M. TECHNOLOGY. 497 



free from iron, and that no iron is introduced in any way 

 during the operation. For use, the powder is stirred into 

 about double the quantity of cold water, and enough boiling 

 water then added, with continued stirring, to produce a vis- 

 cous liquid, into which the articles must be dipped. 14 (7, 

 CCX.,157. 



WEATHER-PROOF WASH FOR WOOD. 



According to Kuhr, a cheap and convenient reddish-brown 

 coating of ferrocyanide of copper can be formed upon wood, 

 which not only adheres firmly and resists the weather, but 

 also preserves the wood by keeping it free from moss, etc., 

 as well as from injurious insects. To produce this result, 

 wash the surface (previously brushed with a solution of half 

 a pound of yellow prussiate of potash in a gallon of water) 

 w r ith a solution of one pound of blue vitriol in a gallon of 

 w T ater. The shade can be regulated by varying the strength 

 of the solutions. Since the wood is stained rather than cov- 

 ered, its texture remains somewhat visible, which is not ob- 

 jectionable ; and by coating it with linseed-oil varnish, not 

 only is its durability increased, but a gloss is imparted, with- 

 out which it is rather dull. 25 (7, XXXIX., 318. 



PROTECTION OF LEAD WATER-PIPES BY A FILM OF SULPHIDE. 



As a result of the following experiments, it is announced 

 that a film of sulphide of lead forms an excellent protection 

 for the metal against the action of water. Lead pipes were 

 coated internally with sulphide, according to the method of 

 Dr. Schwarz, by the action of a solution of sulphide of sodi- 

 um, and were subjected, at the same time with others not so 

 treated, to the action of rain, snow, distilled and ordinary 

 Paris city water. After the first day lead was detected in 

 all cases in the water from the ordinary pipes, except in the 

 city water, and in it also after several days. On the other 

 hand, in no case did the water from the pipes treated with 

 sulphide afford a trace of lead within three months, and with 

 access of air. 14 C, 1874, III., 401. 



WATER-PROOFING LINEN. 



The following process is recommended by Kuhr for this 

 purpose : Pass the linen first through a bath of one part of 



