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刺槐种子浸种时水温可达90℃。
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抚育采伐迹地宜用火烧法清林。
Centuries ago, man discovered that removing moisture from food helps to preserve it, and that the easiest way to do this is to expose the food to sun and wind. In this way the North American Indians produce pemmican, the Scandinavians make stockfish and the Arabs dry dates and apricot leather. All foods contain water-cabbage and other leaf vegetables contain as much as 93% water, potatoes and other root vegetables 80%, lean meat 75% and fish anything from 80% to 60% depending on how fatty it is. If this water is removed, the activity of the bacteria that cause food to deteriorate is checked. Fruit is sun-dried in Asia Minor, Greece, Spain and other Mediterranean countries, and also in California, South Africa and Australia. The methods used vary, but in general, the fruit is spread out on trays in drying yards in the hot sun. In order to prevent darkening, pears, peaches and apricots are exposed to the fumes of burning sulfur before drying. Plums, for making prunes, and certain varieties of grapes for making raisins and currants, are dipped in an alkaline solution in order to crack the skins of the fruit slightly and remove their wax coating, so increasing the rate of drying. Nowadays most foods are dried mechanically. The conventional method of such dehydration is to put food in chambers through which hot air is blown at temperatures of about 110℃ at entry to about 43℃ at exit. This is the usual method for drying such things as vegetables, minced meat, and fish. Liquids such as milk, coffee, tea, soups and eggs may be dried by pouring them over a heated horizontal steel cylinder or by spraying them into a chamber through which a current of hot air passes. In the first case, the dried material is scraped off the roller as a thin film which is then broken up into small, though still relatively coarse flakes;" in the second process it falls to the bottom of the chamber as a fine powder. Where recognizable pieces of meat and vegetables are required, as in soup, the ingredients are dried separately and then mixed. Dried foods take up less room and weigh less than the same food packed in cans or frozen, and they do not need to be stored in special conditions. For these reasons they are invaluable to climbers, explorers and soldiers in battle, who have little storage space. They are also popular with housewives because it takes so little time to cook them. Usually it is just a case of replacing the dried-out moisture with boiling water. Contemporarily the minced meat is most commonly dried______.
树叶色淡、质薄、稀疏的多为阴性树。
As more people live closer together, and as they use machines to produce leisure, they find that their leisure, and even their working hours, become spoilt by a by- product of their machines--namely, noise. Noise is nowadays in the news; it has acquired political status, and public opinions are demanding, more and more insistently, that something must be done about it.46) To control noise is to demand much self-discipline (annoyance arises often from lack of common courtesy) a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.Technical difficulties often arise from the subjective-objective nature of the problem. You can define the excessive speed of a motor-car in terms of a pointer reading on a speedometer. But can you define excessive noise in the same way 47) You find that with any existing simple "noise-meter", vehicles which are judged to be equally noisy may show considerable difference on the meter.Though the ideal cure for noise is to stop it at its source, this may in many cases be impossible. The next remedy is to absorb it on the way to the ear.48) Domestic noises may perhaps be controlled by forethought and courtesy, and industrial noises by good planning and technical improvement. But if we are going to allow fast motor-cycles and heavy diesel lorries to pass continuously through residential and business districts, the community must decide on the control it needs to exercise, for in the long run it has got to pay for it. 49) And if a nation is to take part in modern air trans port, it must enter into international agreements on the noise control measures it will impose at its airports-and here the cost of any real control is to be measured in millions of dollars. Jet engines may be modified to reduce their noise level, or insulation from air traffic noise may be provided by the purchase of land around airports or the insulation of buildings. 50) One estimate is that ＄5.7 billion would be required to equip all existing jet engines with noise control devices; however,, considering the current state of the art, even taking this step will not reduce noise levels at all points to acceptable values. Some combination of methods is probably necessary. To control noise is to demand much self-discipline (annoyance arises often from lack of common courtesy) a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.
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