Heroes of Science: Chemists

by M. M. Pattison Muir

In the work of these two chemists, Liebig and Dumas, we find admirable illustrations of the scientific method of examining natural appearances.

In the broad general views which they both take of the phenomena to be studied, and the patient and persevering working out of details, we have shown us the combination of powers which are generally found in separate individuals.

Dumas has always insisted on the need of comparing properties and reactions of groups of bodies, before any just knowledge can be gained as to the position of a single substance in the series studied by the chemist. It has been his aim as a teacher, we are assured by his friend, Professor Hofmann, never to present to his students "an isolated phenomenon, or a notion not logically linked with others." To him each chemical compound is one in a series which connects it directly with many other similar compounds, and indirectly with other more or less dissimilar compounds.

Amid the overwhelming mass of facts which threaten nowadays to bury the science of chemistry, and crush the life out of it by their weight, Dumas tracks his way by the aid of general principles; but these principles are themselves generalized from the facts, and are not the offspring of his own fancy.

We have, I think, found that throughout the progress of chemical science two dangers have beset the student. He has been often tempted to accumulate facts, to amass analytical details, to forget that he is a chemist in his desire to perfect the instrument of analysis by the use of which he raises the scaffolding of his science; on the other hand, he has been sometimes allured from the path of experiment by his own day-dreams. The discoveries of science have been so wonderful, and the conceptions of some of those who have successfully prosecuted science have been so grand, that the student has not unfrequently been tempted to rest in the prevailing theories of the day, and, forgetting that these ought only "to afford peaceful lodgings to the intellect for the time," he has rather allowed them to circumscribe it, until at last the mind "finds difficulty in breaking down the walls of what has become its prison, instead of its home."

We may think that Dumas fell perhaps slightly into the former of these errors, when he did not allow his imagination a little more scope in dealing with the conception of "atom" and "molecule," the difference between which he had apprehended but not sufficiently marked by the year 1826 (see p. 261).

We know, from his own testimony, that Liebig once fell into the latter error and that the consequences were disastrous. "I know a chemist"—meaning himself—"who ... undertook an investigation of the liquor from the salt-works. He found iodine in it, and observed, moreover, that the iodide of starch turned a fiery yellow by standing over-night. The phenomenon struck him; he saturated a large quantity of the liquor with chlorine, and obtained from this, by distillation, a considerable quantity of a liquid which coloured starch yellow, and externally resembled chloride of iodine, but differed from this compound in many properties. He explained, however, every discrepancy with satisfaction to himself; he contrived for himself a theory. Several months later, he received a paper of M. Balard's," announcing the discovery of bromine, "and on that same day he was able to publish the results of experiments on the behaviour of bromine with iron, platinum, and carbon; for Balard's bromine stood in his laboratory, labelled liquid chloride of iodine. Since that time he makes no more theories unless they are supported and confirmed by trustworthy experiments; and I can positively assert that he has not fared badly by so doing."

Another point which we notice in the life-work of these two chemists is their untiring labour. They were always at work; wherever they might be, they were ready to notice passing events or natural phenomena, and to draw suggestions from these. As Davy proved the elementary character of iodine and established many of the properties of this substance during a visit to Paris, so we find Dumas making many discoveries during brief visits paid to his friends' laboratories when on excursions away from Paris. During a visit to Aix-les-Bains, he noticed that the walls of the bath-room were covered with small crystals of sulphate of lime. The waters of the bath, he knew, were charged with sulphuretted hydrogen, but they contained no sulphuric acid, nor could that acid be detected in the air of the bath-rooms. This observation was followed up by experiments which proved that a porous material, such as a curtain or an ordinary plastered wall, is able to bring about the union of oxygen with sulphuretted hydrogen, provided moisture be present and a somewhat high temperature be maintained.

Again, we find Liebig and Dumas characterized by great mental honesty. "There is no harm in a man committing mistakes," said Liebig, "but great harm indeed in his committing none, for he is sure not to have worked.... An error you have become cognizant of, do not keep in your house from night till morning."

Students of science, more than any other men, ought to be ready to acknowledge and correct the errors into which they fall. It is not difficult for them to do this: they have only to be continually going to Nature; for there they have a court of appeal always ready to hear their case, and to give an absolutely unbiased judgment: they have but to bring their theories and guesses to this judge to have them appraised at their true value.