M. TECHNOLOGY. 495 



and, after the addition of a decoction of two pounds of log- 

 wood and five ounces of indigo carmine, enter the wool, and 

 heat to boiling. 23 C, VIL, 631. 



VAKNISH FOR BLACKBOARDS. 



The following is the recipe, according to the patent of 

 Formhals (which has expired), for a coating for blackboards : 

 Alcohol, 95 per cent., 65 parts, or alcohol, 90 per cent., 67 

 parts ; bleached shellac, 8 parts ; Paris black, 8 parts ; levi- 

 gated pumice-stone, 4 parts ; Paris blue, half a part ; burnt 

 umber, 4 parts ; dryer, 8 parts. The pigments and pumice- 

 stone are carefully mixed with alcohol, the shellac in solution 

 being added last. 6 (7, 1875, 18. 



RENDERING OAK AVOOD A BEAUTIFUL ORANGE-YELLOW. 



Melt together, Avith continued stirring, one pint of oil of 

 turpentine, and about 1200 grains of tallow, and 300 of 

 wax. Rub the wood, in a warm room, with the mixture 

 until a dead lustre is produced, and coat it an hour afterward 

 with thin French polish. Greater brilliancy and a deeper 

 tone may be produced by an additional coat of polish. 26 

 6; XL, 127. 



BROWN STAIN FOR OAK. 



Welger recommends the following as afiording a cheap 

 coating for wood, and which is very adherent, even when ex- 

 posed to the weather: Brush the wood with a solution of 

 persulphate of iron of 2 to 2^ Baume. The bluish -gray 

 tint it acquires on drying changes to an agreeable light-brown 

 shade with linseed-oil varnish. A solution of protosulphate 

 of iron will answer as well as one of persulphate. A dark 

 brown shade may be imparted by subsequent coating with a 

 half per cent, solution of permanganate of potash, and then 

 with linseed-oil. 19 C', VIIL, 26. 



DEEP WALNUT STAIN FOR LIGHT -VVOODS. 



The employment of alkaline manganates for staining light 

 woods in furniture and floors a beautiful, uniform, and du- 

 rable walnut brown is liighly recommended by Viedt. The 

 action depends upon the decomposition of the salt in the 

 pores of the wood, with the separation in them of very finely 



