MECHANICS AND USEFUL ARTS. 45 



one-tenth of an inch, and for every yard of pressure increase or deduct 

 one-hundredth of an inch. 



In calculating the strength of columns great care is necessary. The 

 safe plan is to find the diameter of a solid column necessary to bear the 

 compression, and then distribute the same area of metal in tube form as 

 a hollow column. ... A solid column 10 feet long, and having 

 an area of 10 square inches (good metal), will bear 10 tons pressure. 

 This rule can be conveniently carried out, and it is safe and practical. 



EXPERIMENTS WITH WIRE ROPE. 



Some experiments, important to all persons engaged in the manu- 

 facture of wire ropes, or who may be accustomed to use them, have 

 just been made by Mr. J. Daglish, who has communicated the results to 

 the North of England Institute of Mining Engineers. The conclusions 

 arrived at were, that half the strength of the rope was lost by heating 

 the wire ; that the ordinary joint is much weaker than any other 

 portion of the rope; that if a flat rope was well spliced it was not 

 weakened thereby, but if the workmanship was bad, it lost from 

 twenty-five to thirty-three per cent, of its strength. In either event, a 

 round wire rope spliced became thirteen per cent, weaker than before. 

 Round steel-wire rope will bear more than double the weight required 

 to break iron-wire rope of similar diameter. 



PROTECTION OF IRON AND STEEL. 



Professor Vogel recommends, for the protection of iron and steel 

 tools against rust, a solution of white wax in benzine. Moderately 

 heated benzine dissolves half its weight of wax ; and if this solution 

 be carefully applied to the tool with a brush, the evaporation leaves 

 a very adhesive and permanent coating of wax, which will preserve 

 the metal even from the action of acid vapors. Dingier 's Polytech- 

 nisches Blatt. 



AMERICAN ZINC. 



At Bethlehem, Pa., about thirty tons of metallic zinc are now pro- 

 duced weekly from the ore yielded by the mines of the Lehigh Zinc 

 Co., and when the furnaces are all in operation the production will 

 be increased to two thousand tons per annum. All the articles re- 

 quired in the manufacture of the zinc are made upon the premises, 

 as retorts, muifels, fire-bricks, etc., of ingredients brought from the 

 surrounding country, no foreign material being used. This zinc is 

 claimed to be equal to the best distilled zinc sold by manufacturing 

 chemists. 



Heretofore, we think, metallic zinc has not been produced in quan- 

 tity in the United States. 



SHEET ZINC FOR ROOFING. 



A report of a committee appointed by the Central Society of 

 Architects, in Paris, recommends " that zinc, which was at first 

 rejected, but is now so generally used, should be applied with great 



