898 PROCEEDINGS OF SECTION J. 



In order to make sure that the lime has entirely lost its 

 affinity for water before being laid as mortar in the joints of 

 a building, it is safe to leave the hydraulic limes for from 

 twenty-four to forty-eight honrs after slaking before mixing 

 them into mortar. For want of this precaution mortars have 

 been known to expand and to burst even the heaviest 

 masonry. 



Twelve to twenty-four hours is long enough for pure or 

 feebly hydraulic limes ; they should be left covered up during 

 that time. Hydraulic limes should be used as fresh as possible 

 from the kiln, and as they slake with difficulty they should be 

 ground first to ensure the operation being done perfectly. 

 Brunnell makes the following important observations i-egard- 

 ing the calcination and slaking of diiferent limestones : — 

 " Those which are obtained from the stones containing much 

 silica swell in setting, and are likely to dislocate the masonry 

 executed with them. On the contrary, those in which alumina 

 is in excess are likely to shrink and crack. The magnesian 

 limestones or dolomite appear to be the least exposed to these 

 inconveniences, and to retain without alteration their original 

 bulk." 



The quantity of water required to be thrown on the lime 

 varies with the density and purity of the lime and its freshness, 

 but generally speaking it will be between J and ^ the bulk of 

 the lime. With pure and freshly burned lime more water is 

 evaporated by the heat produced than with a stale, or with 

 a hydraulic lime. 



The heat generated by Victorian hydraulic lime during the 

 (so-called) process of slaking is hardly perceptible, only the 

 slightest warmth being noticeable, whilst with some of the 

 ordinary limes in use the heat given off by the lime when 

 water has been thrown upon it is sufficient to set fire to any 

 woodwork or bagging in close contact to the lime ; indeed 

 many serious conflagrations have been traced to this source. 

 One instance which came under my notice was that of a stable 

 which had been set on fire through someone having carelessly 

 thrown some pieces of newly burned ordinary limestone 

 among the wet straw on the stal^le floor. In point of fact, 

 ordinary limestone when burnt and unslaked, if carelessly 

 stored, may be considered as dangerous as a parcel of lucifer 

 matches when unprotected from rats. This is not the case 

 with cements or burnt hydraulic limes, for the reason that 

 little or no heat is generated by moisture coming in contact 

 therewith, 



