proceedings of the polytechnic association. 589 



New Zealand Paper. 



Paper is now manufactured in New Zealand from flax grown there — the 

 pliormium tenax, a perennial plant. It is predicted that paper making- will 

 .be the staple trade of the islands, and that soon Australia will be supplied 

 from this source. 



Submarine Cable. 



A submarine cable has just been manufactured at Woolwich for the French 

 Government. It is to connect Carthagena in Spain with Oran in Algeria, 

 a distance of 115 nautical miles. The conducting strand consists of three 

 copper wires, each .038 of an inch in diameter; the weight per nautical 

 mile is seventy-two pounds. Over this are three alternate coatings of 

 Chatterton's compound and gutta-percha, increasing the diameter to 0.26 

 of an inch, and the weight to 144 pounds per nautical mile. The Chatter" 

 ton compound consists of gutta-percha, Stockholm tar and resin, and acts 

 *as a cement. The wire thus insulated is covered with two strata of twist 

 ed hemp strings, dipped in a solution of the sulphate of copper. The hemp 

 coated cable is finally covered by a flexible spiral metallic sheathing of 

 phosphoretted copper; that is the best copper, mixed with l-400th by weight 

 of phosphorus, added while the metal is in fusion. It is said that the addi- 

 tion of phosphorus increases the tensile strength of copper, and retards the 

 action of air and sea-water. The weight of the cable is 1| cwt. per knot. 

 Its breaking weight is 26 cwt. Its diameter is nearly half an inch. Its 

 whole length is 13T knots. 



Plate Engraving. 



An improvement for protecting engraved plates has been introduced in 

 France by M. Chardon, which consists in covering the plate with a very 

 thin layer of iron. The deposit is so fine that the smallest lines in the en 

 graving arc found exactly copied, although it does not penetrate the metal 

 elsewhere to any appreciable extent; it is rendered equal by the galvano- 

 plastic process. This has been called "steeling" the plate, but the term 

 misleads, as it has not been found possible to deposit steel. Impressions 

 can be multiplied indefinitely, because when the iron stratum is found to 

 be worn, the plate is plunged into an acid bath, which removes the iron 

 without affecting the coppei-, and a new layer of iron is applied to it. 



Mr. Gavit stated that the use of a covering on the original plate had not 

 been found profitable. It was tried very thoroughly by The London Ar^ 

 Journal and abandoned. From a steel plate 30,000 impressions can be ta- 

 ken, from a copper plate only 3,000; the very delicate outlines represent- 

 ing, for instance, the sky, could not be preserved long on copper. 



The Chairman inquired whether the copying process by the electrotype 

 was not still practiced by the Coast Survey Department at Washington ? 



Mr. Gavit replied that it was, but in that case correctness was of more 

 importance than economy. The original plate of surveys is never used for 

 printing, and they could always refer to it as correct. 



