216 REPORT— 1873. 



If we apply the sand-blast to a cake of resin on which a picture has been pro- 

 duced by photography in gelatin, or drawn by hand in oil or gum, the bare parts 

 of the surface may be cut away to any desired depth. The lines left in relief will 

 be well supported, their base being broader than their top, there being no under 

 cutting, as is apt to occur in etching on metal with acid. 



An electrotype from this matrix can be printed from in an ordinary press as from 

 a stereotype plate. 



The sand-blast has been applied to cutting ornaments in wood, cleaning metals 

 from sand, scale, &c., cleaning the fronts of buildings, graining or frosting metals, 

 cutting and dressing mill-stones, and a variety of other purposes. 



On the Burleigh Roclc-dnU. By John Pl^vnt, F.G.S. 



On the Resistance of the Screw Propeller as affected by Immersion*. 

 By Prof. Osborne IIeynolds, M.A. 



On the Friction of S7iot as affected by different hinds of Bijiing. 

 By Prof. Osborne Reynolds, M.A. 



On the Economical Generation of Steam, By Robert Sutcltffe. 



The steam-boiler as at present constructed seems to be only partially adapted 

 for the economical generation of steam, and this because it is expected to fulfil 

 somewhat dissimilar conditions. It is required as a generator, as a reservoir, and 

 receptacle, and it must resist a pressure always in excess of that which it is intended 

 to put upon the steam-engine. As a reservoir for steam it must have cubic capacity, 

 which of itself diminishes its power of resisting pressure ; and to enable it to resist 

 pressure the plates must be made stronger, and the additional thickness of metal 

 which is thus interposed between the fire and the water diminishes the efficiency 

 of the boiler as a generator of steam. 



As the pressure is increased, the cubic capacity of the boiler must be reduced, 

 thus restricting the reservoir room ; whilst if the reservoir space be enlai-ged, its 

 capability of resisting pressure is diminished ; it is thus found that incompatibilities 

 are involved, and that in trying to accomplish one object, another of primary im- 

 portance must be sacrificed. 



It would therefore seem that the boiler ought to be treated as a compound 

 machine, and be constructed with adjuncts, so that each part may perform its appro- 

 priate functions, and separately contribute to the efficiency of the boiler in its three- 

 fold capacity as a generator, as a reservoii-, and as a vessel capable of containing 

 steam at a great pressure. 



Where intermittent and irregular motion only is required, large steam spaces 

 may not be of much importance ; but in spinning-mills, where extreme and unin- 

 termitting steadiness of motion is required, considerable steam space is indis- 

 pensable, for the reason that a reservoir of force is as necessary in the boiler as a 

 reservoir of motion is necessary in the fly-wheel of the steam-engine. 



The boiler which combines the maximum of advantages with the minimum of 

 drawbacks for mill purposes seems to be the ordinary double-flued Lancashire 

 boiler, strongly made and double-riveted and about seven feet in diameter, and 

 vyith the flues well filled with Galloway tubes, upon which the heat impinges at 

 right angles, and being intercepted is at once communicated to the water inside 

 the boiler. 



This boiler is in itself a good generator ; it aff"ords the requisite reservoir room for 

 steam, and can be made to stand a considerable pressure. It is simple in construc- 

 tion, and acce,ssible in all its parts for cleaning and other purposes; but of itself it 

 * Published in the ' Engineer ' for Oct .S, 1873. 



