| 
192 Roman Cemeni. 
This rust, of the purity of which, none had any doubts, 
as interesting io chemistry It proves that the rust whioh is 
ound in the interior of houses is susceptible of absorbing 
the ammoniacal aes which are so frequeatly disengaged 
from animal substances, and retaining them with considerable 
orce. M. Laugier confirmed this result with rust found in 
ceived traces of sulphurous acid. he rust of iron also 
absorbs animal vapours, for in these experiments, vestiges of 
a brown oil ae scenenty perceived on the sides of the tube. 
— Idem. Sep.1 
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 Sadne and Loire, several 
einen exactly resemble those which 
brought feat the left bank of the T Some of them 
when properly calcined, produced a ave ‘which would set 
under water much quicker than the English, and attain an 
but 
5 equal degree of hardness. Others harden more slowly 
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 See M. Vical, to whom 
we are indebted for so many new facts with respect to mor- 
tars, has recently published one which rfectly agrees with 
the general remark of M. Minard, which is, that chalk feebly 
i gives a mortar capable of setting under water. 
ious experiments induce M. Minard to presume that 
Rous cements owe their quality to a subcarbonate of lime, 
