rnia 1 BRIGK^CLAYRECORD O t-i I O -^>,C3 O UNIVERSITY OF CALIFORNIA LOS ANGELES GIFT OF James W. Lfoncrieff CLAYWORKING PROBLEMS CLAYWORKING PROBLEMS Being One Hundred and One "Questions and Answers" Selected from the pages of Brick and Clay Record A publication devoted to the many branches of the clayworking industry and issued semi-monthly. Chicago Brick and Clay Record 1915 (All Rights Reserved) Copyright, 1915, by I '.rick and Clay Record Chicago PREFACE IX TWO YEARS, more than five hundred questions inti- mately connected with clayworking, have been mailed to the editorial offices of "Brick and Clay Record." Possi- bly two-thirds of these, having presented problems that bore evidences of being of value to more than one plant, were an- swered through the columns of the magazine. The wide range of these questions is indicated by the index which is a part of this volume. The quality of the answers will be determined by the reading. In this connection it is well to quote from one of those an- swers, using the language of R. T. Stull, E. M. (in Cer.) then of Urbana, Illinois, who says: "No doubt you have read Robert Burns' ode to a famous physician who could prescribe curatives based upon evidence sent him in a 'Kale' leaf. There are no doctors in this day and age of enlightenment, who are as wise as the famous doctor of Burns'. With the exception of a few simple cases, the 'ceramic doctor' cannot prescribe intelligently from a few symptoms sent him by mail." The claim is made by some who possess a certain knowl- edge, that the art of claycrafting has advanced more in the last ten years than in the preceding ten thousand years. Per- haps it would have been simpler to have said that it has ad- vanced more in the last ten years than in the thirty years preceding, and this brings the period within the memory of some of our compatriots. At any rate, there has been a great and notable improvement in methods, machines and prod- ucts. The changes have l>een so radical that much of the wisdom PREFACE of the past generation has become as superstition, and men who were experienced in many brandies of clayworking, and who were regarded as experts but a few years ago, now find that their knowledge is as worthless as the ability to weave with a hand loom or to drive four oxen. The position of a trade or technical publication gives it unexampled facilities for the gathering of the best informa- tion that is at hand in the industry it serves. Its news col- umns tell of the improved products and methods, while its advertising columns speak of improved machinery and appli- ances. The system of inquiry that makes it possible to fill these columns with something, new in every issue, brings, at the same time, accurate information as to the men who are responsible for the advances that are being made. How simple it is, therefore, for a trade or technical publi- cation to turn to the best source of knowledge on any par- ticular point. No individual, no business house other than a publisher could do this; so it is that "Brick and Clay Rec- ord," while occupying, to some extent, the position of Burns' doctor (who prescribed by mail) has given solutions to in- tricate problems which have come to it in precisely the same manner as did the Scotch doctor minus, however, the "kale." That these answers have been right that they have solved problems is beyond doubt, for the men who asked the ques- tions have, iu many cases, later written to say that they have tried the solutions offered and so effected actual savings in money, in time and in product. The immense value of this Department of Questions and Answers is beginning to be appreciated. This is evidenced by the ever-increasing number of inquiries that come to us. Without these inquiries, the Department could not exist. Chicago, 1915. CONTENTS A * Absorption Tests on Pace-Brick ............... _ ...... _ ...... _ ..... 134 Alkaline Clay ................. _ ............................. ________________ " 148 Amortization of Bank Indebtedness ___________________ 94 Artificial Drying:. Effect on Clay of- ........................... ____ ................... 166 B Bank Indebtedness, Amortization of ........................... _ ....... 94 Belting. Care of --------------------------- ....... ------------ ....................... 116 Black Coring- ....... ___________ .......... _________ ...... ___ 14 Black Enamel for Enamel Brick ................... ________________ "". 65 Blast Furnace Slag, Brick Made from ___________________________ ...... _101 Blisters on Drain Tile _____ _ _ _ 162 Bloated or Swollen Brick ....... _____________________ ........ _" _______ "'"".'"."'. 14 Blue Enamel for Enamel Brick ...... ...... ____ ..... ______________ ............... 65 Glaze for Stoneware ----------------------------------------------------- 70 V Brick. Absorption Tests on Face- Brick -------------------------------- 134 Analysis in Sand-lime .............. ...... 153 Break in Drying ________ ............................ _____________ ........ _ ................ 167 Color Affected by Change In Fuel...- ........................... __ ...... ____ 43 Crack In Burning.. ...... _________ .......... ____ ..... ___________________ 37 Crack in Drying ........... _____________ ........... _ .................. ____________________ 161 Dipping to Change Color ................ ______ ...................... _______________ 136 Economy of Reburning Soft ................ _ ..................... ---------- ...... 126 Flashed Heads on Gray ___________________________ .......... __________ ..... _____ 121 Made from Blast Furnace Slag ______ ............ ___________________ 101 Making Bullnoses by Hand ___________________________________ ...... 146 Manuf acture of Silica, 155 Mash in Center of Kiln.~.'_.."."L!.L.."!.L~ _____ !!.~"..^""_.!ZZ_.!1! 11 Silica, Manufacture of .......... _ ........ ---------- ..... ______________ .......... ___ 155 To Produce Red Color from Buff Burning Clay .......... _____ 117 Brick Press Checks Brick ....................... _____ .......... __________________ 112-114 Brickwork, Mortar Joints for Interior __________ ......... ______ ............... ___ 98 To Remove Efflorescence from ............... _. ........... ...................... 124 Burning ...................... ......... .................................................. _ ................... 11 Of Alkaline" ciay-_l ---- LlZ""ZZZZ"ZIZ!ZZZ!""Z"!Z"l48 Bullnoses, Making by Hand ...... ........... 146 Calcining Fire-clay.. ......... .181 Capacity of Dry Pans ....... _ .............. ............................... __ .................... 170 Cement Joints in Sewer Pipe _________ .......... ______ ........ ----- ................. 127 Changed Fuel Affects Color of Dry Press Brick..... ..... _ ............ 43 Checks Caused by Brick Press .............................. __________________ ........... 112 Chimney Draft, Substituting for Fan ..... .. ..................... ____ ...... 108-109 Alkaline ________________ ......... _____________________________________ ...... 148 91 Mixing Shale with 149 Indicating of Plastic The Effect of Artificial Drying on 158 IIZIZI"166 140 Slips . . . . ...165 foal. Comparative Cost of Oil and . ... 155 Dust in Brick Burning , . 33 Economy of Various Grades ... 147 Separating from Fire Clay ~ ~ _ 93 CONTENTS Coloring Molding Sand 128-149 Mortar 101 Color of Brick Changed by Dipping 136 Cones vs. Pyrometers 1-9 Copyrighting Trade Names 97 Cost of Car Shipments of Clay 87 Of Clay Haulage 91 Of Electric Power 89-90 Of Natural Gas Fuel 88 Cracked Brick 37 Cracks in Drain Tile 51 in Stove Linings 42 Culvert Pipe, Burned Clay vs. Galvanized D Dies 79 Die Lamination 79 Difficulty in Grinding Wet Shale 178 Dipping Brick to Change Color 136 Discoloration in Painted Hollow Tile Walls 178 "Doby" Clay Burns Many Colors 35 Down-Draft Kilns, Changing Up-Draft to 54 Proper Size of 49 Draft, Substituting Chimney for Fan 108 Drain Tile, Blisters on 162 Cracks in 51 Puffed or Swollen 32 Salt Glazing 64-68 Drying, Brick Crack in 161 Stiff-Mud Brick, Break in 167 Losses Caused by Improper Tempering 160 The Effect of Artificial, on Clay 166 Tile Cracks in 171 Has Trouble with Driep 161 Dry Pan Capacity 170 Duplicate Equipment Economy of 176 E Economy of Duplicate Equipment 176 Efflorescense to Locate Source of ........168-169 To Remove from Brickwork 124 Electric Power, the Cost of ".'.""."".'.'.'.89-90 Enamel Brick 65 Enameling, Recipes for Black, Blue and Green 65 F Face Brick Absorption Tests on 134 Burn to Full Color Range ... 50 Burn to Too Many Shades "" 46 Fire Flashed Fan Draft, Substituting Chimney for . 108 Feathering of Clay Bar "~140 Fire Brick Dimensions 133 Quantity for Kiln Crowns 130 Fire Checks IS Fire Clay Calcining '. Z!!l3t How to Keep Coal Out of 93 Methods of Washing "" 95 Fire Flashed Face Brick Flashed Heads on Gray Dry-Pressed Brick 121 Full Color Ranges in Face Brick 50 CONTENTS G Gas Fuel, the Cost of Natural _ 88 Glaze (Blue) for Stoneware ~ 70 Glazing . . .... 61 Salt for _ 69 Sewer Pipe - ~ 61 Under Side of Kiln Crowns _ .'..'.152 With Salt In Oil-fired Kilns 74 Green Enamel for Enamel Brick 65 Greenish Color in Sewer Pipe _ 25 H Harvard Brick, Imitations of..._ 100 Haulage - _ _ 91 Heat, Controlling Kiln Temperatures _... 53 Heating Kiln Bottoms _ 13 Height of Kiln Crowns _ _ 140 Headers, Imitations of Harvard _ 100 Hollow Tile, Salt Glazing... _ 63 Discoloration in Painted Walls of 178 I Imitations of Harvard Headers _ 100 Interior Brickwork, Mortar Joints for 98 K Kilns, Best Height for Crowns 140 Changing Up-Draft to Down-Draft 54 Claims Has New Type _ 125 Glazing Under Side of Crowns 152 Proper Size of Down-Draft...- _ 49 Proportionate Kiln and Stack Area 112 Quantity of Fire Brick for Crowns 130 Salt Glazing in Oil-flred .... 74 Setting _ _ 24 To Calcine Fire-clay 131 L Lamination .... 79 Lignite Burning in Down-Draft Kilns - 141 Losses Caused by Improper Tempering 160 Lubrication 85 M Manganese in Connection with Shale 105 Miscellaneous -~ _ 87 Molding Sand, Coloring Matter in 128 Mortar Color 101 Mortar Joints for Interior Brickwork 98 N Natural Gas Fuel, the Cost of 88 Off Colored Face Brick .... 35 Oil, Comparative Cost of Coal and 155 Oil Fired Kilns, Salt Glazing in 74 Overburned Tops 24 Oxide of Iron, Adding to Produce Red Color""! ".!....117 Patent Office Registration 97 Power, Electric, the Cost of 89-90 Varying Motor Loads on Shaft J51 10 CONTENTS Preheating- of Plastic Clay 15S Puffed Drain Tile Pyrometers vs. Cones 12'J Roo u ruing S flng Tile. Salt for Glazing Salt Glazing. Does Not Reach Entire Contents of Kiln- Drain Tile Hollow Building Block In Oil Fired Kilns Sewer Pipe Sand-Lime Brick, Analysis in Manufacture Scum, to Locate Source of Trouble To Remove from Brickwork Setting Setting Up-Draft Kilns Sewer Pipe, Cement Joints in Greenish Color in Salt Glazing Shafting, Varying Motor Loads on Shale, Mixing with Surface Clay Silica Brick .'. Made from Silica Sand Manufacture of Silica Sand Slag Brick Slate in Brickmaking Slipping of Clay Bar Soft-brick, Kconomy of Ueburning Soft Brick in Kiln Centers Stacks, Proportionate Kiln and Stack Area Steam Lubrication vs. Water Lubrication Steam Shovels, Using in Shallow Work Stiff-Mud Brick Break in Drying Stoneware, Blue Glaze for Stove Lining Cracks in Burning Swollen Drain Tile Swollen or Bloated Brick Temperatures At Which Brick Are Burned '."."".'. At Which Manganese Is Fused Controlling Heat in Down-Draft Kilns Tempering Tile Cracks in Drying Trade Names, Copyrighting Registering U Cnil'orm Color in Face-Brick 4,; I'p-Draft Kilns, Changing to Down-Draft .".J.......... "" :,4 W Washing Fire Clay <,r, Water Lubrication vs. Steam Lubrication "" sr. Wet Shale, Difficulty in Grinding 17 ^ Whitewash, to Locate Source of Trouble 168-169 To Remove from Brickwork 121 CLAYWOKKIN'G PROBLEMS CHAPTER 1 WHICH DEALS WITH BURNING Temperatures at Which Brick are Burned 5:10. Pennsylvania H'c would like sonic figures giiing us an approximate idea of the temperatures used in burning brick c/ different kinds. The temperatures at which various kinds of brick may be considered burned that is finished are as follows: Com- mon brick (red) 1,600 to 1,800 F. Paving brick or shale vitrified brick. 1,800 to 2,200 F. Face brick made of fire clay, l.'.KK) to 2.200 F. Fire brick. 2.000 to 2.600 F. Brick Mash in Center of Kiln 510. Xorth Carolina MY are hating trouble with some clay we are working and we thought that you, or some of your readers, could help us. Our clay is hard and tough in the bank, but as soon as it is dug, and the air gets to it for a few hours, it pulverizes and works through an auger machine as fine as we could expect, the brick coming through the dryer in perfect shape, ll'e are using a 25-ft. down-draft kiln for burning. In the center and bottom of the kiln, the brick mash and fall all to pieces, just about as lime does when ivater is added to it. On the top and outside of the kiln, the brick vit- rify and burn as hard as pig-iron. F.llis Lovejoy, C. E., answering the above, says: "I cannot determine from the data presented the cause of CLAYWORKING PROBLEMS the trouble. It may be that the bond is so weak that the dry brick crush under the superimposed weight. It may be due to insufficient draft during the water smoking stage in con- nection with too rapid water smoking. The moisture driven off from the brick in the upper part of the kiln is drawn to the bottom of the kiln, where it condenses more or less and softens the brick in the bottom. The draft of the kiln should be such that the moisture is carried away as rapidly as formed and not be allowed to collect in the bottom of the kiln and thereby become absorbed by the bottom brick. It may be that the clay contains excessive lime and if the water smoking is done with a low grade of coal, high in sulphur, there will be formed in the kiln considerable sulphuric acid which will at- tack the lime in the clay and form a sulphate of lime, the bulk of which may be greater than the original lime mineral and the expansion due to this increased bulk destroys the bond and the brick crush under the weight. Sulphuric acid readily destroys the bond in clay wares and even though there is no expansion in consequence of new mineral formations, the bond thus weakened may be insufficient to hold up under the weight. I have experienced all of these difficulties, but the second above mentioned is the one most common." C. S. Kinnison, of the Bureau of Standards, Pittsburgh, Pa., gives the following opinion : "From a distance, it appears that your trouble is due to condensation taking place in the kiln. You may either be setting your ware too wet or you may not have sufficient draft. The respective remedies are apparent. When con- densation of the water vapor takes place, the water obviously trickles down through the ware and affects the courses towards the bottom, worse than the upper ones. The result is, that they become so wet that they do not have sufficient strength to carry the weight imposed upon them and they crush. You might also try allowing the clay to be exposed to the weather for awhile. There is a remote possibility that CLAYWORKING PROBLEMS 13 your clay air-slakes and the proce. is not allowed to finish before they are made into brick." Difficulty in Heating Bottom of Kiln 568. Illinois We hare trouble getting the heat to the bot- tom of our kilns, partly because we do not hai'e good draft, and partly because our bag ii',)(). /t'tc'c/ / bclicrc yon misinterpreted my statement in regard to the looks of the fracture on 7w/ ttv term air- checked pipe. You will note in my prcrious letter that I do not use the term "(/lazed" in referring to the nature of the fracture where the air-checking occurs but I do say that this fracture has a "glasslike"' appearance. U'e get some of ivhat you term fire-cracks directly in front of our fires and some- times in the top courses where tlic flames strike the ware directly in front of the bag-walls. These cracks are, of course always glazed. Xow, what makes me. think that this checking is done while the kiln is cooling and, at the same time, is at a temperature of from 850 to 1,000 degrees Fahr., is the fact that, if I draw a trial piece from the kiln during the salting and break it immediately, it will show a glassy surface where it is broken. This would lead me to think that the ware is thoroughly vitrified but, if this same trial piece, which I hare already broken, is allowed to cool down for tw'o or three minutes (or until it is perfectly black) and is again broken, the fracture is entirely different in appearance and does not resemble a piece of thoroughly ritrified pipe in the least. Is it not true that, if our checking zvas done during the water-smoking, that the cracks would be much larger than those we get in what zvc term "air-checked"? Air-checked pipe hare an almost inrisible hairlike check that runs the full length of the pipe. I might add, for your information, that we do not touch the damper after it has been dropped. I would like to cite an instance of how hard it is to locate the c.ract cause of our trouble. We hare, next to our stacks, what is called a back draft or, in other zvords, an opening by which air may be admitted into the kiln b\< wav of the kiln flues. This is done by dropping the stack damper and pulling off the hack draft that is directly aborc the stack damper. This CLAYWQRK1NG PROBLEMS 21 back draft has aki'ays been left off after the stack damper was dropped. We started to work, assuming that the "air- checking" as we term it, would be most likely to occur dur- ing that stage of the cooling when the kiln is turning from a dark red to a black. One kiln was at this stage of the cooling during very windy weather and the other kiln passed through this stage of the cooling during fair weather and both back drafts were off. Before either one of these kilns were drawn, we prophesied that the one which had the back- draft off during the windy weather u'otild be the one that zcould be "air-checked" and the other would not. This proved to be true when the two kilns were drawn and we naturally supposed that what had been causing our "air-checks" was the fact that, during windy weather, the cold air would be forced on to the bottom of the kiln by way of this back draft, thus being distributed evenly over the bottom of the kilns and causing the ware to be uniformly checked throughout the en- tire bottom courses. If the weather was fair, and no wind blowing, the open back draft would not be a dangerous thing consequently, we proceeded to keep this back draft closed at all stages of the cooling and hoped to thus eliminate any possibility of a con- stant influx of cold air. To our surprise, however, we found in the kiln that we drew today, which happens to be the first kiln in which this new method of cooling has been tried, the air-checks are worse than in any kiln we haz'e drawn for a long time. About the only conditions that seem to remain constant is the fact that this trouble nearly always follows windy weather. Do you think there is any possible chance of the kiln "air- checking" during the time it cools from 2,100 down to 1,600 degrees Fahr. provided this drop in temperature is distribut- ed over a period of si* to eight hoursf Our original answer to your question was based on your CLAYWORKING PROBLEMS final sentence as published in the Dec. 1st issue. This was. "the fracture shows a dense glasslike surface, and yet if you break the same pipe at any other place, the surface is rough and jagged." Our use of the word "glazed" shows where we misinter- preted what you had said and this, we trust you will admit, is a very natural word error, "glasslike" and "glazed" being similar in many minds. In your second letter you give us further information on the point, which changes our opinion. One of these points is where you say "I might add for your information, that we do not touch the damper after it has been dropped." You have cleared up, in your second letter, the point of your making full use of the back draft through the damper manhole. This explanation was neglected in your first let- ter and seems to indicate the road to safety from dunting or air-checks. Note the following and draw your own conclu- sions before you study ours : Downdraft cooling, and cooling through the doors and fire-boxes by means of stack pull will cause currents of cool- ing air to pass down through the ware, following the lines of least resistance. It will cause cross horixontal currents of air and result in a lack of uniformity in cooling which in turn, results in checked ware. Heated air rises naturally. If we cool by up-draft we thus reverse operations in a most natural way. Given the above, how can we apply it so as to produce a lack of extreme fluctuation of cooling curve and compel the cooling advance or heat retard evenly, over the entire con- tents of the kiln? We have the following to consider: 1 back draft open- ing ; 2 top center hole and sixteen smaller holes. Upon the proper manipulation of these two variables depends tin- success or failure of the cooling operation. Operation : 1 drop damper in stack as soon as coal has CLAYWORKING PROBLEMS 23 burned out in the fire boxes in your case in one-half an hour after finishing; 2 mud up the iron plates that you use around the fire boxes so making the boxes tight; 3 open the back draft hole as wide as you wish (it has nothing to do with the amount of the intake of cold air) ; 4 open up the top hole and all other auxiliary crown holes slightly. The heat is carried upwards by the air that is evenly de- livered over the bottom of the kiln through the perforations. The amount (or volume) and its uniformity of distribution over the entire surface of the floor depends on the pull erected by the openings at the top of the kiln. Start cool- ing with not more than 150 square inches of total top holes this is about eight square inches per stack. The result is that the bottom ware is first bathed by air that comes to it already preheated by the body heat of the under-kiln brickwork. Depending on the manipulation of top holes, it never is flushed with a rush of cold air but is cooled gradually. The same operation takes place in con- nection with the ware directly above, and so on to the top. The doors and the fire-boxes are opened in accordance with your past experience. The back plate cover must be used intelligently in windy weather. Answering your question specifically as to whether we think that there is any possible chance of the kiln "air-check- ing" during the time it cools from 2,100 down to 1,600 de- greeswe do not feel that there is any stated time during the cooling when the ware will or will not check. We do think, however, that it is most liable to check during that period when the ware is going from dark red to black. Keep the bottoms clean. Dirty flues prevent the cooling air from circulating and so cooling evenly. The ware that 24 CLAYWORKING PROBLEMS is slighted in this way is bound to suffer when the kiln is opened wide. Has Trouble With Top Burns 480. lozva We arc making a dryprcss brick and arc haz'- ing sonic trouble in getting a good burn on the upper part of the kiln. We are using a common up-draft kiln, set 35 high. We get fair to good brick up to 27 or 28 courses, but the bal- ance of the top courses are soft, zvith no color, and haz'c a ring like a soda cracker. Is there anything that you know which would help us out? The brick in the top courses in your kiln are undoubtedly set too far apart, allowing the heat to pass through the kiln too rapidly. If you will set the brick in your top courses close- ly so as to hold the heat in the kiln longer you will undoubt- edly get a higher percentage in the top of your kiln. Trouble Seems to Be With Setting and Burning 587. Michigan / hare recently replaced a battery of up- draft kilns with a battery of rectangular down-draft kilns. Conditions hare reversed tlictnselres and where I used to get soft, unsalable brick on top, I am now getting oz'cr- burned unsalable brick, zi.c and drain-tile, that contains a considerable amount of Pyrites of iron and also shows a small percentage of lime; the clay is ground to a 16 mesh and is then put through the usual process of preparation. When the ware is put in the kilns, they are gii'cn from 5 to 6 days in burning our object being to give the kilns a gradual increase in tem- perature from the start to the finishing point, which t'arics from cone 01 to 5; this i-ariation may seem rather queer, but is accounted for by the fact that if we finish at cone 01, and keep a smoky atmosphere in the kilns, we can get fairly good glaze, but the pipe, especially the larger sices, show a greenish color which is, of course, undesirable. Pipe finished under these conditions are rery smooth. We hare finished kilns at cone 5, maintaining oxidising conditions at all times during the finishing process, and trial pieces drazvn from kilns furnished in this manner show a mesh, the pipe should not get rough under reduc- ing conditions unless some coarse particles find their way into the wet pan. which is possible. But supposing this does not occur, then the fault is with the manipulation of the draft, it going to extremes, and in one case too much oxidizing, in the other too much reducing takes place. There is a happy medium between the two ways and this cannot be supplied through these columns. It takes a practical man, who has had similar experience, to be on the ground and apply his past experience and knowledge in such matters and learning the existing conditions by overseeing the burning of one or more kilns. This correspondent states that the analysis shows a small percentage of lime. That may be true, as far as the sample CLAYWORK1NG PROBLEMS 27 that was analyzed is concerned. We know that clay from the same mine or deposit often varies in the different stratas and that the average clay used for the manufacture of the pipe may have considerable more lime or alkalies in other forms, than the analysis shows. The same is true with coal; the analysis may show a small percentage of sulphur, but the coal that is used on the kilns may have considerable more, even if coming from the same mine. It's queer, but, nevertheless, it's a fact. Why the man in trouble cannot get a bright glaze, a heavy glaze, under oxidizing conditions with a higher heat cone 5, is due to the fact, that the draft in the kiln at the time of salting is so strong that it carries most of the soda in the salt out of the stack. It slips off, instead of playing around the pipe to deposit the soda, uniting with the silica in the clay of the pipe's surface and that is the reason why he cannot get a heavy glaze under oxidizing conditions. Why he can get a heavier glaze under reducing conditions is due to the contrary of what happens under oxidizing condi- tions. The vapors remain longer in the kiln, and have time to form the glaze and a heavier glaze is produced owing to the ware in the kiln being flashed more under reducing conditions than under oxidizing ones. "But," he says, "the pipe arc rough !" This is due to several causes and no man can correctly de- fine the cause without being on the ground to investigate the matter. By Ellis Lovejoy, E. M. The three conditions mentioned by your correspondent are as follows: (1) Reducing kiln conditions finishing at cone 01 produces a fair glaze, smooth surface, with greenish color. (2) Oxidizing conditions finishing at cone 5 develop a bright glaze and smooth surface but the glaze soon gets dull after exposure. (3) Reducing conditions finishing at cone 5 result in bet- CLAYWORKING PROBLEMS ter color, heavier glaze, but 'the surfaces are very rough (pimpled with iron-silicate spots, we presume). We will discuss these in the above order. A. The greenish color in No. 1 is due to a combination of the lime and iron to form a lime-iron-silicate which is buff to green to black in color, depending upon the amount of iron present. Lime in clay is most frequently present in tl.e form of a carbonate (limestone) which under heat treatment is con- verted into calcium oxide, which we know as "lime." In this form it can readily combine with other compounds, provided the other compounds are also in the proper state for such combination. Iron in the form of pyrite is a sulphur compound. Under heat the sulphur is driven off, leaving the black oxide which combines readily with other compounds, but if we have oxidizing conditions, we may convert the black oxide into the familiar red oxide which cannot enter into combination. Now under the conditions mentioned in No. 1 we get the lime and iron into the proper form and combina- tion results producing the characteristic green to black lime- iron color. In the presence of sulphur and moisture we get sulphuric acid which acts on any lime whatever its condition to form lime sulphate. In water smoking the kiln we have sulphur from the fuel, moisture from the ware, and lime in the ware, and thus we easily form sulphate of lime, or it may be that the sulphate is already in the clay or is formed in the process of drying. Under reducing conditions this sulphate of lime is broken up and when broken up can combine with the iron since in decomposing the sulphate we get the oxide as above mentioned. Therefore, under reducing kiln conditions it matters not whether we have lime carbonate, oxide, or sulphate, the result in the end is the same. Our experience is that salting at such low temperatures dues not give a bright glaze and we arc of the opinion that a CLAYWOKKING PROBLEMS 29 better glaze will develop at the higher cone. We do not know of any way of overcoming the green color produced in No. 1 under No. 1 conditions. B. As mentioned in "A," the sulphate of lime (common scum) is or may be formed in the ware and probably ac- cumulates on the surface. Under oxidizing conditions, even at temperatures at and above cone 5 this sulphate is not broken up and cannot enter into combination. It remains on the surface of the ware and prevents the fumes of the salt from coming in contact with the clay which it must do to get the necessary silica to form the insoluble glaze. Scummed sewer pipe never glazes well and it is our obser- vation that the glaze on scummed pipe soon loses its lustre after exposure but whether due to instability of the glaze through lack of silica or to some chemical reaction between the glaze and the underlying sulphate, we do not know. C. Under strongly reducing conditions prevailing in the kiln at cone 5, the sulphate of lime (scum) is broken up and the conditions are the same as in "A." The grains of iron from the iron pyrite may be fully re- duced but are not dissolved under the low temperature and time of No. 1 but under the higher temperatures, the grains enter rapidly into combination with silica to form an iron silicate which fuses, draws up into globules, and when near the surface of the ware, the globules protrude, forming the black pimples so common in many sewer pipe products. The lime, of course, is taking up its share of the iron but it can- not absorb the larger grains of iron or at least not rapidly enough, but instead we have the grains of iron taking up silica and probably also lime to form the globules. At low temperatures the lime acts as a flux and predom- inates, while the grains of iron are largely dormant, but at higher temperatures the iron becomes the predominating flux locally at least where the pimples develop. The amount of iron in these globules is so predominant over the lime that they are black while between the grains 30 CLAYWORKING PROBLEMS of iron we may have combinations of lime and iron with the green color. We do not understand why there is not some evidence of the green color unless it be that the larger development of the iron at the higher temperature gives a general darker color and mantles the green color. It seems to us that this correspondent must choose the least of the evils because we doubt if all the troubles can be over- come in the burning. The lime content complicates the problem. Where the trouble in rough surfaces is due simply to gran- ular iron in the clay which would be the physical character of the iron in the form of pyrite, we can largely overcome the trouble by alternate oxidizing and reducing conditions. It must be borne in mind that at high temperatures even under oxidizing conditions, oxidization does not take place, but rath- er there is some reduction. We must get the full reduction at low temperatures. By the alternating treatment, we first reduce some of the iron, and this is oxidized, perhaps ab- sorbed, or spread, we do not know. Following this we fur- ther reduce and again oxidize, and in this way completely de- stroy the grains of iron. Whatever the explanation, we find by this treatment that the rough surfaces are greatly lessened. In the presence of lime, however, the iron goes into combina- tion with the lime and the green color is produced. Here we have a choice between smooth surfaces and green color. It will be remembered that during the reduction periods we are at the same time reducing the sulphate of lime and in the end leave the surface of the ware to take the full glaze de- sired. It is possible that the increased amount of iron that we get into general distribution and combination by this treat- ment gives enough darker color to mantle the green color from the lime and especially might this be true if the lime content is small. With the iron thoroughly scattered and the sulphate of lime broken up and dissolved, we may finish the burning and salting at a high temperature which develops CLAYWORKING PROBLEMS 31 the bright heavy glaze without the development of the pimples. We overcome the difficulty entirely in the burning. In case the scum is formed in the watersmoking it can be prevented by watersmoking with wood. To get the scum we must have sulphur, moisture and lime. The sulphur comes from the fuel, the moisture from the ware and the lime is in the ware. The use of wood elimi- nates the sulphur until the water is all off. and then we may return to coal firing without any danger of scumming. If the ware is scummed in the drying, which is often the case, especially if crop clays are used, and the drying is very slow, then the proper course would be to treat the clay with barium carbonate or hydrate to break up and precipitate the lime sulphate so it cannot escape to the surface during the drying period. After this question and reply were published, another re- ply was received, which we give : To answer your question fully would involve a complete discussion of burning hollow ware, which would be beyond the province of a department like "Questions and Answers." There are two essentials to be mentioned, however, in this connection, viz., (1) regarding time allowed for oxidation, and (2) temperature of salting. If the first point is not handled properly, you are very apt to find trouble in the second. It is very important that ample time be given for oxidation. We may say that this takes place between about 1,200 and 1,600 F. Take your kiln up slowly during this interval and make draw trials from time to time, in order to observe the elimination of the black core in the center of the trial. When this spot disappears, the oxidation can be considered as being completed. It should be borne in mind that oxidation is a process which requires time for its procedure, as well as plenty of air. If your ware is not properly oxidized, and you take your CLAYWORKING PROBLEMS kiln on up too soon, you are quite apt to have indications of a bloated and over-fired tile, at the temperature required for salting. We are of the opinion that you probably do not allow enough time for oxidation and in the attempt to avoid an apparently over-fired body, a temperature sufficient for salting is not attained. Salt glazing is an operation which requires a fairly high temperature and the body should be practically mature. It is difficult to understand why you cannot obtain dark ware. It would seem logical that as the percentage of shale was increased in your mixture, the color would darken. In fact if you reach a temperature suitable for salting, it seems as though it would be a difficult matter to avoid dark colors, using shale as you do. The best advice we can offer you, however, is to enlist the service of some expert in this line of work. Tile Puffs in Burning 314. Indiana What causes drain tile to szvcll or puff in burning? We burn our tile in round down-draft kilns and until two years ago used wood for fuel and then ice seldom had tiles swell and had a good burn on the bottom as well as the top. Since using coal, we seldom get a kiln burned flood on the bottom unless we hare the upper lavers swelled. Is there any prcrentatire? Your drain tile may swell in burning for several reasons, among them being, setting the ware wet, black-coring due to imperfect oxidation and finally, overfiring. There should be no difficulty in determining if either the first or last rea- son is responsible, and the remedy is of course apparent in either case. If the second cause is responsible, it will be revealed by the presence of a black core in the center of the body of the tile. The trouble lies in the fact that the kiln is taken up too rapidly, not allowing sufficient time for oxi- CLAYWORKING PROBLEMS 33 dation of the carbon present. As the temperature increases, the surface of the ware, of course, becomes denser, prevent- ing the escape of the gases resulting from the delayed com- bustion of the carbon which brings about bloating. The rem- edy is to take your kiln up more slowly between the tem- peratures of 1,300 F. and 1,650 F. within which interval the carbon oxidizes. Complete oxidation is, of course, revealed by the disappearance of the black core, as shown by draw trials. When this core has disappeared the kiln can be taken up at the usual rate. This trouble is experienced no doubt in the top courses, because in a down-draft kiln the top gets hot first. The lower courses rising in temperature more slow- ly have ample time for complete oxidation. Wood produces a longer flame when burning than does coal, and this gives op- portunity for the kiln to heat up more uniformly, thus avoid- ing the trouble, due to top getting hot first. This is a prob- able explanation of the fact that this trouble was not ex- perienced when using wood as a fuel. It might be a good idea furthermore to change the flue system in the kiln bottom somewhat with the idea of getting the bottom hotter. See also reply to 299 Illinois. Use of Coal Dust in Burning Brick 262. Texas Will you advise me fully as possible as to the use of coal dust mixed in with the clay it, the manufacture of brick? IV ill it open up tender clay that is subject to crack- ing? Will it make harder and stronger brick? Does it assist any in burning? Can brick so mixed be burned in common updraft kilns' About how many pounds of coal dust are used per 1,000 brick? Could lignite be used to produce the same results as coal dust? You do not state whether you are making your brick by the soft or stiff mud process. We assume, however, that you are using the former of the two. If the brick should happen to be made by the stiff mud process, it is apparent CLAYWORKING PROBLEMS that difficulty would be experienced in burning out the coal added, due to the hindrance offered to the entrance of the air into the brick necessary for combustion. If the clay is very plastic, and used as stiff mud, it is practically impossible to burn out the dust. No special difficulty should be en- countered in this respect, however, if the brick are made of soft mud. The important feature in burning brick con- taining coal dust is that plenty of time be given for a slow complete combustion of the dust. Bituminous coals and lignite are not often used for this purpose because of the volatile matter they contain. When the coal in the brick reaches the ignition point the evolution of the volatile hydrocarbons would be so rapid that a bloated brick would be the result. Lignite, being lower in volatile matter than bituminous coal, is, therefore, preferable to the latter. For this reason, viz., low content of volatile matter, anthra- cite coals are most frequently employed for this use. The amount added varies evidently with the clay used, but probably 100 pounds per 1.000 brick represents an average figure. The addition of coal dust would undoubtedly aid in the burning, because of the extra heat available resulting from its combustion, and would tend to make the brick stronger and harder. No difficulty should be experienced in burning brick, so treated, in common updraft scove kilns. If the clay is extremely plastic and difficult to dry, the addition of coal dust might remedy matters somewhat, but the dust cannot be considered as a "leaning" agent, because, if added in amounts large enough to play this role, other difficulties would enter as a result, which would preclude its use in this .respect. There are just two clays that lend themselves to the use of coal dust in the stiff mud process the Chicago dis- trict clay and the Hudson river clays. The Illinois Brick Company, for instance, uses coal dust in the outside courses CLAYWORKING PROBLEMS to hasten burning. These are common brick, however, and the resultant rough face left by the combustion of the coal makes little difference. Diminishing Flash 383. Ohio We are making a high grade face brick from a red burning shale and burn with coal in down-draft kilns. The to{> eight or ten courses of brick have a flash around the edges or an apparent over-burn and the brick are heavier as ICY near the top courses. While these make a I'ery beautiful red center brick, we would prefer to have a uniform red over the entire face. What could I do to oz'ercomc or even dimin- ish this flashf The trouble you are experiencing in the top eight or ten courses is due to reduction. As a remedy we would suggest that in your fire boxes you make use of a coking plate. This is simply an iron plate on which the coal is thrown, where the volatile hydro-carbons are distilled off (coking) and the coal (coke) then pushed on into the fire. This avoids the periodic reducing conditions apt to ensue if the coal is thrown directly into the fire, where the hydro-carbons distill off with a "rush" and ignite. The coking plate brings about a more uniform combustion. Doby Clay Burns Many Colors 340. Arizona In burning our brick this summer I found that there were a few in each kiln which were very near the color of gold. These brick were near the fire but not touch- ing it. The brick are supposed to burn a white but they burn white, blue or red, according to the distance from the fire. tit'/A o few golden brick mixed in. The clay used is a red doby, taken from the top of the ground and has sulphur and some other minerals in it. The kilns used are the open ones of which the casings are torn down after the kiln is burned. CLAYWORKING PROBLEMS / in'ish to ascertain if 1 had a down-draft kiln could I burn a brick so that it would be of uniform golden color? If I should send a sample of the clay and a fczv brick, could you ///TV me more expert adz-ice? Do you knot*.' of any brick t/iat docs burn a rich yoldcn color? From the information given we would say that the color phenomena shown by your brick when burned are due to "flashing." Under normal conditions of burning, the brick develop their normal color, white or rather, a light buff, we presume. This color is developed when the burn is made under oxidizing conditions. The reds and golden yellows are due probably to "flashing," as mentioned above. Flash- ing takes place when oxidizing conditions are followed by conditions strongly reducing and this in turn followed by oxidation during cooling. By this process the coloring qualities of the iron are made more evident and various color tones are produced depending upon the amount of iron pres- ent and the nature of the clay. The more frequently alter- nating oxidizing and reducing conditions are brought about the more easily do the colors develop. The blue color spoken of is due no doubt to strongly reducing conditions. These brick in some way or other have not been oxidized follow- ing the reduction and can hardly be spoken of as being flashed. The remedy, of course, is to endeavor to avoid reducing conditions as far as possible. Keep your fires clean. It is difficult to say whether or not your brick would develop a golden yellow color if burned in a down-draft kiln. Submit your sample to some competent expert foi thorough testing. There are any number of clays that develop a color on burning similar to golden yellow. Most any No. 2 or No. S fire clay behaves in this way. Any of the ceramic depart- ments of the state universities will make the tests for you for a nominal fee. They would require about 1,500 pounds of material to make a thorough test. Prof. Paul Teetor, of CLAYWOKKING PROBLEMS 37 the University of Kansas, at Lawrence, Kans., has a most excellent testing laboratory, and is nearest to you. Brick Crack in Kiln 459. Texas We hand you herewith an analysis of our clay, as git en by the University of Texas. We arc troubled with our brick cracking in the kiln, seemingly caused b\ expan- sion during hot firing. Crack appearing on tu'o-inch face of brick generally about the middle and crack running towards center of brick. It also seems that we hare not enough iron oxide, or coloring agent in our clay to give our ware a good red color, only that rvhich is exposed to intense heat, for we are getting too many pale brick in bottom of kilns that are burned hard enough, but haven't the color. We would like to know if there is any chemical or mineral that we can use with our clay acting as a coloring agent with- out too much additional expense in manufacturing. We are using round down-draft kilns, water smoking or drying with coal and finishing with oil. Please adiise us as to handling fires and time we should take in heating up kiln and burning. At present we are water smoking a thirty-foot kiln containing about 80,000 stiff- mud brick from fire to six days and finishing kiln in about sixty hours. What effect would too much or not enough air going into kiln in heating up period hare on ~<.vare? Any information or adiice would be greatly appreciated. The analysis is as follows : Contains Dry basis Silica 77.38 Alumina ___ _ .... 13.33 Oxide of Iron 3.27 Hme _ .60 Magnesia .". ".". ~""^~."V.V""~. J~ None Carbonic Acid _. None Sulphuric Acid None Loss on Ignition _ ."'......."..". .". 6.16 100.74 This would seem to indicate that it is a variety of silt. 38 CLAYWORKING PROBLEMS The cracking difficulty which you describe is explained by the extremely high silica content. It is a well known fact that silica changes into another form at about 900 C. (1652 F.) known as tridymite, and this conversion is accompanied by an increase in volume. It follows, therefore, that if a clay is extremely high in silica, as yours is, it is very apt to develop cracks when heated above 900 C. due to the strains developed by the increase in volume. This phenomenon (the expansion) is inherent in the material itself and cannot be eliminated. However, you may be able to eliminate the cracks by adding, say. 25 per cent of some suitable plastic clay. The percentage of iron shown in the analysis, while by no means high, should still be enough to produce a red color in burning, provided it is thoroughly disseminated through- out the clay. It would not be practical to attempt to develop a suitable color by the addition of some colorant like ferric oxide be- cause of the impossibility to produce the necessary dissemina- tion. You can probably darken your brick somewhat by firing with reducing conditions or deficiency of air. Unless your clay is extremely tender, the period of water smoking is somewhat lengthy. Thirty-six to forty-eight hours should suffice ordinarily. An excess of air in firing means low fuel economy because of the resultant dilution of the combustion gases. Any ex- cess of air beyond that actually needed for combustion means an increased consumption of fuel from which you derive no benefit. An excess of air would have no effect on the ware other than would mere oxidizing conditions. A deficiency in the amount of air used implies reducing conditions, which as mentioned, among other things, would tend to reduce the iron, giving darker colors. Ellis Lovejoy, E. M., writes : "The analysis which you give is open to question. \Ye CLAYWORKING PROBLEMS do not find common clays without some alkali and if we were assured the analysis was correct, we would advise you not to use the clay simply because it would be very difficult to get a hard burned brick from such a material. The clay is high in silica, but we have made bricks con- taining as high as 85% silica. The cracking which occurs in the kiln may or may not be due to the burning. Many clays crack in the drying but these cracks close when the bricks are fully dry and are in- visible. In burning they open, and, in several instances, we have found that the cracking which was attributed to the burning really occurred in the drying. If the trouble is in the drying there will be many broken bricks in tossing and setting, due to deep cracks, and, if there is such loss, then, unquestionably, many more cracked bricks which withstand the handling, find their way into the kiln. The cracks may be due to the burning and largely be- cause the clay is high in silica and especially will this be true if the silica is very fine grained (silty). It occasionally happens that the cracking is due to the cooling and this is especially true in highly silicious, silty clays which burn to a very dense, almost glassy, body. Cracks due to the cooling can easily be determined because they do not open up and, in fact, are not visible. When such bricks, however, are struck together, the evidence of a crack becomes apparent and when broken the depth of the crack is dis- covered. If there is very little dryer loss and if the cracks, after the bricks are burned, are more or less open, then it is likely that the trouble occurs in the burning. Cracking in the burn- ing is difficult to overcome, but some improvement will result through slower burning. It is evident from the analysis that there is not sufficient iron to give a deep red color. We have tried powdered iron ore and it is frequently recommended as an addition to the 40 CLAYWORKING PROBLEMS clay lacking in iron, but our experience with the use of iron ore has not satisfied us that it is a desirable addition. It will give a darker color to the brick, but the color is a dull, lifeless, brownish red and very unsatisfactory. In sand mold- ed bricks, we have on several occasions, recommended wet- ting the sand with a solution of ferrous sulphate (copperas), followed by drying. This treatment of the sand produces a brilliant red color and this method of coloring the sand for sand molded bricks is in practical use. It has often occurred to us that ferrous sulphate might be used in the same way to intensify the red color of burned clay, especially where the clay is highly silicious, as in this instance. It would involve wetting the dry clay with a solu- tion of ferrous sulphate and then drying it thoroughly in order to oxidize the sulphate. This treatment will leave every grain of the clay mass coated with a red stain which burns to a brilliant red. This, so far as we know, has never been tried out and the objection has been raised to it that the sul- phate so introduced would greatly increase the scumming, which, theoretically, would be true, but in our experience theory and practice do not always agree. In regard to the time of heating up, this depends upon the character of the clay and can only be properly deter- mined by experimental work on the yard. If the bricks are dry when set in the kilns and are not too dense (which would be unlikely in this sandy clay), there is little danger in ad- vancing the fires rapidly in the early stages of the burning. The only moisture present is the hygroscopic water, and this can only be driven off by temperatures above the boiling point and by the heat entering into the clay mass. Ordinary dry- ing is from the surface and the water is brought to the sur- face by capillarity, by hygro-scopic water does not come to the surface by capillarity and must be evaporated by heat in con- tact with the surface of the grains of the clay, or sand, hold- ing the moisture by surface tension. The amount of moisture is necessarily small and there could not be sufficient steam CLAYWORKING PROBLEMS 4t developed at the rate at which the heat will penetrate the brick to cause any rupture of the bond. We hold that in such instances it is generally safe to advance the heat rap- idly in the early stages of the burning, or what is known as the watersmoking period. Oxidation begins at a low red heat and at this tempera- ture or slightly lower (800 to 900 F.) the combined water in the clay is coming off and we recommend that the fir- ing be not loo rapid during this stage. The clayworkers whose material is high in carbon and sulphur are fully ac- quainted with the necessity of slow firing during this oxi- dation period, and they have an excellent guide in the black core, due to the carbon and know that it is only safe to advance the fires after this black core has fully disappeared. Clays which do not contain carbon or sulphur are not troubled with the black coring and its resultant bloating and in consequence there is no evidence that the burning may not progress rapidly during this oxidation period, but it is our opinion that we should go slow during this stage whether we have a high carbon content or not. It has been proven conclusively that in some clays, at least, there is a marked expansion during this oxidation period, or, rather, during the period when the combined water is being driven off, which is coincident with the early stages of oxidation. A highly silicious brick which naturally would have a weak bond, under the strains due to this expansion, would be very likely to crack and slower advance of the heat during this period will give the clay mass greater opportunity to adjust itself to the strains introduced. Beyond the oxidation period we have found it usually safe lo advance the heat rapidly until the maximum temperature in the upper part of the kiln is attained. Then our practice is to check the draft and reduce the firing and under this condition, hold the kiln until the heat has reached the bottom. It is impossible to say how many hours or days should be consumed in wartersmoking, in the oxidation, in advancing CLAYWORKING PROBLEMS the heat to the maximum temperature, and in the final soak- ing heat. Some clays can be burned without damage from start to finish in from four to five days for bricks, and much shorter time in drain tile and hollow ware. Other clays will require fourteen to fifteen days for bricks. From seven to nine days for a complete burn is common practice. The fires should be light, but gradually increasing during the watersmoking, but when the oxidation period is reached there should be no increase in the fires until the oxidation is complete, following which the fires can be advanced as rapid- ly as practical until the maximum temperature Js attained, when again the fires should be checked commensurate with checking the draft. During the water smoking and oxidation the damper should be wide open with the greatest possible draft attainable and a large excess of free air. Following the oxidation the air supply should be reduced to a minimum in order to get economy of fuel. The amount of air which may be admitted during the latter stages of the burning de- pends largely upon the results desired. If dark flashed colors are sought, then the fires must be heavy with a minimum quantity of air, but if clear red colors are wanted, there must be some excess of air going through the fires to avoid flash- ing." Cracks in Stove Lining Burns 264. Vermont We hai'e had some trouble at a fire brick plant in which we are interested and which largely manu- factures stove linings. The trouble is that the brick keep coining out cracked. The cracks usually are someivhcre on the edge of the brick, about midway, and run dozvn toward the center for about one to tzvo inches. We hare been unable to remedy this. W e are using practically the same clay, the same kilns, and the same men, in producing the goods as u-e hare heretofore. ]]'c cannot find that these cracks appear CLAYWOKKING PROBLEMS 43 more often in brick from one part of the kiln than from any other. If you can gii-e us any ad^ice that will help us to right this matter we will much appreciate it. Several explanations may be given for cracks appearing in the stove lining upon being burned. It is understood, of course, that cracks may develop from either an excessive shrinkage or expansion. One or several of the following explanations may fit your case : (1) Although the clay you are now using may come from the same deposit as that used in the manufacture of the brick which did not show cracking, it still may vary con- siderably in composition from the latter. In this instance your clay is probably too silicious, which causes excessive expansion of the brick when burned, which results in crack- ing. (2) You may not be using enough plastic. Increase the amount of bond clay. (3) In case you are using a flint fire clay in the manu- facture of the lining, try using a smaller amount, replacing it with ground bats, or calcine the flint clay before using it. Too much flint clay may cause cracks due to high shrinkage. (4) Careless molding may be responsible, as a result of sand cracks, etc. (5) Probably you are not drying the brick uniformly all over. Try turning them sooner. It should be stated, that in cases of this kind, the clays or the mixture of clays used, should be given. Fuel Changes Color of Dry Press Brick 43. Missouri We are making a dry-press brick from a blue to brown shale, and are having a hard time to get them red enough for a good face-brick. When we burned them with natural gas, we did very well, but since we have used wood and coal, the brick burn to a yellowish color. In all CLAYWORKING PROBLEMS other respects the brick are good and solid, but the color is bad. We burn in tip-draft kilns, thirty-eight brick high. The top fifteen courses come out light red and salmon colored. Those in the arches and paving bench are all right, and hard burned. We would like to know if we can burn these brick in a continuous tunnel kiln, three hundred feet long, twelve feet wide and ten feet high, with four roivs of pot holes on top. Chestnut coal would be burned and a fan be used for draft. We do not care to go in much for making face-brick. ll'hat we do want to get is a good, hard common-brick. We can change to the stiff mud process, and want a kiln that will burn the brick hard from top to bottom. If you do not think that the continuous kiln is suitable for our ware, what kind of a kiln would you recommend? Do you think that mixing clay with the shale would make the brick redder? Red color in clay wares is due to iron, and it should make no difference whether the burning is done with gas, wood or coal, provided proper conditions are maintained in the fur- naces. There are many clays and shales that contain lime, not necessarily lime pehbles but constituent lime which can only be detected by a chemical 'test. Now, a limey clay or shale may contain sufficient iron to give a red color when burned, but in the presence of lime, the iron combines with the lime, and the color of the burned ware may be buff instead of red. It may be possible to burn either pale red or buff, and if ''Missouri's'' clay or shale contains lime, the different color effect may be due to the firing. The iron cannot combine with the lime without being reduced. If in firing with gas he kept an oxidizing condition in the kiln, the product would have been red until a very high temperature was obtained when reduction would take place whether there was excess of air present or not. In firing with wood or coal, he may get reducing condi- tions at much lower temperatures than with the gas, when CLAYWQKK1NG PROBLEMS 45 the color "turned to buff. The fact that he gets pale reds in the top of the updraft kiln is indicative of the presence of lime, if the lower brick are buff. Oxidizing conditions pre- vailed in the upper part of the kiln, and the temperature was not high enough to reduce *the iron and combine it with the lime, hence the brick had a red color. If the shale is not limey, it may be that the discoloration is due to scumming, but this is so well known to brick- makers "that it certainly would have been recognized. The top brick too would be as liable to scumming as in any other part of the kiln. If the trouble is scum it may be accounted for by the sulphur gas from the coal, which might cause the scum, whereas the natural gas would not give this 'trouble in so far as it might be due to the sulphur from the fuel. Dry press brick are not seriously troubled with scum and we do not think this can be the trouble. We, in this instance, are inclined to suspect lime. He can undoubtedly burn the brick in a tunnel continuous kiln using nut coal for firing, and get an all hard product. The continuous kiln will give a different color effect "than the updrafts if the clay contains lime. It may give more red color but the chances are that the red will not be uniform. Sulphur gas is accumulative in a continuous kiln and is converted into sulphuric acid in wa*tersmoking sections of the kiln. The acid attacks the lime and converts it into sul- phate. Sulphate of lime is not easily reduced and in con- sequence does not combine so readily with the iron, thus leav- ing the iron free to produce a red color. However, "the practical result is not a uniform red, but a streaked red and buff, which is not as satisfactory as either the pale reds or the usual limey buffs. The continuous kiln will use very little fuel and burn all hard brick, which makes it a satisfactory kiln for common brick, especially in districts where fuel is high. We cannot tell what effect the clay would have upon the 4 cents for power. This is what we suppose your subscriber in New York wants to know." Voelker & Groff, proprietors of the Winona Brick Yards, Winona, Minn., write : "Our conditions are somewhat different than your sub- scriber's. We run our Wellington Monarch machine with one motor and cable conveying machine with another moto/ pumping water with another large motor on our drag line scraper for scraping our clay motor on centrifugal pump for pumping water out of clay bank. We pay for our power by a sliding scale. The minimum charge is 2^ cents per kilo- watt. Our power costs us 0.234 per M. brick." Cost of Electric Current 353. Nebraska How much per kilowatt does electric cur- rent cost at brick plants bought from power stations, cither municipal or private, generated by steam power? We hare electric drive but believe our price for current is high. We run a Fate bottom dump car, standard size; Fate linnding drum, American Clay Machinery Co. 18-inch disintegrator, 44- ft. conveyor, 7-foot pug mill, a No. 218 American Clay Ma- chinery Co. machine and cutting table, making brick or block. IV c use on an average 40 kilowatts an hour, making about an average of 4,000 common brick per hour, or 1,000 5x8x12 block. This average of pozccr varies some. It takes more if the clay is worked somewhat stiff. We have a sliding scale on electricity from 6 to 7 cents down to 4 cents per kilowatt. CLAYWORKING PROBLEMS 91 We hare a 100-/J. p. Westinghouse motor, 2,200 volts alter- nating current. Local conditions and the nature of the clay are sometimes determining factors in the amount of current necessary per thousand brick. Likewise these things deterimne costs. The Albany Brick Company, Albany, Ore., operates a Potts dis- integrator with clay elevator, one 8-ft. clay pug mill, Bucyrus Acme brick machine, capacity 25,000 per day. During the period of four months operation the average kilowatt-hours per thousand of brick made was 8.16. We do not know the rate of power but if you figured 2J/2 cents per kilowatt-hour, the cost per thousand is slightly over 20 cents. The Enid Vitrified Brick & Tile Company, Enid, Okla., are using a motor for operating one 9-ft. dry pan, one mixer, a six-mold brick machine, capacity 30,000 per 10 hours, one 2.000-lb. hoist elevator and conveyors. Tests made on this plant show 11.2 kilowatt-hours per 1,000 brick. Clay Haulage from Pit 74. Ontario Can you tell me where I can find information in regards to hauling clay from pit to factory a distance of 800 //. or possibly 1.000 ft.? How much could a horse pull on a level tramway per day? Could it pull enough for 60,000 common building brick f U'ould this distance be too long for a drum and cable haulage and what grade would be necessary to allow car to run back empty to pit if we used reversible engine? Any information will be appreciated on tramminy or hauling of clay from pit to plant as to amount hauled in a day and grading of tramway such as would give horse advan- tage in pulling load. The average speed of a horse walking is supposed to be from 2 to 2J4 miles per hour, or about 176 to 196 ft. per min- ute. Taking the lowest figure of the two, and based upon a distance of 1,000 ft. from clay pit to plant, a horse would require about 11 1/2 minutes actual travel. Allowing y/ 2 min- 92 CLAYWORKING PROBLEMS utes for delays at each end, about 15 minutes would be re- quired for a round-trip, or an average of 4 trips per hour. Upon a basis of 60,000 brick, of an average weight of 4JX Ibs. each, the daily capacity required would be about 135 tons per day, or 15 tons per hour, estimated upon a 9-hour day. From the above it can be seen that it would be necessary to carry 7,500 Ibs. of clay per trip, which would be two 1JX yd. cars, or three 1-yd. cars. The weight of these cars load- ed would probably amount to at least 10,000 Ibs., or 5 tons. We would say that the rolling friction for industrial cars as used for this work, would be about 40 Ibs. per ton. A 5- ton load on level track would, therefore, require a pull oi approximately 200 Ibs. The tractive power of the ordinary horse would average from 100 to 125 Ibs. By having a down- grade from pit to plant, of 1 to l l / 2 per cent, it might be possible for a horse to do this work but we doubt very much if it would be at all satisfactory, especially in bad weather. By far, the most practical and economical arrangement would be to install a surface haulage system, in which the cars are pulled one or both ways, by wire rope. In the event the grade from plant to pit could be made sufficient to re- turn empty cars by gravity, only single rope and hoisting drum would be required. If, on the other hand, the grade is not sufficient to return the empty cars by gravity, the tail^ rope system would have to be used, whereby the empty cars would be returned by a small cable or tail rope. Just what grade would be needed to return the empty cars by gravity would vary according to the type of bearings used on the cars, six of truck wheels, and condition of track. For data on this point, we would suggest that you write manufacturers. Whether the aerial tramways such as are manufactured by one of our advertisers will meet your requirements, depends entirely upon local conditions. With an aerial tramway economical results can only be obtained where the clay is CLAYWORKING PROBLEMS 93 brought to a central loading station for loading into tramway buckets. With a two-bucket or jig-back system with power- drive located at loading station, but one attendant would be required for the entire operation of the tramway. This man would be located at the loading station, and control the filling of buckets as well as the power and speed of line. How to Keep Coal Out of Fire Clay 241. Ohio We have a small vein of coal lying above our clay and hare great difficulty in getting the miners to keep the coal out of the cars in which they send the clay to the tipple. As the lumps of coal are comparatively small, and generally buried in the car, they are not discoi-ered until the clay is put into the dry-pan. If it is not eliminated at this point, it is ground up and goes into the brick, where it later burns out and pits the product. It seems impossible to fasten the blame on any one miner. If the coal vein is large enough to be an inducement, try the plan of offering it free of charge, to the men that work in the mine. Arrange matters so that it will be kept separate in the workings, the men understanding that they are saving something that is of value to themselves, and they may be depended upon not to mix any clay with the coal that is to go into their own stoves. When a single carload has been accumulated in any one of the workings, the miner can load it out, marking the car in some way that will enable the man at the tipple to readily identify it and to side-track it to a private coal dump, which will belong to the men. Give them to understand that they are at liberty to send carts to this dump and to take away all the coal they need for their own household use, free of charge. In their effort to accumulate enough free coal to supply their own wants, they will keep it CLAYWORKING PROBLEMS out of the clay cars, even though, by doing so, they may be using up some time that they think should be paid for. Amortization of Bank Indebtedness 243. Tennessee 1 1' hat is the meaning of amortization, as applied to bank indebtedness? I heard a lecturer use the term and from what he said, think he beliei'cd it to be a panacea for all industries that were handicapped by amounts due to local banks, particularly short time notes. Webster defines amortize as follows : "To extinguish, as a debt, usually by means of a sinking fund." This is, we admit, not very enlightening. The process of amortization, as pursued in France (where it is extensively used in con- nection with farm mortgages), is very simple. Let us sup- pose that the mortgage is for $1,000, and bears quarterly interest of !}/> per cent. The borrower, under ordinary con- ditions, would pay $15.00 every three months, and, when the mortgage came due, would still owe the $1,000. The prin- ciple of amortization would be applied, if the borrower made arrangements whereby he could pay, say 2 l / 2 per cent quarterly, or $25.00. At the end of the first quarter, having made this payment, he would owe $990.00. One-and- one-half per cent on that amount would be $14.85. At the end of the second quarter, paying $25.00 would reduce the amount of the mortgage to $979.85. Add interest to this, as before, and pay $25.00 at the end of the third quarter, and the indebtedness would be $969.54. At the end of the first year, the payment of $25.00 would make the indebtedness $959.08. From this it will be seen that while $40.00 -has been paid back in four installments of $10.00 each, the indebtedness has been reduced 92c representing the interest earned. The idea is, that the amounts paid back are so small that they will not embarrass the debtor, but, if persisted in, will event- ually wipe out the original debt. When the same plan is CLAYWORKING PROBLEMS 95 tried with notes, it works very smoothly, for, as the note is renewed, the check for the interest, plus the amortization amount, is given at the same time as the renewal note, with the amount of the latter a little less each time, than the amount of the note that is being taken up. Methods of Washing Fire Clay 562. Tennessee Will you please gire us a description of the best known method and appliances for washing fire clay to rid it of chert (flint) and impurities. In our clay there is about ten per cent chert ranging from pea to walnut size. We should like to recover the chert for other purposes. Also please refer us to the best literature covering this subject. The methods of purifying fire clay depend upon the phys- ical character of the clay, its value and upon the degree of purification required. Your clay may be a loose material like the so-called "kaolins" (micaceous sands) of New Jer- sey, or it may be an earthy or a tough, plastic clay, like some of the fire clays of New Jersey, kaolin in Pennsylvania, crop No. 2 fire clays of the coal measures, kaolins of Georgia, Alabama and Arkansas, fire clays of Texas, or it may be rock-like, such as the solid No. 2 fire clays of the coal meas- ures, or finally, it may be non-plastic flint clay like that of Pennsylvania. Maryland. Ohio and Kentucky. No single method of purification would be applicable to these several varieties of clay. Kaolins are washed by beating them to a thin pulp or slip in a pug mill or granulator type of machine, or a blunger; the course materials may be eliminated in a sand wheel or sand box ; the fine, slow-setting impurities, such as mica, are removed in settling or flotation troughs, and the creamy kaolin slip is collected in settling tanks. After settling, the sur- plus water is drawn off and the remaining slurry is pumped 96 CLAYWORKING PROBLEMS into filter presses. The filter press cakes are air dried in sheds or artificially dried in some type of dryer. Some low grade pottery (including stoneware) clays are simply beaten up and brought into suspension in a blunger, followed by screening. The slip which passes through the screen is collected in a tank or cistern and kept in suspension by a stirring mechanism (agitator) until it can be pumped to the filter presses. The cakes from the filter press are passed through a potter's pug mill and the pugged material taken directly to the potter or stored in damp cellars. Obviously this method of purification would be too ex- pensive for a low grade fire clay to be used in the manu- facture of brick or other low priced wares. It might be prac- tical to blunge the clay, screen out the stones and collect the screened slip in open tanks or basins from which the sur- plus water could be drained off after the clay had settled, then allow the clay mass to air dry until stiff enough to handle. If the clay is very loose and friable, instead of blunging, it could be washed through a screen following the method used in washing gravel, but there still remains the removal of the excess water and subsequent drying to be taken care of. If the clay is friable and dry, or after drying, it could be whipped into a powder and passed over a screen. The courser material, including the flint pebbles, in this case, would pass over the screen while the clay would collect in a bin under the screen. The separation, using this method, however, would not be complete, since the fine pieces of flint would follow the clay while course masses of clay would collect with the flint. This dry method of separating the pebbles from the clay has been successfully used in a number of cases. For instance, we have seen a somewhat similar dry separation car- ried on in a dry pan with raised mullers in several factories. Thus the mullers would not crush the stones but simply loosen them from the clay. The fine clay would pass through the perforated plates, while the stones would remain in the pan. At frequent intervals, the pan would be stopped or slowed CLAYWORKING PROBLEMS 97 down and the stones removed. A very powdery clay could be whipped to dust without in any way reducing the size of the stone and could then be separated from the stones by an air blast similar to the method employed in preparing clays for dry pressed tile. If the clay is a tough, plastic material, it can best be cleaned in a Diesner cleaner. In this operation the clay is pugged in an ordinary mill and put through an auger machine. The bar of clay from the machine is forced against a vertical re- volving slotted disc, the fine clay passing through the slot while the stones are rejected. The resulting mass is in con- dition for immediate manufacture into ware, but the stones would have considerable clay mixed with them and would have to be washed, which could readily be done. We do not know of any publication covering this subject. In the earlier reports of the National Brick Manufacturers' Association will be found a description of a "slumming" process for common clays in which you might be interested. Bulletin No. 53, Mineral Technology No. 1, Bureau of Mines, Mining and Treatment of Feldspar and Kaolin in the South- ern Appalachian Region, by A. S. Watts, which, it is pos- sible, might be secured from the Director, Bureau of Mines, Washington, describes kaolin washing in that field. Wants to "Copyright" Trade Name 593. Missouri We have a brand of brick which we hare been manufacturing for about ten years, and it is of such quality that it has made quite a reputation for us. We have been selling it under this brand for probably ten or eleven years. We notice that lately one or two other fire-brick com- panies are manufacturing a brick under the same brand. We think we are the first who have used this brand, and thought it might be well to protect ourselves by U. S. copyright. We hare never heard of any other brick being copyrighted by the same title as ours, and none is shown in your list. What we CLAYWORKING PROBLEMS would like to know is, should we have the name copyrighted as a trade mark, would we not have preccd :ice over anyone else, even though we might not have first used it? Our im- pression is that we arc the first. Do you know the probable cost of copyrighting a trade mark? The general practice is to register the name in the United States Patent Office. The cost of this will be something in the neighborhood of $25 or $30. Ordinarily, patent office registration is not granted upon any name or word which is either descriptive or geographical. An exception is made, however, when the name or word has been in continuous use for more than ten years. Mortar Joints for Interior Brickwork 120. Illinois We have a customer who is contemplating the decoration of an interior room with rough surfaced face-brick. Can you give us any information in regard to the size and style of mortar joints? Width, grain, finish and color are the four factors in mor- tar joints that determine the texture of the finished brickwork. Width and color are the two factors that determine the gen- eral color-tone. The influence of the width of the joint on the finished work can be appreciated when it is understood that, with a brick 2 l / 4 in. thick, a quarter-inch joint constitutes 10 per cent and a half-inch joint 18 per cent of the finished wall surface. So the design of the brick work and the color of the mortar that is to be used must both be taken into con- sideration in fixing the width of the joint. It is a question of weaving an imperishable fabric with threads of varying thick- ness, the brick being of one measurement, the joint an- other. Harmony of the surface, so that each plane of the finished work will give back the same light, demands that the grain of the joint should be the same as the grain of the brick that is, of equal coarseness. This is given by adding gravel to the CLAYWORKING PROBLEMS sand used in the mortar, a good formula being 10 parts sharp building sand, 4 parts gravel, 2 parts Portland cement and 1 part lime putty. The gravel should be through a quarter- inch mesh screen. On account of the large proportion of cement in this formula, it is necessary to use more coloring matter than would be used in lime mortar and the mistake that most builders make is to accept the color of the wet mor- tar with the feeling that "it will dry out a little lighter" the fact is that "it" dries out a great deal lighter, and a good rule for interior work is to put in "enough" mortar color and then put in about half as much again. If the mortar is mixed properly and only enough water add- ed to make it work stiffly, it will not run down over the sur- face of the brick. Remember, mortar stains on rough finished face brick are very hard to remove. It should feel "rubbery" to the trowel and, if the bricklayer has not laid up rough finished face-brick in interior work before, he will be apt to object to the extra "poorness" of the mortar. If he does not "kick" lookout the mortar is too fluid and will be apt to soil the work. Finish the joints either "rough struck flush" by striking up with the edge of the trowel, in the same way as com- mon backing up work is struck, or "rake" with a wooden "Dutchman." This latter is a wedge shaped piece of wood, the edge being slightly narrower than the width of the joint. The soft wood leaves a surface on the joint that is immeas- urably superior to the surface left by any metal jointing tool. The color must be chosen with relation to the color of the brick and to the color-tone of the finished work. The for- mula given above produces a grayish-white joint and is made warmer by the addition of enough yellow ochre to make the wet mortar a deep lemon. This will dry out a rich cream. By adding half double-strength brown and half black, a dark brown is obtained in the wet mortar, that changes, through the action of the cement, to a grayish-purple when the joint is thoroughly dry. Do not use black alone, in any mortar to 100 CLAYWORKING PROBLEMS which cement is added, as the latter forms a film around the black particles and turns them to a whitish-blue in spots where the moisture has been greatest. Any of these joints are good for shale brick half brown and half yellow color is excellent for fire clay brick in shades from orange to dark brown. Do not use red color alone. Add some black to your white mortar, if no cement is used and so "vaccinate" against the dinginess of the joint as dust and dirt accumulate. Imitation "Harvard" Headers 123. New t York We manufacture red building brick, by the soft mud process, and would like to make some black end brick, commonly known as "Harvard" headers: Can you give us any information as to how to make them? We thought that by dipping green brick in some chemical solution and then burning, we might produce the black end. We do not know of a single instance where the "Har- vard" greenish-black, wrinkled header has been produced artificially, with commercial success. As to "Harvard" Brick 265. Michigan Can you give us any information as to the name and location of the manufacturers of the "Harvard" brick ? Genuine "Harvard" brick are made only in New England that is, in New Hampshire, Vermont, Massachusetts and Connecticut. The greater proportion of the output is con- trolled by the New England Brick Company, with offices at 178 Devonshire St., Boston, Mass. Parry Brothers, of 166 Devonshire St., Boston, Mass., have yards at Epping and at Gonic, N. H., where they make one of the best "Harvards" on the market. The Spiers-Fish Brick Company, of 79 Milk St., and D. Washburn & Sons, of 166 Devonshire St., Bo3- CLAYWORKING PROBLEMS 101 ton, Mass., are also producers the latter making the famous "Washburn" Harvard brick, of which are specified, probably, ten times the number, each year, as the Washburn yards can produce. No "Harvards" that is, no brick that resembles the "Harvard," even distantly, is made anywhere outside of New England. Genuine "Harvards" are made of a peculiar clay, are hand-molded and water struck. They have a cer- tain proportion of the headers ranging in shade from dark red to green the latter shade being produced by burning with wood. The heads are wrinkled and cracked, and never have been successfully imitated in any way other than the New England method of burning, nor in any clay other than that found in the New England states. Wants Formulae for Coloring Mortar 457. Quebec Will you please answer the following ques- tion in the next issue of "Brick and Clay Record" What is the best composition for coloring lime and cement mortar? The greatest difficulty in securing stable colors for lime and cement mortars is due to the action of lime on many colorants. The most satisfactory pigments are the metallic oxides. Hematite or Fe 2 Oj is most commonly employed for the red colors, while the brown oxide of iron is used for buffs and browns. Yellows are obtained by use of ochre. The best greens are obtained by the use of chromium oxide, but this of course is very expensive. Ultramarine green is very satisfactory as far as color is concerned, but it is grad- ually destroyed by lime. Lamp black is most commonly em- ployed as a pigment in the production of black. Brick Made From Blast Furnace Slag 491. Ohio Have you any information as to the manu- facture of brick in this country from blast furnace slag? Do you know of any plants in this country that are using this 102 CLAYWORKING PROBLEMS material for manufacturing brick? As we understand the process, it is similar to that of manufacturing sand-lime brick. We would also like to have the names of the manufacturers. Any information you can give us will be appreciated. Several attempts have been made to manufacture brick from blast furnace slag, a plant having been built in Mil- waukee, and one at Youngstown, Ohio the latter for the Brier Iron and Coal Company. The processes were used, one of them being to crush the cold clinker and mix with a bond- ing member after which they were pressed into brick the other consisting of the immersion of the hot clinker in water and grinding the resultant globule of slag. Difficulties in manufacture were experienced in both methods and the varia- tion in the color of the burned product was such as to make the plants mentioned unprofitable. We believe that every plant that has so far been started in this country for the pur- pose of making brick from blast furnace slag has been closed down. Roofing Tile Manufacture H9G. Kentucky 17 V would like to have some information on the status of the roofing tile business in this country, es- pecially in Kentucky. Is there a good demand for roofing tile? It seems that we are unfortunately located for a drain tile plant and we arc wondering if we could not use our round-down-draft kilns and drain tile machinery profitably in the production of roofing tile provided our clay is suit- able. We understand that we would have to add some more machinery. The manufacture of roofing tile in this country is yet in its infancy. There are only a few plants, and until recently most of the tile used was imported. There is a good demand for the product and the few plants that are making it ship ex- tensively. Most of these plants are located in and around the larger cities, particularly in Indiana and Ohio. The man- CLAYWORKING PROBLEMS 103 ufacture of roofing tile offers many difficulties. A clay that may make a good drain tile may not make roofing tile. Your material, therefore, should not only be thoroughly tested as to its physical and pyrochemical behavior, but the extent and uniformity of character of the deposit should also be studied carefully. There are two kinds of tile made porous and vitrified. What style you make depends upon the kind of clay you have. In the manufacture of the porous tile the manufacturer should make his tile before it goes to the kiln, while the vitrified manufacturer depends upon the burning to make his. In other words the porous tile should receive much the greater atten- tion in the preparation of its raw material and in the form- ing, for, if the tile is not strong and solid when dried, it will scarcely harden and strengthen enough in the firing process to make it frost-proof. The vitrified tile may be made from granular, poorly pre- pared raw material but if it is of the right vitrifying quali- ties it may be made durable by hard-burning. The porous tile manufacturer has much the best of the argument. By using extreme care in handling his crude ma- terial, the working of which can be largely handled by ma- chinery, he obtains a product that goes into the kiln in the best condition that is sound and straight. By stopping the burning at a point where the physical strength, though not at its best, is sufficient, he obtains a product that has not under- gone any severe volume changes and, therefore, remains sound and straight, but not brittle. One of the greatest sources of loss in tile manufacture is the warping, cracking or denting of the ware. The porous tile maker has the minimum of this. The manufacturer of the vitrified tile is apt to have all sorts of trouble. To minimize this he must use some sort of saggers in his burning to support the tile on account of the great shrinkage and the tendency to warp. This means, 104 CLAYWORKING PROBLEMS of course, extra expense and a large amount of extra heat is necessary to heat up this dead material each time. To first ascertain whether your clay is adaptable to the manufacture of roofing tile send a sample at least fifteen hundred pounds to some expert clay analyst. Any of the ceramic departments of the state universities, or even the machinery men, can tell you as to what this charge will be. This analysis is necessary as it may save you several thou- sand dollars in experiments later. In the meantime, write to J. A. Bownocker, state geologist of Ohio, at Columbus, Ohio, and ask him to send you Bulletin No. 11, the price of which is 75 cents. This book is cloth bound and contains nearly 500 pages of exclusive matter on the subject of tile manufacture, and is the latest word on this subject. It was written by Wolsey Garnet Worcester, with Prof. Edward Orton, Jr., as collaborator and editor, and is the most comprehensive treatise on any subject of a similar nature we have found printed in the English language. Silica Sand Won't Make Silica Brick 490. Georgia In your May 19 issue you have an article on "Refractory Brick" by T. E. Montgomery of Alfred, N. Y. In it he states that a sand or clay that has 97 per cent of silica and 3 per cent of impurities gives the best results. Now we have a bank sand that analyzes as follows: Silica (SiO-,) 97.62; Ferric Oxide (Fc 2 O 3 ) .71; Titanium Dioxide (TiOx) .09; Undetermined, 1.36; Loss on Ignition, .22. We would like to find out if a good silica fire brick could be made from this sand and if there is any literature that covers the subject. We know that there are numbers of silica fire brick being made, but arc absolutely in the dark as to where, or hoiv. Can you either give us the information or put us in touch with some one who is competent and reliable? Any assistance you may render us will be greatly appreciated. The manufacture of silica brick from silica sand has been CLAYWORKIXG PROBLEMS 105 tried, but almost invariably with unsatisfactory results. In order that the brick may have the proper porosity, it is neces- sary to grind a material that will make a product coarser than sand, and that will give particles irregular in size and shape. The process of making silica brick includes the crush- ing of gannister rock in very heavy crushers, then putting the ground material through wet pans, where it is mixed with the bonding material, and from these pans it is molded in brick. Manganese in Connection with Shale 456 Quebec Can you tell us to what degree shale brick should be burned, to fuse manganese? Charles F. Binns, director of the New York State School of Clayworking and Ceramics, at Alfred, N. Y., says: "Manganese is used to darken the color of the brick or tile which may be made from a red burning clay or shale, but its principal use is in the production of gray brick from a light burning clay. It is generally considered that in order to produce an effective gray brick, the temperature should be at approximately Cone 6, because at a lower temperature the manganese grains appear as tiny specks, and do not produce a general gray tone. This temperature, however, is far higher than anything generally used for sales. In fact, the use of the manganese must give way to the burning tem- perature of the shale and whenever vitrification is approached or reached, the brown color will be evident when manganese is used." Charles S. Kinnison, of the Bureau of Standards at Pitts- burgh, Pa., says: "Manganese is never used in connection with shale in the manufacture of brick. Manganese finds use only in brick burning to a clean light color and it is absolutely essential that the fire be strictly oxidizing in order fo develop in the 106 CLAYWORKING PROBLEMS brick a clean light color to act as a background for the black manganese specks. The clay most commonly used in connection with manganese is a No. 2 or 3 fire clay. The temperature needed for the development of the black specks is cone 2 to 3." Ellis Lovejoy, E. M., of Columbus, Ohio, writes: "In regard to the temperature to which shale brick should be burned to fuse manganese, we do not know. There is really no relation between the melting point of manganese dioxide and its fusion in connection with other minerals. "In products made of plastic fire clay, it is our experience that the manganese begins to combine with the silica and other minerals in the clay at a temperature of about Cone 3 (2174 F.) and the most satisfactory results were ob- tained above this temperature, up to about Cone 7 (2318 F.). In red burning shale, which matured at kiln tempera- tures below Cone 1, we found very little fusion, in fact, so little that the color effect of the manganese on the ware was practically nil. It may be that other shales would develop color from the manganese at lower temperatures than in our experi- ence, provided the shale vitrified at lower temperatures. We do not believe that anyone can pre-determine at what temperature the manganese will become effective. Minerals which melt at high temperatures combine with other minerals into a fused mass at much lower tempera- tures. As an illustration, we use lime as a flux in the blast furnace, but lime itself is infusible at blast furnace tem- peratures. The elements to be fluxed are silica and alum- ina in the ore and coke, together with some alkalies and alkaline earth. Silica itself is infusible at blast furnace temperatures, and so also is alumina. Here, then, we have three practically infusible minerals, which in combination CLAYWORKING PROBLEMS 107 form a slag which becomes quite liquid at blast furnace tem- peratures. In a clay mass we have silica, alumina, lime, magnesia, iron and alkalies. Except the alkalies, all of these min- erals, individually, are infusible at kiln temperatures, and yet, we combine them very readily at kiln temperatures into vitrified bodies. All clays contain the above minerals in vary- ing proportions, but the temperatures at which they began to vitrify are widely different, due to the variation in quan- tity of the several minerals. We describe the fusion as rock solution. The alkalies or alkali containing minerals, such as feldspar, will melt at rela- tive low temperatures and as they begin to melt they take up (dissolve) silica and alumina together with the other minerals present in increasing degree as the temperature advances and as the alkali solution tends to become fluid. This tendency to fluidity is offset by the increased quantity of silica and alumina taken up and in this way the vitrification advances from a very insipient stage to a completely vitrified or fused mass, in which the rock solution is complete. In some clays the fusion starts at a very low tempera- ture and in such clays we would expect a solution of man- ganese into the fused mass along with the other minerals present, and in such event we would get color effect from the manganese. Clays requiring higher temperatures to vitrify, therefore, will involve such higher temperatures to get the manganese into solution and from it thereby its color effect. We get fusion of the manganese and the color effect there- from in many products in which there is no evidence of fusion except in the manganese spots and in our experience this only occurs at temperatures above Cone 3. In such instances the manganese becomes the fluxing ele- ment and takes up silica, etc., to form a rock solution, where at lower temperatures some mineral which fused at such low- 108 CLAYWORKING PROBLEMS er temperatures is the fluxing mineral and the manganese is simply one of the minerals dissolved in the fused mass. Manganese was formerly largely used in connection with red burning clays to produce a brown brick, but at the pres- ent time there is very little demand for this color as produced from manganese, since we are able to produce various shades of co!or from red, through brown, to gun-metal black by fire flashing the red burning clay, and these colors are more effective than the manganese browns formerly produced." Substituting Chimney for Fan Draft 517. North Carolina We are operating a continuous kiln of the tunnel type and obtain a satisfactory draft by using an American Blower Company's No. 70 fan driven by a seven and one-half horsepower motor. We have occasionally, how- ever, experienced some trouble on account of the irregular- ity of our power supply, finding it next to impossible to keep our engine, generator and motor running continuously. Will you kindly advise us what size and height stack it zvould take to give us tlie same results as we obtain with the fan when we are able to keep it running!' To begin with, without trying to avoid a direct answer to your question, fan draft on a continuous kiln is much bet- ter than stack draft because of its uniformity and perfect control. Nearly all continuous kilns now being built have fan draft, which enables the operator to burn much more quickly than with the weaker, irregular stack draft. It is not possible for us to determine the size and height of a stack suitable for your kiln without more data. The size of the fan is given and the power of the motor, but this is not sufficient to determine the size of the flues nor the size of a stack which will serve your purpose. If the speed of the fan had been given, we could determine the volume of air which the fan would deliver without any resist- CLAYWORKING PROBLEMS 109 ance, but even then we could not estimate the resistance which greatly reduces the volume of air. To determine the proper size of a stack, it is necessary to have full information in re- gard to the size of the kiln, the rapidity of the burning, the quantity of fuel, or in lieu of the latter, the volume of gas to be carried off by the stack. A German engineer gives the following rule of thumb for continuous kiln stacks, namely : the height of the stack should be 0.5 to 0.6 of the length of the tunnel ; and we would add to this that in no case should the stack be less than one hun- dred and twenty-five feet in height. The area of the stack should be 0.16 to 0.17 of the cross section of the tunnel. If your kiln has been designed for fan draft, it is possible that the main flues are smaller than they should be for a stack. Questions Accuracy of Answer to Draft Problem 589. New York In the October 6 issue of "Brick and Clay Record," answer to question 517, I'M the next to last paragraph you make a statement that where a stack is used instead of a mechanical draft "that in no case should the stack be less than one hundred and twenty-five feet in height." You must have some special reason for making this state- ment, as ordinarily the height of chimney required depends directly upon certain data which is easily figured. Under cer- tain conditions, the rate of combustion in a kiln is slow, com- pared to that in a boiler fire box, but usually it is more favorable for producing high temperatures. Naturally also, the temperature of the gases being discharged from a kiln is very high as compared with those coming from an ordinary boiler. A chimney fifty feet in height and connected zrith a boiler, discharging gases having a temperature of five hundred and fifty-tzvo degrees Fahr., has a draft power of 0.365 inches of water and should burn one hundred and five pounds of coal per hour per square foot of chimney section. Figuring 110 CLAYWORKING PROBLEMS roughly, a fifty-foot chimney two feet in diameter, inside measurement, should burn 3.14 times one hundred and five pounds, or three hundred and twenty-nine pounds of coal per hour. Any chimney taking waste heat from a kiln, owing to its high temperature, should be able to do more work than the above as its draft should be greater than 0.365 inches of water. Your statement that a kiln chimney should not be less than one hundred and twenty-five feet is, therefore, in- teresting and the writer would be very grateful for a state- ment of your basis for same. Our statement that in no case should the stack be less than one hundred and twenty-five feet in height is based on prac- tical experience and not upon theoretical data. It is im- possible to figure the proper height of a stack for a con- tinuous kiln. The formulae given in various engineering works on the subject of stack draft apply particularly to boiler stacks, the problem having been thoroughly investi- gated for such work. A continuous kiln stack, however, is an entirely different problem. The efficiency of a stack depends upon its height, the tem- perature of the gases being discharged and upon the re- sistance offered to the draft. The gases from the kiln must pass numerous turns and through a series of closely set checker-work made by the ware set in the kiln. The dis- tance of this checker-work may be fifty or more feet and it is, therefore, impossible to figure the resistance to move- ment of the gases which must be overcome by the stack. Our correspondent is discussing a boiler stack and the data he uses is not applicable to a continuous kiln stack. The temperature of 552 degrees Fahr. is the maximum effi- ciency temperature, and for that reason, it is the temperature which appears most generally in formulae for stacks. His statement that "any chimney taking waste heat from kilns, owing to their high temperature, should be able to do more work than the above, etc.," is not correct. Any tem- perature above 552 degrees Fahr. reduces the efficiency of CLAYWORKING PROBLEMS 111 the stack, and likewise any temperature below this maxi- mum efficiency temperature. We need not consider temperatures above this critical tem- perature, as, in a great majority of cases, waste heat gases run less than 500, and frequently as low as 200 degrees. Part of the economy in the operation of continuous kilns is in using the heat of the waste gases to heat up and watersmoke the brick ahead of the combustion chambers, and the gases are only drawn off into the stack when they become ladened with moisture to approximately the dew point. This is the limit of the use of the products of com- bustion in a continuous kiln, and when this limit is reached, the temperature of the gases has fallen very much. In a continuous kiln stack another factor enters which does not appear to any great degree in boiler stacks, namely, the effect of the vapor which accompanies the kiln gases. In a boiler stack, as the gases rise, they are cooled and the efficiency of the stack varies accordingly. In a continuous kiln stack, starting with a temperature at least not greatly exceeding the boiling point and with a gas loaded to the dew point with water vapor, as the gases cool in their ascent in the stack, condensation takes place and the latent heat of condensation is given up to maintain the temperature of the gases, even to the top of the stack. Also, water vapor is lighter than air, which increases the difference in weight of external and internal columns of air and gas upon which stack formulae are based. Furthermore, continuous kilns use an excess of air and the CO* content in the gas may be even less than five per cent, while boiler stack gases will contain from ten to fifteen per cent. The percentage of this heavy gas materially affects the balance which causes the movement of the gas in the stack. The net balance in weights of air, water vapor and combustion gases, is indeterminate. We made no attempt to figure the proper height of a stack for a continuous kiln and frankly say that the problem is beyond our ability. In such work we figure the problem as 112 CLAYWORKING PROBLEMS far as possible in order to get some information upon which to exercise our judgment, but in exercising this judgment, we are governed more by practical experience than the re- sults of our theoretical estimates. In conclusion we may add that stacks for continuous kilns are becoming a thing of the past. With the low temperature which prevails in the stack sufficient draft cannot be obtained for the rapid operation of present types of kilns and, in consequence, the kiln stacks are being replaced by fans which give a perfect control of the draft and which may be varied to suit the requirements. The draft power applied to con- tinuous kiln suction exceeds one inch of water and it would be difficult to get this power from a stack construction. Proportionate Kiln and Stack Area 103. Missouri / noticed a question in your February issue regarding the proportion of stack area to kiln area. Did any one answer this question f If so, will you put me in posses- sion of the information f The correct area of the stack, as compared to the area of the kiln, is somewha't over one-third stack area (figured in cu. ft.) to the kiln area (figured in sq. ft.), as, for instance, in a kiln 30 ft. in diameter, we have an area of 732.62 sq. ft., one-third of which is, approximately, 243. It is well to increase this number, and, going to a stack 3x3 ft. in 'the clear and 40 ft. high, we have a draft area of 360 cu. ft. A stack of these dimensions is larger than needed at the finish, but is needed in watersmoking and oxidation. Bricks Check After Pressing 53. Alberta We have a Berg dry press and manufacture high-grade face brick, but arc having trouble with checking of brick before they arc burned. We would like to overcome this, as it makes No. 2 brick out of a lot of otherwise No. 1. CLAYWORKING PROBLEMS 113 We haz'e an overburden of thirty feet, so we mine our shale and, working it direct from the mine, have little chance to weather it. We find the brick check less when the clay is run damp and think it would be better if the clay were ground a little coarser. We are using a piano-uire screen, No. 24 wire, nine wires to the inch, and we do not want to run the clay coarser, as it would not give us as smooth a brick nor such li'dl defined edges. The trouble probably lies in the air holes in the top of your press being clogged up or in your running too fast. In either case, the air that is mixed with the clay when it enters the press has too little chance to escape in pressing and, as a consequence, compresses with the clay. It expands after the bricks leave the press, seeking an outlet through the face of the brick, checking them as it makes its exit. Having looked at the air holes, try running your press a little slower and note the result After the above had been published, the correspondent who asked the question wrote another letter, in which he said : "Some time ago I wrote you in regard to our brick check- ing, and you recommended that we examine the air holes on the press and see that we were not running too fast. All this lie had previously done, so we did not gain very much information from your reply, which, by the way, I see the 'Canadian CIa\ Worker 1 for June has copied. However, we thank you for your reply, and would say that we overcame the difficulty in another way. "We built wings to our shale trestle, to the right and left, 14 //. high and 100 ft. long. While we were using up one side we filled up the other uith shale, and also ran a ^-inch stream of water on each day's mining for three hours. This water and the wind and sun has a wonderful effect on our shale in the two weeks 7ir can allow it to weather. We also mix a CLAYWORKING PROBLEMS little grog in the shape of brick bats, and the checking is en- tirely done away with. "We arc burning SO per cent No. 1 face, 10 per cent No. 2 and 10 per cent common, at prices ranging from $9.50 per M. for commons to $15.00 and $40,00 per M. for face brick. Our shale is very rich, fat and plastic, and we manufacture 511,000 per month. "Hoping this ict'// help some fellow out of his troubles, as I lost some sleep over it the first month I ivas here, and thanking you again for your reply, I am Yours very truly, , Supt." Dry Press Brick Check 331. Texas IV c arc running a dry press brick plant, op- erating two presses, one a Ross-Keller, triple pressure and the other a Grath fire-mould special. We have been having considerable trouble with our brick air-checking shortly after it comes from the press usually from one-half of an hour to two hours and this trouble has been more noticeable of late. The air-checking does not occur at all times but is worse when we have a cold, dry, strong north wind. Wind from any other quarter apparently does not check them so much and when the air is damp and foggy, there are no checks at all. Our kilns are not protected from the north winds. The air checks do not seem to burn out. The clay burns a yellow or buff color, which is very pretty and if we could only get rid of the checks, we would have as fine a brick as is manu- factured in this state. The brick takes considerable heat, re- quiring at least 2,000 degrees. We use two barrels of oil and the moisture we use is from six to ten per cent. The trouble you are experiencing, due to the development of air cracks, is a common one to the manufacturer of dry pressed brick, especially where the material used is prac- tically non-plastic. Two possible remedies suggest themselves. CLAYWORKING PROBLEMS 115 One is to store the clay as long a time as is practical (two or three days) before using it. The clay must, of course, be in the moist condition when stored, just about as it will be when used at the press. If your plant is small, you prob- ably will not be able to store it longer than 24 hours but even this short a time may help you somewhat. The second suggestion is, before setting to put the brick into a warm, damp compartment where little drying will be accomplished but yet where the brick can be warmed up. When run out of this damp closet, the ware should show a lessor tendency to develop the air cracks of which you speak. This question was submitted to other authorities on the subject, who replied as follows : Anton Berg, of the Berg Machinery Manufacturing Co., Toronto, makers of the Berg dry press, offers this sugges- tion : "In some cases by having a steamer and steaming the clay so that it will be warm and dry inside of the brick, has proved successful, and again, in some cases, weathering is a remedy for air-checking." Ellis Lovejoy writes: "As a rule the finer ground the clay is and, in consequence, the greater the density of the brick, the greater is the checking difficulty. There are very few dry press brick which will not air-check when left exposed to the air or sun, particularly when the air has very little hu- midity, or, in other words, when it has great drying capacity. It is simply an illustration of the surface drying faster than the moisture within the brick can be brought to the sur- face and the surface drying causes shrinkage on the sur- face and the strains introduced by this shrinkage are coun- teracted by the numerous cracks. When the bond is once broken by these cracks, it will not knit together in the burn- ing. Many years ago the manufacturers of dry press brick began the introduction of dryers in order to reduce the time of drying in the kilns, but almost without exception the dryers were found to be a failure simply because the 116 CLAYWORKING PROBLEMS brick would check more or less in the dryer, but would not check in the kiln and in consequence the manufacturers returned to the usual method of setting the brick from the machine direct into the kiln. The only method we can sug- gest in this instance is to protect the brick from sun and wind. This is not always easy to do in updraft kilns and we have found it necessary in using such kilns for dry press brick to follow the setting very closely with the platting and in a scove kiln it would be necessary to keep the scoving up to the setting. If the kilns are scove kilns and it is not practical to keep the scoving close to the setting, probably dampened burlaps hung over the exposed brick would pro- tect them from the action of the wind and in the kiln, as the setting progresses, the exposed benches can be similarly protected." As to Care of Belting 249. GeorgiaI want some information as to the proper care of belting. We use a great deal of cotton stitched belt. We find it preferable to rubber belt, but the belt gets stretched a great deal when ive hare a high wind and becomes very hard and dry on account of the dust flying around the brick yard. Our belt bill is enormous. We use entirely too much belt and do not get near the life out of the belt that we should. We would like to have some suggestions in re- gard to this and would be glad if you would give it as much publicity as you think practical. We believe a discussion would be valuable to all. We have submitted this problem to a number of practical engineers and to some of the belt manufacturers. One en- gineer, who has to contend with all sorts of belts under all sorts of conditions, suggests the use of castor oil on the can- vas belt to keep it soft and pliable. All belts, especially if exposed to the air much, require a dressing of some sort and castor oil is far better than most of the advertised products. CLAYWORKING PROBLEMS 117 It does not injure the fabric as does linseed oil and other substances. A belt manufacturer solves the problem in this manner: "Some cotton stitched belts are filled with com- pounds which, while affording some lubrication for the fibres of the belt when first installed, soon oxidize, and become hard, causing internal wear. A high grade stitched-canvas belt is filled with a non-oxidizing compound which maintains pliability. Furthermore, a high grade belt of this kind, aside from being filled with a heavy compound which does not get hard, causing internal wear and the breakage of the belt, is covered with an outer coating of a heavy mineral compound which hermetically seals the inner lubrication, keeping the belt pliable. We have known of instances where cheap belts did not give economical service, and the user in looking for relief used too heavy a belt, that is, a belt of too many plies for the too heavy a belt, that is, a belt of too many plies for the size of his pulleys. Care must be exercised in selecting belts to see that too heavy a belt is not used on small pulleys, as, regardless of the quality of belting, if it is too heavy for the pulleys, the belt will soon be broken down." Adding Oxide of Iron to Produce Red Color. 100. Indiana IV e note in your "Questions and Answers" department for April 15 the following by 67 Havana: "What can I add to a white clay in order to obtain a red brick?" You reply that the clay may be burnt red by adding oxide of iron. Can you give us some successful method of adding this to the clay? Ellis Lovejoy, E. M. ( of Columbus, Ohio, gives the follow- ing answer : In reply to your inquiry relative to obtaining a red color from a buff burning clay, your answer "67 Havana" to the question is in the main correct, except the last statement in 118 CLAYWORKING PROBLEMS the first paragraph. This last statement, "Clays con'taining little alumina and much iron burn red," is true enough, but it also may be said that clays containing much alumina and much iron burn red. It is the "much iron" that coun'ts and the content of alum- ina has very little to do with it. We have found that a high- ly aluminous clay containing iron, of course, will burn a dull brown red while a silicious clay will have a bright red color, but both are red. Your correspondent says, "the effectiveness of iron as a coloring agen't depends not only upon the quantity used but also upon the degree of oxidation and upon the physical and chemical condition of the clay," to which we agree, but we would also add that the physical condition of the iron is an important factor. A clay containing five per cent of iron oxide will burn red provided i't is not affected by the "chemical condition" of the clay. This assumes that the iron is in a finely divided state and is distributed through the clay. Suppose that we have a buff burning clay free from lime and containing very little iron. Now let us add to i't a lump of iron ore equal to five per cent, or a few nails equal to five per cent iron oxide. The clay will not burn red in consequence. We may divide the iron into a dozen, a hundred, a thou- sand pieces and still get very little red color from it. I't is the infinitesimal division we get in nature that gives us the effective red color of naturally red burning clays. We cannot get this fine division mechanically. The usual material added 'to clays to get a red color is finely divided hematite ore, or better the extremely finely divided mineral paint made by roasting ferrous sulphate. We have often considered the possibility of coloring buff burning clays chemically and thus duplicating nature's work. If we could add a solution of iron to a clay and then evapo- rate it, or decompose it, as the case may be, we would have CLAYWORKING PROBLEMS 119 each grain of the clay coated with iron in a finely divided state an iron stain we may say, we would produce a red burning material. Iron ores the oxides and carbonate, are not soluble and consequently cannot be added in solution. We can only add them as mixtures and when we add enough of the oxide, let us say, we will get a dark brown red color simply be- cause the color effect of the iron predominates and hides the buff color of the clay. We add manganese to a buff burning clay to produce a gray color, but it is simply a pepper and salt gray and will approach a solid color with increasing degree of fineness of the manganese. Similarly with the oxide of iron. We can make a light burning sand red by soading it in a solution of ferrous sulphate then drying it in the sand dryer such as is used in soft mud brick yards where the brick are sand molded. Perhaps one soaking and drying may be sufficient, but if not we may get the color to any desired depth by repeating the process. We consider this a much better method of improving the color of sand molded brick than by the common method of adding powdered iron ore. Now the question arises, can we do the same with clay and thereby color the entire body of the brick? We do not know. The cheapest iron compound that is soluble is copperas ferrous sulphate. This salt contains 20% iron, or 26% ferrous oxide, or 29% ferric oxide, as- suming that all the oxygen comes from the salt. Our basis of figuring should probably be on the basis of 26% ferrous oxide subsequently oxidized to the red oxide in burning. If one thousand brick requires 6,000 pounds of clay there should be added to it at least (5%) 300 pounds of ferVic oxide, or in round numbers, 1,000 pounds of ferrous sulphate in solution. To one familiar with the behavior of sulphur compounds the objection will be raised that in case the clay contains CLAYWORKING PROBLEMS any lime, the sulphur element in the ferrous sulphate will combine with lime and excessive scumming will result. This will undoubtedly be the case and while we will produce a red color we at the same time bury it under a dirty white scum. Naturally the next s'tep would be to add barium carbonate or barium hydrate to precipitate the sulphur and in so doing we would at the same time precipitate ferric carbonate or ferric hydrate since either are practically insoluble. How- ever, we would accomplish results since the iron would be distributed through the clay in a perfect manner and every grain of clay would be coated with a film of the precipitate, or even if coagulation took place every pore in the clay mass would be more or less filled with iron precipitate. If the clay did no't contain lime, probably the sulphur ele- ment from the decomposition of the ferrous sulphate would pass off without any scumming difficulty and in such a case we believe there may be possibilities in treating a red clay chemically to produce a red colored brick. If, however, scumming results, the double chemical treat- ment, and the uncertainty of introducing proper quantities and getting complete reactions, makes the process a very questionable commercial one. If the clay is high in lime, we have 'the well known com- bination of iron and lime to form a lime iron silicate, with the result that the color is a buff, greenish buff, to a green regardless of the content of iron. In such a case, therefore, it would be useless to try 'to get a red burning product. Since sulphur causes scumming, it might be asked if there is not some other soluble of iron which could be used. We have chlorides, oxalates, and nitrates of iron in both the "ic" and "ous" forms that are soluble, and also the bromide, bu't the cost of such chemicals would be prohibitive, and their effect need not be discussed. In conclusion we have not much confidence in the chemU cal treatment of a buff-burning clay to produce a red color. CLAYWORKING PROBLEMS 13.1 but we believe that a bright red burning sand for sand- molded soft mud brick can be produced in this way and with much more satisfactory results than the present method of adding powdered iron ore. The addition of iron ore, or better the mineral pigment, is the most practical method of getting a red color into a mass of buff-burning clay, or, as suggested by your former correspondent, by the addition of red-burning clay or sand to the buff-burning material. Discolored Heads on Gray Dry-Pressed Brick 671. Texas We manufacture a dry-pressed gray brick made of fire-clay with manganese in it, and burn it in round down-draft kilns, the brick being set five-over-two. We wa- ter-smoke with wood and finish with oil. We hare trouble in getting the heads of the brick the same color as the face, the heads being appreciably darker. We have calculated the amount of water in the green brick to be one-and-a-half pounds. This conclusion was reached by zvcighing a brick that had been burned, and comparing this weight with the zveight of a green brick. The brick are taken direct from the dry-press to the kiln, li'hich is set thirty high. It takes about four days to fill the kiln, when the water-smoking is begun. This takes eight days; we then burn off with oil, which takes four to five days more. In cooling, we cut off the burners and let the eyes stand about thirty minutes; in the meantime, we take the brick off the center hole and off the holes down near the base of the crown, and drop the damper in the main tunnel leading to the stack. After about thirty minutes has elapsed, we daub the brick in the fire-boxes with mud. In about twenty-four hours, we knock a small hole in the brick in the fire-boxes, and lift the damper about two or three inches. After this, we gradually open the fire-boxes and, about the third day, we begin to 122 CLAYWORKING PROBLEMS break the door a little. At the end of seven days, the kiln is cooled sufficiently to work in. We burn to cone 7 (Orton) sixteen courses from the top and to cone 5 two courses from the bottom. We use imported manganese, which is spread over the clay at the dry-pan while the clay is still in lumps. The manganese is in powder form. We use about fifty pounds of manganese per M. brick. We are sending you three samples; the piece marked 1 was drawn from the kiln as a trial piece while the kiln was at a high degree of heat, and this sample appears to be the same color all over. We did not cover this piece up to keep the air from it, but left it out, in the open. Sample marked 2, as you will notice, is clouded on both beds and heads, which arc not at all like the face of the brick. This is the discoloration that we want to overcome, as we want the faces, the beds and the heads to be alike. Sample marked 3 is a part of a brick that was leaked on through the kiln, during a rain that occurred while the kiln was water-smoking. You unit note that where the water streamed doivn upon it, the color of the bed of the brick is the same as the color of the face. We thought that, by send- ing you this sample also, it might help you to reach a conclu- sion as to our trouble. But we will also state, for your information, that this is the third kiln that has given us this trouble (the clouded ef- fect on beds and heads) and we do not want you to be con- fused into thinking that it is due, in any way, to excessive rain. We want to assure you that we will appreciate any help you can give us in this matter, and wish you the best of suc- cess. The discoloration shown on the samples submitted is a scum, developed in the firing, but formed during the drying or water-smoking period, or during the interval immediately after watersmoking. Water-smoking too fast, or two slowly, will develop scum. CLAYWORKING PROBLEMS 125 Heating too fast during this period causes a rapid motion of molecules of water toward the outside of the brick, bring- ing and depositing the salts that are in the clay, onto the sur- faces of the brick, as the water evaporates. It also generates so much steam that the draft and flues are unable to take care of it. This causes a surplus condensation on the exposed sur- faces of the brick and so additional chances for concentra- tion of salts on those surfaces. When the water-smoking is too slow the same results are accomplished. Steam is generated in the top of the kiln and as no appreciable draft has been attained, the steam lingers among the bottom brick, condensing, and increasing the chances for scumming. Incomplete water-smoking, followed by a too rapid raising of the heat results in the quick expulsion of steam, with the same results as are noted above as consequent upon a too tapid watersmoking. Acting on the assumption that your trouble is caused by one of the foregoing (and this assumption is strengthened by the water content of your green brick), we suggest that you try a remedy that was successful on another plant which made gray dry-pressed brick. This was the partial drying of the brick, in the open air, for forty-eight hours before the brick were put into the kiln. The water-smoking period was reduced accordingly, as a much smaller amount of mois- ture was brought into the kiln when the brick were set. Of course, this method has one serious drawback; with some days (and we know of cases where this has occurred), air- drying causes air-slaking, or partial disintegration, due to the releasing of the confined pressure that is given the clay par- ticles in the press. The cohesion of the finely ground clay is overcome, at times, by its plasticity and when too great a period of time elapses between the time of the pressure being given the clay in the press, and the molecular changes that occur during the water-smoking and burning periods, this cohesion 124 CLAYWORKING PROBLEMS is lessened. This does not occur to the same extent with every clay, and yours may, or may not stand the experiment. Since the above question and answer was published a letter has been received from R. H. West, of Alamogordo, New Mex., which gives another solution. His letter reads : "In regard to the discoloration on your dry-pressed brick I have handled southwestern fire-clays for some years and find them very subject to discoloration. In your case, rather than do as you are now doing, I should first weather the clay until it is thoroughly disintegrated and take great care in the setting, trying benches of three high and even setting on head, so that the heads are kept close together when shrunk. Take the usual precautions in watersmoking and raising heat I say this, although I have had very little trouble in these stages, finding, rather, that the main trouble with an oil fuel, comes in the finishing fires. I usually run up the fire-box heat a little, getting a perfectly clear fire, then drop my damper to about four inches and protect the fire-boxes against any wind, but do not brick or daub them up, and do not remove any crown covers under twelve hours. I find the brick do not check and the free admission of air, following a clearing fire, drives off the gases. I think the main fault is in daubing up the finishing fires." To Remove Scum or "Whitewash" from Brick Wall 676. Indiana I have mailed you today a piece of our brick. It is, as you will see, whitwashed in the burning. What I want to know is, if there is a solution of any kind that could be applied to this brick after it is built into the zi'all, that zvould remove this scum and prevent its reappear- ing. I would also like to know if there is any way to pre- vent this scum from appearing on the brick that is, what is the best ivay to treat the clay before or during the pugging, CLAYWORKING PROBLEMS 125 or to regulate the watersmoking or burning so that the white scum will not appear. We do not know of any solution that will remove scum or efflorescence from finished brickwork. It has been tried with varying success, but so far as we have been able to learn, the relief has been only temporary and the white stain has reappeared after a short time. If any of our readers have cause to differ with us, we will be glad to know of their experience. Regarding the prevention of the scum in the brick itself, would suggest your reading Lovejoy's "Scumming and Efflorescence" (50c postpaid) and the many articles that have appeared on this subject in "Brick and Clay Record." Wants to Patent New Type of Kiln 675. Tennessee I want to know if there is a down-draft kiln in use, ivhich is fired on one side, the heat travelling di- rectly across the kiln under the floor and up the bag walls an the opposite side, with the draft travelling down, through the floor, to the stacks. I know of a kiln that is something similar to this, but the stacks take the draft up on the side of the kiln, on top of the floor. This kiln, however, has not proved practical. I have invented a kiln on the lines described in the first part of this letter, and would apply for a patent upon it, if I were sure that no kiln had been built like it. I do not want to infringe on anyone's else ideas, and would be glad to know if you know of any similar kiln that is in suc- cessful operation. The Beaver Clay Manufacturing Company, of New Galilee, Pa., writes as follows : "We have a down-draft, rectangular kiln that we have had in use for many years, and which is fired on each side, and which had two main side flues, and this works on the down draft principle. We also have a little test kiln which fires from one side, but the principle of this test kiln we do not 126 CLAYWORKING PROBLEMS consider as successful as the principle of the larger kiln, which is fired from both sides. If your correspondent would care to pay us a visit, we would be glad to show him our kilns, for of course, if his ideas are practically the same as those embodied in our kilns, it would be useless for him to secure a patent, inasmuch as the kilns have been so long in use that it is doubtful whether a patent would be issued, and, if it were granted, whether it would hold." Burned Clay vs. Galvanized Culvert Pipe 661. Georgia Will you tell us where zue can get literature to be used in a fight which we are making against galvanised culvert pipe? We regret that we are unable to help you in this matter, not knowing of any printed matter on the subject mentioned. We take this occasion to appeal to our readers for help. If any of them have made clippings from articles which could be used to further the cause of burned clay against gal- vanized culvert pipe, we would be glad to learn the names and dates of publication of the periodicals which contained these articles. We would also like to hear from our readers who have had any experience along the line mentioned and to receive letters or articles from them which give good reasons for the advocacy of burned clay pipe, particularly as opposed to galvanized iron. The Economy of Reburning Soft Brick 664. Colorado Knowing that you are familiar with all branches of the clayworking business, I take this means of finding out if it is a good plan to reset dry-press salmon brick in a doii'n-draft kiln and so burn them again. The brick I refer to have not been burned long enough in an updraft kiln, and are real light salmon, or you might call them "dobies." If they are reset in a doivn draft kiln and burned over, will it make good, hard red brick out of them? And is it cheaper to CLAYWORKING PROBLEMS 127 handle them in this manner than it is to make more brick? We have about 200,000 of these brick and would like to know what we can do with them. Wisdom would suggest experimenting with the salmon brick that is, placing several hundred of them in a kiln that is being set with new brick. Set the salmon brick in one col- umn, from bottom to top, and, when the burn is over, make a careful observation of the salable qualities of these re- burned brick. If they are worth next to nothing, now and are worth more than the cost of reburning them, when they have been reburned, then there is a greater economy in re- burning, than there is in making new brick. Another point in favor of reburning is that 200,000 brick that cannot be sold simply occupies space that ought to be given to better ma- terial. But it is well to experiment, first. Otherwise, the reburn- ing might give you nothing better than what you now have, and the fuel and time and kiln room would be wasted. Cement Joints in Clay Sewer Pipes 670. CaliforniaWhat reply can we make to the statement n'hich we have underscored in the enclosed advertisement relative to the use of cement for joints in sewers constructed of burned clay pipef The underscored paragraph, in the advertisement which our correspondent enclosed, reads as follows : And if sewage is so dangerous to cement, how about the cement joint that occurs every two and a half feet in all clay pipe sewers? It is useless for them to say that the sewage does not come in contact with the cement mortar at the joint. Just look in any sewer and see for yourself. Any sane person watching sewer construction will see that the joint which occurs every once in so often in clay pipe is made up of neat cement and is protected by the burnt clay 128 CLAYWORKING PROBLEMS of 'the pipe itself; that is, it is protected in everything but a very small part of the joint. In this it is very much like the joint between brick, and in laying ordinary common- brick, a mortar joint that is one-quarter-of-an-inch thick is actually eight cubic inches in volume, where the brick used measures eight by four inches on the bed. When the brick and the joint is exposed to fire or to any other condition which might produce a chemical change in the mortar joint, a surface which only amounts to two square inches is ex- posed; that is, the surface of the joint is but one-quarter-of- an-inch thick by eight inches long and it is only the surface which is exposed. In the same manner, it is only the edge of the joint in the sewer pipe that is exposed to the chemical action of the sew- age. In the making of cement pipe, neat cement is out of the question on account of the cost and the mixture which is used to make the pipe is very different from the mixture which is used to make the joints in sewers constructed of burned clay pipe. Coloring Matter in Molding Sand 655. Pennsylvania In a recent issue of "Brick and Clay Record" I saw an article on coloring sand with red mortar color, in order to make the brick burn darker. Kindly give me all the information you can on this subject, as the sand I use burns lighter than my clay. Kindly inform me, as near as you can, what proportion of the coloring matter I should use. The quantity of red coloring matter that is necessary to bring the sand to the right color after it is burned, depends upon the strength of the pigment used, as well as on the quality of the sand and the kind of fuel burned". The better way is to experiment with a small batch of brick, keeping a careful account of the amount of color added to the sand, with each batch. Another way is CLAYWORK1NG PROBLEMS lay described by Ellis Lovejoy, E. M., in an answer pub- lished more than a year ago in this department. In it, he said, in part: "In sand-molded brick we have, on several occasions, recommended wetting the sand with ferrous sulphate (copperas) followed by drying. This treatment of the sand produces a brilliant red color and this method of coloring the sand for the molds is in practical use." Cones vs. Pyrometers 662. Ohio / am writing to you as to a "neutral" to clear up a point that is gh-ing me considerable -worry, and which surely makes me doubt the accuracy of both my Seger cones and pyrometers. I formerly used cones exclusively, in burn- ing my product, which is face-brick, and alu'ays reached cone 1. A few mouths ago. I put in a pyrometer system, and since that time I hare stood on the banks of the River of Doubt. The two systems do not check and I do not know which is correct if either. Professor Orton's cone 1 melts at 2.102 degrees Fah. according to the table, but when it melts in my kiln, the temperature reading, according to the pyrometer, is usually about 1.930 degrees Fah., which is a difference of 172 degrees. Can you tell me how to correct this, and whether the cones or the instrument or all of them, are at fault? I am anxious to use both, as the cones are a great help in finish- ing our burn and I hare found, also, that our firemen take a (/reat deal more interest in their work since they arc able to TtYj/f/t the line of heat advance on the pyrometer. The question you ask is an old one and one that is bound to come up periodically, and almost always when anyone using one method decides to use the other also. At the out- set, it must be stated that the cone and the pyrometer do not do the same work, contrary to the almost general opinion. The cone measures the result of heat. The pyrometer measures CLAYWORKING PROBLEMS temperature. Professor Orton has, possibly, sent you a list of temperatures at which the cones are supposed to melt. They may, or may not melt at that particular point, depending upon the rate of firing, the quality of the kiln-gases, etc. He also undoubtedly told you that you should think in cone numbers, not in temperatures, when using his cones. You have found out, by experiment, that your ware matures and is at its best point at the time cone 1 falls over, providing the cone is in the same position in the kiln and also providing that the kiln is burned the same way each time. In other words, you have found that the combination of circumstances controlled by your burns has produced a certain result in your clay brick and in your clay cone, that is. that they both mature at the same time. This does not mean that they both mature at the same temperature, with each burn. It is unfortunate that the temperature dif- ference ever became associated with cones. The cone meas- ures heat-work-accomplishment, and, under stated conditions, and, when intelligently used, is invaluable to any common - clay plant. The cone indicates when the ware has gone through a pyrometrical change, to maturity. The pyrometer is invaluable, to trace the temperature, whether rising in a burning kiln, or falling in a cooling kiln. It indicates the uniformity, or lack of uniformity in firing, and enables the burner to know whether his heat is falling, is stationary, or is rising. Use both cones and pyrometer, but forget abuui temperature in relation to the cones. Quantity of Fire Brick for Kiln Crown 659. Illinois Please let we knoiv how many fire-brick it takes to put a crown on a thirty ft. kiln with a quarter pitch, also the rule yon use to w.">:{. California U'e have noticed frith interest your ra/w- nblc table published in the Superintendent's Department of the March 16 issue. If it is agreeable to you. we should like to use this in a price-list which we will issue within a fezt- months. Will you kindly gire us the dimensions of the key. arch and wedge brick used in your tables? We will be very glad to have our readers use this table in their printed matter, if it is useful to them. The sizes used were as follows : No. 1 Key 9x2^ thick x 4y> to 4 wide =112 brick to circle 12 ft. inside diameter. No. 2 Key 9x2^ thick x 4!/> to :\V> wide = 5 brick to :ircle 6 ft. inside diameter. No. 3 Key 9x2^ thick x 4 J / 2 to 3 wide = 41 brick to circle :s ft. inside diameter. No. 4 Key 9x2 Vi thick x \V 2 to 2'4 wide = 2rt brick to circle \y 2 ft. inside diameter. No. 1 Wedge 9x4^2 wide x V/ 2 to 2 thick, tapering length- wise = 102 brick to circle 5 ft. inside diameter. No. 2 Wedge 9x4^x2^2 to \V 2 thick = 63 brick to circle 134 CLAYWORKING PROBLEMS 2Vj ft. inside diameter. No. 1 Arch 9x4^x2^ to 2 thick, tapering breadthwise = 72 brick to circle 4 ft. inside diameter. No. 2 Arch 9x4^x2*4 to 1 1 / 2 42 brick to circle 2 ft. inside diameter. Absorption Tests on Face-Brick (>54. Illinois fVry recently the writer was led into a dis- cussion relative to the absorption test on various kinds of face-brick. Not being thoroughly versed on the subject, I could not hold up my end of the conversation as I would hare wished. U'ill yon give me what information you have as to the method of making absorption tests, their value and the best way of making use of the results of these tests in connection with the sale of face-brick ? The most common way of making an absorption test is to first dry the brick to be tested particularly if it has been taken from a pile that has stood out-of-doors for any length of time. The drying can be done in the oven of an ordinary cook-stove. Second it should lie accurately weighed. Third it should be immersed in water for at least twenty-four hours. Fourth it should be wiped with a soft-cloth or sponge, to remove all "surface water. 1 ' Fifth it should be again weighed, and with the same care for accuracy. The process may be varied, according to the severity of the test required, by substituting a three-quarter immersion for a complete immersion, the former filling the pores more accu- rately, since the water is absorbed by capilliary attraction, while the air escapes from the upper and non-immersed sur- faces. Or still another variation immerse the brick for twelve hours, bringing the water to a boiling point during the last part of the twelve hour period and continuing it at a boil for not less than half an hour. This opens up pores in the brick that would otherwise remain closed. Regarding the value of these tests this is problematical. CLAYWORKING PROBLEMS 135 The true test of the value of face-brick lies in its ability to make a dry wall, and to keep its face clean. A dry-press brick, absorbent to a great degree, yet flashed on its face, back and heads, will accomplish these purposes quite as well (and it is claimed, better )than the most impervious of stiff- mud brick. When the question of efflorescence is raised, there is little choice between a brick that extracts the free lime from the mortar, bringing it out at the center of the brick, and spreading it toward the edges, as against a brick that, while itself neutral, still receives the limey deposit from the motor joint, and shows the white discoloration after every warm, rainy spell. The value of the absorption test is not nearly so great as the value of the "time and use" test, which can be shown a prospective customer in the house where the brick you are selling him was used perhaps some years ago. That will tell him, if he has a grain of common sense, more than he can learn from these absorption tests, which are not practical, in that they do not approximate any of the conditions that the brick is to meet in its daily work. The principle lying back of the effectiveness of the "best by time's test" demonstration is the old one of "seeing is believing," and while the laboratory test might appeal to the imagination of some people, the vast majority is gen- erally more easily and positively convinced by actual re- sults. As to the best way of using these tests in the marketing of face-brick, we think that you should demand a real absorp- tion test, made along the lines suggested, every time your competitor tries the time-honored (but otherwise without honor) method of pouring a teaspoonful of water on the face of his (and your) brick, and then "leading'' the little lake along the line that shows in the face of your brick, and where your brick has the greatest porosity, and away from C L A Y W ORKI NG P K O B L EM S the same line in his own brick, although he knows, as well as you do. that he is trying to cheat. Dipping Brick to Change Color 627. Indiana Is there any way to get different colors on the face of brick by dipping them and then burning ? In order to answer this question intelligently, it would be necessary for us to have a piece of the brick that you desire to make in a different color and a very exact statement of the process that you use, beginning with the manner in which your clay is harvested up to the point of the kind of fuel used in its burning and the time which you give to water- smoking, burning and cooling. Dipping Brick to Change Color 627. Indiana Is there any way to get different colors on the face of brick by dipping them and then burning? The above question was published in the April 6 issue, and a suggestion made that it would be necessary for this cor- respondent to send us a piece of the brick that he wanted to change in color by the dipping process, and also an exact statement of his process of manufacture. Since publishing this, we have received a letter from James Witte, of 618 South Main Street, Salt Lake City, Utah, which reads as follows : "I have a process by which any desired color can be made no matter what color the brick ordinarily burns. This color is given by either dipping the brick or spraying it with cer- tain chemicals that are inexpensive. I can adapt these chem- icals to become sufficiently fluxed to enable them to set well on the brick, making the face impervious to mcisture. Up to the present time I have worked out a pure white, a gray, a light blue, a dark blue, a dark brown and a sage green. To CLAYWORKING PROBLEMS 137 the best of my knowledge. I am the first one to work this process, which can be used with any color of clay. I have been successful in putting this surface on red brick at cone 4, 1,958 degrees Fah., and am now putting it on a red burning sewer-pipe clay at cone 8, 2,354 degrees Fah. I am an expert in enameled brick manufacture, also porcelain face-brick and have had a life-long experience in the making of enamels. I am prepared to sell my formulas and will be glad to correspond with the manufacturer whose question you published." Coloring Matter Used in Clayworking 652. New York The appearance of an advertisement for rough-cut brick, printed in colors in a recent issue of "Brick tind Clay Record" prompts me to ask just how extensive is the demand for artificial colored brick and the probable quan- tity of color used annually by brick, architectural terra-cotta (ind art tile manufacturers. Also whether this demand for artificially colored burned clay products is increasing, stag- nant or decreasing. As everybody knows, coloring agents are particularly hard to get, at the present time that is, coloring agents that emanate from coal tar. What I would like to know is whether natural earth colors or coal tar colors are used in the various clay products lines. I would also like to learn from first-hand sources, whether brick manufacturers in particular are especially interested in bringing out new colors in their lines of brick, like green, for instance; ivould there be any great demand for brick with these out-of-thc- iirdinary shades? Do common-brick manufacturers use red coloring matter to any extent? What degree of heat would these coloring materials have to withstand? In the brick industry red hematite is used extensively for the giving of a uniform red color to common building brick. It is mixed with molding sand and put on the surface of each brick where it forms but a small portion of a very thin CLAY WORKING PROF. I. EMS film. One concern with an output of about twenty million brick per year uses one carload of red hematite every two years. In the architectural terra-cotta industry the only artificial colors used are those employed by potters and what these consist of can be readily learned by the investigation of glazes in common use. Here again it will be found that the amount of color is very small compared to the bulk of the finished product as the coloring agent forms but a small part of the thin film on the surface of the terra-cotta. In face brick, oxide of manganese has been used for many years in order to give the gray tinge to fire clay brick which would otherwise be a buff-white color. This manganese, if in powdered form, gives a pepper-like speckle which at a very short distance becomes a solid gray. When used in larger lumps, it gives a more speckled appearance and in this way accents the white ground. It has been calculated that the addition of manganese increases the cost of making brick- by about two dollars per thousand and since many factories making the kind of face brick to which manganese can be added, figure their cost of production at between nine and eleven dollars per thousand, you will see that the use of manganese is a rather expensive proposition. For many years theorists have figured that a green brick a brick which would be naturally green, not "go green" in the wall would lie welcomed by architects. There is no knowing, however, what sort of a reception it would get and if it carried a high price, the chances are that it would re- ceive a very cold shoulder. So far as our knowledge goes, coal tar by-products have never been used in connection with the brickmaking industry the reason being that no coal tar dyes could withstand the degree of heat necessary to mature the brick. In the manufacture of the rough-cut brick advertised in the recent issue of "Brick and Clay Record" which advertise- ment was printed in colors, would say that these brick are CLAYWORKING PROBLEMS 139 burned at from 1,800 to 2,100 degrees F. No artificial color- ing matter is added, the color being produced solely by the action of a reducing atmosphere in the kiln. It is much cheaper to close the dampers and allow the smoke and fumes from the coal to act upon the brick than it is to add any coloring matter to it. Brick made from fire-clay which are the kind of brick to which manganese is added are burned to 2,200 degrees F. and sometimes beyond that point. The question asked opens some interesting points, how- ever, and "Brick and Clay Record" will welcome any cor- respondence which might come from those experienced in the use of artificial colors in the manufacture of any burned clay product. Wants Information as to Stack Area 645. Minnesota 7 am thinking of putting in down-draft round kilns, thirty feet in diameter and holding 100,000 brick. There will be ten fire places, which allows one fire place for each 10,000 brick. How much grate surface would be re- quired for each fire place? I am using two square feet of ft. 9 in. inside measurements with a 9 in. spider or separat- ing wall running up the middle. This will leave the inside stack area for each kiln 2 ft. 6 in. by 3 ft. The object of the spider is to prevent the draft of one kiln from interfering with the other. The spider does not in all cases go to the top of the stack but it should go up at least 10 ft. from the CLAYWORKING PROBLEMS base and should he not less than one-third of the stack high. You speak of putting in two round, down-draft kilns, each of 30 ft. diameter and each holding 100,000 brick. Are you at all certain that you will succeed in setting 100,000 hrick in a 30 ft. diameter kiln? Regarding the grate surface, we would suggest that you allow five square feet to each furnace and that your stack he not less than 3.i ft. high. Clay Bar "Feathers " 64(i. \'orth Carolina IV c arc having trouble isith our brick machine which causes the clay bar to "feather" or crack on one or more of the edges as it comes from the die. Our clay has a high percentage of shale and we use an oil die, the column coming out of the machine edgeways. The "feathering'' may he caused by any of several reasons, of which insufficient tempering or its opposite extreme too much tempering may be one; insufficient lubrication may be another ; the die may be too short or too long ; the clay bar may be too soft. The most probable cause is lack of uniform lubrication in the corners of the die. This probably causes friction and consequent holding back of the corners of the column. This difference in the flow of the bar causes strains to be set up that invariably tear or "feather" the edges. Why not write to the manufacturers of the die that you use, tell- ing them of your trouble and asking them to suggest a remedv? Best Height for Kiln Crown (547. Pennsylvania H'hat is the lowest height of spring it would be practical to use for a crown of a thirty-five foot in- CLAYWORKING PROBLEMS 141 side diameter sewer pipe kiln; the crown being built of twelve inch fire brick and banding no object. It appears that you wish to secure as flat an arch as pos- sible and. at the same time, be sure that it is safe. The thrust of an arch on kiln walls and kiln bands is not the only point to be considered. If the arch is too high or too low. the tendency to buckle and to warp is great this tendency usually manifesting itself on the quarters. The smaller the perpendicular distance between the spring of the arch and the apex of the crown, the stronger must be the kiln bands. A height of 8 ft. 6 in., or approximately one-quarter of the inside diameter of the kiln, is generally accepted as the best practice, for it has been found that the kiln crown re- sists deformation strains when the rise is as noted. If you wish a lower crown in order to confine the heat, the best method is to lower the kiln side walls. This procedure will not materially decrease the capacity of the kiln. One thing must be borne in mind that is to secure a sufficient curve in the crown to create a tendency to resume its original con- tour after expansion. Burning Lignite in Down Draft Kilns. 633. West Virginia / have a brick plant proposition under way where it ai'// be economical to use lignite coal. Will you give me what information you have regarding the prac- ticability of using lignite coal in burning brick, especially in down-draft kilns? This is an important question important because fifty per cent of the balance of our coal supply is lignite. Here is a material which, generally speaking, is considered a low grade fuel: within it a great tonnage of immense commercial value lies dormant. Lignite runs low in carbon or heat producing constituents, high in volatile matter, high in moisture. In the volatile matter we find a commercial product that has many times the value of the carbon that is missing. In all CLAYVVORKING PROBLEMS direct firing of lignite we must make allowances for the loss of the heat which is used in evaporating the free moisture, and any attempt to use raw lignite in ordinary direct firing cannot help but result in low efficiency. Since, however, our questioner may be compelled to follow the old methods of firing, we will endeavor to show, as accurately as is possible, the construction of a fire-box for lignite and compare it with the fire-box that is often used to burn bituminous coal. For example, using a 12.000 B.T.U. bituminous coal and 8,000 B.T.U. lignite in the former, with a certain draft, we would consume to an ash approximately 10 Ib. of coal per sq. ft. and, at 100% efficiency, in a 6' 0" grate, or 3 sq. ft. of grate area, we would liberate 720.000 B.T.U. (6X10X12.0001 per fire box per hour, or, for a twelve fire box kiln, 8,640,000 B.T.U. per hour, to obtain the required temperature. To produce the same results with lignite, we would increase llie grate area so as to consume that quantity of lignite which would be required to produce the same quantity of heat per hour, or 720,000+8,000+10=9 sq. ft., instead of 6. Provision should also be made for the proper air supply and for equal distribution over the greater grate area, and also it will add greatly to the efficiency if this air is super- heated and supplied by blast. Every brick yard has an abundant supply of waste heat so that simple and effective means could be provided for supplying superheated air for all combustion and the result produced would pay for the extra expense in a very short time. It would be well for all who contemplate the use of lig- nite in direct firing, and especially those not familiar with its use, to correspond with Mr. Russell, manager of the Dicken- son Fire & Pressed Brick Company, of Dickenson, N. Dak. Mr. Russell has had years of practical experience with lignite in the burning of common-brick and fire-clay products, is a technical man and should furnish valuable practical infor- mation. We cannot help but believe, however, that all pres- ent methods, which consume the total quantity of raw or CLAYWORKING PROBLEMS 143 bituminous coal with such tremendous loss, are entirely wrong and not in keeping with well established scientific methods. All of our lignite coal fields are found in the far West and Northwest, where other fuel is scarce and high priced, due to the long freight haul. If the most economical methods are sought, then the best results up to date can be had by adopting or erecting a lignite carbonization plant similar to the one operating at Minot, N. Dak., in which it requires about two-and-one-eighth tons of raw lignite carbonized to make one ton of high carbon briquettes. The briquetted carbon will practically have the same heating value as anthra- cite and commands about the same price, and about $1.50 to $2.00 net per ton of briquette can be made in the process, while letting all of the gas escape to the atmosphere. The process will produce from 12,000 to 15,000 ft. of 400 B.T.U. gas per ton of briquettes, or from 4,800,000 to 6,000,- 000 B.T.U. of available gas which could be used in the ourn- ing of clay products. This method was established by Prof. E. J. Babcock, dean of the School of Mining Engineering, at Grand Forks, N. Dak., and is giving very good results. But as it is the retort method and periodic, it is to be hoped it will not be long until further developments will result in a continuous and automatic process which will be more eco- nomical and less expensive to construct. Clay products manufacturers, like the steel products people, must devise and adopt a by-product process so as to not only provide economical fuel that can be applied in a man- ner that will produce the best results, but assist in the elimi- nation of our wholesale waste of natural resources. No smelter can successfully operate without coke. Coke is of a certain structure which supports the ore during the smelting process. Hence they erect coke oven by-product plants, and their by-products are gas, ammonium sulphate, tar, etc. The clay product manufacturers require gas that is cool, rich and clean, so that it can be put under pressure, and a valve con- 144 CLAY WORKING PROBLEMS trol which gives them full control of the temperature, re- sulting in a uniform product. To get that kind of a fuel economically they should erect gas by-product plants. They would be highly profitable and are found to be practical by manufacturers in other lines that depend upon heat for the production of their wares. The above question was published in the Feb. 2, 1915, issue and an answer given at that time which was written by one of the best known exponents of the adaptability of low grade coal burning in the manufacture of clay ware. A subscriber has written, protesting against some of the statements that were made and, as his remarks are evidently those of a man who knows, we print them, without altera- tion, addition or omission. He writes: "The writer notes in the Feb. 2 issue the answer you have made to '633 \Yest Virginia' on the subject of burning lignite coal. In this answer you suggest that, for an eco- nomical method, a plant should be erected similar to the one operating at Minot. No. Dak., where lignite is carbon- ized and briquetted. "Perhaps this is none of the writer's business, but for the good of the clay working fraternity, he feels called upon to suggest that the man who wrote the answer might well make a more extended investigation at Minot and that when lie has done so, he will not be so apt to ask other people to invest their money in a similar proposition. "The plant which the writer is running is burning raw lignite in the manufacture of brick and is getting good re- sults in burning common brick in up-draft kilns. It is not. however, giving satisfactory results with pressed brick in down-draft kilns, although we expect to get better results by building larger stacks. "We use fans, and when we built, were advised that, on account of using forced draft, we would not need to build CLAYWORK1NG PROBLEMS high stacks. We think different now, for we cannot get rid of the moisture without trouble and loss of time. "We are awaiting further developments in the carboniz- ing of lignite and the use of by-products before putting any more money into the 'game'. At the present time, the best proposition in this line is the kind of carbonizing plant built by Professor S. M. Darling of Estevan, Sask., who built an experimental plant at Estevan for the Saskatchewan govern- ment. He has just issued his report, a copy of which may be secured by writing to the government office at Regina, Sask. "The writer has examined the plant at Minot and is pre- pared to say that the methods in use there are crude and expensive and not in any way satisfactory. This is largely- due to the fact that the product is not and cannot be held uniform. This is as bad, comparatively, as it would be for one of the large flour mills to make an hourly change in its grade of wheat or in its mixture. The change is reflected in the finished product as well as in the cost of operation. "At Minot every car of carbonized lignite is different. This results in a constant endeavor to meet conditions by change of binder necessary and by other mechanical shifts and there is no doubt but that a large sum of money must have been lost there during the past year, in what seems to be a vain endeavor to make briquettes. "The Darling plant at Estavan was in continuous operation and a uniform carbon resulted. This finished carbon has been used with great success in gas producer engines. Pro- fessor Darling has built no briquetting station but has shipped his product to other plants where good briquettes have been made and there seems no doubt but that he has the right idea. "In conclusion I would ask that you give this letter as much publicity as possible, for the reason that I believe that whoever wrote the answer to the original question was ignorant of the exact state of affairs at Minot and has been careless enough to pass hearsay information to your readers. CLAYWORK1NG PROBLEMS If they in turn acted upon his suggestions, without making a personal examination of the plant, property and product that he praised so highly, the result would he an enormous additional pecuniary loss." To Make Bullnoses by Hand. (W5. North Carolina Please give us a suggestion as to the TEMPLA BOX best method for cutting the corner of bullnosc brick. Ours is an end cut machine. Bullnoses can he cut by hand in hullnose template boxes. CLAYWQRKING PROBLEMS 147 which are made like sketch herewith. The standard size green brick is placed in this box, which is arranged so that the sides will fit the beds of the brick very snugly. A cut- ting wire strung on a bow, or a sharp knife is used to trim the former to the same radius as the sides of the box and the brick is removed and smoothed up with the aid of a scalpel knife and a pan of water. One man can turn out about five hundred of these brick in a day, the number depending upon his ability and the character of the clay he is work- ing, as well as the exactness of the finish required. Economy of Various Grades of Coal. 603. Montana Figuring coal screenings worth $1.00 per ton, pea size at $2.00 and nut at $2.75, which grade is the cheapest to use in a scove kiln. Also how long should grates be and what style? What kind erf coal do you recommend zvhere a burner has the choice between a hot, flashy coal that has very little ash and a slower acting coal with considerable ash. Both coals burn without clinkering and the B. t. it's are about the same? The cost of fuel is determined by points other than the initial cost per ton. Time is a consideration, for it affects capacity and labor cost. The quality of the ware is also to be considered, since this affects the selling price. The coal that combines the small tonnage to mature the ware in the shortest time with the highest percentage of first quality ware is. as a rule, the cheapest, irrespective of its cost per ton. This statement is subject to some cor- rection, since there might be so wide a difference be- tween one initial cost and another as to off-set the sav- ing in time, labor, repairs and spoiled ware. To secure a solution to your problem, it will be necessary for you to keep records records that will show the length of time taken to complete each burn, the quality and quantity of material burned and the cost of the fuel. You are fortunate- CLAYWORKING PROBLEMS ly situated in this regard in that all of the coal mentioned by you has practically the same B. t. u. value. Generally speaking, hot flashy coal with little ash is preferable to the slower acting coal that has more ash, but this again depend? upon local conditions. It may be a good plan to place peep holes through the side of the kiln wall, spacing them two feet apart from bottom to top. Through these the advance or the raising of the heat can be seen and records made that will have a bearing upon your final decision. A comparison of the data thus obtained should bring reliable information. It is impossible to answer your question regarding grates as the size and style depend upon the fuel you intend using. The dimensions also depend upon the construction of the kiln and the furnaces. Sometimes the coal burning fur- naces are entirely away from the arch, in a side wall of the kiln and are, at times, placed in extensions b.uilt out from this wall. It is very difficult to give any positive answer to the problem as it has so many angles, anyone of which might off-set another. The Burning of Alkaline Clay. 62'2. Montana Is there a sure way of burning good brick from clay that contains alkali, potash, etc.? I mean, is there a way to get them hard and yet keep them from fusing to- gether? Is it true that a kiln can be handled so that the alkaline salts will be dissipated before settling takes place and so be absent at that part of the burning period where they would, if present, act as a flux? This depends entirely on the percentage contained of each mineral mentioned. If it be excessive then we know of no way to accomplish the burning in safety. We do not believe that it is true that these salts can be so changed during any part of the water smoking or burning period that they would be rendered harmless. The only change that could take place, so far as we know, is that which would occur when CLAYWORK1NG PROBLEMS 149 they had attained sufficient heat to become chemically active, fluxing and fusing and attracting the surrounding silicates, hut this change is the very one you wish to avoid. We would like to have more information on this point from our readers. Coloring Molding Sand. 610. Minnesota There are brick yards in this vicinity turning out the same kind of brick that I am making but they use a certain coloring matter in the molding sand that fires all of their brick a dark red color. It will please me ays and find that it will add to the quality of our ware and '/// aid in the dry- ing without cracking. The fact that your shale is overlaid by a stratum of limestone would be a big point in favor of mining it. An expensive factor in mining operations is the cost of CLAYWORKING PROBLEMS timbering the roof in order to make the mine a safe place in which to work, and also to conform to the laws gov- erning mine working. The limestone roof, in many cases, does away entirely with timbering, thus decreasing the cost of operating the mine. Mining is certainly more expensive than gathering surface clay, and this point must be considered in de- ciding to use your shale. You must determine whether or not the addition of the shale to your surface clay will increase the value and sale of the finished product. If you can get a better price for your ware by the ad- dition of the shale and be able to sell more of it at a margin that will pay for the added cost of mining and still leave you a little profit, we should say that it would be a good proposition for you to use your shale. Your first step, it seems to us. is to determine the cost of opening a new mine and the tonnage cost of mining in your particular case. This could best be solved by submitting your problem to a reliable mining engineer, who could tell you how much it is going to cost yon per ton to mine vour shale. Thinks Slate Will Make Brick. 638. Arizona Some friends of mine are interested in a slate deposit near here and a recent analysis shows the fol- lowing : Aluminum (A1 2 3 ) 22.4 c / f Silica ( SiOo) 65.8 % Iron (FeO) 5.58% Magnesia (MgO) 1.8 % 95.58% This slate is such that it cleaves well and if the quality is all right it ran be handled so far as working it is concerned. CLAYWORK1NG PROBLEMS 151 Do you think from this analysis that it would make a good quality of pressed brick? There is no way in which we can predict the action of a mineral from chemical analysis. We may hazard a guess and in this instance our guess is that the silica is too high, the alumina too low and this is no guess the working qualities of slate or metamorphosed shale are zero. There are slates and other minerals that, seemingly, have the same chemical composition as clays that have proved use- ful while at the same time, the physical nature of these slates has destroyed the value from a clayworking standpoint. Will Motor Loads on Same Shaft Vary? 617. North Dakota If two motors having the same speed and same sice pulleys should be connected up to drive a ma- chine as shown in the accompanying sketch, ivill there be any difference in the load of the motors provided there is abso- lutely no slippage in the belts, or will motor pulleys have to be slightly different in diameter as in the ordinary tandem drive to give motors an equal load? Provided the two motors in question have the same gen- eral characteristics, the same capacity and speeds, the load 152 CLAYWORKING PROBLEMS would divide equally between them. The pulleys to do this would have to be of the same size. If two motors of different horsepower rating are used, the tendency would be to put a slightly greater load on the large motor, assuming that the speeds were the same. The rea- son for this is due to the fact that the variation in speed from no load to full load is slightly less on a large motor than it is on a small motor, as motors are commercially made. This variation could probably be overcome by placing the large motor inside, that is, between the motor with two belts and the driving shaft, and vary the load on this slightly by belt adjustment. Motors of different capacities with exactly the same char- acteristics would divide the load in proportion to the ratings of the motor when all question of belt slippage is eliminated. In other words, for a thirty horsepower load using a twenty and ten horsepower motor, each motor would be running at full load, or practically so. Wants to Glaze Under Side of Kiln Crown. 623. Indiana Please let us hare your best method of glaz- ing the under side of a kiln crown made of red brick. Ours is a round down-draft kiln and we burn at about 2.000 de- grees Fah. at the crown. Make up a daub of fire clay and salt, the proportion being about one iron wheelbarrow load of the clay to one-half of one shovel full of salt. Mix with water to the consistency of paint and daub over the under side of the crown with a stiff broom. Try the above proportions first on a small patch, for if it contains too much salt it will blister during the glazing. If it does not glaze at all, double the quantity of salt which goes into the next batch and keep on adding at the rate of one-half a shovelful of salt to a wheelbarrow- load of clay, until the correct proportions are ascertained. CLAYWORKING PROBLEMS 153 It is impossible to give you a correct mixture, inasmuch as the alumina-iron content of the brick in the crown bears a definite ratio to the fluxing or melting point of the body silicate. The salt tends to reduce the fluxing point and the amount of salt added has, therefore, a definite work to do. Too much causes a pimpled, viscous structure and not enough causes no reaction and, therefore, no glazing. The same glaze effect may be obtained by throwing four shovelfulls of salt in the furnace at two or three hour in- tervals during the last six or eight hours of burning. In addition to glazing the crown, this will also glaze the ware in the kiln, and if glazed ware is not desirable, the method first described should be adopted. Analysis in Sand-Lime Brick Manufacture 680. Quebec We manufacture a sand-lime brick, and as I found it advisable to analyse the mixture during the process of manufacture and also to analyse the finished brick for the calcium content, I shall be glad if you will g'vve me a few pointers on the subject or refer me to the suitable text books. I may say that I have Treadwell's "Analytical Chemistry" but the process therein described appears to me to be more suitable for the laboratory than for a factory. I presume that the process to be continuous should be that of titration as precipitation is much too slow a system. I should like also to be in a position to analyse the lime (CoO) for CaCo* from time to time as deemed advisable. I want to know just how to make up my normal solutions of hydrochloric acid (HCl) and sodium hydrate (NaOH) and the method of calculating the percentage of the carbonate and oxide after titration. This would be very valuable information both to myself and, no doubt, many of your readers; any light on the subject would be heartily welcomed. E. T. Montgomery, E. M. in Cer., of Alfred, N. Y., says that the best method for the rapid determination of calcium CLAYWORKING PROBLEMS bv titration process is that which is given on pages 22 and 23 and following of "Notes on Metallurgical Analysis," by N. W. Lord, formerly Professor of Metallurgy at the Ohio State University. He suggests that our correspondent will have no difficulty in securing this text, although it was writ- ten in 1903. Hann and Adair, of Columbus, Ohio, are the publishers and printers. For the examination of the lime. Professor Montgomery suggests the use of Schroetter's Alkalimeter which is cata- logued by Eimer & Amend, of New York City, as Alkali- meter No. 1752. Eimer & Amend should be able to give a description of the use of this Alkalimeter or give a reference to some text book which discusses its use, but if our corre- spondent finds it impossible to obtain anything of this kind, Professor Montgomery states that he will be willing to give him a detailed statement relative thereto. We are, of course, assuming that in our correspondent's examination of the lime which he is buying as one of the raw materials, he desires to ascertain only the CO 2 content which is, of course, the measure of the amount of either CaCo- or MgCO 3 present. As far as determining the calcium content of the mortar or raw mix is concerned, it would seem that the examination of the lime would be sufficient unless our correspondent is seeking to ascertain whether a'.l of the CaO in the mortar has been completely hydrated. In the second place, the cal- cium in his finished product exists in three different forms that of calcium silicates, some calcium carbonate and some uncombined calcium hydrate. We do not understand where he will derive any benefit from determining the total calcium in the finished product as the amount which has entered into combination as a silicate is a measure of the efficiency of his hardening process. Technologic Paper No. 16 by W. E. Emley from the U. S. Bureau of Standards at Washington, D. C, will prove of value to this correspondent as will also Bulletin No. 18 CLAYVVORKING PROBLEMS 155 on "Sand-Lime Brick" from the Geological Survey of Illinois at Urbana, 111. Comparative Cost of Coal and Oil Fuel 683. South Dakota Where can I get the best information relative to the cost of burning oil in place of coal for brick and building blocks? I want to know the cost per M. of burning petroleum tailings as compared to the cost of coal at $4.00 per ton. We are advised by an authority on the subject of oil that it is good practice to figure 126 gallons of fuel-oil as being equal to a ton of average quality coal. Fuel-oil costs about 1^4 cents per gallon at the refinery and as the freight rate from the nearest refinery to your plant would be between forty and forty-five cents per cwt. this would make the fuel oil cost you something like 4^4 cents per gallon. At this rate 126 gallons of oil would cost you about $6. Coal at $4 per ton would be very much cheaper. We note your use of the term "petroleum tailings" and wish to explain that this is only another name for fuel-oil. It was, we understand, used by some Oklahoma refineries for the purpose of securing a better freight rate than was given fuel-oil, but the Interstate Commerce Commission has ruled against this lower rate and Oklahoma "petroleum tailings" are again fuel-oil as they always were in everything but name. The Manufacture of Silica Brick 685. Pennsylvania Will you please tell me where I could get a book about lime-bond silica brick about making and burning it? T. E. Montgomery, E. M. (in Cer.) of Alfred, New York, in an article published in "Brick and Clay Record," in May, 1914, has this to say about the manufacture of silica brick: In the development of the siliceous refractories indus- CLAYWORKING PROBLEMS try, an unfortunate confusion of names has arisen. This is partly due to the fact that from the beginning of the industry two different binding materials have been used, viz.: lime and fire clay. The name "Dinas" was first used in the beginning of the 19th century by a Mr. Weston Young, who worked the siliceous materials of the Di- nasfels of Wales into brick, using as a bond the underly- ing cretaceous lime. This process was kept a secret by the Young family until the middle of the century, and in the meantime another siliceous brick was put on the mar- ket in England, which was made by grinding and mixing the gannister rock of Sheffield with fire clay. This was called "Gannister" brick, and the name is still generally applied in England to such siliceous brick bonded with clay. The Germans soon began the manufacture of a clay bonded silica brick and called it "German Dinas," so we have in Europe the term "Dinas" applied to both lime and clay bonded silica brick. In this country we have never used the term Dinas. High grade silica brick bonded with lime are called "Silica," and the term "Quartzite" and "Gannister" have been applied to different grades of clay bonded brick. In the manufacture of silica brick the best results have been obtained in the use of sedimentary sandstones and quartzites containing about 97 per cent of silica and 3 per cent of impurities. In the west, however, in Montana and Utah, crystalline quartz rocks are used. Attempts to use a too pure quartzite 99 per cent SiC>2 have not been successful. There is only one property or quality of major importance in selecting a material for the manufacture of silica brick, while there are two or three other minor ones. It must be remembered that silica brick expand on being burned in the process of manufacture, and are fired up to dimensions instead of shrinking to dimensions, as in the case of fire clay brick. It has been shown in testing dif- CLAYWORKING PROBLEMS 157 ferent quartzites that they vary from 3.2 per cent to 23.5 per cent in volume increase in the first burn. The lowest figure of 3.2 per cent is for a very pure quartz, coarsely crystalline, which disintegrates to a fine powder on burn- ing. The Higher value of 23.5 per cent was for fine grained, hard, tough quartzites with about 3 per cent impurities and which remained firm and hard after burning. It is obvious that we want a material which does practically all of its expanding in the burning it gets before put into use. These quartzites which have a low volume increase in the first burn, change in volume slowly and continuously over a long period, and hence swell after being put in place in actual use. The physical condition of the crushed material is also of importance. Round grained sand cannot be used, as it will not bond properly. Even sharp grained sand is not good, because the size of grain is too uniform. A rock which grinds to splinters and particles of irregular size, which overlap and interlock, makes a brick of the best structure. According to the kind of brick being made, there is added to the crushed rock in making the mix, either 2 per cent of slaked lime or from 20 to 30 per cent of fire-clay. The batch is ground and tempered in a wet pan and then molded by hand in a brick mold by what is called the "slop molding" process, the excess material being cut off at the top of the mold by a scraper. The brick are then dried on a drying floor or rack until they are hard to dent with the finger, when they are repressed. After the brick are thoroughly dried they are set in the kilns and fired to temperatures varying all the way from cone 9 to cone 18 in different plants. The temperature used depends on that required by the material to properly develop the bond and to secure the necessary volume increase, i. e., 158 CLAYWORKING PROBLEMS to bring the volume changes as near as possible to a con- dition of equilibrium. Silica brick are chemically acid and are used not only in positions where an acid brick is necessary, but are yearly finding many other uses due to their high refractoriness, regular expansion and heat diffusivity and ability to carry loads at high temperatures without deformation as long as these temperatures are at a safe interval below their melting point. Silica brick are used in connection with silica sand mass in acid open-hearth furnaces; they are largely used in crowns of by-product and bee-hive coke ovens; in the glass, iron and copper melting business; and in some places for boiler settings and fire box linings. As we would expect from our knowledge of calcium silicates, silica brick have been found to have a well de- fined melting point. There is practically no softening or flow until the melting point has been reached, when it will suddenly fuse to a liquid of low viscosity. Mr. George Brown in load tests on silica brick made in the Bureau of Standards laboratory, has shown that they are not af- fected by the usual test of 50 pounds per square inch at 1,350 degs. C, nor even when the temperature was car- ried as high as 1,470 degs. C. This test was on a silica brick with lime binder. A silica brick with clay binder showed a small de- flection under load of 50 Ibs. at 1,350 degs. Silica brick fuse or melt at about a temperature of 1,750 degs. C. Preheating a Plastic Clay 430. West Virginia / hare a sample of clay before me which has baffled me, H/> to this time, and will ask yoiw as- sistance. It is rery plastic clay and resembles Tennessee ball clay in color and strength. It acts rery differently, however, in drying, cracking all over the surface and is rery tender CLAYWORKIXG PROBLEMS when thoroughly dry. The shrinkage is about seven per cent. I can stop the cracking by adding about twenty per cent Tennessee ball clay, but do not wish to adulterate, as this lowers its fusing point, which is about 4,000 degress F. Can you suggest a method of working this clay and avoiding the cracking? I hare aged the clay for several months and have tried casting, pressing and throwing, with no results. Have added flint and grog to open the clay, and with no results. As I have said, I can cure this fault by adding ball clay, and still have a splendid refractory clay, but I am not willing to do this until I am sure that there is no other way. Professor Bleininger, of the U. S. Bureau of Standards, has shown that the drying behavior of excessively plastic clays can be improved in a decided manner by preheating them to temperatures of from 200 degrees to 400 degrees C, the intensity of the heat treatment depending upon the clay in question. The results of this work showed that; 1. Preheating seems to convert part of the plastic clay substance into a modification which can not be made plastic again. Such clays dry more easily, due principally to in- creased porosity. 2. The preheating should be carried on at as low a tem- perature as possible, only high enough to overcome the dry- ing difficulty. High temperatures with some clays result in excessive pore space which may give rise to burning difficul- ties due to cracking. It is quite likely that some clays cannot be preheated at all owing to the short temperature range with- in which the change takes place. It is impossible to give gen- eral rules ; each clay must be studied by itself. 3. Most clays seem to require more careful lubrication in the preheated than in the normal state. The amount of tempering water should be kept as low as possible. 4. There seems to be a tendency on the part of the pre- heated clay to release its soluble salts more readily than nor- CLAYWORKING PROBLEMS mal clay; this would indicate a greater tendency to show dryer efflorescence. Depending on the amount of clay, the time required varies from 3 to 5 hours. The rotary dryer seems to be the most suitable apparatus for this paper. A more detailed description of this investigation can be found in "Bulletin No. I Technologic Papers of the Bureau of Standards." It can be obtained free of cost by address- ing The Director, Bureau of Standards, Washington, D. C. Improperly Tempered Clay Causes Drying Losses 578. Indiana For the last ten years I hare operated a small yard during the summer season manufacturing brick, but due to the demand for drain tile, I bought a complete second- hand outfit of stiff-mud machinery last summer to supple- ment the existing equipment. This outfit included a pug mill, auger machine and automatic cutter. The outfit works very well, but my drying loss is enormous, sometimes losing forty per cent of a day's run. I am certain of this point, at least, my w'arc is not tempered evenly; some of it comes so wet that it is difficult to handle and the next batch is dry and hard. I have placed the best man I have available on the pug mill but results are but little better than before. Do you know of any scheme that will help the pugger to main- tain an evenly tempered batch of clay all of the time? From the data available in your inquiry, it appears that the pugger not only operates the flow of the water, but also the flow of clay. He has two varying quantities to deal with; he regulates the flow of clay to agree with the output of ware, endeavoring to secure an even flow. He has the tem- per water to regulate to suit the amount of clay in the mill and also has to watch the condition of the ground clay ad- mitted to the mill, with its variation in water content. To eliminate one-half of the difficulty, we recommend the CLAYWORKING PROBLEMS 161 securing of a clay feeder. By its use, the clay flow is regu- lated to suit the output, permitting the pugger to give his entire attention to the "feel" of the mud. Brick Crack in Drying 601. New York / am sending you by parcel post a small quantity of our shale, taken from a pit that -we have recently opened. This sample was taken after it had passed the screen. I am sending it to you in hope that you will be able to find out n'hy it is that, in making standard sice brick, it is ex- tremely fragile. The brick crack in the dryer and even show signs of fracture when they stand in the air, if the car is al- lowed to wait its turn into the tunnels. We are using a home- made, wooden pug-mill, about seven feet long, feeding into an auger machine. The brick look fine when first cut, but are rery fragile. After examining the sample, we are convinced that the trouble lies mainly in the clay's being ground too coarsely. The particles are large and the tendency to bond and be- come plastic enough for suitable working qualities is weak. This can be remedied in part by the installation of a screen that will reject the coarser particles, supplemented by screen plates in the dry-pan that are finer than those you now use. We also suggest that the pug-mill be lengthened to ten or twelve feet and that it be equipped with a feeder. Try hot water for tempering. This Dryer Does Not Dry 619. Pennsylvania We would like to have some advice about our dryer. We are making a soft-mud brick, six in a mold, placed on a wooden pallet, 414 brick to a car, the pal- lets being spaced three inches apart on the cars. The dryer holds 33.000 brick; we set 11,000 in the morning and make 11,000 in the afternoon, draiving the cars as the new ones CLAYWORKING PROBLEMS are put in this is, at the end of three days. Our trouble is that the brick are not always dry at the end of three days, but we hare to draw them, or stop making brick. The dryer is a home-made affair, 75 by 40 feet outside measurement. The outside w'alls are of brick, as well as a nine-inch wall that divides the dryer into tw'o chambers. The roof is about 5 : /2 feet aborc the tracks and is double boarded. On it we have about ten inches of clay, ivith a double pitch roof above this. We hare eight tracks, holding ten cars each, the ground being even with the tics, and our steam pipe is all between the tracks on the tics. There is 10,000 //. of steam pipe in all sixteen lengths by full length of the dryer. The diameter of the pipe is one inch. We have twelve ventilators up through the roof, that are ten inches square, and two stacks 16 by 38 in. and 24 ft. high. There are two sets of doors at the stack end of the dryer, the bottom of the inside doors being ten inches above the tracks. Our idea is to drazv the vapor down, under this door, and up through flic stack. At the other end of the dryer, we have a cold air flue eighteen inches square, the full width of the dryer which is 40 ft. with a ten-inch opening under each track, extending ten feet inside of the dryer, to help drive off tlie vapor. For steam, zvc have two 50-h.p. boilers, carry- ing 80 Ibs. pressure, day and night. Theoretically, there is no reason why this dryer should not dry 33,000 brick in three days. Practically, according to our questioner, it fails. Since the theory is correct and the prac- tice wrong, there is no way of solving the trouble at a dis- tance. \Ye would strongly urge the questioner to send for a brickworks' engineer one who makes a specialty of dryers paying a fee for his advice, but insisting that the advice be given after a personal inspection of the dryer. To Cure Blisters on Drain Tile. 606. Illinois ll'c are having a great deal of trouble mak- ing our large sice drain tile, especially the fifteen inch. They CLAYWQRKING PROBLEMS 163 run fairly well at the machine and do not show up any great loss in drying. They seem to be in first-class condition when set in the kiln, but when we open the kiln sometimes half or more of our large tile are spoiled entirely. They seem to blister or blow out in patches of from four to sixteen inches in diameter. Sometimes we have very little loss and yet so far as we can see, our clay, machinery and general process of manufacture are identical with the conditions that existed before these losses began to occur. We have lately found that some of our tile when dry, show blisters which are about a half-inch high and possibly six inches in diame- ter. When we break these open we find the surface of the clay somewhat polished, just as if there had been laminations which were not knitted together. If you or any of your readers can gire us any pointers, we will appreciate it, and if you want any more information we will be glad to give it to you or them. We are inclined to think that the difficulty lies either in unevenly ground clay or in unevenly tempered clay. Unless you have already taken every precaution to insure an un- varying supply of uniformly ground clay coming to the pug mill and there being mixed with an unvarying quantity of water, this is the most likely place to look for the solution of your blistering problem. If, on the other hand, you have taken every precaution along this line, and the trouble which you report, continues to exist, then there is a possibility that your clay is not sufficiently tempered or that it is forced into the auger or plunger in too dry a condition, and that lamina- tion is set up by friction in passing through the die. This is a very common cause of "bubbles" or "shelling." The reason is obviously a differential flow of clay through the die under high pressure not sufficient lubrication or too much friction. Also if the clay is not tempered thoroughly, it cannot knit together the smooth surfaces that are caused by the action of the auger, and these surfaces do not bond 164 CLAYWORKING PROBLEMS together sufficiently to resist dry shrinkage. It might be well also for you to look at your auger and see whether or not it is very much worn. A worn auger is a common cause of the difficulty which you have mentioned, although it is sel- dom given the proper consideration. Look into this part of your manufacture from the point where you grind your clay to the point where the clay leaves the die and see if you cannot find a remedy there, before going any farther. Trou- ble may, of course, be in the dryer but we are inclined to think that it lies earlier in your process. The above question was published in the Jan. 5th issue and an answer given which has brought forth some criticism. Ed C. Mead of the Enfield Vitrified Brick & Tile Company of Enfield, 111., writes us as follows: "I want to criticise the reply to question No. 606 in 'Brick and Clay Record' of Jan. 5th issue, in regard to blisters on drain tile. This is one trouble I learned to eliminate before I was large enough to do any firing, except slow firing. It is also a trouble encountered on a great many yards, and as a rule, with a little thought a speedy remedy is found. "To me it is absurd to connect the auger lamination with this trouble in hollow ware, nevertheless, it is true, this trouble is met with most frequently in the more plastic material. Lamination in drain tile is of little consequence when the ware is dried and burned properly according to circumstances, and is caused by the friction, 'on both ring and core of die,' of material, allowing the center of wall to travel more freely and naturally faster. It is easily under- stood how this condition will break the bond and leave lam- inations extending lengthwise and around the circle, and in some cases almost unbroken during any continuous operation of machine. Under the same conditions a plunger machine will produce the same results as the auger method. To elim- inate the blisters 'if noticeable in dried ware' dry slower in CLAYWORKING PROBLEMS 165 the early stages and if ware goes into kiln sound and then blisters, the cure would be to fire with less speed, being sure to maintain .an even and gradual increase in temperature. If you will furnish me the address of the brother claycrafter I will gladly furnish him the results of my experience after ascertaining more fully the conditions. ' My motto is : 'Help those in trouble. Boost clay products.' " To Prevent Slipping of Clay Bar 579. Ohio I am making a partition tile 3x12x12 inches in sice. The clay column as it comes from the die has not the weight to give a steady push to the cutter and, there- fore, the wires will not make a vertical cut but tear through diagonally, sometimes causing the bar of clay to crumple up entirely. I hare roughened the boards and have covered the same with course canvas, but in every case, each attempt has helped, but only temporarily. As soon as the boards get wet, the slipping starts again in spite of. my efforts. What do you think is the real trouble and how can we remedy itf There are several serious faults which may be the cause of your trouble. The die lubrication may be excessive, caus- ing a thin, slushy surface to appear on the column. This should be watched, and if you find it the case, this condition can easily be stopped by the adjustment of the lubricating device on your die. Perhaps the boards from the pug mill to the cutter may not be wide enough to give all possible grip to the bar of clay. This also can easily be remedied. The reel may be turn- ing stiffly. If so, loosen the set screws in the uprights. The bar of clay may be running down hill. This we be- lieve to be the most probable cause of your difficulty. In this case, adjust the cutter so that the receiving end is about one-eighth to one-quarter of an inch below the bottom of 166 CLAYWORKING PROBLEMS the lower side of the die, then raise the discharge end of the cutter so that it is from one-half to two inches higher than the receiving end. This causes the clay to flow uphill and the friction is, therefore, increased. Since publishing the above, we have received the following from James J. Hinde, of the Hinde Brick and Tile Company, of Sandusky, Ohio, who says: "A better remedy is to assist driving the cutting table with a small friction belt or sprocket chain which can be driven from the auger mill. The Effect of Artificial Drying on Clay ITS. NCI*.' Jersey ll'HI you kindly let me know what effect as to strength and quality artificial drying has on clay, li'hen dried at a temperature of 140 to 180 degrees F.f Ellis Lovejoy, answering the above question, says; "It depends entire!y upon the character of the clay. Some clays can be put into dryers and immediately subjected to tem- peratures much higher than 180 degrees, without in any way affecting the strength and quality, but there are other clays which are so tender in their drying behavior, that the lower temperature mentioned (140 degrees F.) would cause exces- sive loss. The effect upon ware depends upon two factors. First, the date of evaporation from the surface of the ware; second, the rate at which the water within the ware comes to the surface. Whenever the rate of evaporation is greater than the rate at which the water is brought to the surface by capillarity, the ware invariably cracks. When the rate of evaporation equals the rate of capillary action, we are on the dividing line between sound ware and damaged ware. When capillarity brings the water to the surface faster than it is evaporated from the surface, the ware will dry safely re- CLAYWORKING PROBLEMS 167 gardless of temperature, assuming, of course that the ware is symmetrical in shape and dries uniformly. Stiff Mud Brick Break in Drying 49. Missouri We are hat-ing trouble with our stiff-mud pressed brick. They break so badly, while drying on the yard, as to almost destroy the profits. We burn them very hard, but still they are very brittle. We are using the old-fash- ioned kilns. The clay has just enough sand in it to make it mold zvell. We would be glad to get some pointers for over- coming the trouble. In regard to the troubles of "Missouri", we hesitate to give any opinion whatever because the data is not sufficient. Brick break from a number of causes and one cannot tell at long range just what the cause may be. Clays are very uncertain in behavior and anyone who gives an opinion of a material, or an explanation of a trouble, without knowing the material and investigating the trouble, is merely guess- ing or at best assuming the clay to be of a certain class and the trouble to have a certain cause. Based upon ihis as- sumption one gives an opinion, but it may not at all fit the specific case. Brick oftentimes crack and break in the burning and the fault is attributed to the burning process, to the kilns per- haps or to the carelessness of the burner, when it may be that the trouble did not belong to the kiln at all. It may have been the quality of the clay, it may have been due to machine troubles introducing weaknesses into the brick, or the trouble may have originated in the dryer and only be- came apparent after the product was burned, yet. on the other hand, there are troubles which begin and end in the kiln. The trouble in the dryer may be due to the type of the dryer, to the drying behavior of the clay or to the machine. By changes in the clay mixture we can frequently overcome 168 CLAYWORKING PROBLEMS difficulty in the dryer without any change in the dryer, and frequently we can improve the machine structure of the brick and overcome the dryer difficulty, but on the other hand it sometimes happens that the dryer itself is at fault. Each variety of clay requires very different treatment in order to dry it safely and each treatment requires special dryer conditions. In view of all these difficulties it is absurd for anyone to advise another without some personal knowledge of the difficulty. In spite of this, however, it seems to us that "Missouri's" clay is one of those fine grained materials which has a weak structure and consequently it may break very easily under drying strains. Such clays when burned very hard are brittle, largely because of their uniformity and fineness of grain. They have no body, no skeleton structure; in fact, they are like a piece of brittle glass and any changes in temperature in the burning will cause them to break, and after they are burned they are likewise easily broken because of their brittleness. If his clay does not contain an excess of sand it may be that the clay will stand more dead material and we would suggest the use of coarsely ground kiln clinkers, which make an excellent binder. It seems to us that the weakness of his clay can be overcome by the addi- tion of some sort of binding material, and crushed bats or crushed kiln clinkers are the best binders we know. The addition of coarse sand might accomplish something, but it is not as good a binder as the other materials men- tioned. We merely suggest this as a possible solution to his difficulty, and the expense of making a test along this line will be a small matter. More Scum Trouble 240. Kansas I make a stiff -mud brick and find that it CLAYWORKING PROBLEMS shows scum on one side and on the tivo ends. The side that fosses over the rollers of the off-cutting table does not scum to speak of. The die is lubricated by -water. Assuming that the die lubrication is distributed evenly to all four sides, the clay column is exposed to the same condition at top, bottom and sides, and the passing over the rollers of the cutting table would not affect it sufficiently to prevent any one of the surfaces becoming scummed in the dryer or kiln, if the tendency to scum was in the clay or the green brick. We hazard a guess, however, that the manner of setting the brick, either on the dryer car or in the kiln, is such that the faces and ends of the brick are exposed, and the backs of the brick set close together. The bottom of the clay column, which passes over the rollers of the cut-off, having taken the form of brick, rests upon the off-bearing belt, which may mark it. This would make that side (the lower) the "back." The idea that the change occurs at the cutting table can be eliminated by marking some of the brick "T" for top of co!umn and some "B" for bottom of column, and then seeing that the sides so marked are all treated as "backs" and so set on the dryer cars and in the kilns. Read Professor Binn's article on efflorescence in the Nov. 18 issue of this magazine and do some experimenting with your clay. Watch the water very carefully, also not only the pugging water, but the water you are using for lubrication. Seems to Have the Old Scum Trouble 489. Ontario We are making a wire-cut brick, using a Freese cutter and lubricating the bar with castor oil. The brick are being dried in a continuous tunnel dryer, the heat for which is supplied by a waste heat system, supplemented by an auxiliary wood furnace. We are troubled with a white mark on the surface of the brick. This white mark is discern- ible on the brick as they come from the dryer. We have CLAYWORKING PROBLEMS thought it to be caused by the oil zve arc using, or possibly by the ashes from the auxiliary furnace settling on the oily surfaces. Can you recommend to us some brand of oil that will cure this trouble, of suggest some other remedy? We do not believe that the oil has anything to do with the matter, and are under the impression that your trouble is as old as brickmaking itself or at least as old as artificial drying and burning with coal. It looks like "scum," about which every man who has written about brickmaking has, or will, at some later day, write one or more articles. Scum, or efflorescence is caused by salts in the clay. These are de- veloped, sometimes, in the dryer, while again they may not show until the brick are burned. And then again, many in- stances are known where the "scum" does not show until the brick have been built into the wall. We would advise, first, that you dry at least one car of brick in the open air, under shed cover, and where it is not exposed to any sulphur fumes from burning coal. If, when they are bone dry, they show no white mark, you will have located a part of your trouble that is, that the dryer brings out the "scum." Then go after the scum with carbonate of barytes. Dry Pan Capacity. 5."). Texas Kindly ad?'ise us as to whether one nine-foot dry pan will be sufficient for grinding material of the soft fire-clay variety for tzvo four-mold presses to manufacture forty thousand high grade manganese face-brick per day. Would also appreciate information as to the use of manganese that is what proportion should be used per thousand brick. No one can predetermine how much clay one pan will grind. It is customary to lay out a plant with one pan for each four-mold press but frequently clays are found that grind and screen so rapidly as to make it possible for one pan to grind all of the clay for two presses. If the clay is of the character which insures its being easily ground, you are safe in install- CLAYWORKING PROBLEMS 171 ing a single pan for forty thousand brick but, since there is an element of doubt, it is well for you to provide for a second pan, even going as far as to build the foundations for it. The chances are, however, that if you intend making a high grade product which will require finely screened clay, two pans will be necessary and both will be run to their maximum capacity. Regarding the use of manganese it is well to provide, in the first place, for a measuring device and so secure a uni- form proportion of ground clay and manganese. Otherwise there will be a distinct difference in the color of the product and this will necessitate a great deal of sorting and a large number of small hacks that do not "match up" to the stand- ard product of the plant. It is recommended at times that this manganese be fed into the pan but this is not so practical as arranging for a proper mixing of the clay and manganese after the clay has been reduced to the proper fineness and been passed through the screen. The reasons for this are obvious. The degree of fineness to which the manganese is ground before it is mixed into the clay has a material effect upon the depth of color in the finished product. The amount of manganese which should be used can be determined only by experiment as nearly every clay needs a different amount of manganese in order to produce a given result. Tile Cracks in Drying 687. Iowa This plant has, ever since it started, been both- ered with the tile cracking tchile it was in the dry sheds. We use surface clay, mixing the four top spades. The two top spades are a very dark clay and the two lower ones are yel- low or bluish clay. They are mixed after removing about eight inches of over-burden. We use a machine with a bridge just back of the dies, with a stem, on it to hold the core or center piece. There is only about eight inches between the die and the bridge for the clay to unite and I 172 CLAYWORKING PROBLEMS have thought that a great deal of the cause of the cracking was due to this bridge cutting the clay up b'efore it went through the die. I cannot bclie-rc that ours is a bad clay but do believe that the main fault is in the machine. Before answering this question it was necessary to write our correspondent asking for more information in connec- tion with his process, particularly in connection with clay preparation and the answer follows : My clay is hauled in the clay shed with cars and I keep one man in the shed to level it off as it is dumped, so that it will get mixed thoroughly. It is very wet now and I grind the broken tile in the sheds, using a dry pan and then mix the ground burned clay with the ra^u clay and this makes it stiff enough to insure the ware's coining from the machine suffi- ciently stiff to permit of its being handled. The clay is shov- eled on to a belt or clay conveyor and is dumped from that in- to the crusher rollers which set above the machine. This ma- chine is a pug mill and auger machine combined, consisting of an eight-foot pug mill with about three feet of augers. I de- pend upon the pug mill to do tlic tempering. When my clay gets dry enough I use water in the pug mill and zvould say that this water comes from the supply tank to the boiler. It is neither hot nor cold but just a little warm. When the clay is wet, as it is at present, I do not use any tempering water at all. You will understand that I use the dry pan only to grind broken tile, but do not use it in connection with the raw clay. The bridge plates in the machine are rough (corrugated). The tile crack lengthwise when run soft and when run very still, they have a few cracks which run around them. Some will check two or three inches into the end and others will crack clean through. I have some five-inch tile in the shed now that have cracked in three places and have come apart into three pieces. These cracks are exactly where the wings are on the bridge. It depends on the iveather when they start cracking. If the weather is warm and dry, they will start cracking about the third day after they are put in the shed but if it is wet CLAYWORKING PROBLEMS 173 and cool, they will not crack until about the fifth day. As soon as I notice them starting to check, I put the men in the shed and turn over the tile end for end; this seems to help and stops any more from cracking, but this process is expensive, and if the tile are allowed to go too long without turning, there is an awful waste. I cannot say that there is any "safe" period when the tile do not crack, only as I have stated above. After the tile are in the shed (which is a natural air dryer with doors on the side to raise and lower) I leave these doors closed until the tile are well set and have started to dry; then I open the doors on the opposite side from the wind, but not on both sides, until the tile are about two-thirds dry. At that time I figure that if the wind is not too strong, it will not harm them to open the doors on both sides. It takes me from two to four weeks before the tile are ready for the kiln. Answering your questions as to the formation of the die, etc., n'ould repeat what I have already said regarding the bridge which is that it sets about eight inches back of the die and that the core is fastened to it (the bridge). The augers are about three inches back of the bridge. The five-inch and six- inch are the ivorst sizes for cracking, although the other sises crack a great deal more than they ought. The walls of my five-inch are three-quarters of an inch thick and the walls of the six-inch are thirtccn-sixtcenths of an inch thick. The tile arc cut thirteen inches long and the shrinkage in drying is three-eights of an inch in diameter. The shrinkage in burning is one-eighth of an inch. This burning shrinkage is increased in the case of the tile that are set right around the fire boxes and where, as a rule, the tile are burned black. Here the five-inch will shrink one-quarter of an inch and the six-inch will shrink just a little more than this. The augers I am using at the present time were new in April of this year and I estimate that they have not made more than one hun- dred thousand tile. My five-inch and six-inch dies were new in the spring of nineteen-fourteen. The five-inch die has made about two hundred and twenty-five thousand tile and 174 CLAYWORKING PROBLEMS the six-inch die has made about one hundred thousand. Re- garding the other dies, I fear that I could not say how old they are or how many tile they have made. A short time ago, Professor Stull (then of the University of Illinois) wrote in connection with an answer that he made through this department that it was often-times as difficult and practically impossible to give a remedy for a manufac- turing defect as it was impractical, and generally impossible, for a physician to prescribe for an ailment that was described to him by mail. The patient has a way of telling all of the symptoms excepting the one which will lead to the correct diagnosis. In a case of that kind the doctor can do but little more than hazard a guess and since our correspondent has gone to the trouble of describing his problem so minutely, "Brick and Clay Record" will hazard a guess and it is that the trouble lies largely in the thickness of the walls of the tile. We would suggest that the five-inch tile be reduced to one- half inch thickness (burned) and the six-inch tile to be between nine-sixteenths and five-eighths (burned). This thickness gives sufficient strength and allays in great measure any tendency toward unequal drying. It is, as a rule, un- equal drying that causes the split cracks along the line of the three core supports or the spider bridge. It would be well to wrap a few wires around the bridge plates in order that the clay passing into the die may be torn up and the chances for rebonding increased. There is, from the description that has been given, a great likelihood that the clays are not thoroughly mixed as they come from the pit. One man in a dry shed may be capable of doing this work but there is a good chance that he is not doing it. If it were possible to install a mechanical clay mixer, this machine would be very liable to pay for itself in a very short time, if not in labor saving, then in better ware. There seems to be a hit-and-miss method in connection CLAYWORKING PROBLEMS with the addition of dry ground clay to the wet clay and there is a great question as to whether the same results will be obtained in drying and burning ware that is made from three different clay propositions. This correspondent has, first; semi-wet clay that is used without the addition of grog and without tempering water ; second ; wet clay that is mixed with grog ; third ; dry raw clay that has to be mixed with tempering water. Any number of experiments could be made and improvements added to a drying process but when they were all finished, they would not give any definite re- sults for the reason that it would be hard to calculate the basis that is, the exact character of the clay upon which the experiments were made. This takes us back to the question of, in the first place, a proper clay mixing machine and it looks as though this plant could use to advantage some in- expensive clay storage system which would provide for the clay's being brought in and stored in an open shed where it can be air dried. This shed could be so arranged as to be in itself a clay mixing apparatus. There is no doubt but that it would improve the c'ay to be weather slaked and weather dried before going to the crushing rolls. In this way a mixture will be assured that is reasonably uniform, not only as to the proportions of the clays that compose it, but the dryness of these c!ays. This condition will insure the amount of tempering water that is, no more tempering water will be required at one time than at an- other and, as a consequence, some dependency can be placed upon the action of this tempering water a matter that is very much in doubt at the present time. There is reason to believe that the nose of the auger is too close to the bridge and it would be well to place a wooden washer about two inches think between the bridge and the die support (or head-piece) and the barrel of the machine. This will shove the die about two inches farther from the auger then it at present is and the pressure will not be so intense on the clay passing the bridge. This will have a CLAYWORKING PROBLEMS tendency to prevent the "shining up" of the clay and so help it to knit together as it passes through the die. There is also a possibility that the forms on your auto- matic cutter may be too small and in this way, the tile may be squeezed and bridge cracks open up. The same may happen in handling. Another point is that your tile should be just hard enough to handle safely; too stiff is just as injurious as too soft. Best of all since this correspondent says that the trouble in question has existed for years, (and it is to be presumed that during these years the yard has had several superin- tendents) much could have been saved by the employment of an expert "trouble doctor" several years ago. Too many owners of clay plants and too many superintend- ents are disinclined to admit that they have met with a problem that is entirely beyond them. They have a way of experimenting and of trying to do away with the trouble without expert advice and in this, the man who prefers to dose himself with patent medicines, rather than submit to a thorough medical examination by an approved prac- titioner, they meet with but little success and an organic disease grows worse with the years. In this case the "or- ganic disease" seems to be eating its way into the bank ac- count and there seems reason to say that the hiring of an expert, even though it necessitate the expenditure of a sum that would be several times as great as that paid to the super- intendent, would stop a leak which is seriously threatening the well being of this plant. The Question of a Second Machine 695. Iowa We have a steam dryer and our clay, while very slow to dry, works all right if the dryer is not rushed. W e are considering the advisability of installing a second ma- chine so that we could run part time on drain tile or hollow block and part time on brick. At present if I change the ma- CLAYWORKING PROBLEMS 177 chine die from hollow ware to make brick, I get too much brick in the dryer. If I could keep a quantity of drain tile, hollow block and brick in the dryer I could take them out and burn them as I wanted to the tile soft and the brick and blocks harder. I hare a forty H.P. motor which gives just enough power to run the one machine. Could I run it on a main shaft and then over to the two machines, running only one at a time? In other words, does running to a line shaft tvcaken the power? If your plan is to obviate any loss of time in changing the dies then it is an excellent scheme to have two machines. Otherwise the only advantage that you would get is that you would have some insurance against shut-downs, due to either of the machines breaking down. Another advantage is, possibly that you could adjust the machine that made your hollow ware so as to work better on that particular kind of material and you could certainly get a more exact adjustment on the machine which worked on brick alone. In other words, you could make both of the machines "specialize" on the product that they were producing and in this way get a great economy out of both. The question of setting one ware on the other in the dryer in such quantity as to allow you to draw one kind of ware or the other would not, according to our way of thinking, be settled by the installation of a second machine. It seems to be more a case of calculating just what ware you want to set and how much of it, and then making just that amount of ware. Certainly this situation would not be improved by having a second or even a third machine that is, unless you are using a differently tempered clay, or a different clay al- together for the various kinds of ware that you are making. In that event, different pug mills would be an advantage as well as different machines and dies. In belting your motor to a main line shaft and then string- ing two belts one to each machine you have an additional load to carry, due to the friction of your shaft on its bear- 178 CLAYWORKING PROBLEMS ings and the power required to turn over the additional trans- mission machinery. The power dropped should not exceed five per cent, or approximately two and a half H.P. There- fore, unless you can safely overload your 40 H.P. motor, your available transmitted power would be about 37^2 H.P. Difficulty in Grinding Wet Shale 699. Minnesota We arc having difficulty in getting wet shale through our dry pan. Can you suggest the cheapest and best remedy? Temporary relief may be obtained by mixing the setter's waste (that is, the unburned ware which comes to the kilns, but which is not sufficiently perfect to set) with the wet shale that is fed to the dry-pans ; this, however, is only tem- porary, since all of the available dried clay will be used up in a very short time. We are assuming that you are already using all of the broken burned ware that your clay will stand. On the other hand, there are clay driers advertised in "Brick and Clay Record" that would take care of your problem and do it in a very satisfactory manner. This, however, is an installation that attains its maximum efficiency when the clay is wet all through the year, which we assume is not your case. Your remedy seems to lie in installing a clay storage sys- tem with conveyors that will handle the clay after it has been weather-dried. That will insure a better clay mixture and at least in the majority of cases a better and more uniform product. Discoloration in Painted Hollow Tile Walls 703. Pennsylvania In several cases, where plaster has been applied to the inner surface of our hollow clay tile or clay tile furring, and then painted, it has been noticed that the paint blisters, bubbles or discolors. We hare a case at CLAYWORKING PROBLEMS 179 present, in which our tile was used for the zvalls of a church. The plaster was applied directly to the tile walls, and an oil paint immediately put on the plaster. Large blisters or bub- bles some of them as large as a man's hand are now form- ing on the walls, and under these blisters or bubbles, a creamy, granular substance appears that has a decidedly salty taste. There is a great deal of talk about the occurrence, and some interests are trying to blame the tile. We feel that the tile is in no way to blame. We have had numerous build- ings erected where a lime mortar is used and in these we have had no trouble with any deposit or efflorescence. Our tile is frequently left on the hack heaps for nine months or more and in no case have we found any discoloration upon it. We do find, however, that when the tile is laid up zvith cement mortar, an efflorescence appears on the tile around the joints. We have had our tile tested, and the absorption is under two per cent. In the case alluded to earlier in this let- ter, cement mortar zi'as used, and we feel that the paint was applied to the plaster before it (the plaster) was dry, and perhaps before the cement joint had been given an oppor- tunity to thoroughly dry out. We feel that, in this case, the plaster has absorbed or combined zvith the salts in the cement mortar joints and has taken the substance that causes the blisters in the paint, from the cement. We would like to hear from you as to whether you know anything about similar occurrences and whether or not there is a way of preventing them. We have suggested the use of a waterproofing com- pound in the mortar, but several masons and plasterers, zvith whom zvc have consulted, tell us that there is no satisfactory zt'aterproofing compound made that can be used in this way. They say that the only satisfactory treatment is to use a zva- terproofing paint, applied directly to the entire inner surface of the tile wall, and as we all knozv, this is too expensive a process to be considered as a commercial proposition, at least in a large number of building enterprises. We are of the opinion that the trouble which has arisen in the case mentioned is due entirely to the paint's having 180 CLAYWORK1NG PROBLEMS been applied to the plaster before the latter had been thor- oughly dried, and that the blisters in the paint were caused by the evaporating moisture in the plaster (and perhaps, the joint) which was seeking an outlet. Plaster is, and has been applied directly to the inner surface of tile walls, all over the country, and so far has given very satisfactory results, the case cited by our correspondent being one of very few that have come to our notice. This opinion is strengthened by the fact that the correspondent's tile has a very low absorption much lower than the average. This, and the fact that he has never had any efflorescence appear on the tile that was hacked in his yard even after an exposure of more than nine months is pretty good evidence that the treatment, and not the tile, is at fault. It looks very much as though the blistering was due to some constructional fault and this may be the use of cement with tile of so low an absorption. The fact that the tile takes comparatively none of the mois- ture from the cement leaves only the inner and outer sur- faces of the joint as points where the excess moisture can escape. It may be that the outer surface of the joint dried out much more quickly than the inner surface, particularly as this inner surface was again wetted when the plaster was applied to it. Capillary attraction may have been set up that brought out all of the salt that was in the cement, or in the water with which the cement was mixed (see "How to Pre- vent Efflorescence in Finished Brickwork" in the Sept. 7 issue of "Brick and Clay Record") and that the plaster would have been scummed, even if not painted. This thing has happened in buildings where impervious paving brick were used and where plaster was applied without furring. In that case it was clearly the fault of applying the plaster before the cement joint had been given an opportunity of drying out, and was caused by the church committee's insisting upon the contrac- tor's turning over a finished building within a certain speci- fied time. In the case cited by our correspondent the mois- ture in the plaster was held back by the comparatively im- pervious paint film that was put on by the decorator, and CLAYWORKING PROBLEMS 181 the conditions made so much the worse. With regard to the appearance of efflorescence around the cement joints, it would appear that this is a problem that can be solved by the use of barium. We again refer our readers to the article by Arthur E. Williams in the Sept. 7 issue of this magazine. Brick and Clay Record's nrHESE BOOKS have been selected as having especial in- -* tercst and value to the clayworker. They are confidently offered as the best printed information on 'the subjects cov- ered that has appeared in book form and in the English lan- guage. Any book in the following list unll be sent on receipt of price. None Zfill be sent on approval. Brick Drying (English Edition) .$1.00 Brick Houses and How to Build Them (Radford) i.oo Bungalows, Camps and Mountain Houses 2,00 Ceramic Calculations 1.20 Clay Glazes and Enamels (Grif- fin) 5.00 Clay workers' Handbook (Searle) 2.00 Engineering for Land Drainage (Elliott) 2.00 Estimating and Contracting (Rad- ford) 2.00 Garage and Motor Boat Houses. . i.oo The Glazer's Book (Raes) i.oo The Hollow Tile House (Squiers) 2.50 How to Analyze Clay ( Ashby) . . . i.oo 182 Book Department The Manufacture of Glazed Bricks (English Edition)... 2,50 The Manufacture of Roofing Tile (Worcester) 75 The Manufacture of Roofing Tile (English Edition) i.oo "Masonry" (Howe) 1.50 "Modern Brickmaking" (Searle) . 5.00 One Hundred Bungalows (BBA) .50 Pottery (Cox) 1.25 Practical Brick and Tile Book (Dobson- Hammond) 2.40 Producer Gas and Gas Producers (Wyer) 4.00 Refractories and Furnaces (Ha- vard) 4.00 Scumming and Efflorescence (Lovejoy) 50 Seger's Collected Works (Con- densed) 3-50 Sewage Disposal Works: Their Design and Construction (Easdale) 4-<>o 183 Brick and Clay Record A Semi-Monthly Magazine Special- izing in Clayworking and Ceramics Published the First and Third Tuesdays in each month at Chicago Subscription Price (One Year) $2.00 ($3.00 in Canada and Foreign Countries) Sample Copy Free on Request Brick and Clay Record 445 Plymouth Court Chicago, U. 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