Without repeating details which I have given elsewhere, I will recall herein a few words, adopting this new language:
1. That the acidifying principle or oxygen, when combined with the substance of tire, heat and light, forms the purest air, that which M, Priestley has called dephlogisticated air; it is true that this first proposition is not strictly proved and perhaps is not susceptible of strict proof; so 1 have proposed it only as an idea that I regard as very probable, and in that respect it must not be confused with the propositions which are to follow, which are based on rigorous experiments and proofs;
2. That this same acidifying principle or oxygen, combined with carbon or substances containing carbon, forms the acid of chalk (carbonic acid) or fixed air:
3. That with sulphur it forms vitriolic acid;
4. That with nitrous air it forms nitric acid;
5. That with Kunckel's phosphorus it forms phosphoric acid;
6. That with metallic substances in general it forms metallic calces, with the exception of the cases of which I shall speak in this or a following memoir.
Such is very nearly our present general knowledge of the combinations of oxygen with the different substances in nature, and it is not hard to see that there remains a vast field to explore; that there is a part of chemistry absolutely new and until now unknown, which will be completely investigated only when we shall have succeeded in determining the degree of affinity of this principle with all the substances with which it can combine, and in discovering the different sorts of compounds which result.
All chemists know that the simpler the substances are with which you are working, the nearer you come to reducing substances to their elementary molecules, the more difficult become the means of decomposing and recomposing the substances; we may suppose, therefore, that the analysis and synthesis of acids must present much greater difficulties than does the analysis of the neutral salts into the composition of which they enter. I hope, however, to be able in what follows to show that there is no acid, unless, perhaps, it be that of sea salt, which w T e cannot analyze and put together again and from which we cannot at will abstract the acidifying principle.
This kind of work demands a great variety of means, and the procedures necessary to success in effecting combination vary according to the different substances with which one is working. In some cases w T e must have recourse to combustion, either in atmospheric air or pure air. Such is the case with sulphur, phosphorus and carbon; these substances during combustion absorb the acidifying principle or oxygen, and by the addition of this principle become vitriolic, phosphoric and carbonic acid or fixed air.
