用洁净的烧杯取少量蒸馏水，用酒精灯加热至沸腾，然后将饱和三氯化铁溶液滴入沸水中，并继续煮沸至液体呈透明的红褐色即得氢氧化铁胶体．

（1）将上述氢氧化铁胶体装入U形管中，用石墨做电极，接通直流电源，通电一段时间后发现阴极附近颜色加深，这种现象称为______．

（2）向上述分散系中逐滴加入过量稀硫酸，现象是______，原因是______．

WLANs are increasingly popular because they enable cost-effective connections among people, applications and data that were not possible, or not cost-effective, in the past. For example, WLAN-based applications can enable fine-grained management of supply and distribution (51) to improve their efficienty and reduce (52) . WLANs can also enable entirely new business processes. To cite but one example, hospitals are using WLAN-enabled point-of-care applications to reduce errors and improve overall (53) care. WLAN management solutions provide a variety of other benefits that can be substantial but difficult to measure. For example, they can protect corporate data by preventing (54) through rogue access points. They help control salary costs, by allowing IT staffs to manage larger networks without adding staff. And they can improve overall network mananement by integrating with customers’ existing systems, such as OpenView and UniCenter. Fortunately, it isn’t necessary to measure these benefits to justify investing in WLAN management solutions, which can quickly pay for themselves simply by minimizing time-consuming (55) and administrative chores.

A. personel B. expenses C. overhead D. hardware