338 Analysis of Scientific Books. 



ments of a compound, must be uniform for the species. Thus hy- 

 drogen and oxygen unite in no other proportions than those con- 

 stituting water, which by weight are very nearly 11| of the former 

 to 88| of the latter, or 1 to 7|." In his preface he says, " Every 

 new edition must reject whatever recent experience has proved to 

 be erroneous." Now there are two very remarkable errors in the 

 above sentence. 1, Hydrogen and oxygen were shewn several years 

 ago by Thcnard to unite in other proportions than those constituting 

 water; and 2, The proportions constituting water are known to be 

 not 1 to 7| but 1 to 8. Chlorine and hydrogen would have fur- 

 nished Dr. Henry with a much better illustration of a definite soli- 

 tary combination of two elements. 



The third section of the chapter on affinity is devoted to the 

 atomic theory. Aware of the familiar and daily intercourse which 

 Dr. Henry enjoys with Mr. Dalton, to whom, indeed he dedicates 

 his work, we naturally looked for a more elaborate and consistent 

 exposition of this fundamental subject, than he has given. We 

 regret also to observe that the name of Richter is suppressed, 

 though his labours were directed to the doctrines of chemical 

 equivalents, for some years before Mr. Dalton was known even 

 to have thought on the subject ; and though Richter furnished the 

 only rigid method of discovering the atomic weights of neutro- 

 saline bodies. As to Sir H. Davy's ideas on chemical combination, 

 they are evidently (we do not say intentionally) misunderstood by Dr. 

 Henry. " Sir H. Davy," says he, " has assumed with Mr. Dal- 

 ton, the atom of hydrogen as unity ; but that philosopher, and 

 Berzelius, also have modified the theory, by taking for granted 

 that water is a compound of one proportion (atom) of oxygen, and 

 two proportions (atoms) of hydrogen." We do not know where 

 Dr. Henry has learned this. Sir H. Davy says, " As two volumes 

 of hydrogen to one of oxygen enter into the composition of water, 

 the ratio of the hydrogen in water will be to the oxygen as two to 

 fifteen ; and it may be regarded as composed of two proportions 

 of hydrogen, and one of oxygen ; and the number representing 

 hydrogen will be 1, and that representing oxygen, 15*. Again, 

 u Mr. Higgins has supposed that water is composed of one par- 

 ticle of oxygen, and one of hydrogen, and Mr. Dalton of an atom 

 of each ; but in the doctrine of proportions derived from facts, it 

 is not necessary to consider the combining bodies either as com- 

 posed of indivisible particles, or even as always united one and 

 one, or one and two, or one and three proportions. Cases will 

 hereafter be pointed out, in which the ratios are very different ; 

 and at present, as we have no means whatever of judging either of 

 the relative numbers, figures, or weights of those particles of bodies 

 which are not in contact, our numerical expressions ought to relate 

 only to the results of experiments f." Hence Sir H. Davy's pro- 



• Elements of Chim. Phil. p. 113. f Ibi ^- P- 114 - 



