496 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



lution of the tartrate, and, after mixing, boiling strongly to- 

 gether, and while the steam is issuing violently from the flask, 

 dropping in 20 cubic centimeters of the silver solution, and 

 boiling for another ten minutes. This solution not only keeps, 

 but seems to improve by age. The liquid is to be filtered 

 from the precipitated silver as it is wanted. 



The silvering solution is prepared by taking 900 cubic cen- 

 timeters of distilled water, and adding 80 cubic centimeters 

 of the silver solution and 100 drops of the ammonia solution, 

 and filtering if necessary. 



For silvering, equal volumes of the two solutions are to be 

 carefully and separately filtered, and poured together into a 

 flat glass dish to such a depth that the thoroughly cleansed 

 plate shall be covered by a layer of at least one tenth of an 

 inch. Decomposition of the mixture takes place in ten min- 

 utes, and pure metallic silver is deposited on the plate, which 

 is then washed, dried, and varnished. For the purpose of 

 silvering the interior of glass globes, etc., it is sufficient to 

 pour in successive small quantities of the mixture, turning 

 the vessel continually, so as to keep the whole surface wet 

 uniformly. 21.4, IX., July, 1871. 



MINERAL COTTON. 



The Journal of the Franklin Institute reports the exhibition 

 at one of its meetings, by Mr. Coleman Sellers, of a material 

 which it is thought may be capable of useful applications in 

 the arts. The substance possesses a general resemblance to 

 cotton, for which it may in some cases probably be used to 

 advantage. It is really, however, a form of spun glass, pro- 

 duced by allowing a jet of steam to escape through a stream 

 of liquid slag, by which it is blown into the finest threads, 

 sometimes two or three feet in length. These threads, though 

 somewhat elastic, readily break up into much smaller ones, 

 and the color of the substance being white, the appearance 

 of a compacted mass of it makes the name of mineral cotton, 

 under which it has been described, a very appropriate one. 

 The admirable non-conducting property of the material for 

 heat, as well as the great quantity of air it retains in its in- 

 terstices, would seem to fit it very well for a non-conducting 

 casing to steam boilers and pipes, an application for which it 

 is being tested. 1 D, December, 1871, 361. 



