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.
The dog dung, which is usually obtained from hunting kennels, and of which the composition is given in Chapter [II]., is simply diluted with water in the paddle;[13] five buckets, weighing about 165 lb., are required for the above quantity of goods.[14]
The amount used depends on the state of the goods, the prevailing weather, and, further, on the quality of the puer.[15] When the temperature is maintained at 40° C., ordinary limed goods, which have been washed, come down in from one to three hours.[16]
During puering, the lime soaps in the skin are decomposed, and the fat set free—in an estimation of the fat, 0·151 per cent. on the wet skin was found before puering, and 2·48 per cent. after puering. The fat thus set free can be removed to a great extent by scudding; but in modern practice this is not pushed to extremes, as the grain is liable to be damaged by excessive scudding. The fat is afterwards removed from the dry leather by means of benzine or other solvent, employed in a suitable apparatus.
Fig 6.—Sir John Turney’s Scudding Machine for Sheep Grains.
Scudding.—When the goods are “down,” they are ready for scudding. This operation in the case of grains is performed either by hand over the beam, or by means of a special scudding machine.