OTHER INFREQUENT DEFECTS.--This chapter will be closed with a reference to other small defects which, although infrequent, cannot be classed as minor complaints. In point of fact, when they occur, they assume an importance, in the eyes of the consumer, which is not, perhaps, sufficiently appreciated by producers. DIRT.--Trouble from this source should be absent, but carelessness on the part of packing coolies may be responsible for occasional complaints. How the dirt is incident may remain a mystery, but it has been noted that sheets have at times been thrown upon a cement floor. A certain amount of loose dust may thus adhere to the rubber. ASH.--The source of this surface deposit scarcely needs indication. Where open-hearth furnaces are employed, and the wire-mesh floor screens are not perfectly sound, fine ash may find its way into the upper chamber. If this trouble is persistent in spite of precautions, the sheets should be surface-washed and air-dried before packing. BARK.--Complaints of the presence of particles of bark in sheet rubber used to be fairly frequent, but are now less common. The trouble may be traced to the use of defective straining sieves when the latex is being handled. SPLINTERS.--The use of packing-cases of unplaned soft timber is responsible for complaints of this nature on delivery. Without here discussing the larger question of the ideal packing case, it is sufficient to emphasise that the interior surfaces of wooden chests should be planed. The cases are often so damaged in transit, that splinters of wood may be found throughout the contents. The device adopted on some estates may go far to prevent this. The cases are first lined with loose sheets, and finally other sheets are arranged to overlap at the top of the case. The bulk is thus enclosed in a wrapping of sheets, and any splinters or other deleterious substances are confined to the surface of the mass. PART V GENERAL CHAPTER XIX _CHOICE OF COAGULANT_ Almost without exception, the agent employed in the coagulation of plantation (_Hevea_) rubber is acetic acid, or in some cases formic acid. Under ordinary trade conditions supplies are always obtainable at reasonable prices, but during the recent War the question of possible substitutes was brought greatly to the fore. Fortunately the subject of coagulation and coagulants had been previously studied to such effect in laboratory practice, that there would have been small difficulty in prescribing agents other than acetic acid in cases of expediency. As far as our knowledge extends, all the possible substances which have the power of coagulating latex have been tested. They include mineral acids, organic acids, compounds known chemically under the general term of "salts," alcohols, sugars, etc.