题目

阅读下面短文，然后用60个单词左右概括短文的要点。 Getting rid of dirt, in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt. In the early 16th century, people thought that dirt on the skin was a means to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let ills in. A particular danger was thought to lie in public baths. By 1538, the French king had closed the bath houses in his kingdom. So did the king of England in 1546. Thus began a long time when the rich and 实验室有一包失去标签的白色同体物质，只知道是碳酸钠、氧化钙、氢氧化钠中的一种．为了确定其绀成，某同学大胆假设并设计实验进行探究． [查阅资料]碳酸钠与氢氧化钙溶液反应生成氧氧化钠和碳酸钙沉淀． [提出假设]假设①：白色固体是碳酸钠；假设②：白色固体是氧化钙；假设③：白色固体是氢氧化钠． [实验与分析]根据假没．通过实验及分析，可作出如下判断(填表)： [拓展延伸]假定这包白色固体是混有少量氧化钙的碳酸钠，先将适量此混合物溶于足量水中，可观察到的实验现象是________，反应的化学方程式为________、________；然后将反应后的混合物进行固液分离，其分离的方法是________；再将分离后的溶液蒸干，得到的固体物质是________(填化学式)．