Instead of passing water molecules , these membranes pass ions .

水分子不能透过薄膜，只有离子能渗出。

Such membranes are common in nature .

在自然界中这种薄膜是很普遍的。

Moreover , the membranes employed in electrodialysis are of two types .

此外薄膜使用两种电渗析。

Researchers serendipitously discovered that a mixture of urea , glycerol , and soap makes synthetic membranes transparent .

研究人员意外地发现一种由脲、甘油丙三醇和脂肪酸盐组成的混合物可以使合成的薄膜变得透明。

Economies of scale , better membranes and improved energy-recovery have helped to bring down the cost of reverse-osmosis seawater-desalination .

经济成规模化，更优化的薄膜和改进的能量再生能力，有助于降低采用逆渗透法淡化海水的成本。