Gas Light and Coke Company should be adopted. This consists in having a rudely made trough formed by two wooden battens 2 or 3 inches wide and inch thick nailed together, which is laid beneath and almost touches the service, when it is filled with hot pitch or a mixture of tar and sand which entirely covers the pipe, so that it is thoroughly embedded in the substance employed. By these means the service is rendered practically everlasting at a very trifling cost.

The holes in the mains for services ought always to be drilled, and never cut with a gouge, as when drilled they are tapped with greater facility, while the operation is effected more readily and with less loss of gas than when the gouge is employed; further, there is not the after escape of gas which occurs with an imperfectly formed hole in the main.

A main of 2 inches diameter should never be tapped for a larger pipe than half-inch, otherwise it will be most materially weakened and will probably break with the slightest settlement or jar. For the same reason a 3-inch main may be tapped for a 1-inch pipe, but not larger; and in the event of the services being required of greater dimensions this can be effected by means of diminishing sockets, for a slight reduction in the diameter of the pipe for a very short distance will not impede the flow of gas through a service.

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All service pipes should have a fall to the main if possible, but if this is not practicable, they should then fall in the reverse direction, what is known as a 'bottle syphon" (fig. No. 30 on the Plate), being fixed at the lowest point for the reception of the condensed products. Bottle syphons are made of all sizes to contain from one to three quarts, and attached to each is the suction pipe for withdrawing the liquid. With every precaution, however, service pipes sometimes get choked either with water,

naphthalene, or rust, when it is necessary to resort to the force-pump in order to clear them.

The service pipes to all public lamps are usually of half-inch pipe unless when of considerable length, when they are laid of three-quarter inch pipe.

"If the distance from the main to the meter does not exceed 30 yards, the following sizes of service pipes will supply the number of lights named.

Wrought-iron
Tube.

1

"1 to 10 lights (consuming say 4 cubic ft. per hour each) inch.

"The above sizes allow for partial contraction of the area of the pipe by corrosion or deposition" (Newbigging).

It will be necessary at this stage to say a few words concerning the formation and deposition of naphthalene. Naphthalene, which is one of the hydrocarbons on which the luminosity of coal-gas depends, although generally present in very small quantity, is sometimes exceedingly troublesome, especially when the gas is saturated with it, as in such a case any lowering of temperature causes it to be deposited in the solid form in the apparatus and mains on the gas-works, and in the mains and services on the district, sometimes choking up the service pipes, and reducing the capacity of the mains.

No question in the whole range of gas manufacture has probably been more debated than the subject of the formation and deposition of naphthalene, or with so little progress towards arriving at a definite conclusion.

Naphthalene is generally considered to be produced by employing high temperatures in the distillation of the coal, and is deposited most freely from gas produced from bituminous coal, some descriptions of coal, such as those

from the South Yorkshire and Durham districts, coals which yield on distillation thick tars and a considerable quantity of water, producing more naphthalene than others.

"By the use of a certain proportion of cannel along with the ordinary common coal, the gas is enabled to retain some or the whole of the naphthalene in suspension within it in the gaseous condition" (Newbigging).

Mr. L. T. Wright's remarks on this subject will be of interest: "It seemed as if water vapour in the retort had some protective action on this hydrocarbon. Any coal could be distilled at such a low temperature that no naphthalene would appear, but when the heat was increased this substance made itself manifest, and after certain temperatures were reached it increased more and more. The question of dealing with gas saturated with naphthalene was sometimes very difficult. If one could always insure that the gas should be made and treated in the works at a lower temperature than it would ever be subjected to in its after history, there would be no trouble, but it would often happen that gas was made during the hottest part of the day, and purified and dealt with at temperatures much higher than it was submitted to in the mains and services during the night. As a rule, naphthalene only showed itself in mains and services laid within a foot of the surface of the ground, those buried deeper than this undergoing no appreciable variation in temperature. The cure for this evil would consist in some method of artificially cooling the gas before it left the works."

M. Brèmond, who made some valuable researches on the question of the formation of naphthalene, published his results in the year 1877, and then stated that “ Naphthalene is produced wherever there is condensation of the aqueous vapours contained in the gas; that its deposition is preceded by the phenomenon of the condensation of the