Principles of naval engineering - Historic Naval Ships Association

•5Chapter 7-PRINCIPLES OF MEASUREMENT(K) °C) TF) TR)FREEZING POINT OF GOLD1336.21063.01945.42405.07FREEZING POINT OK SILVER-12 34.0960.81761.42221.07SOILING POINT OF SULFUR-717.8444.6832,31291.97BOILING POINT OF WATER-373,15100.0212.0671.67TRIPLE POINT OF WATERFREEZING POINT OF WATER-273.16273.150.0132.01832.00491.708491 .69BOILING POINT OF OXYGEN-90.18-182.97-297.35162.32ABSOLUTEZEROCONVERSION FACTORSTEMP F -h 40= 1,8 (TEMP C-(-40) KELVIN CELSIUSTEMP F 1.8 (TEMP C) -(- 32 (INTERNATIONALTEMP C = (TEMP F -32)/ 1.8 PRACTICAL)TEMP K = TEMP C -I- 273.15-273.15-459.67(*)(*)(*)(*)FAHRENHEITRANKINE(FAHRENHEIT-ABSOLUTE)Figure33.11(147B)7-1. — Comparison of Kelvin, Celsius, Fahrenheit, and Rankine temperature.range in which the thermometer is to be used.Mercury (or mercury-thallium) is commonlyused because it is a liquid over a wide rangeof temperatures (—60° to 1200° F) and becauseit has anearly constant coefficient of expansion.Almost all liquid-in-glass thermometers aresealed so that atmospheric pressure will notNot all hquids are suitable for use in thermometers.Water, for e.xample. would be an almost impossiblechoice as a thermom.etric liquid at ordinary temperaturesbecause its coefficient of expansion variesenormously at temperatures near 0° C. In the temperaturerange between 0° C and 4° C, water expandswhen cooled and contracts when heated; thus it actuallyhas a negative coefficient of expansion in this range.affect the reading. The space above the liquidin this type of thermometer may be a vacuumor it may be filled with an inert gas such asnitrogen, argon, or carbon dioxide.The capillary bore may be either round orelliptical. In any case, it is very small so thata relatively small expansion or contraction ofthe liquid will cause a relatively large changein the position of the liquid in the capillary tube.Although the capillary bore itself is very smallin diameter, the walls of the capillary tube arequite thick. Most liquid-in-glass thermometersare made with an expansion chamber at the topof the bore to provide a margin of safety forthe instrument if it should accidentally be overheated.129