CLAY—ARGILLACEOUS EARTHS. 
143 
4to, If it be mixed and well kneaded, and worked with a proper 
quantity of water, it forms a soft and plaſtic maſs, not easily diffusible 
or dilutible in more water, and which, if dried well, and afterwards 
burned with a strong heat, becomes very compact and hard, and im 
penetrable by water. 
5to, It has some notable qualities which it ſhews in mixture with 
acids ; the moſt remarkable of which qualities ſhall be mentioned pre 
sently. 
The plaſtic earths, therefore, all contain more or less of this simple 
earth ; and they constitute every where numerous ſtrata. They also 
make a part of every strong and rich soil. 
That property of plastic earth, by which they become so tough 
a paste, and fo difficultly diffusible or penetrable by water, when 
wrought and compressed with a proper quantity of that fluid, occa 
sions their being employed for confining water in canals, and ponds, 
and reservoirs, and other works in which large quantities of water 
are to be confined, or preserved from being wasted by foaking 
through the foil. It also explains the bad effects of what is called 
poaching clayey grounds; that is, allowing cattle to tread on them 
much when they are wet or foft, as they are thus reduced to that 
plaſtic ſtate in which they do not tranſmit water eaſily, but occasion 
it to ſtagnate on their furface, and to rot or sicken the plants; and at 
the ſame time they are ſo dense and viscid, that the roots of plants 
cannot penetrate them without the gréatest difficulty. The remedy 
for this is, to plough them when they are moderately dry, and 
when dry weather or frost is expected. If the clods once become 
dry, the, firſt rain will make them moulder down, and alternations 
of dry weather and ſhowers will completely divide them. 
Mr. Bergmann fays that a fine clay does very well for waſhing 
and cleansing linens. Though it does not chemically combine with 
greasy filth, it adheres to it, and carries much off with it by rub¬