642 CEMENTS, LIMES, AND PLASTERS. 



ment several commercial slags and also a series prepared from pure 

 CaO, Si0 2 , and A1 2 C>3. He decided that the hydraulic properties (both 

 as regards rapidity of set and ultimate strength) of the slag increased 

 as the proportions of lime and alumina increased; and failed to find 

 any indication that a high alumina content causes disintegration. His 

 best results were obtained from slags having the compositions re- 

 spectively of 2SiO 2 , A1 2 O 3 , 3CaO, and 2Si0 2 , A1 2 3 , 4CaO. 



Mahon, in 1893, made a series of experiments to determine the value 

 (for cement-manufacture) of a large series of the slags produced by 

 the furnaces of the Maryland Steel Company: and found that the slags 

 giving the best results were two having respectively the following com- 

 positions : 



(1) Si0 2 , 30%; A1 2 3 , 17%; CaO, 47.5%; S, 2.38%; and (2) Si0 2 , 

 25.3%; A1 2 3 , 20.1%; CaO, 48%; MgO, 3.28%; S, 2.63%. 



The ratios of ^777^- and gA 3 , calculated for these slags are: 



blU 2 felU 2 



At the close of the experiments Mahon recommended that slags 

 be used slightly higher in alumina than those above quoted. 



Composition of slags actually used. The specifications under which 

 slag from the furnaces is accepted by the cement department of the 

 Illinois Steel Company are: 



(1) Slag must analyze within the following limits: 



Si0 2 + Al 2 3 not over 49%; A1 2 O 3 , from 13 to 16%; MgO, under 



4%. 



(2) Slag must be made in a hot furnace and must be of a light-gray 

 color. 



(3) Slag must be thoroughly disintegrated by the action of a large 

 stream of cold water directed against it with considerable force. This 

 contact should be made as near the furnace as is possible. 



A series of over 300 analyses of slags used by this company in their 

 slag (puzzolan) cement, show the following range in composition: 



Si0 2 , 29.60 to 35.60%; A1 2 3 , and Fe 2 3 , 12.80 to 16.80%; CaO, 

 47.99 to 50.48%; MgO, 2.09 to 2.81%. 



The requirements of the Birmingham Cement Company as to the 

 -chemical composition of the slags used for cement are: that the 

 lime content shall not be less than 47.9 per cent; that the silica and 

 lime together shall approximately amount to 81 per cent; and that 

 the alumina and iron oxide together shall equal from 12 to 15 per 

 cent. 



