follow, from the principle of numerical representation, have been en-
tirely overlooked.
Although there may be circumstances that will occasion exceptions to general rules, it appears that 100 numbers may be made correctly to represent nearly all the phenomena of the mutual action of 100 different salts, which, if described separately, would require about 5000 separate articles.
The author, having lately paid much attention to some of the prin- cipal facts in chemistry and pharmacy, has attempted the investiga- tion of a series of numbers adapted to this purpose, and has succeeded in representing nearly 1500 cases of double decomposition enume- rated by Fourcroy, with the exception of not more than twenty cases; and although it cannot be expected that these numbers are accurate measures of the forces they represent, yet they may be supposed to be tolerable approximations; forif any two of them be near the truth, the rest cannot be very far from it.
Dr. Young, however, observes, that if attractive force, which tends to unite any two substances, may always be represented by a con- stant quantity, it will follow, upon general principles, independent of any further hypothesis, that all known facts on this subject may be arranged in an order not liable to further alteration, in such a manner as to enable us to compare, with facility, a multitude of scat- tered phenomena. For if each force be constant, it follows that there must be a sequence in simple elective attractions, and palpable errors may thereby be detected in the common tables; for instance, in the four compounds resulting from the union of phosphoric and sulphuric acids with magnesia and ammonia, either the order of the acids, or the order of the bases, must be the same, otherwise the same force may be shown to be both greater and less than another.
The author observes, secondly, that there must be an agreement betwcen the simple and double elective attractions; for if flnoric acid stands above the nitric under barytes, and below it under lime, the fluate of barytes cannot decompose nitrate of lime.
The author makes a third observation (which is less obvious), that there must be a continued sequence in the order of double elective attractions, and accordingly that between any two acids the several buses may be arranged in such an order, that any two salts will de- compose each other, unless each acid be united to that base which stands nearest to it in the series; and asimilar arrangement will ob- tain for the acid between any two bases. In forming tables of this kind from the cases collected by Fourcroy, the author has been under the necessity of rejecting some facts that were contradictory to otbers; and in admitting some which were not consistent with numerical re- presentation, he has taken care to notice such inconsistency, and by notes of interrogation, or otherwise, to mark whatever remains in doubt. For the purpose of assisting the memory in retaining so nu- merous a series of facts, the author has contrived to express. in fifteen Latin hcxameters, as many as 1260 cases of double afiinity.
