SUO RECORD OF SCIENCE FOR .1886. 



valency as usually held is iucorrect in assuming cliemical affinity to act 

 in units or bonds, and insufficient to account for the various phenomena 

 of varying atomicity, or valency, molecular compounds, crystallization, 

 solution, alloys, etc., and that all these varied phenomena are simply 

 due to the chemical affinity of the elementary atoms; the difficulties 

 disappear if the idea of indivisible units of chemical affinity is aban- 

 doned. This view is illustrated by reference to the compounds HCl, 

 ^NHs, and NH4CI. In HCl we have two monovalent elements combined 

 and their chemical affinities completely neutralized or satisfied. In 

 KH3 we have N considered as a trivalent element satisfied with three 

 monovalent elements. Now these two completed or satisfied compounds 

 combine with one another to form the third compound ]SrH4Cl. This is 

 usually explained by regarding the N as acting with pentavalent force, 

 and the compound is represented thus: 



H 



I 

 H — N — H 



/ \ 

 H CI 



Durham thinks this explanation most unreasonable and incredible, 

 because it supi)Oses that IST, which has usually such a weak affinity for 

 ('1, can nevertheless decompose the HCl into its constituent atoms, and 

 fix the atom of CI to itself. While on the other hand the CI letives the 

 U, for which usually its affinity is so great, and unites itself to the N, 

 for which usually its affinity is so small. Durham explains this action 

 simply thus: The affinity of the CI acts on all the four atoms of H, and 

 the affinity of the N does the same; and thus the whole molecule is 

 held together, and may be represented thus: 



N<H 



Mr. Durham finds that chemists are apparently coming more and more 

 to agree with his views, and quotes Pattison Muir's " Principles of Chem- 

 istry" to substantiate this. By reference to Thomsen's researches in 

 thermo-chemistry, he obtains data which he regards as demonstrating 

 the truth of his views on the subject of solution. He regards solution 

 as due to the affinities of the constituent elements of the body dissolved 

 for the constituent elements of the solvent ; thus NaCl dissolves in water 

 on account of the affinity of the Na for the O and of the CI for the H. 

 These affinities are not strong enough to cause double decomposition, 



