Berthier on Limestones. 313 



of M. Saint-Leger, in the public buildings of Paris. An im- 

 mense consumption of it was made last year, for the canal of 

 St. Martin ; it has been judged superior to the lime of Se- 

 nonches, a superiority of which M. Berthier has convinced him- 

 self by experiments on the small scale. It is sold at the price 

 of 60 francs the cubic metre. 



M. Berthier enters into a pretty full account of the Roman 

 cement of Parker and Wyatt of London. The following is his 

 analysis of the English stone, from which, by a regulated calci- 

 nation, and subsequent pulverization, it is formed : 

 Carbonate of lime . . . 0.657 



magnesia . 0.005 



iron . . . 0.070 



manganese . 0.019 



'Silica 0.180 



Alumina .... 0.066 

 Water 0.013 



•'\Ali 



1.000 

 Lime produced by the above. 



Lime 0.554 



Magnesia ...... 0.000 



Clay 0.360 



Oxide of iron .... 0.086 



1.000 

 The English stone is compact, of a very fine grain, hard, tough, 

 capable of taking a fine polish, and of a grey-brown colour. 

 Its specific gravity is 2.59. It is said to be got in tubercular 

 masses, in marls. There is a similar stone at Boulogne. M. 

 Berthier thinks, that with one part of common plastic clay, 

 containing no sand, and two parts of chalk in bulk, which cor- 

 responds to one part of clay to 2^ parts of chalk in weight, a 

 very good hydraulic lime could be made, which would set as 

 speedily as the English. He acknowledges, however, that it is 

 not probable we can obtain by mixtures, hydraulic limes which 

 can acquire so great hardness and solidity as the natural mor- 

 tar, because these qualities depend, not only on the composi- 

 tion of the substance, but also on its state of compactness. We 

 can conceive, that the greater density a hydraulic lime pos- 

 sesses, which slakes without changing volume, the greater fa- 

 cility its particles will have to become aggregated, and the less 

 shrinking will there be in its consolidation. Whatever, there- 

 fore, we may do, the artificial mixtures will be always lighter 

 than the natural stones. 



The following general inferences, which M. Berthier draws 

 from some subsequent experiments, are important. A limestone 

 which contains 6 per cent, of clay, affords a lime already per- 



