76 
ECONOMICAL MINERALOGY. 
remarked, however, that the French generally employ the term ci?nent, to designate fine 
pounded bricks or tiles; while in this country, the term cement is most commonly used in a 
generic sense, and includes the hydraulic constituent of mortars, whatever that may be. 
It must always be considered as a most fortunate circumstance, that so soon after the com¬ 
mencement of the Erie canal, a material was found in its immediate vicinity, which yielded a 
lime well suited for the construction of locks and aqueducts. It is worthy of inquiry, how¬ 
ever, whether in these and in similar works since constructed, sufficient attention has been 
paid to the selection and preparation of the hydraulic limes thus employed. 
There is still some difference of opinion as to which of the ingredients of these impure lime¬ 
stones the hydraulic property is to be ascribed. • Some of those who have examined the sub¬ 
ject, have fixed upon the oxide of iron as the important ingredient; while the claims of the 
oxide of manganese, silica, alumina, magnesia, and even soda, have each been urged by re¬ 
spectable authority. It is, after all, however, more than probable that the hydraulic property 
is not due to a single ingredient, but belongs rather to several substances, or to a class of 
compounds. 
It appears from the experiments of Berthier and Vicat, the highest authorities upon this 
subject, that no mixture, of which silica does not form a part, acquires hydraulic properties ; 
that limes containing only silica or alumina, or better those containing silica and magnesia, 
acquire a much greater degree of hardness than the silicates of pure lime; and that the 
oxides of iron and manganese contribute nothing to the hardening of these bodies. 
More recently, M. Vicat has asserted that magnesia alone, when in sufficient quantity, will 
render pure lime hydraulic. The proportions of magnesia which he recommends, are from 
thirty to forty parts of it weighed after calcination, to every forty of pure anhydrous lime. 
“ M. Vicat also points out the importance of these observations : hydraulic 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 out of place in a Report of this kind, to enter fully into the consideration of this 
subject. Several important works have recently appeared in reference to it, which should be 
attentively 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 hydraulic limes, cements and mortars. Valuable information will be found upon these 
points, in the extensive treatises of Dumas and Berthier, and in the able work of Vicat. Im¬ 
portant service has also been rendered to the arts of construction in this country by Colonel 
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 consulted. 
London and Edinburgh Philosophical Magazine, etc. Third Series, VIII. 591. 
