When you burn a piece of coal or paper or wood you always have some ash left. The housewife and the stoker consider the ash nothing but a nuisance. It cannot be burnt and therefore is of no heat value. A relatively large percentage of ash in your coal immediately decreases the value of the fuel.

If you burn a piece of meat or any of the common foods, you will also get some ash left. In order to see this ash it will be necessary for you to do a little more burning than the careless housewife does when she manages to spoil her dinner. The chemist burns such food by placing it in a porcelain receptacle which he calls a crucible, and putting the latter in turn in a muffle which can be heated red hot. In time the charry product gives place to a gray and sometimes almost pure white mass, the color depending upon the variety and quantity of the various mineral constituents in the ash. The operation is now complete. All the black carbon has disappeared. What is left is the "ash." It is material in which the elements sodium and potassium and calcium and phosphorus predominate. The ash is called "inorganic" because it is free from carbon. A substance containing carbon - like the meat we started with - would be called "organic."

Mineral Matter Or "Ash" An Essential Part Of The Diet

Useless as this ash is to the housewife and stoker, the ash in our food is an indispensable part of the dietary. We could as easily dispense with the protein as we could with the ash, or, as it is sometimes called, the "mineral matter"; and this is merely another way of saying that the absence from the diet of either one of these would soon cause death.

Not only then must our calorific requirements be fulfilled; not only must there be a careful distribution of our food in the shape of protein, fat and carbohydrate; but the food must also contain a certain amount of ash or mineral matter. Fortunately, all of our foods contain mineral matter to a greater or less degree; so that without necessitating any particular selection on our part, we usually satisfy the mineral requirement without much difficulty.

The Elements In Mineral Matter

When we submit a bundle of cells, consisting of living matter, to chemical analysis, we find that fats, proteins and carbohydrates are present in much the same way as in our foods. The general composition of living matter and of the food we eat is much the same. Another type of chemical examination shows us that living matter consists of such elements as carbon, hydrogen, oxygen and nitrogen, again in much the same way as our foods do. In addition, there are smaller quantities of calcium, phosphorus, potassium, sulphur, sodium, chlorine, iron, iodine, etc. Understand that these elements are not present in the free state. You cannot take a piece of protoplasm and point to the iron or chlorine that it contains. No, the iron and the chlorine and all the other elements in the protoplasm are so combined that they lose their individual properties.

Just as our foods must contain carbon, hydrogen, oxygen and nitrogen not merely to supply the necessary energy, but also to build or rebuild tissue, so, in order to build or rebuild tissue, we must supply such elements as calcium, phosphorus, sodium, etc.; for these elements just as surely enter into the composition of living matter. It is these elements - calcium, phosphorus, etc. - in various chemical combinations, that constitute the ash or mineral matter.

I should, of course, qualify my statement somewhat when I speak of the composition of living matter. Strictly speaking, we do not know the composition of living matter. Every time we submit protoplasm to chemical analysis, those familiar properties which in toto manifest themselves to us as "life" disappear. All that we can say is that the probabilities favor the assumption that while the internal arrangements of the molecules in living matter are different from matter which is no longer "living," the elementary composition of both remains the same.

How Mineral Matter Functions

While an important function of the mineral matter in diet is to supply certain necessary elements that go towards building protoplasmic material, the mineral matter performs other functions equally important; but most of these are of such a nature as not to be very easily intelligible to the layman. In a general way, it may be stated that these mineral constituents play an important part in regulating the concentration of liquid within and without the cell, and in maintaining the body in a state of neutrality.

This last sentence sounds "technical"; but perhaps by amplifying it we can make it less so. Man is made up of millions of cells. These cells are bathed by the lymph and blood which bring food to the cells and carry away the waste material. The cells and blood and lymph may, for our purposes, be considered as liquids in which solids are dissolved - in some such way as the liquid water can dissolve the solid salt. As a matter of fact, physico-chemical studies of cells have shown them to be of far more complex structure than the last sentence would indicate; but no matter. The cells, you will remember, are pictured as more or less spherical in shape. If the liquid outside the cell contains much dissolved solid as compared to the amount of dissolved solid within the cell, the latter shrinks in size. If the reverse is true - if the liquid within the cell contains more dissolved solid than that without - the cell will expand and perhaps burst. In either case we reach an abnormal or pathological condition. It is only when the amount of dissolved solid within and without the cell is equal, or, to put it better, when the pressure exerted within and without the cell is equal, that normal conditions are retained. The dissolved solids regulate these conditions; and the particular solids that are largely responsible for this regulatory mechanism are the mineral salts or "ash."

Body Neutrality

Another function of the mineral salts, that of maintaining neutrality, also deserves further emphasis. The cells are readily responsive to the slightest disturbances due to outside influences. Even slight changes in the cells may give rise to profound disturbances in the body. Usually an amount of acid is formed in the body which might do much harm to the cells and therefore to the body as a whole. In steps the mineral matter and neutralizes the acids. (It should be mentioned that other substances apart from mineral matter also show this property.) Of course there are cases where the mineral matter is powerless to do anything.

Salt

In some instances some very specific functions can be assigned to a number of the constituents of mineral matter, aside from the very general function of the latter of contributing to the structure of protoplasm. Salt (the ordinary "table salt") is one of these. When the masticated and somewhat chemically modified food finds its way into the stomach it there undergoes further changes, and one of the two important substances that bring these changes about is hydrochloric acid. This acid, consisting of the two elements, hydrogen and chlorine in chemical union, is not a constituent of any of our foods, and therefore is not taken into our system. In fact, a concentrated solution of it is a decided poison, and a man contemplating suicide would be apt to think of hydrochloric acid as a means to that end. Yet one of the body's branch factories, situated near the lining of the stomach, manufactures a very weak solution of it for the purpose of helping the digestion of food.

The Acid In The Stomach

Many theories have been advanced to explain just how the body is capable of producing the hydrochloric acid, but none is very satisfactory. Since the acid consists of hydrogen and chlorine in chemical union, there must be a source of these elements in the body. There is; but just how, beginning with the raw material, we can produce the finished article, is a mystery. The source of the chlorine is salt, which itself consists of the elements sodium and chlorine chemically combined. This contribution to the formation of acid in the stomach is a very important function of the salt we eat.

An Illustration Of Chemical Action

It may be of interest, as illustrating just what a chemical action may involve, to say a word or two about the salt. Salt, as we have said, is composed of the two elements sodium and chlorine in chemical combination. The chemist gives the name sodium chloride to salt so as to indicate its composition by name. Sodium itself is a lustrous, grayish-white metal, extremely poisonous, and reacts violently with water the minute it comes in contact with the liquid. Students are warned to store their sodium in bottles containing kerosene. They are also warned to handle the metal with forceps and not with the fingers, and to be careful never to bring it in contact with any water, except under carefully regulated conditions. Chlorine, the other constituent of salt, is a light-yellow gas, of suffocating odor and very poisonous. Its extensive use on the western front in the earlier days of the war is only too well known to this generation. Yet here are these two elements, the one a poisonous solid and the other a poisonous gas, which can be made to unite with one another to give you sodium chloride or salt, which in appearance does not in the least suggest sodium or chlorine, and which has not only the negative virtue of being non-poisonous, but the positive one of being an absolutely indispensable article in our diet.

Though salt, like the other mineral constituents, is present in the foods we eat, it is one of the very few that we deliberately add to the diet. We use it and say that it gives flavor to the food. So it does. But you see now that its function is not limited to that of a mere condiment.