THE YOUNG SCIENTIST. 
123 
only so much from a true line as will be neces- 
sary to feel that each inch of its stroke is 
brought into exact contact with the desired 
portion of the work. 
The movements here referred to, have refer- 
ence to those in which both hands are used 
upon flat work, requmng nicety and trueness 
of finish, and the diflSculties to be overcome in 
producing even a comparatively true flat sur- 
face with a file, require much practice on the 
part of the operator. 
In filing ovals and irregular forms, the move- 
ments, while not considered so difficult or try- 
ing, nevertheless require considerable experi- 
ence, and a good eye, to so blend the strokes 
of the file upon the round or curved surfaces, 
as to give the best effect; the varied nature of 
the work upon this class of surfaces, though 
much might be said, prevents any detailed 
definition as to the movements of the file, 
within the limit of this article. 
In point of economy, the pressure on the 
file should be relieved daring the back stroke; 
this will be apparent to any one who will ex- 
amine the formation of the points of the teeth, 
when it will be seen that the file can only cut 
during the ordinary or advancing stroke, and 
that equal pressure during the back stroke 
must be very damaging to the points of the 
teeth. 
Draw-filing. — Files are sometimes used by 
grasping at each end, and moving them side- 
wise across the work, after the manner of 
using the spoke-shave. This operation is 
known as draw-filing, and is usually performed 
in laying the strokes of turned work length- 
wise, instead of circular, as left from the lathe 
finish, as well as when giving a final fit to the 
shaft that is to receive a coupling — cases, gen- 
erally, in which no considerable amount of 
stock is to be removed. Thus, any defects in 
the principle of construction, or arrangement, 
of the teeth of the file, are not so readily ap- 
parent. 
Files, as they are ordinarily made, are in- 
tended to cut when used with a forward stroke, 
and the same file cannot work smooth, or to 
the best advantage, when moved sidewise, un- 
less care is taken that the face of the teeth 
present themselves, during the forward move- 
ment of the file, at a sufficient angle to cut, 
instead of scratch the work. To accom- 
plish this, the angle at which the file is held, 
with respect to the line of its movement, must 
vary, with different files, depending upon the 
angle at which the last, or up cut is made. 
The pressure should also be relieved during 
the back stroke, as in ordinary filing. 
When properly used, work may be finished 
somewhat finer, and the scratches more closely 
congregated, than in the ordinary use of the 
same file; as in draw-filing the teeth produce a 
shearing or shaving cut. 
Mrst Use of a File. — In economizing the wear 
of files intended for general purposes, consider- 
ation should be given to the kind of material 
which they may be subjected to in the different 
stages of their use. 
In the ordinary use of the machine shop, 
the first wear of these files should be in finish- 
ing the larger surfaces of cast iron, bronze, or 
brass metals, all of which require a keen cut- 
ting tooth; they may then be made to do good 
execution upon the narrower surfaces of these 
metals, also upon wrought iron and soft steel; 
although to obtain the best results, the file 
saited for general purposes is not so well 
adapted to filing brass, or other similar soft 
metals, as those whose teeth are arranged for 
this purpose. 
Mucilage. — A good mucilage to be used for 
pasting newspaper clippings into scrap books, and 
one that will not cause the paper to become trans- 
parent to the detriment of the reading, may be 
made by putting a few cent's worth of gum traga- 
canth into a wide-mouth vial or a small jar, and 
turning in water sufficient to a little more than 
cover the gum. Before putting in the water, add 
a little acid to it; a few drops of vinegar or sul- 
phuric acid will do. This will prevent decompo- 
sition and a disagreeable smell. If desired a few 
drops of any essential oil may be added to impart 
an agreeable odor. 
Th.e American Institute. — The exhibitions of 
this association have for more than half a century 
constituted the "Permanent Exhibition" of New 
York, and whether considered as a means of educa- 
tion, through the display of valuable products and 
processes, or as a most effectual means of bringing 
to the notice of the public the novelties which are 
brought forward every year, the Institute Fairs 
have always stood foremost amongst the exhi- 
bitions of this country— always, of course, except- 
ing the Centennial. The Exhibition opens this 
year on the 11th of September, and those who de- 
sire to avail themselves of its advantages should 
make haste to address the Secretary, whose oflace 
I is in the Cooper Union building. 
