Fig. 35. - Branch Joint, too Long and too Heavy.

11. The length (Art. 24) of a joint being determined by the length of the shaving of the pipes to be joined together, there can be no difficulty in determining it exactly; but as the strength of a joint also depends upon the thickness of the solder wiped upon it - directly over the edge of the outer pipe - and this has to be done with metal in a fluid state very quickly, regulated only by the eye and the feeling of the fingers through a cloth, the joint should be made a little heavier than absolutely necessary, so that its weakest part shall be equal to any strain it may have to bear - shall, in fact, be strong and durable.

12. If the joint-maker must economize, must use as little solder as will only just make the joint strong enough for its purpose, he had better save it in the length of a joint rather than in its thickness; for a joint short and thick is stronger than a joint long and thin.

13. The strength of a joint not only depends upon the quantity of solder upon it, but also upon the quality of it; and this may be deteriorated by the method in which the solder is both used and wiped upon the pipes.

14. The solder in the pot may be poor to start with, i.e., it may have an insufficiency of tin in it; and then, in the process of making a joint, it may become poorer, that is, the solder of the joint may have parted with some of its tin. To pour on a lot of solder to get up a sufficient heat to wipe a joint without an iron means, except to adepts, that the solder finally left on the joint will be coarser than the first ladleful taken out of the pot (or, if a large joint, then the first few ladlefuls); as the richer solder of a pot keeps rising to the top.

15. Tin being of much less specific gravity (Chap. III.) than lead, and its melting-point being also much lower, the tin readily rises to the top, where the alloy is always richer than at the bottom (whether the pot stand over a fire or near the joint-maker), except at the moment when it is stirred, and it is of good heat. The slow joint-maker, trying to make his joint without the use of an iron, generally finds that he has no time to stir the solder every time he dips a ladleful from the pot; and so by the time he is ready to wipe his joint he is not only dipping coarser solder from the pot, he is also working with coarse solder upon the joint; for tin and the richer parts of the solder (being more fluidal) have been ever running off and dropping away from the under part of the joint.

16. When a joint wiped without an iron, and wiped with solder which has parted with some of its tin, " sweats," where the water in the pipe oozes through the joint and stands like drops of dew here, there, and everywhere upon the solder, the man who made it, instead of lifting his eyebrows to the ceiling in wonderment, should sink into his boots for his self-assurance in discarding the use of an iron. Even to the eye a joint so wiped looks porous, and with the aid of a microscope the alloy shows most graphically where it has parted with tin, and become cellulose.

17. When a joint is made with the aid of an iron, less solder is taken from the pot to make it than when it is made without an iron. When sufficient solder has been roughly formed upon the joint, the hot iron is rubbed round the edges of the shaved parts of the pipe to insure good tinning, and to make the pipes hot, and the whole of the solder is so heated and wiped by a good joint-maker, that no part is allowed to cool and set in a manner to part with its tin.

18. Solder for making joints and for wiping purposes should only be heated when it is wanted, and it should never be heated to a higher degree of heat than required, i.e., up to the point when a dry piece of wood put into it would smoke; but an observant mate ought to be able to tell at a glance when it is of the right heat, either by holding a ladleful near his face, or by passing the back part of the hand just over it. During the heating it should be frequently stirred with a ladle, as the tin rises to the top. When it is not stirred, and it is allowed to get to a red heat, it volatilizes.

19. To prevent matters accumulating upon any part of the jointings inside pipes, the ends of the inner pipes should always be fixed the way of the current, as shown by the arrow and at A, fig. 36, and especially so in waste-pipes and soil-pipes, whether the joints are made upright or underhand, and also in the case of branch joints.

20. For joints to soil-pipes, waste-pipes, and ventilating-pipes, where they are not made on the bench or the floor of the shop, where they can be well got at and seen, the ends of the pipes should not only be shaved upon the bench, they should also be tinned, to prevent any foreign matter, as lime, mortar, or cement attaching itself to the shaved parts and tarnishing them, when carrying the pipes to their destination.

21. In shaving the ends of pipes, especially soil-pipes, waste-pipes, and ventilating-pipes, and also in shaving lead, or any part of a pipe to be soldered, do not cut the shave-hook down into the lead to weaken it, as all that is required for the solder to readily tin upon it is a clean bright surface. This evil is somewhat exaggerated in the illustration, fig. 37, but it is not an infrequent thing to come across soldered angles, seams, and joints, not only made by students, but also by plumbers, where the shave-hook has removed half the original thickness of the lead or pipe, as shown at c and S.

Fig. 36.

Fig. 37. - Showing where the Shave-Hook has weakened the Joint.

22. When the ends of pipes are shaved in situ, where they cannot be well seen, it is a good plan to pull the point of the shave-hook round the ends, close to the junctions, and form one or two concentric rings upon them, to insure the solder adhering right round the jointing, as it is possible for a very fine line of the soiled surface to escape, not only the edge of the shave-hook, but also the notice of the shaver. Many faulty joints have been found some years after they have been made through such oversight.

23. In fitting and fixing pipes together to be soldered, see that they fit well and tightly together in every part of the jointing, so that there may be no possible place where the solder can run through to the interior of the pipes. And to prevent them shifting in the slightest degree, secure them well together. [In the examinations which have taken place in London in the last few years, more failures to complete a joint could be set down to poor fixing than poor wiping.]

24. In my " Lectures on the Science and Art of Sanitary Plumbing " I gave the following lengths for making upright and underhand joints, viz.: pipes 3 1/2 in. to 6 in., 3 1/2 in.; 1 1/4 in. to 3 1/2 in., 3 in.; and for smaller pipes a shorter length still. Recognizing the fact that, for easier wiping, most plumbers have a preferable length for certain joints, especially when they have to make them underhand, the following table might be treated as a standard length for joints. And the thickness of the solder upon the external edge of the outer pipe should not be less than about 3/16-in.