STATE OF ILLINOIS HENRY HORNER. Governor DEPARTMENT OF REGISTRATION AND EDUCATION JOHN J. HALLIHAN. Directoc DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief URBANA REPORT OF INVESTIGATIONS— NO. 49 A SUMMARY OF THE USES OF LIMESTONE AND DOLOMITE BY J. E. Lamar and H. B. Willman PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 19 3 8 ILLINOIS STATE GEOLOGICAL SURVEY L13RA..Y STATE OF ILLINOIS Hon. Hknry Hoiinku, Governor DEPARTMENT OP REGISTRATION AND EDUCATION Hon. John J. Hallihan, Director BOARD OF NATURAL RESOURCES AND CONSERVATION Hon. John J. Hallihan, Chairmun Edson S. Bastin, Ph.D., Geology Wh.liam a. Noykk, Ph.D., LL.D., Chem.D., D.Sc, Chemistry Louis R. Howson, C.E., Engineering William Trelease, D.Sc, LL.D., Biology Henry C. Cowles, Ph.D., D.Sc, Forestry Arthur Cutts Wh.lard, D.Engr., LL.D., President of the University of Illinois STATE GEOLOGICAL SUm'EY DIVLSION Urhana :iGHTON, Ph.D., Chief M.S., Assistant to the Chief A.M., Geological Assistant GEOCHEMISTRY M. M. Le En II) Town LEY, Jane Titco.mh, GEOLOGICAL RESOURCES Coal G. H. Cady, Ph.D., Senior Geologist L. C. Mc'Cahe, Ph.D. James M. Suhopf, Ph.D. Earle F. Taylor, M.S. Charles C. Boley, M.S. Non-Fuels J. E. Lamar, B.S. H. B. WiLLMAN, Ph.D. Robert M. Grog an, M.S. H. C. Heilhronner, B.S. Oil and Gas A. H. Bell, Ph.D. Chalmeu L. Cooper, M.S. G. V. CoHEE, Ph.D. Frederick Sc^uires, B.S. Charles W. Carter, Ph.D. James L. Carlton, B.S. Areal and Engineering Geology George E. Ekmlaw, Ph.D. Richard F. Fisher, B.A. Suhswrfacc Geology L. E. Workman, M.S. J. Norman Payne, Ph.D. Elwood Atherton, Ph.D. Gordon Presuott, B.S. kitratigraphy and Paleontology J. Marvin Weller, Ph.D. Petrography Ralph E. Grim, Ph.D. Richards A. Rowland, Ph.D. Physics R. J. PlERSOL, Ph.D. M. C. Watson, Ph.D. Donald O. Holland, M.S. Frank H. Reed, Ph.D., Chief Chemist W. F. Bradley, Ph.D. G. C. Finger, Ph.D. Velma E. Nichols, M.S. Fuels G. R. YoHE, Ph.D. Carl Harman, B.S. Non-Fuels J. S. Machin, Ph.D. F. V. TooLEY, M.S. Analytical 0. W. Rees, Ph.D. Norman H. Nachtriem, B.S. George W. Land, B.Ed. P. W. Hen LINE, B.S. Mathew Kalinowski, B.S. MINERAL ECONOMICS W. H. Voskuil, Ph.D., Mineral Economist Grace N. Oliver, A.B. EDUCATIONAL EXTENSION Don L. Carroll, B.S. PUBLICATIONS AND RECORDS Geor(;e E. Ekhlaw, Ph.D. Chalmer L. Cooper, M.S. Dorothy Rose, B.S. {on leave) Alma R. Sweeny, A.B. M. Frances Harper, M.S. Meredith M. Calkins Consultants: Ceramics, Cullen Warner Parmelee, M.S., D.Sc, University of Illinois; Pleistocene Invcrtehrate Paleontology, Frank Collins Baker, B.S., University of Illinois. Topographic Mapping in Cooperation with the United States Geological Survey. July 1, 1938 (57038) ILLINOIS STATE GEOLOGICAL SURVEY 3 3051 00005 6972 CONTENTS Page Introduction 5 Acknowledgments 7 Limestone production 7 Uses of limestone and dolomite 9 Abrasives 9 Agricultural limestone 9 Alkalies 11 Aluminum oxide 12 Ammonia 12 Asphaltic compounds 12 Aviation fields, yards, playgrounds, etc 12 Baking powders 13 Building stone 13 Cut stone 13 Stone for exterior use 13 Stone for interior use 14 Ashlar 14 Rough building stone 15 Rubble 15 Bulb growing 15 Calcium carbide 15 Calcium nitrate 16 Carbon dioxide 16 Cesspool stone 16 Concrete aggregate 16 Cement concrete 16 Bituminous concrete 17 Dolomite refractories 18 Dye works 20 Epsom salts 21 Explosives 21 Fertilizers 21 Filter stone 22 Flagging and curbing 23 Flux 23 Blast-furnace flux 23 Basic open-hearth flux 24 Nonferrous-metal flux 24 Glass 24 Ground limestone or dolomite 25 Lime 26 Lithographer's stone 29 IVIagnesium 29 Mineral feeds for stock 30 [3] Uses of limestone and dolomite, continued^ Page Monumental stone 30 Mosaics 30 Natural cement 30 Neutralization 31 Paper 31 Sulphite pulp — tower system 31 Sulphite pulp — milk-of-lime system 32 Soda pulp and sulphate pulp 32 Phenol 32 Pipe manufacture 32 Plastic magnesia 32 Portland cement 33 Poultry grit 34 Purification of copper 34 Purification of sulphuric acid 35 Railroad ballast 35 Riprap 36 Road stone 36 Traffic-bound roads 36 Stabilized roads 37 Bituminous macadam roads 38 Waterbound macadam, roads 38 Rock wool 39 Salt refining 39 Soap 40 Stone chips for stucco, terrazzo, roofing, concrete facing, and artificial stone 40 Stone sand 40 Studio snow 42 Sugar 42 Technical carbonate 42 Whiting substitute 43 References 45 Index 49 [4] A Summary of the Uses of Limestone and Dolomite By J. E. Lamar and H. B. Willman INTRODUCTION Tliis l)rief discussion of the uses of limestone and dolomite has been com- piled to provide information for the Illinois stone industry in their search for new outlets for their products. It is by no means intended to be an ex- haustive treatise on the subject ])ut rather a summary to serve as a basis for the selection of those uses which seem to have promise. Such uses may then be studied further by consulting the publications in the list of references and by personal investigation and contact with potential consumers. It should be emphasized that the processes involved in some of the uses of limestone and dolomite are highly technical and that^ before any attempt is made to exploit stone for any given use, the technology of the particular use should be thoroughly investigated. Also the uniformity, extent, and avail- ability of the raw material and the size and availability of the market should be carefully studied. In some cases it has been difficult to distinguish between the uses of lime- stone and the uses of lime. However, if a consumer purchases raw stone, this is considered a use of limestone regardless of the fact that the consumer may subsequently convert the limestone to lime in his process of utilization. Although the specifications presented are considered to be reasonably typi- cal, considerable variations occur and, as a rule, each consumer has his own specifications. For some uses there has been lately an increased tightening of specifications, the details of which have not yet reached the literature. Furthermore specifications are often varied somewhat in order to permit the use of materials which are close at hand and available at low cost. It is felt that, in the main, the specifications given should be considered only as indica- tive of the general requirements which stone must meet. They will serve to indicate probable uses but investigation of the specifications of potential con- sumers should precede and govern any attempts to sell stone. In general the uses of limestone and dolomite may be classified into two groups, "chemical uses" in which the chemical composition of limestone and dolomite is of prime importance, and "physical uses'^ in which the physical character of the stone is most important. For the former it is customary to draw chemical specifications and usually physical specifications as well, but specifications for the latter usually refer only to the physical ])i'operties. r5] 6 USES OF LIMESTOXE AND DOLOMITE In subsequent pages the uses described are arranged in alphabetical order for convenience regardless of whether they are primarily chemical or physi- cal. However, it is generally possible to distinguish between chemical and physical uses by the fact that no chemical specifications are given for the latter. It has not been possible in this report to adhere strictly to any spe- cific definitions of limestone and dolomite because data have been drawn from a great many different sources in which, for the most part, no statements of usage are given. It is believed, however, that the following discussion will enable the reader to judge from the text how the terms are used in most cases. The term "limestone" is often employed as a general term to describe rocks which are composed principally of calcium carbonate or calcium and magnesium carbonates. Limestones are subdivided, as a general rule, into three groups on the basis of chemical composition. In such a classification the term "limestone" is used specifically to designate those rocks which are composed dominantly of calcium carbonate and contain only small amounts of magnesium carbonate. The term "dolomite'' is used to describe rocks com- posed principally of calcium and magnesium carbonates. A pure dolomite contains about 54 per cent calcium carbonate (CaCOg) and 46 per cent mag- nesium carbonate (MgCO^). However, no minimum limit is in common use for the amount of magnesium carbonate which must be present in a rock in order that it be called dolomite. The term has been applied to rocks which contain as low as 30 per cent magnesium carbonate. The terms "magnesium limestone", "magnesian limestone", or "dolomitic limestone" are often em- ployed to describe rocks whose composition is intermediate between limestone and dolomite. The general relationship of these terms i)ossibly is more evi- dent as expressed below. "Limestone — high in CaC03, low in MgCOg Magnesium (magnesian) limestone — amounts of CaCOo and MgCOg intermediate between Limestone . T- ■H 1 o -H O I^ CO LO t^r^ ai ;-> ^ 1 • >flH 0^ CO 1-H r- ^ d d d <6^ <^ 5:^ m o 00 O rM C^l t^ 1 >-0 Oi 1 Oi 1 c^' CO C a; 1 "-H Ot^ 1 CO 3 1 '-H CO CO rrTt-^ >o CO- H^ t-" .22 13 CO -f >- ; go^l:: '^ -h ^ o K* r^ OI - ^ 1 OI .s 1 m or \i ^~* K '^ o 2 o ceo O O j o K-j c s?] ss?; Ct O lO .t? o ?- O^OO 1 CO C -t- o^ ^ -t >0 O CO o~oi 1 t^ 03 fcH H CO OO CO 't CO 00 3 o C^l ococo CO C0_^ ®'i or '*'' Is! 1 CO(MCDOiiO t>-0»OC3<0 0-^CD OCOCMTfiOi O0l-^COCOOOO(MOO . Oi ^H ;_, ^^'^'-"^ OOCr-H^T-H^O < - €^ 00 ^ 00 Ci >0 C: O t- >0 I- Ol CX) 1- >o I H Ol CO O) iO -f ^ 1^ Ol I-- Ol C CO C/3 1 GO O 00 >0 O lO O I- CO O CO 1- c l:- S Cb .^ .^.^^.^.^^.K .^ .^ 3 OI^OIOO -f 'O Ol o -t o o t^ oo c3 •—J r-^ -O OU- O lO 01 O -f ^ CO >o CC CO m > '" CO lO 00 oi 00 CO >o C5 CO '-t^ CO CD a ") o r^ % 1 '"' '~ CO (M I- (M Tt o Ol IQ 1 m €^ *S P ^_^ ooooo oooooooc o ► M >0 CO CO CI 'O O O CO O CO O l^ T- CO ^►. c O CO -f I - o i^ >o CO -t o o CO 1- •"S o CO lO GO >0 O ^COr— ooooooc OI C -^ o c: -r 00 CO lO Ol O CO O 00 -t^ CO o 'A tn OII--fr-HC: ^Or-^-t01.-H,-Hl^ "-t^ 3 o ^t ,-H r-H 1 o CO oi OI !<: 1^ C3 C3 CO ^ >o ^ ^ '« o »^ 1 1 C c3 w t— ' uctio ectur, and -o 03 O -^^ ^ ^ stone — gh constr gh archit^ shed (cut 1 stone- crete a road b stone. . ctories ;tories. ills. . . . t m 'cS uilding Rou Rou Fini ubble. ioran . y. §-s bc^j e^ s o 1 rush( C R luxin Jgar lass : aper gricu ther H « p:5 P^ o Ph iri O ^ 1 CO 'o fl .3 CO CO —1 fl c SB .^ 1 i-s fO ,--^ 03 to d (M ^— '(M t^ c3 3 to CO CVJ o* 3,367, 117, 24, t^ CO CO to q; Oi GO 00 Oi :3 t^ C^l --^ CO 13 00 Ttl l>- 05 > M (U 3 'S CO 03 0) fl C '3 33 P >> -H ^-55 -D ^ w to 'ti CO Oi t^ COCO -H to .-1 CO O* 76,741, cl,006, 2,987, 1,005, L i=l ^ "o tS] N 3 a TS fi oq' . <=^ t CO — ' 1—1 T-H 03 (M d'S d ^ d -'-V o< GO ^—-00 ^ >4 loo'^o ^-^ >,'— 1 '"j >-i S a^ 2 iOC<5 ft a 3 3 O) 0) rtco 3 '-^ft OJ si ,j^ «,_ '3 <*H — < -o Ji^ ^-2 « 3 13 «2 sj2 o'O aj 'Om ALKALIES 11 General chemical specifications. — The ability to counteract acidity or the neutralizing power of a limestone or dolomite depends on its content of cal- cium and magnesium carbonates and is commonly expressed as per cent "calcium carbonate equivalent/^ often abbreviated as C. C. E. The calcium carbonate equivalent is a measure of neutralizing ability in terms of calcium carbonate. As magnesium carbonate has a greater neutralizing value per unit weight than calcium carbonate, namely 1.19 times that of calcium car- bonate, dolomites often show a calcium carbonate equivalent of more than 100 per cent. A calcium carbonate equivalent of roughly 109 per cent is the maximum obtainable with pure dolomite. Most of the agricultural lime- stones produced commercially vary between 90 and 100 per cent calcium car- bonate equivalent. In general, rocks having a calcium carbonate equivalent of less than 85 per cent are not used for agricultural limestone unless stone having a higher calcium carbonate equivalent is not available. General physical specifications. — Agricultural limestone usually passes a 4:-mesh screen and ranges in size down to dust. Many producers make a more finely ground product. A "score card" for rating agricultural lime- stones on the basis of the sizes of the particles has been proposed by the Agricultural Experiment Station of the University of Illinois (4). Remarks. — Both limestone and dolomite are used widely for correcting soil acidity and both are called "agstone" or "agricultural limestone." ALKALIES Use. — The sodium carbonate manufactured in the United States from sodium chloride (salt) is made exclusively by the Solvay or ammonia-soda process {71, p. 59). The Leblanc process is employed in England for mak- ing sodium carbonate from salt, but the use of this process is steadily de- creasing. Both processes involve the use of limestone. In the Solvay pro- cess the limestone is dissociated to lime and carbon dioxide at the manu- facturing plant. The carbon dioxide enters into the manufacture of the sod- ium carbonate. After the lime is hydrated it is employed to recover the ammonia involved in the process (71, pp. 59-60), and is used for causticizing the sodium carbonate to sodium hydroxide in the manufacture of the latter compound (88). General chemical specifications. — The following specifications have been given: a high-calcium limestone (5-2, p. 253); limestone containing "over 93 per cent calcium carbonate, 3 to 5 per cent magnesium carbonate, and 2 to 3 per cent silica" (72, p. 264) ; calcium carbonate 90-99 per cent, silica, alumina, ferric oxide 0-3 per cent, magnesium carbonate 0-6 per cent (^7, p. 52). It is believed that most American manufacturers would insist that silica not exceed 1 per cent (88). 12 USES OF LIMESTONE AND DOLOMITE General physical specifications. — The stone should be two to six inches in diameter {Jf7, p. 56). Remarks. — Caustic soda (NaOH) is made by treating sodium carbonate with milk of lime and also electrolytically from sodium chloride {71, pp. 88-89). ALUMINUM OXIDE Use. — Limestone is used in the manufacture of aluminum oxide by the Bayer process. The limestone is burned to lime which is used to make sodium hydroxide and this alkali in turn is employed to extract aluminum oxide from bauxite (7^, p. 341). The aluminum oxide may be subsequently converted to aluminum or may be used directly for other industrial purposes. General chemical specifications. — A high-calcium limestone containing over 97 per cent calcium carbonate and less than 1 per cent silica is used. AMMONIA Sales of limestone to ammonia works are reported but the use of the limestone is not specified. It may be converted to calcium carbide and used in this form in the cyanamide process of ammonia manufacture {71, p. 116), or it may be burned to lime and used for the recovery of amn^onia from weak ammonia liquors {69). ASPHALTIC COMPOUNDS Although it is common practice in the United States to burn the acid sludge resulting from the refining of petroleum (6'7), some sludge is neu- tralized with lime or limestone and used as fuel oil and to a limited extent in road oils (57). According to the English writer, Knibbs {52, p. 278), "The mixture of lime and sludge is like asphalt and it is used for making roofing materials and generally instead of asphalt," but it is believed that in the United States very little use has been made of the sludge for roofing material because of its staining properties {87). AVIATION FIELDS. YARDS. PLAYGROUNDS. ETC. Use. — Limestone or dolomite is used to surface aviation fields, tennis courts, yards, playgrounds, station platforms, and the like. General physical specifications. — No generally adopted size specifications are known for stone for these purposes. Obviously stone for all such uses should have good weather resistance. Stone for aviation fields should be white to give it good visibility {66, p. 82). Stone for surfacing tennis courts probably should range in size from about Vs i^^ch to dust so that it packs to IJUILDING STONK 13 a relatively dense mass, and it should have a high cementing value so that a firm surface results. For yards, playgrounds, etc., a clean, comparatively fine stone is often used. It has heen found (7^) that for many surfacing purposes^ such as those mentioned above, "Small amounts of V2"i^ch or even %-inch stone mixed with the finer sizes gives a better body to the mass of stone without in any way injuring its packing qualities or smooth surface. This feature is best appreciated in wet weather." BAKING POWDERS (7/, p. 130) Use. — Monocalcium phosphate, a constituent of certain types of baking powders, is made by treating limestone or lime with purified acid. General chemical specifications. — '^Selected" hydrated lime or limestone is used. The limestone probably should be a high-calcium stone. General physical specifications. — Probably ground or pulverized stone is used. BUILDING STONE Limestone and dolomite are used extensively for various building pur- poses and are ])roduced as cut stone, ashlar, rough building stone, and rubble. Cut Stone The term "cut stone^' includes all varieties of limestone or dolomite Avhich are shaped to units of definite size, usually in accordance with detailed drawings {10, p. 23). The stone may be surfaced with any one of a number of finishes, including a polished finish, and is used for a wide variety of pur- poses including construction of walls, for sills, trimming, wainscoting, floor- ing, etc. Some of it is carved for decorative purposes. Those limestones and dolomites which take a good polish are classed commercially as marbles. STONE FOR EXTERIOR USE General phi/sical specifications. — Cut stone for exterior use should possess good weather-resisting qualities, and should therefore be free from such substances as chert, ocher, clay, or shale inclusions. The stone should not contain mineral grains which upon weathering produce colored streaks and stains if such colorations are undesirable. In particular, the minerals pyrite and marcasite, which produce the yellow stain of iron rust, are undesirable in cut stone for many uses. Various strength tests have been devised for determ- ining the suitability of difi^erent types of rock for construction purposes. However, it is likely that, so far as Illinois limestones and dolomites are con- cerned, those stones which successfully withstand weathering in natural out- crops and weathering tests {(SI, p. 44) will be found to be amply strong. Thiel and Button {81, pp. 38-48) have recently discussed tests of the ])hysical properties of building stone. 14 USES OF LIMESTONE AND DOI^MITE In general it is desirable that deposits intended to serve as a source of cut stone be composed of relatively thick strata free from numerous joints and chert nodules or other hard masses. It is often desirable that the stone be "free working/' that is, that it split with approximately equal ease in all directions. Much valuable data regarding the weather resistance of a building stone may be obtained from a study of the effects of the weather on outcrops of the stone and on actual installations in buildings. When such information is not available, or when su])plementary data are desired, freezing and thawing tests or accelerated-soundness tests are sometimes performed and are helpful in predicting the probable reaction of a stone to weathering. However, no gen- erally accepted limits for the desired weather resistance of a good building stone as measured by these weathering tests have been established. STONE FOR INTERIOR USE General pJn/sicaJ specifications. — Stone for interior use is usually finished with a smoothed or a ])olished surface. An attractive color is important in polished stone used for decoration. Floor tile should also have an attractive color and be resistant to abrasion. Any stone subject to frequent washing should be free from pyrite and clay ])artings as these sometimes cause failure. Stone used in large units for interior masonry should have roughly the same properties as stone used for exterior masonry, except that the interior stone need not be as weather resistant. Deposits of limestone or dolomite which are to serve as a source of interior stone should have about the same characteristics as those for exterior stone. However, some relatively thin deposits may be of commercial im])or- tance if the stone is sufficiently attractive or unicjue from the stnndjioint of color, texture, etc. Black marbles are an example. Tntoi'ior stone should be free from chert nodules or other localized impurities which affect the ease of cutting. Colorful stone is much in demand. Ashlar Use. — Ashlar consists of "small rectangular blocks of stone having sawed, planed, or rock-face surfaces, contrasted with cut blocks which are accurately sized and surface tooled'' {10, p. 24). Ashlar is used for the construction of the walls of houses and other buildings. General physical specifications. — Ashlar for exterior or interior use should have roughly the same qualities as cut stone. However, deposits which are to serve as a source of ashlar, especially stone that is to be split to size rather than sawed, need not be in as heavy beds as cut stone; a deposit con- sisting of 2- to 12-inch beds may be desirable. Likewise rather frequent natural joints in the deposit may be an aid to quarrying. ( AT.CIUM (ARUIDE 15 Rough Building Stone Use. — Koiigh building stone ^^consists of rock-faced masses of various shapes and sizes^^ (TO, p. 25). It is used for houses, chimneys, basements, public buildings, bridges, fences, and walls {10, p. 25). General physical specifications. — The physical specifications are the same as for ashlar. Rubble Use. — The term "rubble" is generally applied to irregular stone frag- ments having one good face {10, p. 25). Rubble is used for basements, ex- terior walls, etc., and in the form of comparatively thin slabs as a stone veneer, especially for frame houses. General physical specifications. — Eubble should have good weather re- sistance and at least one face with an attractive color. Chert, clay, or pyrite partings should be avoided because they tend to reduce Aveather resistance. Stain-producing impurities such as pyrite and marcasite grains should be avoided if a stain-marked wall is objectionable. Usually a relatively thin- bedded deposit is easiest to work for rubble. If the rubble is to be used for veneer, a deposit composed of layers roughly 1 to 4 inches thick is commonly desirable. The surfaces of the bedding planes in such a deposit should have an attractive color. BULB GROWING The sale of limestone for bulb growing is reported {JS). The lime- stone probably should have an attractive color and be in small chips. CALCIUM CARBIDE Use. — Limestone is sold for making lime which is used in the manu- facture of calcium carbide. The process of manufacture involves fusing the lime with coke in an electric-arc furnace {60). General chemical specifications. — Goudge {J^O, p. 46) recommends an ex- tremely pure limestone with a phosphorus content less than 0.01 per cent, magnesia less than 2 per cent, and silica less than 3 per cent. Riegel {71, p. 273) states that no phosphates, or almost none, should be present and that the limestone should be free from magnesium carbonate. Mantell {60) speci- fies limestone containing at least 97 per cent calcium carbonate and quotes from Bingham the following maximimi quantities of impurities permissible : magnesia 0.5 per cent, alumina and ferric oxide 0.5 per cent, phosphorus 0.004 per cent, silica 1.2 per cent, sulphur traces only. The data given re- garding phosphorus content are subject to revision as recent developments in the process of manufacturing calcium carbide now permit the use of lime- stone with a considerably higher phosphorus content {Jf^). 16 USES OF LIMESTONE AND DOLOMITE General physical specifications. — Lime burned from the limestone must "have mechanical strength without a tendency to crumble into dusf' (^^)- Remarks. — About two tons of limestone are used in nuiking one ton of calcium carbide {JfO, p. 46). CALCIUM NITRATE Calcium nitrate (5'2^ p. 259) is made by treating limestone with nitric acid. The nitrate is used in the manufacture of explosives, matches, pyrotech- nics, and fertilizers. A high-calcium limestone is required. CARBON DIOXIDE Use. — The burning of limestone to lime is estimated to have supplied 40 per cent of the carbon dioxide of conmierce in 1934 {J^G, p. 850). Some car- bon dioxide is also produced in the manufacture of epsoni salts from dolomite (,see P]psom Salts). The production of carbon dioxide for the beverage trade by treating pulverized marble with acid is reported (lOS). General chemical and physical specifications. — The specifications are the same as for stone for lime. Bsmarhs. — Carbon dioxide is sold in either the liquid or solid form and is used for a great many })urposes among which are refrigeration, manufacture of explosives, food preservatives, manufacture of chemicals, in fire extinguish- ers, and for the carbonation of beverages {1,(), pp. 855-856). CESSPOOL STONE The sale of limestone for cesspool stone is reported (-^^>). This is doubt- less a use of building stone, probably rough building stone or rubble. CONCRETE AGGREGATE Use. — ('rushed limestone or dolomite is mixed with cement or l)itumen to make concrete. Cement concrete is used for the construction of roads, buildings, and other structures, and bituminous concrete is used principally for roads. CEMENT CONCRETE General physical specifications. — Specifications for crushed stone to be used as an aggregate in cement concrete vary, but in general include a mini- mum per cent of wear or French coefficient and recpiire that the stone with- stand without failure a specified number of cycles of the accelerated-sound- ness test, sometimes known as "the sodium sulphate test,^' or repeated freez- ing and thawing. The aggregate may be recpiired to have a certain crush- ing strength but usually most limestone or dolomite aggregates have ample strength. Tests of crushing strength are generally made on the concrete rather than the aggregate. The Illinois Division of Highways specifies CONCKKTE AGGREGATE 17 that the per cent of wear of stone for concrete aggregate to be used in State highways and bridges shall not exceed 7 per cent and that the stone "shall pass the sodium sulphate accelerated-soundness test, except that aggregates failing in the accelerated-soundness test may be used if they pass a satis- factory freezing and thawing test" {105, p. 318). Various materials are considered undesirable in concrete aggregate. Specifications of the Illinois Division of Highways regarding these materials follow {105, p. 318) : The maximum amount of any one of the deleterious substances given below shall not exceed the following percentage by weight: Per cent Removed by decantation 0.5 Shale 1.0 Coal 1.0 Clay lumps 0.5 Shells 1.0 Soft fragments 5.0 Other local deleterious substances such as alkali, friable, thin, elon- gated, or laminated pieces 3.0 The maximum amount of any combination of the deleterious substances listed above, together with material which fails to comply with soundness specifica- tions should not exceed 5 per cent by weight. BITUMINOUS CONCRETE General physical specifications. — Crushed stone for use in the base course of bituminous concrete pavements, according to the American Association of State Highway Officials {92, pp. 25-26), should consist of clean, tough, durable fragments, free from an excess of flat, elongated, soft or distintegrated pieces. It should have a percentage of wear of not more than 6 and a toughness of not less than 6. It is specified that the coarse aggregate be of either (a) the No. 4 to 1-inch size or (b) the No. 4 to 2-inch size, be well graded between these limits, and conform to the following requirements : (a) No. 4 to 1-inch size: Passing Per cent li/^-inch sieve 100 1-inch sieve 90-100 Vz-inch sieve 25-60 No. 4 sieve 0-10 (b) No. 4 to 2-inch size: Passing 21^-inch sieve 100 2-inch sieve 95-100 1-inch sieve 35-70 Va-inch sieve 10-30 No. 4 sieve 0-5 The American Association of State Highway Officials {9.2, p. 31) speci- fies that crushed stone for use in the surface course of fine-graded bituminous concrete pavements, coarse-graded bituminous concrete pavements, and asphal- tic concrete binder consist of clean, tough, durable fragments, free from an excess of flat, elongated, soft, or disintegrated pieces and free from stone coated with dirt or other objectionable matter. The stone should have a per- 18 USES OF LIMESTONE AND DOLOMITE centage of wear of not more than 5 and a toughness of not less than 6. The coarse aggregate for fine-graded bituminous concrete should be of No. 4 to 1/2-inch size and be well graded between these limits. It should conform to the following requirements : Passing Per cent %-inch sieve 100 y2-inch sieve 90-100 No. 4 sieve 0-15 No. 8 sieve 0-5 The coarse aggregate for coarse-graded bituminous concrete or asphaltic concrete binder should be of the No. 4 to 1-inch size and be well graded be- tween these limits. It should conform to the following requirements: Passing Per cent 11/4-inch sieve 100 1-inch sieve 90-100 i/^-inch sieve 35-60 No. 4 sieve 0-10 DOLOMITE REFRACTORIES Introduction. — Dolomite is used as a refractory mainly as "dead-burned dolomite/' This material results from the burning of dolomite or high- magnesium limestone at such temperatures, usually about 1500°C., as to pro- duce a hard, fully-shrunk product (44, p. 4; 75, pp. 314-315). Dead-burned dolomite made from relatively pure dolomite, if not protected from atmos- pheric moisture, disintegrates due to slaking or taking up water and carbon dioxide from the atmosphere (5). Consequently this type of material must be used within a short time of manufacture or protected by a moisture-proof coating. It is usually burned at the steel plant where it is to be used. It has been found that a more suitable variety of dead-burned dolomite is produced, the fomiation of a thoroughly sintered product is facilitated, and the sintering temperature is lowered when iron oxide, silica, and alumina are present in the proper proportions in the raw materials. These compounds may be present naturally in the raw dolomite or, as is more often the case, may be added in any one of a number of forms. Much of the dead-burned dolomite thus prepared is sold under various trade names. Use. — Dead-burned dolomite is used in large quantities in basic open- hearth furnaces. Prepared refractories composed largely or wholly of dead- burned dolomite and sold under various trade names have been employed, be- cause of their lower cost, as substitutes for magnesite chiefly for making the banks of basic open-hearth furnaces {19, p. 31). The greatest use of dead- burned dolomite, however, is for current patching and repair work (59, 61). A considerable tonnage is also used for electric-furnace bottoms {59). Calcined dolomite prepared at the steel plant is used likewise for making banks of the basic open hearth, and for filling holes in the bottom and re- DOLOMITE KKFKACTORIES 19 pairing cuts in the banks of the hearth which develop with use {19, pp. 31, 293, 330). It may also be used for making the bottom of the hearth {19, pp. 305, 315). Dead-burned dolomite is also used in basic Bessemer converters, lead- refining reverberatory furnaces, lead cupelling furnaces, crucibles for lead blast furnaces, and in the form of crucibles for melting metals (^^, p. 3). For a monolithic furnace lining or bottom, dead-burned dolomite is employed with a suitable binder or a fluxing agent (^^, p. 4). For repair work around the open hearth, calcined dolomite is crushed to pass 1/2 inch {19, p. 295). A very large tonnage of raw dolomite is used for patching, principally around the slag line of the open hearth {59). General chemical specifications.- — In general it appears that relatively pure dolomites are used for making dead-burned dolomite, presumably because (a) dolomites containing the requisite impurities in the proper proportions are rare, (b) the calcined product resulting from the dead burning of a relatively pure dolomite has fewer undesirable properties than the product resulting from the burning of impure dolomites in which silica, iron oxide, and alumina are not present in the proper proportions, and (c) a more uniform dead-burned dolomite can be made by sintering a mixture of rela- tively pure dolomite and a flux, such as flue dust, than from a similar mixture wherein is used impure dolomite which is by nature likely to vary in composition. The following limits have been suggested for dolomites to be used for refractory purposes : calcium oxide about 33 per cent, magnesia 18 to 20 per cent, carbon dioxide 42 to 46 per cent, silica less than 7 per cent, iron oxide and alumina less than 5 per cent (75, p. 314). Although dolomite containing as much silica as is indicated above was used some 20 years ago, it would probably be difficult now to sell for refrac- tory purposes dolomite containing more than 2^/2 per cent of silica {59). According to Bowles, dolomite to be dead burned and used in basic bottoms of open-hearth furnaces should contain "less than 1 per cent silica, less than 1.5 per cent combined alumina and ferric oxide, at least 35 per cent magnesium carbonate, and the remainder calcium carbonate" (7, p. 13). The Carnegie Steel Company recommends that calcined dolomite for making the banks of basic open-hearth furnaces and for furnace repairs have approximately the composition shown below {19, pp. 32, 332) : Calcined dolomite Per cent Si02 1.66 AI2O3 1.24 FeoOs 0.94 CaO 55.01 MgO 38.26 20 USES OF LIMESTONE AND DOLOMITE ' Dead-burned or clinkered dolomite is made from dolomite of high purity by the "incorporation of some 3 to 5 per cent of additional iron oxide with the dolomite" (59). General physical specifications. — The dolomite should be in pieces about % inch in diameter (75, p. 314) or passing a i/2-i^ch screen {19, p. 295). Remarks. — As much as one to two tons of dead-burned dolomite may be required to repair a 100-ton basic open-hearth furnace between heats (78). A number of new types of dolomitic refractories have been described (57). One of these, which is receiving considerable attention at the present time, is brick composed of stable dolomite refractories. The latter are pro- duced by forming stable and highly refractory calcium silicates from the lime in the dolomite (59). Basic refractories are manufactured in Canada from "magnesitic dolo- mite" (35). Raw material of good grade has the following analysis (21) : Per cent Per cent Si02 2.0—3.5 CaO 9.0—12.0 AI2O3 0.2—0.3 MgO 32.0—38.0 FeaOs 0.2 — 0.4 Loss on ignition (chiefly CO2) 46.0—48.0 Three principal types of products are made ; clinker, an essentially basic brick, and basic plastic refractories (21). In Ohio a synthetic mixture is used in the manufacture of basic refrac- tories which have the same composition as those produced in Canada from natural stone (25). DYE WORKS Use. — Calcium carbonate is used in the process of halogenation employed in the manufacture of dye inteiTnediates (71, p. 435). Lime is used in the manufacture of dyestuffs and intermediates (a) in the manufacture of naph- thols by the sulphonation process, (b) in the reduction of nitration products, and (c) in the hydrolysis of chlorine derivatives (94). General chemical specifications. — Possibly a high-calcium limestone is used for the halogenation process. For (a) and (b) above, a high-calcium lime is required, and for (c) "any good quality lime is satisfactory'^ (94). For many chemical purposes in dye works, iron and alkali metals undoubtedly should be low. For the production of dye intermediates, particularly sulfonic acid derivatives, magnesium should also be as low as possible (69). General physical specifications. — Limestone for use as a "base for dyes" should be of such size that it will "all pass through a 20-mesh screen and 97 per cent through 100 mesh" (66, p. 91). FKRTILIZKKS 21 EPSOM SALTS (45) Use. — Epsom salts and carbon dioxide are produced from dolomite by a series of processes involving as a primary reaction the treatment of the dolomite with sulphuric acid. General chemiad specifi^cafions. — An average analysis of the rock used is as follows: Per cent CaCOa 54.00 MgCOs 45.00 Fe^Os 0.05 AI2O3 0.05 Si02 0.50 Total 99.60 "The stone is most suitable on account of its freedom from excessive amounts of oxide of iron and aluminum, carbonaceous matter, sulphides, and silica." General physical specifications. — The dolomite is shipped from the quarry in "one man" lumps but is reduced to 60-mesh at the plant. EXPLOSIVES (79) Use. — Limestone is used as a neutralizing agent for acids in many types of blasting explosives. General chemical specifications. — The materials used range from "a rather pure calcium carbonate to marble dust containing as much magnesium as calcium. The impurities in the limestone are of no practical importance in the manufacture of explosives." Remarks. — "The average dynamite contains less than 1.5 per cent of calcium carbonate but special powders have contained as high as 15 per cent." FERTILIZERS Use. — Limestone and dolomite are used as fillers and conditioners of fertilizers. The fillers serve to add weight to and reduce the caking of fer- tilizers. The conditioners also serve to reduce caking; if a fertilizer contains superphosphate they neutralize any "free" phosphoric acid present; and in the case of the so-called "complete" or "standard" fertilizers, many of which have an acid-forming influence on the soil, they are the basic constituents em- ployed to give a "physiologically basic" product (3, 62). Dolomite and high- calcium limestone have both been used satisfactorily but dolomite is generally preferred {27). Limestone is also used "in the manufacture of many nitrogenous fer- tilizers and fertilizer materials, such as cyanamide, calcium nitrate, ammonium citrophosphate, calcium ammonium nitrate, and ammonium sulphate" Ui. p. 373). 22 USES OB' LIMESTONE AND DOLOMITE General chemical specifications. — For filler a reasonably pure limestone or dolomite is required {27) ; for fertilizer manufacture a high-calcium lime- stone is probably desirable. General physical specifications. — The sale of dolomite having a fineness of 20 to 80 mesh as a fertilizer filler is reported {102). FILTER STONE Use. — Crushed limestone or dolomite is used in sewage disposal works to form the beds of the trickling filters over which the liquid portion of the sewage is sprayed. The rock serves as a host for organisms Avhich purify the sewage. The stone is subjected to unusually severe conditions with respect both to mechanical weathering, such as freezing and thawing, and to solution. General physical specifications. — Filter stone should be carefully screened, clean, and free from dust, fine stone, dirt, and other foreign substances {93, p. 10). Various sizes of stone are employed but the usual specification permits a difference of 1 inch between the upper and lower size limits of the stone, as 1 to 2 inches, li/o to 21/0 inches, or 2 to 3 inches. The desired size should be furnished within certain allowable limits; a tolerance of 5 per cent by volume or weight is recommended for both the upper and lower size limits {93, p. 10). An accelerated-soundness test known as the Brard or sodium sulfate soundness test {53) is often employed to determine the soundness of filter stone. Freezing and thawing tests are also sometimes used. Methods of preparation of the sulfate solution for the former test and likewise the test procedure have been described by the American Society for Testing Materials, in Tentative Method C89-32T; and the American Society of Civil Engineers also have a recommended procedure {93. pp. 28-29). Twenty cycles of the test are usually employed when testing filter stone. According to the com- mittee on filtering nuiterials of the American Society of Civil Engineers, "In general, a durable filtering material should withstand twenty cycles of the sodium sulfate test procedure with little or no loss of material. Any material of which 10 per cent of the number of pieces tested fails, or from which the total debris passing a i/^-inch sieve (scjuare openings) amounts to 10 per cent of the total weight of the material tested, should be regarded as unsound and should be used only after careful consideration of all factors and with rigorous restriction of the percentage of the finer material initially included^^ {93, p. 9). The Iowa Engineering Society specifies {101,, p. 51) that all particles passing through a 1-inch circular opening shall be considered as the portion which fails to meet the recjuirements of the sodium sulfate test, and that the per cent by w- eight of particles retained on a sieve having 1-inch circular openings is specified as the sample's rating. Suitable filter stone should have a rating of 85 per cent or better {101, p. 51). FLUX 23 In neither the American Society for Testing Materials test nor the Iowa Engineering Society test is a definite size for the test pieces stated; both specify material "of the same size to be used on the \\'ork." No commonly accepted tests to determine the resistance of filter stone to solution are known. The opinion has been expressed, however, that solution "will not be found a serious matter with rock meeting a high rating on the 20-cycle test" {101 p. 50). Undesirable inaterials. — Substances such as pyrite, clay, shale, ocher, and chert are usually undesirable. Remarks. — Limestone and dolomite are competitive with granite, quart- zite, trap rock, slag, and other materials. The type of materials used depends on its availability, ])rice, and the character of the sewage to be treated. FLAGGING AND CURBING Use. — Formerly limestone and dolomite were used extensively for flag- stone sidewalks and for curbing. Lately the use of concrete has greatly re- stricted these fields of utilization but flagstone is employed for walks in parks, courtyards, estate grounds, rock gardens, etc. Curbing is a minor use. General physical specifications. — Flagstone should occur in natural layers a few inches to about six inches in thickness and the surfaces of the respective layers should be relatively even. The stone should withstand severe weather conditions without cracking or splitting and be sufficiently hard to withstand abrasion, especially if to be used for walks. Few limestones or dolomites are hard enough for curbstones; exceptional! v, siliceous limestones are so used (11). Undesirable materials. — Chert, pyrite veinlets, clay, aud ocherous ma- terials are undesirable as they are likely to cause cracking, splitting, or pitting of the stone. FLUX Limestone and dolomite are used as fluxes in the smelting of various metalliferous ores. They combine with impurities in the ore to form a slag which can be separated from the metals. BLAST-FURNACE FLUX Use. — Both limestone and dolomite are used for flux in tlie production of pig iron in blast furnaces. General chemical specifications. — In either limestone or dolomite the total calcium and magnesium carbonates usually exceeds 90 per cent and often 95 per cent, aud the combined silica aud alumina are less than 5 per cent and often less than 3 per cent. xVccording to Goudge (^0„ p. 45), alumina should not exceed 2 per cent, sulphur and phosphorus shouhl not exceed 0.1 per cent each. Other authors specify a 0.5 per cent ma.xiinum lor sulpliur (1J{). Flux 24 USES OF LIMESTONE AND DOLOMITE for the manufacture of iron by the acid Bessemer process should contain less than 0.01 per cent phosphorus (7, p. 6). General physical specifications. — The stone used is clean, coarse, and usually 1/2 ii^ch to 4 inches in diameter. Some operators use coarser stone (8, p. 16). Goudge (42) specifies as desirable ^*a noncrumbly stone between 1% and 4 inches in size." Eeinarks. — If the slag from the smelting operation is to be used for mak- ing cement, the magnesia content of the slag should be less than 3 per cent (65). A flux low in magnesium carbonate would therefore have to be em- ployed. The best slag for road metal is said to contain 7 to 10 per cent magnesia (7, p. 9). In describing fluxes the term "available carbonates" is applied to "the percentage of calcium and magnesium carbonates available for fluxing the ore after a sufficient percentage has been deducted to neutralize the impurities in the stone itself" (7, p. 4). BASIC OPEN-HEARTH FLUX Use. — Limestone is used as a flux in the basic open-hearth process of making steel. General chemical specifications. — Limestone containing less than 1.5 per cent alumina, 1 per cent silica, and 10 per cent magnesium carbonate (5 per cent magnesia) is used (7. p. 12). Goudge says, "Silica should not exceed 3 per cent" {-k^). Phosphorus and sulphur should be low {J^^O, p. 45). General physical specifications. — Specifications call for coarse clean stone in pieces 2 to 12 inches in diameter (7, p. 12) ; a usual size is between 4 and 8 inches {Ji2). Renfiarks. — High-calcium stone is used rather than dolomite because cal- cium oxide possesses a greater affinity for phosphorous than does magnesia. Phosphorous is the most important material the flux is required to remove {7, p. 13). NONFERROUS-METAL FLUX Use. — Limestone is used as a flux in smelting copper, nickel, lead, zinc, gold, silver, antimony, and other metals (5, pp. 19-22; 1^0, p. 45). General chemical specifications. — In general, fluxes should be high in carbonate; commonly a high-calcium limestone is employed. Remarks.- — High-calcium lime is used as a chemical reagent in flotation and cyanide reflning processes {JiO, p. 45). GLASS Use. — Limestone or dolomite is used as part of the mixture employed for making glass. GROUND LIMESTONE AND DOLOMITE 25 General chemical specificaiions. — Either high-calcmm limestone, or dolo- mite, of uniform composition is "used. Iron oxide is very undesirable. The U. S. Bureau of Standards divides limestone and dolomite for glass making into three classes, class 1 being the highest grade, and gives the following specifications for limestone and dolomite to be used in making the various classes of glass (98). Table 4. — Composition of Nonvolatile Portion of Limestone, Quicklime or Hydrated Lime Class 1 Class 2 Class 3 ^lax. Min. Max. Min. Max. Min. Calcium and magnesium oxides 96 "' 0.'4" 1.0 9.0 5.0 91 ■ 0.8" 1.0 17.0 5.0 83 Ferric oxide 0.2 1.0 4.0 3.0 Sulphuric and phosphoric anhydrides Silica Alumina The amount of ferric oxide allowable in limestone or dolomite for class 1 glass, as shown in the above table, is probably higher than would be acceptable to many manufacturers of high-grade glass. Most of them specify a ferric oxide content of less than 0.10 per cent (88). General physical specifications. — The stone should be crushed to pass a 16-mesh sieve having a 1.19 mm. opening (98). The preferred grading is as follows (35) : Per cent On 16 mesh None On 30 mesh 15-80* On 60 mesh 15-50 On 120 mesh 0-15 Through 120 mesh 0-20 * Presumably the per cent "on 30 mesh" refers to the material passing 16 mesh and retained on 30 mesh. The figures for 60 mesh and 120 mesh are probably to be inter- preted similarly. RemarJcs. — Limestone or dolomite may constitute as much as 30 per cent of some glass batches (JfO, p. 47). It is essential that a deposit of stone to serve as a source of limestone or dolomite for glass, be of uniform character laterally and vertically in order that a product of constant chemical composition may be produced. GROUND LIMESTONE OR DOLOMITE Use. — Ground limestone or dolomite, not necessarily white in color, is used for dusting coal mines to prevent explosions; as rubber filler; as asphalt filler; and as a filler in a number of other products, listed under Avhiting sub- stitute (p. 43), whose color does not require the use of a white material. 26 USES OF LIMESTONE AND DOLOMITE General physical specifications. — Stone free from grit and relatively easy to crush is preferred. Limestone or dolomite for dusing mines is usually pulverized so that about 50 per cent passes a 200-mesh sieve and all of it a 20-mesh sieve. A light colored powder is desired. Usually a relatively pure limestone free from grit is employed {70). Limestone or dolomite for asphalt filler in sheet asphalt or bituminous concrete pavements is required to pass a No. 30 sieve, not less than 95 per cent should pass a No. 80 sieve, and not less than 65 per cent should pass a No. 200 sieve (92, pp. 21-22). A more finely ground filler is used with asphalt for other purposes. Rubber filler must be so finely ground that at least 98 per cent will pass a 300-mesh sieve (5^. p. 128). LIME Introduction. — Lime is made by burning limestone or dolomite at a tem- perature which drives off the carbon dioxide. The technology of lime manu- facture is complex, and the production of satisfactory lime depends on the chemical properties of the raw stone, its physical characteristics, and on the manner in which it is burned (lOJf). Limes may be divided into two general groups, non-hydraulic limes and hydraulic limes. The latter possess the ability to set under water whereas the former have this property only slightly or not at all. Of the varieties of non-hydraulic lime* (Table 5), the high-calcium and high-magnesium limes are of greatest importance in the United States. Although hydraulic limes are common products in Europe only a limited amount of hydraulic lime is made in this country {S3). A classification of limes compiled from several sources is given in Table 5. In this classification the use of 5 per cent as the minimum amount of silica and alumina in hydraulic lime, and the specification that non-hydraulic limes contain over 95 per cent calcium oxide plus magnesium oxide, is based on the statement by Bowles and Banks, in their discussion of non-hydraulic limes, that "commercial limes usually do not contain more than 5 per cent total silica, ferric oxide, and alumina" {15^ p. 2). Also the American Society for Testing Materials specifies that quicklime for structural purposes should contain more than 95 per cent calcium oxide plus magnesium oxide {107). It is important to note, however, that the hydraulic properties of lime are, in large part, dependent on the way in which it is burned {2Jf., p. 14), and therefore a chemical analysis may not accurately indicate the extent to which the lime possesses hydraulic properties. * In European and some American literature on lime, the terms "fat" or "rich" limes are used to describe limes of high purity and the terms "lean" or "poor" lime for more impure limes which are not hydraulic or only slightly so. LIME 21 Table 5. — Classification of JLimes » Non-hydraulic limes more than 95% CaO + MgO High-calcium lime more than 90% CaO less than 5% MgO Low-magnesium lime 5-25% MgO High-magnesium lime b 25-42% MgO Hydraulic limes c more than 60% CaO + MgO more than 5% Si02 + AI2O3 ^Feebly hydraulic lime 5-15% SiO^ + A1,0. Moderately hydraulic lime 15-25% SiO. + AI2O3 Eminently hydraulic lime 25-35% Si02 + AI2O3 a The classification of non-hydraulic limes is from Bowles and Banks (25, p. 2) and that of hydraulic limes from Cowper {2\, p. 16). This classification is on a nonvolatile basis. Bowles and Banks state that commercial limes fresh from the kiln "should contain no water and less than 0.5 per cent carbon dioxide." b Bowles and Banks used 45 per cent as the maximum amount of magnesium oxide in high- , magnesium lime. As 42 per cent magnesium oxide is the maximum amount theoretically obtainable from pure dolomite this figure is used. c Hydraulic limes are made from siliceous or argillaceous limestones {30, p. 176) which usually contain less than 10 per cent magnesium carbonate [52, p. 17). The specification of the American Society for Testing Materials covering quicklimes for structural purposes, according to their chemical composition when calculated to a nonvolatile basis^ is as follows {107) : Calcium lime (Per cent) Calcium oxide, minimum 75 Magnesium oxide, minimum Calcium and magnesium oxides, mini- mum 95 Silica, alumina, and oxides of iron, maximum 5 Carbon dioxide, maximum (a) if sample is taken at the kiln... 3 (b) if sample is taken at any other place 10 Magnesium lime (Per cent) 20 95 10 Use. — Lime possesses a great number and wide variety of uses which are enumerated in detail in a chart prepared by the National Lime Association {66, ^. 110). It is employed in such building materials as mortar, plaster^ slag cement, sand-lime brick, stucco, and cold-water paints; it is used in making silica brick; as an aid to crop production and in some stock feeds; it enters into many processes of drug and chemical manufacture ; it is widely used in the purification of water and in the treatment of sewage; and it is involved in many commercial processes such as tanning of leather, sugar refining, pulp and paper nuiking, and in the manufacture of bleaching powder and caustic soda. In general, high-calcium lime is used in m.ost of those processes involving the production of chemicals and also in the construction and many manu- facturing industries. High-magnesium lime is used chiefly in the building 28 USES OF LIMESTONE AND DOLOMITE industry and in certain chemical and commercial manufacturing processes, such as the manufacture of magnesia and in making certain grades of paper (31), notably sulphite pulp by the milk-of-lime process. Low-magnesium and hydraulic limes are used mainly in construction. General chemical specifications. — Most of the limestones burned for lime in the United States contain more than 97 per cent carbonates {10, p. 388). The approximate composition of limestone and dolomite for making differ- ent types of limes is shown in table 6. The data in this table have been cal- culated from table 5. The figures given should be considered approximate as it has been assumed of necessity that all materials excepting calcium car- bonate and magnesium carbonate would remain in unchanged amounts during the process of lime burning. This is not exactly true. Nor can allowance be made for certain other minor variables. Despite these shortcomings it is felt that the table will indicate in a general way the type of lime which might be produced from a limestone or dolomite of known chemical composition. Table 6. — Approxiiniate Composition of Limestones and Dolomites FOR Making Different Types of Limes Non-hydraulic limes High-calcium lime More than 91% CaCOs Less than 6% MgCOs Less than 3% other constituents Low-magnesium lime 68-95% CaCOs 5-29% MgCOa Less than 3% other constituents High-magnesium lime 54-72% CaCOa 28-46% MgCOa Less than 3% other constituents Hydraulic limes a 'Feebly hydraulic lime 91-97% carbonates 3- 9% other constituents b Moderately hydraulic lime 84-91% carbonates 9-16% other constituents b Eminently hydraulic lime 77-84% carbonates 16-23% other constituents b a The carbonates are calculated as calcium carbonate, inasmuch as magnesium carbonate is minor constituent of rocks used for hydraulic lime (30, p. 176). b Principally silica and alumina. General physical specifications — The stone is commonly in 6- to 10- inch pieces if burned in vertical kilns ; but if burned in rotary kilns, clean dry stone generally in pieces from I/2 to II/2 inches is used {15, p. 32). MAGNESIUM 29 Beniarks. — "Hydrated lime is a fine dry powder, consisting essentially of calcium hydrate and magnesium oxide" (32, p. 10). It is prepared by '^add- ing to quicklime just sufficient water to insure complete slaking" {-I'S, p. 10). Vienna lime is a high-magnesium lime used for buffing numerous ma- terials and for giving an "under surface" blue to nickel after plating (29). The chemical composition of a dolomite used for making Vienna lime is roughly 55 per cent calcium carbonate, 43 per cent magnesium carbonate, with traces of silica, iron, and alumina (29). While the chemical composition of the dolomite from which the lime is made is important, other factors such as texture, porosity, crystallinit}^, and mode of burning also appear to be sig- nificant {u. p. 9; 77). Grappier cements "are made by grinding finely the lumps of unburned and overburned material which remain when a hydraulic lime is slaked. The lumps consist partly of lime silicate and partly of unburned limestone." La- farge cement is a grappier cement made in France {SO, p. 189). Scott^s cement, selenitic cement, or selenitic lime "consists essentially of lime (CaO) plus a small percentage of sulphur trioxide (SO3). The lime used as a basis for this cement is always a more or less hydraulic variety, while the sulphur trioxide may be added to it in the form of either plaster of Paris or sulphuric acid" {30, p. 196). Slag cement is made by finely grinding an intimate mechanical mixture of hydrated lime and granulated slag of suitable chemical composition {30, p. 584). LITHOGRAPHER'S STONE Very pure uniform fine-grained limestone or dolomitic limestone of ex- ceptionally even texture and free from grit or other granular impurities, at one time was used extensively in the lithographic process of printing. Other materials have now supplanted lithographic stone and it is employed only in small amounts for certain types of high-grade work {53, p. 278; 5Jf-, pp. 323- 324). Little, if any, lithographer^s stone is now produced in the United States. MAGNESIUM The magnesium produced in the United States in 1936 was manufac- ured from natural brines {33). However, in 1929 a plant in Utah is reported to have started extracting magnesium from dolomite; the present status of the plant is not known. The process used was in part secret but involved treatment of dolomite with a hot solution which dissolved magnesium car- bonate leaving the calcium carbonate. The leach liquor was clarified and the magnesium recovered electrolytically (i). Magnesium is also reported to be extracted from dolomite in Europe (41, V' 374). 30 USES OF LIMESTONE AND DOLOMITE MINERAL FEEDS FOR STOCK Use. — Mineral mixtures containing limestone are fed to stock to provide a diet containing the proper proportion of minerals. Limestone is used to furnish calcium carbonate which is utilized in the building of bone and in other body processes. General chemical specifications. — A high-calcium limestone containing over 95 per cent calcium carbonate is commonly recommended {63). The limestone should be essentially free from fluorine compounds. ^'The feeding of rations containing approximately 0.03 per cent or more fluorine derived from rock phosphate or sodium flouride impaired growth" and had an un- desirable effect on teeth and bone structure of swine {51). Likewise small amounts of fluorine have also been found to be detrimental to the health and general condition of dairy animals {SO). General physical specifications. — The stone is used in pulverized forms, usually through 200 mesh or finer. MONUMENTAL STONE Use. — Limestone or dolomite is used for nuirkers, headstones, monuments, etc. General physical sped flea I ions. — "Usually stone that takes a good polish is requisite; in fact, the very highest types of flawless, uniform stone are used for monumental purposes. However, monuments with tooled, hammered, or even rough-hewn surfaces are not unusual, and l(\