CEMENT FOR A MODERN STREET. 147 



ns the 'Natural Cement Industry/ but locall}^ in the neighborhood of 

 New York City as the Kosendale Cement Industry. 



Continuing these experiments it was found that the rocks found in 

 a few localities produced cements of a quality superior to those in 

 general use. This was particularly true of a stone found in the Island 

 of Portland. At length artificial mixtures of limestone and clay were 

 made and burned under such conditions that the resulting cement very 

 closely resembled the natural cement made from the Portland rock. 

 These results led to the adoption of the name of Portland for all 

 cements of this class^ whether made in England, where the name 

 originated, or elsewhere. The first attempts to prepare a cement by 

 artificial mixtures, in imitation of the natural Portland rock, were 

 made in France about 1802. 



Portland cements, as at present manufactured, were first made in 

 Ihigland by a process that was patented in 182-i, although there had 

 been several patents for 'Portland Cements' previously issued. In the 

 patent specifications of 1824 occurs the following description of the 

 process used: 



I take a specific quantity of limestone and calcine it. I then take a specific 

 quantity of clay and mix it with water to a state approaching impalpability. 

 After this proceeding I put the above mixture into a slip-pan for evaporation 

 till the water is entirely evaporated. Then I break the said mixture into suit- 

 able lumps and calcine them in a furnace similar to a lime-kiln until the car- 

 bonic acid is entirely expelled. The mixture, so calcined, is to be ground to a 

 line powder, and it is then in a fit state for cementing. The powder is to be 

 mixed with a sufficient quantity of water to bring it into the consistency of 

 mortar, and this applied to the purposes wanted. 



It will thus be seen that at the middle of the last century there were 

 in use: Common lime mortar, consisting of slacked lime and sand; 

 made all over the world and used for common masonry and plastering. 



Also Eoman cement, made by mixing common lime and some dry 

 aluminous material, like pulverized tufa, brick or slag. This was 

 stronger than common mortar and slightly hydraulic. 



Also, natural cement, called Kosendale cement in the United States, 

 made by burning and grinding a natural limestone containing clay. 

 These natural cements are of very varying quality and are hydraulic, 

 ;'. e., will set or harden under Avater. 



Also, Portland cements, called also Artificial cements, made by 

 grinding limestone or marl, both of which are nearly pure carbonate of 

 lime, and mixing it in proper proportions with ground clay, which is a 

 silicate of alumina containing a variable proportion of the oxides of 

 iron. This mixture is calcined at a temperature that will produce semi- 

 fusion and the resulting clinker is ground to a fine powder. The powder 

 is 'aged' in order to partially slack the lime. The powder is mixed with 



