472 



METALLURGY. 



etc., contained in the furnace ; while, if the 

 diameter were too small, there would not be 

 sufficient space to give the required volume 

 for combustion in order to obtain a given out- 

 put. The melting zone above the crucible 

 must also be designed so as to allow an easy 

 penetration of the blast through the materials. 

 When air is blown into a furnace it has to be 

 expanded by the expenditure of heat ; but if air 

 be introduced at a high temperature and already 

 in an expanded state, a more rapid combustion 

 is obtained with a saving of fuel in the furnace. 

 In the case of a cold blast being used, combus- 

 tion does not spread over a large space, and 

 therefore a smaller well suffices. High temper- 

 ature of blast requires a large area in the neigh- 

 borhood of the tuyeres, through which it is ad- 

 mitted. It is necessary that the furnace materials 

 should come down from the upper reaches thor- 

 oughly heated and reduced, and in as level a 

 manner as possible over the entire area. In or- 

 der to obtain capacity and to support the mate- 

 rial, and also to prevent too dense packing near 

 the tuyeres at the zone of fusion, the blast fur- 

 nace is made with boshes that is to say, the 

 interior space enlarges suddenly, the walls tak- 

 ing a slope of from 60 to 80, while the angle of 

 repose for dry materials is about 45 ; but when 

 the minerals become plastic, the angle of the 

 bosh requires to be more steep. Above the slope 

 of the boshes is the maximum diameter of the 

 barrel of the furnace. When, owing to the relative 

 sizes of the wall and the barrel, the bosh occupies 

 a large vertical space, thus retiring a long way 

 back, the materials at the sides are too far re- 

 moved from the ascending current of gas, and 

 will come down raw. In order to get over some 

 of the conflicting conditions referred to, the 

 author and a friend had designed a furnace of 

 comparatively narrow dimensions, but enlarged 

 at the upper part, thus giving, as it were, a sec- 

 ond bosh. In this way, in the higher region 

 where the charge is dry and porous and not sub- 

 ject to extreme pressure, capacity is obtained, 

 while the direct weight upon the lower portions 

 of the materials is reduced. 



Miscellaneous. In a paper on the action of 

 soil on cast-iron pipes, Prof. Weber, of Berlin, 

 represents that the corrosion of such pipes is 

 greatly accelerated if there be sulphureted hy- 

 drogen present along with atmospheric oxygen ; 

 the sulphide which is readily formed is rapidly 

 transformed into oxide by the free oxygen. 

 Chlorides in the soil have a similar effect when 

 free air has access at the same time. In about 

 fifty years cast iron under salt water is con- 

 verted for about one third of its thickness into 

 a gray graphitoid mass. Water containing ni- 

 trates and nitrites is also very energetic in this re- 

 spect, as is also ammoniacal water. The author 

 gave as an illustration pipes in the neighborhood 

 of an old cemetery and a disused unwholesome 

 spring. The water which came in contact with 

 the pipes was so charged with ammonia as to 

 make a precipitate with Nessler's reagent, and 

 also contained chlorides and sulphates of pot- 

 ash, soda, and magnesia, while the pipes had 

 holes eaten in them. Pipes traversing ground 

 of this character ought to be protected by clay 

 a coating of which seems entirely effective by 

 asphalt, or by earthenware pipes. In answer to 



the question why lead pipes are readily cor- 

 roded by the slag used in making up streets. 

 Prof. Weber said that clay and similar vitreous 

 material are decomposed by air and moisture, 

 with formation of free alkaline material, which 

 attacks the lead. Herr Arklarn, of Tegel, told 

 of instances in which wrought-iron pipes had 

 been corroded by slag wool, and recommended 

 a coating of graphite or of manganese cement in 

 varnish. 



A rule for the estimation of the amount of 

 paint for iron-work, given on the authority of 

 T. J. Swift, of the Delaware and Hudson Canal 

 Company, calls for five eighths of a gallon of 

 paint for each ton of iron for the first coat, and 

 three eighths of a gallon per ton for the second 

 coat. The entire cost of painting a 100-ton 

 bridge in Albany was $2.78 per ton; and the 

 amount of paint provided, in accordance with 

 the rule cited above, left a surplus of 50 gallons 

 of the first coating and 8 gallons of the second. 



The chief advantages claimed for the Cowper- 

 Coles cold galvanizing process for shipbuilding 

 and other purposes are cheapness and freedom 

 from distention and reduction in tensile strength 

 in articles of small section. A plant has been 

 erected by Messrs. Laird Brothers for coating 

 the hulls and frames of torpedo boats. A plant 

 erected at Glasgow for zincking machined steel 

 forgings consists of four baths, viz., a cleansing 

 bath, a pickling bath, a washing tank, and the 

 zincking vat, which are arranged in a rectan- 

 gular form, with a radial crane in the center. 

 The articles to be zincked, thickly coated with 

 grease, are passed through the " potash boil," 

 consisting of 1 pound of American potash to the 

 gallon of water ; are then placed in the pickling 

 vat, containing weak solution of sulphuric acid, 

 and then in the washing tank, where they re- 

 main till they are required for zincking. They 

 are then exposed to the electric current as cath- 

 odes suspended on compound copper and steel 

 suspension bars. The zinc applied by the cold 

 process is almost pure, and is found to withstand 

 the sulphate copper test better than zinc applied 

 by the hot process. 



A process has been devised for electroplating 

 the entire hulls of ocean vessels with a continu- 

 ous film of copper one twentieth of an inch thick. 

 The electroplating is effected by means of a num- 

 ber of box baths, constructed to conform closely 

 to the curvature of the ship's bottom, so that the 

 film may be applied while the vessel is afloat. A 

 solution of cyanide of potassium is placed in the 

 baths, and after the sides of the ship have been 

 scraped and cleaned the box baths are fixed to 

 the vessel's side and firmly braced there. When 

 the solution has been used for a few hours it is 

 carefully drawn off, and a strong solution of 

 copper then replaces it. 



In previous experiments on corrosion, Thomas 

 Andrews found that steels corrode more than 

 wrought iron when exposed singly and sepa- 

 rately, without galvanic action other than local, 

 to the action of sea water for long periods. 

 The advantage is about 25 per cent, in favor of 

 the iron. In his more recent experiments the 

 author has found that the galvanic action be- 

 tween wrought iron and steel induces a largely 

 increased total corrosion of the several metals. 

 When different parts of metallic structures are 





