No. 275.] 
26 
it weighed after calcination, to every forty of pure anhydrous lime. 
" M. Vicat also points out the importance of these observations;— hy- 
draulic lime never having been found in the calcareous formation below 
the lias, is because the dolomites have never been examined; but it is 
now probable that it may be found in this lower formation."* 
It would be impossible in the compass of a report like the present, to 
enter fully into the consideration of this subject. Several important 
works have recently appeared in reference to it, which should be atten- 
tively studied by all who have the direction of aquatic structures. In 
France, where the arts of construction have for several years received 
such distinguished attention, much has been done towards establishing 
correct principles in regard to the preparation and mode of using hy- 
draulic limes, cements and mortars. Valuable information will , be 
found upon these points, in the extensive treatises of Dumas and Ber- 
thier, and in the able work of Vicat. Important service has also been 
rendered to the arts of construction in this country, by Col. Totten, who 
has translated and published in the Journal of the Franklin Institute, 
for 1837 and 1838, a very excellent memoir on hydraulic and common 
mortars, by General Treussart; and the same valuable periodical contains 
several other papers on those subjects which may be advantageously con- 
sulted. 
34. As the proper selection and management of hydraulic limes is a 
matter of vast importance, I trust I shall be excused in adverting to a 
few points, to which there is reason to fear that sufficient attention has 
not been heretofore paid, in the construction of our public works. 
1. It is agreed on all hands, that there is a great difference in the hy- 
draulic limes obtained from different limestones, and that the value of 
each, and the proper mode of using it can be determined only by experi- 
ment. 
2. It is admitted that in all cases the process of burning or calcining 
the limestone requires great care. A limestone, very proper in other 
respects, gives, when the heat is urged too high, what is called a dead 
lime^ in consequence of the partial fusion of the mass; whereas, when 
the calcination is effected at too low a temperature, the resulting lime is 
meagre and not hydraulic. 
3. Hydraulic lime should be used as soon as possible after calcination, 
and when kept for any time, it should be carefully protected from the 
* London and Edinburgh Philosophical Magazine, ^c, 3d Series, viii. 591. 
[Assem. No. 275.] 4 
