ELECTRICITY. 



403 



equivalent in heat, of the chemical actions tak- 

 ing place in those batteries. What is really 

 required is, to determine in numbers some con- 

 stant unit or coefficient for the force considered, 

 and which could be easily obtained by each 

 chemist. The most simple of batteries is 

 Smee's the only chemical action normally 

 going on in this being the oxidation and solu- 

 tion of zinc in the acid, with disengagement 

 of hydrogen. The value of the heat corre- 

 sponding to this action was carefully measured 

 by M. Favre, and expressed by the number 

 18,444 for ordinary zinc, and 18,V91 for zinc 

 amalgamated. In preliminary researches with 

 the battery named, including 125 determina- 

 tions of its electro-motive force, M. Davy found 

 variations in this force between 16,886 and 

 20,604, a difference of 2 per cent., where he 

 had been led to expect no more than that of 

 iVo"o tu P ai<t - The researches resulted in show- 

 ing 7 causes of disturbance acting within the 

 cup or battery, and leading to variations in the 

 current force which, independently of all in- 

 fluences outside itself, it can generate. Of 

 . the most important appeared to be the 

 presence of air in solution in the acidulated 

 water, and the influence of the sulphate dis- 

 solved in the liquid during action of the bat- 

 tery; the oxygen of the former acting directly 

 on the zinc, and preventing to a corresponding 

 extent the decomposition of the water, and 

 both causes operating to diminish the electric 

 force of the battery. The third cause of dis- 

 turbance was the influence of concentration of 

 the acid, the force generated however being 

 constant so long as the acid solution contained 

 more than 25 equivalents of water for 1 of 

 acid. The other influences were, that of purity 

 of the zinc and state of the amalgam the 

 electric force from amalgamated zinc being 

 generally stronger ; that of purity of the acid 

 the nitrogen compounds often present in it 

 increasing the strength of the current; that of 

 the water distilled water being preferable; 

 and that of temperature, which causes consid- 

 erable variation in the current generated. 



Finally, in order to secure results under uni- 

 form conditions, M. Davy works a Smee's bat- 

 tery consisting of a plate of platinized platinum 

 immersed vertically in a mixture of sulphuric 

 acid with 8 to 10 times its weight of distilled 

 water, boiled to free it of air, this solution be- 

 ing placed in a vertical glass tube, at bottom 

 of which is a liquid amalgam of pure zinc in 

 pure mercury. A platinum wire traversing 

 the bottom of the tube forms the negative pole 

 of the element, the glass tube containing the 

 arrangement is immersed in a large vessel full 

 of water, which keeps the temperature con- 

 stant, the liquid of the cell being also frequent- 

 ly changed. Fixed resistances in platinum of 

 known temperatures being introduced into the 

 circuit, serve to show the corresponding varia- 

 tions in intensity of the current. M. Davy takes 

 for the electro-motive force of this pile the num- 

 ber 18,510. ("Philos. Magaz.," July, 1862.) 



Measures of Electrical Quantities. Mr. Lati- 

 mer Clark and Sir Charles Bright presented 

 before the British Association, 1861, a paper on 

 the principles which should be observed in 

 measuring electrical quantities and resistance. 

 They believe that four standards or units are in 

 reality required, these being mutually depend- 

 ent on each other; and that by the aid of 

 these every conceivable form of electrical mani- 

 festation, whether static or dynamic, can be 

 precisely expressed. These are : 



A. A unit of electrical tension, potential, or 

 electro-motive force. 



B. A unit of electrical quantity, as applied to 

 static electricity. 



C. A unit of electric current, or quantity in 

 dynamic electricity. 



D. A unit of electrical resistance. 



As the unit of tension they propose that of one 

 Darnell's element or cell, to be named 1 OTtma. 

 As the unit of quantity of static electricity, they 

 propose that corresponding to a tension of 1 

 Daniell's element existing- between two coat- 

 ings oppositely charged, the coatings being 1 

 millimetre apart, of 1 square metre surface, and 

 separated by dry air ; this quantity to be term- 

 ed 1 Farad. As the unit of current, they pro- 

 pose that of one unit of quantity per second de- 

 livered along a conductor, as determined by the 

 galvanometer; this to be known^fc 1 Gahat. 

 But the wire that will conduct 1 unit of elec- 

 tricity in 1 second becomes conversely the stand- 

 ard or unit of resistance, this to be known as 

 1 Volt. Of these units, the first three will in 

 practice require to be measured in multiples of 

 1,000 and 1,000,000 times the unit indicated 

 by the prefixes kilo- and millio- ; the fourth, as 

 too large for defining the resistance of telegraph 

 conductors, will require to be measured in 

 fractions of the unit indicated again by the 

 prefixes kilo-. miUio-, and lillio-. A synopsis 

 of the paper at greater length is given in the 

 "Journal of the Franklin Institute," February, 

 1862. 



Report on a proposed Standard of Electrical 

 Resistance. Mr. F. Jeukin, on behalf of a com- 

 mittee appointed by the British Association to 

 consider this subject, reported at its last meet- 

 ing. In such a standard five qualities are de- 

 sirable ; it should be of convenient magnitude ; 

 should form part of a general and coherent sys- 

 tem of electrical measures ; should bear a defi- 

 nite relation to the unit of work; should be 

 unalterable; and should be reproducible, if 

 accidentally destroyed. Of the units hitherto 

 proposed, the committee conclude that none 

 fulfil all these conditions. Those based on 

 an arbitrary length and section, or weight of 

 some material arbitrarily taken, lacked the 

 first and second qualifications ; the absolute 

 system possessed these, but failed in the third 

 and fourth ; and the system of Messrs Bright 

 and Clark also failed in the third particular. 

 Not being able to advise the unqualified adop- 

 tion of any of the previously proposed stand- 

 ards, the committee recommend that a material 



