Homogeneous substance

It is useful in this sense to make a dear distinction between the conception of an element as a separate homogeneous substance, and as a material but invisible part of a compound. Mercury oxide does not contain two simple bodies, a gas and a metal, but two elements, mercury and oxygen, that, when free, are a gas and a metal. Neither mercury as a metal nor oxygen as a gas is contained in mercury oxide it only contains the substance of the elements, just as steam only contains the substance of ice, but not ice itself, or as corn contains the substance of the seed but not the seed itself (4). 

The entropy of a condensed chemically homogeneous substance vanishes at the zero of absolute temperature ... 

If the independent variables are p and T, we have quite generally for a homogeneous substance ... 

The theoretical basis of the quantitative analysis of powder mixtures was developed by Alexander and Klug [1,45]. When an x-ray beam passes through any homogenous substance, the fractional decrease in the intensity, I, is proportional to the distance traveled, b. This relationship is given by... 

The generalisation expressed by Lavoisier in the words I have quoted is now known as the law of the conservation of mass, it is generally stated in some such form as this — the sum of the masses of all the homogeneous substances which take part in a chemical (or physical) change does not itself change. The science of chemistry rests on this law every... 

Lavoisier uses the word principle, here and elsewhere, to mean a definite homogeneous substance he uses it as synonymous with the more modern terms element and compound. 

Long ago it has been established that nitrocellulose is not a homogeneous substance. The earliest experiments in this field were made by Stepanov [100] who used the method of fractional precipitation from an acetone solution by the addition of water. Stepanov added different amounts of water stepwise to a solution of nitrocellulose in acetone to obtain fractions varying slightly, corresponding with the nitrogen content. The first and least soluble fraction contained 13.15% of nitrogen, while the N-content of the last, fifth portion, was 12.90%. 

The nitration product of starch is a non-homogeneous substance. Nitrostarch may be divided into fractions by adding water to its solution in acetone as demonstrated by T. Urbanski and Cieslak [38], The individual fractions vary slightly in respect of nitrogen content, whereas their viscosity is almost identical. 

From the foregoing it is evident that the lithotypes of anthracite are different. Differences in adsorption characteristics, surface structure, physical properties, and chemical composition conclusively demonstrate that the anthracite lithotypes are unalike and are distinct entities. It is also evident that to interpret research results of anthracite coals correctly, a petrographic knowledge of the coal is necessary. Anthracite cannot be regarded as a homogeneous substance. 

Exsolution The unmixing of an initially homogeneous substance into two or more separate crystalline substances. For example, at 1000 °C and one bar pressure, sodium and potassium can readily substitute for each other in the crystalline structure of the aluminum silicate mineral alkali feldspar to form (Na,K)AlSi30g. At much lower temperatures, the sizes of the sodium and potassium atoms are too dissimilar for the crystalline structure to remain stable and the alkali feldspar separates (exsolves) into NaAlSisOg and KAlSisOg components (Klein, 2002), 143. 

For a homogeneous substance all the above averages are equal for polydisperse substances M, > M > Mn. The extent to which the averages differ from each other is a measure of the polydispersity of the substance.23... 

---