Good lime may be known by the following tests which can readily be applied to any sample: 1. The lime should be free from cinders and clinkers, with not more than 10 per cent of other impurities,—as silica, alumina, etc.
2. It is generally stated that good unslaked lime should be in hard lumps with but little dust. Ordinarily lime is made from a lime stone, in which case the lime should be in lumps when freshly burned, and the presence of any considerable amount of powder or dust indicates that it has been exposed to the air so much since burning that air-slaking has begun; but partially air-slaked lime does not absorb enough water to fully slake it, as the small particles are covered with a fine dust which prevents them from slaking perfectly when water is added later (see 4 222-24). However, lime made from shells, crystalline marbles, soft chalk or shelly limestones, is fre quently in small fragments when fresh from the kiln, in which case dust is no evidence of air-slaking.
3. The lime should slake readily in water, forming a very fine smooth paste, without any residue.
4. The lime should in soft water, when this is added in sufficient quantities.
As lime abstracts water from the atmosphere and is thereby partially slaked, which is a detriment to its perfect slaking later, it should be kept as much as possible from the air, or at least from draughts of damp air. If the lime is in bulk, it is im possible to prevent it from air-slaking for any considerable time. If it is in barrels, it may he preserved for a considerable time by storing it in a dry place; but if stored for a great while, or in a damp place, the lime will absorb moisture from.the air and the consequent swelling will burst the barrels.
If lime is exposed to the air in a thin layer on a dry floor and is frequently stirred, it will finally slake perfectly and become prac tically a dry powder.
____ Lime, when mixed to a paste with water, may be kept for of indefinite time in that condition without deterioration, if pro tected from contact with the air so that the water will not dry out.
It is customary to keep the lime paste in casks, or in the wide, shallow boxes in which it was slaked, or heaped up on the ground, covered over with the sand to be subsequently incorporated with it in making mortar.
Unslaked lime is sold by the barrel (usually about 200 pounds net) or by the bushel (75 pounds). The price of un slaked lime in bulk in car-load lots is usually 50 to 60 cents per barrel, including freight for 100 to 200 miles; and in barrels the cost is from 20 to 25 cents per barrel more to cover the cost of cooperage.