Q. Is salt and snow really colder than snow?
A. Yes, many degrees; and by dipping your hand into the mixture first, and into snow afterwards, the mere snow will seem to be comparatively warm.
Q. What is fire?
A. Combustion is another instance of heat, arising from chemical action.
Q. What two things are essential to produce combustion?
A. Fuel and air.
Q. What are the elements of fuel?
A. As bread is a compound of flour, yeast, and salt; so fuel is a compound of hydrogen and carbon.
Q. What are the elements of atmospheric air?
A. The air is a compound of oxygen and nitrogen mixed together; in the proportion of five gallons of nitrogen, to one of oxygen.