578 REPORT— 1881. 



Atomic Symbols Atomic Values 



B 3,5 



I ....... 1,7 



N 3,5 



P 3,5,7 



As 3,7,9 



Sb 3,5,7,9 



Bi 3,7 



Au 3 (?), 5 



Not only are there elements of which an atom is found iu combination with a 

 greater number of basylous and chlorous monads together than of either kind 

 alone, but there are also elements which are not known to form chemical compounds 

 with hydrogen or potassium alone, and yet which combine with either of theut 

 when also combined with chlorine, fluorine, &c. This is illustrated by the fol- 

 lowing compounds, viz. HAuCl^, H^PtClg, NaBF^, K,SiF„, K^FeF^, KjCuCl,. 

 It is also well known that there are many cases of elements of which an atom 

 cannot combine with as many monads of one kind as of another. For instance an^ 

 atom of nitrogen or of antimony is only known to be trivaleut in combination with 

 hydrogen ; but each of them occurs in the form of a pentavalent compound with 

 chlorine. Antimony forms either no compound with five atoms of bromine, or u 

 compound more unstable than the higher chloride. 



Many more such instances might easily now be given, and a vast number will 

 doubtless be found when the investigations of chemists are directed to the search for 

 them. I have only given these few by way of illustration of the leading conditions 

 of change of atomic values. 



In the course of their investigations of the precise interchanges of atoms which 

 take place between molecules, chemists were frequently led to observe evidences 

 of the order in which the constituent elements are combined ; and with the more 

 wide and accurate knowledge of reactions which is now in their possession, they 

 have been enabled to follow up so far the study of the respective state of combina- 

 tion of each atom in a molecule as to arrive at simple and consistent explanations 

 of facts which had previously eluded the grasp of science. 



Our knowledge of the order of combination of atoms in a molecule and of the- 

 differences between direct and indirect combinations of particular atoms may be 

 said to have originated chiefly in the study of the compounds of nitrogen. Thus 

 it was found that the hydrogen in ammonia differs in many of its chemical 

 functions from hydrogen in hydrocarbons. A base (called methylia) was dis- 

 covered having a molecular composition corresponding to the empirical formula 

 ( CNHj), and this base was found to contain two atoms of hydrogen like those of 

 ammonia and three atoms like thtise in hydrocarbons. Its constitution was accord- 

 ingly represented by a formula describing it as an ammonia, in which one atom 

 of hydrogen is replaced by the monad methyle, or, to be more explicit, a* 

 containing two atoms of hydrogen directly combined with nitrogen, and three 

 atoms of hydrogen indirectly combined with that same atom of nitrogen through 

 the intervening atom of carbon. Writing in juxtaposition to one another thi' 

 svmbols of those atoms which are directly combined, we can express the factt^^ 

 by the following formula, viz. HoNCHj. 



Those marvellous varieties of matter called isomeric compounds found their 

 natural explanation in differences of the respective arrangements of like atoms. 

 Thus two bases were discovered having the same empirical molecular formula, 

 CjNH,. One of them is made by different reactions from the other, and in its- 

 decomposition.s differs from the other. All these chemical differences between them 

 are found to be due to the fact that one of them (called ethylia) contains two 

 atoms of hydrogen directly combined with the nitrogen, and the monovalent 

 hydro-carbon ethyle in place of the third atom of hydrogen ; whilst the other (called 

 dimethylia) contains only one atom of h3'drogen combined directly with nitrogen, 

 the carbon of the two atoms of methyle completing the saturation of the trivalent 

 nitrogen, as expressed by the formula H N (C Hj)^. 



It was subsequently proved that an atom of oxygen may combine with two like 



