CHEMISTRY. 193 



stances in which' the proportions of carbon, hydrogen, and oxy- 

 gen are the same? Why, for instance, should 48 parts by weight 

 of carbon, 10 of hydrogen and 16 of oxygen united together, be 

 capable of existing as 3 different chemical substances, unless we 

 presuppose a different statical arrangement of the parts by which 

 these differences in the deportment of the whole are rendered 

 possible ? 



" If, then, it be true that chemistry cannot give us positive in- 

 formation as to whether matter is infinitely divisible, and there- 

 fore continuous, or consists of atoms, and is discontinuous, we 

 are in some degree assisted in this inquiry by deductions from 

 physical phenomena which have been recently pointed out by the 

 genius of Sir William Thomson. He argues from four different 

 classes of physical phenomena, and comes to the conclusion, not 

 only that matter is discontinuous, and therefore that atoms and 

 molecules do exist, but he even attempts to form an idea of the 

 size of these molecules ; and he states that in any ordinary liquid, 

 transparent or seemingly opaque solid, the mean distance between 

 the centres of contiguous molecules is less than the hundred- 

 millionth, and greater than the two-thousand-millionth of a centi- 

 metre. Or, to form a conception of this coarse-grainedness, 

 imagine a raindrop, or globe of glass as large as a pea, to be 

 magnified up to the size of the earth, each constituent molecule 

 being magnified in the same proportion, the magnified structure 

 would be coarser grained than a heap of small shot, but probably 

 less coarse grained than a heap of cricket-balls. There is, how- 

 ever, another class of physical considerations which render the 

 existence of indivisible particles more than likely. I refer to the 

 mechanical theory of gases by means of which thanks to the 

 labors of eminent English and German philosophers all the 

 physical properties of gases, their equal expansion by heat, the 

 laws of diffusion, the laws of alteration of volume under pressure, 

 can be shown to follow from the simple laws of mechanical 

 motion. This theory, however, presupposes the existence of 

 molecules, and in this direction again we find confirmation of the 

 real existence of Dalton's atoms. Indeed, it has been proved 

 that the average velocity with which the particles of oxygen, 

 nitrogen, or common air are continually projected forward, 

 amounts, at the ordinary atmospheric pressure, to 50,000 centime- 

 tres per second, whilst the average number of impacts of each of 

 these molecules is 5,000 millions per second." 



ORGANIC COMPOUNDS OF SILICON. 



Combinations of Silicon witli Alcoholic Radicals. The results of 

 the researches of Friedel and Crafts, on the ethers of silicic acid, 

 and the discovery of a number of new bodies whose structure 



V 



leads to the conclusion that the atomic weight of silicon is 28, and 

 that the formula of silicic acid, SiO2, were published some time 

 since.* This atomic weight had already been assigned to silicon 



* Amer. Jour. Science, XLIII. (1867), pp. 153 and 331. 



