1822.] Sixth Edition of his System of Chemistry . 247 



something very superior, the reader may judge of my surprise 

 when I found he had adopted the following arrangement : 

 Part I. — Attraction, Heat, Electricity. 

 II.— Radiant Matter. 

 III. — Undecompounded Bodies. 



1. Acidifying Supporters of Combustion. 



2. Aciditiable Combustibles. 



3. Metals. 



IV. — ^Vegetable Chemistry. 

 V. — Animal Chemistry. 



Would not the author of such an arrangement have acted 

 more wisely, if he had not directed the attention of the public 

 to arrangement at all? Do not parts first and second clash with 

 each other? Does not the first part include the second? The 

 division of the simple bodies is obviously my old one. The 

 very terms have been borrowed from me. I abandoned it, 

 because the recent discoveries, for which we are chiefly indebted 

 to Sir H. Davy, have broken down the line of distinction 

 between the simple acidifiable combustibles and the metals : for 

 example, arsenic burns as readily, and at as low a temperature, 

 as charcoal itself. It is acidifiable too ; for arsenic acid is a 

 powerful acid, and neutrahzes the bases as completely as any 

 acid whatever. What can be more preposterous than to class 

 arsenic and tellurium, bodies which enter into gaseous compounds 

 with hydrogen (precisely as phosphorus, sulphur, and selenium, 

 do), with a set of bodies which enter into no gaseous compounds 

 whatever ? He who does not perceive that arsenic and tellurium 

 have a much closer resemblance to sulphur and selenium than to 

 any metal, may indeed amuse the ladies and gentlemen who 

 attend the Royal Institution; but is not hkely to make any 

 arrangement calculated for the improvement of the science. 



My arrangement of the simple bodies was not made without 

 the most careful reflection. If I erred, I must acknowledge that 

 my error was not the effect of haste. Plausible objections may 

 indeed be made to several parts of this arrangement. These 

 objections I examined with all the care of which I was capable, 

 before the fifth edition of my System was put to the press. I am 

 still of opinion, that it is upon the whole the best of which the 

 science in its present state is susceptible. I have divided the 

 simple bodies, as the reader will find by consulting my System, 

 into three sets, viz. 



1. Supporters. 



2. Incombustibles. 



3. Combustibles. 



The supporters are three, oxygen^ chlorine, and iodine. To 

 these I have added a fourth, fluorine, which is still only conjec- 

 tural. No doubt chlorine and iodine might be placed among the 

 incombustibles, as has been done by the French chemists ; but 

 I think that, upon the whole, these bodies bear a much closer 



