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into mild calcareous earth, without having had a sufficiency of water to allow it to chrystallize, it must concrete into a friable mase -exactly resembling chalk: It follows, that this kind of mortar, when as dry as it can be made, and in its highest degree of perfection, will be always soft, and easily crumbled into powder. , "\ :. '' '' • ' •"' '»•

;' .. "§ 16. r ' !";

But if, instead of forming the mortar of pure lime alone, a large proportion of sand be added to it, the water will, in this case, dissolve as much of the lime as in the former; and the particles of hard sand, like sticks or threads when making sugar candy, or other chrystals, while surrounded by the watery solution, will help to forward the chrystallization, and render it more perfect than it otherwise would have been, so as firmly to cement the particles of sand to one another.

And, as the granules of sand are perfectly hard of themselves, so as not to admit of being broke down like the particles of chalk, it necessarily follows, that the cement made of these materials must be much more per* sect, in every respect, than the former.

§ 17.

That the reader may see the full force of the above reasoning, it is necessary he should be informed, that, when calcareous matter is reduced to a caustic calx, it becomes in eyery fense of the word a perfect saline substance, and is, in this state, as entirely soluble in water as common salt or sugar; although with this difference, that lime can be suspended by water only in a much smaller proportion.—Water can dissolve one third of

it* its weight of common salt, and keep it suspended in a fluid state ; but it can hastily dissolve one thirtieth part of quick-lime, before it is saturated *.

But,

* The term saturation is employed tp denote that Ante of a fluid when it Dae uissojved as much of a solid body as it can possibly fnipcad in it at one time.

When any saline substance is put into water, it is dissolved by the water, and Luspended in it till it attains what is called the point of saturation ;—alter U?hich, \i efler so much salt, be added, not one particle jnore will be dissolved,—but it will remain at the "bottom in its original solid state.

Water dissolves very different proportions of dif'fcrcBt salts before it is sefcuraited- It will duSblve its own weight of dauber's salt,—one third .0/ its weight of common salt,—and not one thirtieth of its weight of lime.

'"Hence >it may very readily happen that, artfho* any particular fait could be wholly diflblved in water, a part of the fait ,may remain untouched, if too much jias been added—Thus, if one ounce of lime is put into ten ounces of water, that water will become

satu

[graphic]

But, although lime be as entirely soluble in water, when in its caustic state, as anyother purely saline substance, it so quickly absorbs its air, as to have some part of it rendered mild before it can be wholly dissolved on any occasion, in which state water cannot act upon it;—so that, to obtain a total solution, that proportion of it that becomes mild, requires to be again and again calcined, after fresh solutions have been drawn from it.

As such a large proportion of water is necessary to dissolve any quantity of lime,' it feldom happens, even in making lime-water, but that more lime is added than is sufficient to saturate the whole of the water.— In which case, some of it still remains at the Q^q bottom,

saturated before it shall have dissolved one third of the quick-lime,—and the remainder will remain in a solid state untouched.

bottom, in a condition capable of being dissolved, if more water be added to it.

But lime, it has been already said, differs from purely saline substances in this respect, that it cannot possibly be long suspended in water; for it soon absorbs its air even from that element, and is thus reduced to a mild state, when it immediately chrystallizes, and separates from the water *.

In

. * Although purely saline substances, in every state, continue to be soluble in water, yet many of them become more or less so, in proportion so the quantity of air that is united with them at the time; and in so far resemble lime in this particular, that they are more easily dissolved when deprived of their air than when united with it.

Alkaline *# salts, strictly so called, like lime, may be either in a caustic or mild state; which appellations

they

** The term alkali is employed to denote a certain class of saline bodies, whose most certain distinguishing charisteristic is, that they may be united with acids, and with them form neutral salts, as nitre, common salt, &c.

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