The primitive method of boiling water consisted in heating the water in a hollow dug in the ground by plunging in hot stones taken out of the fire. Later, as the arts of pottery making and metal working became known, utensils were employed.

In some excellent remarks by Williams on the subject of so-called boiled food, he points out that the expression "boiled" beef, or eggs, or potatoes, implying that the food has been boiled in the same manner in which the water is boiled, is an absurdity. The food is merely heated by immersion in boiling water, and even such water as is contained in the meat or potato is not itself boiled in the process, for, he says, "its boiling point is higher than that of the surrounding water, owing to the salts it holds in solution. Thus, as a matter of chemical form the boiled leg of mutton is one that has been cooked but not boiled, while the roasted leg of mutton is one that has been partially boiled. Much of the constituent water of flesh is boiled out and fairly driven away as vapour during roasting or baking, and the fat on its surface is also more or less dissociated into its chemical elements, carbon and water, as shown by the browning due to the separated carbon".

It is a scientific fact which is not appreciated by many persons that when water has once reached the boiling point, its temperature "cannot be further elevated until it is all converted into steam, for all the additional heat which is required above that needed to warm the water and drive off the air-bubbles in the process of ebullition is expended in vapourising the water into steam. Consequently, however hot the fire, or however prolonged the cooking, the tempera-ture of the food suspended in boiling water cannot be increased above that of the water itself; and, in fact, the temperature of the interior of large masses of food, like potatoes or meat, is by no means as great as that of the surrounding water. For this reason, piling fuel upon the fire when water has once reached the boiling point will have no further effect than that of accelerating the rate of ebullition, without actually raising the temperature of the water or any food immersed in it.

Five and a half times as much heat is required to convert water at the boiling point into steam as that which is needed to raise water from the freezing to the boiling point. Count Rumford over a century ago remarked that, while the boiling temperature of water varies considerably at different levels, meat or eggs are just as thoroughly cooked at an elevation in which the water boils at 209.50 as they are at the sea level, where the boiling temperature is 212° F.

There is practically no distinction to be made between "simmering " and boiling as a process of cooking. The violent boiling of some foods tends to soften them somewhat on account of the effect of the commotion produced in the water by the rising bubbles which cause currents to form that carry particles of suspended food with them and triturate them.

The operation of boiling if continued for an hour or more gradually converts the connective tissue of meat fibre into gelatin, which is partially dissolved in water, and the heat of the boiling water usually melts a little of the fat, which, being unable to mix with the water, forms a scum upon the surface. A small proportion of the juices of meat usually osmoses or soaks out into the surrounding water, and the aqueous solution thus formed is called broth or bouillon. The richness of the broth will depend principally upon the method of conducting the boiling process. When it is desired to have the broth as nutritious as possible the meat must be finely minced and put into cold water, which is gradually warmed but not actually brought to the boiling point. By this process the juices of the meat are slightly dissolved out into the warm water, and thereafter, if the temperature is not carried above 1600 F., coagulation of the albumin in the muscle fibres does not occur, and more and more of their constituents are dissolved out into the surrounding water - but this is not true boiling.

In this manner the natural flavour is very much better preserved; in fact, the common extracts of meat are made by soaking finely chopped meat in cold water and subsequently evaporating the water from the ingredients which are found in it.

On the other hand, when broth is not wanted for nutriment it is desirable to prevent the solution of the juices in the water as much as possible, and this is accomplished by immersing the meat suddenly into water actually boiling, where it should be left for five minutes, by which time the outer layer of the mass will be hardened by coagulation and will have a firm coating which is not permeated by the juices within. When meat is cooked in this manner the broth is scarcely of any food value, but the meat is much more palatable. After the boiling temperature of the water has been maintained for five minutes the further cooking should be continued at a lower temperature of, say, 1650 to 1700 F. If the heat is less than this, the interior of the joint or other piece of meat is imperfectly cooked and its albumin is insufficiently coagulated, so that it has a raw appearance. If the actual boiling point is long maintained, the albumin is too firmly coagulated, and the meat becomes tough and stringy.

The latter error in boiling is very commonly perpetrated by cooks, and it must be observed that the coagulation point of different forms of albumin varies considerably, ranging from below 900 to above 1650 F., and since many varieties of albumin occur in the different kinds of animal food which are in common use, it will be found that they are not all equally well cooked by exactly the same temperature. It is important that the coagulation temperature of a given albumin should not be greatly exceeded or long maintained if the food is to remain tender and digestible. Parkes says that ammonium sulphite is liberated by continued boiling, and also an acid resembling acetic acid.

When meat is plunged into boiling water so that the external layers are solidified some of the water which they contain is squeezed out into the surrounding fluid, and an actual loss of weight in the meat occurs which may reach as high as 30 per cent.

The addition of salt to water in boiling fish or meat is described by Williams as having a threefold action: (1) It directly acts on superficial albumin with coagulating effect; (2) it slightly raises the boiling point of the water; (3) by increasing the density of the water, the exosmosis or oozing out of the juices is less active, and hence the flavour is better retained.

When very salt meat is to be cooked, if steeped too long in boiling water its nutritive properties are impaired, the muscle sarcolem-ma becomes too hard, and the meat tasteless and tough. In such cases it may be well to boil meat less completely, and finish the cooking by some other method, such as frying.