公共英语80篇背诵阅读带翻译(三十二)1.docx

公共英语80篇背诵阅读带翻译(三十二)1To understand the emulsifying process, we must first accept the scientific principle that oil and water do not naturally mix. Quite literally, they find each other”s presence repulsive. A good illustration of this aversion is homemade oil and vinegar salad dressing.When you shake or beat your salad dressing, you do more than disperse the oil throughout the vinegar: you also break down the oil into droplets minute enough to remain temporarily suspended in the vinegar (which from now on we will call water, because that tart condiment is in effect mainly water). The second you stop agitating 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 density 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 repulse oil. Third, the agent gives the surfaces of the oil droplets identical electrical charges; since like charges repel each other the droplets repel each other. 油和水 为理解乳化过程的发生，我们必需首先熟悉到这样一条科学原理：水和油不能自 然混合，它们实实在在相互排斥。

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，你不仅使油集中到醋里，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，由于事实上这种酸性调味品的主要成份就是水) 一旦你停顿了搅动，油滴就会分散， 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别了 由于油的密度小，所以 油会浮在水上 假如想得到稳定的乳化，就需要一种乳化剂 它可以不让油形成大的油滴 自然界中，许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挡油滴 分散 一、 乳化剂包裹住油滴，在油滴间形成一道物质屏障 二、 乳化剂降低水的外表 张力，从而降低了水排斥油的力量 三、 乳化剂使油滴外表带上了同种电荷，由于同种电 荷相互排斥，油滴之间也相互排斥。