Regarding the first of these claims, it has been shown[31] that the rubber is not uniform in its behaviour on vulcanisation, and that its variability is similar to that of rubber prepared by other processes. [31] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918. The second claim has been the subject of much controversy. Experiments made on estates under the supervision of, or in the absence of, the patentees have given conflicting results. When varying factors have been eliminated, the general conclusion was that no increase in weight of rubber was obtained. Private laboratory investigations led to a similar verdict, and Eaton[32] records a confirmatory finding. More recently the claims made for the process were investigated in Java[33] under varying conditions. Three series of experiments were made: [32] _Ibid._ [33] "Archief voor de Rubbercultuur" (De Vries and Spoon), Central Rubber Station, Java, May, 1921. (1) During the rainy monsoon and at a height of 1,800 feet. (2) During the dry monsoon on a low-country estate. (3) In the experimental gardens at Buitenzorg during bright sunny weather and the most favourable conditions. The agents used were (_a_) a mixture of alcohol and fusel oil, (_b_) alcohol and petrol (benzene). In these experiments no advantage in weight of rubber was obtained by the Ilcken-Down process, and it would thus appear that the principal claim fails to be substantiated. The general composition of the rubber was approximately the same as ordinary crepe obtained from undiluted latex. The rubber on vulcanisation was found to be normal in behaviour, and was similar to the controls. The coagulum ordinarily is affected by oxidation, and does not produce a fine pale crepe. To remedy this defect the freshly prepared crepe is soaked in a solution of sodium bisulphite and sulphuric acid. It may be noted that in the recent experiments coagulation was effected in vacuum in a specially designed wooden tank. From a study of the previous section on "Spontaneous Coagulation," the reader will perceive that results equal to those obtained by the Ilcken-Down process can be obtained _without_ the necessity of using such agents as alcohol, petrol, or fusel oil. SLAB RUBBER.--This type of preparation has been the subject of much discussion of recent years. There is nothing really special in the mode of preparation, and in its original form "slab" rubber is only a thick sheet which may be obtained by coagulation with acetic acid or other agents. The coagulum, when removed from the serum, is subjected to comparatively slight pressure, and the "slab" thus made is either placed to air-dry at once, or may be subject to treatment in other liquids before drying. The rubber is not allowed to remain until wholly dry, but is shipped while still containing an appreciable percentage of enclosed moisture.