After this treatment the theoretical quantity of hydrochloric acid, diluted with plenty of water, is run in through the axle of the tumbler, and the skins run another half hour. The reactions are-- (1) CaSO_{3} + 2HCl = CaCl_{2} + SO_{2} + H_{2}O (2) Na_{2}SO_{3} + 2HCl = 2NaCl + SO_{2} + H_{2}O The sulphurous acid evolved in this way slightly swells the skins, and also removes stains due to the alkaline polysulphides; it is also said to remove salt stains. [Illustration: Fig. 3.--Puer Wheel, with Cover Removed.] [Illustration: Fig. 4.--Elevation of Puer Wheel (back).] A more interesting process, introduced by Dr. Gr. Eberle[12] as a bating process, but which is really a deliming process, consists in using organic acids in the form of their anhydrides, lactones, or lactides. During the process these anhydrides, lactones, or lactides, are gradually decomposed with formation of the free acids, which in a nascent condition unite directly with the lime in the skins. The anhydrides of acetic, propionic, butyric and lactic acid have been tried, the lactone of γ-oxybutyric acid CH_{2} CH_{2} \ O, and the lactide of lactic acid. / CH_{2} CO [12] Verfahren zum Beizen von Haüten, Ledertechnische Rundschau, No. 24, 1910. Coll. 1910, p. 372. After washing and deliming, the goods, warmed to a temperature of 90° to 100° F., are now measured in the truck above described, and put as quickly as possible into the bating paddle. This is constructed to carry two trucks. The figures (Figs. 3, 4 and 5) show a modern paddle adapted for puering light skins, such as goat, sheep, splits (grains), either with dung or with an artificial bate. [Illustration: Fig. 5.--End Elevation of Puer Wheel.] The inside dimensions are: length, 4 ft. 6 in.; width, 4 ft.; depth, 2 ft. 6 in. A copper pipe of two coils is provided at the back, through which steam is passed for maintaining the temperature of the wheel--the goods are prevented from coming in contact with this pipe by a perforated board. Another steam pipe, jointed so that it may be turned in and out of the paddle, is provided for heating up the wheel to the required temperature before beginning the bating. This pipe is not shown in the drawing. The thermometer can be read while the paddle is in motion. A suitable speed to keep the goods in motion is twenty revolutions per minute. The whole wheel is covered in, for the purpose of preserving the heat, and also to exclude light and air, which are prejudicial to the action of the bacteria. Such a paddle, or wheel, has a capacity of 200 gallons liquor, or 900 litres, and will bate 25 dozens of average grains, weighing in the wet state 1100 lb. or 500 kilos.