SCIENCE. 



185 



compound halogen of sulphuric acid, as is the case in a 

 Darnell's cell. 



If a galvanic current passes through any conductor, a 

 metallic wire, or an electrolytic fluid, it evolves heat. Mr. 

 Prescott Joule was the first who proved experimentally 

 that if no other work is done by the current the total 

 amount of heat evolved in a galvanic circuit during a cer- 

 tain time is exactly equal to that which ought to have been 

 generated by the chemical actions which have been per- 

 formed during that time. But this heat is not evolved at 

 the surface of the electrodes, where these chemical actions 

 take place, but it is evolved in all the parts of the circuit, 

 proportionally to the galvanic resistance of every part. 

 From this it is evident that the heat evolved is an imme- 

 diate effect, not of the chemical action, but of the gal- 

 vanic current, and that the chemical work of the battery 

 has been spent in producing only the electric action. 



If we apply Faraday's law, a definite amount of elec- 

 tricity passing through the circuit corresponds to a defi- 

 nite amount of chemical decomposition going on in every 

 electrolytic cell of the same circuit. According to the 

 theory of electricity the work done by such a definite 

 quantity of electricity which passes, producing a current, 

 is proportionate to the electromotive force acting between 

 both ends of the conductor. You see, therefore, that the 

 electromotive force of a galvanic circuit must be, and is, 

 indeed, proportionate to the heat generated by the sum of 

 all the chemical actions going on in all the electrolytic 

 cells during the passage of the same quantity of elec- 

 tricity. In cells of the galvanic battery chemical forces 

 are brought into action able to produce work ; in cells 

 in which decomposition is occurring work must be done 

 against opposing chemical forces ; the rest of the work 

 done appears as heat evolved by the current, as far as it 

 is not used up to produce motions of magnets or other 

 equivalents of work. 



Hitherto we have supposed that the ion with its electric 

 charge is separated from the fluid. But the ponderable 

 atoms can give off their electricity to the electrode, and 

 remain in the liquid, being now electrically neutral. This 

 makes almost no difference in the value of the electro- 

 motive force. For instance, if chlorine is separated at 

 the anode, it will remain at first absorbed by the liquid ; 

 if the solution becomes saturated, or if we make a 

 vacuum over the liquid, the gas will rise in bubbles. The 

 electromotive power remains unaltered. The same may 

 be observed with all the other gases. You see in this 

 case that the change of electrically negative chlorine into 

 neutral chlorine is the process which requires so great an 

 amount of work, even if the ponderable matter of the 

 atoms remains where it was. 



The more the surface of the positive electrode is cov- 

 ered with negative atoms of the anion, and the negative 

 with the positive ones of the cation, the more the attract- 

 ing force of the electrodes exerted upon the ions of the 

 liquid is diminished by this second stratum of opposite 

 electricity covering them. On the contrary, the force with 

 which the positive electricity of an atom of hydrogen is 

 attracted towards the negatively charged metal increases 

 in proportion as more negative electricity collects before 

 it on the metal, and the more negative electricity collects 

 behind it in the fluid. 



Such is the mechanism by which electric force is concen- 

 trated and increased in its intensity to such a degree that 

 it becomes able to overpower the mightiest chemical 

 affinities we know of. If this can be done by a polarized 

 surface, acting like a condenser, charged by a very moder- 

 ate electromotive force, can the attractions between the 

 enormous electric charges of anions and cations play an 

 unimportant and indifferent part in chemical affinity ? 



You see, therefore, if we use the language of the dual- 

 istic theory and treat positive and negative electricities as 

 two substances, the phenomena are the same as if equiva- 

 lents of positive and negative electricity were attracted by 

 different atoms, and perhaps also by the different values 



of affinity ^belonging to the same atom with different 

 force. Potassium, sodium, zinc, must have strong at- 

 traction to a positive charge ; oxygen, chlorine, bromine 

 to a negative charge. 



Faraday very often recurs to this to express his con- 

 viction that the forces termed chemical affinity and elec- 

 tricity are one and the same. I have endeavored to give 

 you a survey of _the facts in their mutual connection, 

 avoiding, as far as possible, introducing other hypotheses, 

 except the atomic theory of modern chemistry. I think 

 the facts leave no doubt that the very mightiest among 

 the chemical forces are of electric origin. The atoms 

 cling to their electric charges and the opposite electric 

 charges cling to the atoms. But I don't suppose that 

 other molecular forces are excluded, working directly from 

 atom to atom. Several of our leading chemists have be- 

 gun lately to distinguish two classes of compounds, 

 molecular aggregates and typical compounds. The latter 

 are united by atomic affinities, the former not. Electro- 

 lytes belong to the latter class. 



If we conclude from the facts that every unit of affinity 

 of every atom is charged always with one equivalent 

 either of positive or of negative electricity, they can form 

 compounds, being- electrically neutral, only if every unit 

 charged positively unites under the influence of a mighty 

 electric attraction with another unit charged negatively. 

 You see that this ought to produce compounds in which 

 every unit of affinity of every atom is connected with one 

 and only with one other unit of another atom. This is, 

 as you will see immediately, indeed, the modern chemical 

 theory of quantivalence, comprising all the saturated 

 compounds. The fact that even elementary substances, 

 with few exceptions, have molecules composed of two 

 atoms, makes it probable that even in these cases electric 

 neutralization is produced by the combination of two 

 atoms, each charged with its electric equivalent, not by 

 neutralization of every single unit of affinity. 



But I abstain from entering into mere specialties, as 

 for instance, the question of unsaturated compounds; 

 perhaps I have gone already too far. I would not have 

 dared to do it if I did not feel myself sheltered by the 

 authority of that great man who was guided by a never- 

 erring instinct of truth. I thought that the best I could 

 do for his memory was to recall to the minds of the men, 

 by the energy and intelligence of whom chemistry has 

 undergone its modern astonishing development, what im- 

 portant treasures of knowledge lie still hidden in the 

 works of that wonderful genius. I am not sufficiently ac- 

 quainted with chemistry to be confident that I have given 

 the right interpretation, that interpretation which Fara- 

 day himself would have given perhaps, if he had known 

 the law of chemical quantivalence, if he had had the ex- 

 perimental means of ascertaining how large the extent, 

 how unexceptional the accuracy of his law really is ; and 

 if he had known the precise formulation of the law of 

 energy applied to chemical work, and of the laws which 

 determine the distribution of electric forces in space as 

 well as in ponderable bodies transmitting electric current 

 or forming condensers. I shall consider my work of to- 

 day well rewarded if I have succeeded in kindling anew 

 the interest of chemists for the electro-chemical part of 

 their science. 



Manufacture of Soda from Sulphate. — Salt-cake is 

 produced in quantity in California in the manufacture of 

 nitric acid. As coal and lime-stone are dear in California, 

 Le Blanc's process is not economical. The author there- 

 fore proposes to mix a solution of salt cake with calcium 

 sulphite and pass in sulphurous acid. Soluble calcium 

 bisulphite is formed, and by decomposition calcium sul- 

 phate and sodium bisulphite. The two salts are separated 

 by filtration, and the sodium bisulphite is treated with milk 

 of lime. The result is a solution of caustic soda, retaining 

 a certain quanttty of sodium sulphite and sulphate, which 

 is evaporated down in the usual manner, and calcium sul- 

 phite, which is used again in the process. — J. Putzkow, 



