From a chemical standpoint we know that a high percentage of iron in the average brick-earth is not conducive8 to the production of a good brick. In the same119 manner by “rule of thumb” we learn that a high percentage of lime prevents the manufacture of the raw material into a fire-brick, unless, indeed, we are making basic bricks. The chemist tells us also of the respective values of potash and soda10. Too much iron will cause the brick to “run”; salt has a similar effect; but beyond this the chemist cannot go, except that in the broad sense he explains what unions take place to produce such results.
The microscope, on the other hand, enables one to see exactly what has taken place; the deleterious constituents11 are detected at their work, and careful chemical investigation12 teaches us what to add to the brick-earth to neutralise the effects observed; for it is only from its effects that the artificial constitution of the brick-earth can be properly regulated.
The same instrument is extremely useful in all questions concerning the relations subsisting13 between a brick and the glaze14 upon it, the cause and prevention of the cracking of the latter, and its general quality from a physical aspect. And, speaking of cracks, we may again draw attention to the influence these have on the strength and durability15 of the brick: many of these minute fissures16 cannot be seen by the naked eye. In a similar way can the microscope be made use of in the manufacture of terra-cotta and fa?ence. The cracking of glazes17 is one of the most troublesome features the high-class brick and tile manufacturer has to deal with. If the character of the surface of the brick is not suitable for “taking” the glaze, the maker18 knows in a moment; the trouble is where the glaze takes readily and then, some time after the operation is finished, it becomes covered with “spider-web” cracks, unsightly and considerably19 detracting from the value of the brick. The120 cause of the cracking is commonly attributed to the composition of the glaze, and the manner in which the latter is allowed to cool, and no doubt a great deal is due on both those heads. At the same time, we know of many instances where the same glaze being used under similar conditions on two different surfaces of bricks made from one and the same brick-earth, the glaze cracks in the one case, and hardly ever in the other. The direction of the cracks points to their origin, and the character of the surface is brought in guilty. And yet the average manufacturer would not detect any difference in the quality of the surface—he could not, without a good lens or low power objective, perceive the slightest discrepancy20.
The ordinary glaze behaves very much like Canada balsam with reference to surfaces on which it is laid, and something akin9 to what petrologists call “perlitic” cracks is produced in the glaze. We can make these cracks, and imitate the structure artificially, by suitably distributing the Canada balsam over the surface of a piece of ground glass, and in other ways. That direct relationship exists between the cracks and the grain of the surface on which the preparation is laid, is certain, for we may vary the distribution of the cracks by varying the grain of the surface. An intelligent appreciation21 of the disposition22 of cracks in glazes should be the means of preventing them altogether, and not only with bricks, but with fa?ence and vitrified work generally, the study may be best carried on by aid of the microscope.
The microscope, also, may be made use of in identifying bricks in case of dispute, though its applications in this respect are not so important as in dealing with building stones.
121 Questions of durability may frequently be decided23 on appeal to that instrument. Take a case in which a brick is known to contain a rather high percentage of lime: if the lime were in a combined state, the quality of the brick would not be materially affected24; but assuming it were not so employed, it is possible that in a short space of time the brick would be thoroughly decomposed25 by atmospheric26 agencies. The microscope tells us at a glance the state in which that and other ingredients exist, in a well-burnt brick. We draw the line at bricks intended for the “jerry” builder; they may well be left to take care of themselves; we allude27 only to high-class productions in which science may be some aid to the manufacturer.
And now as to the microscope—for we do not use an ordinary one in such investigations28. The best kinds of microscope are those used by petrologists in the study of the minute structure of rocks and minerals. The reader will find these fully6 described in works specially29 devoted30 to the subject,13 but we may say a few words thereon.
A common form of “Student’s” petrological microscope, as manufactured by Swift of London, may be described as follows:—
Eye Pieces and Objectives.—These need not be expensive, clear definition being the principal object to aim at; the objectives should be of low power, 2-inch, 1-inch and ?-inch objectives being plenty for the purpose. Unless the reader desires to follow the subject122 from a purely31 petrological point of view, to study the development of trichites, globulites, skeleton crystals, etc., in vitrified bricks, in such places as these latter have cooled from igneous32 fusion33, there is no occasion to resort to higher powers. We are far from saying that the brickmaker of the present day would not derive34 any advantage from studying this subject in its higher aspects, for the origin of crystallization appeals strongly to the imaginative mind, and is one of the most remarkable35 problems that Nature offers for our investigation. But in an elementary treatise36 of this kind we cannot go into the matter; and, as previously37 remarked, low power objectives are sufficient for our present purpose. The eye-pieces should be fitted with cross-wires, the use of which will presently be explained.
The Stage.—In the instrument we are now describing this is circular with a hole in the middle, and is so arranged as to revolve38 horizontally on a collar about an axis39, the centre of which comes exactly underneath40 the centre of the objective. In other words, a straight line drawn41 through the eye-piece down the centre of the barrel of the microscope, and passing through the objective passes through that axis. To assist in more accurately42 centreing than is otherwise possible (depending on the lenses) with this cheap form of instrument, a collar with adjustable43 screws is ordinarily affixed44 to the lower part of the barrel of the microscope. The stage, with suitable clips to hold the object to be examined, is graduated so that on its being revolved46 it is easy to ascertain the number of degrees, at any period of the revolution, through which it has been turned. Thus, it will be observed that the object revolves47 with the stage. A pointer is placed in a suitable position on the frame of the microscope to facilitate the observation.
123The Polariscope.—This is an indispensable adjunct, for determinative purposes it is often necessary to observe the object in polarised light. Briefly48, the polariscope consists of two parts—the analyser, placed in the barrel of the microscope above the objective, and the polariser, arranged underneath the revolving49 stage. The analyser is so fitted that it may be shot in and out of the barrel in order that the polariser alone may be used, or the latter may be removed, leaving only the analyser in position, or both may be removed to enable the object to be examined in ordinary light, either reflected or transmitted. The lower nicol14 is made to revolve, and the collar in which it is fixed45 is broadly graduated and furnished with a pointer.
Reflector.—An ordinary reversible and adjustable reflector is arranged beneath all.
Accessories.—For the more accurate determination of minerals, a quartz50 wedge, a quartz plate, etc., are used by the petrologist, but the description of these is beyond the scope of the present work. For examination in reflected light it is highly desirable to have a “bull’s-eye” condenser51.
An ordinary microscope with a revolving stage may be readily converted to petrological purposes, though it is better to have a special instrument.
* * * * *
The object to be examined may be in the form of (a) a fragment of the brick, or (b) a very thin slice of the same.
The fragment may be securely clipped and held in position on the stage, the “bull’s-eye” condenser being brought into use to throw a strong light on the part immediately under the objective. The polarising apparatus52 is no use for this, and may be thrown out of gear.124 A very low power should be employed. The observation may be directed towards ascertaining53 how far the fragments composing the brick are agglutinated, and their size may be noted54. Anything like a discolouration should be specially observed, and a minute description jotted55 down. In bricks that have not been burnt very hard, and in those that have merely been baked, we shall often be able to detect particles of mineral matter which further investigation, after the manner presently to be described, shows are opaque56. Different forms of iron, iron pyrite, fragments of clay that have merely been dried in the process of baking, and minute pieces of chalk (now converted into lime) are amongst the most prominent opaque substances met with in common bricks. These may generally be differentiated57 and determined58 at sight, and bricks thus composed are never of good quality, though the ingredients have been ground very fine, and there may be nothing superficially to find fault with. Their bad qualities are usually brought out in the weathering. A great deal may, therefore, be learned from a careful examination of fragments in this manner.
In regard to the examination of very thin slices, that is in the majority of instances the most instructive, and, if we may say so, the most interesting method of investigation, though it must always go hand in hand with the other. The slice of the brick is so thin that the bulk of the constituents is rendered transparent59, or semi-transparent. The preparation of such slices15 is not difficult,125 but demands some experience; those who have neither the time nor patience to make them will find it convenient to send the fragments of brick to Damon, of Weymouth, or some other first-class dealer60 in geological and mineralogical specimens61. The price charged, per slide, is usually 1s. 6d. At the same time, the student will find it eminently62 to his advantage to prepare the slices himself. In the process he will learn much that escapes attention when the work is done by another.
The thin slice mounted on a slip of glass is placed on the stage of the microscope and firmly clipped, as with the fragment. The reflector is brought into position, and a beam of light thrown through the slice—the thin section is now being examined in transmitted light. At first it will be convenient to study it with the polariser and analyser thrown out of position. A certain proportion of the constituents is found to be opaque, and should be examined in reflected light, as above described. The remainder are more or less transparent, and some of the grains will, possibly, be coloured. We notice the way in which the whole of the fragments are bound together—say, by some opaque mineral such as iron—or whether they seem to be partially63 or wholly fused together. In the case of a vitrified brick, the latter phenomenon is most usual, and we shall find that although crystalline fragments have been melted, or partially fused, there is commonly a centre or nucleus64 of each fragment in its original condition remaining, which passes through insensible gradations from the crystalline to the non-crystalline, or amorphous65 state. This latter circumstance may be ascertained66 by using the polariscope. Ignoring the opaque matter adverted67 to, we shall then126 see that what was transparent in ordinary light appears, for the most part, to be opaque in polarised light. Those portions which still let the light through are truly crystalline, and by revolving the stage we notice that they frequently change tint68, becoming alternately light and dark. In that brick where the particles are agglutinated by igneous fusion, we shall observe the light decreasing in intensity69 from the crystalline portion (forming the nucleus, as it were, of each particle) outwards70, and where the crystal fragment has been melted, so as to become fused to its neighbour, the periphery71, or rather what was originally the boundary of the fragment, is quite dark. Polarised light cannot pass through non-crystalline matter, and in being melted that portion of the crystal fragment had passed from the crystalline to the non-crystalline stage. It is very easy, therefore, to determine how far the fragments composing a vitrified brick have been melted down and fused together; but to observe the phenomena72 under the most favourable73 conditions, the brick must be thoroughly well-burnt, and the section taken, by preference, from near the outside surface of the brick.
In some instances, partial fusion is so well exemplified (especially in bricks from fairly pure china clay), and the brick, after being burnt, has been permitted to cool so slowly, that devitrification has set in, when we are presented with aggregates74 of crystallites closely resembling the “felspathic matter” of petrologists. That is a circumstance which the maker should note well, for he has burnt the brick to the best advantage, and it is not then so brittle75 as it might have been had more “glass” made its appearance in the section. Prolonged heat,127 just above the agglutinating point, has accomplished76 this, and the microscope here clearly shows the advantage of allowing the kiln77 to cool slowly, and to permit the lapse78 of several days in the operation.
点击
收听单词发音
收听单词发音 |
1
tempted
|
|
| v.怂恿（某人）干不正当的事；冒…的险（tempt的过去分词） | |
参考例句： |
|
|
|
|
2
enquire
|
|
| v.打听，询问；调查，查问 | |
参考例句： |
|
|
|
|
3
dealing
|
|
| n.经商方法，待人态度 | |
参考例句： |
|
|
|
|
4
ascertain
|
|
| vt.发现，确定，查明，弄清 | |
参考例句： |
|
|
|
|
5
thoroughly
|
|
| adv.完全地，彻底地，十足地 | |
参考例句： |
|
|
|
|
6
fully
|
|
| adv.完全地，全部地，彻底地；充分地 | |
参考例句： |
|
|
|
|
7
perfectly
|
|
| adv.完美地，无可非议地，彻底地 | |
参考例句： |
|
|
|
|
8
conducive
|
|
| adj.有益的，有助的 | |
参考例句： |
|
|
|
|
9
akin
|
|
| adj.同族的，类似的 | |
参考例句： |
|
|
|
|
10
soda
|
|
| n.苏打水；汽水 | |
参考例句： |
|
|
|
|
11
constituents
|
|
| n.选民( constituent的名词复数 )；成分；构成部分；要素 | |
参考例句： |
|
|
|
|
12
investigation
|
|
| n.调查，调查研究 | |
参考例句： |
|
|
|
|
13
subsisting
|
|
| v.（靠很少的钱或食物）维持生活，生存下去( subsist的现在分词 ) | |
参考例句： |
|
|
|
|
14
glaze
|
|
| v.因疲倦、疲劳等指眼睛变得呆滞，毫无表情 | |
参考例句： |
|
|
|
|
15
durability
|
|
| n.经久性，耐用性 | |
参考例句： |
|
|
|
|
16
fissures
|
|
| n.狭长裂缝或裂隙( fissure的名词复数 )；裂伤；分歧；分裂v.裂开( fissure的第三人称单数 ) | |
参考例句： |
|
|
|
|
17
glazes
|
|
| n.上釉的表面( glaze的名词复数 )；釉料；（浇在糕点上增加光泽的）蛋浆v.装玻璃( glaze的第三人称单数 )；上釉于，上光；（目光）变得呆滞无神 | |
参考例句： |
|
|
|
|
18
maker
|
|
| n.制造者，制造商 | |
参考例句： |
|
|
|
|
19
considerably
|
|
| adv.极大地；相当大地；在很大程度上 | |
参考例句： |
|
|
|
|
20
discrepancy
|
|
| n.不同；不符；差异；矛盾 | |
参考例句： |
|
|
|
|
21
appreciation
|
|
| n.评价；欣赏；感谢；领会，理解；价格上涨 | |
参考例句： |
|
|
|
|
22
disposition
|
|
| n.性情，性格；意向，倾向；排列，部署 | |
参考例句： |
|
|
|
|
23
decided
|
|
| adj.决定了的，坚决的；明显的，明确的 | |
参考例句： |
|
|
|
|
24
affected
|
|
| adj.不自然的，假装的 | |
参考例句： |
|
|
|
|
25
decomposed
|
|
| 已分解的，已腐烂的 | |
参考例句： |
|
|
|
|
26
atmospheric
|
|
| adj.大气的，空气的；大气层的；大气所引起的 | |
参考例句： |
|
|
|
|
27
allude
|
|
| v.提及，暗指 | |
参考例句： |
|
|
|
|
28
investigations
|
|
| （正式的）调查( investigation的名词复数 )； 侦查； 科学研究； 学术研究 | |
参考例句： |
|
|
|
|
29
specially
|
|
| adv.特定地；特殊地；明确地 | |
参考例句： |
|
|
|
|
30
devoted
|
|
| adj.忠诚的，忠实的，热心的，献身于...的 | |
参考例句： |
|
|
|
|
31
purely
|
|
| adv.纯粹地，完全地 | |
参考例句： |
|
|
|
|
32
igneous
|
|
| adj.火的，火绒的 | |
参考例句： |
|
|
|
|
33
fusion
|
|
| n.溶化；熔解；熔化状态，熔和；熔接 | |
参考例句： |
|
|
|
|
34
derive
|
|
| v.取得；导出；引申；来自；源自；出自 | |
参考例句： |
|
|
|
|
35
remarkable
|
|
| adj.显著的，异常的，非凡的，值得注意的 | |
参考例句： |
|
|
|
|
36
treatise
|
|
| n.专著；(专题)论文 | |
参考例句： |
|
|
|
|
37
previously
|
|
| adv.以前，先前（地） | |
参考例句： |
|
|
|
|
38
revolve
|
|
| vi.(使)旋转；循环出现 | |
参考例句： |
|
|
|
|
39
axis
|
|
| n.轴，轴线，中心线；坐标轴，基准线 | |
参考例句： |
|
|
|
|
40
underneath
|
|
| adj.在...下面，在...底下；adv.在下面 | |
参考例句： |
|
|
|
|
41
drawn
|
|
| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
参考例句： |
|
|
|
|
42
accurately
|
|
| adv.准确地，精确地 | |
参考例句： |
|
|
|
|
43
adjustable
|
|
| adj.可调整的，可校准的 | |
参考例句： |
|
|
|
|
44
affixed
|
|
| adj.[医]附着的，附着的v.附加( affix的过去式和过去分词 )；粘贴；加以；盖（印章） | |
参考例句： |
|
|
|
|
45
fixed
|
|
| adj.固定的，不变的，准备好的；(计算机)固定的 | |
参考例句： |
|
|
|
|
46
revolved
|
|
| v.（使）旋转( revolve的过去式和过去分词 )；细想 | |
参考例句： |
|
|
|
|
47
revolves
|
|
| v.（使）旋转( revolve的第三人称单数 )；细想 | |
参考例句： |
|
|
|
|
48
briefly
|
|
| adv.简单地，简短地 | |
参考例句： |
|
|
|
|
49
revolving
|
|
| adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想 | |
参考例句： |
|
|
|
|
50
quartz
|
|
| n.石英 | |
参考例句： |
|
|
|
|
51
condenser
|
|
| n.冷凝器；电容器 | |
参考例句： |
|
|
|
|
52
apparatus
|
|
| n.装置，器械；器具，设备 | |
参考例句： |
|
|
|
|
53
ascertaining
|
|
| v.弄清，确定，查明( ascertain的现在分词 ) | |
参考例句： |
|
|
|
|
54
noted
|
|
| adj.著名的，知名的 | |
参考例句： |
|
|
|
|
55
jotted
|
|
| v.匆忙记下( jot的过去式和过去分词 )；草草记下，匆匆记下 | |
参考例句： |
|
|
|
|
56
opaque
|
|
| adj.不透光的；不反光的，不传导的；晦涩的 | |
参考例句： |
|
|
|
|
57
differentiated
|
|
| 区分，区别，辨别( differentiate的过去式和过去分词 )； 区别对待； 表明…间的差别，构成…间差别的特征 | |
参考例句： |
|
|
|
|
58
determined
|
|
| adj.坚定的；有决心的 | |
参考例句： |
|
|
|
|
59
transparent
|
|
| adj.明显的，无疑的；透明的 | |
参考例句： |
|
|
|
|
60
dealer
|
|
| n.商人，贩子 | |
参考例句： |
|
|
|
|
61
specimens
|
|
| n.样品( specimen的名词复数 )；范例；（化验的）抽样；某种类型的人 | |
参考例句： |
|
|
|
|
62
eminently
|
|
| adv.突出地；显著地；不寻常地 | |
参考例句： |
|
|
|
|
63
partially
|
|
| adv.部分地，从某些方面讲 | |
参考例句： |
|
|
|
|
64
nucleus
|
|
| n.核，核心，原子核 | |
参考例句： |
|
|
|
|
65
amorphous
|
|
| adj.无定形的 | |
参考例句： |
|
|
|
|
66
ascertained
|
|
| v.弄清，确定，查明( ascertain的过去式和过去分词 ) | |
参考例句： |
|
|
|
|
67
adverted
|
|
| 引起注意（advert的过去式与过去分词形式） | |
参考例句： |
|
|
|
|
68
tint
|
|
| n.淡色，浅色；染发剂；vt.着以淡淡的颜色 | |
参考例句： |
|
|
|
|
69
intensity
|
|
| n.强烈，剧烈；强度；烈度 | |
参考例句： |
|
|
|
|
70
outwards
|
|
| adj.外面的，公开的，向外的；adv.向外；n.外形 | |
参考例句： |
|
|
|
|
71
periphery
|
|
| n.(圆体的)外面；周围 | |
参考例句： |
|
|
|
|
72
phenomena
|
|
| n.现象 | |
参考例句： |
|
|
|
|
73
favourable
|
|
| adj.赞成的，称赞的，有利的，良好的，顺利的 | |
参考例句： |
|
|
|
|
74
aggregates
|
|
| 数( aggregate的名词复数 )； 总计； 骨料； 集料（可成混凝土或修路等用的） | |
参考例句： |
|
|
|
|
75
brittle
|
|
| adj.易碎的；脆弱的；冷淡的；(声音)尖利的 | |
参考例句： |
|
|
|
|
76
accomplished
|
|
| adj.有才艺的；有造诣的；达到了的 | |
参考例句： |
|
|
|
|
77
kiln
|
|
| n.（砖、石灰等）窑，炉；v.烧窑 | |
参考例句： |
|
|
|
|
78
lapse
|
|
| n.过失，流逝，失效，抛弃信仰，间隔；vi.堕落，停止，失效，流逝；vt.使失效 | |
参考例句： |
|
|
|
| 欢迎访问英文小说网 |