Polytechnic Association Proceedings. 609 



and thus becoming the oxy-chloride of copper (cwpamadat), the 

 latter heated to a temperature of 400^ C, i. e. 75 2** R, parts with 

 its oxygen, and returns to the state of proto-chloride, when it is 

 again exposed to air, and becomes oxy-chloride. The advan- 

 tage this process, for obtaining oxygen, has over Mothay's is, that 

 it is not necessary to use steam. A kilogram of the oxy-chloride 

 exposed to a current of hot air, will yield from twenty-eight to 

 thirty litres of oxygen, while a kilogram of the manganate exposed 

 to steam will yield about forty-six litres of gas. The oxy-chloride 

 does not give out oxygen faster than it is obtained by decomposing 

 chlorate of potash; the operation can therefore be carried on in 

 glass vessels and on a small scale. 



STEEL WIRE- 



The use of steel wire has been greatly extended since it became 

 known that a wire could be produced which combined the advan- 

 tages of lightness, with hardness and extreme tenacity. It is now 

 employed not only in the manufacture of needles, fish-hooks, springs, 

 music strings, small tools, umbrella frames, and crinolines, but also 

 for ropes and cables. Steele wire rope is now used in many of the 

 deep pits of the collieries of Great Brittan, where the lightweight 

 of the rope is of such importance both in respect to safety and 

 economy; also on railway engines, and for drawing plows where 

 stationary steam-power is used for preparing the soil. Large, 

 quantities have been required during the last five years for sub- 

 marine telegraphic cables. For many years steel wire ropes hav<» 

 been used on the Morris canal, in New Jersey, for the purpose of 

 drawiug boats up its numerous incline planes. Some idea of tho 

 quantity of steel wire used, may be formed from the fact that 

 one ^tablishment in Great Britain has made, during the last year, 

 more than 30,000 miles of one size, No. 13, equal in diameter to 

 .095 of an inch. 



AEROSCOPE. 



A very sensitive barometer, invented by Mr. A. H. Clum, of this 

 countr}^ was lately exhibited at a conversazione at the residence of 

 Gen. Sabin, President of the Royal Society, London. It consists 

 of a cistern containing seventy pounds of mercuiy, and a cen- 

 tral column, two and a half inches in diameter, in which rests a float 

 or buoy, supporting large cylinders or air chambers, made of Ger- 

 man silver; these, owing to their large displacement of air, are so 

 sensitive of atmospheric changes that exceedingly slight fluctuations 



[LvsT.] 39 



