M. TECHNOLOGY. 509 



ground glass; one of dammar resin in benzole, when mixed 

 with ether, also gives a good dead surface ; water, instead of 

 the ether, renders it, at the same time, semi-opaque. A mixt- 

 ure of benzole with common negative varnish frequently, 

 but not always, gives a beautiful dead surface. In all cases 

 a great deal depends on the purity of the ingredients. It is 

 recommended to dissolve from 3 to 15 parts of sandarach in 

 48 parts of ether, and to add 24 parts of benzole, or as much 

 as may be necessary to produce the desired result. The fol- 

 lowing, by Hughes, is said to give a perfectly colorless var- 

 nish of this kind : Ether, 560 grains ; benzole, 240 ; sandarach, 

 40; Canada balsam, 10. The resins are first to be dissolved 

 in the ether, and the benzole added to the solution. 5 C, 

 1873, xlv., 350. 



rose-colored stain for w r ood. 



Monnier recommends steeping the wood for several hours 

 in a bath of 1200 grains of iodide of potassium to the quart 

 of w T ater, and then immersing it in a bath of 375 grains of 

 corrosive sublimate, when it will assume a beautiful rose-red 

 color by chemical precipitation. It should subsequently be 

 covered with a glossy varnish. The baths will not need re- 

 newal for a long time. 



ELECTRO-STANNUS. 



Several years ago a patent was taken out in London in re- 

 gard to a process called electro-stannus, which is in reality a 

 method of coating with tin objects intended for subsequent 

 plating with silver, so as to give a body, and reduce the 

 amount of silver necessary to cover the original material. 

 This is applicable to all kinds of iron substances, and has 

 lately received an extended application. The principal diffi- 

 culty has been to keep the tin of the electric floating bath in 

 solution, as it has a tendency to fall to the bottom in the 

 form of a precipitate. To prevent this, grain tin is dissolved 

 in nitro-muriatic acid, or in nitric acid, and thus a solution 

 of nitro-muriate, or of nitrate of tin, is obtained. To this is 

 added a solution of cyanide of potassium and water, the 

 quantity used being sufficient to precipitate the tin contained 

 in the nitro-muriate or nitrate solution. The oxide of tin 

 thus obtained is washed with water in a filter, and either 



