双语有声阅读：油和水

Oil and Water

 

To understand the emulsifying¹ process, we must first accept the scientific principle that oil and water do not naturally mix. Quite literally², they find each other's presence repulsive³. A good illustration of this aversion is homemade oil and vinegar salad dressing⁴.When you shake or beat your salad dressing, you do more than disperse⁵ the oil throughout the vinegar: you also break down the oil into droplets⁶ minute enough to remain temporarily suspended in the vinegar (which from now on we will call water, because that tart⁷ condiment⁸ is in effect mainly water). The second you stop agitating⁹ the dressing, the oil droplets start to combine into units too large to be suspended in the water, and thus slither their way upward, separating from the water in the process.

 

The oil rises to the top and the water sinks because oil has a lower specific density¹⁰ than water. If you want a stable emulsion, you need an emulsifying agent which prevents the oil droplets from combining into larger units. Emulsifying agents occur naturally in many animal substances including egg yolks and milk. An emulsifying agent helps to keep the oil particles from combining in three basic ways. First, the agent coats the oil, serving as a physical barrier between the droplets.

 

Second, it reduces the water's surface tension, which, in turn, reduces the water's ability to repulse¹¹ oil. Third, the agent gives the surfaces of the oil droplets identical electrical charges; since like charges repel¹² each other the droplets repel each other.

 

油和水

 

为理解乳化过程的发生，我们必须首先认识到这样一条科学原理：水和油不能自然混合，它们实实在在互相排斥。 家制的油醋沙拉调料就是一个好例子。 当你搅拌沙拉调料时，你不仅使油扩散到醋里，而且使油滴被搅得很小可以悬浮在醋中( 自此我们改称它为水，因为事实上这种酸性调味品的主要成份就是水)。 一旦你停止了搅动，油滴就会凝聚，大到再也不能悬浮在水中时，它们就向上滑动出来而与水分离了。 因为油的密度小，所以油会浮在水上。如果想得到稳定的乳化，就需要一种乳化剂。它可以不让油形成大的油滴。

 

自然界中，很多动物体中含有乳化剂，如蛋黄和牛奶。 乳化剂可以从以下三方面阻止油滴凝聚。 一、 乳化剂包裹住油滴，在油滴间形成一道物质屏障。 二、 乳化剂降低水的表面张力，从而降低了水排斥油的能力。 三、 乳化剂使油滴表面带上了同种电荷，因为同种电荷互相排斥，油滴之间也相互排斥。

1 emulsifying   

v.使乳化( emulsify的现在分词 )

参考例句：

• Egg yolk serves as the emulsifying agent in salad dressing. 在色拉调味时，蛋黄能作为乳化剂。 来自辞典例句
• No colloid, surfactants or emulsifying agents are employed in the process. 本法不使用胶、表面活化剂或乳化剂。 来自辞典例句

2 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

3 repulsive   

adj.排斥的，使人反感的

参考例句：

• She found the idea deeply repulsive.她发现这个想法很恶心。
• The repulsive force within the nucleus is enormous.核子内部的斥力是巨大的。

4 dressing   

n.(食物)调料；包扎伤口的用品，敷料

参考例句：

• Don't spend such a lot of time in dressing yourself.别花那么多时间来打扮自己。
• The children enjoy dressing up in mother's old clothes.孩子们喜欢穿上妈妈旧时的衣服玩。

5 disperse   

vi.使分散；使消失；vt.分散；驱散

参考例句：

• The cattle were swinging their tails to disperse the flies.那些牛甩动着尾巴驱赶苍蝇。
• The children disperse for the holidays.孩子们放假了。

6 droplets   

n.小滴( droplet的名词复数 )

参考例句：

• Droplets of sweat were welling up on his forehead. 他额头上冒出了滴滴汗珠。 来自辞典例句
• In constrast, exhaled smoke contains relatively large water droplets and appears white. 相反，从人嘴里呼出的烟则包含相当大的水滴，所以呈白色。 来自辞典例句

7 tart   

adj.酸的；尖酸的，刻薄的；n.果馅饼；淫妇

参考例句：

• She was learning how to make a fruit tart in class.她正在课上学习如何制作水果馅饼。
• She replied in her usual tart and offhand way.她开口回答了，用她平常那种尖酸刻薄的声调随口说道。

8 condiment   

n.调味品

参考例句：

• It has long been a precious condiment.它一直都是一种珍贵的调味料。
• Fish sauce is a traditional fermented condiment in coastal areas.鱼露是沿海地区的传统发酵调味品。

9 agitating   

搅动( agitate的现在分词 )； 激怒； 使焦虑不安； （尤指为法律、社会状况的改变而）激烈争论

参考例句：

• political groups agitating for social change 鼓吹社会变革的政治团体
• They are agitating to assert autonomy. 他们正在鼓吹实行自治。

10 density   

n.密集，密度，浓度

参考例句：

• The population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
• The region has a very high population density.该地区的人口密度很高。

11 repulse   

n.击退，拒绝；vt.逐退，击退，拒绝

参考例句：

• The armed forces were prepared to repulse any attacks.武装部队已作好击退任何进攻的准备。
• After the second repulse,the enemy surrendered.在第二次击退之后，敌人投降了。

12 repel   

v.击退，抵制，拒绝，排斥

参考例句：

• A country must have the will to repel any invader.一个国家得有决心击退任何入侵者。
• Particles with similar electric charges repel each other.电荷同性的分子互相排斥。