676 Transactions of tee American Institute. 



his time enormous ; and only to mention one instance, France saved, 

 in the cost of bridge building until 1845, almost seventy millions 

 francs. The credit, however, of having established the first scientific 

 explanation of the process of solidification, and of having indicated 

 the way of composing hydraulic cement, from materials occuring 

 almost everywhere, in the shortest and most certain manner, belongs 

 to the German chemist and academician, Justus Fuchs. His inves- 

 tigations are published in two memoirs, both of which were published 

 in 1828, in " Ueber Kalk und Mortel " ( On Lime and Mortar), and 

 in " Ueber die Eigenschaften, Bcstandthelie und chemischen Ver- 

 bindungen des hydraulischen Mortels" (On the Properties, the Com- 

 position and the Chemical Combinations of Hydraulic Mortar). The 

 results of the latter essay being of the utmost importance for Holland, 

 the Dutch Academy of Science resolved, a few years later, to award 

 him their golden medal. The credit for further valuable information 

 on this topic is due to the Frenchmen, Berthier, Fremy, Mene, Rivot, 

 Chatoney ; to the Englishmen, Pasleo, White & Sons and Macleod ; 

 and to the Germans, Pettenkofer, Winkler, Feichtinger, Manger, 

 Heldt, Michaelis, and others. 



Hydraulic ^Mortars — Their Adaptability for* Useful and Orna- 

 mental Purposes. 



i 

 The last named author divides the hydraulic mortar into the follow- 

 in »• three classes : 



1. Pozzuolana, or pozzolana mortars, are prepared from poz- 

 zuolana and lime. The pozzuolana, for a long time the only and 

 still an important substance for the preparation of hydraulic mortars, 

 is a volcanic tufa, and was first used by the Romans, as mentioned 

 above. This name has become a collective name for volcanic tufas in 

 general, pyroxenic minerals, calcined clay, slate (the psammites of 

 the French), and clays', brick-dust, volcanic sand (les arenes), ashes 

 and slags ; and it is the more justified, as the Italian pozzuolana must 

 be regarded as prototype of these materials. 



2. Hydraulic limes are such natural and artificial limes which 

 solidify more or less under water, and which are not so strongly 

 burned that vitrification has taken place. They yet contain free lime 

 in their calcined state. To these belong, among our American 

 cements, the Eosendale, and the cements from the following named 

 localities, viz. : Cumberland, Maryland ; Louisville, Kentucky ; 

 Coplay, Pennsylvania ; Sheperdstown, Virginia ; Round Top, near 



