of the water to be treated. In some cases, from 45 minutes to 1 hour is required to make the passage around the basin, but usually only from 25 to 35 minutes is required. The object of the settling basin is to give the alum plenty of time to act and thoroughly coagulate the organic matter, some of which settles to the bottom of the basin, while the remainder passes into the filters. This is a very convenient arrangement, as it requires no special attention and supplies a uniform proportion of alum to the water; for as the flow of the water varies, the speed of the pump varies, and, therefore, the flow of the alum solution will vary. When the quantity of alum is to be reduced, it can be accomplished by plugging up one or more of the arms; hence, the operator generally speaks of using so many “plugs” of alum, meaning the number of arms that have been left open. If the water contains considerable organic matter, it is customary to use about 1 grain of alum to every gallon of water filtered. The following analysis shows the composition of a good alum for filter-plant use: Sulphate of aluminum Sulphate of iron . . Insoluble. Free alumina . . . . Water. Total. Per Cent. 53.98 .42 .71 .52 44.37 100.00 There are several forms of pressure filters used in some mills, but the gravity filters are the ones most generally adopted. 50 MANUFACTURE OF PAPER §17 FILTERS 68. Warren Filter. — The Warren filter, which is shown in Fig. 17, is usually constructed of wood and is 8 feet in diameter, having a bed with an area of 50 square feet. This filter contains from 20 to 24 inches of quartz sand c, supported on a perforated copper bottom b. The unfiltered water from the settling basin enters from the main j through the valve e , passes up into the filter tanka, and thence down¬ wards through the bed of sand c, the perforated plate b, and through the valve / to the filtered-water main i, through which it is conducted to a storage tank. When it becomes necessary to clean the filter, which will be evident from its sluggish action, the valve e is closed, shutting off the unfiltered water, and the valve on pipe g opened, allowing the water in tank a to pass into the sewer. When the level in a falls, the water flows back from the main i up through the bed of sand c, passing down the space p and gutter n, and then through waste pipe g. While this operation is going on, the agitator d, which should be set in motion as soon as the water commences to flow back through i, is caused to revolve by means of the mechanical arrange¬ ment k. While the agitator is in motion, the teeth of the rake, which is lowered mechanically by the screw m , stirs up all the sand. When the water flowing up through the bed becomes clear, the agitator is raised and the waste pipe closed, and when the tank is partly filled, the valve e is opened and filtration is carried on as before. Each 8-foot filter, when using alum, has a capacity of about 250,000 gallons in 24 hours. 69. Jewell Filter. —In the Jewell filter, which is shown in Fig. 18, the water coming direct from the alum treatment enters the subsidence basin a through inlet valve /, which is located a short distance above the bottom. This water is deflected in front of the inlet valve and flows slowly around the basin, thus depositing a great deal of the sedi¬ ment before reaching the filter bed. In order to reach the 17 MANUFACTURE OF PAPER 51 filter bed, the water passes up through the central stand pipe b and overflows. Enough water is kept above the sand to prevent the incoming water from cutting channels through it. The Jewell filter differs from the Warren filter in being a double tank, and instead of having a perforated plate, it has a bottom made up of a series of small strainers, which empty into small horizontal pipes. These pipes empty into larger ones c , and thence into the main outlet pipe h. Fig. 18 These strainers catch any sediment that passes through the sand. In washing the Jewell filter, the rakes of the agitator, which is set in motion, stir up the sand, and the water passing through it flows over the side of the inner tank into the outer tank, and thence out at the valve /. 70. The coagulant used in both the Jewell and the Warren filter is generally sulphate of aluminum, which is 52 MANUFACTURE OF PAPER §17 precipitated as hydrate by the alkalinity of the water, which, if not alkaline enough, should have a small amount of caustic lime added to it. This flocculent hydrate coagulates the organic matter present in the water and carries it down, thus freeing the water of its impurity. MANUFACTURE OF PAPER (PART 3) ANALYSES AND TESTS OF MATERIALS USED AND OF FINISHED PRODUCTS APPARATUS AND CHEMICALS 1. This Section will deal with methods of analysis of the chemicals, liquors, etc. used in the manufacture of paper, and will also contain methods of making several quick tests, by means of which the manufacturer may be enabled to operate his plant on an economical basis. It is important that the chemist in charge shall have on hand from the outset all the apparatus and chemicals that are likely to be needed at any time. Therefore, in order to give an idea of what will be required, a list of the apparatus and chemicals necessary for this purpose is here given. 2. Apparatus. —The following apparatus will be found necessary for the analytical work about to be described: A sensitive balance (enclosed in a glass case, the interior of which should be well desiccated) provided with a rider beam divided into tenths of milligrams, and a set of weights ran¬ ging from 1 milligram to 100 grams; one large and one small desiccator; several air-tight boxes with screw lids, for taking pulp samples; one large steam bath (which should be con¬ nected with a still); one hot-air bath and one water bath for slow evaporation; porcelain dishes, sizes 4 and 6 inches; COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS' HALL, LONDON 218 2 MANUFACTURE OF PAPER 18 measuring- flasks of the following capacities: 20, 50, 100, 250, 500, and 1,000 cubic centimeters, when filled to mark on neck; plain ungraduated flasks of the following capacities: 100, 250, 500, and 1,000 cubic centimeters; several 50-cubic- centimeter burettes, graduated into cubic centimeters and tenths of cubic centimeters, each provided with a stand; a set of pipettes, including the following sizes: 1, 2, 5, 10, 25, 50, and 100 cubic centimeters; a set of graduated cylinders of the following capacities: 100, 500, and 1,000 cubic centimeters (preferably glass-stoppered for mixing standards); several ungraduated cylinders, each having a capacity of about 200 cubic centimeters; beakers, lipped Griffin shape, from Nos. 1 to 6; watch glasses of various sizes and a pair of ground glasses and clips; one iron, one large porcelain, one small porcelain, and one agate mortar, with pestle; funnels of various sizes; a separating funnel; glass and rubber tubing, various sizes; a platinum dish having a capacity of 50 cubic centimeters; platinum crucibles, 15 and 25 grams capacity, respectively; platinum triangles for crucibles, and light and heavy platinum wire; ring-lamp stands and Bunsen burners; test tubes, various sizes; porcelain crucibles, various sizes; a condenser for distilling liquids; filter paper, various sizes; a filtering stand; a set of reagent bottles; sample bottles, various sizes; several liter bottles for standard solution; a wash bottle; a drying apparatus and train for CO, determina¬ tions; thermometers, 212° F. and 200° C.; short-stem Baume hydrometers of the following ranges: 3° to 4°, 0° to 5°, 0° to 8°, 0° to 15°, and 15° to 40°; stirring rods; forceps; spatulas; and pinch cocks. 3. Hydrometers.—The hydrometer, whether it be on a Twaddell or a Baume scale, is very useful about a paper mill. This instrument is used in all departments of the mill for the efficient regulation of the strengths of solu¬ tions used. The reading of the hydrometer is affected by the temperature, an increase in temperature decreasing the density of solutions. For this reason it is customary to add 1° Baume for each 30° of temperature over 60° F. This §18 MANUFACTURE OF PAPER 3 allowance, however, will only hold good for temperatures up to about 150° F. A greater allowance should be made for temperatures above this, about 4|° Baume being allowed for a temperature of about 185° F. 4. Drying Ovens. —There are several kinds of drying ovens, some of which are filled with water and heated by means of a gas burner under the bath. The bath shown in Fig. 1 has proved on all occasions to be a very convenient form of drying oven. It consists of a large copper box a, which has two drying compartments b closed by means of doors perforated at the bottom, each having a chimney c extending to the outside, to permit the free passage of air through the bath. In each compartment there are perforated shelves, which can be removed if desired. The compartments are so arranged that steam circulates all around them. The bath is connected with the still /, which serves as a feed for it by means of the small connecting pipe i, the water in the bath being kept at a constant level with the overflow pipe l of the still. The pipe g comes from 4 MANUFACTURE OF PAPER 18 the top of the bath and connects with the worm of the still, the distilled water escaping at m. The cooling water is fur¬ nished to the still through pipe h. The still is at such a height that the bath is always half full of water, which is kept at a slow boil by means of the steam coil, which enters at d and passes out at e. A pipe j extends into the bath between the two compartments, and is provided with a valve, which when open stops the preparation of distilled water. As a precaution against the steam being turned off, a gas line k provided with two burners is run under the bath. 5. Knofler Oven. —The Knofler drying oven is so arranged that the sample to be tested can be suspended on a balance beam and lowered into the drying compartments by means of a wire cage. The weight of the pulp can be read off at any time. This oven is convenient in that it is easy to determine when the pulp has become quite dry. 6. Chemicals. —The following is a list of the chem¬ icals necessary for all analytical tests given in the following pages. All chemicals used should be chemically pure or what is known as “analyzed chemicals.’’ Hydrochloric acid Barium hydrate Sulphuric acid Barium chloride Nitric acid Barium peroxide Acetic acid Bromine Oxalic acid Calcium chloride Arsenious acid Ether Sulphanilic acid Carbon bisulphide Alcohol Iron perchloride Aniline sulphate Iron protosulphate Ammonium oxalate Iron piano wire Ammonium phosphate Iron sulphide Ammonium sulphide Lead acetate Ammonium chloride Lead peroxide Ammonium sulphocyanide Mercury Methyl orange Sodium sulphate Manganese chloride Sodium phosphate §18 MANUFACTURE OF PAPER 5 Marble chips Phenol Platinic chloride Phloroglucine Phenol phthalein Potassium iodide Potassium ferrocyanide Potassium permanganate Potassium bisulphate Potassium chromate Potassium sulphate Potassium sulphocyanide Potassium chlorate Potassium hydrate Sodium carbonate, dry Sodium chloride Sodium sulphite Sodium hydrate Sodium acetate Sodium nitrate Soda lime Silver nitrate Starch Zinc sulphate Zinc chloride Zinc oxide Zinc shot standard 7 . Standard Solutions. —The following solutions will be found necessary: Normal sulphuric acid Normal hydrochloric acid Normal oxalic acid Normal sodium hydrate Normal sodium carbonate — sulphuric acid 10 — sodium hydrate — iodine 10 — sodium chloride 10 — silver nitrate 10 Standard potassium perman¬ ganate Standard size — sodium arsenite 10 Note.— means tenth normal. 8. The preceding standard solutions used in volumetric analysis are made up as follows: Normal sulphuric acid should be made up very carefully, as it will furnish a good standard, by the aid of which all the other standard acids and alkalies can be made up Take 30 cubic centimeters of H*SO< of about 1.84 specific gravity and mix with about 200 cubic centimeters of water. After cooling, transfer to a graduated mixing cylinder and dilute to 6 MANUFACTURE OF PAPER §18 1 liter. Two samples are taken to standardize, or rectify, this standard. They should be measured carefully from a clean burette that has first been rinsed with some of this acid. Take the two samples, one of 10 cubic centimeters and the other of 20 cubic centimeters, and dilute to about 250 cubic centimeters in separate beakers. Bring to a boil, and, while stirring, precipitate with a BaCl 2 solution containing 1 gram of BaCL in 10 cubic centimeters of water, taking care that all of the sulphuric acid is precipitated. Allow this to settle for about 2 hours, filter, wash well with hot water, dry, ignite, and weigh as BaSO<. The amount of NSO, in each sample is found, the two tests averaged, and the weight of H^SO^ in grams, in 1 cubic centimeter of the acid solution calculated. This divided into 49 will give the number of cubic centi¬ meters required to make 1 liter of the normal acid. In practical work, it will be found that much time cannot be spent in making up standard solutions, and it is therefore advisable to save this well-rectified standard and to use it for no other purpose than that of checking other standards. Tenth normal (—rj sulphuric acid can be prepared by measuring 100 cubic centimeters of the normal H 2 S0 t in an accurately graduated pipette that has been well cleaned and rinsed with the acid. The contents of the pipette is care¬ fully rinsed into a liter flask and diluted to the mark. This standard can be. rectified, if desired, in the same way as in the preceding case. Normal sodium carbonate is prepared by weighing out about 53 grams of dry sodium carbonate, dissolving in about 500 cubic centimeters of hot water, cooling, transferring to a liter flask, and diluting to the mark. This should be matched against the normal acid, using methyl orange as an indicator. Normal sodium hydrate is prepared by dissolving 50 grams of NaOH and diluting to 1 liter. Match against the normal acid, using methyl orange as an indicator. Dilute, if neces¬ sary, until 1 cubic centimeter is just equivalent to 1 cubic centimeter of normal acid. §18 MANUFACTURE OF PAPER 7 Tenth normal y—y sodium hydrate can be made by care¬ fully measuring- 100 cubic centimeters of the normal solution and diluting to 1 liter. This can be verified by matching against sulphuric acid. Normal hydrochloric acid is prepared by taking 100 cubic centimeters of HCl (1.2 specific gravity), diluting to 1 liter, and matching against normal soda solution, using methyl orange as an indicator. This acid can be further rectified by precipitating with silver nitrate and calculating the num¬ ber of cubic centimeters necessary to make 1 liter of strictly normal acid, as in the rectification of normal sulphuric acid. Normal oxalic acid is made by dissolving 63 grams of pure crystals of oxalic acid in distilled water and diluting almost to 1 liter. This normal solution can be rectified by match¬ ing against a strictly normal alkali. It should be kept in a dark place. Tenth normal sodium-arsenite solution is prepared as follows: Dissolve 50 grams of sodium bicarbonate in about 200 cubic centimeters of hot water and add 4.95 grams (accu¬ rately weighed) of chemically pure, dry, powdered arsenious acid, As 3 0 3 . Cover the beaker with a watch glass and allow the contents to remain almost at a boil, stirring from time to time, until all the arsenious acid is dissolved. Cool, transfer to a liter flask, and dilute to the mark. Arsenious acid dissolves more readily in the normal carbonate, but its use is not advisable, owing to secondary reactions, which interfere with the reaction between sodium arsenite and iodine. n 10 Tenth normal ( ) iodine solution is prepared by dissolving 12.7 grams of iodine with 18 grams of potassium iodide in 100 cubic centimeters of distilled water. If the potassium iodide is dissolved in a small amount of water, as directed, and the iodine then added, solution will take place very readily. The solution should not be heated. When dis- MANUFACTURE OF PAPER 8 §18 solved, the iodine solution is transferred to a liter flask and diluted almost to the mark. In order to rectify this solu- 71 tion, it is matched against the — sodium arsenite, using starch as an indicator. Standard potassium-pei'manganate solution is prepared as follows: Dissolve about 3.25 grams of pure crystals of potas¬ sium permanganate in 200 cubic centimeters of distilled water. Filter through a layer of asbestos, cool, dilute to about 1,000 cubic centimeters and mix thoroughly. The value of this solution in terms of iron is determined by titra¬ ting a solution containing a known quantity of iron. This can be done by the use of a solution of piano wire that is known to contain 99.6 per cent, of iron. Take a small flask having a capacity of about 250 cubic centimeters, and fill it one-third full of dilute sulphuric acid (1 volume of acid to 3 volumes of water); then add a few grains of sodium-carbon¬ ate crystals. Weigh accurately .2 gram of the wire into a flask, close with a rubber stopper provided with a valve, as shown in Fig. 2, and heat gently. When the wire is all dis¬ solved, the flask is cooled as rapidly as possible and the con¬ tents rinsed into a large beaker partly filled with recently boiled distilled water. This solution is now diluted to about 500 cubic centimeters and titrated with the permanganate solution until the faint pink tint is permanent. Since the iron wire is only 99.6 per cent, pure, there has been dissolved in reality only .2 X .996, or .1992 gram of pure iron. If it requires 25 cubic centimeters of permanganate, 1 cubic cen¬ timeter will be equivalent to .1992 -f- 25, or .007968 gram of iron. Standard size solution is prepared as follows: Dissolve 20 to 25 grams of good, heavy rosin size in about 250 cubic centimeters of 95-per-cent, alcohol, filter, and dilute almost to 1 liter with a 60-per-cent, alcohol solution. Add a little phenol phthalein and then add a solution of caustic soda, drop by drop, from a burette, shaking after each addition, until a faint pink color appears. This neutral-size solution §18 MANUFACTURE OF PAPER 9 is used as a standard after first determining its value. The value is determined by means of pure crystallized potassium alum, 1 part of which precipitates 2.36 parts of neutral rosin size. Weigh out 10 grams of the crystals that have pre¬ viously been pressed between two filter papers, dissolve, and dilute to 1 liter. One cubic centimeter will then contain .01 gram of alum. A flask with a capacity of about 200 cubic centimeters is then filled about two-thirds full of distilled water, and 20 cubic centimeters of this size solution is run in from a burette. The alum solution is then run in from another burette, a few drops at a time. The flask is then closed with a stopper, shaken vigorously, and allowed to stand after each addition until the precipitate rises to the top, which it will do very rapidly. This is continued until the solution is left perfectly clear, after the precipitate has risen. The number of cubic centimeters of alum used multiplied by .01 will give the amount of alum, in grams, required to pre¬ cipitate 20 cubic centimeters of standard size; this multiplied by 2.36 will give the number of grams of neutral size in 20 cubic centimeters of this solution. If 10 cubic centimeters of the alum solution is used, 20 cubic centimeters of the standard size will contain .236 gram of neutral rosin size. sodium-chloride solution is prepared by accurately weighing 5.837 grams of chemically pure sodium chloride (which has been previously heated in a covered platinum crucible to a low red heat for several minutes and cooled in a desiccator), dissolving in distilled water, and making up to 1 liter. It is always advisable to keep this 71 standard solution on hand to assist in making up silver- nitrate solutions. solution is prepared by weighing out 17 grams of pure crystallized silver nitrate, dis¬ solving, and diluting to almost 1 liter. This solution is then matched sodium-chloride solution, using MANUFACTURE OF PAPER 10 §18 potassium chromate as an indicator, and adjusted to exact 7Z — solution. One cubic centimeter of this silver-nitrate solution will then be equivalent to .00355 gram of chlorine, or .00585 gram of sodium chloride. 9. Indicators. —The following indicators will be found necessary: Phenol phthalein is soluble in 50-per-cent, alcohol, and is made up for use as follows: Take a mixture of 105 cubic centimeters of alcohol (95 per cent.)' and 95 cubic centi¬ meters of water. Add to this 2 grams of phenol phthalein and stir until all is dissolved. A few drops of this indicator will be sufficient for titrating; it will produce no color in acid liquids, but the slightest trace of caustic alkali will change it to purple red. This indicator can be used in alcoholic solutions and is useful in titrating organic acids, but it is not reliable in the presence of carbonates in cold solution. Methyl orange containing impurities that are not soluble in water should be recrystallized from alcohol. This indicator should not be used for titrating organic acids. A convenient strength is .1 gram to 100 cubic centimeters of water. One or two drops is sufficient for 100 to 150 cubic centimeters of the solution to be titrated. A good end reaction cannot be obtained if too much of the indicator is used. This indicator gives a very sharp end point in the presence of carbonates, and is therefore very useful in the titration of the alkali carbonates. Starch is prepared as follows: About 300 cubic centimeters of water is brought to a boil in a flask having a capacity of about 1 liter. Four grams of starch is then mixed in a little cold water until all the lumps are broken and it forms a thin, pasty mass; this is added to the boiling water, and the whole allowed to boil for 5 minutes. A mixture of 5 grams of zinc chloride in a little water is then added, and the whole allowed to boil 1 minute longer. This mixture is then removed from the flame, diluted to about 900 cubic centimeters, well §18 MANUFACTURE OF PAPER 11 mixed, and allowed to stand overnight. The clear starch solution is then decanted into a bottle and is ready for use. Iodized starch is made by taking some of the starch solu¬ tion just mentioned and adding a small amount of a solution of potassium iodide. Potassium chromate of a convenient strength is made by adding 1 gram to 10 cubic centimeters of water. A few drops of the solution will be sufficient for 100 to 150 cubic centimeters of the solution to be titrated. ANALYTICAL METHODS 10. Analysis of Soda Ash. —The usual determination made in soda ash is for sodium oxide; if it falls below the requirement in this, free caustic soda and sulphuric acid are determined. The material should first be carefully sampled. If the soda ash is received in bags, a portion should be taken from each of seven or eight bags selected at random from each car and thoroughly mixed. This composite sample should then be quartered down until a sample of convenient size is obtained. Determination of Sodium Oxide. —Weigh out 15.5 grams of the sample, dissolve in about 400 cubic centimeters of hot water, let cool, wash into a liter flask, and dilute to the mark. Measure out 100 cubic centimeters of this solution into a beaker by means of a pipette, add two drops of methyl orange, and titrate with a normal acid. The number of cubic centimeters of the normal acid used multiplied by 2 will give the percentage of sodium oxide in the sample. Good soda ash made by the Solvay process should contain 58 per cent, of sodium oxide; that made by the LeBlanc process, about 48 per cent, of sodium oxide. Determination of Free Caustic Soda. —If it is desired to test for caustic soda, measure out 100 cubic centimeters of the original solution and add a slight excess of neutral barium chloride, to precipitate all the carbonate. Filter off the precipitated BaCO 2 and titrate the filtrate with normal acid, using phenol phthalein as an indicator. 199--32 12 MANUFACTURE OF PAPER §18 Determination of Sulphuric Acid. —Take 100 cubic centi¬ meters of the solution, equivalent to 1.55 grams of ash, acidify carefully with hydrochloric acid, bring to a boil, and precipitate the H 2 S0 4 as BaSO t by means of barium chloride. Let stand in a warm place for about 2 hours, to settle the precipitate. Decant the clear liquid through an ashless filter paper, then wash the precipitate upon it, and wash thoroughly with hot water. Dry, ignite, and weigh as BaSO t . The weight of the BaSO t multiplied by the factor .34335 will give the weight of the S0 3 , and this multiplied by 100 and divided by 1.55, the weight of ash taken, will give the per¬ centage of S0 3 in the ash. This is calculated to Na 3 S0 4 , according to the following proportion: S0 3 : Na 3 S0 4 = percentage of S0 3 : percentage of Na 3 S0 4 °, or, 80 : 142 = percentage of S0 3 : x; whence, x = percentage of Na 2 S0 4 Soda ash is usually sold on the New Castle test, which is based on the erroneous atomic weight of sodium (24). When getting the actual alkali, it is advisable also to report it in terms of the New Castle test, by multiplying actual alkali found by 1.032. Soda is sold on a guarantee of 58 per cent. Na 2 0, and many chemists have rejected cars that have fallen below this test, to find later that the soda had been bought on a guarantee of 58 per cent., according to the New Castle test. 11. Analysis of Causticizing Lime.—Causticizing lime is used for converting the carbonate of soda into caustic soda. The caustic lime when added to the carbonate solu¬ tion is first converted into Ca{OH) 3 , which reacts with the sodium carbonate, forming caustic soda and calcium car¬ bonate, the latter settling to the bottom of the tank as lime sludge. A good lime for this purpose should be well burned, as free as possible from impurities, and contain a high per¬ centage of CaO. Lime that is slaked when received is not suitable for causticizing, as more of it is required to do the same work than if unslaked. In analyzing lime ordinarily, calcium oxide, carbon dioxide, and water only are determined. 18 MANUFACTURE OF PAPER 13 Sampling the Lime. —A very large sample should be taken from different parts of the car and the whole broken up into lumps about the size of a pea. This sample should then be mixed thoroughly and quartered several times, to reduce to a small sample. This small sample should be ground very fine, well mixed, and kept in a tightly corked bottle. Determination of Calcium Oxide. —Weigh out 10 grams of the sample, slake, and wash carefully into a 500-cubic-centi¬ meter flask, filling it to the mark. Take 50 cubic centimeters of the clear solution, which is equivalent to 1 gram of lime, wash into a beaker, and titrate with normal oxalic acid, using phenol phthalein as an indicator. The number of cubic centimeters of normal acid used multiplied by 2.8 will give the percentage of CaO in the sample, which includes also the magnesium oxide; but as the percentage of the latter oxide in this lime is very low, its presence can for all prac¬ tical purposes be disregarded. Determination of Carbon Dioxide. —Carbon dioxide can be very accurately determined by treating a carefully weighed sample in a flask with hydrochloric acid and absorbing the liberated C0 2 in a Geissler bulb containing a solution of potassium hydroxide (1 to 1). This method, however, necessitates the use of a drying apparatus for the air that passes through the flask and also a train of U tubes with an aspirating bottle at the end of the train. For all practical purposes, the C0 3 may be determined as follows: After shaking, take 50 cubic centimeters of the solution used for the calcium-oxide determination, add from a burette an excess of normal hydrochloric acid, and titrate the excess of acid with normal sodium hydrate. The number of cubic centimeters of hydrochloric acid used less the number of cubic centimeters in excess, as found by the sodium-hydrate titra¬ tion, is the total number of cubic centimeters neutralized by the CaO and CaC0 3 . The number of cubic centimeters thus found less the number of cubic centimeters of normal oxalic acid used in the estimation of calcium oxide, is the number of cubic centimeters of hydrochloric acid used in titrating the 14 MANUFACTURE OF PAPER 18 CaC0 3 . This number multiplied by 5 will give the percentage of CaC0 3 in the sample. To find the percentage of C0 3 , mul¬ tiply the percentage of CaC0 3 by .44. Determination of Water.— The amount of water can be determined by weighing 1 gram of the lime sample in a platinum crucible, gently heating at first, and gradually rais¬ ing the temperature to a strong red heat. Cool in a desic¬ cator and weigh quickly. Repeat until a constant weight is obtained. The loss in weight will be due to water and C0 2 . Determine the C0 3 as in the previous case. Subtract the weight of the C0 2 in 1 gram from the total loss of weight on heating. The difference will be the loss due to water. This weight multiplied by 100 will give the percentage of water in the sample. 12 . Complete Analysis of Dime. —When a complete analysis of lime is desired, the following determinations are usually made: Silica, sesquioxides of iron and aluminum, calcium oxide, magnesium oxide, sulphuric acid, and carbon dioxide. Determination of Silica. —Weigh out 2 grams of the care¬ fully prepared sample and fuse in a platinum crucible with about 8 grams of sodium carbonate. Dissolve the fused mass with hot water in a porcelain dish with the use of a slight excess of dilute hydrochloric acid, keeping it well cov¬ ered with a watch glass. Boil and evaporate to dryness. Moisten thoroughly with strong hydrochloric acid, and again evaporate to complete dryness. Take up in dilute hydro¬ chloric acid, boil, and filter through an ashless filter, using a “policeman,” or rubber-tipped glass rod, to remove the fine particles of silica from the dish. Wash thoroughly with hot water. Collect the filtrate and washing in a 200-cubic- centimeter flask, cool, and fill to the mark. Transfer the filter paper and residue to a crucible, ignite, and weigh. The weight of the residue multiplied by 50 will give the percentage of Si0 3 in the sample. Determination of Sesquioxides of Iron and Aluminum. —Take 100 cubic centimeters of the filtrate from the silica deter- 18 MANUFACTURE OF PAPER 15 mination, heat nearly to boiling, add a few drops of nitric acid, and precipitate the iron and aluminum with a slight excess of ammonium hydrate. Then take up again in a slight excess of hydrochloric acid, and reprecipitate with a slight excess of ammonium hydrate, bring to a boil, and allow to boil gently until the odor of ammonia is no longer perceptible. Allow the precipitate to settle, decant the clear liquid through an ashless filter, wash several times by decantation, boiling with water each time, and finally collect the precipitate on the filter. Dry in an oven, transfer to a weighed crucible, ignite, and weigh as Al 2 O a + Fe 2 0 3 . This weight multiplied by 100 will give the percentage of these mixed oxides in the sample. Determi?iation of Calcium Oxide. —Heat the filtrate from the previous analysis to boiling and add a slight excess of ammonium-oxalate solution, stirring for several minutes. Allow this to settle for about 3 hours, wash well with hot water, and dry. Transfer the precipitate to a platinum crucible, burn the filter paper, and add its ash. Treat with a few drops of dilute sulphuric acid, heat gently, to drive off the excess of H 3 S0 4 , then heat to redness, cool in a desic¬ cator, and weigh as calcium sulphate. This weight, multi¬ plied by .412 X 100 will give the percentage of CaO in the sample. Instead of treating the precipitate with H 3 SO t , it may be converted directly into CaO by igniting to constant weight, which requires a long ignition over the blast lamp. This weight multiplied by 100 will give the percentage of CaO. Determination of Magnesium Oxide. —The filtrate from the calcium-oxide determination is acidified with HCl , an excess of sodium phosphate added, and concentrated by evaporation to about 200 cubic centimeters. It is then cooled, preferably in ice water, and NFLO FI added drop by drop, while stirring, until a precipitate begins to form. After standing about 15 minutes, 50 cubic centimeters of strong NIhOH is added. Allow to settle for about 2 hours, filter, and wash with ammonia water made of 1 part of ammonia hydroxide (.96 specific gravity) and 4 parts of water. Dry, transfer 16 MANUFACTURE OF PAPER §18 the precipitate to a porcelain crucible, burn the filter, and add its ash. Then ignite to constant weight, over the blast, and weigh as magnesium pyrophosphate, Mg^P^O.,. This weight multiplied by .36036 X 100 will give the percentage of MgO in the sample. Determination of Sulphuric Acid. —Take the remaining 100 cubic centimeters of the filtrate from the silica deter¬ mination, heat to boiling, and precipitate the sulphuric acid as BaSOt with barium chloride. Let stand in a warm place for about 2 hours, or until the precipitate is settled. Decant the clear liquid through an ashless filter, wash twice by decantation with hot water, and finally on the filter with hot water, until a few drops of the filtrate give no test for chlorides with silver nitrate. Dry, transfer to a crucible, burn the filter as before, and ignite to constant weight. The weight of the BaSO 4 multiplied by .34335 X 100 will give the percentage of S0 3 in the sample. Determination of Carbon Dioxide. — The carbon-dioxide determination should be made as described in Art. 11. The following analysis shows the composition of a good causticizing lime: Per Cent. Silica, Si0 2 . .62 Be 2 0 3 -f- Al 2 0 3 .84 Calcium oxide, CaO .95.91 Magnesium oxide, MgO . .51 Carbon dioxide, C0 2 . .92 Water. 1.15 Undetermined . .05 Total.100.00 13. Analysis of Magnesia Lime. —Magnesia lime is used for making up bisulphite liquors for the sulphite process. The lime should be well burned, contain high percentages of both calcium and magnesium oxides, and be fairly free from impurities. The same determinations are made as in causticizing lime and the same methods used. In the determination of calcium and magnesium oxides, owing to the fact that some magnesium oxalate will be pre- 18 MANUFACTURE OF PAPER 17 cipitated with the calcium oxalate, the following precautions should be taken: Precipitate the calcium oxalate in the usual manner, and, after a slight washing, redissolve the precipitate in hydrochloric acid, make ammoniacal, reprecipitate the cal¬ cium, filter, wash, and treat the calcium oxalate, as previously described. The filtrates are combined, the whole acidified with HCl , sodium phosphate added, evaporated to 200 cubic centimeters, cooled, and the magnesium precipitated with ammonia, as in the preceding article. In accurate work, it is essential that a double precipitation of the calcium be made, both in the case of a causticizing lime and a magnesia lime. It is also advisable to make a double precipitation of the magnesia. The following is an analysis of a good magnesia lime for the sulphite process: Per Cent. Silica and insoluble. .22 Fe,0, + Al,O a .19 Calcium oxide, CaO . 50.92 Magnesium oxide, MgO .. 44.32 5a ... .. i.5i Water. 1.23 Carbon dioxide, CO, . 1.48 Undetermined . .13 Total.100.00 14 . Analysis of Sludge From Causticizing Pans. The sludge from the causticizing pans is tested in order to determine the loss in per cent, of soda, etc. at this point. After the liquor from the third wash has been run off as low as possible, the sludge is well agitated and a sample taken. The determinations usually made are insoluble matter, sodium oxide, calcium oxide, calcium carbonate, and moisture. Determination of Insoluble Matter .—Weigh out 20 grams, or more if necessary, of the sample in a small beaker. Trans¬ fer to a porcelain dish, take up with an excess of hydro¬ chloric acid, and evaporate to dryness to expel all HCl. 18 MANUFACTURE OF PAPER §18 Take up again in hydrochloric acid and water, boil, filter, and wash the residue thoroughly with hot water. Ignite in a crucible to constant weight. This weight multiplied by 100 and divided by the weight of the sample taken will give the percentage of insoluble matter. Determination of Sodium Oxide. — Weigh out approxi¬ mately 45 or 50 grams of the sample, transfer to a porcelain dish and evaporate to dryness with a little ammonium car¬ bonate. Take up with water and repeat this evaporation with ammonium carbonate. Take up again in hot water and allow to remain almost at a boil for some time. Filter into a 500-cubic-centimeter flask, wash thoroughly with hot water, cool filtrate and washings, and fill up to the mark. Take 100 cubic centimeters of this filtrate and titrate with a normal acid, using methyl orange as an indicator. The num¬ ber of cubic centimeters of acid required multiplied by .031 will give the weight, in grams, of the sodium oxide in 100 cubic centimeters of the solution. This weight multi¬ plied by 5 X 100 and divided by the weight of sludge used in making the sample solution will give the percentage of Na 2 0 in the sludge. Determination of Caustic Lime. — Take 100 cubic centi¬ meters of the sludge, weigh in a 100-cubic-centimeter flask, wash into a beaker, and titrate with normal oxalic acid, using phenol phthalein as an indicator. The number of cubic centimeters required less the number of cubic centimeters neutralized by the Na^O, as calculated for the weight of sludge used from the data obtained in the sodium-oxide determination, is the number of cubic centimeters of normal oxalic acid neutralized by the CaO. This number multiplied by .028 (the value of 1 cubic centimeter of normal oxalic acid in lime) X 100 and divided by the weight of the sludge taken will give the percentage of calcium oxide, or caustic lime. Determination of Calcium Carbo?iate. —Take about 10 grams of the sludge, after agitating well, and titrate with normal hydrochloric acid, using methyl orange as an indicator. The number of cubic centimeters of acid used less the number §18 MANUFACTURE OF PAPER 19 required for sodium oxide and for caustic lime, as previously determined for the same weight of sample, is the number of cubic centimeters of normal. acid neutralized by the calcium carbonate. This number multiplied by .05 will give the weight of calcium carbonate in the sample taken. This weight multiplied by 100 and divided by the weight of sludge taken will give the percentage of calcium carbonate. Determination of Moisture .—The determination of the amount of moisture is made by weighing out about 50 grams of the sample as quickly as possible and drying at 100° C. to constant weight. The loss in weight multiplied by 100 and divided by the weight of sample taken will give the percent¬ age of moisture. Other constituents of sludge may be determined by methods given in Art. 12. The following is an analysis of a lime sludge: Per Cent. Moisture . 76.780 Silica, Si0 2 . .090 Fe 2 0 3 -f- Al 2 0 3 . .250 Magnesium oxide, MgO . .085 Sodium oxide, Na 2 0 . .350 Calcium hydrate, Ca{OH) 2 . 1.070 Calcium carbonate, CaC0 3 . 21.290 Undetermined.•. .085 Total. 100.000 15. Analysis of Bleaching Powder. —The value of bleaching powder depends on the percentage of available chlorine in it. On standing, bleaching powder loses its strength, especially if kept in a damp place. A good bleach¬ ing powder should contain from 36 to 37 per cent, of avail¬ able chlorine, but it is generally accepted if it tests over 35 per cent. Sampling .—In order to get a fair sample from a car, small samples should be taken from at least five casks. This is best done by means of a long, i-inch copper tube, which is thrust into the cask after boring a hole in it, withdrawn, and the contents transferred to the sample bottle by gently tap¬ ping the tube. The sample bottle should be perfectly dry 20 MANUFACTURE OF PAPER 18 and kept closed as much as possible. Analysis should be made as soon as sample is taken, and as quickly as possible. Determination of Available Chlorine. —Weigh out 7.1 grams of the well-mixed sample, transfer to a porcelain mortar, add a little water, and grind with the pestle, taking care to avoid loss. Allow to settle for a moment and decant into a liter flask. Repeat this three times, and finally wash the contents of the mortar into the flask, using a clean finger to rub off the mortar and pestle. Fill to the mark with water, shake well, and transfer 50 cubic centimeters to a beaker by means of a pipette. Titrate with — sodium-arsenite solution, stir- 10 ring while adding the standard. The end point is reached when a drop of the solution no longer gives the blue colora¬ tion to iodized-starch paper (this paper is prepared by soaking strips of filter paper in iodized-starch solution). When the quantity of sample just mentioned is used, each cubic centimeter of the standard used is equivalent to 1 per cent, of available chlorine. With practice, this test can be made rapidly and with good results. The bleaching powder should be tested as soon as possible after sampling, and after starting to test there should be no delay, as otherwise the results will come too low. Determhiatio7i of Chlorate. —Sometimes it is necessary to determine the amount of chlorate present in bleaching powder. For all practical purposes, this can be done by adding a little dilute sulphuric acid to the sample that has been titrated for available chlorine and rapidly titrating again, thus determining the chlorine present as chlorate. The following is a complete analysis of bleaching powder: Per Cent. Available chlorine . . . 36.80 Chlorine as chlorate. .22 Chlorine as chloride. .42 Lime, CaO . 43.98 Magnesia, MgO . .39 Fe^O* + Al t O . . .41 Water (by difference). 17.78 Total. 100.00 §18 MANUFACTURE OF PAPER . 21 16 . Analysis of Bleacli Sludge.— It is important that the bleach sludge should be tested from time to time, to ascertain the loss of available chlorine in the dump. The sludge, after drawing off the wash as closely as possible, should be agitated and the sample taken. Determination of Available Chlorine. —Measure 50 cubic centimeters of the well-mixed sample into a beaker by means of a pipette, which is rinsed out into the beaker. Titrate with — sodium arsenite as before. The number of cubic centimeters used multiplied by .071 gives the number of grams of available chlorine per liter of sludge, and this multiplied by 3.785 (the number of liters in 1 gallon) gives the weight of available chlorine in 1 gallon. This weight multiplied by 3 gives the approximate loss of bleaching powder in 1 gallon, and, knowing the cubical contents of the tank and the number of inches dumped, the loss in the dump can be easily calculated. In a bleach that settles well, this loss ranges from .6 per cent, to 1 per cent, of the bleach mixed. If the bleach does not settle well, the loss will reach 3 per cent, and may go even higher. 17 . Analysis of Black Asli. —Black ash is the ash that is recovered after the liquor used in the soda process, in which the wood has been cooked, has been evaporated and burned. Preparation of Sample. —Quite a large sample should be taken, ground up, mixed, and quartered several times. The last portion should be ground very fine and well mixed in the sample bottle. Weigh out 50 grams of this carefully prepared sample and boil up with water. Stir well from time to time for at least 1 hour, filter into a liter flask, wash well, cool, and dilute to the mark. It is customary to make determinations of caustic soda, sodium sulphide, sodium carbonate, sodium sulphate, and sodium chloride. Determination of Caustic Soda. Take 50 cubic centimeters of the clear liquid and precipitate the carbonate with a slight 22 MANUFACTURE OF PAPER §18 excess of neutral barium-chloride solution in a 200-cubic- centimeter flask, add hot water, shake well, cool, fill to the mark, and after again shaking, allow to settle. Take 100 cubic centimeters of the clear portion and titrate with normal acid, using methyl orange as an indicator. Multiplying the number of cubic centimeters of acid used by 4 and dividing by 1.25 will give the percentage of NaOH in the ash. This also includes any JVa 2 S present, and if it is considerable, the number of cubic centimeters of standard ahid neutralized by it must be deducted from the whole before the calculation of the caustic soda is made. Determination of Sodium Sulphide .—Take 25 cubic centi¬ meters of the clear liquor, equivalent to 1.25 grams of the ash, dilute to 200 cubic centimeters with recently boiled water, acidify with acetic acid, and titrate quickly with 71 — iodine solution, using starch as an indicator. The num¬ ber of cubic centimeters of standard used multiplied by .39 and divided by 1.25 will give the percentage of Na 2 S in the ash. Determination of Sodium Carbonate .—Take 25 cubic centi¬ meters of the original clear liquor and titrate with normal hydrochloric acid, using methyl orange as an indicator. The number of cubic centimeters of acid used less the number of cubic centimeters neutralized by the caustic soda, as determined for the same volume of liquor, multiplied by 5.3 and divided by 1.25 will give the percentage of Na 2 C0 3 in the ash. Determination of Sodium Chloride .—Take 25 cubic centi¬ meters of the clear liquor, neutralize with nitric acid, and boil to expel hydrogen sulphide. Filter, wash, cool, add a * 71 little potassium-chromate indicator, and titrate with -- silver- nitrate solution. The number of cubic centimeters of silver nitrate required multiplied by .585 and divided by 1.25 will give the percentage of sodium chloride in the ash. Determination of Sodium Sulphate .—The amount of sodium sulphate can be determined by dissolving 25 grams of ash in 18 MANUFACTURE OF PAPER 23 hot water, filtering and washing well, acidifying the filtrate slightly with hydrochloric acid, boiling to expel all C0 2 , and precipitating with a slight excess of barium-chloride sol¬ ution. Let stand in a warm place until settled, filter, and wash thoroughly with hot water. Dry, ignite in a crucible, and weigh as BaSO A . Calculate to Na 2 SO A by multiplying by .6094. The weight of Na a SO A multiplied by 4 will give its percentage in the ash. The following is an analysis of a sample of black ash: Per Cent. Sodium carbonate. 78.15 Sodium hydrate. 1-83 Sodium sulphate. 2.55 Sodium sulphide. .50 Sodium chloride .. 6.60 Carbon. 4.30 Silica. 5.10 Calcium carbonate.. . . -72 Undetermined (difference). .25 Total.100.00 18. Analysis of Alum. —In the paper industry, the term alum is applied to sulphate of aluminum, AL{SO a ) 3 - 18 H 2 0, which, strictly speaking, is not an alum. The analysis of an alum is quite long and complicated, but if carried on with care, very good results can be obtained. The following determinations and tests are usually made: Determination of Water— Weigh out 2 grams of the well- mixed sample into a platinum crucible. Heat gradually until a low red heat is reached, and allow to remain at this temperature until fumes of S0 3 are perceptible. Cool in a desiccator and weigh. The loss of weight gives the amount of water, together with some S0 3 . The loss of SO a may be determined as follows: Add about 10 cubic centimeters of hot, concentrated, hydrochloric acid to the contents of the crucible and allow to stand in a warm place for about half an hour, when the lumps will be all broken down, provided the heating was not 24 MANUFACTURE OF PAPER §18 too high or too long when driving off the water. The con¬ tents of the crucible should then be washed into a small beaker with hot water, diluted to about 50 cubic centimeters, and heated until all is dissolved, except what little insoluble matter there may be in the alum. Filter and wash well with hot water. Precipitate the sulphuric acid in the filtrate with barium chloride, as in the determination of sulphuric acid described in Art. 10 . Filter, wash well with hot water, dry, and ignite to constant weight. The weight of BaSO, multi¬ plied by .34835 will give the weight of S0 3 . This weight sub¬ tracted from the weight of the total in the same weight of sample, as found by a separate determination, will give the loss of weight due to S0 3 . Subtracting this loss from the total loss on heating will give the loss due to water, and this multiplied by 50 will give the percentage of water in the alum. Determination of Insoluble Matter. —Weigh out 20 grams of the alum and dissolve in about 300 cubic centimeters of hot water. Filter through an ashless filter into a liter flask, and wash well with hot water. Dry, ignite, and weigh the residue, the weight of which multiplied by 5 will give the percentage of insoluble matter in the alum. Cool the filtrate and dilute to the mark. Determination of Alumina. —The alumina and ferric oxide are determined together. The ferric oxide is determined in a separate portion and subtracted from the mixed oxides, giving the alumina. Take 50 cubic centimeters of the filtrate from the insol¬ uble determination (equivalent to 1 gram of alum), dilute to 200 cubic centimeters, add a few drops of nitric acid, and precipitate with a slight excess of ammonium hydrate. Neutralize the excess of ammonia with hydrochloric acid, add NH a ft fejo—; 4> rt G Oh C/2 Tt LD VO VO 00 00 o o HH 01 CO Tt in vo LO lO m m m m VO VO VO VO vO vo VO vo vo y >* tG -ft rx 00 On o 01 CO Tt in VO tx 00 ON o HH 'o > (U Cfi oi 01 Ol CO co CO co co co co co CO co Tt Tt co CO co CO co co co CO co CO co CO CO CO CO cvfc tcO M HH M HH HH HH w HH *"* HH HH 1-1 HH HH ±i ft* 3 G O ft VC 00 VO Tt VO Tt Cl Tt 01 Tt 01 Tt 01 Tt 01 o , cc .-t: Cl co Tt" m VO rx 00 On o HH 01 co Tt in VO HH t-H HH HH HH HH HH HH 01 01 Cl 01 N 01 01 , cc ,ti 00 ON o HH 01 co Tt in VO 00 On o HH ON On On o o o o o o O o o O HH HH g P-i cc 6 HH CN| co Tt m VO tx 00 On o HH Ol co Tt HH HH HH HH HH HH Cl Cl Cl Cl Cl Cl co Tt m VO 00 O' o M Cl co Tt m VO o > a> ctf 00 00 00 00 00 00 00 00 ON On On On ON On ON 01 01 01 01 01 01 01 01 Cl 01 Ol 01 01 01 01 a, *-< HH HH . HH HH HH HI M w M HH ►H HH ►H l-t 45 46 MANUFACTURE OF PAPER §18 well with hot water. The residue can be ignited and weighed for the determination of insoluble matter. Dilute the filtrate to the mark, take 100 cubic centimeters and precipitate the sulphur as BaSO t with barium chloride in the usual manner, filter, dry, ignite, and weigh as BaSO<, and calculate to sulphur by multiplying by .13734. The weight of the sulphur thus found multiplied by 1,000 will give its percentage in the sample. The following is an analysis of sulphur: Per Cent. Moisture . • • Foreign matter Sulphur . • • Total . . • Ash. .24 .63 99.13 100.00 .27 28. Analysis of Jiisulpliite Liquor. —Bisulphite liquor, which is used in the manufacture of sulphite pulp, consists principally of calcium bisulphite, CaH,S,0 6 , mag¬ nesium bisulphite, MgH,S,0 & , and calcium sulphate, CaSO 4 , together with free sulphur dioxide, SO,. The ordinary tests made to control the working of the liquor are volumetric tests for total sulphur dioxide, S0. 2 , by titrating with iodine solution, using starch as an indicator, and for free SO, by titrating with ~ sodium-hydrate solution, using phenol phthalein as an indicator. For each of these tests, 2 cubic centimeters of liquor should be used. The difference between the total SO, and the free SO, is the com¬ bined SO,. The term available SO, would be better to use than free SO, to express the total acidity. There would then be no confusion about what is meant. Some designate as free SO, only that SO, which is in excess of that necessary to form bisulphites with the bases present, while others call free SO, all that is present in excess of that necessary to form monosulphites with the bases present. A complete gravimetric analysis of the hquor is often required, and can be made according to the following methods: §18 MANUFACTURE OF PAPER 47 Determination of Silica. —Take 10 cubic centimeters of the liquor in a porcelain dish and weigh; add 5 cubic centi¬ meters of hydrochloric acid and evaporate to dryness. Drive off the excess of acid by gently heating, and take up in 5 cubic centimeters of dilute hydrochloric acid. Dilute to about 100 cubic centimeters, boil, filter, wash well with hot water, dry, ignite, and weigh as SiO t . The specific gravity of the liquor should be taken, and this multiplied by 10 will give the weight in grams of the liquor taken for the test. The weight of silica found multi¬ plied by 100 and divided by the weight of liquor taken will give the percentage of silica. Determination of Sesguioxides of Iron and Aluminum. —Treat the filtrate from the silica determination with N1DOH, to pre¬ cipitate the hydrates of iron and aluminum. Proceed as in Art. 12. The weight of the oxides multiplied by 100 and divi¬ ded by the weight of liquor taken, as found in the silica deter¬ mination, will give the percentage of these oxides in the liquor. Determination of Calcium Oxide. —Concentrate the filtrate from the preceding determination to about 200 cubic centi¬ meters. Heat to boiling, and precipitate the calcium as oxalate with ammonium oxalate, as in Art. 12. Calculate the percentage of CaO in the usual manner. Determination of Magnesium Oxide. —Evaporate the filtrate from the calcium-oxide determination, and proceed as directed in Art. 12. The weight of the magnesium pyrophosphate multiplied by 100 X .36036 and divided by the weight of liquor taken will give the percentage of MgO in the sample. Determination of Sodium Oxide. —Take 25 cubic centimeters of the liquor, precipitate the heavy bases with ammonia car¬ bonate, filter and wash, and after treating with a little dilute sulphuric acid, evaporate the filtrate in a platinum dish. Ignite until all sulphuric acid is driven off, cool, and weigh as Na^SO*. The weight of the Na^SO^ multiplied by .43694 X 100 and divided by the weight of the sample taken will give the percentage of sodium oxide. Determination of Sulphuric Acid. —Treat 10 cubic centi¬ meters of the liquor in a porcelain dish with 5 cubic centi- 48 MANUFACTURE OF PAPER §18 meters of hydrochloric acid, and evaporate nearly to dryness to drive off the sulphur dioxide; dilute and precipitate with BaCl ,. If the mixture of sulphuric and hydrochloric acids should come to dryness, take up with a little hydrochloric acid, dilute, and precipitate with barium chloride, as directed in Art. 12. The weight of BaSO 4 multiplied by 100 X .34335 and divided by the weight of the sample taken will give the percentage of S0 3 in the liquor. Determinatio7i of Sulphur Dioxide. —Oxidize 10 cubic cen¬ timeters of the liquor with 10 cubic centimeters of bromine water, pouring the liquor into the bromine water. Heat, dilute, and boil to drive off the excess of bromine. Precipi¬ tate with barium chloride, as in Art. 12. Calculate the S0 3 as in the previous analysis, and subtract the amount found there from the amount just found. The difference will be the S0 3 from the oxidation of the S0 3 . This weight multi¬ plied by 100 X .18001 and divided by the weight of the sample taken will give the percentage of S0 3 in the liquor. In calculating the results of the liquor analysis, the sulphuric acid is combined with lime to form calcium sulphate, CaSO t . If there is less lime than is necessary to saturate the S0 3 , the balance of the S0 3 is calculated to magnesium sulphate, MgSO<. Any excess of lime is calculated to calcium bisulphite, CaH 3 S 3 0 3 . If there is more S0 3 than is necessary to combine with all the lime, the magnesium oxide is calculated first to the monosulphite, MgS0 3 , and if there is an excess of S0 2 , to the bisulphite, MgH 3 S 3 O e . Any further excess is reported as free S0 3 . The following is an analysis of a good bisulphite liquor: Per Cent. Silica, Si0 3 .07 Fe,0 3 + A 1,0, .02 Bisulphite of lime, CaH 2 S 3 0 3 . 2.76 Bisulphite of magnesia, MgH 3 S 3 0, . 3.19 Calcium sulphate, CaSO . .16 Free sulphur dioxide, S0 3 . . ..14 Water and undetermined.93.66 Total..‘.10a00 §18 MANUFACTURE OF PAPER 49 Ordinarily, the total acidity as determined by titration with standard soda solution, with phenol phthalein as an indicator, is calculated as free S0 2 . This is, of course, the SO, over and above that required to form the monosulphite instead of the bisulphite, as expressed in the preceding analysis. 29. Analysis of Caustic Liquor. —Caustic liquor is used for digesting the wood in the soda process. The strength of this liquor varies in different mills from 11° to 12° Baume at 60° F. In order to get good results, the liquor should be from 93.5 to 94 per cent, caustic; that is, this per¬ centage of the soda present should be caustic. This test is practically the only one made. Determinatioji of Causticity .—Make up a weak solution of sulphuric acid (about 6 cubic centimeters of strong acid to 1 liter of water is a convenient strength). Take about 5 cubic centimeters of the caustic liquor (the amount should be varied according to the strength, but should never be so great as to require more than 50 cubic centimeters of the acid), dilute in a small beaker to about 50 cubic centimeters, and add a few drops of phenol phthalein. Titrate with the dilute sul¬ phuric acid until the pink color just leaves, and take a reading. Now add a drop of methyl-orange solution, titrate cautiously until a slight pink tint is reached, and take a second reading. Subtract the first reading from the second, multiply the dif¬ ference by 2, and subtract from the second reading. This remainder divided by the second reading and the result mul¬ tiplied by 100 will give the percentage of causticity. Illustration. —The first reading when the pink color disappeared was 42.6 cubic centimeters. After adding methyl orange and titrating again until pink, the reading was 43.9 cubic centimeters. Following out the calculations as explained, 43.9 — 42.6 = 1.3; 1.3 X 2 = 2.6; 43.9 - 2.6 = 41.3; 41.3 -4- 43.9 = .9407; .9407 X 100 = 94.07, which is the percentage of causticity. Another method that gives very accurate results is as follows: Measure out 25 cubic centimeters of the caustic liquor and titrate with a normal acid, using methyl orange as an indicator. This will give the total alkali. Take 100 cubic, centimeters of the same liquor and precipitate the carbonate 50 MANUFACTURE OF PAPER §18 and sulphate with neutral barium chloride in slight excess. Dilute to the mark in a 200-cubic-centimeter flask, shake well, and allow to settle. Take 50 cubic centimeters of this clear solution and titrate with the normal acid, using phenol phthalein as an indicator. This will give the amount of NaOH in 25 cubic centimeters of the caustic liquor. The number of cubic centimeters of acid used in the second titration divided by the number of cubic centimeters used in the first titration and multiplied by 100 will give the percent¬ age of causticity. The liquor should also be tested for salt, especially where caustic liquor from an electric bleach plant is used in the liquor. This is done by titrating 5 cubic centimeters of the liquor with silver nitrate, using potassium chromate as an indicator. 30. Color Value of Pigments. —The price of a pig¬ ment does not always indicate its value. This is determined by the coloring power of the pigment. A chemical analysis will determine the value of a pigment, but there are simple methods of comparing colors and dyes that can be applied by persons not having a knowledge of chemistry. Under the analysis of ochers, in Art. 21, a method was given for com¬ paring colors, by mixing the ocher with zinc white and lin¬ seed oil. A method similar to this may be used for comparing all colors and dyes. Comparison of Pigments .—To compare two pigments, weigh out 1 gram of the higher-priced one and mix with 10 grams of a good, dry china clay. Now weigh out as many grams of the lower-priced pigment as can be bought for the price of 1 gram of the higher-priced one, and mix with 10 grams of the same clay. Mix separately in a mortar with water to a thin, pasty mass. Spread each upon a strip of glass side by side and dry in a steam bath. The colors can now be com¬ pared, and the pigment having the higher color value selected. This test may be carried still further by weighing out a larger amount of clay and adding to the one giving the strongest tint in the preceding test until it matches the other. §18 MANUFACTURE OF PAPER 51 By noting the difference in the amount of clay used, the difference in value of the two pigments can be determined. Comparison of Soluble Colors .—All soluble colors, such as aniline colors, are dissolved, in the proportion of 1 gram to the liter. Some colors have greater affinity for paper fibers than have others; also, some colors have greater affinity for one kind of fiber than they have for other kinds of fibers. In order to compare such colors in regard to their relative coloring power, the comparison must be made on the same paper stock, or combination of fibers, on which the colors are intended to be used. If, for instance, it is desired to compare the relative strength of two aniline^ blues for use in coloring or whiten¬ ing newspaper made up of 75 per cent, of ground spruce wood and 25 per cent, of spruce sulphite fiber, then some newspaper stock made up of those two pulps in the propor¬ tions given should be used in making the comparison. This is done as follows: A quantity of the pulp is taken, thinned with water, and thoroughly mixed to a uniform mixture. The dilution should be such that 200 cubic centimeters will contain about 1 gram of dry fiber. Of this thinned pulp, exactly the same volume (200 cubic centimeters) is measured out for each color to be compared. These portions are poured into white-china bowls. With a pipette, the same measured amount of each color solution is run into each of the bowls. In the case of acid colors, alum is added, the same quantity of alum solution being added to each vessel, so that everything connected with each test is the same. In case of basic colors, no alum is added, as none is required; in fact, alum may prove inju¬ rious to colors of this kind. The mixtures of pulp and color are stirred from time to time and allowed to stand for about i hour. By this time the colors have gone on to the fibers to their maximum extent. The contents of each bowl is now poured on a wire cloth of fine mesh, and the water draining off, leaves a sheet of colored paper formed on the wire. A sheet of muslin is spread over this sheet of wet paper, and a sheet of blotting paper is then placed on this 52 MANUFACTURE OF PAPER §18 muslin and pressed so as to absorb some of the water from the wet paper. When the muslin is stripped off, it carries the sheet of colored paper with it. This is next pressed between two fresh pieces of muslin and blotting paper, and the sheet of colored paper is then stripped off from the pieces of muslin and hung up to dry. When dry, the sheets are compared as to the strength or depth of color. All con¬ ditions being identical, the color that produces the strongest coloring effect is, of course, the strongest color. In order to tell just how much stronger one color is than another, the same measured quantity of the same thinned pulp used in the first comparative test is taken, and 5 per cent, less of the stronger color than was used in the first test is added. To another measured portion 10 per cent, less color is added; to another 15 per cent, less; and so on, until a sheet is obtained that is colored to exactly the same extent as with the weaker color. This, of course, shows how much stronger the one color is than the other. In order to determine whether a dry, powdered soluble color is a straight color or a mixture of two or more colors, a very simple test is to wet a piece of filter paper and then blow some of the powdered color on it. Where each speck of color strikes the wet filter paper, it colors the paper with its own individual color. For example, suppose it is desired to learn whether a red-shade blue color, such as is ordinarily used for newspaper, is a straight blue of uniform red shade or a mixture of a blue-shade blue with some red color. By blowing some of the powder on a wet sheet of filter paper it will be found that if the color is straight, each particle will produce the same kind of blue spot on the wet paper, but if the color is mixed, there will appear both blue and red spots. It is sometimes preferable to wet the filter paper with alcohol instead of water, as the former dissolves some colors better than the latter and consequently the colored spots show up better. 31 . Analysis of Wood Pulp. —The analysis of soda and sulphite pulps are taken up separately. §18 MANUFACTURE OF PAPER 53 Determination of Cellulose in Wood .—-Weigh out 5 grams of the finely divided substance and boil four or five times in water, using 100 cubic centimeters each time. Pour off the water and dry at 100° C. Now exhaust with a mixture of equal parts, by measure, of benzine and strong alcohol, to remove the rosin, fat, wax, etc. Dry the residue and boil several times in water, to every 100 cubic centimeters of which 1 cubic centimeter of strong ammonia has been added. This treatment removes the pectous substances and coloring matter. Treat the residue in a closed bottle with 250 cubic centimeters of water and 20 cubic centimeters of bromine water containing 4 cubic centimeters of bromine to the liter. TABLE III PERCENTAGE OF CELLULOSE IN VARIOUS WOODS Wood Percentage of Cellulose Wood ^Percentage of Cellulose Alder . 54.61 Oak ...... 39-50 Beech. 45-49 Pine. 57.OO Birch. 55-52 Poplar ..... 62.80 Chestnut .... 52.64 Scotch pine . . . 53-27 Ebony . 30.00 Spruce ..... 53-00 Fir. 53-30 Willow. 55-72 Linden . 55-09 1 When the yellow color of the liquid disappears, add more bromine water and repeat until the yellow color remains and bromine can be detected after standing 12 hours. Filter off the liquid, wash the residue with water, and heat to boiling with 1 liter of water containing 5 cubic centimeters of strong ammonia. If the liquid and tissue are colored brown, filter off the undissolved matter, wash, and treat again with bromine water, as before. When the action seems complete, heat the residue as before with ammonia water, and if the brownish tint is again imparted to the liquid, repeat the preceding operation. The cellulose is thus obtained in a pure white state. Wash with boiling water and then with hot alcohol. 54 MANUFACTURE OF PAPER §18 Dry at 100° C. and weigh. The percentage of cellulose is calculated in the usual manner. Table III gives the percentage of cellulose in representa¬ tive woods as determined by the foregoing method. 32. Analysis of Soda Pulp.—Soda pulp is made by the soda process. Samples from the rolls and from the wet and the pulp machine should be taken from time to time and tested. In taking samples from the roll for shipment, cut through at least ten layers of the pulp and take two strips about 12 inches long and I inch wide. Tear these into small pieces and put them in a weighed sample box, keeping the lid on as much as possible. A sample should be taken from every tenth roll. Determination of Total Moisture. —Weigh the box containing the sample and empty it on a clean piece of paper in the drying oven. Dry at 100° C. for about 6 hours. Return the sample to the box, cool in a desiccator, and weigh again. Repeat until the weight is constant. The loss in weight multiplied by 100 and divided by the weight of the sample taken will give the percentage of moisture in the pulp. The folds from the wet machine are tested in the same way. Determination of Air-Dry Moisture. —Pulp that contains moisture due only to the atmosphere is known as air-dry pulp. The amount of moisture present is rather indefinite, owing to the difference in humidity. It is determined by drying a sample until bone dry, weighing, and exposing to the atmosphere at ordinary temperature for at least 24 hours. The increase in weight will indicate the amount of air-dry moisture. All pulp is generally sold on the air-dry basis, and not on the bone-dry basis. It is an almost universal custom to figure air-dry pulp as containing 10 per cent, of moisture. This is calculated by determining the bone-dry weight, which is then multiplied by 100 and divided by 90. Some pulp testers add to the bone-dry weight 10 per cent, of itself and call the result the air-dry weight; this, however, is obviously incorrect. §18 MANUFACTURE OF PAPER 55 Determination of Ash .—Weigh out about 5 grams of the pulp sample in a platinum crucible. Ignite until all carbo¬ naceous matter is burned off. Cool in a desiccator and weigh. The weight of the ash multiplied by 100 and divided by the weight of the sample taken will give its percentage in the pulp. Soda pulp that has been run over the driers usually contains‘from 7 to 8 per cent, of moisture and about 1 per cent, of ash. Pulp after leaving the last press roll and before passing over the driers contains about 65 per cent, of moisture. 33. Analysis of Sulphite Pulp.— Sulphite pulp is made by the sulphite process. It is shipped in folds from the wet machine, and contains from 60 to 70 per cent, of moisture. Determination of Moisture .—Cut strips 10 inches long and i inch wide from folds taken at random from different parts of the lot sampled, taking care that a good average sample is selected. Tear these strips into small pieces and put them in a sample box. Weigh the box and contents and transfer the sample to the drying oven. Dry at 100° C. for from 18 to 24 hours. Return to the box and weigh again. Sub¬ tract the weight of the box to get the weight of bone-dry fiber. Dividing by the weight of wet pulp taken will give the percentage of bone-dry fiber. The weight of the bone- dry fiber divided by 90 and multiplied by 100 will give the percentage of air-dry fiber in the sample. The following is a convenient method for the determina¬ tion of moisture and gives results sufficiently accurate for all practical purposes. The results are expressed in per¬ centage of air-dry fiber. This method is used when samples are taken from time to time from the wet machine to ascer¬ tain how the pulp is running and to figure out the percent¬ age of fiber made daily. Take 100 grams of the sample, weighing as quickly as possible, and transfer to the drying oven, after separating the different layers as much as possible. Dry from 18 to 24 hours and rapidly weigh again. The weight of the dried 56 MANUFACTURE OF PAPER §18 sample divided by 90 and multiplied by 100 will give the percentage of the air-dry fiber. Determination of Ash. —The ash of sulphite pulp is deter¬ mined the same as* the ash of soda pulp in Art. 32. For sulphite pulp, it is usually from .6 to 1 per cent. 34. Paper Testing.— Samples of paper are tested in the same way as pulp for moisture and ash, taking about 50 grams for the determination of moisture and 3 or 4 grams for the ash. Determinatioyi of Retentio?i of Filler. —The retention of filler is determined as follows: The percentage of ash of the paper and the percentage of ash in the paper stock itself to which no filler has been added are determined. This latter percentage is deducted from the former, and the difference is the ash due to the filler used. As the fillers ordinarily used suffer more or less loss in weight on ignition, a sample of the filler used must be ignited by itself and the loss on ignition determined. Agalite ordinarily loses about 4 per cent., while clay loses from 15 to 20 per cent. The percentage of “ash due to filler,” as just determined, must therefore be corrected for the “loss on ignition” of the filler used, in order to get the true percentage of original filler contained in the paper. The percentage of filler furnished to the paper maker being known, it is of course a simple matter to calculate what percentage of this amount was found in the paper, or, in other words, the percentage retained. Microscopic Fiber Test. —The various fibers in paper are detected by means of a microscopic examination, while at the same time there are several chemical tests that are useful in identification. Prepare the sample to be examined under the microscope as follows: Cut small pieces of paper from different parts of the sample and boil in a 1-per-cent, solution of caustic soda. The fibers may now be separated by shaking in a bottle con¬ taining a few pieces of broken glass. The fibers are placed on a glass and covered with a drop of glycerine and a cover glass. §18 MANUFACTURE OF PAPER 57 Mechanical Wood Fiber.— Under the microscope, mechanical wood fiber is distinguished from chemical wood fiber by the fact that the fibers are rarely separated, they being generally bound together in bundles. The ends also are torn and jagged. Linen Fiber. —In Fig. 3 is shown an illustration of linen fiber. The ends of this fiber are usually drawn out into numerous fibrils and fibers of a cylindrical form. Esparto and Straw Fibers. The esparto and straw fibers are very much alike, and consist of serrated cells and fibrovascular bundles. Straw may be distinguished from esparto by the presence of small, oval-shaped cells and the absence of the fine hairs that always line the inner surface of the leaf of the esparto plant. Chemical Wood Fiber. The fibers of chemical wood are flat and ribbon¬ like and have unbroken ends, very much like cot¬ ton, but are distinguished from it in that they are not twisted. Pine-wood fiber is detected by the presence of small pitted vessels. Cotton fiber is shown in Fig. 4, poplar fiber in Fig. 5, and spruce fiber in Fig. 6. To assist in the determination of different fibers under the microscope, a reagent made up as follows will be found of great help: Dissolve 2.1 grams of potassium iodide and 58 MANUFACTURE OF PAPER 18 .1 gram of iodine in 5 cubic centimeters of water and mix with 20 grams of zinc chloride dissolved in 10 cubic centi¬ meters of water. The mixture should be allowed to stand and the clear liquid de¬ canted. This reagent will color cotton, linen, and hemp, wine red; esparto, straw, and wood cellulose, bluish violet; mechanical wood pulp and unbleached jute, yellow; and manila hemp, blue and bluish gray to yellow. Chemical Tests for Con- stituents of Paper. —When a small quantity of paper that has been beaten up, separated, and moistened with iodine is examined under the glass, the fibers can be separated, owing to the fact that the ground wood and jute will be colored yellow; cotton, hemp, and linen, brown; and chemical wood fiber will remain uncolored. Detection of Mechanical Wood Pulp. —Nitric acid gives a brown stain on paper containing mechan¬ ical wood pulp. Phloro- glucinol gives a deep magenta in the presence of mechanical wood pulp. The latter test is the one mostly used for this pur¬ pose. Phloroglucinol is prepared by dissolving 2 grams of the reagent in 25 cubic centimeters of 95-per¬ cent. alcohol and adding 5 cubic centimeters of con¬ centrated hydrochloric acid. Apply a drop to the paper to be while bleached straw, esparto, Fig. 6 §18 MANUFACTURE OF PAPER 59 tested and allow to evaporate. In the presence of ground- wood pulp, the deep magenta coloration will be developed. In some papers, the coloring matter used acts as an indicator for acids and will turn red when treated with acid. In papers where these colors are present, it is difficult to test for ground wood with phloroglucinol, as the acid in the mix develops the red color. In papers where “yellow mix” is, used, this color is developed by the acid in the phloro¬ glucinol. Aniline sulphate develops a deep yellow in pres¬ ence of ground wood, and is prepared by dissolving in water. This reagent should be substituted for phloroglucinol in tests where colors such as those just mentioned have been used in the paper. The percentage of ground wood may be roughly estimated by comparing the depth of color produced by the phloro¬ glucinol on the sample with the depth of color produced on several standard samples in which the percentage of ground wood is known. This test can be applied only when the chemical fiber present has been perfectly reduced. Detection of Sulphite Pulp. —Sulphite pulp can be detected by means of a dilute solution of sodium-auric chloride, which imparts to the paper moistened with it a reddish-brown color when unbleached sulphite pulp is present, and a bluish color when bleached sulphite pulp is present. Detectio?i of Straw and Esparto. —Straw and esparto can be detected by boiling the paper for some time in a 1-per-cent, solution of aniline sulphate, which produces a red color in the presence of these substances. Detection of Animal Size. —Heat a small fragment of paper in a test tube with distilled water, transfer the clear solution to another tube, cool, and add a solution of tannic acid. If any animal size is present, a milky, flocculent precipitate will be formed, the consistency of which will depend on the amount of animal size present. A very delicate test for animal size is to soak a small strip of paper in a reagent prepared by dissolving a small amount of quicksilver in an equal weight of fuming nitric acid, cool¬ ing, and adding an equal volume of water. In the presence 60 MANUFACTURE OF PAPER 18 of animal size, the paper will develop a red color, the depth of which will depend on the amount of size present. This reagent will keep only about a month, and hence must be made up frequently. Detection of Starch .—Starch may be detected in paper by adding a drop of very dilute solution of iodine, which, if starch is present, will develop a deep-blue color. This test is better carried out by boiling some of the paper in water for about 20 minutes, pouring off the water into another vessel, and adding the dilute iodine solution. Detection of Rosin Size .—The presence of rosin size may be detected by heating some of the paper in absolute alcohol and pouring the alcoholic solution, after cooling, into five times its volume of distilled water. If a precipitate is formed or there is a cloudiness, the presence of rosin size is indicated. By wetting the sheet with the mouth and holding it to the light, a well-sized paper will not be transparent, while if poorly sized, it will be transparent, the degree of transpar¬ ency varying inversely with the amount of size used. Detection of Chlorides .—Boil the paper in distilled water, filter, add a few drops of nitric acid, and then a few drops of silver-nitrate solution. A cloudiness or a. precipitate indi¬ cates the presence of chlorides. Detection of Alum .—An excess of alum can be detected by boiling a quantity of the paper in a small amount of water, filtering, and testing the filtrate for aluminum by precipita¬ ting with ammonium hydrate and ammonium chloride. The nature of the filler can be determined by an analysis of the ash. Determination of Coloring Matters. —Sometimes, coloring matters can be determined by an examination of the ash. When ultramarine has been used, the ash is blue. 35. Mechanical Tests of Paper.—There are several mechanical tests to which paper should be subjected in order to determine its quality. Determination of the Direction in Which the Paper Came from the Machine .—In order to determine the strength of §18 MANUFACTURE OF PAPER 61 paper, the direction in which the paper came from the machine must be ascertained. This is done as follows: Cut a disk from the center of the sheet of paper, float it on water, and allow it to rest on the palm of the hand, when it will curl up. The direction of the axis of the cylinder formed is the direction in which the paper came from the machine. Determination of the Strength of Paper .—The strength of paper can be determined roughly by tearing the sheet. Two papers can be compared in this respect by means of a testing machine, for which test strips are cut (taking care that they are cut in the same way, as to coming from machine, and are of the same size). The strips are then subjected to tension in the testing machine, and the weight necessary to break them read off and compared. Two sheets can be roughly compared in this respect by cutting strips an inch in width from each sample, and suspending them from an iron bar. Weights are then cautiously attached to each until the sheets break; the difference in weights required will give the comparative strength of sheets. Detection of Dirt .—Dirt in paper can be detected by hold¬ ing a sheet to the light. A SERIES OF QUESTIONS Relating to the Subjects Treated of in This Volume. It will be noticed that the questions contained in the fol¬ lowing pages are divided into sections corresponding to the sections of the text of the preceding pages, so that each section has a headline that is the same as the headline of the section to which the questions refer. No attempt should be made to answer any of the questions until the corre¬ sponding part of the text has been carefully studied. 199—36 SULPHURIC ACID (PART 1) EXAMINATION QUESTIONS (1) Does sulphur trioxide form definite combinations with water, and if so, describe some of their characteristics. (2) Name and give the chemical formulas of two impor¬ tant hydrates of sulphur trioxide. (3) In what manner is the strength of sulphuric acid usually indicated? (4) Give the general principles governing the conversion of sulphur into sulphuric acid. (5) Name the principal substances from which sulphur is derived. (6) What are the constituents of burner gas ? (7) In roasting metallic sulphides, to what is the loss in sulphur due ? (8) State briefly how burner gas is produced. (9) By what means is a uniform supply of burner gas obtained ? (10) Describe the Spence reciprocating furnace. (11) Give a brief description of Reich’s test for sulphur dioxide in burner gas. (12) In making burner gas, 11,500 pounds of available sulphur is burned in 24 hours, and the resulting burner gas 2i 2 SULPHURIC ACID 1 at 0' C. and normal pressure contains 8.5 per cent, of sul¬ phur dioxide. How many cubic feet of burner gas is deliv¬ ered per minute at a temperature of 15° C.? (13) What is meant by a contact reaction ? (14) Mention two contact masses and describe their preparation. (15) Give in as few words as possible an outline of the catalytic process. (16) Describe the tower system for purifying burner gas. SULPHURIC ACID (PART 2) EXAMINATION QUESTIONS (1) Describe the Glover tower and its functions. (2) Give the main chemical reactions of the chamber process. (3) What is nitration and how is it accomplished ? (4) For what purpose are surface condensers used ? (5) Describe the Falding condenser. (6) What is the function of the Gay-Lussac tower ? (7) Describe the Kestner pump. (8) What materials enter into the manufacture of sul¬ phuric acid by the chamber process ? (9) How is the progress of the reactions in the chambers indicated ? (10) In what portions of the chambers are the reactions most energetic ? (11) For what purpose is steam admitted to the cham¬ bers ? (12) What conditions will cause irregular working of the chamber process, and how may the cause of the irreg¬ ularity be located ? n 2 SULPHURIC ACID §2 (13) How are samples of acid for testing taken from the interior of the chambers ? (14) What impurities are found in chamber acid ? (15) Describe briefly the Freiberg process for removing arsenic. (16) Describe the method of concentration and distilla¬ tion, starting with the Glover tower. (17) In vessels of what materials may (a) dilute acid be concentrated ? ($) strong acid ? (18) Describe the Lunge freezing process for the pro¬ duction of sulphuric monohydrate. ALKALIES AND HYDRO¬ CHLORIC ACID (PART 1) EXAMINATION QUESTIONS (1) (a) What is the chief raw material from which prac¬ tically all the products mentioned in this Section are derived? ( b ) How does it occur in nature? (2) The Solvay process for the manufacture of soda depends on substituting the weak carbonic acid for the strong hydrochloric acid in the sodium chloride. Explain this displacement of a strong acid by a weak one. (3) In the cryolite-soda process, what weight of cal¬ cium carbonate, theoretically, is it necessary to mix with 425 pounds of cryolite in the reverberatory furnace? (4) In the Solvay process, the soda is the main product and ammonium chloride a by-product. Why is it necessary to recover the ammonia? (5) Give a brief outline of the Le Blanc soda process, dwelling principally on the chemical principles involved. (6) What valuable by-product is obtained in the Le Blanc process that goes to waste in the ammonia-soda process? (7) In the manufacture of salt cake, how much sulphuric acid is it necessary to mix with 800 pounds of salt? § 3 2 ALKALIES AND HYDROCHLORIC ACID 3 (8) In the Le Blanc process, what weights of calcium carbonate and carbon, theoretically, should be mixed with 1,500 pounds of salt cake in the furnace? (9) Describe the method of recovering the sulphur in the Le Blanc process? ALKALIES AND HYDRO¬ CHLORIC ACID (PART 2) EXAMINATION QUESTIONS (1) Describe briefly the manufacture of hydrochloric acid. (2) How is chlorine usually obtained? (3) Theoretically, what weight of limestone containing 98 per cent, of calcium carbonate will be needed in making 100 pounds of potassium chlorate? (4) ( a ) What percentage of chlorine should bleaching powder theoretically contain? ( b) How much available chlorine does it usually contain? (5) [a) Describe commercial hydrochloric acid, {b) Give a method of purifying it. (6) For what purpose is chlorine mostly used? (7) In generating chlorine by the action of hydrochloric acid on manganese dioxide, what weight of acid containing 33 per cent, of HCl is theoretically necessary to yield 10 pounds of chlorine? (8) In preparing chlorine directly from salt, if a temper¬ ature above 120° C. is maintained, what weight of sulphuric acid containing 90 per cent, of H a SO t should theoretically be used with 100 pounds of salt? (9) In preparing chlorine by Deacon’s process, what volume of the gaseous mixture at standard temperature and pressure containing 50 per cent, of HCl is theoretically necessary to produce 10 grams of chlorine? a ALKALIES AND HYDRO¬ CHLORIC ACID (PART 3) EXAMINATION QUESTIONS (1) (a) If a current of electricity is passed through a copper-sulphate solution so that copper is dissolved from one plate and deposited on another that has been weighed, and at the end of the operation 7 milligrams of copper is found to have been deposited, how many coulombs have passed? (b) If the 7 milligrams of copper was deposited in 7 seconds, what is the rate of flow of current? (2) What is meant by the dissociation theory? (3) Describe the Acker electrolytical process. (4) Describe the Castner-Kellner process for the elec¬ trolysis of salt. (5) Define the term ohm. (6) What is meant by the term coulomb? (7) How is the electric conductivity of solutions deter¬ mined? (8) What is meant by an electric conductor of the first class? (9) Describe the Townsend process used in the manu¬ facture of caustic soda. 2 ALKALIES AND HYDROCHLORIC ACID §5 (10) State the conditions favoring the electrolysis of salt that should be taken into consideration in selecting an electrolytical process for the manufacture of sodium hydrate and chlorine. ALKALIES AND HYDRO¬ CHLORIC ACID (PART 4) EXAMINATION QUESTIONS (1) In determining the salt in brine, if 10 cubic centi¬ meters of the brine is diluted to 1 liter and 10 cubic centi- 71 meters of this solution requires 3.8 cubic centimeters of —^ silver nitrate for titration, about how many grapis of salt will a liter of the brine contain ? (2) How would you determine sodium bicarbonate in the presence of sodium carbonate, if no other compounds are present ? (3) In the determination of ammonia in gas liquor of 1.1 sp. gr., if 3 cubic centimeters of the liquor is taken for the sample, and 25 cubic centimeters of normal alkali is used in titrating the excess of normal sulphuric acid, what per¬ centage of NH % does the liquor contain ? (4) In the determination of salt in ammoniacal brine, let us suppose that 10 cubic centimeters of the brine is made up to a liter and 100 cubic centimeters of this solution is taken 7t for titration. If 43.6 cubic centimeters of — silver nitrate is taken to precipitate the chlorine, and after adding the indi¬ cator 4.6 cubic centimeters of sulphocyanide is used to titrate back, how much salt does a liter of the solution contain ? 6 2 ALKALIES AND HYDROCHLORIC ACID 6 (5) In determining salt, why do we titrate the natural brine directly with a.silver-nitrate solution, using potassium chromate as indicator, while in the case of ammoniacal brine the Volhard method is employed ? (6) In determining the salt in brine, if the brine contains 234 grams of salt per liter and 10 cubic centimeters of it is fl diluted to 1 liter, how much — silver-nitrate solution will be required for 10 cubic centimeters of this solution ? (7) How many cubic centimeters of normal sodium hydrate will be required to change 1 gram of sodium bicar¬ bonate to the normal carbonate ? (8) In determining the excess of lime in the waste liquor from the ammonia stills, taking the molecular weight of H 2 S0 4 as 98, of Ca(OH\ as 74, and of NH S as 17; if 17 cubic centimeters of normal alkali is required to neutral¬ ize the excess of acid when 50 cubic centimeters of normal sulphuric acid is taken, how many grams of Ca(OH) a does a liter of the waste liquoi contain ? (9) In determining the sulphur trioxide in salt for the salt-cake process, if 10 grams of the sample is dissolved, diluted to 500 cubic centimeters, and 250 cubic centimeters taken for analysis and the precipitate weighs .068 gram, what percentage would you have and how would you ordi¬ narily report it ? (10) In determining the free acid in salt cake containing considerable quantities of iron and aluminum salts, if you wish to exclude the acidity due to these, how would you proceed ? (11) Describe the determination of available oxygen in manganese ore. (12) How would you determine the amount of hydro¬ chloric acid of the strength being used in the process neces¬ sary to decompose a given weight of manganese ore ? MANUFACTURE OF PAPER (PART 1) EXAMINATION QUESTIONS (1) Describe the method of charging and cooking the chips in the sulphite process. (2) Describe the process of manufacturing ground-wood pulp. (3) Describe briefly the method of recovering soda from the exhausted liquor of the soda process. (4) From what materials is paper made? (5) Mention some of the materials used for lining the digesters used in the sulphite process. (6) What are the most important processes for the manufacture of pulp from wood? (7) Give the reactions that represent the formation of calcium bisulphite. (8) (a) In the soda process, by what agency is the dis¬ integration of the wood brought about? ( b ) Describe the process of cooking the wood. (9) (a) By what agency is the disintegration of the wood brought about in the sulphite process? ( b ) What wood is most generally used? (10) What is meant by causticizing sodium-carbonate liquor, and how is it accomplished? (11) Describe the preparation and absorption of sulphur dioxide in making the bisulphite liquor. § 16 MANUFACTURE OF PAPER (PART 2) EXAMINATION QUESTIONS (1) In the purification of water, what is the object of the alum treatment? (2) (a) What compound of chlorine is used most exten¬ sively as a bleaching- agent? ( b) To what is its bleaching action due? (3) (a) What substances are used for whitening and coloring paper? ( b) How are such substances treated before being added to the beater? (4) On what principle is the electrolytic preparation of chlorine based? (5) How is parchment paper made? (6) In addition to the percentage of available chlorine, what quality must a good bleaching powder have? (7) Describe briefly the fourdrinier. (8) What is the purpose of sizing? (9) How are cardboards with two different faces made? (10) What substances are most largely used as fillers? (11) For what purposes is alum (sulphate of aluminum) used in paper making? (12) Describe briefly the process of making paper by hand. 199—37 g 17 MANUFACTURE OF PAPER (PART 3) EXAMINATION QUESTIONS (1) How are two soluble blue colors compared to deter¬ mine which is the stronger? (2) Why is it important to determine the percentage of silica in ultramarine? (3) What chemical test is sometimes used to determine whether sulphite pulp has been used in making a paper? (4) (a) What is the effect of temperature on the density of solutions? ( b) What allowance must be made for tem¬ perature on the Baume reading? (5) Describe the method employed to determine cellulose in wood. (6) How is the true percentage of retention of a filler determined? (7) How is a sample of paper prepared for examination with the microscope? (8) In the determination of calcium and magnesium in magnesia lime, what precaution is necessary? (9) How are the values of glues compared? (10) Why should the available chlorine in bleach sludge be determined? (11) Describe the sizing test for alum. (12) How should causticizing lime be sampled for analysis? 218 A KKY TO ALL THE QUESTIONS AND EXAMPLES INCLUDED IN THE Examination Questions in This Volume It will be noticed that the Keys have been given the same section numbers as the Examination Questions to which they refer. All article references refer to the Instruction Paper bearing the same section number as the Key in which they occur, unless the title of some other Instruction Paper is given in connection with the references. SULPHURIC ACID (PART 1) (1) See Arts. 2 and 3. (2) See Arts. 5 and 6. (3) See Art. 7. (4) See Art. 10. (5) See Art. 11. (6) See Art. 20. (7) See Art. 24. (8) See Arts. 31 and 32 (9) See Art. 32. (10) See Art. 44. (11) See Arts. 49, 50, and 51. (12) Substituting in formula 6, Art. 53, x .77722 X 11,500 ' 8.5 1,051.5 cu. ft. per min. Correcting for temperature by formula 7, Art. 55, v t = 1 , 051.5 + lo ~ = 1 > 109 - 2 cu. ft - P er min - at 15 ° C> (13) See Art. 57. (14) See Arts. 60, 61, and 62. (15) See Arts. 57 to 74, inclusive. (16) See Art. 66. §1 SULPHURIC ACID (PART 2) (1) See Arts. 8 to 10, inclusive. (2) See Arts. 3 and 4. (3) See Arts. 6 and 7. (4) See Art. 13. (5) See Art. 16. (6) See Art. 18. (7) See Art. 21. (8) See Arts. 19 and 23. (9) By the temperature. See Art. 26. (10) See Arts. 28 and 29. (11) See Art. 30. (12) See Arts. 34 to 36, inclusive. (13) By means of the curtain drip. See Art. 37. (14) See Arts.. 38 and 39. (15) See Arts. 41 to 45, inclusive. (16) See Arts. 55 and 56. (17) See Arts. 43 to 52, inclusive. (18) See Art. 57. §2 ALKALIES AND HYDRO¬ CHLORIC ACID (PART 1) (1) (a) Sodium chloride. ( b ) It occurs in the ocean, in salt lakes, in certain springs and wells, and in deposits of solid salt left by the drying up of inland salt lakes or seas. (2) The weak carbonic acid acting alone on the salt could not decompose it; but in this case, ammonium carbonate, or, rather, bicar¬ bonate, is acting on the salt. It is probable that the affinities of the sodium and the ammonium for the two acids are about balanced, so that it is easy for part of the carbonic acid to unite with sodium and for hydrochloric acid to take its place, forming ammonium chloride. Hence, to a certain extent, it may be regarded as a displacement of the weak carbonic acid of the ammonium bicarbonate by the strong hydrochloric acid of the salt. There is also a rule to the effect that when there is a mixture of the solution of two compounds, if an insoluble compound would be formed by a transference of the elements of these compounds, such transference will usually take place either partly or completely. Consequently, as sodium bicarbonate is less soluble than the original compounds, there is a tendency for it to form and thus separate from the solution. (3) Na 2 AlF 6 + 3CaCO a = Na t Al0 3 + 3 CaF, + 3 CO,. Then, for 209.01 parts of cryolite, 297.93 parts of calcium carbonate is required; hence, 209.01 : 297.93 = 425 : x\ or x = 605.8+ lb. Ans. (4) See Art. 40. (5) See Art. 69, etc. (6) In the Le Blanc process, chlorine is recovered in the form of, hydrochloric acid; in the Solvay process, it goes to waste. 23 2 ALKALIES AND HYDROCHLORIC ACID §3 (7) From the equations given in Art. 69, it will be seen that for every 58.5 parts of salt 49 parts of sulphuric acid is required; hence, the following proportion is obtained: 58.5 : 49 = 800 : x\ or x = 670+ lb. Ans. (8) In Art. 74 it is stated that for 100 lb. of salt cake, 70 lb. of calcium carbonate and 17 lb. of carbon are required. Hence, for 1,500 lb. of salt cake, 1,050 lb. of calcium carbonate and 255 lb. of carbon are needed. (9) See Art. 104, etc. ALKALIES AND HYDRO- CHLORIC ACID (PART 2) (1) See Art. 17, etc. (2) See Art. 36, etc. (3) According to the equations: 6 Ca{OH ) 2 + 6 Cl „ = bCaCl, + Ca{Cl0 3 ) t + 6 H,0 and Ca {CIO 3)3 + 2A r Cl = CaCl t + 2KCl0 3 it requires 6 molecules of Ca{OH ) 3 to produce 2 molecules of KC10 3 , or 3 molecules of Ca{OH ) 3 for \KC10 3 . As 1 molecule of Ca{OH ) 2 can be made from 1 molecule of CaC0 3 , 3 molecules of CaC0 3 will be required for 1 molecule of KC10 3 . Taking the molecular weight of KC10 3 as 121.64 and that of CaCV 3 as 99.31, 121.64 : 297.93 = 100 : andx= 244.92 lb. of CaC0 3 . But as the limestone is only 98 per cent. CaC0 3 , there is 244.92 -5- .98 = 249.92 lb. of limestone. Ans. (4) (a) The molecular weight of CaClOCl is 126 and of the chlorine contained in it, 70.36; hence, the percentage of chlorine is 70.36 -f- 126 = 58.84. Ans. {b) See Art. 72. (5) (a) See Art. 28. (5) See Art. 29, etc. (6) Chlorine is used almost exclusively in the manufacture of bleaching compounds and especially in the manufacture of bleaching powder. (7) In this process, half the chlorine of the acid is theoretically available; hence, 2 molecules of HCl will be required to yield 1 atom of chlorine. This therefore gives the proportion 35.18 : 72.36 = 10 : x, and x = 20.57 lb. of HCl. But as the acid only contains 33 per cent, of HCl, the number of pounds of acid is 20.57 -f- .33 = 62.33. Ans. u 2 ALKALIES AND HYDROCHLORIC ACID §4 (8) As 2 molecules of NaCl requires 2 molecules of H^SO^ they must be present in the ratio of their molecular weights. Taking their weights as 58.06 and 97.35, respectively, there would be 58.06 : 97.35 = 100 : x, or x = 167.67 lb. of H a SO t . But as the acid is only 90 per cent. H 2 SO it there is 167.67 -5- .90 = 186.3 lb. of acid. Ans. (9) As 1 gram of chlorine occupies 314.7 c. c., 10 grams would occupy 3,147 c. c.; and as it requires 2 molecules of HCl to yield 1 molecule of chlorine, it would require twice this volume of HCl, or 3,147 X 2 = 6,294 c. c. of HCl. But as the gaseous mixture is only half HCl, it would require twice this, or 12,588 c. c. of the mixture. Ans. ALKALIES AND HYDRO¬ CHLORIC ACID (PART 3) (1) ( a ) As .329 mg. of copper is deposited by 1 coulomb, to deposit 7 mg. it would require 7 -5- .329 = 21.28 coulombs. Ans. (b) The rate of flow is determined by dividing the number of cou¬ lombs that pass by the number of seconds required for them to pass; hence, there are 21.28 7 = 3.04 amperes. Ans. (2) See Art. 24. (3) See Art. 35. (4) See Art. 48. (5) The ohm is the unit of resistance at 0° C. of a column of mercury 1 sq. mm. in section and 1.0626 m. long. Ans. (6) The coulomb is the unit quantity of electricity that will deposit 1.118 mg. of silver from the solution of a silver salt. See Art. 3. (7) See Art. 11. (8) See Art. 21. (9) See Art. 40, etc. (10) See Art. 31. ?*5 ALKALIES AND HYDRO¬ CHLORIC ACID (PART 4) (1) According to Art. 1, 7, 3.8 X .00585 X 10,000 = 222.3 g. of NaCl per li., approximately. Ans. (2) See Art. 13. (3) If 25 c. cm. of alkali is required, 50 — 25 = 25 c. cm. of acid will be used by the ammonia; hence, taking the molecular weights of N 3 SO t and A T H 3 as 97.35 and 16.93, respectively, and noting that 1 molecule of H^SO^ unites with 2 molecules of NH 3 , 98 : 34 = 1.225 : x, and x = .425 g. of NH 3 found. As 3 c. cm. of liquor of 1.10 sp. gr. is used, the sample weighed 3.3 g.; hence, the percentage of NH 3 is (.425 3.3) X 100 = 12.88. Ans. (4) As 43.6 c. cm. of silver nitrate was added, and 4.6 c. cm. of sulphocyanide was required to titrate back, 39 c. cm. of silver nitrate was used in precipitating salt; and as each cubic centimeter of silver nitrate precipitates .00585 g. of salt, there results .00585 X 39 = .22815 g. of NaCl. As 10 c. cm. of the original solution was diluted to 1 li., and 100 c. cm. of this solution was taken for titration, the sample contained 1 c. cm. of the original solution; hence, 1 c. cm. of the original solu¬ tion contains .22815 g. of NaCl , and 1 li. contains .22815 X 1 000 = 228.15 g. of NaCl. Ans. (5) Silver chromate is a bright-red compound, insoluble in water and ordinary neutral solutions, but soluble in both acids and alkalies; consequently, it gives a sharp end reaction in neutral solutions, but if the solution is either acid or alkaline, the end reaction is very unsatis¬ factory. The natural brine is practically neutral, and, consequently, this can be used, but the ammoniacal brine is alkaline, and, con¬ sequently, the Volhard method must be employed. §6 199—38 2 ALKALIES AND HYDROCHLORIC ACID 6 (6) If 1 li. of the brine contains 234 g., 10 c. cm. will contain 2.34 g., or the dilute solution made up will contain 2.34 g. per li.; 10 c. cm. of this will contain .0234 g. of NaCl, and as 1 c. cm. of the silver solution precipitates .00585 g. of NaCl, .0234 4 - .00585 = 4 c. cm. of silver nitrate will be required. Ans. (7) According to Art. 13, the reaction is NaHCO a + NaOH = Na 3 C0 3 + H 2 0. Consequently, taking the molecular weight of NaHC0 3 as 83.43, 1 c. cm. of NaOH = .08343 g. of NaHC0 3 , and to change 1 g. will require 1 4- .08343 = 11.98 c. cm. of sodium hydrate. Ans. (8) If 17 c. cm. of alkali is required, 50 — 17 = 33 c. cm. of acid has been neutralized by ammonia; 33 X .049 = 1.617 g. of H 3 SO 4 neutralized by ammonia. Then, by proportion, 98 : 34 = 1.617 : x. x = .561 g. of NH 3 ; but 34A7/ 3 requires 74 Ca{OH) 3 , hence, 34 : 74 = .561 : x. .*• = 1.221 g. Ca{OH) 3 in 100 c. cm. of solution, or 1.221 X 10 = 12.21 g. Ca ( OH ) 2 per li. Ans. (9) The sulphur trioxide in this case is usually reported as calcium sulphate; hence, taking the molecular weights of barium sulphate and calcium sulphate as 231.74 and 135.11, respectively, 231.74 : 135.11 = .068 : x, and = .039646 g. CaSO t . But as 5 g. of sample was taken, .039646 4 - 5 = .793 per cent. CaSO t . If the percentage of sulphur trioxide is wanted, it can be obtained by multiplying the weight of barium sulphate by the factor for S0 3 , .34335, and dividing this result by 5. (10) See Art. 19. (11) See Art. 46. (12) See Art. 46. MANUFACTURE OF PAPER (PART 1) (1) See Art. 66. (2) See Arts. 23 to 28. (3) See Arts. 45 to 51. (4) See Arts. 3 to 11. (5) See Art. 64. (6) The mechanical, or ground-wood, process, the soda process, and the sulphite process. (7) See Art. 62. (8) (a) See Art. 29. ( b) See Art. 33. (9) (a) See Art. 54. ( b) Spruce principally, but also hemlock, poplar, and fir. (10) See Art. 42. (11) See Arts. 53 to 62. |] 6 MANUFACTURE OF PAPER (PART 2) (1) To coagulate the organic matter present, which then settles and is removed. See Art. 67. (2) (a) Chloride of lime, or bleaching powder, Ca^^Qci- ( b ) See Art. 1. (3) See Arts. 40, 41, and 42. (4) On the principle that the electric current has the power to decompose an aqueous solution of sodium or other metallic chloride into chlorine and a metallic base. See Art. 15. (5) See Art. 63. (6) See Art. 3. (7) See Arts, , 45 to 54 (8) See Art. 27. (9) See Art. 62. (10) See Art . 39. (11) Alum is used in sizing paper; it accomplishes the precipitation of the rosin size on the fiber in the beating engine. (12) See Art. 44. in MANUFACTURE OF PAPER (PART 3) (1) See Art. 30. (2) See Art. 22. (3) See Art. 34. (4) See Art. 3. (5) See Art. 31. (6) See Art. 34. (7) See Art. 34. (8) See Art. 13. (9) See Art. 25. (10) In order to ascertain whether the full bleaching power of the powder is utilized. See Art. 16. (11) See Art. 18. (12) See Art. 11. §18 INDEX N OTE — A 11 items in this index refer first to the section (see the Preface), and then to the page of the section Thus Brimstone burners, §1, p25,” means that brimstone burners will be lound on page 2o of section 1. A Absorption apparatus for sulphur dioxide, §16, p45. chambers for bleaching powder, §4, p47. of sulphur dioxide, §16, p45. Acid, free, Determination of, in salt cake, §6, pl9. free, Determination of, in still liquor, §6, p43. Mixed, §2, p58. Nordhausen or fuming sulphuric, §1, p4. pumps, §2, p25. sulphuric, Definition of, §1, p3. Acker’s process for the electrolysis of salt, §5, p28. Adaptability of various sizes for paper, §17, p26. Agalite, §17, p27. Analysis of, §18, p28. Alkali, total, Determination of, in black ash, §6, p22. total, Determination of, in caustic bottoms §6, p35. total, Determination of, in caustic liquor, §6, p34. total, Determination of, in caustic mud, §6, P 35. total, Determination of, in caustic soda, §6, p36. total, Determination of, in fished salts, §6, p34. total, Determination of, in lye from extrac¬ tion of black ash, §6, p23. total, Determination of, in soda ash, §6, p28. Alkaline sodium compounds, Determination of, in tank waste, §6, p27. Alum, Analysis of, §18, p23. Sizing test for, §18, p27. treatment of water, §17, p46. Alumina, Determination of, in lye from extraction of black ash, §6, p24. Alumina—(Continued) Determination of, in salt cake, §6, pl9. Determination of, in soda ash, §6, pl6. in brine, Determination of, §6, p2. Ammeters, §5, pl2. Ammonia, Determination of, in ammonia liquor, §6, p7. Determination of, in ammoniacal brine, §6, p7. Determination of, in bicarbonate from filters, §6, pl3. Determination of, in mother liquor, §6, pl4. liquor, Analysis of, §6, p6. liquor, Determination of ammonia in, §6, p7. liquor, Determination of specific gravity of, §6, p6. lost in Solvay process, §3, p31. recovery in Solvay process, §3, p29. soda, Analysis of, §6, pi. soda, Properties of, §3, p32. used in Solvay process, §3, pl4. Ammoniacal brine, §3, p21. brine. Analysis of, §6, p7. brine, Carbonating, §3, p22. brine, Determination of ammonia in, §6, p7. brine, Determination of salt in, §6, p7. Analysis of salt, §18, p42. Animal size or glue for paper, §17, p25. size or glue, Testing of, §18, p41. Anions, §5, pl7. Antichlor, §17, p8. Apparatus employed in the chamber process for sulphuric acid, §2, p5. for paper analysis, §18, pi. Arsenic, Determination of, in hydrochloric acid, §6, p39. Freiberg process for removing, from chamber acid, §2, p43. Precipitation of, in the Freiberg process, §2, p46. ix 199—39 X INDEX Arsenic—(Continued) Purification of chamber acid from, §2, p43. Stahl method for removing, from chamber acid, §2, p47. Available sulphur, §1, pl5. sulphur in burner gas, §1, pl4. B Barium chlorate, §4, p61. sulphate, §17, p28. Barre and Bondel’s nitric-acid process for wood pulp, §16, p60. Baume specific-gravity scale, European, §1, p6. specific-gravity scale, United States, §1, p6. Beating engine, §17, pl6. engine, Jordan’s, §17, pl9. of fibers, §17, pi 6. Bertam’s boiler for rags, §16, p9. Bicarbonate from filters, Analysis ot, §6, pll. from filters, Determination of ammonia in, §6, pl3. from filters, Determination of moisture in, §6, pl3. from filters, Determination of sodium bicarbonate in, §6, pll. from filters, Determination of total alkali in, §6, pll. Bisulphite liquor, Analysis of, §18, p46. liquor for the sulphite process, §16, p42. Black ash, Analysis of, §6, p21; §18, p21. ash, Analysis of lye from extraction of, §6, p23. ash, Composition of, §3, p59. ash, Cyanides in, §3, p57. ash, Determination of caustic soda in, §6, p22. ash, Determination of free lime in, §6, p21. ash, Determination of salt in, §6, p23. ash, Determination of sodium carbonate in, §6, p23. ash, Determination of sodium sulphate in, §6, p22. ash, Determination of total alkali in, §6, p22. ash, Leaching of, §16, p40. ash, Lixiviation of, §3, p59. ash, Properties of, §3, p58. ash, Sampling of, §6, p21. Blanc fix, §17, p28. Bleach, Electrolytic, §5, p44. liquors, Analysis of, §6, p50. liquors, Determination of available chlorine in, §6, p48. liquors, Determination of carbonates in, §6, p49. Bleach—(Continued) liquors, Determination of caustic alkali in, §6, p49. liquors, Determination of chlorates in, §6, p48. liquors, Determination of chlorides in, §6, p48. sludge, Analysis of, §18, p21. Valuation of, §4, p51. Bleached stock, Treatment of, §17, pl4. Bleaching, Electrolytic, §17, p8. of chemical wood fiber, §17, po. of esparto, §17, p4. of fibers, §17, pi. of ground wood, §17, p5. of jute, §17, p5. of manila, §17, p5. of pulp from rags, §17, p4. of sulphite pulp, §17, p6. of straw, §17, p5. powder, §4, p46. powder, Absorption chambers for, §4, p47. powder, Analysis of, §6, p50; §18, pl9. powder, Chlorine for making of, §4, p48. powder, Composition of, §4, p50. powder, Lime for making of, §4, p46. powder, Preparation of solution of, §17, p2. powder, Properties of, §4, p50. powder, Uses of, §4, p52. Blind roaster for salt cake, §3, p42. Blumberg electrolytic process for potassium chlorate, §5, p48. Bombonnes for condensing hydrochloric acid, §4, pl5. Brimstone, §1, p8. burner, Harrison-Blair, §1, p26. burners, §1, p25. or sulphur, Analysis of, §18, p43. Brine, Ammoniacal, §3, p21. ammonical, Analysis of, §6, ppl, 7. ammoniacal, Determination of ammonia in, §6, p7. ammoniacal, Determination of salt in, §6, P 7. Determination of calcium oxide in, §6, p3. Determination of ferric oxide and alumina in, §6, p2. Determination of inorganic sediment in, §6, p2. Determination of magnesia in, §6, p3. Determination of sodium chloride in, §6, p3. Determination of specific gravity of, §6, pi. Determination of sulphur trioxide in, §6, p3. Evaporation of, by grainers, §3, p6. for Solvay process, Purification of, §3, p20. Kettle evaporation of, §3, p5. INDEX xi Brine—(Continued) Open-pan process for evaporation of, §3, p5. Salt from, §3, p3. Solar evaporation of, §3, p4. used in Solvay process, §3, pl4. Vacuum-pan process for the evaporation of, §3, p6. Broke beater, §17, pl9. Brown size for paper, §17, p22. Bunte Burette, §6, p8. Burette, Reagents for, §6, pll. Burette, Bunte, §6, p8. Burgess absorption apparatus for sulphur dioxide, §16, p46. Burner gas, §1, pl3. gas, Available sulphur in, §1, pl4. gas, Calculation of volume of, §1, p40. gas, Collecting sample of, §1, p36. gas, Furnaces and burners for the pro¬ duction of, §1, p23. gas, Production of, §1, p21. gas, Purification of, §1, p50. • gas, Reheating of, §1, p52. gas, Reich’s test for sulphur dioxide in, §1, p36. gas. Testing, §1, p36. Harrison-Blair brimstone, §1, p26. Burners and furnaces for the production of burner gas, §1, p23. Brimstone, §1, p25. Pyrites, §1, p27. C Calcination of sodium bicarbonate, §3, p26. Calcining furnace for sodium bicarbonate, §3, p26. of soda crystals, §3, p65. Calcium carbonate, Determination of, in quicklime, §6, p6. carbonate, Determination of, in soda ash, §6, pl6. carbonate for the Le Blanc soda process, §3, p50. chloride, Determination of, in still liquor, §6, p44. fluoride from cryolite-soda process, §3, p34. oxide, Determination of, in brine, §6, p3. oxide, free, Determination of, in quicklime, §6, p6. sulphate or gypsum, §17, p27. Calender, §17, p39. Calendering of paper, §17, p38. Carbonated lye, Analysis of, §6, p24. lye, Determination of sodium bicarbonate in, §6, p25. Carbonates, Determination of, in bleach liquors, §6, p49. Carbonating ammoniacal brine, §3, p22. tower for Solvay process, §3, p22. Carbon dioxide, Determination of, in man¬ ganese ore, §6, p42. dioxide, Determination of, in slaked lime, §6, p43 dioxide for Solvay process, §3, pl5. dioxide for Solvay process, Washing of, §3, pl8. for the Le Blanc soda process, §3, paO. Cardboard or pasteboard, §17, p44. Casein sizing for paper, §17, p26. Castner-Kellner electrolytic process for salt, §5, p39. Catalytic or contact process for the manu¬ facture of sulphuric acid, §1, p43. Cations, §5, pl7. Caustic alkali, Determination of, in bleach liquors, §6, p49. bottoms, Analysis of, §6, p34. bottoms, Determination of insoluble matter in, §6, p35. bottoms, Determination of salt in, §6, p35. bottoms, Determination of sodium car¬ bonate in, §6, p35. bottoms, Determination of total alkali in, §6, p35. lime, Determination of, in caustic mud, §6, p35. liquor, Analysis of, §6, p33. liquor, Determination of salt in, §6, p34. liquor, Determination of specific gravity of, §6, p33. liquor, Determination of total alkali and sodium carbonate in, §6, p34. liquor, Filtration of, §4, p4. mud, §4, p9. mud, Analysis of, §6, p35; §18, p49. mud, Determination of calcium carbonate in, §6, p35. mud, Determination of total alkali in, §6, p35. pots, §4, p7. soda, Analysis of, §6, p36. soda, crude materials for, Analysis of, §6, p32. soda, Determination of, in black ash, §6, p22. soda, Determination of, in lye from extrac¬ tion of black ash, §6, p23. soda, Determination of, in soda ash, §6, p28. soda, Determination of total alkali in, §6, p36. Causticizing lime, Analysis of, §18, pl2. pans, Analysis of sludge from, §18, pl7. INDEX Causticizing—(Continued) sodium carbonate, §4, p3. Cellulose, §16, p2. Chamber acid, Freiberg process for removing arsenic from, §2, p43. acid, Purification of, §2, p42. acid, Purification of, from arsenic, §2, p43. acid, Stahl method for removing arsenic from, §2, p47. crystals, §2, p3. process, Diagram of, §2, p33. process for sulphuric acid, §2, pi. process for sulphuric acid, Control of, §2, p38. process for sulphuric acid, Operation of, §2, p28. process for sulphuric acid, Reactions of, §2, p2. process for sulphuric acid, Starting of, §2, p35. Chambers, Lead, §2, pll. Chance-Claus process for recovery of sulphur from tank waste, §3, p71. Charging sulphite digesters, §16, p51. Chemical wood fiber, Bleaching of, §17, p5. Chemicals for paper analysis, §18, pi. China clay or kaolin, §17, p27. Chlorate, Potassium, Analysis of, §6, p50. Chlorates, Analysis of, §6, p50. Determination of, in bleach liquors, §6, §48. Chlorides, Determination of, in bleach liquors, §6, p48. Chlorine, §4, p25. available, Determination of, in bleach liquors, §6, p48. by the Weldon process, §4, p37. Deacon’s process for, §4, p39. direct from salt, §4, p26. for making bleaching powder, §4, p48. from hydrochloric acid, §4, p27. Liquid, §4, p45. Source of, §4, p26. used in the manufacture of potassium chlorate, §4, p55. Clay, Analysis of, §18, p31. Claus kiln for sulphur recovery, §3, p73. Clear liquor, Determination of calcium chloride in, §6, p44. Coal, Analysis of, §6, p7. used in Solvay process, §3, pl5. Coke, Analysis of, §6, p7. towers for condensing hydrochloric acid, §4, pl6. used in Solvay process, §3, pl5. Color of ground wood, §16, pl8. value of pigments, §18, p50. Coloring material for paper, §17, p28. of paper, §17, p28. Combustion of sulphur, §1, pl2. Commercial methods for determining the strength of sulphuric-acid solutions weaker than the monohydrate, §1, p5. Comparison of pigments, §18, p50. of soluble colors, §18, p51. Concentrating pots for the manufacture of potassium chlorate, §4, p58. Concentration and distillation of sulphuric acid starting with the Glover tower, §2, p56. of dilute sulphuric-acid solutions, §2, p4S. of sulphuric acid by the Kessler process, §2, p55. of sulphuric acid in glass retorts or stills, §2, p52. of suphuric acid in iron, §2, p51. of sulphuric acid in lead pans, §2, p48. of sulphuric acid in platinum, §2, p49. of sulphuric acid in porcelain or glass beakers or dishes, §2, p53. Condensation of hydrochloric acid, §4, pl3. Condenser, Falding, §2, pl9. Gilchrist, §2, pl8. Lunge, §2, pl6. Condensers, Surface, §2, pl6. Conditions in the chambers in the manu¬ facture of sulphuric acid, §2, p30. in the Glover tower, §2, p29. Conductivity of solutions, §5, p6. of solutions, Determination of, §5, p8. of solutions, The effect of temperature on §5, p6. vessel, §5, p7. Conductors, Electric, §5, pl6. Constant-temperature bath, §5, p7. Contact mass or material used in the manu¬ facture of sulphuric acid in the contact process, §1, p45. ovens, §1, p53. process for sulphuric acid, Diagram of, §1, p54. process for the manufacture of sulphuric acid, §1, p43. Converter, Frasch, §1, p49. Cooking, or digesting of wood for pulp, §16, p23. Copper-nickel pyrrhotites, §1, p8. Copperas slate, §1, p8. Corbin electrolytic process for potassium chlorate, §5, p48. Cotton, §16, p3. Cryolite-soda process, §3, p33. -soda process, Calcium fluoride from, §3, p34. INDEX xiii Cryolite—(Continued) -soda process, Sodium aluminate from, §3, p34. Crystal soda, Analysis of, §6, p29. Crystallizing pans for the manufacture of potassium chlorate, §4, p58. Curtain drip, §2, p40. Cutting of paper, §17, p41. Cyanides in black ash, §3, p57. D Deacon-Hasenclever process for the purifica¬ tion of hydrochloric acid, §4, p41. Deacon’s plus-pressure furnace for salt cake, §3, p43. process for chlorine, §4, p39. Deckle, §17, p31. Density of sulphuric acid, Determination of, §1, p5- Diagram of chamber process, §2, p33. of contact process for sulphuric acid, §1, p54. of manufacture of sulphuric acid, §2, p60. Digesters for wood pulp, §16, p20. Sulphite, §16, p50. sulphite, Charging of, §16, p51. Digesting, or cooking of wood for pulp, §16, p23. Disposition of waste sulphite liquor, §16, p56. Dissociation, Electrolytic, §5, pl9. Distiller liquor in Solvay process, §3, p30. Drying ovens, §18, p3. E Eau de Javel, §4, p53. de Labarraque, §4, p53. Electric conductors, §5, pl6. current. Sources of, §5, pi. polarization, §5, p20. Electricity, Quality of, §5, pll. Electrodes, §5, pl7. for the electrolysis of salt, §5, p25. Platinizing, §5, p8. Electrolysis, §5, pi7. of salt, §5, p24. of salt by Acker’s process, §5, p28. of salt by Castner-Kellner process, §5, p39. of salt by Hulin’s process, §5, p26. of salt by Le Sueur process, §5, p35. of salt by processes using a mercury cathode, §5, p39. of salt by the Hargreaves-and-Bird process, §5, p37. of salt by the Townsend process, §5, p31. of salt, Conditions favoring, §5, p24. Electrolysis—(Continued) of salt with dissolved electrolyte, §5, p30. of salt with fused electrolyte, §5, p26. Electrolytes, §5, pi7. Electrolytic bleach, §5, p44. bleaching, §17, p8. dissociation, §5, pl9. methods for the production of alkali and chlorine, §5, p23. Electromotive force, §5, pl3. force, Measurement of, §5, pl3. force of polarization, Calculation of, from heat of reaction, §5, p21. Engine sizing of paper, §17, p21. Esparto, Bleaching of, §17, p4. grass, §16, p4. pulp, §16, pl2. pulp, Washing of, §16, pl2. Evaporation of brine by grainers, §3, p6. of brine by vacuum-pan process, §3, p6. of brine, Kettle, §3, p5. of brine, Open-pan process for, §3, p5. of brine, Solar, §3, p4. of sodium hydrate, §4, p5. of tank liquor, §3, p63. Evaporator, Yaryan, §4, p5. Exit gas, Determination of percentage of sul¬ phur dioxide in, §1, p39. F Falding condenser, §2, pl9. lamp burner, §1, p27. Faraday’s law, §5, pl8. Ferric oxide, Determination of, in lye from extraction of black ash, §6, p24. oxide, Determination of, in salt cake, §6, pl9. oxide, Determination of, in soda ash, §6, pl6. oxide in brine, Determination of, §6, p2. Fibers, Beating of, §17, pl6. Bleaching of, §17, pi. Miscellaneous, used in the manufacture of paper, §16, p6. Filters for Solvay process, §3, p24. Filtration of caustic liquor, §4, p4. of water, §17, p46. Finishing the paper, §17, p44. Fished salts, Analysis of, §6, p34. salts, Determination of oxidizable com¬ pounds in, §6, p34. salts, Determination of sodium sulphate in, §6, p34. salts, Determination of total alkali in, §6, p34. Fourdrinier, or paper machine, §17, p31. Frasch converter, §1, p49. XIV INDEX Free acid, Determination of, in salt cake, §6, pl9. lime, Determination of, in black ash, §6, P 21. Freezing process for the production of sul¬ phuric monohydrate, Lunge, §2, p59. Freiberg process for removing arsenic from chamber acid, §2, p43. sulphureted hydrogen generator, §2, p44. Fuming sulphuric acid, §1, p4. Furnace for calcining sodium bicarbonate, §3, p26. Herreshoff, of the MacDougall type, §1, p30. Maletra-Falding, §1, p30. muffled, MacDougall type of, §1, p34. Rhenania muffled type of, §1, p34. Spence reciprocating type of, §1, p31. Furnaces and burners for the production of burner gas, § 1, p23. for the Le Blanc process, Hand, §3, p51. Le Blanc soda process, Mechanical, §3, p54. G Gall-and-Montlaur electrolytic process for potassium chlorate, §5, p47. Gas, Burner, §1, pl3. from bleaching-powder chambers, Testing of, §6, p47.' from decomposer, Analysis of, §6, p46. from gasometer, Analysis of, §6, p30. from sulphate pan, Analysis of, §6, p45. Gases from ammonia saturator, Washing, §3, p24. lime-kiln, Analysis of, §6 p30. Gay-Lussac tower, §2, p21. -Lussac towers, Number of, §2, p37. Gerster’s formula, §1, p21. Gibbs electrolytic process for potassium chlorate, §5, p49. electrolytic process for the manufacture of potassium chlorate, §5, p49. Gilchrist condenser, §2, pl8. Glauber’s salt, §3, p36. Glover tower, §2, p8. tower, Conditions in, §2, p29. Glue or animal size for paper, §17, p25. or animal size, Testing of, §18, p41. Gotham screen for washing wood pulp, §16, p27. Grading of crude sulphur, §1, p9. Grainers for evaporation of brine, §3, p6. Grass, Esparto, §16, p4. Grinding crystals of potassium chlorate, §4, p60. of soda ash, §3, p65. of wood, §16, pl4. Ground plan of sulphite pulp mill, §16, p58. wood, §16, pl4. wood, Bleaching of, §17, p5. wood, Color of, §16, pl8. Guillotine paper cutter, §17, p43. Gypsum or calcium sulphate, §17, p27. H Hargreaves-and-Bird process for the electrol¬ ysis of salt, §5, p37. Harrison-Blair brimstone burner, §1, p26. Hart system for absorption of hydrochloric acid, §4, pl9. Hasenclever method for purification of hydro¬ chloric acid, §4, p20. Herreshoff furnace of the MacDougall type, §1, p30. Hulin’s process for the electrolysis of salt, §5, p26. Hydrates and solutions of sulphur trioxide, §1, Pl¬ ot sulphur trioxide, Nomenclature of, §1, p3. Hydrochloric acid, Analysis of, §6, p36. acid, Analysis of finished product, §6, p38. acid, Analysis of waste gases from absorp¬ tion of, §6, p36. acid, Apparatus used for condensing, §4, pl4. acid, Commercial, §4, pl9. acid, Condensation of, §4, pl3. acid, Determination of arsenic in, §6, p39. acid, Determination of hydrochloric acid in, §6, p41. acid, Determination of selenium in, §6, p40. acid, Determination of sulphuric acid in, §6, p39. acid, Determination of sulphurous acid in, §6, p39. acid, Manufacture of, by electrolysis, §4, p21. acid, Process of manufacture of, §4, pl2. acid, Purification of, §4, p20. acid, Purification of, by the Deacon-Hasen- clever process, §4, p41. acid, Qualitative tests for arsenic in, §6, p40. acid, Uses of, §4, p22. Hydrogen sulphide, §1, p8. sulphide generator, Freiberg, §2, p44. Sulphureted, §1, plO. Hydrometers, §18, p2. I Indicators for paper analysis, §18, plO. Inorganic sediment in brine, Determination of, §6, p2. INDEX xv Insoluble matter, Determination of, in caustic bottoms, §6, p35. matter in limestone, Determination of, §6, p4. matter in quicklime. Determination of, §6, p6. Ions, §5, pl7. Migration velocity of, §5, pl9. Iron pyrites, §1, p8. J Jewell filter, §17, p50. Jordan’s beating engine, §17, pl9. Jute, §16, p6. Bleaching of, §17, p5. pulp, §16, pl4. K Kaolin or china clay, §17, p27. Kessler process, Concentration of sulphuric acid by, §2, p55. Kestner automatic pump, §2, p25. Kettle evaporation of brine, §3, p5. Knofler drying oven, §18, p4. L Laid paper, §17, p37. Le Blanc process, Advantages and disad¬ vantages of mechanical furnace in, §3, p57. Blanc process, Management of the mechan¬ ical furnace for, §3, p55. Blanc process, Tank waste, §3, p69. Blanc soda process, §3, p48. Blanc soda process, Calcium carbonate for, §3, p50. Blanc soda process, Carbon for, §3, p50. Blanc soda process. Charge for the mechan¬ ical furnace for, §3, p55. Blanc soda process, Details of, §3, p51. Blanc soda process, Hand furnaces for, §3, p51. Blanc soda process. Management of fur¬ nace for, §3, p52. Blanc soda process. Mechanical furnaces for, §3, p54. Blanc soda process, Raw materials for, §3, p50. Sueur process for the electrolysis of salt, §5, p35. Leaching of black ash, §16, p40. Lead chambers, §2, pll. chambers, Admission of steam to, §2, p33. chambers, Conditions in, §2, p30. Leaf pulp, §16, pl8. Lime, caustic, Determination of, in caustic mud, §6, p35. Lime—(Continued) causticizing, Analysis of, §18, pl2. Complete analysis of, §18, pl4. Determination of, in limestone, §6, p4. Determination of, in salt cakes, §6, p20. free, Determination of, in black ash, §6, p21. kiln for making carbon dioxide for, Solvay process, §3, pl5. -kiln gases, Analysis of, §6, pp7, 30. milk of, Analysis of, §6, pl4. milk of, Determination of specific gravity of, §6, pl4. slaked, Analysis of, §6, p43. total, Determination of, in black ash, §6, p21. used in making bleaching powder, §4, p46. used in the manufacture of potassium chlorate, §4, p55. used in the manufacture of sodium hydrate, §4, p3. Limestone, Analysis of, §6, p4. Determination of insoluble matter in, §6, p4. Determination of lime in, §6, p5. Determination of magnesia in, §6, p5. used in Solvay process, §3, pl3. Linen, §16, p3. Liquid chlorine, §4, p45. Liquor, caustic, Analysis of, §6, p33. from carbonators, Analysis of, §6, pll. Lixiviation of black ash, §3, p59. Loading of paper, §17, p27. Loewig’s process for the manufacture of sodium hydrate, §4, plO. Lump burner, Falding, §1, p27. Lunge condenser, §2, pl6. freezing process for the production of sul¬ phuric monohydrate, §2, p59. plate column, §2, pl6. plate tower for condensing hydrochloric acid, §4, pl8. Lye, carbonated, Analysis of, §6, p24. from black ash, Analysis of, §6, p23. from black ash, Determination of caustic soda in, §6, p23. from black ash, Determination of salt in, §6, p23. from black ash, Determination of silica, ferric oxide, and alumina in, §6, p24. from black ash, Determination of sodium carbonate in, §6, p23. from black ash, Determination of sodium ferrocyanide in, §6, p24. from black ash, Determination of sodium sulphate in §6, p24. XVI INDEX Lye—(Continued) from black ash, Determination of sodium sulphide in, §6, p23. from black ash, Determination of specific gravity of, §6, p23. from black ash, Determination of total alkali in, §6, p23. from black ash, Determination of total sul¬ phur in, §6, p24. Purification of, §3, p61. M MacDougall type of muffled furnace, §1, p34. Magnesia, Determination of, in brine, §6, p3. Determination of, in limestone, §6, p5. Determination of, in quicklime, §6, p6. Determination of, in salt cake, §6, p20. lime, Analysis of, §18, pl6. Magnesium carbonate, Determination of, in soda ash, §6, pl7. Maletra-Falding furnace, §1, p30. Manganese in Weldon mud. Determination of, §6, p44. ore, Analysis of, §6, p41. ore, Determination of acid necessary to decompose, §6, p43. ore, Determination of available oxygen in, §6, p42. ore, Determination of carbon dioxide in, §6, p43. ore, Determination of moisture in, §6, p41. Weldon’s process, for the recovery of, from still liquors, §4, p33. Manila, Bleaching of, §17, p5. Materials, Principal, used in the manufacture of paper, §16, p3. McDougald absorption apparatus for sulphur dioxide, §16, p45. Mechanical furnaces for salt cake, §3, p45. pans for the evaporation of tank liquor, §3, p64. pulp, Preparation of, §16, pl4. tests of paper, §18, p60. Microscopic fiber test of paper, §18, p56. Migration velocity of ions, §5, pl9. Milk of lime, Analysis of, §6, pl4. of lime, Specific gravity of, §6, pl4. Mirabilite, §3, p36. Miscellaneous sizes for paper, §17, p26. Mixed acid, §2, p58. Moisture, Determination of, in bicarbonate from filters, §6, pl3. Determination of, in manganese ore, §6, p41. Monohydrate of sulphur trioxide, §1, p3. Monteju’s pump with acid egg, §2, p26. Mother liquor, Analysis of, §6, pl3. Mother—(Continued) liquor, Determination of ammonia in, § 6 , pl4. liquor, Determination of salt in, §6, pl4. Mud, Caustic, §4, p9. caustic, Analysis of, §6, p35. Weldon, §4, p36. Weldon, Analysis of, §4, p44. Muffle roaster for salt cake, §3, p42. Muffled furnace, MacDougall type of, §1, p34. type of furnace, Rhenania, §1, p34. N Niter oven, Definition of, §1, p25. Nitrating by potting, §2, p5. by use of nitric acid, §2, p7. oven, §2, p5. Nitric-acid chlorine process, §4, p45. Nitrohydrochloric-acid process for wood pulp, §16, p60. Nitrosulphuric acid, §2, p3. Nitrous vitriol, §2, p5. Nomenclature of solutions and hydrates of sulphur trioxide, §1, p3. Nordhausen sulphuric acid, §1, p4. O Ocher, Analysis of, §18, p32. Ohm’s law, §5, pl6. Open-pan process for the evaporation of brine, §3, p5. roasters for salt cake, §3, p38. Oven, Contact, §1, p53. Nitrating, §2, p5. Oxygen, available, Determination of, in manganese ore, §6, p42. P Paper analysis, Apparatus for, §18, pi. analysis, Chemicals for, §18, pi. analysis, Indicators for, §18, plO. analysis, Standard solutions for, §18, p5. Animal size or glue for, §17, p25. Brown size for, §17, p22. Calendering of, §17, p38. Chemical tests for constituents of, §18, p58. Coloring material for, §17, p28. Coloring of, §17, p28. cutter, Guillotine, §17, p43. Cutting of, §17, p41. Determination of retention of filler in, §18, p56. Engine sizing of, §17, p21. Finishing of, §17, p44. History of, §16, pi. Loading of, §17, p27. machine, or fourdrinier, §17, p81. made by hand, §17, p30. INDEX XVII Paper — (Continued) made by machine, §17, p31. Mechanical tests of, §18, p60. Microscopic fiber test of, §18, p56. Miscellaneous sizes for, §17, p26. Parchment, §17, p45. Principal materials used in the manufacture of, §16, p3. Rosin size for, §17, p21. Sizing of, §17, p21. Sizing of, with casein, §17, p26. Sizing of, with starch, §17, p26. Slitting and rewinding machine for, §17, p42. Supercalendering of, §17, p39. testing, §18, p56. Tub sizing of, §17, p37. Water finish of, §17, p39. White size for, §17, p22. Parchment paper, §17, p45. Pasteboard or cardboard, §17, p44. Pauli’s method for purification of lye, §3, p62. Pictet and Brelaz’s process for wood pulp, §16, p60. Pigments, Color value of, §18, p50. Comparison of, §18, p50. Plate column, Lunge, §2, pl6. tower, Lunge, for condensing hydrochloric acid, §4, pl8. Platinizing electrodes, §5, p8. Platinum black, §1, p46. Polarization, Electric, §5, p20. Potassium chlorate, §4, p54. chlorate, Analysis of, §6, p50. chlorate, Apparatus used in the manufac¬ ture of. §4, p56. chlorate by electrolysis, §5, p46. chlorate by Gall-and-Montlaur electrolytic process, §5, p47. chlorate by the Blumenberg electrolytic process, §5, p48. chlorate by the Corbin electrolytic process, §5, p48. chlorate, Chlorine used in the manufacture of, §4, p55. chlorate, Determination of potassium chloride in, §6, p50. chlorate, Drying the crystals of, §4, p60. chlorate, Grinding the crystals of, §4, p60. chlorate, Lime used in the manufacture of, §4, p55. chlorate, Potassium chloride used in the manufacture of, §4, p55. chlorate, Raw materials used in the manu¬ facture of, §4, p55. chlorate, Recrvstallization of, §4, p59. chloride, Determination of, in potassium chlorate, §6, p50. Potassium — (Continued) chloride used in the manufacture of potas¬ sium chlorate, §4, p55. Pots, Caustic, §4, p7. Potting, §1, p25. Precipitation of arsenic in the Freiberg process, §2, p46. Preparation of solution of bleaching powder for fibers, §17, p2. Pulp, Digesters of wood for, §16, p20. Digesting, or cooking of wood for, §16, p23. Esparto, §16, pl2. esparto, Washing of, §16, pl2. from rags, §16, p7. from straw, jute, and other materials, §16, pl3. Leaf, §16, pl8. Manufacture of, §16, p7. Soft, §16, pl8. Wood, §16, pl4. wood, Analysis of, §18, p52. Wood, by Barre and Bondel’s nitric-acid process, §16, p60. Wood, by nitrohydrochloric-acid process, §16, p60. Wood, by Pictet and Brelaz’s process, §16, p60. Wood, by soda process, §16, pl9. Wood, by sulphate process, §16, p.59. wood, Liquor for soda-process, §16, p29. wood, Screening of, §16, pi7. wood, Screens for washing of, §16, p25. wood, Washing of, §16, p23. , Pump, Kestner automatic, §2, p25. Monteju’s, with acid egg, §2, p26. Pumps, Acid, §2, p25. Purification of brine for Solvay process, §3, § 20 . of chamber acid, §2, p42. of chamber acid, from arsenic, §2, p43. of lye, §3, p61. of water, §17, p46. Pyrites burners, §1, p27. Copper and iron, §1, p8. Pyrrhotites, Copper-nickel, §1, p8. Q Qualitative tests for arsenic in hydrochloric acid, §6, p40. Quicklime, Analysis of, §6, p5, Determination of calcium carbonate in §6, p6. Determination of free calcium oxide in, §6, p6. Determination of insoluble matter in, §6, p6. Determination of magnesia in, §6, p6. INDEX xviii R Rag boiler, §16, p9. engine, §16, pll. pulp, Bleaching of, §17, p4. Rags, Bleaching of, §16, pll. Cutting and boiling of, §16, p8. Sorting of, §16, p6. Washing and breaking of, §16, pll. Reactions of the chamber process for sul¬ phuric acid, §2, p2. Reagents for Bunte burette, §6, pll. Reciprocating type of furnace, Spence, §1, p31. Recovery of soda, §16, p34. of soda, Calculation of, §16, p41. Red liquors, Analysis of, §6, p25. liquors, Determination of sodium sulphide, sulphite, thiosulphate, and sulphate in, §6, p25. Reheating of burner gas, §1, p52. Reich’s test for sulphur dioxide in burner gas, §1, p36. Resistance capacity, §5, plO. electrical, Measurement of, §5, p4. Retention of filler, Determination of, in paper, §18, p56. Rhenania muffled type of furnace, §1, p34. Roasting, Sources of loss of sulphur in, § 1, pl5. Rock salt, §3, p3. Rosin, Analysis of, §18, p38. size, Analysis of, §18, p38. size for paper, §17, p21. Rotary drying furnaces for soda recovery, §16, p38. S Salem white, §17, p28. Salt, Analysis of, §6, pl7. cake, §3, p35. cake, Analysis of, §6, pl9. cake, Apparatus and method of manufac¬ ture of, §3, p38. cake, Blind, or muffle, roaster for, §3, p41. cake, Crude materials for, §3, p36. cake, Deacon’s plus-pressure furnace for, §3, P 43. cake, Determination of alumina in, §6, pl9. cake, Determination of ferric oxide in, §6, pl9. cake, Determination of free acid in, §6, pl9. cake, Determination of lime in, §6, p20. cake, Determination of magnesia in, §6, p20. cake, Determination of matter insoluble in acids in, §6, pl9. cake, Determination of sodium sulphate in, §6, p20. cake, Mechanical furnaces for, §3, p45. cake, Open roasters for, §3, p38. Salt—(Continued) -cake process, Analysis of materials for, §6, pl7. cake, Properties of, §3, p48. cake, Salt for making, §3, p36. cake, Sulphuric acid for making, §3, p37. cake, Uses of, §3, p48. cake, Yield of, §3, p47. Determination of, in ammoniacal brine, §6, p7. Determination of, in black ash, §6, p23. Determination of, in caustic bottoms, §6, p35. Determination of, in caustic liquor, §6, p34. Determination of, in fished salts, §6, p34. Determination of, in lye from extraction of black ash, §6, p23. Determination of, in mother liquor, §6, pl4. Determination of, in salt cake, §6, pl9. Determination of salt in, §6, pl9. Determination of sodium chloride in, §6, pl7. Determination of sulphur trioxide in, §6, pl8. Determination of water in, §6, pl7. Electrolysis of, §5, p24. Electrolysis of, by Castner-Kellner process, §5, p39. Electrolysis of, by Hargreaves-and-Bird process, §5, p37. Electrolysis of, by Le Sueur process, §5, p35. Electrolysis of, by processes using a mercury cathode, §5, ,p39. Electrolysis of, by processes using dia¬ phragms, §5 ; p31. Electrolysis of, by Townsend process, §5, p31. Electrolysis of, with dissolved electrolyte, §5, p30. for making salt cake, §3, p36. from brine, §3, p3. from sea-water, §3, pi. Occurrence of, §3, pi. Schweitzer’s reagent, §16, p3. Screens for washing wood pulp, §16, p25. Sea-water, Salt from, §3, pi. Selenium, Determination of, in hydrochloric acid, §6, p40. Settling pans for manufacture of potassium chlorate, §4, p58. Shank’s lixiviation system of black ash, §3, p60. Shunt circuit, §5, pl5. Silica, Determination of, in lye from extrac¬ tion of black ash, §6, p24. Determination of, in soda ash, §6, pl6. INDEX xix Sizes for paper, Adaptability of, §17, p26. Sizing of paper with casein, §17, p26. of paper with starch, §17, p26. paper, §17, p21. test for alum, §18, p27. Slaked lime, Analysis of, §6, p43. lime, Determination of carbon dioxide in, §6, p43. lime, Determination of water in, §6, p43. Slitting and rewinding machine for paper, §17, p42. Sludge from causticizing pans, Analysis of, §18, pl7. Soda, ammonia, Analysis of, §6, pi. ammonia, Properties of, §3, p32. Artificial, §3, plO. ash, Analysis of, §6, ppl6, 27; §18, pll. ash, Determination of caustic soda in, §6, p28. ash, Determination of ferric oxide and alumina in, §6, pl6. ash, Determination of magnesium carbon¬ ate in, §6, pl7. ash, Determination of silica in, §6, pl6. ash, Determination of sodium bicarbonate in, §6, pl6. ash, Determination of sodium carbonate in, §6, p28. ash, Determination of sodium chloride in, §6, pl6. ash, Determination of sodium sulphate in, §6, pl7. ash, Determination of sodium sulphide in, §6, p28. ash, Determination of total alkali in, §6, p28. ash, Finished, §3, p67. ash, Grinding of, §3, p6.5. ash, Methods of stating strength of, §3, p68. ash used in the manufacture of sodium hydrate, §4, p2. by the Le Blanc process, §3, p48. caustic, Analysis of, §6, p36. crystal, Analysis of, §6, p29. crystals, §3, p66. crystals, Calcining of, §3, p65. Natural, §3, p9. process, Cryolite, §3, p33. process for wood pulp, §16, pl9. pulp, Analysis of, §18, p54. pulp mill, Ground plan of, §16, p33. recovery, Calculation of, §16, p41. Recovery of, §16, p34. recovery, Rotary drying furnaces, §16, p38. Sodium aluminate from cryolite-soda process, §3, p34. bicarbonate, §4, pll. Sodium—(Continued) bicarbonate, Analysis of, §4, pl2; §6, p32. bicarbonate, Calcination of, §3, p26. bicarbonate, Determination of, in bicar¬ bonate from filters, §6, pll. bicarbonate, Determination of, in carbon¬ ated lye, §6, p25. bicarbonate, Determination of, in soda ash, §6, P 16. bicarbonate, Dry process for purification of, §4, pl2. bicarbonate, Wet process for purification of, §4, pll. carbonate, §3, p9. carbonate, Causticizing the, §4, p3. carbonate, Crystals of, §3, p66. carbonate, Determination of, in black ash, §6, p23. carbonate, Determination of, in caustic bottoms, §6, p35. carbonate, Determination of, in caustic liquor, §6, p34. carbonate, Determination of, in lye from extraction of black ash, §6, p23. carbonate, Determination of, in soda ash, §6, ppl6, 28. carbonate, Uses of, §3, p67. chlorate, §4, p60. chloride, §3, pi. chloride, Determination of, in brine, §6, p3. chloride, Determination of, in salt, §6, pl7. chloride, Determination of, in soda ash, §6, pl6. compounds, total, Determination of, in tank waste, §6, p27. ferrocyanide, Determination of, in lye from extraction of black ash, §6, p24. hydrate, §4, pi. hydrate, Crude materials used in manufac¬ ture of, §4, p2. hydrate, Details of process of manufacture of, §4, p3. hydrate, Evaporation of, §4, p5. hydrate, Lime used in the manufacture of, §4, p3. hydrate, Loewig’s process for manufacture of, §4, plO. hydrate, Removal of sulphur from, §4, p8. hydrate, Soda ash used in the manufacture of, §4, p2. hydrate, Uses of, §4, plO. sulphate, §3, p35. sulphate, Determination of, in black ash, §6, p23. sulphate, Determination of, in fished salts, §6, p34. XX INDEX Sodium—(Continued) sulphate, Determination ot, in lye from extraction of black ash, §6, p24. sulphate, Determination of, in red liquors, §6, p25. sulphate, Determination of, in salt cake, §6, p20. sulphate, Determination of, in soda ash, §6, pl7. sulphate for Le Blanc soda process, §3, p,50. sulphide, Determination of, in black ash, §6, p32. sulphide. Determination of, in lye from extraction of black ash, §6, p23. sulphide, Determination of, in red liquors, §6, p25. sulphide, Determination of, in soda ash, §6, p28. thiosulphate, §3, p78. thiosulphate, Determination of, in red liquors, §6, p25. Soft pulp, §16, pl8. Soluble colors, Comparison of, §18, p51. Solutions for resistance capacity, §5, pll. Solvay process, §3, pll. process, Ammonia lost in, §3, p31. process, Ammonia recovery in, §3, p29. process, Ammonia used in, §3, pl4. process, Ammoniacal brine of, §3, p21. process, Brine used in, §3, pl4. process, Carbon dioxide for, §3, pl5. process, Carbonating ammoniacal brine for, §3, p22. process, Carbonating tower for, §3, p22. process, Coal and coke used in, §3, pl5. process, Details of, §3, pl5. process, Distiller liquor in, §3, p30. process, Filters for, §3, p24. process, Limestone used in, §3, pl3. process, Purification of brine for, §3, p20. process, Raw materials used in, §3, pl3. process, Washing of carbon dioxide for, §3, pl8. Sorting of rags, §16, p7. Specific gravity, Determination of, of lye from extraction of black ash, §6, p23. gravity of ammonia liquor, Determination of, §6, p6. gravity of brine, Determination of, §6, pi. gravity of caustic liquor, Determination of, §6, p33. gravity of milk of lime, Determination of, §6, pl4. gravity of sulphuric acid, Determination of, §1, p5. -gravity scale, European Baume, §1, p6 -gravity scale, Twaddell, §1, p6. Specific—(Continued) -gravity scale, United States Baumd, §1, p6. Spence reciprocating type of furnace, §1, p31. Stahl method for removing arsenic from chamber acid, §2, p47. Standard solutions for paper analysis, §18, p5. Starch as sizing for paper, §17, p26. Steam, Admission of, to the lead chambers, §2, p33. Still liquor, Determination of free acid in, §6, p43. for decomposition of hydrochloric acid by manganese dioxide, §4, p28. for recovery of ammonia in Solvay process, §3, p29. liquors for the decomposition of hydro¬ chloric acid by manganese dioxide, §4, p32. Straw, §16, p4. Bleaching of, §17, p5. pulp, §16, pl3. Strength of solutions weaker than the mono¬ hydrates, Commercial methods for deter¬ mining the, §1, p5. Success screen for washing wood pulp, §16, p27. Sulphate process of wood pulp, §16, p59. Sulphides, metallic, Preparation of, §1, pll. Sulphite digesters, §16, p50. liquor, Disposition of waste, §16, p56. process, Bisulphite liquor, §16, p42. process of wood pulp, §16, p42. process, Sulphur burners, §16, p42. pulp, Analysis of, §18, p55. pulp, Bleaching of, §17, p6. pulp mill. Ground plan of, §16, p58. Sulphur, Available, §1, pl5. available, Determination of, in tank waste, §6, p29. Available, in burner gas, §1, pl4. burners, Sulphite process,* §16, p42. Combustion of, §1, pi2. compounds, oxidizable, Determination of, in fished salts, §6, p34. dioxide, Absorption apparatus for, §16, p45. dioxide, Absorption of, §16, p45. dioxide or burner gas, Production of, §1, p21. dioxide, Reich’s test for, in burner gas, §1, p36. Grading of crude, §1, p9. in tank waste, Recovery of, by Chance- Claus process, §3, p71. or brimstone, Analysis of, §18, p43. recovered, §1, p8. INDEX xxi Sulphur—(Continued) Removal of, from Le Blanc caustic soda, §4, p8. Sources of loss of, in roasting, §1, pi 5. Thermochemistry of the combustion of, §1, pl2. total, Determination of, in lye from extrac¬ tion of black ash, §6, p24. trioxide, Determination of, in salt, §6, pl8. trioxide, Hydrates and solutions of, §1, pi. trioxide in brine, Determination of, §6, p3. trioxide, Monohydrate of, §1, p3. trioxide, Nomenclature of solutions and hydrates of, §1, p3. Sulphureted hydrogen, §1, p8. hydrogen generator, Freiberg, §2, p44. Sulphuric acid, Catalytic or contact process for the manufacture of, §1, p43. acid, Chamber process for, §2, pi. acid, Concentration and distillation of, starting with the Glover tower, §2, p56. acid, Concentration of, by the Kessler proc¬ ess, §2, p55. acid, Concentration of dilute solutions of, §2, p48. acid, Concentration of, in glass beakers or dishes, §2, p53. acid, Concentration of, in glass retorts or stills, §2, p52. acid, Concentration of, in iron, §2, p51. acid, Concentration of, in lead pans, §2, p48. acid, Concentration of, in platinum, §2, p49. acid, Conditions of, in the chambers, §2, p30. acid, Conditions of, in the Glover tower, §2, p29. acid, Contact mass or material used in the manufacture of, by the contact process, §1, p45. acid, Control of chamber process for, §2, p38. acid, Definition of, §1, p3. acid, Determination of, in hydrochloric acid, §6, p39. acid, Determination of specific gravity or density of, §1, p5. acid, Diagram of manufacture of, §2, p60. acid for making salt cake, §3, p37. acid, Nordhausen or fuming, §1, p4. acid. Operation of chamber process for, §2, p28. acid, Preparation of raw material for manu¬ facture of, §1, p9. acid, Principles governing the manufacture of, §1, p7. Sulphuric—(Continued) acid, Raw materials used in the manufao ture of, §1, p8. acid, Reactions of the chamber process, for §2, P 2. acid, Starting the chamber process for, §2, p35. hydrate, Yield and method of calculating yield of, §1, pi7. monohydrate, Lunge freezing process for the production of, §2, p59. Supercalendering of paper, §17, p39. Supercalenders, §17, p39. Surface condensers, §2, pl6. -heat evaporation of tank liquor, §3, p63. T Tank liquor, Evaporation of, §3, p63. liquor, Evaporation of, in mechanical pans, §3, p64. liquor, Evaporation of, in pans with heat below, §3, p64. liquor, Evaporation of, with surface-heat, §3, p63. waste,. Analysis of, §6, p26. waste, Determination of alkaline com¬ pounds in, §6, p27. waste, Determination of available sulphur in, §6, p29. waste, Determination of total sodium com¬ pounds in, §6, p27. waste in Le Blanc process, §3, p69. Temperature, Allowance for, in determining the Baume gravity of sulphuric acid, §1, p20. Testing burner gas, §1, p36. of paper, §18, p56. Thenardite, §3, p36. Thermochemistry of the combustion of sul¬ phur, §1, pi2. Total alkali, Determination of, in bicarbonate from filters, §6, pll. Tower, Carbonating, for Solvay process, §3, p22. Gay-Lussac, §2, p21. Glover, §2, p8. Towers, Gay-Lussac, Number of, §2, p37. Townsend cell, §5, p31. process for the electrolysis of salt, §5, p31. Treatment of bleached stock, §17, pl4. Tub sizing of paper, §17, p37. Twaddell specific-gravity scale, §1, p6. U Ultramarine, Analysis of, §18, p35. Units of electrical measurement, §5, p3. XXII INDEX v Vacuum-pan process for evaporating brine, §3, P 6. Vitriol, Nitrous, §2, p5. Voltmeter, §5, pl5. W Warren filter, §17, p50. Washer, Worm, §16, p53. Washing gases from ammonia saturator, §3, p24. of wood pulp, §16, p23. Waste from ammonia stills, Analysis of, §6, pl4. gas from Claus kiln, Analysis of, §6, p29. gases from hydrochloric acid absorption, Analysis of, §6, p36. Water, Alum treatment of, §17, p46. Determination of, in salt, §6, pl7. Determination of, in slaked lime, §6, p43. Filtration of, §17, p46. finish of paper, §17, p39. Purification of, §17, p46. Weldon and Deacon processes for chlorine, Comparison of, §4, p44. mud, §4, p36. mud, Analysis of, §6, p44. mud, Determination of manganese in, §6, p44. mud, Determination of total base in, §6, p44. process for chlorine, §4, p37. Weldon’s process for the recovery of man¬ ganese from still liquors, §4, p33. Wet machine for wood pulp, §16, p29. Wheatstone bridge, §5, p4. White size for paper, §17, p22. Wood, §16, p4. Chipping of, §16, pl9. Cooking of, in sulphite digesters, §16, p51. fiber, chemical, Bleaching of, §17, p5. Grinding of, §16, pl4. ground, Bleaching of, §17, p5. ground, Color of, §16, pl8. Preparation of, for the sulphite process, §16, p50. pulp, §16, pl4. pulp, Analysis of, §18, p52. pulp by Barre and Bondel’s nitric-acid process, §16, p60. pulp by nitrohydrochloric-acid process, §16, p60. pulp by Pictet and Brelaz’s process, §16, p60. pulp by sulphate process, §16, p59. pulp, Liquor for soda-process, §16, p29. pulp, Screening of, §16, pi7. pulp, Soda-process, §16, pl9. pulp, Sulphite-process, §16, p42. pulp, Washing of, §16, p23. pulp, Wet machine for, §16, p29. Worm-washer, §16, p53. Wove paper, §17, p37. Y Yaryan evaporator, §4, p5. Yield and method of calculating yield of sul¬ phuric hydrate, §1, pl7. Z Zinc blends, §1, p8.