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Joseph-Louis Proust (1754-1826)
Researches on Copper
excerpted from Ann. chim. 32, 26-54 (1799) [as translated and repro-duced in Henry M. Leicester and Herbert S. Klickstein, A Source Book in Chemistry, 1400-1900 (Cambridge, MA: Harvard, 1952)]. Da Carmen Giunta's Classic Chemistry Page - http://maple.lemoyne.edu/~giunta/ - do Le Moyne College Department of Chemistry, Syracuse, NY, procede o texto a seguir (http://maple.lemoyne.edu/~giunta/proust.html)
(Editores: LJL & WS).
O site de Carmen Giunta contém também outras interessantes páginas e links referentes à história da Química.
On Carbonate of Copper
One hundred pounds of copper, dissolved in sulfuric or nitric acids and precipitated by the carbonates of soda or potash, invariably gives 180 pounds of green copper carbonate. If this quantity be submitted to a gradual distillation it gives 10 pounds of water, which appears as essential to the color and composition of this carbonate as the carbonic acid itself, since this water only passes over successively and conjointly with the acid. Deprived of these two components the carbonate leaves 125 pounds of black oxide at the bottom of the retort. This oxide dissolves in nitric acid with heat without decomposing the same. Likewise it dissolves in oxidized muriatic acid, from which, then, the oxygen escapes in bubbles, since copper is unable to combine with more than 25 parts of oxygen per 100. One may, then, in all analysis take 180 pounds of carbonate or 125 pounds found in this ratio of oxidation. Here are the components of the artificial carbonate.
Carbonic acid 46
The color of this carbonate is as constant as its proportions when it is not at all mixed with hydrate: it is a brilliant apple green, the shade of tone of fine malachite. But to give it its greatest luster it is necessary to direct some attention to the manner of its preparation. As the uniformity of its color depends also on a certain density, it is necessary in obtaining it to precipitate from boiling water or, in default of this, place the vessel in the sun. By this means the molecules come together, diminish in volume, and gather in a crystalline powder which has only to be washed and dried in a porcelain cup.
To convert the carbonate to the black oxide state in the wet way it is necessary to boil it a minute in caustic potash, which reduces it to 125 parts for 180 parts of carbonate.
On Native Carbonate of Copper
If 100 parts of this carbonate, dissolved in nitric acid and separated by the alkaline carbonates, gives us 100 parts of artificial carbonate, and if the base of these two combinations is the black oxide, we must recognize that invisible hand which holds the balance for us in the formation of compounds and fashions properties according to its will. We must conclude that nature operates not otherwise in the depths of the world than at its surface or in the hands of man. These ever-invariable proportions, these constant attributes, which characterize true compounds of art or of nature, in a word, this pondus naturae so well seen by Stahl; all this, I say, is no more at the power of the chemist than the law of election which presides at all combinations. From these considerations is it not right to believe that the native carbonate of copper will never differ from that which art produces in its imitation? Is there actually any difference between native carbonate of soda and the natural? No. Why, therefore, should there be any difference between those of copper or of other metals when no other perturbing cause has disarranged the reciprocal forces of the factors of these combinations?
The malachites of Aragon in nitric acid lose carbonic acid and leave one-hundredth part of sandy clay. By precipitation we reproduce 99 parts of artificial carbonate in which we discover scarcely a grain of calcerous carbonate. This solution, made warm, never shows any nitrous gas, which proves well that copper completely refuses further oxidation.
One hundred grains of the same, calcined in a crucible at a moderate temperature leaves 71 grains of black oxide. If we now subtract from this 2 parts for 100 of foreign earth, we have 69 to express the oxide contained in the malachite; but, differing only by a small fraction, these 69 grains correspond to 99 of artificial carbonate. There is, then, no difference between these two oxides, and in nature, as in art, the degree of their oxidation is evidently the same.