ther 



MKTAI.S. 



of black oxide, and charcoal, are then placed 



~ in a plumbago crucible, which is i 



i cluiTcoal, mill exposed to a great heat. 

 hole is molted, tho heat in nllwud to 

 gradually, and the alloy of ino and copper 

 i when the temperature U juxt loffloitM to 

 us d.nie, the erueil.lu is taken from tho 

 contents stirred with a hazel-stick. Tho 

 .tiled, first being wrapped in paper and 

 dropped into the crucible. The alloy is apain 

 1, and finally poured into the mould ; k is then 

 rolled and wrought just like silver. A 

 at portion of tho zinc is volatilized in the net i 

 so that a verv littlo remains in the alloy." 

 he superiority of this metal is said to depend prin- 

 ' !! the cobalt, to which is due ila peculiar 

 ne lu>tre. 



mentation of Metals. Metals can bo 

 ea-ily colored by forming on their surface a 

 film of sulphide, which is deposited by placing 

 the article to be colored in some solution con- 

 taining sulphur. In a few minutes brass or 

 gun-metal articles can be given tho color of 

 gold, of copper, of carmine, dark red, bright 

 blue, pale blue, or pinky white, according to 

 tho thickness of the coat, which depends on 

 the length of time the metal remains m the so- 

 lution used. The colors possess a very good 

 lustre, and if the articles to be colored have 

 been previously well cleaned by means of acids 

 and alkalies, they adhere so firmly that they 

 may be polished without injury. 



To prepare the solution, dissolve li ounce 

 of hyposulphite of soda in 1 pound of water, 

 and add 1 ounce of acetate of lead dissolved 

 in pound of water. "When this clear solution 

 is heated to from 100 to 210 Fahr., it decom- 

 poses slowly, and precipitates sulphide of lead 

 in brown flakes. If some metal or article to 

 be colored is now present, a part of the sul- 

 phide of lead is deposited thereon, and, accord- 

 ing to the thickness of the deposited sulphide 

 of lead, the above colors are produced. To 

 produce an even coloring the articles must be 

 evenly heated. Iron treated with this solution 

 takes a steel-blue color ; zinc, a brown color ; 

 in the case of copper objects, the gold-color 

 does not at first appear; lead and zinc are 

 entirely indifferent. 



If, instead of the acetate of lead, an equal 

 weight of sulphuric acid is added to the hypo- 

 sulphite of soda, and the process carried on as 

 before, the brass is covered with a very beau- 

 tiful red, which is followed by a green (which 

 is not in the first-mentioned scale of colors), 

 and changes finally to a splendid brown, with 

 green and red iris-glitter. This last is a very 

 durable coating, and may find special attention 

 in manufactures, especially as some of the 

 others are not very permanent. 



Very beautiful marble designs can be pro- 

 duced by using a lead solution thickened with 

 gura-tragacanth, on brass which has been 

 heated to 210 Fahr., and is afterward treated 

 by the usual solution of sulphide of lead. The 

 solution may be used several times. 



Much time and attention have been devoted 

 by Prof. Kick, of Prague, to the subject of 



etching iron with acids. After many experi- 

 ments with tho different acid* and Home other 

 etching solutions, i'rof. Kick found that n mist- 

 s' equal parts of li \drochloric. acid uud 

 water with a drop of chloride of antimony to 

 quart of tin- mixture was the l>. -t etch- 

 ing solution. Some kinds of iron showed w hat 

 is called a passive state, acids not act in- upon 

 it until this condition IHIH been destn.\ . <1 l.v 

 ln-atiiig, and then the surfaces seemed quick 

 to rust ; but tho action of the chloride in the 

 solution appears to arrest this tendency. The 

 smooth surface to be etched is surrounded with 

 a ridge of wax, and tho acid is poured into the 

 disk thus formed. At a temperature of 56 to 

 65 Fahr. tho action soon begins, as shown by 

 the gas evolved ; in winter tho etching is poor. 

 The time required is from one to two hours, 

 but the etching should go on until the texture 

 is visible. Every half-hour the acid can be 

 poured off without removing the wax, the car- 

 bon rinsed off, and the surface examined. If 

 too much chloride of antimony is added to the 

 acid, a black precipitate will soon form, which 

 can easily be distinguished from the carbon. 

 When the etching is finished, the wax rim is 

 removed, the iron washed, first in water con- 

 taining a little alkali, then in clean water, 

 brushed, dried, and varnished. If in a few 

 hours it begins to rust, the varnish should be 

 removed with turpentine, which will also take 

 off the rust, and then varnish again. 



The appearance of different kinds of iron 

 when etched is essentially as follows : Soft or 

 sinewy wrought-iron of excellent quality is at- 

 tacked so equally by the acid, and so little car- 

 bon is separated, even after several hours' ac- 

 tion, that the surface remains bright and 

 smooth. Fine-grained iron acts the same ; the 

 surface is still smoother, but a little darker. 

 Coarse-grained and cold-short iron is attacked 

 much more violently by acid than the above. 

 In ten minutes, especially with the latter, the 

 surface is black. After thirty minutes a black 

 slime can be washed off*, and the surface will 

 remain black in spite of repeated washings, 

 and exhibits numerous little holes. Certain 

 parts of the iron are usually eaten deeper, 

 while others, although black and porous, offer 

 more resistance. By allowing the acid to act 

 for an hour or so, then washing, drying, and 

 polishing with a file, a distinct picture is ob- 

 tained. Malleable cast-iron rusts more easily 

 than wrought-iron, and it is interesting to 

 know that the action of acids is also vio- 

 lent, the surface being attacked more vigor- 

 ously. Gray pig-iron acts like steel ; the 

 etched surfaces have quite a uniform gray 

 color. In puddled steel the color, after etch- 

 ing and washing, is gray, with quite a uniform 

 shade, and the lines are scarcely visible. Ce- 

 ment steel has a very similar appearance, the 

 lines being very weak. In Bessemer and cast- 

 steel the etched surfaces are of a perfectly uni- 

 form gray color, with few, if any, uneven places. 

 The softer the steel the lighter the color 



