288 



SCIENCE. 



[Vol. II., No. 80. 



PAPERS READ BEFORE SECTION C. 



On y-dichlordibrompropionic and y-dichlor- 

 bromacrylic acids. 



BY C. F. MABEKT AND H. H. NICHOLSOJf. 



When" dry chlorine is passed througli ;3-dibroma- 

 crylic acid, tlie reaction is easily accomplished, and 

 the product may be purified without difficulty by 

 crystallization from carbonic disulphide. This acid 

 is very sparingly soluble in water, more soluble in 

 hot than in cold carbonic disulphide and chloroform. 

 It melts at 100°. Its salts were carefully studied, 

 but the silver salt was found so unstable that it 

 could not be prepared in a state of purity. Since 

 /3-dibromacrylic acid has, without doubt, the form 

 CBr, 

 II 

 CH , the chlorine addition product would have 



COOH 



CBr,Cl 



I 

 the form CHCl . This acid is entirely decomposed 



COOH 



when heated with an excess of any alkaline hydrate. 

 If, however, the reaction is allowed to progress in 

 the cold, keeping the hydrate in slight excess, the 

 elements of hydrobromic acid are easily removed, 

 with the formation of the corresponding dichlordi- 

 bromacrylic acid. In order to distinguish this from 

 two other products which have already been obtained, 

 it will be called the y-acid. It is prepared by the ac- 

 tion of baric hydrate upon y-dichlordibrompropionic 

 acid, and the reaction proceeds so rapidly that it is 

 difficult to keep the solution alkaline. Upon acidi- 

 fying the baric hydrate solution with hydrochloric 

 acid, 7-diohlorbromacrylic acid is precipitated partly 

 as a crystalline solid, and is easily purified by crys- 

 tallization from hot water. It is sparingly soluble 

 in cold, readily in hot water, and in alcohol, ether, 

 carbonic disulphide, and chloroform. It crystallizes 

 in pearly-white scales, which melt at 78° to 80°. For 

 further identification, the acid was analyzed, and its 

 salts submitted to careful study. 



The sub-aqueous dissociation of certain salts. 



BY JOHN W. LANGLEY AND CHARLES K. M°GBE 

 OF ANN AKBOK, MICH. 



The question as to whether salts are dissociated 

 into their components when simply dissolved in water 

 has been attacked by different chemists in various 

 ways. The method described in this paper seems to 

 have furnished some remarkable results, which may 

 help in pointing the way to the final answer of this 

 Important problem. 



Sainte Claire Deville has called attention to ap- 

 parent chemical changes which a salt may undergo 

 by the mere fact of solution, and that such changes 

 may increase in extent with the mere addition of 

 water. He concludes that there is no absolute dis- 

 tinction between solution and chemical union ; that 



the difference is rather of degree than of kind. 

 From this point of view, a salt in dissolving has its 

 particles separated much as if it were vaporized by 

 heat, and the heat units necessary to perform this 

 sort of vaporization are taken from surrounding 

 bodies. As the heat absorbed increases with the de- 

 gree of dilution, it will eventually become sufficient to 

 dissociate into its elements a salt dissolved in a suita- 

 bly large quantity of a neutral solvent, such as water. 



Assuming that salts tend to dissociate by solution, 

 and are decomposed when sufficiently diluted, we 

 should expect them to break into simpler molecules 

 first, and, of course, along the lines of least resist- 

 ance. We may take three views of the possible con- 

 dition of a salt dissolved in a small quantity of water 

 — as, for instance, one molecule of sodic sulphate in 

 two molecules of water: 1. That it is attached to 

 the water by a sort of physical adhesion, which may 

 be represented byENaj SO., , 2H., O]. 2. That the 

 water and salt are united in a new group which acts 

 as a compound molecule so long as the amount of the 

 solvent is small; this might be [2 (Na OH) , H^ SO4], 

 the comma indicating a molecular as distinguished 

 from an atomic union. 3. That we have in these 

 cases a certain quantity of different kinds of mat- 

 ter held momentarily in equilibrium, but ready to 

 form definite combinations when the external forces 

 change. The last view would be expressed by [Na.., 

 H, SO,i], and does not require that Na be combined 

 with H, S, or SO4. 



The heat of combination between H^ SO., and 

 2Na OH is less than that in the formation of sodium 

 hydrate starting with metallic sodium and water, or 

 of sulphuric acid starting with SO 3 and water. There- 

 fore, in the group Na., H» SO,;, the line of least resist- 

 ance probably passes through where the comma is 

 placed in the arrangement [2 (Na OH) , S., SOj]. 

 Then the first stage of dissociation will be the appear- 

 ance of free sodium hydrate and free sulphuric acid. 

 The change will be partial for finite ratios between 

 quantities of the salt and the water, and should grad- 

 ually increase with augmented dilution to a peint 

 where free acid can be shown quantitatively. 



For the present occasion, advantage was taken of 

 the circumstance that in some neutral salts the bases 

 have less power to turn litmus blue than the acids 

 have to turn it red ; and also, that in certain other 

 salts the converse is true. Thus the power of the 

 hydrates of zinc, iron, and copper, to turn litmus blue, 

 is quite feeble; while the power of the mineral acids 

 to redden litmus is very great. On the other hand, 

 the hydrates of the alkaline metals are singularly 

 powerful in turning litmus blue. Now, if the power 

 of the base to produce the blue is not the exact quan- 

 titative counterpart of the acid to produce red, the 

 difference of color-producing power must increase in 

 proportion as the solution becomes more dilute, if the 

 theory of dissociation is well founded. 



The method of experiment may be briefly stated. 

 A series of test tubes was prepared, holding respect- 

 ively one, two, three, four, etc., portions of sul- 

 phuric acid ; and each was then diluted with litmus 

 solution to an equal amount. The tubes thus filled 



