Insulators exhibited at the 1862 International Exhibition

THE INTERNATIONAL EXHIBITION, 1862.

(Continued from page 78.)

6. Insulators for Land and Aerial Lines.

No change of importance has occurred in the construction of land lines since 1851. Iron wire of about No. 8, B.W.G. (1/6 inch diameter) is still generally adopted for the conductor in England; larger gauges, such as No. 4, or even No. 1, are adopted for direct transmission over long circuits). In France, wire of 4 millimetres diameter (=0.16 inch nearly) is used.

Earthenware, stoneware, and glass insulators are now considered inferior to those made of porcelain. Stoneware is generally porous; glass is found to break easily, and to condense surface moisture to a great extent. Porcelain insulators are imported in large numbers from the Continent, and some apparently good specimens are shown by J. B. Cappellemans, Sen. H. M., Brussels (Belgium, 860), and by H. Schomburg, Berlin (Prussia, 2177).

S. W. Silver & Co., M. (United Kingdom, 2960), exhibit insulators made entirely of hardened india-rubber or ebonite, a material which has been used to a considerable extent in coating the iron pins of porcelain and other insulators. From tests made by Messrs. Silver, it would appear that the hygrometric qualities of ebonite are extremely good, and no serious deterioration of the material has been observed during an experience of about two years.

Mr. Meyer (Hamburg, 130) also exhibits good ebonite insulators.

C. F. Varley, M. (United Kingdom, 2981), exhibits insulators intended for use where very good insulation is required, as in lines of 200 miles and upwards. They consist of an upright iron bolt or pin, the head of which is covered with ebonite, or vulcanite, as it is sometimes called, on which rests a porcelain inverted cup. This cup is again covered by a second cup of porcelain, on the top of which the wire to be insulated rests. By this arrangement, one, or even two, of the three insulating covers may be cracked or porous, or otherwise defective, without sensibly injuring the insulation of the line. Mr. Varley's insulators are also made with a special quality of stoneware made by compression from a peculiar clay. This stoneware is at least equal to porcelain.

Mr. Varley showed the Jury a record of experiments in which the deflection indicating a loss during heavy rain from lines insulated in this manner was not more than 5 divisions, when the deflection from a wire of equal length, fixed on similar insulators, without vulcanite on the pins, was 90 divisions, and from a wire supported by single inverts, 370 divisions. During a fog the relative losses were 23, 55, and 405 respectively; these numbers were examples taken at hazard from a great number of experiments.

Mr. Varley considers that the insulation resistence of a line in the worst weather, expressed in Mr. Varley's units, should not fall below the quotient of 40,000 by the length in miles. Mr. Varley's unit is equal to 26.6 of Siemens' units.

The British and Irish Magnetic Telegraph Company, M. (United Kingdom, 2864), exhibit two forms of insulator designed by Sir Charles Bright.

1. A porcelain invert with vertical sides and a small spread of surface, cemented over a straight iron bolt and nut; soft India-rubber is placed round the bolt inside the cement, to prevent the expansion of rust from cracking the porcelain cup. This plan of using india-rubber is said not to be of much use, but the insulator affords good insulation at a low price.

2. A double bell, with a shackle bolt, intended for use where great strain comes on the wire. The double bell is held in a wrought-iron fork, by a bolt passing through the axis of the two bells, and two eyes of the fork. The other end of this fork forma a hinged shackle. The wire is attached between the two bells; it ends at each post, and is connected across to the next section by a short wire outside the insulators. This form is specially suitable to terminal poles and over-house work, where great spans are combined with sharp curves or angles; the hinge of the shackle allows each insulator fork to take the line of the wire attached to it. These insulators are extensively employed for over-house work in London, Dublin, Glasgow, &c.

Siemens, Halske, & Co., M. (United Kingdom, 2959), exhibit two forms of insulator, which they call respectively the strainer and intermediate insulator. They use the strainer to secure the wire at about every 500 yards with six or eight "intermediate insulators," supporting the wire by hooks, in which it can slip when a change of weather expands or contracts the wire.

The strainer is composed of the following parts:—An inverted porcelain cup is firmly cemented in a cast-iron bell, provided with a vertical flange bracket. By means of this flange the insulator is fastened to the post with wood screws. A wrought-iron stalk is cemented inside the porcelain cup; this stalk is enlarged at the end, where two notches or recesses are formed of such shape as to allow the wire to be secured by wedges or cottars. The wire between the notches is bent into a circular loop to allow the wire to be slackened in cold weather, or when repairs require it.

The intermediate insulator is of similar construction, but the stalk ends in a hook, in which the line wire rests free to move to and fro. The cast-iron bell protects the porcelain cup from injury, and also from wet, improving the insulation. These insulators are strong but heavy, and are not so cheap as some of the forms usually adopted. The intermediate insulators are quoted at 1s. 3d. complete, and the straining insulator at 3s. 3d. They are extremely well adapted for use in countries where repairs are difficult, and supervision imperfect, owing to their strength and good fastenings.

Reid Brothers (United Kingdom, 2949) exhibit several insulators. 1. A large glass invert with stout glass stem, used in South America. The glass stem is simply dropped into a hole bored in a wooden cross-bar. 2. A double bell insulator, supported by an iron bracket from beneath, with a vertical iron bolt through the centre of the two bells; the glass or porcelain part of this insulator is similar to that exhibited by the British and Irish Magnetic Company, and already described. It can be removed and replaced without withdrawing any bolts or nails from, the wooden post. 3. A cap insulator used between Birmingham and London. This insulator, made entirely of stoneware, without any iron fastening, is slipped over the top of the post, which it protects against wet. It is a cheap form. 4. An insulator intended for lines to be erected in haste without poles. The upright pin of a common invert is bolted to the butt end of a strong horizontal wrought-iron spike. This spike can be driven into trees, walls, houses, &c., and the insulators fixed with great rapidity. A large number of them have been supplied to the army.

The Danish State Telegraph (Denmark, 123) exhibits some good and strong insulators used in Denmark.

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