146 POPULAR SCIENCE MONTHLY. 



In the year 1756, the celebrated engineer, John Smeaton, was 

 wrestling with the problem of constructing the Eddystone Lighthouse, 

 While experimenting with different varieties of mortar, he discovered 

 that certain limestones produced an hydraulic lime. He found that a 

 mortar made of pure lime and pozzuolana or powdered bricks gave 

 only unsatisfactory results, but when an impure lime from the 

 'Alberthaw' was used the hydraulic properties were more fully de- 

 veloped. Continuing his experiments, he at length announced that 

 o]ily limestones containing clay produced a lime of satisfactory 

 hydraulic properties. 



Speaking of this discovery, Smeaton says in his 'JSTarrative of the 

 Eddystone Lighthouse' : 



It remains a curious question, which I must leave for learned naturalists 

 and chemists, why an intermediate mixture of clay in the composition of lime- 

 stone of any kind, either hard or soft, should render it capable of setting in 

 water in a manner no pure lime I have yet seen, from any kind of stone what- 

 ever, is capable of doing. 



It is easy to add clay in any proportion to pure lime, but it produces 

 no such effect ; it is easy to add brick dust, either finely or coarsely powdered, to 

 such lime in any proportions also; but this seems unattended with any other 

 effect than what arises from other bodies, becoming porous and spongy and 

 therefore absorbent of water as already hinted and excepting what may reason- 

 ably be attributed to the irony particles that red brick dust may contain. 



In short, I have as yet found no treatment of pure calcareous lime that 

 renders it more fit to set in water than it is by nature, except what is to be 

 derived from the admixture of trass, pozzuolana and some ferruginous substance 

 of similar nature. 



These investigations and the conclusions that he drew from them led 

 Smeaton to use in the construction of the Eddystone Lighthouse a 

 mortar or cement composed of hydraulic lime from the Alberthaw and 

 Italian pozzuolana. A step or two farther in his investigations, which 

 he did not take and which were not taken until the middle of the last 

 century, would have led to the Portland Cement of the present time. 



In 1796, a Mr. Parker, of London, patented a process for what he 

 called 'Poman Cement." He used for this purpose certain nodules of 

 limestone containing clay that were found along the coasts of the Isle of 

 Sheppy and certain parts of Kent and Essex. These nodules were first 

 calcined and then reduced to fine powder in mills. The result was a 

 cement of a better quality than Smeaton's. In 1818, one Canvass 

 White discovered and patented in the United States a process for 

 making cement from a similar rock, found at Payetteville, in central 

 I^Tew York. Large quantities were manufactured and used in the con- 

 struction of locks on the Erie Canal, which was then being built. The 

 State of New York purchased the patent and made it public property. 

 This laid the foundation of a great industry, which is known generally 



