It has been said above that various compounds result from a mixture of bukhár and dukhán, which themselves consist of light and heavy elements. Besides, bukhár is wet or dry; and a complete union of the two sets in, sometimes before and after the mixture, and sometimes in either of these conditions. It is on this account that a compound whose fiery and airy particles are more numerous than its watery and earthy particles, is lighter than a mineral in which there are more watery and earthy particles; and likewise, every mineral in which the bukhár predominates over the dukhán, is lighter than a mineral, in which the opposite is the case. Again, a mineral in which the complete union of the bukhár and dukhán has set in, is heavier than one which has not reached this degree, because the interstices between the particles, and the entering of air, make a body large and light. Bearing this in mind, we have a means of discovering the weight and lightness of every body. Some one,* now long ago dead, has expressed the weight of several bodies in verses, (metre Mujtass)—

“Quicksilver* is 71; Rúi is 46; Tin is 38; Gold 100; Lead 59; Iron 40; Brass and Copper 45; Silver 54.” Others have expressed the numbers by mnemotechnical words in rhyme, (metre Ramal)—

“If you weigh equal volumes of the following nine metals, you will doubtlessly find their different weights as follows:—gold lakan,* quicksilver alam, lead dahan, tin hal, silver nad, iron yakí, copper and brass mah, rúi máh.” If of these nine metals, pieces be taken of equal dimensions, their weights will be different. Some sages ascribe this variety in weight to the difference in the qualitative constitution of the bodies, and trace to it their lightness or heaviness, their floating or sinking in water, and their weights as indicated by common and hydrostatic balances.

Several deep-sighted philosophers compute the weight of bodies with a reference to water. They fill a suitable vessel with water, and throw into it 100 misqáls of each metal; and from the quantities of water thrown out upon the introduction of the metals, are found the differences between them in volume and weight. The greater the quantity of the water is which 100 misqáls of a body displace, the greater is its volume, and the less its weight; and reversely. Thus 100 m. of silver displace 92/3 m. of water, and the same quantity of gold, 5¼ m. If the weight of the water displaced by a body be subtracted from its weight in air, its weight in water will be found. The scales of the air-balance are both suspended in air: those of the hydrostatic balance are both on the surface of the water. As the heavier body possesses the greater power for sinking, it will, in any case, move in the direction of the perpendicular; but, if either of the two scales be on the surface of the water, and the other in the air, the latter scale, although perhaps the lighter, will necessarily sink, as air, being a finer substance than water, does not offer so much resistance. A body will sink in water, if the quantity of water displaced by it be less than the weight of the body; and a body will float, if that quantity be greater; and if the water displaced be equal to the weight of the body, its upper side will coincide with the surface of the water. Abú Raihán has drawn up a table, which I shall insert here.