203 
ticular of that of scratching the hardest bo- 
dies. The details of the experiment are as 
follow :—If several sticks of phosphorus be 
introduced into a matrass containing carbu- 
ret of sulphur, covered with water, the mo- 
ment the phosphorus comes in contact with 
the carburet, it melts as if it were plunged 
into water, having the temperature of 60 
or 70 degrees of the centigrade scale, and, 
becoming liquid, it unites to the lower part 
of the matrass. The whole mass is then di- 
vided into three distinct strata—the first 
formed of pure water, the second of carbu- 
ret of sulphur, the third of liquefied phospho- 
rus: if, then, the vessel be shaken, so that 
these different substances become mixed to- 
gether, the liquor becomes turbid and milky, 
and, after resting for some time, it separates 
again, but only into two strata—the upper 
one formed of pure water, the lower one of 
the phosphorus and the sulphur ; and there 
may be observed, between the stratum of 
water and that of the phosphorus and sul- 
phur, a very thin layer of a white powder, 
which when the matrass is exposed to the rays 
of the sun, displays prismatic colours, and 
which consequently appears to be formed of 
a multitude of small crystals. M. Gannal, 
encouraged by this experiment, endeavoured 
to obtain larger crystals, and has succeeded. 
He introduced into a matrass, placed in a 
perfectly quiet situation, at first eight ounces 
of water, then eight ounces of carburet of 
sulphur, and the same quantity of phospho- 
rus. As in the former experiment, the 
phosphorus was at first liquefied, and the 
three liquids arranged themselves according 
to their specific gravities. After twenty- 
four hours, there was found, between the 
stratum of water and that of the carburet of 
sulphur, an extremely thin pellicule of white 
powder, which contained some few bubbles 
of air, and different centres of crystallization, 
some formed by needles and extremely thin 
laminz, and the others by stars. At the 
end of some days, this pellicule gradually in- 
_creased in thickness. At the same time, 
the separation of the two inferior liquids 
became less well defined, and, after three 
months, they appeared to form only one and 
the same substance. Another month was 
allowed to elapse, but no farther change 
took place; and a method of separating the 
crystallized substance from the phosphorus 
and the sulphur, was then investigated, but, 
on account of the inflammability of the 
mixture, great difficulties were met with here. 
After many attempts, more or less unsuc- 
cessful, M. Gannal resolved to filter the 
whole through some chamois leather, which 
he then placed under a glass bell, in which 
he occasionally removed the air. At the 
end of a month, as this skin might be han- 
dled withoutinconvenience, it was folded up 
again, washed, and dried; and then this 
ingenious philosopher could examine the 
crystallized substance which remained upon 
it. Exposed to the solar ray, this substance 
presented.to him numerous crystals, reflect~ 
Varieties- 
[ Fes. 
ing all the colours of the rainbow. Twenty 
of these were sufficiently large to be taken 
up with the point of a knife: three others 
were of the size of a grain of millet. The 
last three being put into the hands of an ex- 
perienced jeweller, appeared to him real 
diamonds. They have since been submitted 
to the Institute of France, whose decision 
upon the subject we shall not fail to make 
known. 
Fossil Turtle.—Another of those inter- 
esting productions of nature, the fossil or- 
ganic remains of a sea-turtle, has been dis- 
covered, and is now in the possession of Mr. 
Deck, of Cambridge. It is imbedded in a 
mass of septaria, weighing upwards of a 
hundred and fifty pounds, with two fine 
specimens of fossil wood, and exhibits, in a 
most perfect state, this singular animal of a 
former world, once undoubtedly an inha- 
bitant of our shores. It was obtained in 
dredging for cement-stone, about five miles 
from Harwich, in three fathoms water, and 
as a mass of stone, been used for some 
time as a stepping block, from which hum- 
ble station it was accidentally removed, by 
its present possessor, for the admiration of 
the virtuosi. 
Friction of Screws and Screw-Presses. 
—An examination of the friction in screws, 
having their threads of various forms, has 
led a French engineer to this very important 
conclusion—that the friction in screws with 
square threads is, to that of equal screws with 
triangular threads, as 2°30 to 4°78, proving 
“a very important advantage of the former 
over the latter, relative to the loss of power 
incurred in both by friction. 
To render Platinum malleable.—The 
only paper of any consequence which has 
been communicated to the Royal Society, 
during the present session, is one by the 
late Dr. Wollaston, on a method of render- 
ing platinum malleable; and the details of 
the process, which, from long experience, 
he regards as the most effectual for the pur- 
pose, are as follow :—When the platinum 
is purified by solution in aqua regia and 
precipitation with sal ammoniac, sufficient 
care is seldom taken to avoid dissolving the 
iridiunr contained in the ore by due dilution 
of the solvent. The digestion should be 
continued for three or four days with a heat 
which ought gradually to be raised, and the 
fine pulverulent ore of iridium allowed to 
subside completely, before the sal ammoniac 
isadded. The yellow precipitate thus ob- 
tained, after being well washed and pressed, 
must be heated with the utmost caution, so 
as to expel the sal ammoniac, but, at the 
same time, produce as little cohesion as pos~ 
sible among the particles of platinum. It is 
then to be reduced to powder, first by rub- 
bing between the hands, and next by grind- 
ing the coarser parts in a wooden mortar; 
with a wooden pestle, because the friction 
with any harder surface would, by producing 
burnished surfaces, render them incapable 
of being welded together by heat. The 
