Snow-melting Agent A heavy snow can kill pests and this means a good harvest next year.This will bring as well as trouble to urbanites. On Nov.16,2003,a cold air current brought a heavy snow to Beijing.To prevent traffic jams,related government departments mobilized people to clear off snow on streets. One of the most effective ways to clear off snow on roads is to scatter snow-melting agent on the roads.The major component of the snow-melting agent is salt.The snow-melting agent can make snow stop from freezing,make it easier to clear off the road,and allow traffic to flow smoothly.But it also brings about some hidden dangers.In the spring of 2003,over 300 000 trees in Beijing urban districts died.After analyzing soil around these trees,experts discovered that the salt content of these soils was 392 times higher than normal.Where did the excessive salt come from?After investigating,forestry experts found that when clearing snow in the winter,people usually heap snow containing snow-melting agent at trees' roots,and that when the snow melts,this agent penetrates the soil and increases its salt content.The snow-melting agent indirectly killed the trees. Statistics show that during a heavy snow in 2002,over 1000 tons of snow-melting agent was scatterred on streets in Beijing.Snow water containing a large amount of snow-melting agent got into the soil through sewers. In addition,salt in the snow-melting agent can expedite the corrosion of steel bars in concrete buildings and cause the concrete to crack and peel,shortening the life of roads. Scientists and government officials are required to solve traffic problems caused by heavy snows as soon as possible and at the same time try to reduce the negative effects of the snow-melting agent.This is a difficult problem placed before them.Related authorities have framed some local criteria to regulate the production and use of snow-melting agents. Now,more harmless snow-melting agents are being developed.Now that even snow-melting agents that meet today's criteria must still be used carefully,we have to rely more on our manpower and machines to clear off snow. This year,in addition to using snow-melting agents,Beijing will use a large number of snow vehicles to clear snow on roads.In more places,citizens are mobilized to clear snow with their hands.This may be a test of a city's civilization level. Salt is a snow-melting agent while   _   is a cleaning agent.
water soap a washing-machine a housewife