392 



THE. liNUiA RUBBER WORLD 



September 



1906. 



high tension will be made with combined insulations of 

 varying capacities, rather llian with a homogeneous insula- 

 tion of any insulating material now in use. 



Cables are, roughly, of two classes : those whose insulat- 

 ing material is not injured by submersion in reasonably 

 clean water, and a second class which will not withstand 

 such test. For cables of the first class the metallic sheath is 

 primarily for the purpose of lessening the rate of deteriora- 

 tion, and secondarily to protect against mechanical injury 

 during installation. The sheath on these cables should be 

 comparatively thin and be proportioned tt) the weight of the 

 cable. The second class of insulation will only be service- 

 able so long as the sheath is intact, and therefore the metal 

 should be heavier and show less variation as to its thickness 

 with the weight of the cable. The writer does not mean to 

 be understood as endorsing the s])ecifications which call for 

 V inch lead on No. 6 wires, but rather the suggestion of a 

 minimum thickness of ^-'o inch on paper and jute insulated 

 cables, increasing gradually in proportion to weight and 

 diameter to saj' ,"., inch on the largest cables (2 j inch) now 

 in common commercial use. 



Mr. Clark hopes to see actively taken up the stanilardi/.a- 

 tiiin of some of the principal dimensions of underground 

 cables. In conclusion, he commends the following specifica- 

 tions, as better than any other he has seen : 

 Specikic.-vtions 30 Per Cent. Rubbkr Insulating Compound, 

 rubbur-coverkd wrre engineers' association. 

 The compound sliall contain not less than 30 per cent, by 

 weight of fine dry I'ard rubber which has not previously been used 

 ill rubber compounds. Tlie composition of the remaining 70 per 

 cent, shall tie left to the discretion of the inaiuifacturer. 



Cheinical. — The vulcanized rubber compound shall contain not 

 more than 6 per cent, by weight of acetone extract. For this de- 

 terniinatioii the acetone extraction shall be carried on for 5 hours 

 in a Soxhlel extractor, as improved by Dr. C. O. Weber. 



Mfihaiiical. — The rubber insulation shall be homogeneous in 

 character, shall be placed concentrically about the conductor, and 

 shall have a tensile strength of not less than Soo pounds per 

 S(iuare inch. .\ sample of vulcani7.e<l ruljber compound, not less 

 than 4 inches in length shall be out from the wire with a sharp 

 knife held tangent to the copper. Marks shall be placed on the 

 sample 2 inches apart The sample shall be stretched until the 

 marks are 6 inches apart and then immediately released ; one 

 minute after such release the marks shall not be over 2J^ inches 

 apart. The sample shall then be stretcheil until the marks are 9 

 inches apart before breaking. For the purpose of these tests, care 

 must be used in cutting to obtain a proper sample, and the nianu- 

 faclurer shall not be responsible for results obtained from samples 

 imperfectly cut. 



Eleclr'ual. — Each and every length of conductor sliall coiuplj- 

 with the requirements given in lh« following table. [The table is 

 too extensive to be embraced here. It shows the results required 

 in the case ot rubber insulation of various thicknesses, from ,,■', to 

 \% inch.] The tests shall be made at the works of the nianufac- 

 tuier when the conductor is covered with vulcanized rubber, and 

 before the application of other coverings than tape or braid. 

 Tests shall be made after at least 12 hours' submersion in water 

 and while still immersed. The voltage s])ecifie(l shall be applied 

 for 5 minutes. The insulation test shall follow the voltage test, 

 shall be made with a battery of not less than 100 nor more than 

 500 volts, and the reading shall be taken after one minute's elec- 

 trification. Where te.sts for acceptance are made by the purchaser 

 on his own premises, such tests shall be made within to days on 

 receipt of wire or cable by purchaser. 



Inspection. — The purchaser may send to the works of the manu- 



facturer, a representative who shall beallorded all necessary facili- 

 ties to make the above specified electrical and michaiiical tests, 

 and also to assure himself that the 30 per cent, of rubber above 

 specified is actually put into the coiii]iound ; but he shall not be 

 privileged to inquire what ingredients are used Lo make up the re- 

 maining 70 per cent, of the coniiiouud. 



THE HIGHEST TENSION CABLES. 



' I ^ 1 1 1 V notable rubber manufacturing firm of I'irelli & Co., 

 -*- at Milan, Italy, as was to be expected, figure to an im- 

 portant extent in the Milan exhibition, and particularlj- in 

 their display of high tension cables. At the St. Louis ex- 

 hibition, in 1904, the firm showed a cable designed for a 

 normal working voltage of 50,000, while now at Milan they 

 exhibit a cable designed for 100,000 volts, normal working 

 pressure, which is expected to stand with ease 200,000 volts, 

 and which will be tested with a special 300,000 volt trans- 

 former .It the time of the Milan electrical congress, in 

 Sejjteiuber. 



Ill this cable, sa\s the I'.lcctiical World advant;ige is taken 

 of all theoretic. illy imiiortant points, the stranded conductor 

 being covered with a lead sheath, thus jnoducing a snitoth 

 surface of much greater radius, and by this simple device 

 alone the static strain is considered to be reduced more than 

 10 per cent. The insulation is then wrapped in layeis dis- 

 posed in the order of decreased specific inductive capacity 

 from the center of the cable to the circumference, and by 

 careful choice of the materials an extremely uniform peittn- 

 tial gradient to alternating current is presented. 



An important tlieorj' of the grading of cables for capacity 

 has been developed by the chief engineer of the Pirelli firm, 

 Mr. Kmmanuel Jona. now also president of the Italian Insti- 

 tute of Electrical ICngineers. He was the author of an im- 

 portant paper read at St. Louis, in 1904, and wlsicli was 

 abstracted shortly after in The India Rubber Would. 



Tlie Pirelli firm are reported to be doing an important ex- 

 port trade. A recent purchase of their high tension cables 

 by the Ontario Power Development Co., at Niagara Falls, 

 has created much comment. 



RUBBER IN hlSH BAITS. 



IT is safe to say that there is no article of the s])ortsman's 

 equipment that has been derived from materials of 

 greater variety' and diversity than the fish lures which we 

 designate by the general name of artificial baits, says 1 he 

 Sporting Goods Gazette. After discussing the artificial fly, 

 the writer says : Rubber both soft and vulcanized is largely 

 used and the former is also used in the making of artificial 

 w-ornis for bass and trout, the rubber cord being coated with 

 what is known as ox-blood hued Japalac, a red enamel 

 which is very durable and dries easily in the sun and air. 

 The vulcanized rubber is most useful because it takes the 

 color necessary to imitate the minnow, and if it be well var- 

 nished and dried hard, the hard rubber bait is one of the 

 most durable and is the best material ever used for that pur- 

 pose. Wood is used also and the hardest wood is the ash. 

 It takes the color well and is easily formed to the right 

 shape. Metal, especially nickel, is the material of some of 

 the best of these baits, and the Devon minnow wliich is so 

 much used for trout in Devonshire, England, and in New 

 England is silver-plated and very brilliant and strong. 



