346 Analysis of Scientific Books. 



it was promulgated, before the theory of equivalents was pro- 

 perly developed, what defence can Dr. Henry offer, for incorporat- 

 ing it in his systematic compilation of 1823? 



Another supposed law of Berzelius' which Dr. Henry calls im- 

 portant, is enunciated as follows: " The quantities of different bases 

 required to saturate a given quantity of any acid, all contain the 

 same quantity of oxygen." This is our old friend with a new face. 

 Let any one take up Dr. Wollaston's scale, and slide any number op- 

 posite to a given acid, it is obvious that the number opposite oxygen 

 is the equivalent to all the protoxide bases in the list. By taking 

 such partial views, we may fabricate as many canons as we please. 



In his general discussion on metallic alloys, Dr. Henry says, 

 " To estimate exactly, however, either the increase or diminution 

 of density, requires an attention to several circumstances." He 

 then refers in a fOot note to Aikin's dictionary, article Alloy. Is 

 not Dr. Henry aware that the rule given in that respectable work, 

 for computing the mean density of an alloy, is a false one, and 

 leads to very erroneous results ? 



We cannot approve of his systematic arrangement of the metals, 

 which he has indeed copied from Thenard, along with several 

 tables. His two general classes of the metals have been long received; 

 the oxides of the first class are not red ucible by heat alone, those of 

 the second are. The firstclass has three subdivisions. 1. " Metals 

 that are either laroien from experiment, or believed from analogy, to 

 absorb oxygen, at high degrees of heat, and to decompose water at 

 common temperatures." Here are placed the 6 metals, potassium, 

 sodium, lithium, calcium, barium, and strontium. Those presumed 

 by analogy to belong to this subdivision, arc the metallic bases of 

 the earths proper. 2. " The second subdivision includes those metals 

 which absorb oxi/gen from atmospheric air at high temperatures, and 

 decompose water, but not under a red heat. These are 5 in number, 

 viz., manganese, zinc, iron, tin, and cadmium. 3. " Metals of the 

 third subdivision are capable, like the foregoing, of absorbing 

 oxygen at high temperatures, but not of decomposing water at any 

 temperature." Here we have 14 metals, out of Thenard's 15, Dr. 

 Henry having transferred nickel to the 2nd class of noble metals. 



We beg leave to remark, that the metals of the first subdivision 

 absorb oxygen, not merely at high degrees of heat, but at ordinary 

 temperatures. Potassium and sodium, tarnish and oxidize speedily 

 in dry air. Their characteristic property is to decompose cold 

 water with explosive violence. The metals of the second sub- 

 division are not truly represented by Dr. Henry, when he says, 

 " they absorb oxygen from the air, at high temperatures, and de- 

 compose water, but not under a red heat." We shall give him 

 three authorities for our opinion, which he will not venture to 

 gainsay. "* Manganese, when exposed to the air, attracts oxygen 



* Thonwn's System of Chem. 6th Edit. /. 410. 



