1 the folution will be effected without any effervefcence at all. As vitriolated tartar is not readily foluble in water, a confiderable quantity requires to be employed, which ought always to be hot, that the folution may be effected the more readily. $ 3. It has also been faid (p. 274. § 5.) that the only extraneous matter contained in limeftone is fand. But, altho' fand in general does predominate fo much over the other extraneous matters in lime-fone, as to authorise the expreffion in general, yet there are fome exceptions that ought to be taken notice of. ift, There are fome kinds of lime-stone, that, when analyzed, are found to contain a refiduum, confifting of a soft flimy-like fubftance. This is always in very fmall pro portions, portions, and has probably been formed by a fediment ubfiding from the water while the rock was forming. It seems probable, that this kind of lime would be lefs proper to be employed as a cement than as a manure. 2d, Altho' marle and lime-stone are justly enough diftinguished in the text (p. 274.§ 5.); yet, it happens, that clay and fand are found naturally mixed with one another in fuch various proportions, and in these ftates joined with calcareous matter, that there is no poffibility of afcertaining the exact point where marle ends and lime-ftone begins. A very inall proportion of clay is fufficient to make an exceeding hard lime-ftone relent in time in the air, and fall to pieces; fo that there are many forts of ftone marle that confit chiefly of fand and calcareous earth, and only a very little clay. These very hard kinds of marle may be cafily burnt intó lime,-fo that they may be be indifferently called marle or limeftone. 3d, The fame may be faid of the diftinction between marle and chalk, (p. 274. § 5.) Many fubftances, which have the appearance and diftinguishing properties of chalk, contain clay in different proportions. Thefe diffolve in the air, or run, as it is termed, more readily than the pure hard kinds of chalk, and feel more unctuous or fatty to the touch, from whence they are called fat chalks.-Thefe, however, may be converted into lime, fo that they might indifferently be called chalk, marle, or lime-flone. The lime that is made from any of those fubftances that contain clay in their compofition, is more proper for manure than for cement, especially that made from those substances that may be made to fall after they have undergone only a fmall degree of heat in calcining them, as in chalk; because, in these cases, the clay will not be sufficiently burnt to prevent it from being affected by water, and rendered soft by it. The proportion of clay and fand contained in any lime-tone or marle, may be afcertained, by diffufing, in water, the refiduum obtained by the analysis § 12. p. 408.— allowing it to fubfide a little, and gently pouring off the fluid parts from the coarser sediment that fubfides to the bottom; for, as clay remains much longer fufpended in water than fand, it may be thus feparated from the fand entirely; when the water comes off clear, after having been left to fubfide a little, the refiduum may be evaporated to dryness,→ and the lofs of weight it has fuftained by this operation, denotes the quantity of clay. -- This is rather a mechanical, than a chemical procefs, which is called elutriation. It has been demonftrated above, p. 338. $25. that the quality of lime, confidered as a cement, is greatly altered, by being more or lefs lefs perfectly calcined; it may therefore be, on many occafions, of ufe to those who are concerned in building, to be able to af certain what proportion of any particular kind of lime is really reduced to a cauftic ftate. This may be done as under. Take a known quantity of the quick-lime, perfectly dry,—add to that its own weight, or more, of common crude fal ammoniac * previously diffolved in a large proportion of water, and filtred,-digeft this nearly in a boiling heat for fome hours, till no more fmell of volatile alkali is found to arife from it, adding fresh water as it as it evaporates. When the volatile alkaline fmell is no longer perceived, throw the whole into a filtre,-let that pass off,-add more hot water,-and more ftill, till it comes through the filtre tastelefs and pure ;-then dry the refiduum and weigh it ;-the difference between that and the weight of the original lime, denotes the Obferve, it is not volatile fal ammoniac. |