It's the Heat

I'm amazed how often my understanding of a known fact turns out to contain an error. I've been reading "How a steam locomotive really works". It's filled with technical discussions about things like how to stay a firebox, and how to equalize driver axlebox springs. In the chapter on making steam, there is a discourse on the quantity of heat required when ice changes to water and when water changes to steam. In between those two state changes, it says that one calorie is the amount of heat required to raise the tempurature of 1 gram of water 1 degree centigrade. I kind of remember that from 8th grade science. So far so good.

Then comes the twist. It says that a calorie of food energy is actually one thousand times larger; enough energy to raise 1 kilogram of water 1 degree centigrade. I'd never heared that before. I'd always assumed that all calories were alike. This is a British book, do they use a different unit of heat to measure their food than we do?

According to "The Readers' Digest Great Encyclopedic Dictionary" a calorie is one of two recognized units of heat. In food: "The large, great, greater, or kilogram calorie (Abbr.Cal.) is the amount of heat required to raise the tempurature of one kilogram of water 1 degree C. The small, lesser, or gram calorie (Abbr. cal.) is the amount of heat required to raise one gram of water 1 degree C. Who knew? I guess that changes everything.