One of the peculiar things about this engine is the failure to realize anywhere near boiler pressure, noticeable in every case that has come under my notice.  The considerable lead gives it for an instant, but it soon falls away, indicating the steam chest pressure only by a peak at the junction of the admission and steam lines.  This is probably due to the fact that the cut off valve commences closing the steam passage so soon after steam is admitted, and in this particular does not satisfy the requirements of a perfect valve.  There is this about the engine, that above all others of this type there has come under my notice fewer engines of this type with a maladjustment of valves from tampering by incompetent engineers.

* * * * *

FIRING POINTS OF VARIOUS EXPLOSIVES.

An apparatus, devised by Horsley, was used, which consisted of an iron stand with a ring support holding a hemispherical iron vessel, in which paraffin or tin was put.  Above this was another movable support, from which a thermometer was suspended and so adjusted that its bulb was immersed in molten material in the iron vessel.  A thin copper cartridge case, 5/8 in. in diameter and 1-5/16 in. long, was suspended over the bath by means of a triangle, so that the end of the case was 1 in. below the surface of the liquid.  On beginning the experiment the material in the bath was heated to just above the melting point, the thermometer was inserted in it, and a minute quantity of the explosive was placed in the bottom of the cartridge case.  The temperature marked by the thermometer was noted as the initial temperature, the cartridge case containing the explosive was inserted in the bath, and the temperature quickly raised until the explosive flashed off or exploded, when the temperature marked by the thermometer was again noted as the firing point.  The tables given show the results of about six experiments with each explosive.  The initial temperatures range from 65 deg. to 280 deg.  C. in some cases, but as the firing points remained fairly constant, only the extremes of the latter are quoted in the following table: 

--------------------------------+----------------------

-
Description of Explosive.    |  Firing Point in  deg.  C.
--------------------------------+-----------------------
Compressed military gun-cotton. |      186 — 201
Air-dried military gun-cotton.  |      179 — 186
"        "         "        |      186 — 189
"        "         "        |      137 — 139
"        "         "        |      154 — 161
Gun-cotton dried at 65 deg.  C.      |      136 — 141
Air-dried collodion gun-cotton. |      186 — 191
"        "         "        |      197 — 199
"        "         "        |      193 — 195
Air-dried gun-cotton.           |      192 — 197
"          "                |      194 — 199
Hydro-nitrocellulose.           |      201 — 213
Nitroglycerin.                  |      203 — 205