386 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



plastic paste with water. Important properties are its tenacity 

 or cohesion, and its power of retaining water. 



The tenacity of a clay may be tested by working up a small 

 quantity with water into a thoroughly plastic condition, and 

 forming it by hand into a roll about 1 to 1J inch diameter by 

 10 to 12 inches in length. If such a roll is sufficiently cohesive 

 as not to break on being suspended by one end when wet, the 

 tenacity of the material is ample. To test its power of retaining 

 water, 1 to 2 cubic yards of the clay should be worked with water 

 by the usual methods to a compact homogeneous plastic con- 

 dition, and then a hollow should be formed in the centre of the 

 mass capable of holding 4 or 5 gallons of water. After filling 

 the hollow, it should be covered over to prevent evaporation, 

 and left for about 24 hours, when its capability of retaining 

 water will indicate its suitability or unsuitability for making 

 puddle. 



Tempering the clay is effected by working it up with water 

 so that its original formation is broken up and a new arrange- 

 ment of particles formed, with additional water to fill up every 

 pore. Tempering is greatly facilitated by exposing the material 

 to the atmosphere, especially in winter, when the changes of 

 weather and temperature materially assist in disintegrating the 

 material. 



In putting in the puddle, it is important that great care 

 be taken to screen it from the too rapid action of the sun 

 or quick-drying winds. Cracks or fissures due to this cause 

 may, if the layer of clay, from motives of economy, is made 

 too thin, extend quite through, and thus allow the water 

 to escape. 



Puddling Bottoms of Basins. When the basins are excavated 

 in gravel or other pervious material, and there is in consequence 

 a risk of the water leaking through at low tides to a dangerous 

 extent as regards the ships in the basin, or injurious to the 

 adjoining lands and buildings, it may be necessary to cover the 

 whole surface of the bottom with puddled clay. In carrying 

 out this work, particular care is required to guard against 

 cracks occurring, through which the water may subsequently 

 leak away. 



Boring. A most important preliminary operation towards 

 ascertaining the character of the ground is boring. Scattered 

 at wide intervals over large areas, boring affords no 



