396 RECENT PROGRESS IN PHYSICS. 



and the fluid mass, free from air bubbles, poured upon it ; when tlie mass 

 is cooled and hardened it can be taken off without difficulty. Moulds 

 of plaster of Paris must afterwards be soaked in melted wax to make 

 them water-proof. Gutta percha is also used for moulds ; it is slowly 

 heated in water, and when dried exposed to a moderate pressure in 

 a vise in contact with the object to be moulded. To render these or 

 wooden moulds conducting, Spencer, (Dingler's Journal, vol. 77, p. 

 343,) after finding gilding with gold leaf or dusting with graphite 

 either too expensive or unsatisfactory, took 3 Jo of phosphorus, dis- 

 solved it in one part of strong alcohol in a water bath, immersed the 

 mould for some seconds in a weak solution of nitrate of silver, and 

 exposed it to the vapors evolved from the solution of phosphorus 

 heated in a watch glass on a sand bath. Instead of this last process, 

 Bottger proposed to place the mould, when soaked in nitrate of silver, 

 in a vessel into which non-inflammable phosphuretted hydrogen is con- 

 ducted. The latter is obtained by gently heating in a retort a few 

 small pieces of phosphorus with alcohol and caustic potassa. At 

 present such moulds are commonly powdered over with finely elutriated 

 graphite or finely divided silver, and the excess removed with a soft 

 brush. 



The reproduction of round forms by the electrotype offers consid- 

 erable difficulties ; a separate decomposing cell has generally to be 

 used, and the surface of the element must be nearly equal to or larger 

 than that to be coated. Jacobi proceeded in the>following manner : 

 He made a conducting surface on a bust, in alio relievo, moulded in 

 wax, covered it very thinly by means of galvanism, removed the wax 

 by melting, cleaned the mould thus obtained with spirits of turpen- 

 tine, and then precipitated upon the inside a thicker layer of copper, 

 from which he attempted to scale off the exterior thin cover, (Ding- 

 ler's Journal, vol. 78,) but did not succeed without injuring the copy 

 obtained. A Mr. Soyer, in Paris, (Dingler's Journal, vol. 78,) repro- 

 duced, in this way, a bust tolerably free from imperfections, and im- 

 mediately offered to make, for the sum of 200,000 francs, an electro- 

 type copy of the well known great elephant. Fortunately for bioa, 

 nobody accepted the offer. The Duke Max Von Leuchtenberg fol- 

 lowed a similar method, (Dingler's Journal, vol. 80.) His electrotype 

 operations are conducted on the grandest scale, as may be seen from 

 the fact that the black powder deposited on the copper anodes, from 

 impurities in the copper and sulphuric acid employed, and which had 

 to be removed every twelve hours, amounted in a period of about two 

 years to forty "puds," (about 1,444 pounds.) 



In the laboratory of Stiglemeyer they were not more successful in 

 reproducing statues on a large scale. A Mr. Moyle, (Dingler's Jour- 

 nal, vol. 80, Sturgeon's Annals of Electricity,) says that he produced 

 such figures over moulds of wax, which he afterwards melted out, but 

 alleges that he has also obtained with silver results of the greatest 

 perfection. The Society for Encouraging Industry, in Prussia, offered 

 a premium for the electrotype production of a larger statue, which 

 was awarded to Mr. Von Hackewitz, (Dingler's Journal, vol. 108 ; 

 Transactions of the Society of 1848.) He made, over the model, a 

 mould in pieces, of two parts wax, two turpentine, one rosin, and five 



