ON ELECTROTYPING OPERATIONS. 



[1853. 



posed to sunshine ^Tould separate with ■veiy great facility; -while 

 a plate iodized ou a rainy da^-, and placed in a dark I'oom tor a 

 few houi-s befoi'C introducing it into the vat, might stick so hard 

 as to requiie some of the old resorts of heating and jarring to 

 separate it from the rnatiix. 



The ])rocess of iodizing and exyiosiiig to light has now leen 

 applied to a very great extent of finely engraved surface, and in 

 no case has the le;ist difficulty been found m lifting one plate oil 

 the other when the requisite thickness had been obtained. 



I am aware that it may be thought that the iodine acts only 

 by intervening between the plates ; but the quantity of iodine 

 apyilied to a plate must be thought insufficient to effect it by 

 mei'e mechanical separation when we consider the large quantity 

 of silex and carbon found in ordinar}' copper. If but one ounce 

 of copper be dissolved from a square foot of ordinary plate, a \ ery 

 heavy deposit of impurities is left, (sometimes 5 per cent.J and 

 the quantity of wax ■which may be applied to a plate, and fail to 

 prevent sticking, is ten thousand times more than the quantity of 

 iodine which prevents it. 



In preparing our largest plates, ha\'ing ten square feet of lace, 

 I use a solution of one graiu of iodine in tvventy thousand grains 

 of strong alcohol. If one grain of the solution is required to wet 

 a square foot, it will give but one-twenty-thousandth pait of a 

 grain of iodine on a square foot. But as the iodine evaporates 

 rapidl}' with the alcohol, pi'obably the actual quantity on a 

 square foot does not exceed oue-hundretl-thousandth part of a 

 grain. 



Taking the weight of a cubic inch of iodine at 1,250 grains, 

 and supposing that it remains on tiie silver surface in its elemen- 

 tary state, instead of forming iodid of silver, then we have 1,250 

 X 144X100,000^1 8,000,000,000, only one-eightecn-tl.ousand- 

 miilionth part of an inch for the thickness of the coating of iodine. 

 Even if we suppose that the solar rays decompose the iodid of 

 silver, and leave the iodine in vapor on the plate, it will still be 

 only one-forty-four millionth jiart of an inch — a thickness to be 

 taken as nothing in a mechanical view. 



To test the effect of the chemical method of preventing adhe- 

 sion on the sharpness of the engra\'ed lines, an engraving was 

 seven times successively transferred from plate to plate, when 

 the closest inspection failed to show any inferiority of impressions 

 from the last plate as compared with those from the first. 



Time and expense of electro-sasting. — Next in importance to 

 securing a certain and easy separation of the matrix and casting- 

 is bringing the entire time and expense of electrotyping within 

 the narrowest limits. 



Mr. Smee and othei-s have shown that the quality of electro- 

 metal is determined by certain relations between thera]iidity of 

 forming the plate and the strength of the solution in -vvhich it is 

 formed. Both the common operations of the electro-metallur- 

 gist, and the iraprovnucnts he jiroposes, must conlbrm to these 

 relations. 



As small (|uaiititics of electricity arc easily set in motion, 

 small-sized elect lo-castings are readily made in six or eight days. 

 To makc^ Liin- ■ r,iNiiii;j;s in a short time requires a powerful current. 

 To accomplish the lorresponding augmentation in the eifective 

 electric action has proved a fomewhat difficult matter. 



At the date of the "Aide Mcmoire to the Military Sciences," 

 it is .stated that in the ordnance survey one pound of copper was 

 deposited in twenty-four hours on a plate of eight square feet, the 

 l)lates being male dm-tilo enougji to bear hammering onh- by 

 continued agitation of the electrolytic solutions. 



At this rate, to make a plate one-eighth of an inch thick will 



require forty-five davs. So far as I am informed, the above 

 perlbrmanee has not been excelled, as to quality and time, on 

 large woi'k anv"here prior to its being attained as now to Le 

 described. 



The fii-st and n.ost obnous suggestion for increasing the rate 

 of dejiosition is to enlarge the battery ; this, however, is incapa- 

 ble of producing the desired end. 



To present this subject in a clear and satisfactory manner, I 

 will make use of the celebrated formula of Piofessor Ohm, who 

 deduced from mathematical reasoning, and established by exjier- 

 iment, that the effective force of the current from any battery 

 w-as directly as the electr motive force, and inversely as the re- 

 sist ance offered to that force. 



E 



To express this, he gave the equation --j—^o i'l which E 



I'epresents the electromotive force, or affinity of acid for zinc, 

 and K-\-r the resistance to the current generated b}' that force; 

 11 representing the resistance offered to it from the liquid con- 

 tained between the positive and negative elements of the batteiy, 

 and r the re.-istance offered by the object on which the battery 

 is working, and Q the amount of work executed, or the quantitj' 

 of the current obtained. 



The resistance of conductors has been found to be directly as 

 the length, and inversely as the section. 



So far as concerns form of arrangement, E is constant for the 

 materials used, as it depends on their chemical relations, Q can 

 therefore be favorably aflected only by varying El or r. Now, 

 as R represents the resistance of the liquid contjiined between the 

 battery plat&«, to increase the size of the plates is only to increase 

 the section of the liquid, or, in other ■words, to diminish the re- 



E 



sistance represented by R. The expression, Q, sho^ws 



that, if the resistance in the battery is small compared to the ex- 

 ternal resistance, the gain of effect from enlarging the battery 

 plates is but small. 



To determine the relative value of R, as compared with r, a 

 battery vsps constructed so as to collect and me;isure the gas 

 evolved by its action , 



The plates were placed in contact ■with each other, and the 

 gas evolved in thirty minutes taken as a unit of effect. As in 

 this case the current did not pass through anything but the bat- 

 tery, there is no resistance to be represented by r, or r in the for- 



E 



nnila will be equal to and Q 1. 



The battery ■vvas then attached to a pair of electrodes, in a 

 certain solution of sulphate of copper and sulphuric acid, especially 

 recommended by all the writers on electro metallurgy, the 

 arrangement being snch as to produce good metal. The gas 

 now evolved in thirty minutes w;is found only one-twentieth of 

 the former amount; hence the introduction of the resistance, r, 



E E 



had diminished Q twent^\' times, .and Tr-r-=Q =Trr--> ■^vlience 

 •' E-f )■ 20 !■!. 



r is equal to 19 R. To exhibit the effect of battery enlargement, 



we now have Q= tt.- If m,=^ , then Q=-05 : if m=2, 



,;,Xl9 I -V , 



Q=0512; if m=;i, Q=-0518; if m=i, Q--0524, etc., &c. 

 This shows a gain of only a fortieth from doubling th-i size of 

 the batteriy, etc., — an advantage too small to rejiay for the en- 

 largement. These calculations are in accordance with experi- 

 mental results from small batteries, but in large ones the neces- 

 sity of further separating the plates, in increa-sing their size, makes 

 ihj re^istenco increase, instead of diminish, _ but there is conse- 



