The Crystalline Cements.—Eckel. 151 
and sets more rapidly than a pure lime. To this class belong 
the well known and long used limes from Canaan (Conn.), 
Tuckahoe, Pleasantville and Ossining (N. Y.), various local- 
ities in New Jersey, and Cedar Hollow ( Penn.) 
Under certain conditions of burning magnesian limes yield 
hydraulic products, but in this case, as in the case of the pro- 
duct from pure magnesite, the set seems to be due to the form- 
ation of a hydrate rather than of a carbonate. At present 
advantage is not taken of this principle in the manufacture of 
hydraulic cements. 
Il. COMPLEX CEMENTS. 
The cements of this group, though differing somewhat in 
other characters, agree in one very prominent feature; the 
(rational) composition of the cement, after setting is mark- 
edly different from that of the material, or mixture of mater- 
ials, from which the cement was manufactured. Of the sub- 
groups (silicilate cements and oxychloride cements), the 
former is of great commercial importance, while the latter is of 
interest chiefly because of the use of certain oxychloride cem- 
ents in the fabrication of several artificial stones of some im- 
portance. 
II. a. SILICILATE CEMENTS. 
The silicilate cements form a very well marked and distinct 
natural group. All the cements of this class are hydraulic, 
though varying much in the degree of hydraulicity; and, in 
all, this property of setting under water is due largely or en- 
tirely to the formation of tri-calcic silicilate (3CaO. SiO,) 
though an extensive series of other silicate or of silico-alumin- 
ates may also be found (Under the head of hydraulic limes 
will be noted one possible exception to this statement.) 
Le Chatelier has discussed this subject in great detail, one 
of his principal contributions being now readily accessible.* 
In this group are included the three great classes of cem- 
ents, (natural, Portland, pozzuolanic,) as that term is used 
by engineers, together with the hydraulic limes. 
So far as processes of manufacture are concerned, two 
very distinct sub-groups can be formed. One of these is char- 
acterized by the fact that the calcareous and siliceous elements 
*Le CHATELIER Tests of Hydraulic Cements. Trans. Am. Inst. M. Bo XVil, 
