670 NEW YOKK STATE MUSEUM : 



are formed. Tlie formation of these salts, when mixed together, 

 constitutes an insoluble soap, which is technically called rock, 

 and facilitates the subsequent separation of the solid and liquid 

 constituents of the tallow. 



Tannings 

 In tanning lime is used to remove the hair from the hides, 

 this being done in what are known as lime pits. 



Bone-ash 



In bone-ash manufacture the lime is employed to precipitate 

 the substances dissolved out of the bones by hydrochloric acid, 

 a fertilizer being obtained as a by-product and known as pre- 

 cipitated phosphate of lime. 



Gas manufacture^ 



Lime is sometimes used in the purification of gas from hydrogen 

 sulfid and carbonic acid gas. It can also be used to remove the 

 carbon disulfid when special methods are employed. The lime 

 is prepared in the ordinary manner and converted into hydrate 

 by slaking. In order to get the lime in a fit condition for use 

 however, it should be slaked two or three days before its use, for, 

 if used as soon as formed, it is liable to cake in the purifiers and 

 . thus prevent the free passage of the gas through it. Before being 

 placed in the purifiers, it is moistened with water till it attains 

 such a consistency that, when pressed together in the hand, it 

 will pack like snow. It is placed in the purifiers in 4 to 6 inch 

 layers. The removal of COg involves the formation of CaCOg, 

 and when HgS is extracted, CaS, HaS is formed. Both reactions 

 may go on at once, but the lime has stronger affinity for the CO2 

 than the IlgS. 



In gas manufacture lime may be also used to form ammonia 

 from ammonium chlorid or from ammonium carbonate contained 

 in the gas water from the gas works, the reaction being ximCl 



1 Hornby, J. Gas manufacture, p. 117. 



