CHAPTER XV. ABRASION, SPECIFIC GRAVITY.

 Abrasion¹.—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 modification² is to line the “rattler” with the bricks to be tested and then put in loose scrap³ 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 obviated⁴ 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 sand147 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 situated⁵ near the edge of the table. Conversely, those bricks near the periphery⁶ would be subjected to greater grinding action, from the circumstance that the table would move faster underneath⁷ 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 abrading⁸ 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 (c?teris paribus), by the abrasion tests as usually adopted, give a much higher result than would the lighter⁹ brick. On the other hand, if the 7 lbs. brick be weighted another 7 lbs., then the results would be strictly¹⁰ 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 “rattling¹¹” cannot possibly give truly comparative148 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 shales¹² for the manufacture of paving bricks, as well as the influence, if any, of the method of manufacture adopted. Twenty-two varieties of shale¹³ bricks, or bricks the largest constituent¹⁴ 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

Inches. Cubic

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.

149 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 ascertaining¹⁵ this property. Foremost, we have to mention its value in conjunction with absorption in arriving at a rough and ready means of gauging¹⁶ 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 allude¹⁷ to the fact that some experimenters take the specific gravity of a porous¹⁸ 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, worthy¹⁹ the name, either render the brick waterproof²⁰, 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 treatise²¹ like the present, however, it is not desirable to enlarge on this subject.
 

THE END. 

1 abrasion   

n.磨（擦）破，表面磨损

参考例句：

• Diamonds have extreme resistance to abrasion.钻石极抗磨损。
• This analysis is helpful to the research of derailment and abrasion machenism.该分析有助于脱轨和磨耗机理的探讨。

2 modification   

n.修改，改进，缓和，减轻

参考例句：

• The law,in its present form,is unjust;it needs modification.现行的法律是不公正的，它需要修改。
• The design requires considerable modification.这个设计需要作大的修改。

3 scrap   

n.碎片；废料；v.废弃，报废

参考例句：

• A man comes round regularly collecting scrap.有个男人定时来收废品。
• Sell that car for scrap.把那辆汽车当残品卖了吧。

4 obviated   

v.避免，消除（贫困、不方便等）( obviate的过去式和过去分词 )

参考例句：

5 situated   

adj.坐落在...的，处于某种境地的

参考例句：

• The village is situated at the margin of a forest.村子位于森林的边缘。
• She is awkwardly situated.她的处境困难。

6 periphery   

n.(圆体的)外面；周围

参考例句：

• Geographically, the UK is on the periphery of Europe.从地理位置上讲，英国处于欧洲边缘。
• The periphery of the retina is very sensitive to motion.视网膜的外围对运动非常敏感。

7 underneath   

adj.在...下面，在...底下；adv.在下面

参考例句：

• Working underneath the car is always a messy job.在汽车底下工作是件脏活。
• She wore a coat with a dress underneath.她穿着一件大衣，里面套着一条连衣裙。

8 abrading   

v.刮擦( abrade的现在分词 )；（在精神方面）折磨（人）；消磨（意志、精神等）；使精疲力尽

参考例句：

9 lighter   

n.打火机，点火器；驳船；v.用驳船运送；light的比较级

参考例句：

• The portrait was touched up so as to make it lighter.这张画经过润色，色调明朗了一些。
• The lighter works off the car battery.引燃器利用汽车蓄电池打火。

10 strictly   

adv.严厉地，严格地；严密地

参考例句：

• His doctor is dieting him strictly.他的医生严格规定他的饮食。
• The guests were seated strictly in order of precedence.客人严格按照地位高低就座。

11 rattling   

adj. 格格作响的, 活泼的, 很好的 adv. 极其, 很, 非常 动词rattle的现在分词

参考例句：

• This book is a rattling good read. 这是一本非常好的读物。
• At that same instant,a deafening explosion set the windows rattling. 正在这时，一声震耳欲聋的爆炸突然袭来，把窗玻璃震得当当地响。

12 shales   

n.页岩( shale的名词复数 )

参考例句：

• Sandstones are, as a rule, interbedded with shales. 砂岩通常都与页岩互层。 来自辞典例句
• Oil-yielding organic matter is contained in the shales. 在这些页岩里有产油的有机物质。 来自辞典例句

13 shale   

n.页岩，泥板岩

参考例句：

• We can extract oil from shale.我们可以从页岩中提取石油。
• Most of the rock in this mountain is shale.这座山上大部分的岩石都是页岩。

14 constituent   

n.选民；成分，组分；adj.组成的，构成的

参考例句：

• Sugar is the main constituent of candy.食糖是糖果的主要成分。
• Fibre is a natural constituent of a healthy diet.纤维是健康饮食的天然组成部分。

15 ascertaining   

v.弄清，确定，查明( ascertain的现在分词 )

参考例句：

• I was ascertaining whether the cellar stretched out in front or behind. 我当时是要弄清楚地下室是朝前还是朝后延伸的。 来自辞典例句
• The design and ascertaining of permanent-magnet-biased magnetic bearing parameter are detailed introduced. 并对永磁偏置磁悬浮轴承参数的设计和确定进行了详细介绍。 来自互联网

16 gauging   

n.测量[试]，测定，计量v.（用仪器）测量( gauge的现在分词 )；估计；计量；划分

参考例句：

• The method is especially attractive for gauging natural streams. 该方法对于测量天然的流注具有特殊的吸引力。 来自辞典例句
• Incommunicative as he was, some time elapsed before I had an opportunity of gauging his mind. 由于他不爱说话，我过了一些时候才有机会探测他的心灵。 来自辞典例句

17 allude   

v.提及，暗指

参考例句：

• Many passages in Scripture allude to this concept.圣经中有许多经文间接地提到这样的概念。
• She also alluded to her rival's past marital troubles.她还影射了对手过去的婚姻问题。

18 porous   

adj.可渗透的，多孔的

参考例句：

• He added sand to the soil to make it more porous.他往土里掺沙子以提高渗水性能。
• The shell has to be slightly porous to enable oxygen to pass in.外壳不得不有些细小的孔以便能使氧气通过。

19 worthy   

adj.(of)值得的，配得上的；有价值的

参考例句：

• I did not esteem him to be worthy of trust.我认为他不值得信赖。
• There occurred nothing that was worthy to be mentioned.没有值得一提的事发生。

20 waterproof   

n.防水材料；adj.防水的；v.使...能防水

参考例句：

• My mother bought me a waterproof watch.我妈妈给我买了一块防水手表。
• All the electronics are housed in a waterproof box.所有电子设备都储放在一个防水盒中。

21 treatise   

n.专著；(专题)论文

参考例句：

• The doctor wrote a treatise on alcoholism.那位医生写了一篇关于酗酒问题的论文。
• This is not a treatise on statistical theory.这不是一篇有关统计理论的论文。