BUBBLES.--The presence of bubbles in sheet-rubber has for years been the bane of some managers' existence, and the bone of contention between sellers and buyers. Taking the argument down to bed-rock, producers urge that the presence of bubbles has no influence upon the ultimate quality of the rubber on vulcanisation. They assert that the alleged defect is merely a peg upon which to hang an unreal grievance, serving the purpose of the buyer under the existing conditions of sale. All this may be true, but as long as the present system continues, it must be recognised that "kicking against the pricks" is a futile recreation. The sympathy of the writers is certainly on the side of the producers, inasmuch as they realise how extremely difficult, and even impossible at times, it is for the most careful individual to prepare sheet-rubber free from this blemish. Much has been written, and many have been the discussions, on this vexed subject; and it is recognised that sometimes, in spite of all precautions, there may suddenly be an incidence of bubbles in rubber which is ordinarily free from them. It must be allowed that climatic conditions and physiological variations affecting the metabolic functions of the trees exert an influence which is difficult at times to combat, and often beyond human control. The contributory causes are many and varied. It should be premised that, although the defect is described as "air-bubbles," it is seldom that the appellation is strictly correct. Rarely do the bubbles contain air. In the vast majority of cases they contain gases in minute quantity. These gases may be considered to arise, broadly, from some decomposition of substances (other than rubber), contained either in the coagulum or in the serum. In a general way, if this decomposition is evidenced by an unpleasant odour, it is described under the term of "putrefaction." We are not concerned here with the question as to how far such decomposition may be ascribed to a purely chemical action, or to the indirect result of the presence of certain bacteria or other micro-organisms. Suffice it to state that, at least as far as field operations influence the result, the decomposition is generally to be attributed to the work of micro-organisms. Conditions favourable to the incidence and development of these are to be found when absolute cleanliness in all details is not aimed at. With this preamble we may proceed to classify possible causes of the formation of bubbles into two groups: (_a_) Those originating in field operations. (_b_) Others which may arise after the arrival of the latex at the factory. IN THE FIELD.--Decomposition may be caused by: