EARTHS. 265 



white light, into quick lime. When the amalgam of calcium was 

 thrown into water, hydrogen gas was evolved, and lime water re- 

 mained. 



(c.) Lime is the protoxide, of calcium. Its composition is estima- 

 ted by Berzelius at calcium, 71.73, oxygen, 28.27 = 100.00. 



Thenard says, that it ought to contain by calculation, 39 of oxygen. 



5. ITS EQUIVALENT WEIGHT is stated at 20, and therefore, 

 oxygen being 8*, lime, or the protoxide is represented by 28. 



6. POLARITY. Electro positive ; it goes to the negative pole in 

 the galvanic series. 



7. USES OF LIME. They are numerous and important. In med- 

 icine, the caustic earth is not used, except to prepare lime water ; 

 in the solid form, the pure earth is too acrid for internal use ; it 

 was formerly used as an escharotic, and its caustic properties are still 

 employed in removing the hair from skins, preparatory to tanning. 

 It is almost constantly used in the laboratory ; in the form of lime 

 water, it is an important reagent, and we have seen that it is employ- 

 ed to disengage the alkalies in a caustic state ; it is largely used for 

 the same purpose in soap making. In a word, it is of great value in 

 medicine, in architecture, in agriculture, and in many arts. 



Mortar is a mixture of sand, or gravel, or both and lime ; in the 

 proportions of fine sand 3 parts, coarse sand 4, quick lime 1, recent- 

 ly slacked with as little water as possible. 



It is well to add some pulverized lime, that has not been slacked ; 

 it absorbs water, and solidifies the other ingredients. Roman mor- 

 tar was made of the same materials as the modern, but of the best 

 quality, and accurately proportioned ; time has done much to give it 

 hardness. According to Pliny, the Romans made their best cement a 

 year before it was used, so that it was partly combined with carbonic 

 acid before it was laid in the work. In old Roman stone buildings, 

 the stone will often break as soon as the mortar. 



Another recipe for mortar. Fine sand, 3, brick powder, 3, (well 

 baked,) slacked lime, 2, unslacked lime 2. If very little water be 

 used, the mortar sets the sooner. Burnt bones, not exceeding one 

 fourth part, improve the tenacity of mortar. 



Manganese and puzzolana cause mortal- to harden beneath the 

 water. Puzzolana is decomposed lava, and consists of silica, alu- 

 mina, and oxide of iron. The mortar for the Eddystone light-house 

 on the S. W. coast of 'Cornwall, (Eng.) was composed of equal parts 

 of slacked lime and puzzolana. 



For 71.73 : 28.27 : : 100 : 39.4 and 39.4 : 100 : : 8 : 20.3. Henry. 



34 



