Scientific American Supplement, No. 787, January 31, 1891 | Page 8

the main valve. In our perfect valve, as we outlined it, the valve does not move after the port is closed. The exhausting functions of the valve are very good, giving a quick opening and a full opening, because this opening occurs when the eccentric is moving its fastest. The engine also possesses a distinct advantage in having remarkably small clearance spaces. The length of the steam passage is very small in comparison with any form of engine, and having but two ports instead of four, as in the Corliss and four valve type.
In these there must be included in the clearance, that to the exhaust port as well as the steam port, adding a considerable amount where the piston comes close to the head. As the engines leave the maker's hand the engines are provided with a considerable amount of lap to give plenty of compression, but are, of course, capable of having more added to increase compression, or some planed off to decrease it.
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.
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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° to 280° 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 ° 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° 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 Kieselghur dynamite. No. 1. | 197 - 200 Explosive gelatin. | 203 - 209 Explosive gelatin, camphorated. | 174 - 182 Mercury fulminate. | 175 - 181 Gunpowder. | 278 - 287 Hill's picric powder. | 273 - 283 " " " | 273 - 290 Forcite, No. 1. | 184 - 200 Atlas powder, 75 per cent. | 175 - 185 Emmensite, No. 1. | 167 - 184 Emmensite, No. 2. | 165 - 177 Emmensite, No. 5. | 205 - 217 --------------------------------+----------------------- _--C.E. Munroe, J. Amer. Chem. Soc._
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STATION FOR TESTING AGRICULTURAL MACHINES.
The minister of agriculture has recently established a special laboratory for testing agricultural materiel. This establishment, which is as yet but little known, is destined to render the greatest services to manufacturers and cultivators.
In fact, agriculture now has recourse to physics and mechanics as well as to chemistry. Now, although there were agricultural laboratories whose mission it was to fix the choice of the cultivator upon such or such a seed or fertilizer, there was no official establishment