Part 31

“Would you dare to operate thus on a patient?” asked Van Swieten.

“Willingly, Master,” was the reply.

“Then operate on me,” said the Professor.

To this proposal, however, they demurred, and the Empress supported their objection. An appointment for further experiment a few days later was made, but when the day arrived Van Swieten was ill. He died on May 18, and Maria Theresa was at the time immersed in political troubles. The sequel to that strange history has never been told, but some of the old books tell of the “Holland Oil,” which is believed to have been the mysterious medicament employed. Professor Franck thinks one of the strangers was Gautier Van Decoren, a physician of Flemish Holland.

SYNTHETIC REMEDIES.

EARLY DISTINCTION BETWEEN INORGANIC AND ORGANIC CHEMISTRY.

The development of organic chemistry in the course of the nineteenth century is a subject so vast that it is mentioned in this place with something approaching despair. The great chemists who, in the latter part of the eighteenth and in the early years of the nineteenth century, had rescued their science from the superstitious and fantastic theories and conceits which had encumbered it, Lavoisier, Priestley, Scheele, Cavendish, Dalton, Fourcroy, Berzelius, and many others who might be named, distinguished sharply between the products of the mineral kingdom and those which they called organic, that is, substances of vegetable or animal origin, combined, it was agreed, under the influence of what was described as vital force. This force, it was considered, inherent in living bodies, could never be imitated in the laboratory, and its achievements were beyond human skill. It was even doubted whether the elements composing organic substances were subject to the same laws of combination as were those of the mineral world.

Lavoisier, it is true, regarded organic bodies as consisting of radical compounds, hydrocarbon radicals, as he called them, instead of the metallic bases. His last scientific work was the investigation of the statics of organic chemistry, and on this subject his clear vision would probably have enabled him to anticipate many modern conclusions. He had already recognised some of the transformations of sugar, had analysed alcohol, and had declared that in animal and vegetable chemistry no less than in the inorganic kingdom nothing is ever destroyed, but that vegetation and animalisation are only inverse phenomena of combustion and putrefaction.

SYNTHETIC ORGANIC COMPOUNDS.

Some isolated results of the artificial productions of organic substances are recorded which do not seem to have been recognised as challenging the reign of vital force. Scheele, in 1786, formed oxalic acid by oxidising sugar by nitric acid; and in 1822 Döbereiner produced formic acid, previously known as a distillate of ants, by oxidising tartaric acid. In both these cases, however, the transformation was essentially one from a previous organic substance.

The inauguration of synthetic chemistry is understood to date from the year 1828 when Wöhler, then a professor of chemistry at Berlin, produced a supposed cyanate of ammonium by the action of ammonium chloride on silver cyanate. Wöhler was surprised to find the cyanate of ammonium which he had obtained did not correspond with other ammonium salts, but resembled, and as he afterwards proved, was identical with the organic substance, urea, a crystalline compound which constitutes about half of the solid matter dissolved in urine. Wöhler and Liebig next collaborated in a study of organic substances, and one of the early results of their investigations was the discovery of the compound radical, benzoyl, as they termed it, C{7}H{5}O, which they found could be combined with chlorine, bromine, iodine, sulphur, ammonium, and other substances, always retaining its own individuality. It was, in fact, a compound radical, and though it has never been isolated, its compounds prove its character. Berzelius was so struck by this discovery that he suggested the name of proine or orthrine, either meaning the dawn, in substitution for benzoyl.

(From the Royal Collection of Etchings at Munich.)

Born at Eschersheim, near Frankfort, 1800; died at Göttingen, 1882. Wöhler’s notable discovery of the artificial production of urea in 1828 is famous as the starting point of synthetic chemistry. ]

Henceforward discoveries and theories based on them, or propounded to explain them, so crowd the field that even in bulky volumes the story is only told in outline. But several of the famous theories or laws or expositions, on which modern chemistry relies, have been so fertile in consequences that they must be very briefly mentioned.

SUBSTITUTION.

Before 1840 the famous French chemist J. B. A. Dumas developed the theory of substitution, or “metalepsy,” showing that the hydrogen atoms in organic substances can be removed one by one from their molecules, other atoms being substituted for them. A simple illustration of this process is manifest in the action of potassium on water, though this is not an example of organic substitution. The water, H{2}O takes up one atom of potassium, K, in place of one of its hydrogen atoms, becoming caustic potash, KOH. It is further possible by an indirect method to replace the remaining hydrogen atom by another of potassium, yielding potassium oxide, K{2}O. Changes of organic bodies are always proceeding on these lines, and Frankland said the recognition of the process had contributed more to the progress of the science than any other generalisation.

HOMOLOGUES.

About 1850 C. F. Gerhardt, one of Liebig’s pupils who settled in France (and died in 1856 at the age of 40), gave the next great impetus to the development of organic chemistry, or the chemistry of carbon compounds, as it was coming to be termed, by showing how vast numbers of organic compounds could be classified and grouped into homologous series. Starting, for example, with marsh gas, CH{4}, which is chemically known as methane, he showed how from this type methyl alcohol, CH{4}O, and formic acid, CH{2}O{2}, are formed. Ethane, C{2}H{6}, comes next in the series and ethyl alcohol and acetic acid follow just as methyl alcohol and formic acid follow from methane. The addition of CH{2} to ethane gives propane; propyl alcohol and propionic acid following; another addition of CH{2} results in butane with butyl alcohol and butyric acid; and the next type is pentane, with amyl alcohol and valeric acid in its train. Thus it was perceived that all the multitude of complex bodies included in the organic kingdom were compounded in an orderly system.

VALENCY.

The English chemist Edward Frankland next put forward the doctrine of valency. According to this theory atoms possess one, two, three, four, or more links each, and require that number of other atoms of minimum combining capacity to “saturate” them in a molecule. Carbon, for example, is usually considered to be quadrivalent, and as shown in the instance of methane, requires four hydrogen atoms to saturate it. But how is it then that in the case of the next type, ethane, C{2}H{6}, the conditions are satisfied? The explanation is that the molecule is arranged in this manner:

H H | | H--C--C--H | | H H

each carbon atom having three hydrogen atoms attached to it, the fourth bond uniting it with the other carbon atom. This and other difficulties led to the theory of

STRUCTURAL FORMULAS,

towards which Kekulé, of Heidelberg, was the principal contributor. “Rational formulæ” as distinguished from “empiric formulæ” were already recognised as shown by the homologous series of Gerhardt. Let this be illustrated by the instance of alcohol. The atomic composition of compound bodies was ascertained by many of the earlier chemists. Lavoisier analysed alcohol, and assigned to it almost the same composition as we know it to be. Its empirical formula is C{2}H{6}O; but that does not explain how it is built up. By deductive reasoning it is established that alcohol is ethane with one hydrogen atom in each molecule replaced by hydroxyl (OH). Ethane is C{2}H{6}; alcohol is thus formulated--C{2}H{5}OH. That is its “rational formula.” Alcohol is a comparatively simple substance; we shall deal with some formulas of much greater complexity presently.

Born at Darmstadt, 1829; died at Bonn, 1896.]

But these explanations were by no means sufficient to meet all the cases which were coming before chemists, and now Kekulé’s brilliant “closed ring” theory was conceived, and on this most of the wonderful building up of the synthetic compounds has been planned. Kekulé was puzzling over the formula C{6}H{6} which had been found to represent benzene, now so famous as the starting point of the aromatic series. He stated that the solution of the problem came to his mind on the top of a London omnibus in 1865, when he was an assistant in the chemical laboratory of St. Bartholomew’s Hospital Medical School. He conceived the idea of a hexagonal structure with an atom of carbon at each angle, each united to one atom of hydrogen, and on one side a double link or bond, and on the other a single one, connecting it with the next carbon atom, the quadrivalency of each atom being thereby satisfied.

The formula is depicted in the margin, and is generally accepted; but it ought to be stated that it has rivals, though all are founded on the necessity of providing for the saturation of the four links of the carbon atoms.

H C /\\ HC CH || | HC CH \ // C ||