298 THE REVIVAL OF INORGANIC CHEMISTRY. 



largely the backward state of our knowledge of them. Our inability 

 to determine the true molecular weight of insoluble and nonvolatile 

 substances; the difficulty of limiting reactions so as to obtain interme- 

 diate products; of preventing condensations; of separating mixtures 

 and identifying their constituents by such simple methods as melting 

 and boiling-point determinations; of building up step by step; of dis- 

 secting atom by atom; of explaining molecular compounds — these are 

 hindrances which can only be overcome by greater perfection of our 

 experimental methods, and which often render the study of the consti- 

 tution of inorganic bodies a problem of great difficulty, even in the 

 case of many of the simplest. 



At the very time that the organic structural formula was beginning 

 to turn the attention of organic chemists away from a further develop- 

 ment of theory to a greater elaboration of details the Englishman New- 

 lands was publishing papers which contained the germ of the Periodic 

 Law. In 1865 Kekule announced his theory of the benzene ring; in* 

 1864 Newlands showed that if the elements be arranged in the order of 

 their atomic weights "the eighth element, starting from a given one, is 

 a kind of repetition of the first, like the eighth note of an octave in 

 music." The discovery of Newlands of a fact which later developed 

 into the Periodic Law does not, however, mark the beginning of a new 

 direction in chemical thought. It marks rather that point in a long 

 series of speculations at which chemists were beginning to grasp an 

 idea after which they had been groping blindly for many years, the 

 conception that the elements # are not wholly unrelated bodies, but that 

 there is some definite law connecting their properties with their atomic 

 weights. Beginning in 1815, with the claim of Prout that the atomic 

 weights of the elements are multiples of that of hydrogen, which led 

 him to suggest that hydrogen is the primitive element from which the 

 others are built up, we find numerous speculations, some devoted 

 merely to finding arithmetical relations among the atomic weights, such 

 as the law of triads, others attempting to show how the elements could 

 be built up from one or more primitive constituents. Most of these 

 did not lead to any marked advance of chemical theory, but Prout's 

 hypothesis found very able defenders and greatly encouraged accurate 

 atomic- weight determinations. The labors of Dumas, Marignac, and 

 especially of Stas, in this field, are directly due to the desire to test 

 the validity of Prout's suggestion. Up to 1860 not only were the 

 atomic weights uncertain to within a few decimals, but, for other 

 reasons, even the relative position of the elements in an ascending 

 series was often uncertain; our present empirical formulas had not 

 been fully established; it was uncertain, for instance, whether water 

 was HO with 0=8 or H 2 with 0=16, or whether silica was Si0 2 with 

 Si=28 or Si0 3 with Si=21. So when Gladstone, in 1853, arranged the 

 elements in the order of ascending atomic weights he failed to perceive 

 any noteworthy relation. Nine years later the French engineer and 



