242 Prof. Draper on the Existence and Effects ofAllotropism 



Asiswell known, to these singular modifications M.Berzelius 

 gave the designation of allotropic forms, and the whole phaeno- 

 menon passes conveniently under the designation of allotropism. 

 He shows that the peculiarity assumed is often of such a per- 

 sistent nature that it is not lost, even though the substance 

 affected should go into combination with others. Thus there 

 are two forms of silicon ; one combustible, and the other re- 

 markably incombustible. Each, by uniting with oxygen, gives 

 rise to a silicic acid ; the acid in one case being soluble in water 

 and in hydrochloric acid, and in the other the reverse. And in 

 like manner, metallic arsenic, which exhibits the same duality 

 of condition, gives rise to two different arsenious acids. Of 

 phosphorus there are at least two modifications; and accord- 

 ingly we have two compounds of that body with hydrogen, 

 one of which is spontaneously inflammable, and the other not; 

 and at least two oxygen acids, the monobasic and tribasic, in 

 which the essential difference rests in the state of the phos- 

 phorus they contain. 



It is to be remarked, that, so far as observation extends, the 

 most common cause of producing these singular differences is 

 the action of that class of agents which we term imponderable 

 substances. In very many cases change of temperature brings 

 about allotropic change; in others it is the agency of light, as 

 in chlorine and phosphorus ; and again, in others, association 

 with foreign bodies, which apparently establish new voltaic 

 relations. Heat, light and electricity seem to be the general 

 modifying agents. 



M. Berzelius, following the suggestion of M. Frankenheim, 

 proposes a nomenclature for pointing out the peculiar form 

 referred to in any special case. It de[)ends on the use of 

 Greek letters. Thus we have the three forms of carbon just 

 alluded to, designated on these principles by Ca, C/3, Cy. 

 But in a paper which I published in this Journal on the allo- 

 tropism of chlorine (Nov. 1845, p. 327), it is remarked that 

 we may often with greater convenience use the simple expres- 

 sions "active" and "passive." Thus active chlorine is that 

 which will decompose water in the dark, passive chlorine fail- 

 ing to do so. In this paper the same expressions will be em- 

 ployed. 



Hitherto allotropism has only been considered as affecting 

 inorganic states of matter, but its influence can be plainly 

 traced in the far more interesting case of organic beings; and, 

 when placed in a proper point of view, yields a remarkable 

 explanation of some of the most obscure but important facts 

 in physiology and pathology. These explanations I propose 

 now to point out. 



