220 



UNDOLATORY FORCES. ELECTRO-METALLURGY, [zmo SOIUTIOSH rrc. 



the sulphate, chloride, nitrate, and acetate. The sul- 

 phate may bo formed by dissolving zinc to saturation in 

 a mixture of sulphuric acid and water, filtering and 

 evaporating the liquid, and setting it in a cold place to 

 crystallise. The chloride is formed by saturating hydro- 

 chloric acid with cine, filtering, evaporating, and crys- 

 tallising. The acetate, may be made either by dissolving 

 sine in strong acetic aoid to saturation, then evaporating 

 and crystallising the solution ; or by adding a solution 

 of acetate of lead to a solution of sulphate of cine as 

 long as it produces a precipitate ; then filter, evaporate, 

 and crystallise tlio liquid. 



105. Zinc Solution. The sulphate of zinc solution 

 for depositing may be formed by dissolving two pounds 

 of I ho salt in a gallon of water, and filtering the mix- 

 ture ; but the best sulphate depositing solution wo have 

 used has been the spent liquid taken from a cell of a 

 Smeo's battery, in which there had occurred a very good 

 deposit of cine upon the platinised silver plate; but 

 with this and other solutions of zinc there is a great 

 tendency to the evolution of hydrogen gas at the cathode 

 during deposition ; they require, therefore, to be worked 

 very carefully, and with very feeble battery power. Zinc 

 may be readily deposited, cither by the single cell, or by 

 the battery process, from a neutral solution of the 

 sulphate; but the single cell is less adapted for its 

 deposition than the battery, because the acid, set free by 

 the deposition of the metal, reacts upon the deposit, 

 and diminishes its cohesion. The other solutions, such 

 as the chloride, nitrate, acetate, or the various double 

 salts of zinc, with ammonia, or potash, do not appear to 

 possess any general advantages over the sulphate. 



Amongst other liquids, that of cyanide of zinc dissolved 

 in a solution of cyanide of potassium, has been recom- 

 mended ; but it is a bad conductor with a zinc anode, 

 and requires to bo used hot to make it conduct at all 

 freely, or make the anode dissolve. This might easily 

 have been foreseen from a knowledge of the fact, that 

 the affinity of cyanogen for all, or nearly all, the base 

 metals is comparatively feeble. Wo have found by 

 experiment, that a solution of cyanide of potassium will 

 dissolve only about one-half as much cyanide of zinc as 

 it will of cyanide of copper. Zinc oxide dissolves some- 

 what freely in a boiling solution of cyanide of potassium. 

 Cyanide of zinc dissolves freely in a solution of eesuui- 

 carbonate of ammonia. Ferro-cyanide of zinc is but 

 feebly soluble in a boiling solution either of ferro-cya- 

 nide (yellow prussiate) or of ferri-cyanide (red prussiatc) 

 of potassium, but it is freely soluble in a boiling solution 

 of cyanide of potassium. Zinc deposits spread over 

 blackleaded surfaces by the battery process, in the same 

 manner as copper. 



100. Cadmium Solution. A patent was taken out, 

 March 19th, 1849, by Messrs. Russell and Woolrich, for 

 the electro-deposition of cadmium ; and the following is 

 their description of the process: "Take cadmium and 

 dissolve it in nitric acid diluted with five or six times its 

 bulk of water, at a temperature of about 80 or 100 

 Fah., adding the dilute acid by degrees until the metal 

 is all dissolved ; to this solution of cadmium a solution 

 of carbonate of soda (made by dissolving one pound of 

 the ordinary crystals of soda in one gallon of water) is to 

 be added until the cadmium is all precipitated ; the 

 precipitate thus obtained is to bo washed four or five 

 times with tepid water; next add as much of a solution 

 of cyanide of potassium as will dissolve the precipitate ; 

 after which, one-tenth more of the solution of cyanide 

 of potassium is to be added, to form free cyanide. The 

 strength of this solution may vary ; but the patentees 

 prefer a solution containing six troy ounces of metal to 

 the gallon. The solution is worked at about 100 Fah., 

 with a plate of cadmium as an anode." 



107. Tin Salt*. The most common salts of tin are 

 the peroxide and protochlorido : in addition to these 

 there are two others, used extensively in Manchester, 

 mid the cotton-printing districts viz., the bichloride 

 and the stannate of soda, i.e., oxide of tin combined with 

 caustic coda. Peroxide of tin is formed by dissolving 

 protochloride of tin in water containing a few drops of 



hydrochloric acid, and then adding liquid ammonia, or 

 a solution of carbonate of potash, as long as a precipitate 

 can be produced ; the precipitated peroxide of tin should 

 be washed and dried. Protochloride of tin is easily 

 made by adding grain tin to strong hydrochloric acid, 

 and keeping it at 160" or 200 Fah., until gas ceases to be 

 evolved from the metal ; the resulting solution should 

 then be evaporated and crystallised. Aqueous bichlo- 

 ride of tin may be made by dissolving tin in aqua regia 

 not containing too much nitric acid ; a mixture of nitric 

 acid with sal-ammoniac or common salt may likewise be 

 used. Stannate of potash may be formed by f\i,-m:' 

 together one equivalent (75 parts) of freshly precipitated 

 peroxide of tin, and one equivalent either of caustic 

 potass (66 '2 parts), or of crystallised carbonate of potash 

 (87-2 parts). 



108. Tin Solutions. M. Roseleur has patented the 

 following liquid* for the deposition of tin : 



1st. For simple immersion or wash process, which 

 may bo used for small articles generally dissolve 17} 

 ounces of ammoniacal alum in 22 pounds of boiling 

 water, and, when dissolved, add one ounce of protochlo 

 ride of tin : the articles to be coated should bo well 

 cleaned, and then immersed in the liquid, and moved 

 about in it until they are sufficiently white. 



2nd. For depositing tin upon lead, iron, steel, copper, 

 or brass, by connecting the articles with a piece of zinc, 

 and immersing them in the solution dissolve 10} 

 ounces of bitartrate of potash in 17 ; pints of water ; then 

 add three-quarters of an ounce of protochloride of tin, 

 and boil it a few minutes : the articles to bo coated are 

 immersed in the solution in contact with a piece of zinc 

 of proportionate size. 



3rd. For coating zinc, iron, copper, and many other 

 metals by the battery process dissolve 11 ounces of 

 pyrophosphate of potash or soda in 17} pounds of v. 

 then add 4} ounces of protochloride of tin, and operate 

 by tho battery process with an anode of tin. By this 

 process, M. Roseleur states that he can tin mctala 

 beautifully and to any thickness. Pyrophosphate of 

 soda is easily formed by heating to redness the common 

 diphosphate of soda. 



109. A protochlorido of tin depositing liquid, may 

 easily be formed by dissolving the ordinary commercial 

 protochloride in water, and adding a little hydrochloric 

 acid to remove any cloudiness or white precipitate which 

 may be formed; a similar liquid may bo mode by tho 

 battery processj by passing a current through dilute 

 hydrochloric acid by means of a large tin anode, until 

 sufficient metal is dissolved. This or any other chloride 

 of tin is not a good solution to obtain rcguline metal 

 from ; it has a very great tendency to deposit tho tin in 

 the form of long crystalline needles, of a fcmlike ap- 

 pearance, which often project from tho corners and 

 edges of the cathode to a distance of upwards of half an 

 inch. A solution composed of eleven ounces of water, 

 one ounce of hydrochloric acid, and eighty grains of 

 protochloride of tin, admits of this effect being produced 

 in a striking degree : nearly all the compounds of tin, 

 and especially those formed with mineral acids, exhibit 

 this tendency in a greater or less degree when acted 

 upon by electrolysis, rendering the deposition of tin in 

 thick layers of fine white coherent metal a matter of 

 considerable difficulty. 



110. The stannate of potash solution is easily formed 

 either by dissolving tho crystallised salt in water, or by 

 dissolving freshly precipitated peroxide of tin (109), whilst 

 still moist, in a boiling solution of caustic potash. It 

 may also bo easily formed by the lttcry process, by 

 passing a strong current of electricity, by a largo tin 

 anode, through a strong and boiling solution of caustic 

 potash, until tho immersed cathode receives a free white 

 deposit. This solution, if worked at 150 Fah., yields a 

 good deposit of fine white metal ; but it decomposes by 

 exposure to the atmosphere, and soon deposit* all its 

 nirtal as oxide of tin. A solution of cyanide of potas- 

 sium and tin has boon proposed as a depositing liquid ; 

 but it is a had conductor with a tin anode, even if hot, 

 and does not dissolve tho metal freely. 



