After the third round the joint between the D. and D. rings opened slightly on the top, and measured after the 13th round showed that the opening was about 0.004 in. wide.  It cannot at present be stated whether or not this opening increased during firing, but the defect has been noted and will be carefully observed.  Enough cocoa powder remains to allow a comparison to be made with such brown prismatic powder as may be adopted finally.  No firing has been done as yet to test the best position for the bands, but it will take place as soon as enough of some standard powder is obtained to fire ten consecutive rounds.—­Army and Navy Journal.

* * * * *

COMBUSTION, FIRE-BOXES, AND STEAM BOILERS.[1]

  [Footnote 1:  Address before the June Convention of the Master
  Mechanics’ Association.]

By John A. Coleman.

Mr. Chairman and gentlemen:  I was rash enough some time ago to promise to prepare a paper for this occasion, the fulfillment of which prior engagements have absolutely prevented.

I would greatly prefer to be let off altogether, but I do not like to break down when expected to do anything; and if you have the patience to listen for a few minutes to the reflections of an “outsider,” I will endeavor to put what I have to say in as concise form as I can, in such manner as will do no harm, even if it does no good.

For many years I was connected with steam engineering.  I was once with the Corliss Steam Engine Company, and afterward was the agent of Mr. Joseph Harrison, of Russian fame, for the introduction of his safety boilers.

That brought me into contact with the heavy manufacturers throughout the Eastern States, and during that long experience I was particularly impressed with a peculiarity common to the mill owners, which, I believe it may be said with truth, is equally common to those interested in locomotive engineering, namely, how much we overlook common, every-day facts.  For instance, we burn coal; that is, we think we do, and boilers are put into mills and upon railroads, and we suppose we are burning coal under them, when in reality we are only partially doing so.  We think that because coal is consumed it necessarily is burned, but such is frequently very far from the fact.

I wish upon the present occasion to make merely a sort of general statement of what I conceive to be combustion, and what I conceive to be a boiler, and then to try to make a useful application of these ideas to the locomotive.

Treating first the subject of combustion, let us take the top of the grate-bars as our starting point.  When we shovel coal upon the grate bars and ignite it, what happens first?  We separate the two constituents of coal, the carbon from the hydrogen.  We make a gas works.  Carbon by itself will burn no more than a stone; neither will hydrogen.  It requires a given number of equivalents of oxygen to mix with so many equivalents of carbon, and a given number of equivalents of oxygen to mix with so many of hydrogen to form that union which is necessary to produce heat.  This requires time, space, and air, and one thing more, viz., heat.