have no history of the manner in which iron was rendered malleable; but we know that platinum could only have been worked by a person of the most refined chemical resources.-Sir H. Davy.

Why is the apparatus essential to the modern chemist much less bulky and expensive than that used by the ancients?

Because an air-pump, an electrical machine, a voltaic battery, (all upon a small scale) a blowpipe apparatus, a bellows and forge, a mercurial and water-gas apparatus, cups and basins of platinum and glass, and the common re-agents of chemistry, are all that are required. All the implements absolutely necessary, may be carried in a small trunk; and some of the best and most refined researches of modern chemists, have been made by an apparatus which might with ease be contained in a small travelling carriage, and the expense of which is only a few pounds. Chemistry is not injurious to the health; the modern chemist is not like the ancient one, who passed the greater part of his time exposed to the heat and smoke of a furnace, and the unwholesome vapours of acids and alkalies, and other menstrua, of which, for a single experiment, he consumed several pounds.-Sir H. Davy.

ATTRACTION OR AFFINITY.

Why is our earth a globe?

Because of the general attraction by which all its parts are drawn towards each other, that is, towards a common centre; by which means the mass assumes the spherical or rounded form.

We have interesting instances of roundness from the same cause in minute masses,-as the particles of a mist or fog floating in air,—there, mutually attracting and coalescing into larger drops, and then forming rain—dew-drops-water trickling on a duck's wing— the tear dropping from the cheek-drops of laudanum -globules of mercury, like pure silver beads, coalescing

when near, and forming larger ones-melted lead allowed to rain down from an elevated sieve, which, by cooling as it descends, retains the form of its liquid drops, and becomes the spherical shot-lead of the sportsman.-Arnott.

Why is the prescription of medicine by drops an unsafe method?

Because, not only do drops of fluid from the same vessel, and often of the same fluid of different vessels, differ in size, but also drops of the same fluid, to the extent of a third, from different parts of the lip of the same vessel.

Why has it been said that the whole world, if the atoms could be brought into absolute contact, might be compressed into a nutshell ?

Because of the exceedingly little of really solid matter even in the densest mass, as evident in the noncontact of atoms, even in the most solid parts of bodies; from the very great space obviously occupied by pores; the mass often having no more solidity than a heap of empty boxes, of which the apparently solid parts may still be as porous in a second degree, and so on; and from the great readiness with which light passes in all directions through dense bodies, like glass, rock crystal, diamond, &c. We have as yet no means of ascertaining exactly what relation this idea has to truth.-Arnott.

Why may the doctrine of ultimate atoms be considered as established?

Because, according to the late Dr. Wollaston, the earth's atmosphere is limited, and consequently matter has a finite divisibility. "Yet," observes another, "of the smallest atom we can always imagine the half."

Why is the density, or the quantity of atoms which exist in a given space, very different in different bodies? Because of three different circumstances: first, of the size or weight of the individual atoms; secondly,

on the degree of porosity just now explained; thirdly, on the proximity of the atoms in the more solid parts, which stand between the pores. As an example of the different degrees of density, a cubic inch of lead is 40 times heavier than the same bulk of cork.-Arnott.

Why are certain bodies solid?

Because their parts cohere so firmly as to resist impression.

Lavoisier has explained solidity thus:-"The particles of all bodies may be considered as subject to the action of two opposite powers, repulsion and attraction, between which they remain in equilibrio. So long as the attractive force remains stronger, the body must continue in a state of solidity; but if, on the contrary, heat has so far removed these particles from each other, as to place them beyond the sphere of attraction, they lose the cohesion which they before had with each other, and the body ceases to be solid."

Why do blue and yellow powders, when mixed, form a green powder?

Because of the mere effect arising in the eye from the intimate mixture of the yellow and blue light separately and independently, reflected from the minute particles of each; and the proof is had by examining the mixture with a microscope, when the yellow and blue grains will be seen separately and quite unaltered.-J.F. W. Herschel.

Why cannot a similar separation be detected in liquid green?

Because of the excessive minuteness of the parts, and their perfect intermixture, by agitating the blue and yellow liquids together. From the mixture of two powders, extreme patience would enable any one, by picking out with a magnifier grain after grain, to separate the ingredients. But when liquids are mixed, no mechanical separation is any longer practicable: the particles are all so minute as to elude all search. -J.F. W. Herschel.

Why do we use the term specific gravity to express the relative weight of bodies?

Because it denotes the weight of the matter of which any body is composed, compared with the weight of pure distilled water, at 60o Fahrenheit, assumed as a standard.

Why is there a difference in the specific gravity of different bodies?

"Because one body is larger, or takes up more room than another of the same weight, when the first is said to be specifically lighter than the other, and vice versâ.

The specific gravity of bodies is denoted, in chemical writings, by comparing it with the specific gravity of pure water, in decimal figures, water being always considered as 1.000. Thus the specific gravity of the strongest sulphuric acid is 1.850, or nearly nine tenths heavier than water. Iron is 7.650, or more than 7 times heavier than water; that is, a cubic inch of iron, if put into a scale, would require 7 inches to balance it; silver is 10.478; gold, 19.300; and platinum, 23.000, or 23 times heavier than water. The specific gravity of all bodies is noted in the same way.-Parkes. Why does some stone decay rapidly, although very hard when first dug from the quarry?

Because it abounds with clay, or alumine, which has so great an affinity for water as to absorb moisture from the atmosphere, and thus destroy itself.

Why will not oil and water mix in a vial upon being violently shaken?

Because the water and the oil have no affinity for each other; but if some caustic ammonia be added, and the vial then agitated, the whole will be mixed into an ammoniacal soap. This is what is called disposing affinity, or uniting bodies, which apparently have no tendency to unite of themselves, by the addition of another substance.

Why do small needles float on water?

Because the particles of water cohere among them

selves, and the weight of the needles is not sufficient to overcome that cohesion.

Why do a pound of water, and a pound of salt when mixed, form two pounds of brine, but then occupy much less bulk than when separate?

Because the atoms of the one are partially received into what were vacant spaces in the other. A similar condensation is observed in many other mixtures; as a pound of sugar in a pound of water. Tin and copper, melted together to form bronze, occupy less space by one fifteenth, than they do when separate.—Arnott.

Why are a hundred pints of common air to be compressed into a pint vessel, as in the chamber of an air-gun?

Because, in aeriform masses, the atoms are very distant, and hence the masses are more easily compressed. In this case, if the pressure be much further increased, the atoms will at last collapse, and form an oily liquid. The heat which was contained in such air, and gave it its form, is squeezed out in this operation, and becomes sensible all around.-Arnott.

Why are liquids said to be saturated?

Because they cannot combine with, or take up, more than a certain quantity of any solid or aëriform body; the point at which this action ceases is saturation: thus, water will only take up a certain known weight of alum, salt, &c.

Why is gravitation the first and most general cause of changes on the earth?

Because water, raised in vapour by the heat of the sun, is precipitated by the cool air in the atmosphere; it is carried down by gravitation to the surface; and gains its mechanical force by this law.-Sir H. Davy. Why does the pyramid last longer than other forms? Because it is most fitted to resist the force of gravitation.

Why is an apartment never literally empty?

Because, if it offer to view nothing but the naked