128 POPULAR SCIENCE MONTHLY. 



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 prop- 

 osition 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 prob- 

 able, 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 (car- 

 bonic 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 combina- 

 tions 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 deter- 

 mining the degree of affinity of this principle with all the substances 

 with which it can combine, and in discovering the different sorts of com- 

 pounds 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 decompos- 

 ing 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 ab- 

 stract the acidifying principle. 



This kind of work demands a great variety of means, and the pro- 

 cedures 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. 



