468 



NATURE 



[December 23, 1915 



THE WORKING AND MAINTENANCE OF 

 • STEAM BOILERS. 



IN these days of high-priced coal, the memorandum 

 which has recently been issued by Mr. C, E. Stro- 

 meyer, chief engineer of the Manchester Steam Users' 

 Association, will be read with much interest by 

 engineers and boiler owners. The coal bill for a 

 Lancashire boiler amounts to from 300Z. to 600L per 

 annum, and careless stoking may easily increase this 

 cost in a very large proportion. Lack of proper atten- 

 tion to minor defects, which should be remedied as 

 soon as detected, may also greatly increase the coal 

 bill and shorten the life of the boiler. The menror- 

 andum covers a very wide field, such as economiser 

 defects, external and internal corrosion, leakage, etc. 

 Of special interest are Mr. Stromeyer's remarks re- 

 garding mechanical stokers. 



Experience indicates that mechanical stokers, which 

 naturally aim at improved efficiency and therefore 

 high furnace temperatures, require not only that they 

 should be carefully looked after and kept in good 

 repair, but also that the boiler should receive far more 

 care and attention than are necessary with hand-firing. 

 Scale, and to a certain extent grease, may be tolerated 

 in hand-fired boilers, but every effort should be made 

 to remove these injurious substances if increased 

 economy is aimed at by the adoption of mechanical 

 stokers. Mr. Stromeyer gives some illustrations of 

 the increased liability to damage due to increase in 

 the temperature of the furnace. The boilers of a 

 large steamer had been giving no trouble until an 

 improved fire-grate was fitted. A saving of about 

 10 per cent, in the coal bill resulted, but during the 

 next voyage all the eighteen furnaces gradually 

 bulged, in spite of a reduction of speed and power. 

 The bulging could have been stopped if the improve- 

 ment due to the new grate had been nullified either 

 by keeping the furnace doors open and admitting an 

 excess of cold air, or by closing all airholes in the 

 doors, restricting the air admission but spoiling the 

 efficiency. 



Mechanical stokers designed to burn anthracite will 

 almost certainly fail if fed with coking coal, aqd vice 

 versa. It is not possible to design a mechanical 

 stoker which shall be satisfactory with all classes of 

 coal. 



From an economical point of view it is more im- 

 portant to keep the boiler heating surfaces free from 

 soot and tarry matter than to remove the scale from 

 the interior surfaces; the wear and tear question, 

 however, demands that the inside of a boiler should be 

 kept clean. Scale and grease hinder the heat which 

 enters the plate from passing into the water. The 

 radiating power of incandescent fuels, or flames, in- 

 creases as the fourth power of the temperature, hence 

 boilers which have worked satisfactorily, but in- 

 efficiently, with a comparatively low furnace tempera- 

 ture, even though the plates may be covered with 

 scale or grease, are likely to give trouble if the 

 furnace temperature, and with it the efficiency, are 

 increased. It is not strictly true to say that scale and 

 grease reduce the efficiency of a boiler ; they merely 

 make it unprofitable to adopt an efficient system of 

 combustion. 



Slow bulging of the furnaces may be caused by the 

 deposition of scales of crystals from any boiler water 

 containing more than 4 per cent, of soluble salts. It 

 is more than probable that plates which on one side 

 are exposed to an intense heat, are on the other side 

 covered chiefly with bubbles and sprays of burst 

 bubbles, which leave their dissolved salt on the boiler 

 plate while the water is evaporated. If the intense 

 heat and rapid evaporation can be maintained locally, 

 and this seems to be the case if mechanical stokers 



NO. 2408, VOL. 96] 



are worked very hard, crusts of salt will form here 

 and there on the heating surface. Sometimes they 

 will be washed away with a slight change of evapora- 

 tion or circulation, but sometimes they will remain 

 attached to the plates for a sufficiently long period 

 to cause overheating. Drops of water which fall on 

 hot plates are in a spheroidal condition, do not wef 

 the plate, and consequently will not dissolve any salt 

 scale which has formed there. As soon as a little 

 bulging has been effected, the salt crusts will doubt- 

 less break off, but as bulges are exposed to the flames 

 more than other parts, salt crusts are likely to reform 

 in them, and gradually the bulge grows larger and 

 larger until it is detected. As soon as the fire is 

 drawn the salt crusts are dissolved away, and the 

 bulges are said to be due to mysterious causes. This 

 danger is naturally greatest with boilers having a 

 had circulation. 



BEHAVIOUR OF PLANTS IN RESPONSE 

 TO THE LIGHT.^ 



IN the whole realm of biological science there is 

 perhaps no phenomenon of greater fundamental 

 importance than that exhibited by green plants in the 

 transformation of carbon dioxide and water into 

 starch and sugar. That this can only take place 

 through the action of light upon chlorophyll is 

 commonplace knowledge, but exactly hov/ it is effected 

 we do not know. Of the light that falls upon a green 

 leaf a part is reflected from its surface, a part is 

 transmitted, and another part is absorbed. That 

 which is reflected and transmitted gives to the leaf 

 its green colour ; that which is absorbed, consisting 

 of certain red, blue, and violet rays, is the source 

 of the energy by means of which the leaf is enabled 

 to carry on its work. 



The extraordinary molecdlar complexity of chloro- 

 phyll has recently been made clear to us by the re- 

 searches of Willstatter and his pupils ; _ Usher and 

 Priestley and others have shown us something of what 

 takes place in chlorophyll when light acts upon it; 

 and we are now beginning to realise more fully what 

 a very complex photo-sensitive system the chlorophyll 

 must be, and how much has yet to be accomplished 

 before we can picture to our minds with any degree 

 of certainty the changes that take place when light 

 is absorbed by it. But the evidence afforded by the 

 action of light upon other organic compounds, 

 especially those which, like chlorophyll, are 

 fluorescent, and the conclusion according to modern 

 physics teaching that we may regard it as practically 

 certain that the first stage in any photo-chemical re- 

 action consists in the separation, either partial or 

 complete, of negative electrons under the Influence 

 of light, leads us to conjecture that, when absorbed 

 by chlorophyll, the energy of the light-waves becomes 

 transformed into the energy of electrified particles, 

 and that this initiates a whole train_ of chemical 

 reactions resulting in the building up of the complex 

 organic molecules which are the ultimate products of 

 the plant's activity. 



The absorption of light by the leaf is therefore of 

 great physiological Importance, and we have only to 

 look at any of the plants around us to see how suc- 

 cessfully they contrive to arrange their leaves to 

 obtain the maximum advantage from the light that 

 falls upon them. A plant organ responds to the 

 directive influence of light by a curvature which 

 places it either in a direct line with the rays of light 

 as in grass seedlings, or at right angles to the light 

 as in ordinary foliage leaves. 



1 Evenine discourse delivered before the British Association at Man- 

 chester on September 9, by Dr. Harold Wager, F. K.S. 



