PROPORTIONS DETERMINATE. 



177 



Determi- 

 nate. 



ilton. 



likewise; so that each new addition of oxygen or sul- 

 phur take-; place />(/ xii llu-n \sitlmit any intermediate 

 tage. H. ithnlit-t defended himself with so much 

 sagacity, that the impartial reader, though in the secret 

 and pel hips obscure sentiment derived from a^; 

 Mirvey of chemistry, he might decide for I'rou-t, yet 

 felt himself compelled to suspend his find judgment. 

 1'roust however enjoyed at h<t the triumph of observ- 

 ing that, in proportion as this department of sei. nee 

 began to receive a more sedulous cultivation, as doubt- 

 ful points were cleared up, the results, obtained by 

 impartial chemists confirmed h ; s statement. 



time before the works of Messrs. Richter and 

 Berthollet appeared, Mr. Hujgins, professor of chemis- 

 try at Dublin, in a publication named, A Comparative 

 I l''i/--<fi\tit; arid Antiphlogistic Theories, 



(lf89,j started the idea of explaining the different de- 

 grees in which certain bodies combine, azote and 

 sulphur, for example, with oxygen, by regarding them 

 as united for each new degree of oxidation to an addi- 

 tional particle of oxygen ; so that nitrous gas should 

 contain two particles of oxygen, nitrous acid three, and 

 nitric acid four particles, for each particle of azote. 

 But as Mr. Higgins attached little importance to this 

 happy idea, and applied it very sparingly, it excited 

 no attention whatever among chemists. 



About fifteen years later, Mr. Dalton, another English 

 chemist, struck out the same idea; tried it by a compari- 

 son with the best analyses then known ; and finding suf- 

 cient reasons to consider it as just, made it the basis of a 

 chemical system, the details of which he published in a 

 work, entitled, A New System of Chemical Philosophy, 

 (1808.) According to this system; elementary sub- 

 stances combine together, in such a manner, that an 

 atom or indestructible particle of the one always unites 

 itself to 1,2, 3, 4-, c. whole atoms of the other; each 

 new addition taking place in a multiple ratio. Nume- 

 rous experiments atterwards confirmed this hypothe- 

 sis ; none has contradicted it ; and without exagger- 

 ation, it may be marked as one of the greatest im- 

 provements which chemistry has ever received. In 

 his new system, Mr. Dalton supposes that elementary 

 molecules unite most readily one to one ; and hence, 

 if but a single proportion is known in which two 

 bodies unite, it must be considered as that of one atom 

 to one atom. If several are known, the minimum of 

 one element is considered as the proportion of one to 

 one ; the second as that of one to two, and so on. But 

 when it happens that in the second combination the 

 element added is multiplied only by 14; the compound 

 is looked upon as formed by two atoms of the one and 

 three of the other. In the second volume of the work 

 just quoted, (printed in 1810.) Mr. Dalton has exa- 

 mined the simple combustibles with their oxides, and 

 given the number of atoms, which, in his opinion, 

 those oxides must contain. To the method of Mr. 

 Dalton, it may be objected that his principle ia hypo- 

 thetical ; that he has shown little scruple in the ap- 

 plication of it; that his analytical experiments are 

 not always very exact ; and that a desire, on the 

 part of the operator, to obtain a preconceived result, 

 seems often to have influenced the actual result ; a cir- 

 cumstance which, in these researches, it is impossible 

 too carefully to guard against, and which often misleads, 

 above all, when the system is framed first, and the proofs 

 sought afterwards. Mr. Dalton's new system is.moreover, 

 mingled, like the work of M. Kichter, with results less 

 BolicJIy founded; to which, no less than his predeces- 

 sor, he has endeavoured to add probability by giving 



VOL. XVII. PART I. 



them a mathematical colour. Mr. Dalton was even of 

 opinion that he had found the mathematical laws, ac- 

 cording to which gasiform substance* are absorbed and 

 retained by liquids. He spek of having determined 

 by experiments, which are very exact, and, to judge 

 from his own account of them, very conclusive, that 

 gases, excepting such as disengage a great quantity of 

 caloric in combining with water, are absorbed by that 

 substance, either in a volume equal to that of the wa- 

 ter, or else in a volume equal to {, i f , or *, of that of 

 the water. These numbers being the cube* of }, $, ^, 

 and }, he infers that the distance betweeen the mole- 

 cules of gasiform substances, absorbed by water, is al- 

 ways some multiple of their distance when out oT wa- 

 ter. Every liquid absorbs the same quantity of gas as 

 water ; with this single difference, that viscous liquids 

 require more time for saturation. 



Vet upon repeating those experiments, with all po- 

 sible care as it would seem, M. de Sausure has jut 

 found that Mr. Dalton'a results are without foundation ; 

 and that not only different liquids absorb different 

 quantities of the same gas, but that even the same liquid, 

 mixed with a substance soluble in it, loses much of its 

 absorbent power. Nor has the ratio which, according 

 to Mr. Dalton, the volume of the absorbed gas bears 

 to that of the absorbent liquid, been better confirmed 

 by the experiments of De Saussure. The following is a 

 comparison between some of their result*. 



1 00 measures of water absorb of 



(According to Sautsure.) (According to Dalton. J 

 Carbonic acid gas, 

 Sulphurated hydrogen gas 

 Nitrous oxide gas, 

 Olefiant gas, 

 Oxygen gas, 

 Nitrogen gas, 



These differences serve to show how science may be 

 injured, when the cultivator of it is one who, with little 

 accuracy in experimenting, possesses great confidence 

 in his own labours, and enough of sagacity to diffuse 

 a mathematical plausibility over his results. It is 

 much to be feared, that, notwithstanding the new in- 

 formation which we owe to the doctrine of chemical 

 proportions, the abuse made of that principle by un- 

 scrupulous chemists may occasion very considerable 

 mistakes. 



Mr. Dalton's opinions at first excited little interest ; 

 but some experiments of Dr. Wollaston awakened the 

 attention of chemists. It is a necessary consequence 

 from the atomic system of Mr. Dalton, that if A can 

 combine with B in more than one proportion, the latter 

 must be 2, 3, &c. times B. Wollaston weighed a por- 

 tion of the superoxalate of potass, and expelled its acid 

 by fire. The potass that remained, when added to a 

 portion of the superoxalate, equal to that which had 

 just been burned, rendered it exactly neutral. Another 

 portion of the superoxalate being dissolved in diluted 

 muriatic acid, and evaporated to crystallization, pro- 

 duced a superoxalate with a greater excess of acid. 

 Having roasted a certain quantity of it, he now ob- 

 served how much of the same salt not burned wa re- 

 quired to neutralize the potass obtained ; three parts 

 of the burned potass were required to saturate one part 

 of the unburned maximum superoxalate. From the-e 

 experiments, no less simple than ingenious, it follows 

 that potass combines with three portions of oxalic acid, 

 bearing to one another the ratio of 1, 2, and 4. Wol- 

 laston subjoined some other experiments, the result* cf 



Propor- 



. 



Deurmi 

 natr. 



