RECENT PROGRESS IN PHYSICS. 6\)b 



vol.) How far tins idea has been practically successful, for instance, 

 "by precipitating silver upon iron, I do not know. Knoblaucli proposed, 

 (Dingler's Journal, 105 vol.,) by deposition upon a well made copper 

 plate, to produce plates for engravers ; because they would be without 

 any defective places and already formed with a plane and polished 

 surface. Stereotype plates may be immediately deposited upon im- 

 pressions made on wax covered with lead foil. Such plates, as well as 

 electrotype copies of wood-cuts are always made very thin and after- 

 wards tinned on the back by the aid of chloride of zinc, and then 

 filled up with type metal. From wood-cuts, the mould is made either 

 by an electrotype, the surface of the wood having been made to con- 

 duct by graphite, or else by impression in wax, &c. But when wood 

 has to be immersed in a fluid, the parts not to be covered should be 

 doubly protected — first, by a coating of sheet lead, and over this again 

 by another of wax. Von Kobell made a peculiar application of the 

 galvanic production of copper plates, under the name of galvan- 

 ography. — (Presented to the academy at Munich, May 4, 1840.) He 

 painted, after the manner used with India ink, wdth a solution of 

 damar resin in spirits of turpentine, with the addition of oxide of iron, 

 upon a polished copper plate, and had it galvanically covered with 

 copper without previously making it conducting. The plate thus 

 obtained is immediately ready for printing ; the brightest lights are 

 the places where no varnish has been applied. The overgrowing of 

 the varnished places proceeds in part from points of the copper un- 

 derneath acting through the varnish, but also in part from the uncov- 

 ered places. But since these plates do not allow of many impressions, 

 they may be multiplied by the electrotype method. Yon Kobell has 

 explained this process in a separate treatise. — (Munich, published by 

 Cotta.) 



For electrotype copies of other objects than copper plates^ moulds 

 usually must be made first. They are obtained either by impressions 

 made in soft lead plates or from cliches in a fusible alloy, or by casts 

 of plaster and wax, or of plaster alone, or else of wax alone, or of a 

 mixture of equal parts of wax and rosin. 



As to the metallic moulds no metal can be used which is acted upon 

 by the solution of sulphate of copper, as iron, tin, zinc ; these require 

 a previous electro-plating with silver. Bottger, in the Frankfort Gew- 

 erhefreund of 1840, (Dingler's Journal, vol. 78,) recommends an alloy 

 of 8 bismuth, 8 lead, 3 tin, (melting at 86°R.,) and advises the use 

 of metallic moulds wherever they are applicable. He pours the fused 

 metal into a paper box, stirs it with an iron wire until it begins to 

 thicken, and then presses the object to be moulded upon it until it 

 cools. Impressions in thin lead which has been cleaned with ley, are 

 also recommended by BOttger ; they are taken in a press or vise upon 

 moistened pasteboard. Very fragile objects may be covered with lead 

 foil, (tin foil is not applicable,) rubbing it carefully with a little pad 

 of cotton ; before taking it ofi", a mixture of wax and rosin must be 

 poured over it ; but for such objects casts are preferable. 



For casting moulds with melted wax combined with plaster or with 

 plaster alone, or with a mixture of wax and rosin, it is only necessary 

 that the object to be copied should be surrounded by a strip of paper 



