Indefinite proportions

Acetates. Anhydrous iron(II) acetate [3094-87-9J, Ee(C2H202)2, can be prepared by dissolving iron scraps or turnings in anhydrous acetic acid ( 2% acetic anhydride) under an inert atmosphere. It is a colorless compound that can be recrystaUized from water to afford hydrated species. Iron(II) acetate is used in the preparation of dark shades of inks (qv) and dyes and is used as a mordant in dyeing (see Dyes and dye intermediates). An iron acetate salt [2140-52-5] that is a mixture of indefinite proportions of iron(II) and iron(III) can be obtained by concentration of the black Hquors obtained by dissolution of scrap iron in acetic acid. It is used as a catalyst of acetylation and carbonylation reactions. 

Whether or not pure substances have the same proportion by mass of their constituents was by no means initially obvious. Around 1800 two French chemists, Claude Berthollet and Joseph Proust, supported opposite views on this topic. If a metal such as lead is heated in air, there is a gradual color change as lead oxide is slowly formed. Berthollet argued for a combination of indefinite proportions as this transformation occurs the reactant is lead, the product is lead oxide, and there is an indefinite number of intermediates. Proust argued for definite proportions in that the system would at all times consist only of lead mixed with lead oxide (for simplicity we can ignore that more than one oxide of lead exists). The ratio of lead to lead oxide would change as the reaction proceeded but the system would have only two components. The wide acceptance of English... 

Gay-Lussac mentions Berthollet s theory of indefinite proportions (see Vol. Ill, p. 644) and Dalton s idea that compoxmds of two bodies are formed in such a way that one atom of the one unites with one, two, three, or more atoms of the other . He points out that carbonic oxide is lighter than oxygen and gases may unite with increase of total volume 100 of nitrous oxide and 50... 

Berthollet (see p. 576) regarded solutions as compounds in indefinite proportions Ta dissolution est une veritable combinaison. Thomson defined a... 

Lavoisier also says the acidifying and the acidified principle can exist in different proportions, which constitute the points of equilibrium and of saturation . He seems to have inclined to the idea of indefinite proportions in some special cases, and linked it in an interesting way with the operation of affinity in a manner afterwards developed by Berthollet, who was a co-author and participated in the discussions leading to this publication. 

Dalton s atomic theory and Wollaston s experiments (see p. 701) were criticised by Berthollet and he maintained his theory of indefinite proportions in certain cases. Ladenburg pointed out that the work of Richter, Dalton s atomic theory, Gay-Lussac s law of gaseous volumes, andthe work of Berzelius on combining proportions, had by then reinforced Proust s arguments, and nearly all chemists had returned to the view (held, for example, by Bergman) that chemical compounds were of definite composition. Most chemists decided in favour of Proust about 1808. Unfortunately, in rejecting Berthol-let s law of indefinite proportions, they also put aside the correct law of mass action, which was not really incompatible with the law of constant proportions and the atomic theory. Chemists then were interested in other matters, Probably the adoption of Dalton s atomic theory was at least as important as Proust s researches in the neglect of Berthollet s theory of variable proportions. ... 

W. Henry gives a good summary of BerthoUet s theory of mass action and combination in indefinite proportions and raises five objections against it ... 

Formation of non-stoichiometric compounds The transition elements on account of their variable valency can form non-stoichiometric compounds, i.e., compoimds of indefinite proportion. These compounds do not follow the general valency rules. For example, in ferrous oxide (FeO) the ratio of iron and oxygen is not 1 1, but it varies from Feo.940 to Feo.840- Therefore, it is a non-stoichiometric compoimd. SimilOTly, vanadium emd selenium also form non-stoichiometric compoimds VSeg gs. VSe 2 etc. 

Physical Theory La theorie physique, son objet, sa structure. Why, we might ask, did he choose to use the term mixt in 1902 when it no longer formed part of the contemporary chemist s vocabulary A century earlier, the debate between Joseph-Louis Proust and Claude-Louis BerthoUet concerning the nature of chemical combinations had given rise to a new consensual terminology. Henceforth, the (mechanical) combination of chemical species in indefinite proportions would be termed a mixture , while their chemical combination in definite proportions would be called a compound . Thus, Duhem deployed the word mixt as a self-conscious evocation of an outmoded chemical concept, in order to explore Its philosophical associations. 

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