Polytechnic Association. 675 



which he had to select a mortar capable of permanently resisting the 

 action of water. For this purpose, he subjected the best specimens 

 of English limestones to chemical tests. Upon finding that in treat- 

 ing them with dilute nitric acid, an argilliferous residue remained, he 

 was able to declare that " all limestones which leave a residue of clay 

 on dissolving them in acids, will, if calcined, solidify under water, 

 while all limestones not deporting themselves in this manner, are 

 unavailable as hydraulic mortar." {John Smeaton : A Narrative of 

 the Building, and a DeserijAion, of the Eddy stone Light-house, etc., 

 2d edition, London, 1793.) 



In the year 1796, the so-called Roman cement was discovered by 

 James Parker ; and, regardless of its cost, it was for a quarter of a 

 century nearly exclusively used in England for building on land and 

 in the sea. The same was prepared from the spheroidal concretions 

 of marl, occurring in the so-called London clay ; in composition, it is 

 similar to the volcanic earth of the ancients. 



In 1822, two Frenchmen, Giralt and St. Leger, and in 182-1, Joseph 

 Aspdin, in England, produced for the first time artificial cement of 

 decidedly superior quality. The latter, a common mason, secured on 

 October 21, 1821, a patent for a new improvement in the making of 

 artificial stones. II© first gave to his cement the name of Portland 

 cement, from the fact that it was very similar in appearance and 

 quality to the Portland stone, the uppermost strata of the English 

 clnilk formation, from which the most beautiful and imposing build- 

 ings of Great Britain have been erected. 



The making of artificial cements, in spite of the patents secured by 

 Aspdin and others, would probably have remained a mystery for a 

 long time, had not scientific men begun to examine into the process 

 of solidification, the composition and the requirements of hydraulic 

 mortar. How difficult these investigations were is proved by the 

 fact that numerous examinations by the most skillful chemists were 

 necessary to establish a few facts, which might be related to you in 

 one-tenth of the time occupied by my paper. We may pardon the 

 manufacturers for their caution, since they acquired, almost exclu- 

 sively by long study and great sacrifices, the necessary certainty . in 

 the fabrication. Should they freely lay before the world their costly 

 experiments ? This was certainly not in their interest. 



Great merit is due to the French engineer Yicat for making the 

 most extensive use of the hydraulic limestones of France, of which he 

 discovered numerous deposits. The savings, caused by their appli- 

 cation in the building of bridges, locks, viaducts and canals, were in 



