| ee anew br eS 
| CEMENT. 
| 
| most common of all cements are mortar and hy- 
draulic cements. See Mortar. Jn many ce- 
ments, pulverulent substances are mingled with 
a glutinous or very adhesive material, and do not 
|| combine chemically, in others a chemical com- 
bination ensues. ‘Those designed to stop up cre- 
|| vices and joints in apparatus temporarily put to- 
gether are termed lutes. The following are some 
of the numerous recipes for cements :— 
Lutes—1. Gypsum cast between paper; it may 
be mixed with water, or better with milk, glue- 
water, &c. 2. Dry slacked lime and strong glue- 
water mixed to a stiff paste; or the same with 
white of egg is well adapted for porcelain, &c.; 
it may also be made of lime and blood. This 
lute will not bear much moisture. 3. Cheese, 
boiled with a little water, and rubbed to a paste 
with slacked lime, hardens readily. 4. Clay, 
iron-filings, and gum mucilage becomes hard and 
adheres tenaciously. 5. Ground flax-seed made 
into a stiff paste with water, milk, glue-water, 
or lime-water, closes perfectly, hardens soon, and 
resists acids, &c. 6. Boil linseed oil, fuse caout- 
chouc in it, add pipe-clay, and incorporate them 
thoroughly ; more caoutchouc prevents too rapid 
hardening ; it should be kept in a moist and cool 
place. It resists acids more or less, and not har- 
dening during distillation, &c., the parts of the 
apparatus may be moved about without causing 
openings, or, if it does, the pressure of the finger 
closes them. 7. Fused caoutchoue alone resists 
acid vapours, and the temperature of boiling sul- 
phuric acid. 
Resinous cements.—1. Any varnish may answer 
the purpose where a thick layer is not required, 
for the resinous cements are apt to shrink. 2. 
Fish-glue is softened in a little water, dissolved 
in boiling brandy, and mixed with a very con- 
centrated solution of mastic, gum ammonia, &ec. ; 
it should be kept in a corked vial, and warmed 
when used. It cements porcelain, glass, &c., 
powerfully, and resists moisture to some extent. 
Keller recommends the following mode of pre- 
paring it:—Two parts fish-glue, cut into fine 
pieces, are left for 24 hours covered with 16 parts 
water, then boiled down to 8 parts, mixed with 
8 parts alcohol, and strained through linen. This 
liquid is mixed while hot with a solution of 1 
part mastic in 9 parts alcohol, and to the whole 
4 part gum ammoniac, finely pulverized, added 
| gradually, and the liquid rendered perfectly ho- 
'| mogeneous. In using it, both cement and the 
fragments are made as warm as possible, both 
pieces allowed to dry, then again rubbed over 
with the cement, and pressed together. After 
|| five or six hours it is perfectly hard. It is not 
applicable to vessels of porous earthenware; the 
| 
best cement in this case is a thick solution of 
shell-lac in spirits of wine. 3. Rosin and wax 
melted together and mixed with fine brick-dust 
forms a good cement between brass and glass, as 
in many kinds of physical apparatus ; it is applied 
CENTAUREA. 
(Spanish brown or ochre) are good proportions. | 
Wax and turpentine form a good cement, which, 
for convenience, may be cast into sticks, and 
melted off by a hot iron. White wax, white ro- 
sin, and a little Canada balsam form a good and 
nearly colourless cement. 4, As a cement for 
glass and porcelain, M. Hanle recommends a mix- 
ture of 2 parts shell-lac and 1 part turpentine, 
which are fused together and formed into sticks. 
This may also be employed for cementing wood, 
&c., when tissolved in spirit and evaporated to | 
the consistence of a syrup. Hensler grinds 3 
parts litharge, 2 parts of recently burnt lime in 
| powder, and 1 part white bole, to a mass with 
linseed-oil varnish. This cement is very tena- 
cious when allowed to dry sufficiently long. 
Fire cements.—1. For furnaces, crucibles, &c. 
Fire-clay and brick-dust, or fire-clay and burned 
clay (broken crucibles) kneaded well together 
with water, and spread in layers on joints, and 
thoroughly air-dried, resists heat without crack- 
ing. It may also be employed for coating glass 
retorts, by spreading it as a stiff paste or thin- 
ning it with water and spreading with a brush. 
A little hair added to it gives greater tenacity. 
2. Clay and brick-dust mixed with water and yo | 
part borax gives a difficultly fusible cement ; clay 
and red lead may be used. To make it less fu- 
sible, common clay and sand may be employed. 
3. For iron vessels, &c., mix 50 to 58 parts fine | 
and pounded cast-iron turnings with 2 parts pow- | 
dered sal-ammoniac and 1 part flowers of sul- 
phur into a paste with water, and apply it imme- 
diately ; it forms a chemical union, and hardens 
rapidly. According to some the sulphur may be 
omitted. 4. Four parts iron filings or turnings 
and 3 parts of a mixture of common and burned 
clay are made into a paste with salt water. See 
also Mastic and Morar. 
CENCHRUS. A genus of grasses, of the lolium 
tribe. The echinated species, C. echinatus, is a 
curious, hothouse biennial, of two feet in height, 
long ago introduced from the West Indies; the 
thorn-bearing species, O. spinifex, is a curious 
perennial, of about a foot in height, introduced 
about 25 years ago, from South America ; and the 
tribulus-like and the southern species, are hardy 
annuals, of about a foot in height, recently brought 
from North America and New Holland. Hight 
or nine other species are known. The word Cen- 
chrus is the Greek name for millet. Several of 
the species are prickly. 
CENTAUREA. A large genus of ornamental 
plants, of the thistle division of the composite 
family. Several species are annoying but beau- 
tiful weeds of Britain; and not a few are culti- 
vated as ornaments of our gardens. About 160 
species exist in Great Britain; and about 25 
other species have been scientifically described. 
Those within Britain have been systematically 
divided and subdivided so as to constitute a num- 
ber of very distinct groups——One group, com- 
prising upwards of a dozen species, have plumose 
