192 Roman Cement. 



This rust, of the purity of which, none had any doubts, 

 submitted to the same experiment, gave exactly the same 

 resuh, and thus, by destroying the suspicions relative to the 

 spots on the instruments, furnished a fact as useful to justice, 

 as interesting to chemistry. It proves that the rust which is 

 found in the interior of houses is susceptible of absorbing 

 the ammoniacal vapours which are so frequently disengaged 

 from animal substances, and retaining them with considerable 

 force. M Laugier confirmed this result with rust found in 

 his laboratory. Toward the end of the operation he per- 

 ceived traces of sulphurous acid. The rust of iron also 

 absorbs animal vapours, for in these experiments, vestiges of 

 a brown oil are constantly perceived on the sides of the tube. 

 -Idem, Sep. 1S23. 



26. Roman Cement. — A letter from M. Clement to the 

 president of the French Academy of Sciences, states, that his 

 friend M. Minard, engineer of the canal of the centre, who 

 has been occupied five or six months in an inquiry on this sub- 

 ject, has found in the department of Saone and Loire, several 

 quarries of calcareous stone, which yield Roman cement as 

 good as the English. In one of the quarries is a bed of 

 this limestone five metres in thickness- Several of the spe- 

 cimens exactly resemble those which had recently been 

 brought from the left bank of the Thames. Some of them 

 when properly calcined, produced a cement which would set 

 under water much quicker than the English, and attain an 

 equal degree of hardness. Others harden more slowly but 

 become more solid. 



M. Minard has further discovered that the property which 

 he Roman cement possesses of setting under water, belongs 

 to almost all calcareous stones. Certain limestones, employ- 

 ed from time immemorial in the production of lime, give, at 

 pleasure, a Roman cement which sets in a quarter of an hour, 

 another which requires four or five days, and also a rich lime 

 which will not harden at all. To this effect the stone must 

 lose, 8, 12, or 30 per cent, by calcination. M. Vical, to whom 

 we are indebted for so many new facts with respect to mor- 

 tars, has recentlv published one which perfectly agrees with 

 the general remark of M Minard, which is, that chalk feebly 

 calcined gives a mortar capable of setting under waier. 



Various experiments induce iVI. Minard to presume that 

 Roman cements owe their quality to a subcarbonate of lime, 



