In fig. 72 an illustration is given showing the internal surfaces drawn to scale of a closet D-trap, omitting the soldered angle, but showing where the surfaces would become coated over with filth. There are the inner sides of the two cheeks, A and b, the inner side of the band, c, the under side of the top, d, the outer side of the dip-pipe, e - which stands inside the trap - and its inner side, f. All these surfaces, A, b, c, d, e, are exposed to any matter sent into the trap from the water-closet upon it.

The misfortune is that when the large exposed surface became coated over with faecal matter, from splashings and accumulations, it could not be thoroughly cleansed again, even by several flushes of water; for no scouring flush could be sent round upon the exterior of the dip-pipe, nor upon the upper part of the cheeks and the band at the back of the dip-pipe, nor over the under side of the top.

SCALE-7/8 = |FT.

Fig. 72. - Showing Inner Surfaces of a 9 in. D-Trap.

The matter sent into the trap may have come from a patient suffering from a most infectious disease; and, instead of trying to wash it out of the trap by several pulls of the closet-handle, only one flush of water may be given, and the larger portion of the infectious discharge be left in the trap to generate noxious gases to be sent up through the closet into the house by the next usage of the apparatus, to be added to by further secretions. The gases generated, as well as the stench given forth from such a storage of filth, would not only find their way out at the ventilating-pipe of the soil-pipe, to pollute the atmosphere surrounding the house, but often at a more serious place still, viz., at the disconnection at the foot of the soil-pipe. With an unventi-lated valve-box, and with the closet at rest, gases would also collect in the dip-pipe, as in an inverted jar, to be displaced by the next discharge of the closet, and sent up into the face of the person pulling the closet-handle.

11. Apart from the evil of fixing a trap which can never be properly cleansed, as the D-trap, there is great risk in fixing a trap with its dip-pipe, or part of its dip-pipe, standing inside the trap. There is always a danger of the dip-pipe, or that part of it which partitions off the air in the soil-pipe from the house side of the water-seal of the trap, becoming defective, and that, too, in a part where a defect would never be disclosed, except to the olfactory nerves; for no matter how large such a defect might be, there would be no leakage of water from it to indicate any defect, as would at once be the case with a defect in the dip of a round-pipe trap, as fig. 83, or in the "Anti-D," fig. 81.

Fig. 73.- Internal View of anold D-Trap, showing the evil of a Dip-Pipe being inside a Trap.

Although no water-leakage would be indicated by any number of defects in that part of a dip-pipe which stands within a trap, the bad air in the soil-pipe would find an easy passage to the house side of the water-seal of the trap through only a small defect, as shown by the arrows in fig. 73.

12. At the discussion which followed my lectures ten years ago, an "improved" D-trap was talked about, a trap which had no existence prior to my criticism of the D-trap in general use. But, as I have explained elsewhere, this trap possesses all the great evils of the old trap. The improvement consists in bringing the two cheeks (the sides) of the trap closer together, so as to leave as little space as possible between the dip-pipe and the inner sides of the cheeks, as shown on plan, fig. 74, i.e., in the full-sized D-trap, the band, c, fig. 72, is 6 in. wide, but in this trap, figs. 74 and 75, it is only 4 1/4 in. wide, so that the cheeks of the trap stand closer together by 1 3/4 in., making the trap more compact, and less difficult to flush out. But to call this trap self-cleansing would be misleading, for the inner surfaces of the trap are just the same as in the full-sized D-trap, minus about 5 in. sup., for the narrower band and narrower top, i.e., the internal surface of this " narrowband" D-trap would be equal to about 3 ft. sup. No scouring flush could be sent up the two vertical angles, a and B, fig. 74, nor at d and c, so that these parts would become lodgments for filth; and the dip-pipe, though it would often get splashed over with excremental matter, would rarely, if ever, get thoroughly cleansed, for no frictional force could be brought to bear upon it, from F G H, and upwards. Then there is the evil of the clip-pipe being inside the walls of the trap (Art. 11).

Fig. 74. - Plan of Trap, Fig. 75.

Fig. 75. - View of the "Narrow-Band " D-Trap, with Square Pipe Outlet (j).

13. The criticisms on the usual form of D-trap brought the " Helmet" D-trap into notice, but a moment's examination of the trap, illustrated in fig. 76, will suffice to show, that whilst the lower part of the trap is improved, all the bad principles of its elder brother are retained. As a matter of fact, nearly a quarter of a century ago I had our D-traps made up in a similar fashion, except that instead of burning the edges of the lead together, they were soldered. The lower part of the trap, the body, was bossed up on a hardwood block, in shape as shown in fig. 76.

14. In Table No. 1, in the following chapter, the results of several tests made with both " non-cleansing' and self-cleansing closet-traps are given, to show at a glance the difference in the number of clean-water flushes required to rid the various traps of certain matters put into them. And as a practical proof was given to the audience, in one of my lectures in the rooms of the Society of Arts, of the difficulty of freeing even a small-size D-trap from filth, when once it had become fouled, an illustration of the trap used is given on the next page; and an extract from the " Lectures " is also made, as the result of the experiments may not be without interest to the student plumber.

Fig. 76. - View of the "Helmet" Trap.

"I will not say any more on the D-trap for water-closets; and instead of occupying your time with a lengthy criticism on the smaller sizes for trapping off what are called ' dirty water' wastes (to distinguish them from sewage wastes, soil-pipes, drains, etc.), we will give a few practical experiments to show their unfitness for such purposes. In doing this, we will not aggravate the case by using the trap unfairly, for instead of using such adhesive matter as greasy water from saucepans, etc., we will use a little soapy water, and after that some plain water with a little stone-blue put into it to colour it.

"I have had a small-size D-trap made with glass cheeks to it, for you to see the working inside, and this trap is connected to a small wash-hand-basin with 1 in. brass plug-and-washer, the usual size being only 3/4 in. This trap is made much smaller than the usual' small-size' handmade D-trap, or than the small-size cast-lead D-trap, so that any experiment made upon it will be more favourable for cleansing it than would be the case with the D-traps as generally used in practice." Fig. 77 illustrates this trap, b, with a small wash-hand-basin, A, fixed upon it. The depth from the top to the band is 4 in., the width of the band, between the cheeks, 3 in., and the length along the top 6 in. The dip-pipe first used was 1 in., and the distance from the bottom of the basin to the standing water of the trap is 8 in. The short length of waste-pipe, c, consisted of a piece of glass tubing. [In some subsequent experiments the dip-pipe was increased in size to 1 1/2 in., with a similar result, a non-cleansing of the trap.]

Fig. 77. - Small-Size D-Trap, with Glass Cheeks.

"Two or three experiments were then made with this model, to show the non-cleansing nature of D-traps. Some blue water, i.e., water coloured with stone-blue, was put into the trap, and though two or three charges of clean water from the basin were sent into it, the whole of the blue water was not removed. The trap was then charged with soapy water, as in practice when fixed under lavatories would be the case, but though several flushes of clean water from the basin were sent into the trap, every vestige of soapy water was not removed, and with one flush the suds remained strongly in the trap, floating about and around the dip-pipe.

"The experiments showed clearly enough how such traps become cesspools, or filth- collecting boxes. And yet there are thousands of such traps in use in England to-day, under baths, sinks, urinals, safes, lavatories, and water-closets."

15. The bell-trap is only introduced here to show the student plumber how poor a trap sufficed to satisfy the ideas of plumbers of a past generation; for to-day no plumber with any sanitary notions would venture to palm off so inadequate an appliance for preventing the passage of bad air into a house.

Its depth of water-seal is so small that the banging to of the door of the room where it is fixed, with the windows shut, would almost suffice to break the seal; but apart from the effect of any concussion of air upon the seal, it would soon be diminished by evaporation, or by capillary attraction from a piece of rag, hair, cotton, or worsted hanging over the weir of the trap, at c. Nor is its aptitilde to lose its water-seal the only grievance caused by it; for to the cook, housemaid, and scullery-maid the great grievance is that they have to waste so much time in getting their slops through it.

Fig. 78. - Section of a Bell-Trap.

16. As all mechanical appliances get out of order sooner or later, and as traps with mechanical seals, or check valves, have such devices fixed inside them where they cannot be seen, it is better not to trust to them, but to fix traps which have no parts or appliances to get out of order - traps which, with an anti-syphoning pipe, may be trusted to last as long as the fixture under which they are fixed, so that the failure first of that part which is visible shall lead to an examination of that part which, in the case of certain fixtures, is always out of sight. I have treated this subject more fully in "Dulce Domum."