Jg FAMILIAR LETTERS ON CHEMISTRY. 



one case by a regular, in the other by an irregular arrangement of its atoms: one 

 is crystalline, the other amorphous. 



Applying these facts to natural productions, we have reason to believe that clay- 

 elate and many kinds of greywacke are amorphous feldspar, as transition limestone 

 is amorphous marble, basalt and lava mixtures of amorphous zeolite and augite. 

 Any thing that influences the cohesion, must also in a certain degree alter the pro- 

 perties of bodies. Carbonate of lime, if crystallized at ordinary temperatures, 

 possesses the crystalline form, hardness, and refracting power of common spar ; if 

 crystallized at a higher temperature, it has the form and properties of arragonite. 



Finally. Isomorphism, or the equality of form of many chemical compounds having 

 a different composition, tends to prove that matter consists of atoms the mere 

 arrangement of which produces all the properties of bodies. But when we find 

 that a different arrangement of the same elements gives rise to various physicial and 

 chemical properties, and a similar arrangement of different elements produces 

 properties very much the same, may we not inquire whether some of those bodies 

 which we regard as elements may not be merely modifications of the same sub- 

 stance ? whether they are not the same matter in a different state of arrangement ? 

 We know, in fact, the existence of iron in two states, so dissimilar, that in the one, 

 it is to the electric chain like platinum, and in the other it is like zinc ; so that 

 powerful galvanic machines have been constructed of this one metal. 



Among the elements are several instances of remarkable similarity of properties. 

 Thus there is a strong resemblance between platinum and iridium ; bromine and 

 iodine ; iron, manganese and magnesium ; cobalt and nickel, phosphorus and 

 arsenic ; but this resemblance consists mainly in their forming isomorphous com- 

 pounds in which these elements exist in the same relative proportion. These com- 

 pounds are similar, because the atoms of which they are composed are arranged in 

 the same manner. The converse of this is also true : nitrate of stroutia becomes 

 quite dissimilar to its common state if a certain proportion of water is taken into 

 its composition. 



If we suppose selenium to be merely modified sulphur and phosphorus, modified 

 arsenic, how does it happen, we must inquire, that sulphuric acid and selenic acid, 

 phosphoric and arsenic acid, respectively form compounds which it is impossible to 

 distinguish by their form and solubility ? Were these merely isomeric they ought 

 to exhibit properties quite dissimilar ! 



We have not, I believe, at present the remotest ground to suppose that any one of 

 those substances which chemists regard as elements, can be converted into 

 another. Such a conversion, indeed, would presuppose that the element was com- 

 posed of two or more ingredients, and was, in fact, not an element ; and until the 

 decomposition of these bodies is accomplished, and their constituents discovered, 

 all pretensions to such conversions deserve no notice. 



Mr. Brown, of Edinburgh, thought he had converted iron into rhodium, and 

 carbon or paracyanogen into silicon. His paper upon this subject was published 

 in the Transactions of the Royal Society of Edinburgh, and contained internal 

 evidence, without a repitition of his experiments, that he was totally unacquainted 

 with the principles of chemical analysis. But his experiments have been carefully 

 repeated by qualified persons, and they have completely proved his ignorance j his 

 rhodium is iron, and his silicon an impure incombustible coal. 



LETTER 



MY DEAR SIR : 



One of the most remarkable effects of the recent progress of science is the 

 alliance of chemistry with physiology, by which a new and unexpected light has 

 been^thrown upon the vital processes of plants and animals. We have now no 

 longer any difficulty in understanding the different actions of aliments, poisons, 

 and remedial agents we have a clear conception of the causes of hunger, of the 

 exact nature of death ; and we are not, as formerly, obliged to content ourselves 

 with a mere description of their symptoms. It is now ascertained with positive 

 certainty, that all the substances which constitute the food of man must be divided 

 into two great classes, one of w^ich serves for the nitrition and reproduction of the 

 animal body, while the other^ Ministers to quite different purposes. Thus starch, 



