AF F

AFF

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chemically with different proportions of oxygen,if WO of the metal take 9 of oxygen for thelowest degree of oxygenation, all the other de-grees will be in the proportion of 100 of metalto twice 9 (18) of oxygen; or 100 of metal tothree times 9 (27) of oxygen ; or 100 of metalto four times 9 (36) of oxygen, &c. &c. A rea-son for this simplicity in the ratio of binarycompounds maybe found in the general principleassumed by Mr. Dalton, which is, that in allcases the simple elements of bodies are disposedto unite atom to atom, singly, or if either is inexcess it exceeds fyy a ratio to be expressed by•some simple multiple of the number of itsatoms.

Hence, from the relative weights of the con-stituent parts of, a compound, Mr. Dalton infersthe relative weights of the ultimate particle oratom of each of these parts; and, this beingfound, the number of atoms of each constituentwhich enters into the formation of the com-pound particle is also deduced.

Thus (taking a compound of two constituent-parts A and B. as the simplest case) if its ele-ments are found by experiment to unite in theproportion of 5 of A to 7 of B, it is inferred byMr. Dalton that the numbers 5 and 7 expressthe comparative weight of an atom of A and B.respectively. And these elements, though uni-ting in several proportions, will yet be foundby experiment to be confined to either 5 A to14, 21, 28, &c. ofB. which is, one atom of Ato 2, 3, 4, See. atoms of B ; or conversely itwill be 7 B to 10, 15, 20, Zee. of A, which iscne atom of B, to 2, 3, 4, &c. atoms of A. Itis essential to the consistency of this systemtherefore, that there should be no other propor-tions of combination between these two ele-ments, unless indeed it be one that is expressedby an even sub-division of one of these propor-tions, as for example, 5 A to 7, 10f, 14, &c.of B ; in which case the lOf being resolvableinto three portions of 3j each, the number ex-pressing the relative weight of an atom of B,must be reduced to 3f instead of 7, and conse-quently the several proportions of 7, 10|-, 14,and 21 of B, will be resolved respectively into2, 3, 4, and 6 atoms of B.

To verify the numbers expressing the relativeWeights of an atom of A and B, (supposingthat of A to be assumed as 5, and that of B as7) let them each be examined in their separatecompounds with a third body, C. Then, sup-pose that in the simplest binary compound ofA and C, analysis discovers 3 parts by weightof C> to 5 of A, it is assumed, that, as 5 is

taken as the numerical expression of an atomof A, the number expressing an atom of C.must be 3; and consequently , if this mode ofestimation be just, it will also be found by ex-periment that in the simplest combination of Cwith B, 7 parts of B will unite exactly with 3parts of C. This supposes indeed that thissimple combination of one atom of, each bodyis known by experiment; but even if thisshould not be the case, the general principlewill not be contravened, if, instead of a singleportion of C being found, there should be adouble, triple, or quadruple portion, providedthe radical number or common divi c or is 3, thatof B being 7.

To illustrate this by an example from Mr.Dalton (in which however the numbers as-sumed are not perfectly accurate though suffi-cient for the present purpose.) The substanceof which as far as we yet know the smallestrelative weight enters into chemical combina-tion is hydrogen, and on this account theweight of its atom is assumed as unity, and is thestandard of comparison for the relative weightof the atom of all other bodies. The only com-pound of hydrogen and oxygen that we knowis water, in which the oxygen is to the hydrogenas 7 to 1. The number 7 therefore is assumedas the relative weight of the atom of oxygen,and water is a binary compound containing anatom of hydrogen with an atom of oxygen inevery atom of water. Sulphuretted hydrogenis composed according to Mr. Dalton of 13parts by weight of sulphur and 1 of hydrogen.If it be assumed that an atom of sulphurettedhydrogen contains an atom of sulphur united toan atom of hydrogen, the relative weight ofan atom of sulphur must be 13. To prove thatthis number 13 may be assumed as the weightof an atom of sulphur, let it be examined in itscompounds with oxygen, and if correct, all thecompounds'of these two elements will containfor every 13 parts by weight of sulphur, either7, or 14, or 21, &c. parts of oxygen, according,as the compound contains to every atom of sul-phur one, or two, or three atoms of oxygen.

Now according to Mr. Dalton Sulphureousacid actually contains 13 parts by weight ofsulphur to 14 of oxygen, and therefore itsatom consists of one atom of sulphur to twoatoms of oxygen ; and Sulphuric acid consistsof 13 parts by weight of sulphur to 21 of oxy-gen, or one atom of the former to three atoms-of the latter.

This hypothesis therefore is perfectly con-sistent in the above examples-