1825.] M. Berzelim's Hypothesis of the Atomic Theory. 189 



to the most compound. Berzellus divides these several combi- 

 nations into separate orders — the simplest, or the atoms of the 

 first order, are composed of simple elementary atoms, and are 

 either inorganic or orgaijic. The former contain only two ele- 

 ments, the latter always three at least. Compound atoms of the 

 second order are produced by the union of compound atoms of 

 the first order ; those of the third by the union of atoms of the 

 second order, &c. Thus sulphuric acid, potash, and water, are 

 cou)pound atoms of the first order, since they consist oidy of a 

 base and oxygen. Sulphate oi potash and sulphate of alumina 

 are atoms of the second order, being formed by the union of 

 compound atoms of the first order. Anhydrous alum, which is 

 composed of the two last mentioned salts, belongs to the third 

 order; and crystallized alum, which, besides those elements, 

 also contains several atoms of water, is an instance of a com- 

 pound of the fourth order. 



But taking it for granted that bodies are composed of indivisi- 

 ble atoms, certain laws must regulate their combinations, in order 

 to establish them in definite chemical proportions, and on which 

 the constancy of those proportions must depend. The existence 

 of such laws and the probable manner in which elementary atoms 

 combine, is inferred from experiment, which teaches us that 



1 . A>i atum of one element cunihines with one, two, three, or 

 more atoms of another element. This is of most frequent occur- 

 rence, so that in the greater number of compound atoms, one of 

 the elements enters only as a single atom. 



2. Tioo atoms of one clement combine with three atoms of another 

 element. This may happen whenever the quantity of oxygen in 

 a protoxide is to that in the deutoxide as 1 : 1^; as is the case 

 with iron. If the first oxide be composed of an atom of base 

 united to an atom of oxygen, the second must contain two atoms 

 of base united to three atoms of oxygen ; for there can be no 

 such thing as half an aton). This apparent anomaly may be 

 reconciled in a different manner, by supposing that there may be 

 another hitherto unkuuvvu oxide of iron, containing half the 

 quantity of oxygen tliat is contained in the lowest of the two 

 known oxides. According to this view, an atom of base in the 

 unknown oxide is united to one atom of oxygen, and in the two 

 known oxides to two and three atoms respectively. Dr. Thorn- 

 sou with Berzelius adopts the former solution. 



In the compound atoms of the second order, the ratio of two 

 atoms of one element to three of another is found less equivo- 

 cally, though the instances are rare. Thus the hydrated red 

 oxide of iron is composed of two atoms of oxide combined with 

 three atoms of water; the subsulphale of copper contains two 

 atoms of acid and three atoms of base. Unless we consider 

 these as the true proportions of the elements of the above com- 

 pounds, we must suppose the oxide of iron, as well as the 



