1822,] Sixth Edition of his Si/stem of Che mist ty. 249^^^ 



repeated in the new review, we may presume that he has seen 

 the propriety of the arrangement. Indeed this improvement was 

 not made by me ; but by Mr. Smithson and Professor Berzehus. 

 I was satisfied of its justice by their arguments ; and the number 

 of sihcates which I have described in my sixth edition cannot, I 

 think, leave any doubt on the subject in the mind of any well 

 informed chemist. 



I have been blamed for not classing chromium, molybdenum, 

 tungsten, and columbium, with the acidifiable combustibles. 

 My reason for leaving them out was that they do not enter into , 

 any gaseous compounds, and that they decidedly belong to the' 

 class of intermediate combustibles. 



The intermediate combustibles are those bodies which have the 

 property of forming both bases and acids when they unite with' 

 oxygen. In one proportion, they form compounds capable of' 

 uniting with acids, and, therefore, perform the function of? 

 alkalies. In another proportion, they form compounds capable 

 of uniting with alkalies, and, therefore, perform the function 

 of acids. Hence they cannot with propriety be classed either 

 with the acidifiable or alkalifiable combustibles, but are interme- 

 diate between both. It is not unlikely that some bodies may 

 deserve a place in this class which I have ranked with the alka- 

 lifiable combustibles. Thus manganese seems capable of form- 

 ing an alkali when united to a minimum of oxygen, and an acid 

 when united to a maximum. My reason for leaving it in its old 

 place was a wish to verify the recent experiments respecting 

 manganesic acid ; and this I have not yet found leisure to do. 



These remarks will supersede the necessity of noticing parti- 

 cularly the vast mass of abuse which the Reviewer has contrived 

 to heap together. The first volume of course contains the whold' 

 of my arrangement, because it contains the whole of the simple 

 bodies. The science is not yet far enough advanced to admit 

 the compound bodies to be systematically arranged. I have 

 adopted the plan which appears to me most convenient for the 

 student ; but other methods might be adopted, and in fact have 

 been adopted by others. 



The sneers in which the Reviewer so frequently indulged 

 respecting my general observations are most uncandid. Every 

 one of the observations to which he alludes was rigidly correct 

 when I first wrote it. Subsequent discoveries have, in some 

 cases, introduced one or two exceptions. These I have not 

 always had it in my power to notice. I was anxious to swell 

 the book as little as possible, and did not scruple to pass over 

 the few existing exceptions ; because an attentive reader of the 

 first volume was enabled without difficulty to state them for him- 

 self I am not willing to abandon the character for precision^ 

 which I have long enjoyed, though the Reviewer has thought 

 proper to call it in question : on the contrary, 1 flatter myself 

 that I possess it in no common degree. If some of my earhef 



