is manifest. It is by surface-tension that ultra-microscopic particles are brought together in the first floccular precipitate or coagulum;
Fig. 201. A ãcrustã of close-packed calôÙcarôÙeous conôÙcreôÙtions, preôÙcipôÙiôÙtated at the surôÙface of an alôÙbumôÙiôÙnous soôÙluôÙtion. (After HarôÙting.) Fig. 202. AgôÙgreôÙgated calôÙcoôÙspherôÙites. (After HarôÙting.)
by the same agency, the coarser particles are in turn agglutinated into visible lumps; and the form of the calôÙcoôÙspheôÙrites, whether it be that of the solitary spheres or that assumed in various stages of aggregation (e.g. Fig. 202)25, is likewise due to the same agency.
From the point of view of colloid chemistry the whole phenomenon is very important and significant; and not the least significant part is this tendency of the solidified deposits to assume the form of ãspherulites,ã and other rounded contours. In the phraseology of that science, we are dealing with a two-phase system, which finally consists of solid particles in suspension in a liquid (the former being styled the disperse phase, the latter the {426} dispersion medium). In accordance with a rule first recognised by Ostwald26, when a substance begins to separate out from a solution, so making its appearance as a new phase, it always makes its appearance first as a liquid27. Here is a case in point. The