CHAPTER IX. 

 HYDRATED LIME: ITS PREPARATION AND PROPERTIES. 



IN the preceding chapter it has been stated that quicklime (CaO) 

 combines with about one-third of its own weight of water to form slaked 

 or hydrated lime (CaH^C^). It has been further stated that lime-slak- 

 ing when done on construction Fork by ordinary laborers is very 

 inefficiently accomplished. This has always been realized, but it has 

 only been within the past few years that any extensive effort has been 

 made to provide a more satisfactory article for the contractor or builder. 



Under the names of " new-process lime ", " hydrated lime ", 

 " limoid ", etc., a large number of lime-plants have within recent years 

 placed a ready-slaked lime on the market. When this product is care- 

 fully prepared, it does away with all the trouble, waste, and unsatis- 

 factory results entailed by the old method of slaking lump lime on the 

 work. It seems probable, therefore, that increased knowledge of its 

 valuable properties and increased care in its preparation will result in 

 a great extension of its production and a corresponding decrease in 

 the amount of lime marketed in the unhydrated form. 



Preparation of hydrated lime. In preparing hydrated lime on a 

 commercial scale three stages of manufacture are necessary. These are: 



(1) The lump quicklime must be ground to a fairly uniform small 

 size. 



(2) The powder or grains resulting must be thoroughly mixed with 

 sufficient water. 



(3) The slaked lime must finally be sieved or otherwise brought to 

 a uniform fine powder. 



Numberless patents have been issued to cover one or more of the 

 points above named, but the general stages are the same in all. These 

 will now be taken up separately and briefly discussed. 



Grinding the quicklime. Though grinding is practiced at most lime 

 hydrate plants, great variation exists in the extent to which it is carried. 

 In some plants the quicklime is simply crushed to, say, inch or 1 inch 

 size, while in others the grinding is much finer. At a recently installed 



124 



