M. TECHNOLOGY. 601 



cent, of that employed in washing. The process is also 

 adapted to the separation of the oil from the fulling wash- 

 water, and is superior to previous methods in which acids are 

 used in rapidity, ease, and neatness, as well as in the quantity 

 obtained. The refuse from 10,000 cwt. of unwashed wool 

 would contain the following ingredients, having about the an- 

 nexed values : 



500 cwt. crude potash, at $4 26 $2130 00 



160 cwt. saponifiable fat, at $5 68, at least 908 80 



310 cwt. unsaponifiable fat, at $1 26, at least 1448 40 , 



225 cwt. soda (being 45 per cent, of 500) 798 75 



Total $5285 95 



Cost of recovery, about $2130 00 



23 C,3farch 16, 1873, 102. 



IXERASIBLE INK. 



According to Nissen, when a solution of the yellow prus- 

 siate of potash is added to any kind of ink, attempts to erase 

 it by means of oxalic acid or other chemical substances sim- 

 ply convert the characters into Prussian blue. This method 

 is therefore believed to be well adapted for the treatment of 

 inks to be used in banking and other operations. 1 C, 1873, 

 XII., 188. 



NEW MODE OP COPYING DESIGNS. 



Renault has communicated to the Academy of Sciences in 

 Paris an ingenious process for copying designs, based upon 

 the reduction of salts of silver, on paper or other organic 

 material, by copper, hydrogen, or vapor of phosphorus. To 

 eifect this the sheet of paper on which the drawing is made 

 is placed on the top of a sheet of card-board, which has pre- 

 viously been exposed to vapor of hj^drochloric acid, and 

 above the drawing is laid a sheet of paper sensitized with art 

 oxygen salt of silver; the double nitrate of iron and silver is 

 one of the best for this purpose. The vapors of the hydro- 

 chloric acid rising from the pasteboard beneath pass through 

 the paper at all points except those at which the lines of the 

 picture are found. The oxy-salt in the sensitized paper 

 quickly becomes converted into chloride of silver ; but those 

 points at which the hydrochloric acid has not penetrated re- 

 main in their old condition. When the paper thus treated 



Cc 



