[CHAPTER XII]
THE REIGN OF LAW—DALTON, JOULE
In the middle of the eighteenth century, when Lambert and Kant were recognizing system and design in the heavens, little progress had been made toward discovering the constitution of matter or revealing the laws of the hidden motions of things. Boyle had, indeed, made a beginning, not only by his study of the elasticity of the air, but by his distinction of the elements and compounds and his definition of chemistry as the science of the composition of substances. How little had been accomplished, however, is evident from the fact that in 1750 the so-called elements—earth, air, fire, water—which Bacon had marked for examination in 1620, were still unanalyzed, and that no advance had been made beyond his conception of the nature of heat, the majority, indeed, of the learned world holding that heat is a substance (variously identified with sulphur, carbon, or hydrogen) rather than a mode of motion.
How scientific thought succeeded in bringing order out of confusion and chaos in the subsequent one hundred years, and especially at the beginning of the nineteenth century, can well be illustrated by these very matters, the study of combustion, of heat as a form of energy, of the constituents of the atmosphere, and of the chemistry of water and of the earth.
Reference has already been made to Black's discovery of carbonic acid, and of the phenomena which he ascribed to latent heat. The first discovery (1754) was the result of the preparation of quicklime in the practice of medicine; the second (1761) involving experiments on the temperatures of melting ice, boiling water, and steam, stimulated Watt in his improvement of the steam engine. In 1766 Joseph Priestley began his study of airs, or gases. In the following year observation of work in a brewery roused his curiosity in reference to carbonic acid. In 1772 he experimented with nitric oxide. In the previous century Mayow had obtained nitric oxide by treating iron with nitric acid. He had then introduced this gas into ordinary air confined over water, and found that the mixture suffered a reduction of volume. Priestley applied this process to the analysis of common air, which he discovered to be complex and not simple. In 1774, by heating red oxide of mercury by means of a burning-glass, he obtained a gas which supported combustion better than common air. He inhaled it, and experienced a sense of exhilaration. "Who can tell," he writes, "but in time this pure air may become a fashionable article in luxury? Hitherto only two mice and myself have had the privilege of breathing it."
The Swedish investigator Scheele had, however, discovered this same constituent of the air before 1773. He thought that the atmosphere must consist of at least two gases, and he proved that carbonic acid results from combustion and respiration. In 1772 the great French scientist Lavoisier found that sulphur, when burned, gains weight instead of losing weight, and five years later he concluded that air consists of two gases, one capable of absorption by burning bodies, the other incapable of supporting combustion. He called the first "oxygen." In his Elements of Chemistry Lavoisier gave a clear exposition of his system of chemistry and of the discoveries of other European chemists. After his studies the atmosphere was no longer regarded as mysterious and chaotic. It was known to consist largely of oxygen and nitrogen, and to contain in addition aqueous vapor, carbonic acid, and ammonia which might be brought to earth by rain.
Cavendish obtained nitrogen from air by using nitric oxide to remove the oxygen, and found that air consists of about seventy-nine per cent nitrogen and about twenty-one per cent oxygen. He also by use of the electric spark caused the oxygen and nitrogen of the air to unite to form nitric acid. When the nitrogen was exhausted and the redundant oxygen removed, "only a small bubble of air remained unabsorbed." Similarly Cavendish had found that water results from the combination of oxygen and hydrogen. Watt had likewise held that water is not an element, but a compound of two elementary substances. Thus the great masses,—earth, air, fire, water,—assumed as simple by many philosophers from the earliest times, were resolving into their constituent parts. At the same time other problems were demanding solution. What are the laws of chemical combination? What is the relation of heat to other forms of energy? To the answering of these questions (as of those from which these grew) the great manufacturing centers contributed, and no city more potently than Manchester through Dalton and his pupil and follower Joule.
John Dalton (1766-1844) was born in Cumberland, went to Kendal to teach school at the age of fifteen, and remained in the Lake District of England till 1793. In this region, where the annual rainfall exceeds forty inches, and in some localities is almost tropical, the young student's attention was early drawn to meteorology. His apparatus consisted of rude home-made rain-gauges, thermometers, and barometers. His interest in the heat, moisture, and constituents of the atmosphere continued throughout life, and Dalton made in all some 200,000 meteorological observations. We gain a clue to his motive in these studies from a letter written in his twenty-second year, in which he speaks of the advantages that might accrue to the husbandman, the mariner, and to mankind in general if we were able to predict the state of the weather with tolerable precision.