LAVA PROM VBSUVIUS 851

ROTATION OF A MAGNET POLE.BY H. E. HADI^Y,Kidderminster.

The following experiment, to demonstrate the rotation of a magnetpole around a wire conveymg a current, may be new to some readersof SCHOOL SCIENCE; AND MATHEMATICS. An oak disc C, about 10 cm.diameter, with a central hole 1 cm. diameter, carries five strongly

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mag-netized knitting needles with similarpoles uppermost. The needles areabout 15 cm. long, and at least onehalf of each needle is below the sur-face of the disk. D is a band of thicksheet copper fitting inside a widebeaker and with a terminal wire Eof thick copper soldered to it. Thebeaker is filled to a level above Dwith a strong solution of copper sul-phate to which 5 per cent sulphuricacid has been added. AB is a thickcopper wire terminating just belowthe liquid in a spirally bent piece ofthick sheet copper, as shown in theinset.When the apparatus is arranged as

shown in the diagram, and a currentof 4 to 5 amperes sent down AB,through the liquid, and out at E, thedisc rotates in a clockwise direction ifthe north-seeking poles of the magnetsare uppermost. The speed of rotation

can be varied by varying the current strength, and the rotation ofa south-seeking pole can be observed by reversing the disc. It isadvisable to varnish the disc and needles.�School World.

LAVA FROM VESUVIUS.BY NICHOLAS KNIGHT,

Cornell College.

During the eruption of Vesuvius in the spring of 1906, some fine, lightcolored, dust-like material was borne by the winds to Pompeii, and inplaces formed a layer two or three inches thick in the streets of theancient city. On a visit to Pompeii the following year we secured aboutfifteen or twenty grams of the fine dust, an analysis of which resultedas follows:

Si02 .....................ALOs .....................CaO .....................MgO .....................Ti02 .....................C02 ......................K^O ......................Na^O ...................P205 ....................FesOs ...................

.....................47.45 %......................40.86 "..................... 3.63 "...................... 0.80 "...................... 0.16 "...................... 1.41 (<

...................... 2.32 "

...................... 1.24 "

...................... 1.71 "

...................... 0.30 "

99.88 %

852 SCHOOL SCIHNCB AND MATHUMAT1CS

The material is therefore largely aluminum silicate.In the great eruption of 79 A. D. which engulfed the entire city and

buried it completely, several kinds of rock material were ejected. Oneof the interesting varieties was pumice stone. An analysis of a lightgray specimen obtained there in 1908 resulted as follows:

SiOz ..........................................52.85 %ALOs .........................................21.79 "CaO .......................................... 7.07 "MgO ......................................... 1.60 "Ti02 .......................................... 0.91 "C02 ........................................... 0.00 "K^O ........................................... 6.20 "Na20 ......................................... 6.64 "P^Os .......................................... 0.78 <(

FeaOs ......................................... 2.65 "

100.49 %This rock is also a silicate.Another variety of rock which contributed to the overthrow of the

ancient city is what is known as lava. The specimen obtained foranalysis was slightly green in color, hard, compact, and fine grained. Itanalyzed as follows:

SiOz ...........................................43.21 %ALOs .........................................31.28 "CaO .......................................... 4.85 "MgO .......................................... 2.21 "Ti02 .......................................... 0.47 "COz ........................................... 0.00 "KsO .......................................... 2.54 (<

Na^O ......................................... 4.57 "P^Os .......................................... 1.14 "FesOs ......................................... 10.26 "

100.53 %This is also a silicate in which aluminum predominates.We desire to express our thanks to Miss Guinnevere Sheets, Neil T.

Lutes, and Rubee J. Pearse for carrying out the foregoing analyses.

TUNGSTEN FILAMENTS.One of the recent methods of producing tungsten filaments for lamps

consists, first, of a process of converting the metal into tungsten phosphide,the phosphorus being introduced into a practically closed crucible containingtungsten particles. A phosphide ingot is secured and this is used as thecathode in an electrolytic bath, which reconverts the material into metallictungsten in a more or less porous condition. The metal is subjected to whiteheat and worked by hammering and rolling. The process is repeated torender the metal more homogeneous and ductile, and the ingot is thenhammered and compressed into a long drawn out rod, which is cooled andthen heated and drawn out into wire by passing it through suitable dies.It is claimed that this wire is so ductile and flexible that it can be formedinto any shape of filament.