118 
THE YOUNG SCIENTIST. 
gether with their eggs. If this statement 
is confirmed, the ingenious inventor may 
reasonably expect the prize of 100,000 
francs, which has been offered for the de- 
struction of the phylloxera." I 
It strikes us that this is a good deal like 
the Dutchman's powder for killing fleas, 
the method of using which was, first to 
catch the flea and then put the powder in 
its mouth. 
. 
Planting for Timber and Fuel. 
The attention of our people in the older States 
is being properly turned to planting rocky 
ridges and worn-out pastures with forest trees. 
This work is done by those having no expecta- 
tion of cutting timber themselves, but with a 
view to improve their property for future sale 
or for their heirs. These old pastures are now- 
worth $10 or less per acre. Forty or fifty years 
hence, covered with heavy timber, they would be 
worth $300 or more per acre. Two elements may 
safely enter into this calculation of the profit of 
tree planting : the steady growth of the trees, 
and the constant increase in the price of fuel 
and timber. There is great difference in the 
price of the varieties of wood, but still more in 
the rapidity of their growth. Hickory grows 
more rapidly than white-oak, and in most mar- 
kets is worth a quarter more for fuel. Chestnut 
grows about three times as fast as white-oak, 
and for many purposes makes quite as good 
timber. It is in great demand by the ship- 
builders and cabinet-makers. The chestnut, 
the tulip tree, and the hickory attain a good 
size for timber in twenty or twenty-five years, 
and the spruce and pine want about fifty years. 
The maples grow quite rapidly, and are highly 
prized, both for fuel and for cabinet purposes. 
On light sandy soil, the white pine will grow 
rapidly, and cannot fail to be a good investment 
for the next generation. As a rule, the more 
rapid growing trees, if the wood is valuable, 
will pay better than tlie oaks. 
►-»-• 
Glycerine as an Anti-Freezing Agent. 
The growing use of hydraulic machinery for 
riveting, flanging, etc., in our iron works, and 
for elevators, hoisting machinery, cranes, etc., 
makes the question of avoiding the danger inci- 
dent to the freezing of water in the pipes an im- 
portant one. The Engineer states that in Eng- 
land there is no generally adopted method. An 
admixture of alcohol, salt or glycerine has been 
tried, and Mr. Tweddell, well known in connec- 
tion with hydrauHc machinery, made some ex- 
periments on the effect of the addition of glycer- 
ine. In open vessels, at a temperature of 28°, j 
when pure water froze rapidly, only a lump of 
rotten ice was formed when 1 per cent, of gly- i 
cerine was present, less still with 2 per cent., i 
the ice formed not being sufficiently solid to ' 
flow, especially with a pressure of 1,500 lbs. per 
square inch. One firm found that in adding 
one gallon of glycerine to 300 gallons of water , 
no trouble whatever was experienced, while 
another firm uses 25 per cent., although they 
believe 10 per cent, to be enough for ordinary 
purposes. Salt is much cheaper, but while 
glycerine rather preserves leather packings 
than otherwise, common salt destroys them, 
especially when in cast iron. Glycerine has I 
also been used with good effect in gas-meters. j 
Deterioration in Thermometers and 
Hydrometers. 
M. Saleran, in Comptes Rendus, calls atten- 
tion to defects liable to be produced in ther- 
mometers and hydrometers if used for certain 
purposes. Changes in tliermometers ranging 
as high as 8° to 10° C. occur at printing-ink 
works, where oils are heated for several days 
to 670°, in glycerine works, and with rectifiers 
of beuzol. Glass is not only modified when 
heated to 300°, but it undergoes true deforma- 
tion at far lower temperatures. Thus, the hy- 
drometers used in sugar works, which are often 
exposed for a considerable time to temperatures 
of 95° are affected. After an immersion of some 
days they are completely modified, their weight 
decreases and they become erroneous to the 
extent of 7° to 8° B. The London Chemical News 
adds that in many chemical works it has been 
found necessary to submit all hydrometers used 
for hot liquids to a weekly comparison with a 
standard instrument. 
Hardening and Testing. 
To really test the hardness of the surface of 
metal, we must take a new, or at least a good, 
dead smooth file and apply one corner of it to a 
corner rather than on a fiat surface of the metal 
to be tested, pressing the file very firmly against 
the work. A coarse file, even if a new one, is 
useless to test with. The greatest degree of 
hardness is obtained by plunging the red-hot 
steel into mercury. Steel hardened from the 
surface inward is hardest on the surface, while 
in steel that has been tempered the exterior is 
the softest. In the one case because the surface 
I was cooled in advance, in the other because it 
! was heated in advance. Files are hardened in 
the following mixture: 2 parts (by weight) of 
