60 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ing its lustre for a long time. The author of the process has 

 applied it to great advantage in his laboratory for the pur- 

 pose of coating articles of iron, steel, and copper, thereby pro- 

 jecting them against rust. One difficulty in tke process re- 

 sults from the fact that only a very thin layer of tin can be 

 applied. Should it become practicable to impart a thicker 

 coating, it will probably acquire great importance. Exp'eri- 

 ments upon nickelizing metallic substances in a similar man- 

 ner are in course of progress by the author, although thus far 

 without satisfactory result. 1 4 C^CX-CVIII., December 4, 308. 

 We learn that Professor Stolba's experiments have been re- 

 peated with much success. The tinning of cast-iron, wrought 

 iron, steel, copper, and brass is found to be very satisfactory, 

 the tin adhering very firmly, even when in very thin layers. 

 Diluted sulphuric acid, however, it is said, generally produced 

 dark spots and removed the coating. Experiments have been 

 made to apply the same process for the ornamentation of me- 

 tallic objects. These were tried especially upon cast-iron ar- 

 ticles electroplated with copper, where the projecting edges 

 were tinned, with excellent effect. As greasy spots can not 

 be tinned, it is only necessary to apply very thin layers of oil 

 to the places where no deposit is desired in order to coat the 

 remainder of the article with tin, thus producing a striking 

 contrast. 6 C, v., 49. 



GALVANOPLASTIC COPIES FROM ORGANIC MATRICES. 



The usual method of obtaining galvanoplastic plates from 

 matrices of an organic nature consists in either coating the 

 surface with graphite or a powdery deposit of silver, or else 

 imparting conductivity by sulphide of silver. These methods 

 are only suitable for rough work, since the delicate gelatine 

 reliefs produced in the operation are decidedly affected by the 

 sprinkling of the substances mentioned, which destroy the 

 sharpness of the detail. It is, therefore, much better to pro- 

 duce a deposit of silver directly upon the gelatine in the sun- 

 light, which, in consequence of the presence of an organic 

 substance, will be in a state of purity, and attached uniformly 

 and continuously upon the surface. For this purpose the 

 gelatine relief sheet is to be fixed to a glass plate by means 

 of copal varnish, and allowed to remain for an hour in a con- 

 centrated solution of tannin, in order to render it insoluble in 



