CHEMICAL EQUIVALENTS.] UNDULATORY FORCE S. ELECTRO-MET ALLUKGY. 211 



bined acid, the cathode will receive a constant supply o 

 metallic salt, and deposition will continue without in 

 terniption. 2nd. If the two electrodes are vertical in 

 the liquid, aud opposite to each other, similar difference! 

 of specific gravity will came the lower part of the liquit 

 to become saturated with metallic salt, and its upper par 

 to consist of free acid mixed with the water : in con 

 sequence of this, the current of electricity will abnosi 

 wholly pass from the upper part of the anode diagonally 

 downwards through the liquid, to the lower part of the 

 cathode, and thus the upper part of the anode wil 

 dissolve rapidly, whilst its lower part will dissolve bu1 

 slowly, and the cathode will receive a rapid deposit ai 

 its lower part, and but very little at its upper part. In 

 this position, vertical lines, and even deep grooves, are 

 sometimes produced in the deposit (especially if the 

 position of the cathode be slightly overhanging), by the 

 ascent of streams of the lighter acid liquid from which 

 the metal has been exhausted by deposition. If the 

 sol ut inn be nearly a saturated one, and has been freely 

 worked without stirring or disturbance for some time, 

 crystals of the metallic salt are apt to form all over the 

 lower part of the anode, which will be dissolved very 

 rapidly at the surface of the liquid, and appear as if cut 

 by a knife. In addition to these effects, if the solution 

 be a very deep one, with much free acid, two inde- 

 pendent currents of electricity will be developed, one 

 in each electrode, by the unequal action of the two 

 different strata of liquid upon their upper and lower 

 parts. An instance of this will be found in " One Metal 

 aud Two Liquids" (9), in which these currents leave them 

 upper parts, pass down through the liquid, and 

 re-enter them at their lower extremities. 



54. Form of the Electrodes. If either of the electrodes 

 be of an irregular form, or have unequal projections or 

 hollows, the anode will dissolve most freely, and the 

 cathode receive the greatest deposit of metal at those 

 parts at wliich they are nearest each other, and least in 

 the hollows and more distant parts. If the surface of 

 the cathode be rough, it greatly increases the tendency 

 of the deposit to become crystalline. 



65. Mathematical Conditions. Definite Chemical Ac- 

 tion. In the combination of different elementary and 

 compound substances with each other, by ordinary che- 

 mical affinity, it has been observed, and accurately 

 proved by analysis, that their combinations invariably 

 take place in certain definite proportions, or in very 

 simple multiples of those proportions ; aud as in the first 

 of these cases it is inferred that their combinations with 

 each other occur, atom with atom, the numbers which 

 represent those simple proportions represent also the 

 relative weights of those atoms to each other. The 

 following table contains the names, symbols, and ato- 

 mic weights of most of tho simple or elementary 

 substances : 



Name. Symbol. 



ITyilrnion 



Atomic 

 weight. 



. H 1-0 



Beryllium Ba 4-7 



Carbon C 6-0 



Lithium Li 8-5 



Oiyiren O 8-0 



Boron B 10-9 



Ma<rneium Mj 12-2 



Aluminum Al 13-7 



11 N 140 



Sulphur 8 16-0 



10 Fl 18 9 



C 200 



:, :............ 81 Sl-3 



im Zr 22-4 



Sodium Na S3 



Titanium Ti 25-0 



Chromium Cr 88-7 



Manganese Mn 27*6 



Iron Fe 28-0 



Cobalt Co 293 



Nickel M 2K-6 



Copper Cu 81-7 



Phwphoriu P 32 



Zinc Zn SH 



Chlorine Cl K't 



Potaulum K J9-J 



in Be 89-5 



Strontium Sr 40-8 



N.imo. Symbol. *^ 



Molybdenum Mo 40-0 



Lanthanum La 47'0 



Cerium Ce 47-0 



Uidymium D 40-0 



Hhauimn R 42-2 



Ruthenium Ra 52-2 



Palladium Pd 43-S 



Cadmium Cd 480 



Tin Sn 59-0 



Thorinuni Th 49'6 



Uranium U 60-0 



Tellurium Te .. .. 64-2 



68-S 

 G8-8 

 74-0 

 80-0 

 94-0 

 B8-7 

 99-0 

 99-8 



Barium Ba 



Vanadium Va 



Arsenic A 



Bromine Br 



Tunifntai w 



Platina Ft 



Indium Ir 



Osmium.. Oi 



Mercury Hg 100-0 



Lead .: Pb 103-7 



Silrcr Ag 108-1 



Iodine I 127 1 



Antimony Sb 129 



Tantalum Ta 184-0 



Gold Au 107-0 



BUmuth Bi 213-0 



56. As there is a number of compound substances 

 used in electro-deposition, such as sulphuric acid, cya- 



nide of potassium, <fec., and it will be useful to the 

 practical depositor to know their combining proportions 

 in making the different salts, used in the art, we have 

 selected those which are likely to bo required, and give 

 their names, symbols, and atomic weights or combining 

 proportions : 



Water, HO; 9'0. 



Common Oil of Vitriol, specific gravity, 1-848 ; SO 3 , 

 HO; 49-0. 



Strongest Hydrochloric Acid, sp. gr. 1 -21 ; IICJ, 6IIO : 

 90-5 (i.e., 90 and 5-tenths). 



Strongest Nitric Acid, sp. gr. 1-52; NO 5 , 2HO ; 72 O. 

 Sesquicarbonate of Ammonia (Sal- volatile) ; 2NH ;i , 

 3C0 2 , 2HO; 118 '0. 



Hydrochlorate of Ammonia (Sal-ammoniac); NIT 3 , 

 HC1; 53-5. 



Hydrate of Potash (fused Caustic Potash); KO, 

 HO; 56-2. 



Crystallised Carbonate of Potash ; KO, CO 3 , HO ; 78 -2. 

 Carbonate of Soda (ordinary washing Soda) ; NaO, 

 CO 1 , 10HO; 143-0. 

 Chloride of Sodium; Na Cl; 58 '5. 

 Caustic Lime; CaO; 28 '0. 

 Calcined Magnesia ; MgO; 20'2. 

 Ordinary Carbonate of Magnesia; MgO, CO 3 , HO; 

 51-2. 



Oxide of Zinc ; ZnO ; 40 '6. 



Commercial Sulphate of Zinc (White Vitriol) ; ZnO, 

 SO 3 , THO; 143-6. 



Sesquioxide of Iron (Crocus, Colcothar) ; Fe'0 11 , 80 -0. 

 Commercial Sulphate of Iron (Green Vitriol) ; FcO, 

 SO 3 , 7HO; 139-0. 



Protoxide of Copper (Black Oxide of Copper) C..O ; 

 397. 



Oxide of Silver ; AgO ; 116-1. 



Commercial Sulphate of Copper (Blue Vitriol) ; CuO. 

 SO', 5HO; 124-7. 



Chloride of Silver ; AgCl; 143-0. 

 Nitrate of Silver ; AgO NO 5 ; 170 '1. 

 Oxide of Gold ; AuO ; 205 '0. 

 Terchloride of Gold; Au Cl s ; 303 '5. 

 Bichloride of Platinum ; Pt CT; 109 7. 

 Cyanogen; Cy ; 26 '0. 

 Cyanide of Potassium ; KCy; 65 -2. 

 Cyanide of Zinc ; Zu Cy ; 58 'C. 

 Sesquicyanide of Copper ; Cu 3 , Cy s ; 147 '1. 

 Cyanide of Mercury ; Hg Cy ; 120 '0. 

 Cyanide of Silver; Ag Cy; 134-1. 

 Cyanide of Gold; Au Cy ; 223 0. 



67. Definite Electro- Chemical Action. The chief ma- 

 thematical condition of electro-deposition is, that in 

 every case, all the actions, both of combination and de- 

 composition, take place in certain mathematical propor- 

 ;ions ; that is, according to the relative atomic weights 

 of the substances combining or being decomposed. For 

 instance 



1st. With One Metal and One Liquid. If a piece of 

 )ure iron bo immersed in a solution of sulphate of 

 :opper, it will be dissolved, and copper deposited ; and 

 or every 28 parts, or one atomic combining equivalents 

 of iron dissolved, 31 '7 parts, or one atom, of copper are 

 deposited, and 49 parts (one equivalent) of hydrated 

 lulphuric acid (common oil of vitriol) are separated from 

 he copper, and combine with the iron, forming there- 

 with one equivalent of protosnlphate of iron. 



2nd. With Tico Mtttils and One Liquid. If a piece of 

 /inc and a piece of silver in mutual contact are immersed 

 n a solution of nitrate of silver, the zinc will dissolve 

 and tho silver receive a deposit; and for every 108-1 

 >arts of silver deposited, 32 '6 parts of zinc will be 

 dissolved. 



3rd. With One Metiil and Two Liquid*. If one piece 



if copper be immersed in a solution of sulphate of copper, 



and another in dilute sulphuric acid, the two being con- 



ected together by a wire, and the liquids separated by 



porous partition, copper will be dissolved in the dilute 



cid in tho proportion of 31 "7 parts for every 31 '7 parts 



if copper deposited in the metallic solutions; and for 



