18S 



JOUENAIi OP HORTICULTUKE AND COTTAGE GARDENER. 



[ September 5, 1872. 



trary directly the reverse, because it shews the -water has been 

 longer in the pipes to give off its heat before returning to the 

 boiler, and must remain longer in the boiler to regain the heat 

 that is lost. . The water in the pipes and boiler being in the first 

 instance in a state of rest or equilibrium, and the motion or cir- 

 culation of water through the pipes and back into the boiler 

 being only caused by the action of the heat on the water in the 

 boiler, the relative motion of the water throughout all the pipes 

 must be the same. It cannot move quicker through any one 

 foot of pipe than another. As it is an axiom that under equal 

 conditions the heat radiated from equal lengths of piping 

 in a certain period of time will be the same, it shows, if the 

 water in one boiler returns colder after passing through a 

 certain number of feet of piping than it does in another boiler 

 under equal conditions, that the circulation in one boiler is 

 slower than in the other, or, in other words, that the water has 

 been longer in the pipes to give off its heat in one case than the 

 other. 



This will be so self-evident to most people, that it would seem 

 hardly necessary to demonstrate it had it not been that at Bir- 

 mingham we heard the directly contrary remark made by one 

 who has written a good deal on the subject of boilers, who could 

 not be persuaded he was wrong, and who wished to have this 

 point raised for discussion. Experiments made on the specific 

 gravity of water at different temperatures show that water ex- 

 pands slowly from 40° to 68°, very nearly uniformly from 68° to 

 176°, but it expands rather more rapidly as it increases in tem- 

 perature, and that from 176° to the boiling point it expands 

 more rapidly still. Thus, 1000 parts of water at 212° contract 

 to 986 at 176°, and to 960 at 68°, and 957 at 40°, or, in other 

 words, 960 gallons of water at 68° expand to 9S6 at 176°, and to 

 1000 at 212°, boiling point. Apply this to the mctive power in 

 a horticultural boiler, and it will be seen that the force is only 

 a weak one. One thousand feet of 4-inch piping contain at a 

 rough estimate five hundred gallons of water. Now, five hundred 

 gallons of water as the water increases in temperature loses 

 1^ lb., or 20 ozs. on an average for every degree it rises from 

 70° to 170°, or at the rate of one-twenty-fifth of an ounce for every 

 gallon ; or, to put it in other words, a gallon of water diminishes 

 1 oz. in weight for every 25 c it gains in temperature, and as a 

 gallon of water at 60° weighs 10 lbs., it only loses on an average 

 one one-hundred-and-sixtieth part of its weight as it increases 

 25° in temperature, and the motive, power is the difference in 

 weight between one gallon as it returns in the return-pipe, and 

 one gallon as it leaves the boiler by the flow-pipe. 



It can easily be seen, then, that in order to insure a rapid 

 circulation no impediment must be placed either in the boiler 

 or elsewhere in the pipes to the flow of the water. These 

 figures are rather dry details, and may be uninteresting to 

 many of your readers, but they help to give a sort of general 

 idea of the motive power in horticultural boilers, and. will, 

 perhaps, help to correct the idea that there is great pressure by 

 neat, and ample power to overcome engineering difficulties. It 

 also shows that too many horizontal surfaces in boilers are so 

 many impediments to the circulation if the water has to flow 

 horizontally from one end to the other, as in horizontal tubular 

 pipes or flat plates laid one on the top of the other. It shows 

 also why the old form of saddle and conical boilers has so long 

 stood the test of time and experience — because there is nothing 

 in the construction of them to hinder the water rising in a 

 natural way as it becomes heated. It also shows that it is wrong 

 to run hot-water pipes too long on a level, that the pipes ought 

 to rise gradually from the boiler till they reach the farthest 

 point of the flow, and then fall gradually to the boiler again. In 

 other words, if there were 1000 feet of piping, 500 of it ought to 

 be flow, 500 return, and we need hardly point out that there 

 can be no worse system adopted to prevent circulation than that 

 of connecting the pipes to the boiler by smaller pipes, making 

 either the flow or return pipe into the boiler 2 inches, or as we 

 have sometimes seen it, 1-inch piping, and the rest of the pipes 

 3 or 4 inches, as the case may be. However, this plan is fast 

 being exploded, and we very seldom now see new boilers erected 

 with diminishing pipes either as flows or returns. 



To return to the boilers exhibited at Birmingham, we may 

 divide them into tubular, including upright and horizontal, of 

 which we noted six specimens, three upright and three horizon- 

 tal ; and secondly, into saddle ormodifications of the saddleboiler, 

 such as conical ; saddle-and-flue, Cornish, &c, of which there 

 was a great variety — five for competition — viz., Mee's double 

 saddle, Cannell's circulator, Lumby's independent, Hartley and 

 Sugden's saddle boiler with extended water way, and Green's 

 saddle boiler with shelves. Besides these five for competition 

 there were also exhibited — Glover's improved Cornish, and also 

 a saddle-and-flue boiler by Gray, of Chelsea ; Jones & Bowes' 

 Witley Court horticultural boiler with extended water way ; 

 conical and cylindrical boilers by Green ; independent tank 

 boiler, dome-top, and conical boilers by Hartley & Sugden ; 

 Ormson's convoluted and Premier flued Cornish boilers, and 

 others. 

 We hav forgot to mention another form of boiler, a spiral 



pipe, by Deard, of Harlow, in Essex, which cannot be classed 

 either with the tubular or the saddle, and which we shall notice 

 again afterwards. 



We will begin our remarks on the boilers by taking the up- 

 right tubulars — Weeks's duplex, Harlow's upright tubular, and 

 Clarke's upright tubular with cylindrical jacket — only one of 

 which, Mr. Harlow's, was entered for competition. Weeks's 



Kg. 1. 



boiler, of which we annex an engraving ( fig. 1), ought, in our 

 opinion, to have been called the complex. The merit claimed for 

 it, besides that of its being according to Messrs. Weeks's opinion 

 the most powerful form of boiler extant, is that it is capable 

 of being divided into two sections, so that in case of one part of 

 the boiler being out of order the other part can be used. This 

 would, no doubt, be of advan- 

 tage, but from the appearance of 

 the boiler exhibited it would 

 require an immense amount of 

 fuel, and would be both costly to 

 put up and costly to work. Mr. 

 Harlow's boiler, which obtained 

 a silver medal as the best tubular 

 exhibited, has an improvement 

 in the form of pipes (see fig. 2), 

 one great merit of which is that 

 it gives room for expansion and 

 contraction, and also allows of 

 any one of the pipes being easily 

 removed in case of injury. The 

 boiler is a powerful one, and a 

 little modification of it would 

 improve it. We like the position 

 of the flow, and the way the 

 pipes all meet together in a 

 smaller cylinder at the top, the 

 flow being from the upper part 

 of the cylinder instead of the 

 side. There is, however, too 

 direct a draught to the flue, and 

 we are of opinion that the coke 

 or coal might easily get lodged 

 or jambed between the extended 

 gills of the pipes, which con- 

 verge inwards into the fire-box. 

 A cylindrical water-jacket con- 

 nected with the lower water-bars 

 would materially increase the 

 heating power and economy of 

 fuel. 



Mr. Harlow also received a 

 medal for his pipe-junctions, con- 

 sisting of flanges with annular grooves, having an indiarubler 



