FAMILIAR LETTERS ON CHEMISTRY. 



The materials from which gas is manufactured in England bears a direct pro- 

 portion to the price of corn ; there the prices of tallow and oil are twice as great 

 as in Germany, but iron and coal are two thirds cheaper ; and even in England the 

 manufacture of gas is only advantageous when the other products of the distillation 

 of coal, the coke, &c., can be sold. 



It would certainly be esteemed one of the greatest discoveries of the age if any 

 one could succeed in condensing coal gas into a white, dry, solid, odorless sub- 

 stance, portable, and capable of being placed upon a candlestick, and burned in a 

 lamp. Wax, tallow, and oil, are combustible gases in a solid or fluid form, which 

 offer many advantages for lighting, not performed by gas : they furnish, in well- 

 constructed lamps, as much light, without requiring the expensive apparatus 

 necessary for the combustion of gas, and they are generally more economical. In 

 large towns, or such establishments as hotels, where coke is in demand, and where 

 losses in stolen tallow or oil must be considered, together with the labor in snuffing 

 candles and cleaning lamps, the higher price of gas is compensated. In places 

 where gas can be manufactured from resin, oil of turpentine, and other cheap oil, 

 as at Frankfort, this is advantageous so long as it is pursued on a small scale only. 

 If large towns were lighted in the same manner, the materials would rise in price : 

 the whole amount at present produced would scarcely suffice for two such towns as 

 Berlin and Munich. But no just calculation can be made from the present prices 

 of turpentine, resin, &c., which are not produced upon any large scale. 



LETTER V. 



MY DEAR SIR : 



Until very recently it was supposed that the physical qualities of bodies,. that 

 is, hardness, color, density, transparency, &c., and still more their chemical pro- 

 perties, must depend upon the nature of their elements, or upon their composition. 

 It was tacitly received as a principle, that two bodies containing the same elements 

 in the same proportion, must of necessity possess the same properties. We could 

 not imagine an exact identity of composition, giving rise to two bodies entirely 

 different in their sensible appearance and chemical relations. The most ingenious 

 philosophers entertained the opinion that chemical combination is an inter-penetra- 

 tion of the particles of different kinds of matter, and that all matter is susceptible 

 of infinite division. This has proved to be altogether a mistake. If matter were 

 infinitely divisible in this sense, its particles must be imponderable, and a million 

 of such molecules could not weigh more than an infinitely small one. But the 

 particles of that imponderable matter, which, striking upon the retina, gives us the 

 sensation of light, are not in a mathematical sense infinitely small. 



Inter-penetration of elements in the production of a chemical compound, sup- 

 poses two distinct bodies, A and B, to occupy one and the same space at the same 

 time. If this were so, different properties could not exist with an equal and 

 identical composition. 



That hypothesis, however, has shared the fate of innumerable imaginative 

 explanations of natural phenomena, in which our predecessors indulged. They 

 have now no advocate. The force of truth dependent upon observation is irresis- 

 tible. A great many substances have been discovered among organic bodies, 

 composed of the same elements in the same relative proportions, and yet exhibiting 

 physical and chemical properties perfectly distinct one from another. To such 

 substances the term Isomeric (from KJOJ equal and ^ poj part] is applied. A great 

 class of bodies, known as the volatile oils, oils of turpentine, essence of lemons, 

 oil of balsam, of copaiba, oil of rosemary, oil of juniper, and many others, differing 

 widely from each other in their odor, in their medicinal effects, in their boiling 

 point, in their specific gravity, &c., are exactly identical in composition, they 

 contain the same elements, carbon and hydrogen, in the same proportions. 



How admirably simple does the chemistry of organic nature present itself to us 

 from this point of view. An extraordinary variety of compound bodies produced 

 with equal weights of two elements ! and how wide their dissimilarity ! The 

 crystallised part of the oil of roses, the delicious fragrancy of which is so well 

 known, a solid at ordinary temperatures, although readily volatile, is a compound 

 body containing exactly the same elements, and in the same proportion, as the gas 



