142 



JOUBNAL OF HOETICULTUEE AND COTTAGE GARDENER. 



[ August 25, 186S. 



plan given at page 85 would be well worth trying, and I should 

 like to hear of its having been cai-ried into effect in all its 

 details. Meanwhile, I wish to offer a few further remarks on 

 the subject, for although I believe it is one that more directly 

 concerns employers, still it is also important that gardeners 

 should make themselves thoroughly acquainted with it, and 

 this most of them have opportunities of doing, both from their 

 own practice and from the reports of the experience of others. 



In the first place, I would criticise what " G. A. " says 

 in regard to the nature of heat, not in a spirit of opposition, 

 but with the object of inquiring further into the matter. 

 From what " G. A." observes, the natural tendency of heat 

 is to dii'ect its course upwards. Now, in my view, it is to 

 diffuse itself eqxiaUy on all sides from the point of com- 

 bustion into the surrounding ail-. The ail' thus heated 

 becomes lighter, and is quickly borne up by colder, and, 

 consequently, heavier air; so that, heat being diffused, 

 heated air has no motion in itself vnitil displaced by that 

 which is heavier — in other words, that which has a greater 

 specific gravity. It may not be possible to distinguish be- 

 tween heat itself and heated au', and perhaps it is of little 

 consequence whether we can or not ; but it is worth while 

 ascertaining the truth while we are about it, and I will en- 

 deavour to make my meaning more clear by illustration. 



If you light a candle and place it in the middle of a dark 

 room, the light is diti'used equally on aU sides — that is, as 

 nearly equally as we can judge ; and it is my belief that the 

 heat would be equaDy diffused, but, that being less subtle 

 than the light, it, in combination with the air into which it 

 is diffused, is more readily acted on by the cooler air, and is 

 quickly borne upwards. The fact that there is more heat at 

 2 inches above the light than at half an inch from the side 

 of it does not alter the case, since the heat that would 

 otherwise be equally diffused all round is concentrated at 

 the top by the upward cun'ent of air. 



According to "G. A.," in speaking of the action of fire on 

 boilers, the greatest heat is directed to that part which is 

 directly over the lire. Now, I am not sure that this is 

 correct. For instance : the blacksmith does not place the 

 iron to be heated over the fti-e, where, according to " G. A.'s " 

 theory, the greatest heat would be, but he thrusts it right 

 into the fire — to the very spot where the blast of cold air, 

 driven in by a powerful pair of bellows, comes in contact 

 with the fuel ; or if you take a common pair of bellows and 

 blow up your parlour fire, you wUl perceive that where the 

 nozzle of the bellows is directed there wUl be the hottest 

 part of the fire, and, further, if you look into a fiu-nace fii-e 

 you wiU see that the greatest heat is about the bars, and 

 although there may be more heat at 1 foot above the fire 

 than at 3 inches below it, there will be more heat 1 inch 

 below the fire than at 1 inch above it, for the greatest heat 

 is where the air comes in contact with the burning fuel. 

 Presuming this view to be correct, it shows the advantage 

 of having hollow bars to the furnace, and that a great deal 

 of heat is thus encoui-aged, but that is not enough. 



I have said the greatest heat is at the point of contact 

 between the fire and the ib-aught of air, but the question is 

 how to adapt this to the economisation of heat. Here I 

 must confess myself at fault, for although, as I believe, the 

 greatest heat is at the bottom of the fire, still the liottoms 

 of the baxs where the ah- comes in contact with them on its 

 way to the fire are comparatively cool, and the same effect 

 would be produced if a current of air could be made to play 

 on other points than the bottom of the furnace. Leaving 

 this ground, then, as untenable, we come back to the question 

 of how to utilise the heat in its upward course — upwar-d, not 

 because of its tendency to fly off, but because it is pushed 

 up by that which is to replace it. The most rea.ionable 

 method of utilising this heat appears to be to intercept it, 

 by breaking its direct progress, and throwing it into nu- 

 merous directions instead of allowing it to pass off in a 

 body, and this must be done in such a manner that sufficient 

 draught is allowed for the fire to burn clear. This must not 

 be overlooked, for it not unfi-equently happens that in di- 

 recting our attention to one point we are apt to overlook 

 others. It is on this account, that although improvements 

 are made from time to time, a perfect boUer has not yet 

 appeared, and it is possible never will; yet "G. A." has 

 .suggested some changes, and I freely coincide with him 

 that what he suggests would be a decided improvement. 



He provides horizontal cods of pipes for the heat to strike 

 against in its upward course, and having passed there it is 

 again to break against the water-jacket, which is grooved to 

 receive it. Still, in my opinion, a great body of heat is 

 aUowed to pass off unintercepted — for tliis reason : that al- 

 though I believe the natural tendency of heat is to diffuse 

 itself, stiU the pressure of the atmosphere tends to con- 

 centrate it into a column in its upward progress, narrower 

 as it mounts higher, as is seen in the foi-m the flame of a 

 candle assumes. This, then, would allow the strongest heat 

 even in such a boiler to pass into the flue. 



It appears, then, that what is wanted is the means of in- 

 tercepting, breaking, turning, and appropriating this column 

 of heat, so that it shall not pass away from the boiler until no 

 more heat is allowed to escape than will carry the smoke up 

 the flue. This, of coui-se, must be aUowed for, or the whole con- 

 trivance will fail ; and tliis probably will be a point of some 

 nicety, for the boiler itself may be as nearly perfect as it 

 could possibly be, and yet the least fault in the setting 

 might spoil it. It would, however, be possible to avoid this ; 

 and I will follow the example of " G. A.," and give a few 

 suggestions of my own, which, as a matter of course, are 

 open to criticism, and so far from fearing to have defects 

 pointed out, I shall be glad to be set right if I am proved 

 to be wrong. 



I do not know whether it is generally known, that when 

 a piece of wire gauze or fine wire netting is held in the flame 

 of a candle that the flame becomes dispersed, takes a wider 

 scope, but unites after passing through it. Tliis wire natu- 

 rally intercepts a gi-eat deal of heat. Two or three such 

 layers would absorb nearly all the heat, and allow the air 

 to pass off comparatively cooled. Now, although I do not 

 remember seeing anytlung of the sort, I do not think it 

 would be impossible to cast hollow plates perforated with 

 holes of about three-quarters of an inch in diameter, so that 

 the plates would hold water and yet allow flame to pass 

 through the perforations. By way of illustration I wiU 

 suppose a metal dish such as is used to serve up large joints 

 of meat, and which are made to hold hot water. Suppose 

 this dish could be pierced with holes half an inch in dia- 

 meter and about an inch apart, the holes to go through 

 from top to bottom so that you could see through them, 

 and yet the dish to hold hot water the same as before ; 

 and ftirther, suppose three or four of such perforated water- 

 plates to be cast of different sizes, of from 18 inches or 

 2 feet for the largest, and 1 foot or it may be less for the 

 smallest ; then we should have a water-jacket or a boiler 

 made somewhat similar in form to Weeks's boiler — that 

 is, tapering towards the top, only pipes either upright or 

 horizontal are unnecessary excepting for the furnace-bai's, 

 which I would assuredly have hollow. The main part of the 

 boiler would be a plain hollow water-jacket, and the perfo- 

 rated hollow plates would be fitted within this ; the largest 

 say a foot above the fire, the next about 9 inches above that, 

 the next at an inch or so less distance above that, and, if 

 another, a still less distance to be allowed between them — 

 the hollow plates and water-jacket to be all connected, so 

 that the water could pass freely through them all ; the flow, 

 of course, to be fi-om the top of the water-jacket, and the 

 return at the bottom of it in connection with the hollow 

 furnace-bars. 



There should be openings through the water-jacket to 

 allow of a wire brush being introduced for clearing the 

 boiler of accumulated soot, for this would be a matter of 

 necessity in such a boiler ; but with a ready means of intro- 

 ducing a brush the cleaning would involve a very trifling 

 amount of trouble on the part of the stoker. With regard 

 to the circvdation of water, the boiler should bo made so that 

 the water could pass freely from the bottom to the top. 

 This is all that is necessary as regards the boiler in the 

 circulation of the water, for that chiefly depends on the fall 

 of water in the return-pipe. If we examine into the prin- 

 ciples on which hot water circulates wo shall find that it 

 does not depend on the nature of hot water to ascend, but 

 on the power of colder water to push it up or displace it, 

 and that the greater tlie weight of water in the return-pipe 

 the more rapidly is the hot water made to ascend. If the 

 retiu-n-pipes were twice as thick and lield twice as much 

 water as the flow-pipes, the mere construction of the boUer 

 could offer no obstruction to the circulation of the water. 



