M. W. Nelligan, of South Boston, writes:

"I have rather a peculiar question and come to you for advice. One of my customers is a baker and in his oven he has used a water-back such as is used in set ranges, and it lasted two years, then he put in another of the same make which lasted two weeks and burst in the same place that the first one did. I advised him to put in a brass coil, but he said it would work all right as far as heating water was concerned, but it would make a great deal of noise within the boiler, placed in the position it is.

"He says if the boiler was'placed so as it would be all above the water back it would work all right. Now. I would like to know why it would not work, all right in either position. He has had trouble with a coil before, and that is the reason he will not put one in now until I convince him that it will work The boiler that is in is very near the ceiling."

[Our correspondent has made on his letter a rough sketch of the water-back that broke, which is V-shaped and apparently of cast iron. Another sketch shows the position of the boiler, which is about as usual, the top of the water-back being about level with the top of the lower third of the boiler and distant from it about 5 feet.

If the baker has already had trouble from a coil, it is not wise to advise him to use one again, since a coil may cause noise where a cast water-back would not.

If the oven is hot enough to make steam, the resistance of a coil to the flow of the water may detain it in the coil long enough to permit steam to form and by its sudden condensation to cause the shocks due to "water hammer" in the pipe. The steam when it is formed will momentarily force the water from the coil and the colder water as it enters again will condense the steam and make a noise. The same thing may occur in a water-back, but not to as great an extent, other things being the same. The burning of the water-back would seem to indicate that something of this kind had occurred in this case.

Put in a water-back and enlarge the connections throughout their entire length, and the trouble is likely to cease, as the resistance to the flow of the water will be lessened so that it will get through the water-back before it can be converted into steam.

We have so far assumed that the water-back of which you speak is of cast iron, of the usual pattern. If, however, your "water-back" is simply a coil of iron pipe it would not improve matters to make it of brass unless you enlarge the diameter of the pipe and connections.]