«The General Character and the Definition of the Colloidal Condition.»—Recent investigations have shown that the colloidal condition is possible, not only for a limited class of substances, but is, in general, possible for all substances.[252] Thus, even such an eminently crystallizable, readily soluble (in water) substance as sodium chloride may be obtained, under certain conditions, in colloidal suspension in benzene,[253] in which it is insoluble. For our purposes it will be sufficient to define the colloidal condition, on the basis of these results, as the condition of an insoluble substance in which, as far as ordinary observation and the common methods for separation of heterogeneous phases (filtration, sedimentation, etc.) are concerned, ‹the substance appears to be present in a homogeneous clear solution›, whereas ‹in reality› it is present in a ‹heterogeneous mixture›. An extremely finely divided solid suspended in a liquid, or an emulsified liquid suspended in another liquid, are the most common types[254] of such mixtures. [p131] «Relations to Analysis.»—Since the colloidal condition of insoluble substances interferes with the precipitation of the latter, and with their separation by filtration from the liquids in which they are suspended, and since the majority of the separations and tests of analytical chemistry depend on the successful formation of precipitates and on their successful separation by filtration, analytical chemistry is primarily[255] concerned with the colloidal condition as a condition that is to be ‹avoided as completely as possible› in order to escape error. In other fields of chemistry, notably in physiological chemistry and in some branches of technical chemistry, it is a source of effects so momentous and specific that a new branch of chemistry, the chemistry of colloids,[256] has grown out of the investigations of its relations and laws. The present discussion will be limited to the presentation of such of the fundamental facts concerning the colloidal condition as are of chief importance in analytical work.[257]