(_c_) Occasionally by abnormally wet weather. (_d_) Allowing piles of crepe to remain too long before hanging. (_e_) Using excessive quantities of deteriorated sodium bisulphite. In short, any factor contributing towards a retarded rate of drying may be responsible for the appearance of surface mildews. The last mentioned cause is of not infrequent occurrence. Knowing the chemical to be of poor quality, relatively more is used to produce the desired anti-oxidant effect. Unless the rubber is particularly well washed on the rolls, there remains within it a residue of sodium _bisulphate_, an oxidation product of the bisulphite. This is hygroscopic to some degree--_i.e._, it takes up moisture from the atmosphere. Hence drying is delayed, and even should mildews not develop the chemical may sometimes be seen on the surface of the rubber as a whitish "bloom." The enumeration of the possible causes of mildews on crepe rubber is sufficient to indicate the necessary precautions to be taken, and the discussion will not be extended further. TACKINESS IN RUBBER.--"Tackiness" is a term used to denote a deterioration of rubber which renders it sticky, and, beyond this, implies that some physical and chemical change in the nature of the substance has taken place. In fact, it is no longer "rubber," but an oxidation product containing much resinous matter. It does not behave as rubber, and hence its value is much depreciated.