76 ECONOMICAL MINERALOGY. 



remarked, however, that the French generally employ the term ciment, 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 constnicted, sufficient attention has been 

 paid to the selection and preparation of tlie 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 ingi-edient, 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 proportiorts 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 tiiis 

 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 tlie 

 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. 



* L'mdon and Edinburgh Philosophical Magazine, err. Third Series, VIII. 591. 



