Alchemy: Ancient and Modern / Being a Brief Account of the Alchemistic Doctrines, and Their Relations, to Mysticism on the One Hand, and to Recent Discoveries in Physical Science on the Other Hand; Together with Some Particulars Regarding the Lives and Teachings of the Most Noted Alchemists

by H. Stanley Redgrove

The Stoichiometric Laws.

§ 74. With the study of the relative weights in which substances combine, certain generalisations or “natural laws” of supreme importance were discovered. These stoichiometric laws, as they are called, are as follows:—

1. “The Law of Constant Proportion”—The same chemical compound always contains the same elements, and there is a constant ratio between the weights of the constituent elements present.

2. “The Law of Multiple Proportions”—If two substances combine chemically in more than one proportion, the weights of the one which combine with a given weight of the other, stand in a simple rational ratio to one another.

3. “The Law of Combining Weights”—Substances combine either in the ratio of their combining numbers, or in simple rational multiples or submultiples of these numbers. (The weights of different substances which combine with a given weight of some particular substance, which is taken as the unit, are called the combining numbers of such substances with reference to this unit. The usual unit now chosen is 8 grammes of Oxygen.)[90]

---

[90] In order that these laws may hold good, it is, of course, necessary that the substances are weighed under precisely similar conditions. To state these laws in a more absolute form, we can replace the term “weight” by “mass,” or in preference, “inertia”; for the inertias of bodies are proportional to their weights, providing that they are weighed under precisely similar conditions. For a discussion of the exact significance of these terms “mass” and “inertia,” the reader is referred to the present writer’s Matter, Spirit and the Cosmos (Rider, 1910), Chapter I., “On the Doctrine of the Indestructibility of Matter.”

---

As examples of these laws we may take the few following simple facts:—

1. Pure water is found always to consist of oxygen and hydrogen combined in the ratio of 1·008 parts by weight of the latter to 8 parts by weight of the former; and pure sulphur-dioxide, to take another example, is found always to consist of sulphur and oxygen combined in the ratio of 8·02 parts by weight of sulphur to 8 parts by weight of oxygen. (The Law of Constant Proportion.)

2. Another compound is known consisting only of oxygen and hydrogen, which, however, differs entirely in its properties from water. It is found always to consist of oxygen and hydrogen combined in the ratio of 1·008 parts by weight of the latter to 16 parts by weight of the former, i.e., in it a definite weight of hydrogen is combined with an amount of oxygen exactly twice that which is combined with the same weight of hydrogen in water. No definite compound has been discovered with a constitution intermediate between these two. Other compounds consisting only of sulphur and oxygen are also known. One of these (viz., sulphur-trioxide, or sulphuric anhydride) is found always to consist of sulphur and oxygen combined in the ratio of 5·35 parts by weight of sulphur to 8 parts by weight of oxygen. We see, therefore, that the weights of sulphur combined with a definite weight of oxygen in the two compounds called respectively “sulphur-dioxide” and “sulphur-trioxide,” are in the proportion of 8·02 to 5·35, i.e., 3 : 2. Similar simple ratios are obtained in the case of all the other compounds. (The Law of Multiple Proportions.)

3. From the data given in (1) above we can fix the combining number of hydrogen as 1·008, that of sulphur as 8·02. Now, compounds are known containing sulphur and hydrogen, and, in each case, the weight of sulphur combined with 1·008 grammes of hydrogen is found always to be either 8·02 grammes or some multiple or submultiple of this quantity. Thus, in the simplest compound of this sort, containing only hydrogen and sulphur (viz., sulphuretted-hydrogen or hydrogen sulphide), 1·008 grammes of hydrogen is found always to be combined with 16·04 grammes of sulphur, i.e., exactly twice the above quantity. (The Law of Combining Weights.)

Berthollet (1748-1822) denied the truth of the law of constant proportion, and a controversy ensued between this chemist and Proust (1755-1826), who undertook a research to settle the question, the results of which were in entire agreement with the law, and were regarded as completely substantiating it.

PLATE 16.

[by Worthington, after Allen]

PORTRAIT OF JOHN DALTON.]

To face page 100]