SCIENTIFIC NOTES.

New Zealand Times, Volume XXX, Issue 4457, 2 July 1875, Page 3

SCIENTIFIC NOTES.

KATIAVAY WHEEL TIKES AND EKOST. A very general impression prevails that frost renders metal more brittle than summer warmth, but this part of the subject has been investigated with some care, and experiments demonstrate the truth of analytical, calculations, and both show that the depression of temperature down say to 15deg. of frost exercises no appreciable ill effects in this respect on steel or iron. More than this, tires most often, so railway men in severe climates say, give way not during the frost, but just when a thaw has commenced, and this at once indicates, at least with our present unfortunately limited knowledge of the laws affecting tires, that it is the road which is the cause of the evil ; during frost the wheel rolls over an adamantine road, and suffer much vibration ; it may, and as a rule happily does, endure this, but presently a thaw comes ; it of course softens the upper ground first, and the sleepers being deeper sot remain for some time longer rigid; the result is that the rails become so many bridges with much defective play, and a wheel rolled rapidly over such a road is subjected to violent vibration, and the crystalisation thus set up in the tiro, in our opinion, is the cause of the fracture. —Practical Magazine. * COST OP HOUSEHOLD FUEL IN N. CHINA. The Rev. I. Pierson, American missionary, writes from Paotinghi, 100 miles south of Pekin :—“ The coal used here is a flaky friable anthracite of poor quality. It costs 7dols. per ton, or, allowing for the rate of exchange, SJdols. U.S. currency. To earn this amount a Chinese carpenter or mason, doing first-class work, would have to labor sixty days. Coal dust can bo bought at a reduction of 25 percent.,• and is used more than the pieces. The people take two parts of clay dust and eight parts of the coal dust, mix them thoroughly, and add water to make mud or mortar. This is spread on the ground, about an inch and a half thick, to dry. When partially dry, a shovel cuts or marks the surface into small squares. When nearly dry, these are broken up. Generally at this stage a coarse sieve is used, and the cakes, rolling together, lose their corners, and become round. In this form they burn readily in small stoves formed of sundried bricks and laid in clay mud. —Scientific American. DOES SUNSHINE PUT OUT A PIKE. A good deal of discussion has lately taken place in this country over the old questions whether sunshine checks combustion. It is an old notion, that sunlight lessens the intensity of a fire, and may even put it out, and the theory was that the sun’s heat by expanding the air caused a diminished supply of oxygen to the coal. This and all other explanations are now condemned, and the act is denied. One writer says that if a few pieces of charcoal are ignited in a chauffer, and placed in a sunny room provided with closely fitting shutters, the fire will appear to die away in the sun’s light. But if the shutters are closed, the coals will be seen to be in full combustion. There is no phenomenon at all, but only the appearance of one, which is due not to the sun’s heat, but to the fact that its light being stronger than that of the coals, overcomes and subdues it. The fact of combustion is so intimately connected with glowing ignition in our minds, that anything which lessens the glow appears also to diminish the combustion.