164 
THE YOUNG SCIENTIST. 
by any means expensive. Sulphate of am- 
monia is objectionable, from the fact that it 
acts on the irons and moulds the fabric. The 
tungstate of soda is neither injurious to the 
texture or color, or in any degree difficult of 
application in the washing process. The iron 
passes over the material quite as smoothly as if 
no solution had been employed. The solution 
increases the stififness of the fabric, and its pro- 
tecting power against fire is perfect. This salt 
offers only one difficulty, viz. : the formation of 
a bitungstate, of little solubility, which crystal- 
lizes from the solution; but it was found that a 
very small percentage of phosphate of soda 
rendered the tungstate quite stable. The best 
method of applying these salts is to take one 
ounce of tungstate of soda and a quarter of an 
ounce of phosphate of soda, and dissolve them 
in a quart of water. The goods are moistened 
with this solution before being starched, and 
they may be afterwards ironed and finished 
without the least difficulty. 
Articles prepared in this way are perfectly 
uninflammable. They may be charred by ex- 
posure to fire, but they do not bum readily 
unless there is some extraneous source of heat, 
and they can not be made to burst into flame. 
By the aid of this discovery, a lady dressed in 
the lightest muslin might walk over a row of 
footlights, and the only result would be that 
the lower part of her dress would be injured. 
Unless her person actually came in contact with 
the gas flames, she herself would sufter no in- 
jury. In country places, where tungstate of 
soda cannot be procured, a mixture of three 
parts borax, and two and a half parts sulphate 
of magnesia, in twenty parts of water, may be 
used with good effect. 
Hints on Filing. 
Gleaning the tile.— The dust or small parti- 
cles removed from the material operated upon, 
are always more or less liable to clog and till 
the teeth; this tendency is especially aggra- 
vated when the file is used upon wood, horn, 
and such other materials, as, upon being mixed 
with the oil in the teeth, become baked when 
dry, and thus prevent the teeth from pene- 
trating the work, to say nothing of the appear- 
ance of being worn, or the tendency to injury 
from rust. xu 4. *u «i 
It therefore becomes necessary that the nle 
should be cleaned, not only at intervals during 
its use, but carefully before being laid aside, if 
the best results are to be attained. 
This cleaning is done in several ways; some- 
times, in the finer files, by rubbing the hand 
over them, or by drawing them across the 
apron of the workman; at others, by striking 
their edge upon the bench or vise, and again 
(which is a more common method upon the 
larger files), by the use of a strip of old or 
worn out card clothing, tacked to a piece of 
wood, having a handle shape at one end— a 
device which is usually rudely constructed by 
the operator. 
In removing oil from the teeth of a new file, 
a ready way is to rub chalk or charcoal across 
the teeth and brush thoroughly. By repeating 
the operation a few times, the oil will be en- 
tirely absorbed, and the file will be in its best 
possible condition for use upon cast iron. 
When the teeth of files are clogged with 
wood, or other soft substance which has be- 
come baked into them, if held in boiling hot 
water for a few moments, the imbedded sub- 
stance becomes so loosened, that it may easily 
be carded out of the teeth. If the operation 
be quickly performed, any moisture remaining 
will be readily evaporated by the heat retained 
in the file. 
Care in Putting Away. — One of the most de- 
structive customs among a large number of 
mechanics ot the present day is that of loosely 
throwing their files, fine and coarse, small and 
large, into a drawer filled with cold chisels, 
hammers, turning tools, etc., and then throw- 
ing the chisels, hammers and other tools on to 
the files. 
Now when we consider the small portion of 
the points of the teeth which is worn off by 
use in an extreme wear, and that to effectually 
dull them for some kinds of work requires but 
the slightest rubbing upon a hard substance, it 
will be easily seen that the evils of this habit 
should be more carefully considered, and suit- 
able provision made to avoid its destructive 
tendencies. 
. 
Starch Paste. — Two ounces of starch, one 
ounce of white glue, half an ounce of acetic acid, 
a few drops of oil of cloves. Dissolve the glue in 
cold water and then boil. Mix the starch with cold 
water, and pour into the glue while boiling. 
To Polisli Steel and Iron._It is a fact well 
known to chemists that potash and soda, particu- 
larly the carbonate of the latter, prevent rust in 
iron. Mechanics are also well aware that cutting 
tools moistened with soap, leave a much cleaner 
surface on iron than when dry or used merely with 
oil or water. These facts have led to the use of a 
mixture of emery and soap, with excess of carbon- 
ate of soda, for polishing steel and iron, and the re- 
sults have been very satisfactory. 
The Population of the World._The latest 
edition of Behm and Wagner's " Bevolkerung der 
Erde " gives the present population of the earth 
at 1,439,000,000, as compared with 1,424,000,000, as 
given in the previous issue. These figures are 
based upon the most recent censuses taken in vari- 
ous countries. The population is divided as fol- 
lows: Europe, 312,398,480; Asia, 831,000,000; Africa, 
205,219,500; Australia and Polynesia, 4,411,300; 
America, 86, J 16,000. 
