A Popular Record of Scientific Experiments, Liventions and Progress 
Copyriglit Secured, 1877. 
Vol. I. NEW YORK, FEBRUARY, 1878. No. 2. 
General Rules to be Observed in Using 
Cements. 
Concluded from page 3. 
NOTHER very im- 
portant point is 
that as little ce- 
ment as possible 
should be used. 
When the united 
surfaces are sep- 
arated by a large 
mass of cement, 
we have to de- 
pend upon the 
strength of the 
cement itself, and 
not upon its adhesion to the surfaces which 
it is used to join; and in general cements 
are comparatively brittle. At first sight one 
would suppose that the more cement there 
is used, the stronger will be the joint, and 
this is an error into which most inexperi- 
enced persons fall. Two pieces of earthen- 
ware, joined together by a layer of shellac 
as thin as possible, will adhere together and 
will be as strong at the junction as at any 
other part, while the same pieces ninited by 
means of a layer of the same cement an 
eighth of an inch thick, would fall apart on 
receiving the slightest jar. The rule which 
directs us to use as little cement as possible 
admits of no exceptions, and as a general 
thing the only way to obtain thin layers of 
cements that are to be used in a fused state^ 
is to heat thoroughly the pieces that are to' 
be united, and press them forcibly together. 
The last point to which we shall call at- 
tention is the necessity for cleanliness, both 
in the preparation of the cements and in the 
application of them. It may be safely laid 
down as a positive rule that every extrane- 
ous substance that is mixed with the mate- 
rial of a cement is an injury to it. Glue 
prepared in a greasy pot cannot be expected 
to make a strong joint, and the presence of 
dust and dirt tends to weaken all cements. 
So, too, in the application of cements. If 
we attempt to glue together two surfaces of 
wood that are covered' with dirt, the sub- 
stances that are to be united are not wood 
to wood, but dirt to dirt, and the joint, in- 
stead of possessing the strength of woodl 
