O^O RECORD OF SCIENCE FOR 1886. 



valeucy as usually held is incorrect in assuminsi- chemical 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 arc simplj'- 

 due to the chemical affinity of tlie 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* ITCl, 

 NHs, and Xn4Cl. In ITCl we have two monovalent elements combined 

 and their chemical athnities completely neutralized or satisfied. In 

 iN'Hs 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 NH4CI. This is 

 usually explained by regarding the Nas 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 supposes that Is, which has usually such a weak affinity for 

 CI, can nevertheless decompose the HCl into its constituent atoms, and 

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

 II, 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: 



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

 to agree with his views, and quotes Pattison Muir's " Princii)les 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. lie regards solution 

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

 for the constituent elements of the solvent ; thusNaCl dissolves in water 

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

 These affinities are not strong enough to cause double decomposition, 



