Everything in mineralogy is not a compound (combinaison) ... there is a large number of substances to which this name should not be applied indiscriminately, as some authors do for want of having thought sufficiently about what is understood by this word in chemistry. Because they have not noticed that the science has made a rule of reserving its use, they have applied it indifferently to substances which it deliberately avoids describing thus. They therefore confuse compounds with certain concrete solutions, certain combinations, certain systems of compound bodies to which it attaches a quite contrary idea. Nature, for example, presents us with compounds of elements, but also with combinations formed by a multiple aggregation of these same compounds.
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Let us stop for a moment to satisfy an objection which D'Aubuisson certainly addresses to me, when he says in a memour in which he so justly sees the futility of certain definitions, "The analyses of the copper ore (cuivre gris), which Klaproth has just published, are a new example of compounds formed in variable proportions." I would reply that the copper ore does not belong at all to the order of compounds which chemists are examining at the moment in order to unravel the principles of their formation. A compound according to our principles, as Klaproth would tell you, is something like sulphide of silver, of antimony, of mercury, of copper; it is an acidified combustible substance, etc.; it is a privileged product to which nature assigns fixed proportions; it is in a word a being which she never creates, even in the hands of man, except with the aid of a balance, pondere et mensura.
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