122 



CEMENTS, LIMES, AND PLASTERS. 



and becoming, in fact, artificial limestones. As this absorption can 

 take place only on the surface of the masonry, the lime mortar in the 

 interior of a wall never becomes properly hardened. In this process 

 the sand of the mortar takes no active part. It is merely an inert mate- 

 rial, added solely in order to prevent shrinkage and consequent crack- 

 ing. In this connection the reader may be referred to a discussion 

 on pages 132, 133 of the theory of lime-sand brick manufacture. 



Strength of lime mortars. Few recent determinations have been 

 made on this point, as lime is steadily decreasing in importance as an 

 engineering material. 



The following tests, made by Mr. George S. Mills of Toledo, Ohio, 

 have been recently published.* They are directly related to the point 

 under discussion and furnish strong evidence of the superiority of the 

 highly magnesian limes. 



The limes tested were made by burning limestones of the following 

 composition: 



The limes resulting from burning the above limestones were slaked, 

 mixed with sand in the proportion of one part slaked lime to two parts 

 sand by weight, and made into briquettes, which were tested at various 

 ages, with the results shown below. The figures given are in pounds 

 per square inch and each value represents the average of the tests of 

 from four to six briquettes. 



TABLE 41. 

 TENSILE STRENGTH OF MAGNESIAN AND HIGH-CALCIUM LIMES. (MILLS.) 



* Rhines, G. V. Tensile strength of high-calcium and magnesium limes 

 Municipal Engineering, vol. 28, pp. 4-7. Jan. 1905. 



