MECEAmCAL. 791 



hard finish, same as for a room. About 2% hours will be required to set, on a 

 hot pipe. 



2. Steam Pipes, Protection Efficient and Cheap.— A mechanic 

 reports through the Detroit Post and TrUmtie, a little different from the above, 

 you will see, using hair and leaving out the flour. He says: " One hundred 

 lbs. of clay are mixed with water, and 100 lbs. of fine ashes added and well 

 kneaded, then mix with 1 lb. of hair. This mixture is well incorporated and 

 allowed to stand until needed to use. Just before using, 10 lbs. of ground 

 plaster of Paris are mixed with it. The mixture, of course, soon sets, and 

 cannot be kept over 12 hours after the plaster is added." 



llemarks.—i:h.e clay should, no doubt, be dry, then made fine, else allow- 

 ance made for the moisture in it; and this latter make no distinction as to ashes, 

 whether wood or coal I think cleanly sifted coal ashes preferable. The plas- 

 ter of Paris, it will be seen too, is not calcined (dried in a hot kettle.) If so 

 done, it sets quicker, which is its only advantage, and it may be an advantage, 

 sometimes, not to have it set too quick. The hair, I think, a decided advan- 

 tage, but it should be thoroughly whipped- If good for pipes, it must be 

 equally good for boUers. 



"Zincing Iron "—Without a Battery.— " The following" is an 

 excellent and cheap method for preventing iron articles, exposed to the air, 

 from rust. They are to be first cleaned by placing them in open wooden 

 vessels, in water, containing ^ to 1 per cent. (" ^ to 1 per cent.," means % to 

 to 1 pt., or part, to 100 pta. or parts, in the "wooden vessel" of water), of 

 common siJphuric acid, and allow them to r emain in it until the surface 

 appears clean, (bright) or may be rendered so by scouring with a rag or wet 

 sand. [This may be done in a revolving cylinder by machinery.] According 

 to the amount of acid, they may require to remain in from 6 to 24 hours. 

 [Then, if time is of any account, use more acid, up 5 or 6 per cent.] Fresh 

 acid must be added according to the extent of use, and the amount of liquid; 

 and when this is saturated with the sulphate of iron (the rust of iron f rcwn the 

 articles being cleaned) it must be renewed. After removal from this bath 

 ("wooden vessels,") the articles are rinsed in fresh water and scoured imtil 

 they acquire a clean metallic surface (become " bright," as above remarked); 

 and then they are to be placed in water, in which a little slacked lime has 

 been stirred, and kept there until the next afternoon. When thus freed 

 from rust, they are to be coated with a tliin film of zinc, while cold, by 

 means of chloride (more commonly called muriate) of zinc, which is made 

 by filling three-fourths full a glazed earthen vessel with muriatic acid, then 

 adding zinc clippings (little pieces of zinc) until effervescence ceases. 



[Effervescence is shown by the rising of bubbles; when these stop rising, 

 it has dissolved all the zinc it will cut, is saturated, as chemists say, and 

 is then called muriate of zinc, and is the same as tinners use upon their 

 seams before applying solder.] 



" This liquid (muriate of zinc) is now to be turned off from the undi^ 

 solved zinc and preserved in glass vessels. 



