Part 16 (1/2)
The ancients drew no such distinction between portions of their chemical knowledge, limited as it was, as is implied by the modern terms ”organic”
and ”inorganic chemistry.” An organic acid--acetic--was one of the earliest known substances belonging to the cla.s.s of acids; many processes of chemical handicraft practised in the olden times dealt with the manufacture of substances, such as soap, leather or gum, which we should now call organic substances. Nor did the early alchemists, although working chiefly with mineral or inorganic substances, draw any strict division between the two branches of chemistry. The medical chemists of the sixteenth century dealt much with substances derived from plants and animals, such as benzoic and succinic acids, spirit of wine, oils, etc. But neither in their nomenclature nor in their practice did they sharply distinguish inorganic from organic compounds. They spoke of the _quintessence_ of a.r.s.enic and the _quintessence_ of alcohol; they applied the term ”oil” alike to the products of the action of acids on metallic salts and to substances obtained from vegetables. But towards the end of the seventeenth century, at the time that is when the phlogistic theory began to gain pre-eminence, we find gradually springing up a division of chemical substances into mineral, animal and vegetable substances--a division which was based rather on a consideration of the sources whence the substances were derived than on the properties of the substances themselves, and therefore a division which was essentially a non-chemical one.
About a century after this, systematic attempts began to be made to trace some peculiarity of composition as belonging to all compounds of organic, that is, of animal or vegetable, origin. As very many of the substances then known belonging to this cla.s.s were more or less oil-like in their properties--oils, fats, balsams, gums, sugar, etc.--organic substances generally were said to be characterized by the presence in them of the _principle of oil_.
Such a statement as this, although suited to the conceptions of that time, could not be received when Lavoisier had shown chemists how Nature ought be examined. With the definite conception of element introduced by the new chemistry, came an attempt to prove that organic compounds were built up of elements which were rarely found together in any one compound of inorganic origin. Substances of vegetable origin were said by Lavoisier to be composed of carbon, hydrogen and oxygen, while phosphorus and nitrogen, in addition to those three elements, entered into the composition of substances derived from animals. But neither could this definition of organic compounds be upheld in the face of facts. Wax and many oils contained only carbon and hydrogen, yet they were undoubtedly substances of vegetable or animal origin. If the presence of any two of the three elements, carbon, hydrogen and oxygen, were to be regarded as a sufficient criterion for the cla.s.sification of a compound, then it was necessary that carbonic acid--obtained by the action of a mineral acid on chalk--should be called an organic compound.
To Berzelius belongs the honour of being the chemist who first applied the general laws of chemical combination to all compounds alike, whether derived from minerals, animals, or vegetables. The ultimate particles, or molecules, of every compound were regarded by Berzelius as built up of two parts, each of which might itself be an elementary atom, or a group of elementary atoms. One of these parts, he said, was characterized by positive, the other by negative electricity. Every compound molecule, whatever was the nature or number of the elementary atoms composing it, was a dual structure (see p. 164). Organic chemistry came again to be a term somewhat loosely applied to the compounds derived from animals or vegetables, or in the formation of which the agency of living things was necessary. Most, if not all of these compounds contained carbon and some other element or elements, especially hydrogen, oxygen and nitrogen.
But the progress of this branch of chemistry was impeded by the want of any trustworthy methods for a.n.a.lysing compounds containing carbon, oxygen and hydrogen. This want was to be supplied, and the science of organic chemistry, and so of chemistry in general, was to be immensely advanced by the labours of a new school of chemists, chief among whom were Liebig and Dumas.
Let us shortly trace the work of these two renowned naturalists. The life-work of the first is finished; I write this story of the progress of his favourite science on the eighty-second birthday of the second of these great men, who is still with us a veteran crowned with glory, a true soldier in the battle against ignorance and so against want and crime.
JUSTUS LIEBIG was born at Darmstadt, on the 12th of May 1803. The main facts which mark his life regarded apart from his work as a chemist are soon told. Showing a taste for making experiments he was apprenticed by his father to an apothecary. Fortunately for science he did not long remain as a concoctor of drugs, but was allowed to enter the University of Bonn as a student of medicine. From Bonn he went to Erlangen, at which university he graduated in 1821. A year or two before this time Liebig had begun his career as an investigator of Nature, and he had already made such progress that the Grand Duke of Hesse-Darmstadt was prevailed on to grant him a small pension and allow him to prosecute his researches at Paris, which was then almost the only place where he could hope to find the conditions of success for the study of scientific chemistry. To Paris accordingly he went in 1823. He was so fortunate--thanks to the good graces of the renowned naturalist Alexander von Humboldt--as to be allowed to enter the laboratory of Gay-Lussac, where he continued the research on a cla.s.s of explosive compounds, called _fulminates_, which he had begun before leaving Darmstadt.
A year later Liebig was invited to return to his native country as Professor of Chemistry in the small University of Giessen--a name soon to be known wherever chemistry was studied, and now held dear by many eminent chemists who there learned what is meant by the scientific study of Nature.
The year before Liebig entered the laboratory of Gay-Lussac there came to Paris a young and enthusiastic student who had already made himself known in the scientific world by his physiological researches, and who was now about to begin his career as a chemist.
In that southern part of France which is rich in memories of the Roman occupation, not far from the remains of the great aqueduct which spans the valley of the Gardon, at no great distance from the famous cities of Arles and Nimes, was born, in the town of Alais, on the 14th of July 1800, JEAN BAPTISTE ANDRe DUMAS.
The father of Dumas was a man of considerable culture; he gave his son as good an education as could be obtained in the little town of his birth. At the age of fourteen young Dumas was a good cla.s.sical scholar, and had acquired a fair knowledge of natural science. But for his deficiency in mathematics he would probably have entered for the examination which admitted those who pa.s.sed it to join the French navy. But before he had made good his mathematical deficiencies the troublous nature of the times (1814-15) obliged his parents to think of some other profession for their son which would entail less sacrifice on their part.
Like his great fellow-worker in after life he was apprenticed to an apothecary, and like him also, he soon forsook this sphere of usefulness.
Desirous of better opportunities for the study of science, and overpowered by the miseries which war had brought upon the district of his birth, Dumas persuaded his father to allow him to go to Geneva. At Geneva Dumas found an atmosphere more suited to his scientific progress; chemistry, physics, botany, and other branches of natural science were taught by men whose names were everywhere known. He began experiments in chemistry with the crudest and most limited apparatus, but even with these he made discoveries which afterwards led to important work on the volumes occupied by the atoms of elementary substances.
About the year 1818 Dumas became acquainted with Dr. J. L. Prevost, who had returned from studying in many of the most famous medical schools of Europe. Invited by Prevost to join in an investigation requiring medical, botanical and chemical knowledge, Dumas now began a series of researches which soon pa.s.sed into the domain of animal physiology, and by the prosecution of which under many difficulties he laid the foundations of his future fame.
But along with his physiological work Dumas carried on a research into the expansion of various ethers. This necessitated the preparation of a series of ethers in a state of purity; but so difficult did Dumas find this to be, so much time did he consume in this preliminary work, and so interested did he become in the chemical part of the investigation, that he abandoned the experiments on expansion, and set himself to solve some of the problems presented by the composition and chemical properties of the ethers.
Dumas would probably have remained in Geneva had he not had a morning visit paid him in the year 1822. When at work in his laboratory one day, some one knocked and was bidden come in. ”I was surprised to find myself face to face with a gentleman in a light-blue coat with metal b.u.t.tons, a white waistcoat, nankeen breeches, and top-boots.... The wearer of this costume, his head somewhat bent, his eyes deep-set but keen, advanced with a pleasant smile, saying, 'Monsieur Dumas.' 'The same, sir; but excuse me.'
'I am M. de Humboldt, and did not wish to pa.s.s through Geneva without having had the pleasure of seeing you.'... I had only one chair. My visitor was pleased to accept it, whilst I resumed my elevated perch on the drawing stool.... 'I intend,' said M. de Humboldt, 'to spend some days in Geneva, to see old friends and to make new ones, and more especially to become acquainted with young people who are beginning their career. Will you act as my cicerone? I warn you however that my rambles begin early and end late. Now, could you be at my disposal, say from six in the morning till midnight?'” After some days spent as Humboldt had indicated the great naturalist left Geneva. Dumas tells us that the town seemed empty to him.
”I felt as if spell-bound. The memorable hours I had spent with that irresistible enchanter had opened a new world to my mind.” Dumas felt that he must go to Paris--that there he would have more scope and more opportunities for prosecuting science. A few kind words, a little genuine sympathy, and a little help from Humboldt were thus the means of fairly launching in their career of scientific inquiry these two young men, Liebig and Dumas.
In Paris, whither he went in 1823, Dumas found a welcome. He soon made the acquaintance and gained the friends.h.i.+p of the great men who then made natural science so much esteemed in the French capital. When the year 1826 came, it saw him Professor of Chemistry at the Athenaeum, and married to the lady whom he loved, and who has ever since fought the battle of life by his side.
Liebig left Paris in 1824. By the year 1830 he had perfected and applied that method for the a.n.a.lysis of organic compounds which is now in constant use wherever organic chemistry is studied; by the same year Dumas had given the first warning of the attack which he was about to make on the great structure of dualism raised by Berzelius. In a paper, ”On Some Points of the Atomic Theory,” published in 1826, Dumas adopted the distinction made by Avogadro between molecules and atoms, or between the small particles of substances which remain undivided during physical actions, and the particles, smaller than these, which are undivided during chemical actions.
But, unfortunately, Dumas did not mark these two conceptions by names sufficiently definite to enable the readers of his memoir to bear the distinction clearly in mind. The terms ”atom” and ”molecule” were not introduced into chemistry with the precise meanings now attached to them until some time after 1826.
Although the idea of two orders of small particles underlies all the experimental work described by Dumas in this paper, yet the numbers which he obtained as representing the actual atomic weights of several elements--_e.g._ phosphorus, a.r.s.enic, tin, silicon--show that he had not himself carried out Avogadro's hypothesis to its legitimate conclusions.
Two years after this Dumas employed the reaction wherein two volumes of gaseous hydrochloric acid are produced by the union of one volume of hydrogen with one volume of chlorine, as an argument which obliged him to conclude that, if Avogadro's physical hypothesis be accepted, the molecules of hydrogen and chlorine split, each into two parts, when these gases combine chemically. But Dumas did not at this time conclude that the molecular weight of hydrogen must be taken as twice its atomic weight, and that--hydrogen being the standard substance--the molecular weights of all gases must be represented by the specific gravities of these gases, referred to hydrogen as 2.
I have already shortly discussed the method for finding the relative weights of elementary atoms which is founded on Avogadro's hypothesis, and, I think, have shown that this hypothesis leads to the definition of ”atom” as the smallest amount of an element in one molecule of any compound of that element (see p. 142).
This deduction from Avogadro's law is now a part and parcel of our general chemical knowledge. We wonder why it was not made by Dumas; but we must remember that a great ma.s.s of facts has been acc.u.mulated since 1826, and that this definition of ”atom” has been gradually forced on chemists by the c.u.mulative evidence of those facts.
One thing Dumas did do, for which the thanks of every chemist ought to be given him; he saw the need of a convenient method for determining the densities of compounds in the gaseous state, and he supplied this need by that simple, elegant and trustworthy method, still in constant use, known as _Dumas's vapour density process_.