Test of Insulators

Test of Insulators.

WE are indebted to Mr. DAVID BROOKS for the following tests of insulators, made at his works in Philadelphia during the past five years:

March 1, 1868, there were exposed for galvanometrical measurement ten Prussian insulators of best Berlin standard.

Ten large size Varley's double inverts with ebonite covered supports.

Ten Western Union glass insulators, on brackets painted red.

Ten Brooks insulators for cross-arms, taken from a lot then being made for the Central Pacific Railroad.

During the intervening period of five years to March 1, 1873, there were ninety-three recorded tests in rain of these different insulators, averaging as follows:

For the Prussian, a resistance of twenty-eight and three tenth millions units per insulator.

For Varley's double inverts (English), eight and six tenth millions units per insulator.

For the Western Union, eight and three tenth millions units per insulator.

For the Brooks there have been but eleven rains in which they have fallen below ten thousand millions units per insulator, and the lowest was on January 15, 1873, when they stood at 2,300 millions.

The lowest point to which the Western Union have fallen was, on January 3, 1873, to 2.6 millions.

The lowest point to which the Prussian have fallen was January 17, 1873, to 19 millions.

The lowest point to which the English have fallen was February 16, 1873, to three millions per insulator.

The following results were obtained with some of the later styles of glass insulators:

March 1, 1872, there were exposed --

Ten Boston screw glass, "cutting its own thread."

Ten Chester's Patent, "three pointed contacts."

Ten Western Union new style tie wire, near top of insulator.

There have been twenty-one recorded measures in rain of these three varieties during the past year, the average of which is as follows:

For the Boston, 14.6 millions units per insulator.

For the Western Union, new style, 24 millions units per insulator.

For Chester's Patent, 71 millions units per insulator.

The lowest resistance for the Boston was on January 3d, this year, 6.4 millions units per insulator. For the Western Union new style, same date, 3.5 millions. For Chester's, October 26, 1872, 11 millions.

As compared with Western Union old style, for the first year's exposure, the new style and Boston are both below, but Chester's is above, or something of an improvement.

The new style of Western Union glass has the groove for tie wire placed near the top of the insulator, upon the principle of giving the outside insulating surface greater length. The old style has the tie wire placed about one and a half inches from the bottom of the glass, while the new is three inches above. Five of the new glass were measured in eight rains, with a small copper wire wound round one and a half inches above the bottom, and compared with five with the tie wire properly placed in the groove, to determine the advantage gained by this one and a half additional length of outside surface. The five insulators with the tie wire in the groove gave an average greater resistance, in the proportion of 60 to 59 - not quite 2 per cent.