One of the most significant facts to be observed in these processes is the coagulation effect of the operation. As an illustration, when a little salt or acid of almost any kind is added to soapy water, the soap collects in flocculent masses ; we say the soap has coagulated. So in this ore-treatment operation it will be observed that the sulphides are coagulated in masses, some of which are of appreciable size even when they have not gathered sufficient air bubbles to float them. The gangue, on the other hand, has not coagulated ; but, due to the fact that the sulphides have coagulated, the gangue assumes an appreciably different and generally lighter colour than was the original ore. If the sulphides have not been floated as a froth (due to insufficient gasification), it will be observed that the ore as it settles has a streaky or mottled appearance, due to the fact that the darker sulphides have coalesced in considerable masses. It is not to be inferred that coagulation is a condition necessarily precedent to successful flotation, for it is not ; but in tests, and in the operation of a working plant, coagulation is a ' sign of good work.' R. Storm says: " Fine slime cannot be treated by these processes because, as the volume and area of the particles approach zero, they will have no adhesion effect." This is just where coagulation becomes a factor in rescuing the slime, and, contrary to his opinion, establishes the fact that adhesion does act, and that coagulation is simply one of the manifestations of adhesion. By a process that gives violent agitation with aeration and warming, the slimed sulphides coalesce together in the form of coagules, and then become, if they were not before, amenable to the forces of gas-adhesion and surface tension. This coagulation of the sulphides is similar to that in the case of butter, when, after a period of agitation of the cream, the butter-fat particles in the cream begin to adhere together, and finally grow into balls of butter of appreciable size, and the dairyman says : " The butter has come." So in the case of an ore-pulp with a small portion of oil added, with or without acid, if it is stirred for a suitable length of time with a rolling motion, the sulphide particles begin to adhere together, and if the rolling motion is sufficiently prolonged, the sulphides can be made to gather together into balls an inch in diameter free from any gangue particles. If this coagulation effect is stopped in its incipient stages, and if a multitude of infinitesimally small gas-bubbles are released in the pulp, each bubble lays hold of a ' coagule ' of sulphides and buoys it to the surface where the mixed bubbles and sulphides rest in the form of what we call ' froth.'