Description of the Process of Manufacturing Coal Gas, for the Lighting of Streets Houses, and Public Buildings / With Elevations, Sections, and Plans of the Most Improved Sorts of Apparatus Now Employed at the Gas Works in London and the Principal Provincial Towns of Great Britain; Accompanied With Comparative Estimates, Exhibiting the Most Economical Mode of Procuring This Species of Light

by Friedrich Christian Accum

A degree of action takes place among the ingredients and the iron surfaces to which it is applied, which at last causes the whole to unite into one mass. In fact, after a time, the mixture and the surfaces of the flanches become a species of pyrites (containing a very large proportion of iron) all the parts of which cohere strongly together, and form one mass. It is essential that no larger quantity of the ingredients of the cement should be mixed up with water, than is required for immediate use.

Fig. 15, [plate V.], represents a longitudinal section of a spigot and faucet pipe. These pipes are most commonly used as gas mains. a, is called the spigot, b, the faucet. The cavity between the inside of one, and the outside of the other, is partly filled with rope yarn, or oakum, and a good fitting of the two pipes being thus effected, melted lead is poured into the cavity, which when set, is hammered in by the end of a punch.

The inner parts of the faucet of these pipes ought to be no larger in diameter than just to fit the spigot. This supports the pipe, independently of the interposed lead and rope yarn, and prevents the risk of hurting the joint from any external stress. The inner faucet is commonly made about two and a half inches deep, and has the spigot inserted one and a half inch into it. The practice of some manufacturers is to make the outer faucet, or that which contains the lead six inches deep, for all pipes above six inches in diameter; and to make the faucets of all pipes below six inches, the same depth as the diameter of the pipes. It is usual to make the space for the oakum and lead all round the spigot, from one inch to one and a quarter inch; that width is required, in order that the lead may be firmly driven into the joint. When the space is very narrow, this cannot be done. On the other hand, when too wide, there is a waste of lead, and a risk of injury from the unequal expansion of the two metals.

All gas mains laid in public streets should be placed at least eighteen inches below the surface of the ground, to secure them from being disturbed by carriages, or interfering with the paving of the street; they should be placed perfectly firm, so that they may not easily give way.

The course of all gas mains should be rectilinear, with a dip of about one inch, in every ten feet distance.

In all wide streets, where the number of houses on both sides of the streets, to be supplied with gas, is numerous, it is more economical to employ a separate gas main for each side of the street, than to make use of one larger main for both sides; because smaller mains may then be employed, and the collateral branch pipes leading into the houses are shorter; these circumstances amply compensate for the additional main. All branch pipes proceeding from a main, should have a dip of about one inch in ten feet, towards the main from which they proceed, so that any fluid that may happen to collect in these pipes must run into the mains.

All small wrought iron branch pipes proceeding from the mains into the houses or places to be lighted with gas, should be covered with a thick coat of coal tar, before they are laid down into the ground; this may easily be done by heating the pipe, and laying on the boiled tar with a brush.

Every separate length of branch pipe should be tried by condensing the pipe under water, in order to be certain that the pipe is sound. The junctures of these pipes should be made by dipping the male screw of the pipe into a mixture of white lead and linseed oil, before they are screwed together.

Notwithstanding the usual care which can be taken in proving pipes, before the gas is admitted into them, a slight leakage may be sometimes subsequently detected.

Therefore, before the gas is suffered to enter the mains, they should be again proved, in order to be certain that all the junctures are air tight. The most convenient manner of proving the mains when laid, is by means of a small portable gas holder filled with common air, and connected by means of a small pipe, with the system of the mains to be tried. This gas holder should be made to act with a pressure at least four times greater than the pressure which the pipes will have to sustain by the gas they are to convey. If the mains are air tight, the gas holder will remain stationary, but if they are not sound, the gas holder will descend, in proportion to the leak of the mains, the quantity of gas lost may be thus ascertained.