PROPORTIONS DETERMINATE. 



181 



Proper- cules in the greater part of oxides may be inferred with 

 r.-.!)lf certainty. It follows that most of the 



Det.rmi- ov j ( |,. s v .j,; ( |, aieouling to Datton, contain oidy 1 mo- 

 ^, Ircule of oxygen, contain in re.ility - or 3. Yet there 

 are oxi<! -. tin- number of \\lio--e molecules cannot be 

 di t< -rinined by any experiment; such are potass and 

 the earths in general. Berxelius has attempted to sup- 

 ply this deficiency by a train of analogical reasoning, 

 v hicli, though it no doubt occasionally misleads, is in 

 this case the only clue we have to guide us. The ana- 

 logy of potass to Mida induces a supposition that, in 

 each of those two alkalies, the number of atoms is the 

 same ; but we know, from analyzing the superoxide of 

 ! i, that this alkali must contain 2 molecules of oxy- 

 gen ; from which, we may perhaps conclude, that po- 

 tass contains 2 likewise. Besides, on comparing toge- 

 ther those metallic oxides which are electro-positive, 

 (that is to say, which give salts with acids,) it appears 

 that such as contain 2 molecules of oxygen form always 

 the strongest saline base, and show the closest analogy 

 to alkalies. Such as contain but one molecule, either 

 do not at all combine with acids, or constitute a sepa- 

 rate class of faline bases ; they have a strong mutual 

 resemblance in their general properties, and their salts 

 differ in a characteristic manner from those of oxides 

 containing 2 molecules of oxygen : such are the mini- 

 mum oxides of copper, of mercury, platina, rhodium, 

 and gold. With regard to such as contain 3 molecules 

 of oxygen, they likewise, in general, form weaker sa- 

 line bases, and even frequently, in the state of electro- 

 negative oxides, themselves combine with saline bases. 

 From all this, Berzelius concludes, that, for the pre- 

 sent, the fixed alkalies and the earths may, with most 

 plausibility, be looked upon as containing 2 molecules 

 of oxygen. As to alumina, on examining the propor- 

 tions in which this earth is found combined with po- 

 tass in alum and feldspar, with magnesia and the oxide 

 of zinc, in the spinelle and gahnite, Berzelius imagined 

 it to contain 3 molecules of oxygen. The same is pro- 

 bably true of glucina. 



To express the composition of a compound body, 

 M. Berzelius has proposed signs, by means of which, a 



glance will suffice to show what otherwise muit have 

 required a long periphrase to enunciate. Each radical 

 is represented by the initial of its Latin name. If t*o 

 radical) have the same initial letter, they are dittin- 

 guished in the following manner. Combustible bodiec, 

 not metallic, are designated by the first letter alone ; 

 such metals as have the same initial being distinguished 

 by a second letter. Thus C denotes carboniun 

 =r cobaltum ; CH. =r cuprum ; fin. =r stannum ; .S'/. 

 = stibium ; O signifies oxygen ; but as in compound 

 bodies it is a more general ingredient than any other 

 element, Berzelius proposes to mark the number of its 

 atoms by dots placed above the initial letter. Thus, 

 for example, C = C + 2 O = carbonic acid ; c = 

 Fe -f- 3 = red oxide of iron. . This expedient render* 

 the formulae shorter and more easily understood. 

 When a compound body contains several molecules of 

 a combustible element, the number of its atoms is an- 

 nexed on the right, like an exponent in algebra. Thus 



Al. .S'. 3 =. sulphate of alumina, means that there are 

 three molecule- of sulphur or sulphuric acid for one of 

 alumina ; but if it were required to denote that a body 

 contains, for example, two particles of the sulphate of 

 alumina, the number is placed on the left; arm it then 

 multiplies all the letters which follow it. Thus, 

 K. S.* -f- 2 Al. S.* is the formula, exhibiting the compo- 

 sition of alum. To determine the relative weight of 

 the molecules, Berzelius compares them with that of 

 oxygen, supposed to be unity ; a method which has 

 likewise been proposed by Dr. Wollaston. The num- 

 ber of molecules contained in an oxide being known, 

 it is easy to find the weight of a molecule of the radical. 

 The oxideof iron, for instance, is composed of 100 parts 

 iron, and 44.25 parts oxygen : these 44.25 parts form 

 three molecules of oxygen ; from which it follows that 



44 25 



' : 100: : 1, (the weight of oxygen,) : 6.78, the 



O 



weight of the molecule of iron. M. Berzelius has 

 given the following table, exhibiting the weight of the 

 several radicals, and the composition as well as weight 

 of their oxides. 



