THE FORERUNNERS OF CHEMISTRY. In the Seventeenth Century we find the Englishman Robert Boyle (1627-91) grasping truth with an insight unprecedented. and in many respects not yet surpassed. Boyle understood that •hem istry must be treated as an independent science •- i.e. prima rily without reference to applications of any sort, and that only in this. manner could the relationships between chemical phenomena proper be discovered. He maintained that •hem ists should consider as an element only a sub stance which, in spite of exhaustive actual ef forts. they have not succeeded in decomposing. And even this method, though necessary and suf ficient for the purposes of seience. he did not re gard as proving the elementary nature of a sub stance absolutely beyond doubt. Still, he inclined to consider the metals as elements, and, proving experimentally that the products of the destructive distillation of wood are compound, he refuted the opinion—then generally prevalent —that 41 ry distillation breaks up substances into their elements. lie further defined the distine- . Lion between a chemical compound and a mix lure: the properties cf a chemical compound, he maintained, are quite different from of its components, while in a mixture each •onstituent its characteristic properties practically unaffected. _thove all, he ea riwstly warned •hem ists against adopting hypotheses and general theories di pc-iori. Theories are necessary: but Hitless they are generalizations cautiously made from observed facts, they may be dangerously mislead lug.
Boyle's views are now accepted Had he grasped and succeeded in spreading abroad one more idea—viz. the absolute neces sity of quantitative investigation—he would have doubtless become the founder of the science of chemistry—that is to say, with hint would have commenced the epoch enlightened by truth and free from fundamental errors. This he did not accomplish: nor teas it. possible to accomplish it before the characteristics of gaseous matter came to be known better than they wire in his day. And so it value about that chemists failed to appreciate his great warning against hypothe ses that are not rigidly correlated with facts, adopted a belief in a fiery 'phlogiston.' and thus created a period of darkness that lasted a century. It must be remembered that the im portant phenomena of what we now call oxida tion engaged the attention of chemists toward the end of the Seventeenth Century and through the entire Eighteenth CenIllrv. These pla.110111 ena were explained by the supposed existence of phlogiston. a substance which may have been first produced in the erring mind of some a] chemist. hut the first clear reference to which, under the name of been pinguis, we find in the works of Becher (B135-S2). Stahl (106o-1734) named it. phlogiston, endowed it with certain imaginary properties, and it as the basis of a doctrine which was soon accepted through out the civilized world.
To give a clear and precise account of this, as of any other doctrine, is a matter of considerable difficulty. For when ingenhms men are dominated by error. they usually mold it into a variety of forms in their efforts to give it the appearance of truth and render it consistent with itself. The phlogistians handled their hy pothesis with much dexterity. Yet their thought, lacking the character of quantitative precision, was weak; for quantitative conceptions, while already mastered by the physicist, were still in a state of confusion in the mind of the chemist.
Distinguishing clearly between the absolute weight of bodies and their specific gravity, we have no difficulty in understanding that although water vapor is lighter than air, its addition to a. given body must increase the weight of the lat ter, because water, whether liquid or vaporized, has weight. Stahl believed that the conversion of a a metallic oxide—into metal was paused by the addition of phlogiston. Ile knew that the conversion was accompanied by a dimi mition of weight ; but from this fact he only de duced that phlogiston must be `lighter than air,' failing to grasp that such au addition may make a body Iighicr in the 'Was(' of producing a sys tem of lower specific gravity, but must neves sarily make it hrnricr in the of increasing its absolute weight. It is more probable, how ever, that Stahl understood this in a general way, hut thought that the metals had a fewer specific gravity than their cakes. At least, June keg, a pupil of Stahl's, asserts this about metals and calces as a matter of fact, although Boyle had long since shown experimentally that the specific gravity of metals is really higher than that of their cakes. ,Nlit•h more extraordinary is the conception that we find itt the writings of Guyton de Alorveau, Alacquer, and others, \vita taught that phlogiston had /css Man no crciy/di! Stahl conceived of phlogiston as a fiery principle, `nint(ria (cunt prineipinin ignis, non ipse ignis.' Seeing that charcoal burns up completely, and is capable of producing metals by adding itself, as he thought, to their (cakes, he considered char coal as made lip ClItirely of phlogiston. Cavendish, knowing that 'inflammable air' is given off when metals are in acids, adopted the view that that, inflammable air (hydrogen) Waa phlogiston. with which metals part on coming into contact with acids. .111 in convenient faet in connection with the phlogistie theory was that combustion, including the trans formation of metals, into (cakes, could only take place in the air. Stahl and his followers referred to this fact as if it were quite natural that if phlogiston was to he absorbed from metals there must he a medium capable of absorbing it. There were thoughtful men, however, who would not be satisfied with explanations of this kind. Boerhaave, whose E/cmento Che nr ia. ( 1732) served for many- yc:1r:: as the standard text-book of taught distinctly that the conver sion of metals into cakes involved the absorp tion of something front the air. This he deduced by combining- the fact that the presence of air was necessary with the fact that the .onversion involved increase in weight. The latter fact he even freed from an erroneous explanation at tached to it by Boyle, who had thought that the increase in weight was due to absorption of heat during calcination: by the use of the balance Boerhaave showed that metals have precisely the same weight when glowing hot as when cold, and thus proved that heat has no weight. So near the truth were some. Fit none rose to combat, the phlogistie theory, and all—even 110erhaa•e—NNVIT dominated by it more or less.