RECENT PROGRESS IN PHYSICS. 397 



graphite; rendered first the lower pieces and their joints conducting, 

 and suspended zinc in dilute sulphuric acid in bags of" animal mem- 

 brane so that it was nowhere in contact with the mould. He then 

 added the solution of the sulphate of copper and connected the zinc 

 with the conducting mould. When the first thin coating was formed 

 in two successive pieces of tlie mould, they were placed together, and 

 the zinc in the bag put in conducting connexion with the joint ; more 

 copper was then precipitated, and in this way the separate thin pieces 

 were united into one. In this manner all the parts of the statue were 

 connected, with the exception of the arms, which were made separately 

 in a similar way. As no bags with zinc could be introduced into the 

 very narrow parts, separate batteries had to be used in such cases for 

 the first coating. Such a procedure may be adopted for the sake of 

 obtaining a premium, but it certainly proves that so far no really 

 practical results have been obtained. A method similar to that used 

 in this case for uniting the separate pieces h&s been employed for 

 soldering copper rings by means of galvanism; the rings are protected 

 by varnish, but the surfaces to be joined are left bright, and the 

 copper is deposited until the whole space is filled. 



A peculiar application of tlie electrotype was made by I\Iallet and 

 Meillet, in covering glass and porcelain vessels with a thin copper 

 co&ting on the parts to be exposed to fire. Mallet covered the vessels 

 with Canada balsam and graphite, but Meillet used gum and nitrate 

 of silver dried in a flame ; intense heat, however, destroys this con- 

 ducting coating between the vessel and the copper deposited upon it, 

 which latter becomes loose. M. Simson, in 1843, proposed (Dingler's 

 Journal, vols. 89 and 91) to act upon the places to be covered by ade- ' 

 posit of copper with hydrofluoric acid to remove the jDolished surface, 

 and then to rub them over with graphite by means of a cork. Mohr 

 saw such vessels in the Paris exhibition of 1844 ; reported on them as 

 quite new in Dingler's Journal, vol. 103, and tried to imitate them. 

 But he used copal varnish and bronze powder, and therefore his coating 

 was only firm where it could embrace the vessel, as in retorts, but not 

 in evaporating dishes. Afterwards experiments were again made on 

 this subject by Eisner. — (Dingler's Journal, vol. 108.) He again 

 made use of varnish and graphite, and also applied the etching pro- 

 cess ; when the places had been covered Avith a mixture of flour-spar 

 and sulphuric acid for twenty-four hours, and then, after washing, 

 rubbed over with graphite, the deposit adhered firmly even upon 

 evaporating dishes, exactly as stated by Simson years before, though 

 Eisner does not mention this. It has been attempted by Mallet to 

 connect glass tubes in this manner; their ends were ground even, and 

 for a distance of one-half to one inch rendered conducting by means of 

 varnish and graphite. But the joining of the ends as well as the im- 

 mersion of the tubes present peculiar difficulties. For the latter 

 purpose the vessel must be perforated, and the openings closed with 

 clay after the introduction of the tubes, before pouring in the solution 

 of sulphate of copper. 



Talbot, Steinheil, and also Wheatstonehave experimented in re-pro- 

 ducing metallic mirrors by the electrotype process. Talbot endeavored 

 to make the copper mirrors white by exposing them to the vapor of 



