It is of the first importance that the mechanism of the oven to be used, be thoroughly understood by the cook, and she should test its heating capacity under various conditions, with a light, quick fire and with a more steady one; she should carefully note the kind and amount of fuel requisite to produce a certain degree of heat; in short, she should thoroughly know her “machine” and its capabilities before attempting to use it for the cooking of food.  An oven thermometer is of the utmost value for testing the heat, but unfortunately, such thermometers are not common.  They are obtainable in England, although quite expensive.  It is also possible at the present time to obtain ranges with a very reliable thermometer attachment to the oven door.

[Illustration:  An Oven Thermometer]

A cook of good judgment by careful observation and comparison of results, can soon learn to form quite a correct idea of the heat of her oven by the length of time she can hold her hand inside it without discomfort, but since much depends upon the construction of stoves and the kind of fuel used, and since the degree of heat bearable will vary with every hand that tries it, each person who depends upon this test must make her own standard.  When the heat of the oven is found to be too great, it may be lessened by placing in it a dish of cold water.

Boiling is the cooking of food in a boiling liquid.  Water is the usual medium employed for this purpose.  When water is heated, as its temperature is increased, minute bubbles of air which have been dissolved by it are given off.  As the temperature rises, bubbles of steam will begin to form at the bottom of the vessel.  At first these will be condensed as they rise into the cooler water above, causing a simmering sound; but as the heat increases, the bubbles will rise higher and higher before collapsing, and in a short time will pass entirely through the water, escaping from its surface, causing more or less agitation, according to the rapidity with which they are formed.  Water boils when the bubbles thus rise to the surface, and steam is thrown off.  If the temperature is now tested, it will be found to be about 212 deg.  F. When water begins to boil, it is impossible to increase its temperature, as the steam carries off the heat as rapidly as it is communicated to the water.  The only way in which the temperature can be raised, is by the confinement of the steam; but owing to its enormous expansive force, this is not practicable with ordinary cooking utensils.  The mechanical action of the water is increased by rapid bubbling, but not the heat; and to boil anything violently does not expedite the cooking process, save that by the mechanical action of the water the food is broken into smaller pieces, which are for this reason more readily softened.  But violent boiling occasions an enormous waste of fuel, and by driving away in the steam the volatile and savory elements of the food, renders it much less palatable, if not altogether tasteless.  The solvent properties of water are so increased by heat that it permeates the food, rendering its hard and tough constituents soft and easy of digestion.