Sino4ka

11.05.2021 07:50 •  Английский язык

Перевод текста. change in volume on change of state1 (a) solid to liquid. on solidification a liquid may either expand or contract . water expands when it becomes ice, increasing its volume by about 10%. this expansion accounts for the bursting of pipes and is of great importance in refrigeration . in general, food in cold storage is kept at a temperature just above freezing point so that the quality of the food is maintained and the multiplication of bacteria prevented . the crumbling of rocks is largely due to the freezing of water in the fissures which causes further " splitting. in a similar manner, large lumps of soil are broken into small pieces during frosty weather. most substances, unlike water, contract on solidification. in making a casting, due allowance has to be made for the contraction of the molten metal on solidification. type metal is an exception to this rule, for it is a special alloy which expands on solidifying, thereby producing a very sharp cast. the contraction of fats and waxes is shown by the depressed surfaces formed as they change to the solid state. a solid which contracts on melting floats in its own liquid, e.g. ice floats on water, but solids in the other class sink in their own liquids. (b) liquid to vapour. when a liquid boils, it produces vapour which, at atmospheric pressure, occupies a volume greater than that of the liquid: e.g. steam at atmospheric pressure has a volume 1,700 times that of the water from which it is formed. if a liquid is boiled in an enclosed space, the escaping vapour will create a high pressure and perhaps burst the enclosing vessel . we are told that watt, the inventor of the steam engine, boiled water in a kettle which had its lid fastened down and a cork in its spout . very soon the cork was shot out with terrific force! the diagram (fig. 2) shows the essential parts of a simple steam engine. steam from the boiler is passed into the box в fitted on the side of the cylinder c. in the cylinder the piston p which is driven first to one end and then to the other by steam which enters in turn through ports x and y. this is made possible by the slide valve s. when the valve is in the position shown, steam is passed into the cylinder through y and, at the same time, the used steam from the other end of the cylinder passes out through the exhaust o. the slide valve is moved by an eccentric fitted to the shaft carrying the flywheel f, hence it works in harmony with the piston.