Dr. Ure's Chemical Dktionary . 57 



which this Dictionary seems to have been originally compiled, 

 and the circumstances muler which its present regeneration has 

 been attempted. This exposition will naturally lead to an ac- 

 count of the principles on which the investigations of chemical 

 theory and facts have been conducted, which distinguish this Work 

 from a mere compilation. Some notice is then given of a Trea- 

 tise on Practical Chemistry, publicly announced by me upwards 

 of three years ago, and of the peculiar circumstances of my situa- 

 tion as a teacher, which prompted me to undertake it, though its 

 execution has been delayed by various obstructions. 



" The forms of matter are numberless, and subject to incessant 

 change. Amid all this variety which perplexes the common 

 mind, the eye of science discerns a few unchangeable primary bo- 

 dies, by whose reciprocal actions and combinations this marvel- 

 lous diversity and rotation of existence are produced and main- 

 tained. These bodies having resisted every attempt to resolve 

 them into simpler forms of matter, are called undecompounded, 

 and must be regarded in the present state of our knowledge as ex- 

 perimental elevients. It:is possible that the elements of nature are 

 very dissimilar ; it is probai)Ie that they are altogether unknown ; 

 and that they are so recondite, as for ever to elude the sagacity 

 of human research. 



" The primary substances which can be subjected to measure- 

 ment and weight, are fifty-three in number. To these, some che- 

 mists add the impondenilile elements, — light, heat, electricity, 

 and magnetism. But their separate identity is not clearly ascer- 

 tained. 



" Of the fifty-three ponderable principles, certainly three, pos- 

 sibly four, recjuire a distinct collocation from the marked peculi- 

 arity of their powers and properties. These are named Chlorine, 

 Oxygen, Iodine (and Fluorine ?) These bodies display a pre- 

 eminent activity of combination, an intense affinity for most of 

 the other forty-nine bodies, which they corrode, penetrate, and 

 dissolve ; or, by uniting with them, so impair their cohesive force, 

 that they become friable, brittle, or soluble in water, however 

 dense, refractory, and insoluble they previously were. Such 

 changes, for example, are effected on platinum, gold, silver, 

 and iron, by the agency of chlorine, oxvgcn, or iodine. But the 

 characteristic feature of these archeal elements is this, that when 

 a compound consisting of one of them, and one of the other forty- 

 nine more passive elements, is exposed to voltaic electrization, 

 the former is uniformly evolved at the positive or vitreo-clcctric 

 polo, while the latter appears at the negative or resino-elecuic 

 pole. 



" The singular strength of their attractions for the other sini- 



Vol.57. No. 273. J«//. 18^1. H pIc 



