CHAPTER XIII

CHEMICAL AND BOTANICAL THEORIES

The World War served to demonstrate the degree of perfection which has been attained in chemistry. The wonderful high explosives used, the poisonous gases, the lubricating and motor oils and a multitude of valuable chemicals employed for military and naval purposes, many of which were developed at short notice, showed the modern chemist's command of his science. Yet chemistry is a new science. Practically it began with Robert Boyle, in England, in 1661. Boyle conducted experiments on the rarefaction of air and the nature of gases, and in his book, "The Sceptical Chemist," he made this remarkable statement: "I am apt to think that men will never be able to explain the phenomena of nature, while they endeavor to deduce them only from the presence and proportions of such or such ingredients, and consider such ingredients or elements as bodies in a state of rest; whereas, indeed, the greatest part of the affections of matter, and consequently of the phenomena of nature, seem to depend upon the motion and contrivance of the small parts of bodies."

Thus Boyle anticipated the chemical theories of matter developed in the nineteenth century.

Lavoisier, about 1777, advancing from the quantitative study of one chemical change to another was able to describe many processes, and to distinguish between an element and a compound. He cast aside all the alchemical formulæ and expressed the results of his experiments in fractions and proportions.

J. B. Richter between 1791 and 1802 made a series of experiments by which he secured the weights of various bases neutralized by constant weights of several acids, and the weights of several acids neutralized by constant weights of several bases. He found that the composition of chemical compounds is constant, as had been assumed by Lavoisier and Boyle.

Dalton described the atomic constitution of gases in 1808, and sketched the law of multiple proportions in chemical combinations and described binary, ternary and quaternary combinations.

Prussic acid was investigated by Gay-Lussac in 1815, when he isolated cyanogen and found that although it is a compound it plays the part of an element with hydrogen and the metals. Berzelius also found that ammonium possessed all the properties of an alkali metal.

Ten years after the above discoveries were made, Faraday prepared a compound of carbon and hydrogen from liquefied coal gas which led to the general study of isomerism and the great discoveries of the organic radicals with their important combinations.

When isomeric combinations were studied by Jacob Berzelius (1779-1848), he was led to devise a means of expressing organic reactions. He wrote to Wöhler and Liebig a letter outlining his new method in which he said: "From the moment when one has learned to recognize with certainty the existence of ternary atoms of the first order which enter compounds after the manner of simple substances, it will be a great relief in the expression of the language of formulæ to denote each radical by its own symbol, whereby the idea of composition it is desired to express will be placed clearly before the eye of the reader."

An example of this method of expressing reactions was given in the case of the action of chlorine on benzoic acid. He wrote B₂O for benzoic acid, B₂CL₂ for chlorbenzol and B₂ + NH₂ for benzamide. With certain simple improvements made subsequently by Gmelin, the method devised by Berzelius was generally adopted and is in use to-day.

The numerous investigations now being made with the object of discovering the various combinations of the elements led to many improvements in chemical analyses. When we read Berzelius' accounts of his analyses they seem to have been written only yesterday. He and his contemporaries developed analytical and synthetic methods to almost the efficiency that we see to-day.

We also owe to Berzelius a table of the elements showing their electrical qualities, an electrochemical theory, identifying chemical affinity with electric attraction, and a new nomenclature, besides a vast amount of descriptive chemistry.

The discovery of the specific heats of various solid elements by Dulong and Petit in 1819, and Mitscherlich's finding of the isomorphic phenomena in 1818, resulted in the publication of a new atomic weight table in 1826 by Berzelius.

The experiments made in isomorphism by Mitscherlich led him to discover dimorphism and study crystallography. He used his knowledge of crystal measurement extensively and developed synthetic chemistry and the laws of crystallization.

Thompson, Prout, and Wollaston were working on problems in England similar to those examined in Sweden by Berzelius and Mitscherlich.

Molecules were discriminated from atoms in 1826 by Jean Baptiste Dumas and Faraday discovered his law of electrochemical action in 1834.

Organic chemistry originated in Manchester, England, when Dalton read his paper before the Manchester Philosophic Society in 1803 on the theory of atomic weights. This paper led Gay-Lussac, Thenard, Berthollet, de Saussure and others to study organic analyses as devised by Dalton. Gay-Lussac and Thenard greatly improved Dalton's methods and in 1824, as shown by Chevreul's work on fats and greases, organic analyses had been brought to high perfection.

The phenomena of substitution in hydrocarbon compounds like the petroleum oils were studied by Laurent who proposed a theory of basic nuclei. C₁₀H₈ being the nucleus of the naphthalene group and C₂H₄ that of the ethylene group, derived nuclei can be obtained from these by substitution and hydrogen and other elements acting on derived nuclei from numerous hydrocarbon series.

The homology of the hydrocarbons was discovered by Gerhardt in 1844 while he was investigating the alcohols. Wurtz's work on the ammonia compounds, Williamson's on the ethers, Hoffmann's on anilines, Graham's and Liebig's on the citrates, and Frankland's, Kolbe's and Kekulé's work on other compounds raised organic chemistry to such a high plane that industrial chemists were able to use their theoretical conclusions and build a great number of important industries upon organic principles.

Lothar Meyer, in 1868, and Mendeléeff, in 1869, published atomic weights showing improvements in the theories of valency and the interrelationship of atomic weights. Mendeléeff was able to predict from the vacant positions in his table the discovery of important new elements. A number of these elements have since been discovered.

The aniline dye industries have grown out of the discoveries of many chemists. The basic work was done by Faraday, Laurent, and Runge, who isolated valuable hydrocarbons from coal gas tar. Hoffmann discovered aniline and Perkin obtained mauve in 1856 by the oxidation of aniline with chromic acid. It was this and subsequent discoveries by Perkin which gave the greatest impetus to synthetic dyes. The solubility of a dye was improved by increasing its acidity (sulphonation) or by increasing its alkalinity (alkylation). Similar dyes are now made by the same methods from many common aromatic substances.

The chemistry of explosives was developed by Van Helmont, Debus, Bunsen, Abel, Nobel, and, others. Fulminates were used for detonators by Ure in 1831, picrates were employed as explosives by Fontaine and Abel; nitrocellulose (guncotton) discovered by Braconnot in 1832 and used as an explosive by Schönbein in 1846, and nitroglycerine was produced by Sobrero in 1847. Smokeless powders made from guncotton, dynamite, and gelatine were introduced by Nobel in 1890.

Pasteur showed, in 1848, that when the double sodium ammonium racemate was crystallized, two kinds of crystals separated from the solution. When one set of crystals was dissolved in water the solution rotated a beam of polarized light to the left, while the aqueous solution of the other crystals rotated the light to the right. These crystals thus revealed their geometrical properties with perfect light while in solution in water. Pasteur noted that optical activity of this kind is the expression of some form of molecular asymmetry.

Le Bel in 1874 also pointed out that optical activity is an expression of the asymmetry of the chemical molecule and showed that all carbon compounds which are optically active contain a carbon atom combined with four different atoms, or groups. Van't Hoff showed in 1875 that there were definite relations between the arrangements of tetrahedral carbon atoms and polarization phenomena and established the theory of such atoms.

Willard Gibbs, of Yale, discovered what is known as the phase rule, which shows, by thermodynamic methods, how the conditions of chemical equilibria can be systematically grouped.

Van't Hoff, Pfeffer, and others noticed that when two solutions are brought together, if one is more concentrated than the other, diffusion begins in the concentrated and extends to the weaker solution. This shows a talent force in concentrated solutions which is now known as osmotic pressure. Van't Hoff and Arrhenius showed that for comparable concentrations the osmotic pressure of a solution is exactly equal to the pressure of a gas. These discoveries led to a brilliant series of investigations into electrolytic chemistry.

The theory of electrolytic dissociation advanced by Ostwald shows that the molecules of electrolytes in aqueous solutions are broken down into electrically charged parts called ions. In very dilute solutions the dissociation of strong acids, bases, and salts is practically complete as was suggested by Williamson in 1851.

Catalysis, or reaction brought about by agents which do not enter into the chemical changes, was discovered by Berzelius. Ostwald investigated and developed catalytic reactions which are now extensively employed in industry, particularly in refining oils and in the fixation of nitrogen. Hot platinum, for example, is used to act catalytically in causing sulphur dioxide and oxygen to combine and form the basis of sulphuric acid, sulphur trioxide.

One of the most important applications of catalysis to industry is the Haber process for securing nitrogen from the air. When air and hydrogen are compressed and heated to a high temperature in the presence of a catalyzer such as metallic uranium or iron carbide, the nitrogen and hydrogen combine and form ammonia.

The experiments of Sir William Crookes on vacuum tubes subjected to electrical impulses led the way to the discovery of radioactivity, and investigations of radium have revolutionized our conceptions of the nature and properties of matter.

The discovery of helium, argon, the niton emanation from radium and other elements by Ramsay, Collie, Soddy, and others will be referred to later.

Carl Linnæus, who is called the father of modern botany, established the genera and species of plants upon philosophical principles. He established a binomial nomenclature and formulated modern descriptive methods. Thus he prepared the way for the systematic works of De Jussieu and De Candolle.

De Candolle, in 1819, published a new method of classification based upon morphological characters. He defined and illustrated the doctrine of the symmetry of plant organs and asserted that a natural classification must be based on a plan of symmetry.

The relationships between the endosperm and embryo were shown in 1810 by Robert Brown in his monograph on the Australian Proteaceæ. The morphological nature of seed reserves was described by him. He also discovered the functions of the cell nucleus and founded cytology. He showed that the oscillation of minute particles in the fluids of plants when viewed under high microscopic powers, known as the Brownian movement, is due to purely physical causes.

Schultze, Unger, and others, working on suggestions previously made by Knight, Robert Brown, and Hooke, discovered the rôle of protoplasm in plant cells. Alexander Braun and De Bary correlated the movements of protoplasm with the locomotory movements of free zoögonidia and the amœboid movements of Mycetozoa. These investigations directed research to further studies of the structure and constitution of protoplasm and helped develop the cellular theory.

The Algæ were studied and classified by Naegeli, Unger, Von Mohl, Haustein, and others in 1847-1850.

The vascular cryptogams were studied by Hofmeister. He found that the alternation of a sexual with an asexual generation is common to all plants of the mosses, vascular cryptogams, and gymnosperms, as well as among angiosperms.

Hofmeister's work led to appreciation of the fact that a natural system of plant classification must be based, not on balancing the values of the morphological parts of fruits and flowers, but on the anatomy of the real and concealed reproductive organs.

Fossil botany, or paleophytology, was founded, in 1828, by Adolphe Brongniart. Witham, Goeppert, Unger, Corda, and others helped to advance this science.

The publication of Darwin's "Origin of Species" in 1859 found the various botanical sciences already well worked out by numerous capable experts. A huge amount of data and descriptive matter had been assembled and botany, like the other sciences, was ready to be quickened by the Darwinian theories.

The idea of a progressive evolution in plants had been suspected by many botanists, but the genius of Darwin developed it. Living plants were pictured as a multitude of units competing for food, light, air, and room for growth, and struggling against unfavorable environments. The classification of tissues was begun, and the phenomena of absorption of water and salts, the ascent of sap, the absorption of minerals and nitrogen, and metabolism and growth were elucidated. Investigations were made into the nature and functions of chlorophyll and other plant substances. These studies resulted in suggesting means for improving crops by artificial selection, as shown in the work of Luther Burbank.