1821.] An Essay on Chemical Analysis. 14L 



work I had before met with, it struck me that if translated into 

 our language, it could not fail to be of great utiUty to the English 

 chemist." Mr. Children then observes, that to the first edition 

 of the author he had added the valuable matter contained in 

 the second edition, which appeared while the translation wa» 

 proceeding. 



Mr. Children was, I think, judicious in the choice of the 

 author whom he selected, for giving to the English chemist a 

 more full account of the minutiae of analysis, than had ever 

 appeared in our own language. 



Those parts of the work which depended merely upon the trans- 

 lator, it is hardly requisite to state have been accurately per- 

 formed by Mr. Children ; but it would be doing him great injus- 

 tice not to mention, that much new and valuable information, not 

 to be found in the original work, has been added : in saying this^ 

 I do not mean merely that such notices have been collected as are 

 within the reach of every one who inspects the various sources 

 of chemical knowledge ; but on several occasions Mr. Children 

 has given us the results of his own experiments and observations, 

 and which, I think, cannot fail to be useful. The directions for 

 the use of the blow-pipe, and the appearance which certain sub- 

 stances present after its action, form a very excellent part of the 

 appendix ; and Mr. Children shows, by the attention which he 

 has paid to the subject, that he has duly appreciated the value of 

 Bergman's remarks upon the blow-pipe, with which he very 

 aptly concludes his remarks on this useful instrument. 



On the subjects of the analyses of vegetable and animal sub- 

 stances, a concise but clear account of the proximate principles^ 

 of vegetable bodies has been introduced. It is, however, to be 

 observed, that by an oversight, the very widely diffused and 

 valuable vegetable product tannin has been totally omitted, nor 

 is its combination with gelatine and albumen mentioned. 



On the subject of the atomic theory, Mr. Children justly 

 remarks, " that in the great progress which chemistry has made 

 within a few years, one of its most important steps towards per- 

 fection as a science, is the establishment of the atomic theory.'* 

 A knowledge of the principles upon which it is founded, afford- 

 ing, he observes, to the practical analyst an easy and almost in- 

 fallible test of the accuracy of his experiments. 



Mr. Children then gives a sketch of the atomic theory, which 

 will afford the young chemist much useful information on this 

 curious and highly interesting topic. It may be, perhaps, out of 

 place here, but 1 cannot help remarking, the difference which 

 exists among chemical philosophers as to the numbers by which 

 they represent hydrogen and oxygen ; for it will be found that 

 they differ considerably both in quantity and proportion. Thus 

 Mr. Dalton represents hydrogen by 1 ; and oxygen by 7. Sir 

 H. Davy, hydrogen, 2, and oxygen, 15. Dr.' Henry, hydro- 

 gen, 1, and oxygen, 7*5. Mr. Brande agrees with Dr. Henry 



