52-53) (Vicat, 1837): In what follows, we shall term every substance ' very energetic,' which, when kneaded to a clayey consistency with very rich lime, slaked by the ordinary process, forms cement or mortar capable, 1st, of setting from the first to the third day after immersion; 2nd, of acquiring after one year the hardness of good brick; 3rd, of yielding a dry powder under the spring-saw..."
Lastly, we shall say that a substance is 'inert,' when its presence in proper proportions in rich lime in paste makes no alteration whatever in the manner in which the lime would behave, if immersed without mixture."
And his opinion is emphasized by: "There is nothing in the physical characters, either of the arenes, the psammites, or the clays, which will enable us to prognosticate with entire certainty, what their action on rich lime will be." (on p.
86: "One thing which we know to be quite certain, and which we ought never to lose sight of, it this--that there is no sand whatever, be it red or yellow, grey or white, with round grains or angular ones, &c., which can, if it be inert, form a good mortar with rich lime."