PROPORTIONS, DETERMINATE, in chemistry, are those invariable and fixed proporttons, in which ele mentary substances combine to form cumpouud bodies, organic as well as inorganic.
It appears that whenever the idea of bodies composed of simple elements had begun to be formed, it was looked upon as certain, that the same characters and properties, existing in different compounds, indicated the same ele ments combined in the same proportions. At a remote era, before scientific speculations could be founded on an adequate system of experiments, this opinion is to be found in the writings of philosophers. It even forms part of the doctrines of Pythagoras. And Philo, who has collected, in his Li1'ri Sapientiae, the choicest philosophical ideas of his time, says, in cap. xi. v. 22, 7ravra ef0; FLIT& ,CX1 Cte !AV corcih.tc0 " God made all things by measure, number, and weight." And, judging from his manner of introducing this reflection, he takes it for a thing fully de cided anti generally acknowledged. It may be affirmed, however, that, till our own times, this opinion has continued rather an obscure anticipation among philosophers, than a truth completely admitted and established by experience in general, or by researches entered into with this particular design. No doubt, the first attempt towards a quantitative analysis is clue.to a belief in this opinion; yet this first at tempt bears no very ancient date. Though we cannot spe cify with certainty what chemist v as the foremost to find the quantitative composition of any substance by analyti cal experiment- is evident enough, that the art of •; • 'ySes with accuracy did not origi. • i he past century ; and to the per we owe the discovery of deter , .:...ictent chemists appear to have laid it down as an axiom, that the same elements, united in the same pro portions, produce always the same compound substance. Wenzel, Bergman, and Richter, arc the first chemists in whose writings we discover proof of their having perceived that these proportions have a more general relation to each other. In his academical dissertation, printed at Upsal in 1780, and entitled, De diversa phlogisti quantitate in metallis, Bergman exhibits a great number of experiments OD the precipitation of Metals by each other, and draws from his facts the following conclusion : Phlogisti mutuas quantitates praecipitantis et praecipitandi ponder/bus esse inverse proportionales ; which, in the language of the an tiphlogistic theory, signifies, that to neutralize a given quantity of any acid, each of these metals combines with the same quantity of oxygen. Bergman laboured zealously
to acquire information concerning the elective affinities and mutual decompositions of several saline substances. He confirmed the general observation, that salts maintain their neutrality in this case ; but he does not seem to have had just notions about the latter phenomenon, which indeed stands in direct opposition to the results deduced by Berg man himself, from his analytical experiments upon the composition of a great number of salts.
Wenzel, a German chemist, contemporary with Berg man, examined this matter more carefully, in a memoir on affinities, (Lehre von den Verwandischaften0 printed at Dresden in 1777. Be proved by experiments, perform ed with wonderful exactness, that the reason why two neu tral salts, decomposing each other, preserve their neu trality, is that the relative quantities of alkalis or earths which neutralize acids, are the same, whatever be the acid requiring saturation : in other words, that when, for ex ample, the neutral nitrate of lime is decomposed by the neutral sulphate of potass, the gypsum and the saltpetre which result from the process are also neutral, because the quantity of potass which saturates a given portion of nitric acid is to the quantity of lime which saturates an equal portion of that acid, in the same proportion as the potass is to the lime which saturates a given quantity of sulphuric acid ; from which it follows, that the neutrality of the two salts must continue even after their mutual decomposition. The numerical results of WTenzel's experiments are won derfully accurate, and have generally been confirmed by the more careful analysis of later times. It appears, how ever, that little attention was given to them at the date of their appearance ; and the sanction of more noted chemists secured a preference for results, not only less exact, but even contradicted by the phenomenon which Wenzel had so ingeniously explained.