All About Engines

8° All About Engines is withdrawn the temperature will fall and the pressure will gradually decrease, but for an hour or more it may be sufficiently high to drive the engine, though not with maximum load nor with the same speed. Yet if the boiler bursts the whole of that energy will be expended within a second, the building in which it is situated will be wrecked, huge pieces of steel will be flung a mile away, and men in the im- mediate neighbourhood will be killed. In the year 1910 there were one hundred explosions in the United Kingdom, resulting in the death of thirteen persons and injury to sixty-one others. In the United States, in the same year, the number was more than five times as great, and both deaths and injuries much greater in proportion. But in both countries the number is gradually decreasing, and for this we have to thank better design and workmanship, more intelli- gent management, and more frequent inspection. It has already been pointed out that in designing a boiler the first essential is to avoid strains, and in management the most necessary precaution is to keep the boiler clean. All natural waters contain dis- solved salts which are deposited as the water is boiled away. From time to time men have to get inside boilers and scrape this off. Some may be got rid of by occasionally opening a “ blow-off ” cock situated near the bottom of the boiler, and the amount may be considerably reduced by softening the water before it is admitted. The addition of sodium carbonate to water containing calcium bicarbonate and sulphate causes the calcium salts to be thrown out, while the