In general, all bodies are expanded by an increase of temperature and contracted by its diminution. The ratio of expansion however differs greatly in different substances. Thus liquids expand by the same degrees of heat much more than solids, and aeriform bodies most of all. There is a difference also in the same class of substances. Thus by the same increase of heat, one solid, or one fluid expands more than another.
Illus. On making experiments on the expansibility of all the malleable metals, and many of their alloys, it has been ascertained that no two of them expand equally, when submitted to equal increments of heat.
Exp. 1. Fit to a bar of iron or large iron wire, a ring of metal so that the bar will just pass through it when cold. Then heat one end of the bar, or wire and it will not pass through the ring.
2. Enlarge the ring, so that the iron will pass it when red hot. Then take a bar of copper of the exact size of the iron when cold ; heat this red hot and it will be found too large to pass the ring.
Corol. The metals are expanded by heat, but some of them more than others.
19. The same increase of heat expands some liquids more than others.
Exp. Take two glass tubes terminated at one end by large bulbs; fig. 17, fix a mark about half way up the tubes, and at the same height on each ; fill one of them up to the mark, with water, and the other with alcohol; then place the bulbs of both in the same vessel of boiling hot water.— Both of the fluids expand and rise up in the tubes, but the alcohol rises about twice as high above the mark as the water.
20. The expansibility of aeriform bodies of different kinds, is in the same ratio, at equal increments of caloric.
Obs. The degree of expansion which a body of this kind undergoes, is equal to 1-483 parts of its bulk for each degree of Fahrenheit, between the freezing and the boiling points.
Exp. 1. The expansion of air may be shown by partly filling a bladder by blowing into it; then tying the mouth so that none of it can escape, and holding it near the fire. The bladder soon becomes distended, and may .Joe burst with an explosion by continuing the heat.
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These oils are soluble in alcohol, and very sparingly so in water. When dissolved in the former they constitute essences, a great variety of which are manufactured particularly at Paris, and are used as perfumes. Waters holding a small portion of aromatic oil, in solution, are called distilled tenters. A variety of these are used in medicioe.
2. The volatile oils when pure, pass off by evaporation, without leaving any stain on white paper. Hence a good test of the purity of these oils, is to let a drop fall on paper, and if an oily spot is left after the paper is warmed, it is certain that it has been adulterated by some fixed oil.
QUESTIONS ON VEGETATION.
What are the Elementary Substances of which VegetaBles are composed ?
What are the essential Organs of plants ?
What change does the Farinaceous Substance of seeds undergo during their germination?
What circumstances are necessary to the Healthy GerMination of seeds ?
flow is it shown that seeds will Not Germinate without
AIR?
IVhat u said of the germination of seeds in the exhausted receiver of an air pump ?
What effect does Oxygen have on the Germination of seeds ?
What is said of Van Helmonfs willow ?
What is ascertained concerning the Growth of Plants in Pure Water?
How is it proved that plants absorb matter from the soil?
What particular Ingredients must a Soil contain in order to make it Productive ?
Is it necessary that the Pood of plants should be Soluble in Water ?
What Change does the Sap undergo in the Leaves ?