CHAPTER XV.

ABRASION, SPECIFIC GRAVITY.

_Abrasion._--In this country it is not customary to test bricks and stone by means of the abrasion process, though many English materials have been dealt with in this manner on the continent.

Abrasion tests are of special value in regard to paving bricks, and this mode of experiment is largely carried out in the United States. As Mr. H. Ries remarks,[21] the abrasion test approximates closely the conditions under which the paving brick is used, and is, therefore, an important one. The usual method of conducting this test is to put the bricks in an ordinary “foundry rattler,” filling it about one-third full. It is then rotated at the rate of about 30 revolutions per minute, and about 1,000 turns are sufficient. The bricks are weighed before and after to determine loss by abrasion.

A more recent modification is to line the “rattler” with the bricks to be tested and then put in loose scrap iron. This is claimed to give more accurate results, and avoids loss by chipping due to the bricks knocking against each other, as in the previous method, although that has been somewhat obviated by Professor Orton, jun., by the introduction of a few billets of wood into the rattler.

The abrasion test may also be made by putting the weighed bricks on a grinding table covered with sand and water, and noting the weight before and after grinding. This last method seems to us to be decidedly the best, provided the bricks be weighted, that the weight is constant, that the feed of sand and water is uniform, and that the bricks to be tested are placed equidistant from the centre of the turning table. If this last point be not attended to, it will be obvious that in course of the revolutions the sand will tend to accumulate towards the centre of the table, and the bricks placed in that vicinity would receive more than their fair share of abrasion, as compared with those bricks situated near the edge of the table. Conversely, those bricks near the periphery would be subjected to greater grinding action, from the circumstance that the table would move faster underneath them than under those bricks nearer the centre of the table.

The bricks should certainly be weighted in such abrasion tests, and it seems desirable that the weights should be so adjusted that the weight of the brick is also taken into account. It is obvious that the abrading action of, say, street traffic, will be the same on a brick, no matter what the latter weighs, depending on the area of surface exposed to traffic. And if we experiment with one brick, weighing say 7 lbs., and another weighing 14 lbs., the greater weight of the latter, will (_cæteris paribus_), by the abrasion tests as usually adopted, give a much higher result than would the lighter brick. On the other hand, if the 7 lbs. brick be weighted another 7 lbs., then the results would be strictly comparable, provided always that the area exposed to abrasion in each case be the same, and that the other conditions we have laid down are strictly observed.

Knowing as we do that the rough and ready method of “rattling” cannot possibly give truly comparative results, we do not intend to enlarge much on the results of the American tests; but the following are suggestive as shewing the connexion between the tests for absorption, rattling, and strength combined.

Some valuable and interesting tests were recently made by the Ohio Geological Survey, to determine the relative merits of fire-clays and shales for the manufacture of paving bricks, as well as the influence, if any, of the method of manufacture adopted. Twenty-two varieties of shale bricks, or bricks the largest constituent of which is shale, were grouped together: fifteen varieties of fire-clay brick; four varieties composed of shale and fire-clay mixed in equal proportion; and three varieties made from Ohio River sedimentary clays. The averages of these four classes of results were as follow:--

-------------------------------------------------- TESTS OF FIRE-CLAY AND SHALES.--PAVING BRICKS. ----------+-----------+---------+----------------- |Absorption.|Rattling.| Crushing. +-----------+---------+--------+-------- | | |Square | Cubic | | |Inches. | Inches. | | +--------+-------- Shales | 1.17 | 17.61 | 7,307 | 1,764 Fire-clay | 1.62 | 17.32 | 6,876 | 1,678 Mixture | 1.44 | 18.72 | 5,788 | 1,400 River Clay| 1.36 | 19.02 | 4,605 | 1,176 ----------+-----------+---------+--------+--------

From a series of tests recently made by Mr. Fickes,[22] the following factors were educed:--

1. A brick which stands the “rattling” test well, has ample crushing strength and rarely chips under less than 5,000 lbs. per square inch, or crushes under less than 10,000 lbs. The crushing strength tends to vary with the resistance to abrasion, however, but more slowly and irregularly.

2. The transverse strength also tends to vary with the resistance to abrasion, but more slowly and irregularly.

3. The toughest bricks usually absorb the least water.

_Specific Gravity._--The practical value of knowing the specific gravity of a brick has, perhaps, been a little over-rated by writers on the subject. At the same time we do not deny that there is some use in ascertaining this property. Foremost, we have to mention its value in conjunction with absorption in arriving at a rough and ready means of gauging the strength of a brick, without having actual recourse to the crushing machine. It appears to us, however, that the specific gravity of bricks is rarely quoted in a proper manner, and until there is one uniform method, the results will always be at a discount. We allude to the fact that some experimenters take the specific gravity of a porous brick, without stating whether the amount of water absorbed, during the process, was taken into account in arriving at the specific gravity or not. Theoretically, of course, the substance to be dealt with is non-porous, and experimenters, worthy the name, either render the brick waterproof, or, ascertaining the amount of water the brick has absorbed, take that into consideration in calculating results.

The writer is in the habit of quoting the specific gravity in two ways, viz.: (_a_) the true specific gravity, and (_b_) the specific gravity of the particles. In an elementary treatise like the present, however, it is not desirable to enlarge on this subject.

THE END.

FOOTNOTES

[1] This, and all other technical terms used, will be explained in an alphabetical glossary at the end of the book.

[2] “Canal and River Engineering,” p. 315.

[3] See, Geikie’s “Text Book of Geology,” 1882, p. 72.

[4] Information on this subject will be found in Mr. J. H. Collins’ work, “The Hensbarrow Granite District.” Truro, 1878.

[5] “Text Book of Geology,” 1882, p. 85.

[6] “Aids in Practical Geology,” 1893, page 36.

[7] See E. S. Dana, “Minerals and How to Study Them,” 1895, p. 154.

[8] Consult “Applications of Geology,” etc., by Prof. Ansted, 1865, p. 116, _et seq._

[9] “Industrial Resources of the Tyne, Wear and Tees,” 1864, p. 204.

[10] R. H. Scott, “Elementary Meteorology,” 1883, p. 137.

[11] Report of British Association for 1846, Part II., p. 17.

[12] Geological Magazine, N.S., Dec. III., Vol. V, 1888, pp. 26 _et seq._

[13] Such as “The Study of Rocks,” by F. Rutley: “Aids in Practical Geology,” by Prof. Grenville Cole; “Tables for the Determination of the Rock-forming Minerals,” by Prof. Lœwinson Lessing; “Petrology for Students,” by A. Harker; and especially “Microscopic Physiography of the Rockmaking Minerals,” by Rosenbusch (transl. Iddings).

[14] Consult the works on petrology previously mentioned.

[15] The mode of preparation of thin rock sections for examination by the microscope is described in much detail in the works of Mr. Rutley and Professor Cole previously alluded to; also in “Outlines of Field Geology,” by Sir Archibald Geikie, 1882, p. 202 _et seq._

[16] 16th Ann. Rep. U. S. Geol. Surv. (1894–95), pt. IV., p. 532.

[17] 16th Ann. Rep. U. S. Geol. Surv. (1894–95), pt. IV., p. 539.

[18] “Testing of Materials of Construction,” 1888, p. 438.

[19] _British Clayworker_, April, 1896, Supplement, p. iv.

[20] _Op. cit._ p. iv.

[21] 16th Ann. Rep. U.S. Geol. Surv. Pt. IV., 1895, p. 532.

[22] _Engineering News_ (U.S.), Dec. 13th, 1894.

INDEX, &c.

Abrasion tests, 146

Absorption of bricks, 132

Acids defined, 76

Actinolite, 69

Air, chemical composition of, 105

Albite felspar, chemical composition, 34

Almandite, 68

Aluminium, under blowpipe, 73

Anorthite felspar, chemical composition, 34

Aragonite, 49

Bases defined, 76

Basic bricks, 90 dolomite for, 55 magnesite for, 56

Biotite mica, 43 under blowpipe, 73

Black bricks, 101

Blowpipe, 58

Blue bricks, 101

Bluish-black brick-earths, 27

Boulder clay, 50

Bourges, Oxford clay of, 24

Bovey Heathfield clays, 20

Bracknell bricks, 135

Brick earths, artificial mixing, 42 artificial mixtures, 94, 95 bluish-black, 27 boulder clay, 50 brown, 27 chalk pebbles in, 50 changes in character on being dug into, 2, 5, 10 chemical composition of, 23, 52, 83, 84, 85 chemistry of, 58, 75 chert in, 41, 42 coprolites found in, 51 Cornwall, 35 Crayford, 1 Devon, 35 Erith, 1 estuarine, 21 fluviatile--Chapter I., 1–16 fossil shells in, 50 Ilford, 1 Kimeridge clay, 26 lacustrine--Chapter II., 17–21 Lincolnshire, 21 London clay, 33 marine, 22 mineral constitution, 28 minerals found in (see Kaolin, Felspar, Quartz, Flint, Mica, Iron, Calcite, Aragonite, Selenite, Dolomite, Salt, etc.). Northamptonshire, 21 North-Eastern France, 20 Oxford clay, 33 Reading mottled clay, 19 of river terraces, 12 salt in, 25 sea-shore, 25 section of fluviatile brick-earths, 10 several kinds of fluviatile, discussed, 14, 15 Switzerland, 89 Thames Valley, 1, 2, 3, 4, 5 value of chemical analyses of, 28, 29

Brickmaking: earths suitable for (see Brick-earths)

Bricks, abrasion tests, 146 absorption of, 132 basic, 90 Bracknell, 135 colour of, 100 Dinas, 81 discolouration of, 114 durability of, 103 effect of conflagrations on, 117 efflorescence on, 110 London stock, 97 micro-structure of, 29, 118, 128 rubber, 29 specific gravity, 146, 149 Staffordshire blue, 99 Stourbridge, 82 strength of, 136 vegetable growth on, 113 weathering of, 105, 113

British Museum, fossils in, from brick-earths, 3, 26

Bronzite, 69

Brown brick-earths, 27

Burning bricks, 94 changes produced by, 98 temperature, 89

Calc spar, 49

Calcite, 39, 49 behaviour in kiln, 39 micro-structure of, 131 under blow-pipe, 74

Californian magnesite, 56

Carbon dioxide in quartz, 41

Carbonate of lime (see Calcite, Aragonite)

Chalk in brick-earths, 1 mixed with brick-earths, 53 pebbles in brick-earths, 50

Chateauroux, Oxford clay of, 24

Chemical affinity, 76 analyses of brick-earths, 28 analysis, 77 composition of air, 106 composition of brick-earths, Dinas, 52 composition, china clays, 78 composition of fire-clays, 80 composition of Kieselguhr, 92 composition of magnesian limestones, 90 composition, pottery clays, 82 composition of slates, 87 disintegration of rocks, 20 re-agents, 60, 63, 71

Chemistry of brick-earths, 58, 75

Chert, 41

Cheshire, salt in clays in, 25

China-clays, behaviour in the kiln, 36 chemical composition, 78 Cornwall, 35, 36, 37 Devon, 35

China-clay (see Kaolin and Felspar) thickness of, 38

China-stone, decomposed, 37

Colour in the kiln, 98, 99

Colouring matter of bricks, 45 of bricks, 53

Colour of bricks (see Blue, Black, etc.).

Coprolites: impure varieties of phosphate of lime found in brick-earths, 51

Cornish granite, 35

Cornwall, china-clays, 35, 36, 37

Cracks formed in bricks, 52

Crayford, brick-earth at, 1

Dartmoor granite, 55

Denudation, agents of, described, 6, 7 of sea-cliffs, 22

Devon, china-clays, 35

Diatomaceous earth, 42, 91

Dinas bricks, 52, 81

Discolouration of bricks, 114, 135

Dolomite in brick-earths, 55 micro-structure of, 131 under blow-pipe, 74

Drying bricks, 94

Durability of bricks, 103

Efflorescence on bricks, 110

Electric furnace, 33

Elephants’ remains, found in brick-earth, 2, 3

Erith, brick-earth at, 1

Estuarine brick-earths, 21

Expansion of bricks and variations of temperature, 115

Felspar, 34 chemical composition of, 34 micro-structure of, 129 under blow-pipe, 73

Ferruginous matter (see Iron)

Fire-bricks, Dinas, 52 earths suitable for making, 21 effect of lime in, 53 Kieselguhr for, 42, 91 strength of, 136

Fire-clays, chemical composition of, 80, 81 Newcastle-on-Tyne, 80 tests, 148 Welsh localities, 81

Fishes, fossil, 25

Flint, 39, 41 behaviour of in the kiln, 42, 43 implement: an implement, or tool, made of flint--in the sense indicated in this work an implement made by pre-historic man. implements, found in brick-earths, 3, 5 micro-structure of, 129 origin of, 41

Fluid inclusions in quartz, 41

Fluorine in clays, 59

Fluviatile brick-earths: brick-earths that have been deposited in rivers

Fossil shells, carbonate of lime in, 50 shells found in brick-earths, 4 sponges, in flint, 42

Fusion of brick-earths in the kiln, 29, 31

Gault clay, 51

Glaze, micro-structure of, 119, 120

Glazing, salt, 57

Granite, Cornish, 35 Dartmoor, 35

Granites, weathering of, 36

Greece, magnesite in, 56

Green bricks, 101

Grizzly bear’s remains found in brick-earth, 2

Gypsum in brick-earths, 54 under blow-pipe, 74

Heat, bricks affected by, 117

Hippopotamus remains found in brick-earth, 2

Ilford, brick-earth at, 1

Infusorial earth, Tuscany, 92

Iron, 44 a constituent of brick-earths, 44 behaviour in the kiln, 45 bricks, Saarbrücken, 92 micro-structure of, 130 mode of occurrence in brick-earths, 45 under blow-pipe, 73, 74 vapour in the kiln, 46 pyrites, 46, 131 pyrites, behaviour in the kiln, 48 pyrites, under blow-pipe, 74 pyrites, weathering of in bricks, 48

Jurassic estuarine clays, 21

Kangaroo rats, fossil, 25

Kaolin: a hydrous silicate of alumina, derived chiefly from the decomposition of felspars

Kaolin, 31 behaviour in the kiln, 32, 33 chemical composition of, 78 micro-structure, 32, 33 under blow-pipe, 73

“Kaolinised” matter, 33

Kilns, temperature in, 98

Kieselguhr: a diatomaceous earth

Kieselguhr, 91 chemical composition of, 92 of the Isle of Skye, 42

Kimeridge clay brick-earth, 26

Labradorite felspar, chemical composition, 34

Lacustrine brick-earth: that laid down or deposited in lakes brick-earths--Chapter II., 17–21 brick-earths, formation of, 17, 18

Lime, builder’s, 52 in bricks, 52 in manufacture of fire-bricks, 53

Limestone, a flux, 54

Limonite, under blow-pipe, 73

Lincolnshire brick-earths, 21

Loam: sandy clay

London stock bricks, 97, 140

Magnesian limestones, chemical composition of, 90 limestone (see Dolomite)

Magnesite, 55 behaviour in the kiln, 56 Californian, 56 in Greece, 56 Styrian, 56 under blow-pipe, 74

Malachite, 67

Malm bricks, 53, 86

Manganese, under blow-pipe, 74

Marcasite, 46, 47 behaviour in the kiln, 48 weathering of, 47, 48

Marine brick-earths: those laid down or deposited on the sea-floor

Marine brick-earths, not so variable in character as river, lacustrine, or estuarine, 23 brick-earths--Chapter III., 22–27 brick-earths, origin of, 23

Marl: clay containing much lime.

Mica, 43 behaviour in the kiln, 44 micro-structure of, 130 under blow-pipe, 73

Microscopes, 121

Microscopes, use of, 59 useful in analysing earths, 30

Micro structure as a means of determining fusibility of minerals and brick-earths, 43 of bricks, 118, 128

Minerals, their behaviour in the kiln (see Kaolin, Felspar, Quartz, Flint, Mica, Iron, Calcite, Aragonite, Selenite, Dolomite, Salt, etc.). behaviour under the blow-pipe (see Quartz, Felspar, Mica, Calcite, etc.).

Mississippi, sediments of the Delta of, 7

Mortar and Scum, 112

Muscovite mica, 43 mica, under blow-pipe, 73

Musk-sheep remains, found in brick-earth, 2, 3

Natrolite, 68

Newcastle-on-Tyne fire-clays, 80

Newton Abbot, clays near, 20

Northamptonshire brick-earths, 21

Oligoclase felspar, chemical composition, 34 felspar, under blow-pipe, 73

Origin of fluviatile brick-earths--Chapter I., 1–16

Orthoclase, 69 felspar, chemical composition, 34 felspar, under blow-pipe, 73

Overburden: the material for the most part useless, overlying the good brick-earth, sand, limestone, or other rock for which the pit or quarry was exploited, and which, in the majority of cases, has to be removed to obtain the material sought for.

Oxford clay, 24, 25, 33

Oxidising flame, 65

Paving bricks, tests, 148

Peterborough bricks, 24 clays, 51

Plants, fossil, 21, 26

Platinum wire, 60, 63, 66

Plesiosaurus, fossil reptile, 26

Porcelain earths, 30

Pottery clays, chemical composition, 82

Power of transport of sediment by rivers, 8

Pumice for brickmaking, 93

Pyrite, 46 behaviour in the kiln, 48 under blow-pipe, 74

Pyrometers, 99, 100

Quartz, behaviour in the kiln, 39, 42, 43 cavities in, 40, 41 characters of, 39 imperishable, 40 micro-structure of, 128 occurrence in brick-earths, 40 under blowpipe, 72 vein, 40

Race: concretions of carbonate of lime, commonly found in brick-earths in brick-earths, 50

Rainfall and the durability of bricks, 108

“Rattling” tests, 148

Reading mottled clay, 18

Red brick, 100

Red brick clay, 86

Red bricks, colouring matter of, 45

Reducing flame, 65

Refractory minerals (see Calcite, Dolomite, Magnesite, Quartz, etc.).

Reindeer remains, found in brick-earth, 2, 3

Reptiles, fossil, 25

Rhinoceros’ remains, found in brick-earth, 2, 3

River deposits, typical section, 10, 11

River terraces, brick-earths of, 12, 13

Rock crystal, 40

Rock salt, under blow-pipe, 74

Ruabon bricks and terra-cotta, 84 terra-cotta, 116

Rubbers, 29, 86

Saarbrücken “iron bricks,” 92

Salt, a powerful flux, 57 behaviour in the kiln, 57 glazing, 57 in brick-earths, 25, 27, 56 in quartz crystals, 41 under blow-pipe, 74

Schorl, 40

Scum, 110

Sea-shore, brick-earths from the, 25

Selenite, 54, 131 under blow-pipe, 74

Septaria: tabular or rounded concretions of argillaceous limestone, commonly found in clays

Septaria, 51

Shrinkage of brick-earth in the kiln, 85

Silica, behaviour in the kiln, 28 group of minerals, 39

Slates, chemical composition of, 87 débris for brickmaking, 87 refuse, 47 used in brickmaking, 47

Snails, found in brick-earth, 4

Specific gravity of bricks, 146, 149

Stacking in the kiln, 97

Staffordshire blue bricks, 99

Stibnite, 68, 70

Stocks, London, 140

Stoneware, earths for making, 21

Stourbridge bricks, 82

Strength of bricks, 136

Styrian magnesite, 56

Swiss brick-earths, 89

Temperature and weathering of bricks, 115 in kilns, 98

Terra-cotta earths, 19, 30 earth, chemical composition of, 84 expansion of in weathering, 115 Ruabon, 116

Tests for bricks (see strength, absorption, specific gravity, chemical composition, micro-structure, etc.).

Thames, mineral salts in solution in the, 7

Thames Valley brick-earths, 1, 2, 3, 4, 5

Tuscany, infusorial earth, 92

Variable character of brick-earths, 10

Variability in character of marine brick-earths, 23, 24 of estuarine brick-earths, 21 of lacustrine brick-earths, 17

Vegetable growth on bricks, 113

Vein quartz, 40

Volcanic ejectamenta for brickmaking, 93

Wales, fire-clays of, 81

Warping, 98

“Weathering” agents which affect bricks, 6

Weathering of brick-earths, 27

White bricks, 100

Yellow bricks, 101

Transcriber’s Notes

As Footnote 1 states, technical terms are explained in the Index at the end of the book.

Punctuation and spelling were made consistent when a predominant preference was found in the original book; otherwise they were not changed.

Inconsistent hyphenation was not changed.

Simple typographical errors were corrected; unbalanced quotation marks were remedied when the change was obvious, and otherwise left unbalanced.

Figures 1 and 4 were repositioned slightly in the paragraphs that reference them, thereby splitting those paragraphs.

The uncaptioned illustration above the second advertisement is an image of that advertisement. The uncaptioned illustration at the end of the book is decorative.

In this Plain Text version of the eBook, the chemical formulas on pages 76–77 are shown unsubscripted, e.g., H2O.

The original book used middle-dots to represent decimal points; this eBook uses baseline periods.

The index was not checked for proper alphabetization or correct page references.

End of Project Gutenberg's The Science of Brickmaking, by Georg F. Harris