FAMILIAR LETTERS ON CHEMISTRY. 17 



we employ for lighting our streets ; and, in short, the same elements, in the same 

 relative quantities, are found in a dozen other compounds, all differing essentially 

 in their physical and chemical properties. 



These remarkable truths, so highly important in their applications, were not 

 received and admitted as sufficiently established, without abundant proofs. Many 

 examples have long been known where the analysis of two different bodies gave 

 the same composition ; but such cases were regarded as doubtful : at any rate, 

 they were isolated observations, homeless in the realms of science, until, at length, 

 examples were discovered of two or more bodies, whose absolute identity of com- 

 position, with totally distinct properties, could be demonstrated in a more obvious 

 and conclusive manner than by mere analysis ; that is, they can be converted and 

 reconverted into each other without addition and without subtraction. 



In cyanuric acid, hydrated cyanic acid, and cyamelide, we have three such 

 isomeric compounds. 



Cyanuric acid is crystalline, soluble in water and capable of forming salts with 

 metallic oxides. 



Hydrated cyanic acid is a volatile and highly blistering fluid, which cannot be 

 brought into contact with water, without being instantaneously decomposed. 



Cyamelide is a white substance very like porcelain, absolutely insoluble in 

 water. 



Now, if we place the first, cyanuric acid, in a vessel hermetically sealed, and 

 apply a high degree of heat, it is converted by its influence into hydratic cyanic 

 acid ; and, then, if this is kept for some time at the common temperature, it passes 

 into cyamelide, no other element being present. And again inversely, cyamelide 

 can be converted into cyanuric acid and hydrated cyanic acid. 



We have three other bodies which pass through similar changes, in aldehyde, 

 metaldehyde, and eltaldehyde ; and, again two, in urea and cyanuret of ammonia. 

 Further, one hundred parts of aldehyde hydrated butyric acid and acetic ether 

 contain the same elements in the same proportion. Tnus one substance may be 

 converted into another without addition or subtraction, and without the partici- 

 pation of any foreign bodies in the change. 



The doctrine that matter is npt infinitely divisible, but on the contrary, consists 

 of atoms incapable of further division, alone furnishes us with a satisfactory ex- 

 planation of these phenomena. In chemical combinations, the ultimate atoms of 

 bodies do ndt penetrate each other, they are only arranged side by side in a certain 

 order, and the properties of the compound depend entirely upon this order. If 

 they are made to change their place their mode of arrangement by an impulse 

 from without, they combine again in a different manner, and another compound is 

 formed with totally different properties. We may suppose that one atom combines 

 with one atom of another element to form a compound atom, while in other bodies, 

 two and two, four and four, eight and eight, are united ; so that in all such com- 

 pounds the amount per cent, of the elements is absolutely equal ; and yet their 

 physical and chemical properties must be totally different, the constitution of each 

 atom being peculiar, in one body consisting of two, in another of four, in the third 

 of eight, and in a fourth of sixteen simple atoms. 



The discovery of these facts immediately led to many most beautiful and inter- 

 esting results ; they furnished us with a satisfactory explanation of observations 

 which were before veiled in mystery a key to many of nature's most curious 

 recesses. 



Again, solid bodies, whether simple or compound, are capable of existing in two 

 states, which are known by the terms amorphous and crystalline. 



When matter is passing from a gaseous or liquid state slowly into a solid, an 

 incessant motion is observed, as if the molecules were minute magnets : they are 

 seen to repel each other in one direction, and to attract and cohere together in 

 another and in the end become arranged into a regular form, which, under equal 

 circumstances, is always the same for any given kind of matter : that is, crystals are 

 formed. 



Time and freedom of motion for the particles of bodies are necessary to the 

 formation of crystals. If we force a fluid or a gas to become suddenly solid, 

 leaving no time for its particles to arrange themselves, and cohere in that direction 

 in which the cohesive attraction is strongest, no crystals will be formed, but the 

 resulting solid will have a different color, a different degree of hardness and 

 cohesion, and will retract light differently ; in one word, will be amorphous. Thus 

 we have cinnabar as a red and a jet-black substance; sulphur a fixed and brittle 

 body, and soft, semi-transparent and ductile ; glass as a milk-white opaque sub- 

 stance, so hard that it strikes fire with steel, and in its ordinary and well-known 

 state. These dissimilar states and properties of the same body are occasioned in 



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