282 



CASSELL'S POPULAR GARDENING. 



draught leads to the formation of carbonic oxide 

 and loss of heat. 



The Tank System. — Mr. Rendle, the in- 

 ventor of one of the methods of glazing without 

 2:)utt3^, some years ago introduced a novel mode of 

 heating, which he termed the " tank system." The 

 object is to aiford a moist bottom heat to plants 

 without the aid of fermenting materials, which 

 are troublesome and expensive. The plan recom- 

 mended is to construct a tank either of brick, slate, 

 or other imj^erishable material, of any width, to 

 suit the purpose for which it is intended, the length 

 of the house or j)it, and about five inches deep, 

 '.rhe apparatus is very simple, as will be gathered 

 from a glance at Fig. 70, which represents a long 

 shallow trough, divided longitudinally as far as a, 

 some four inches 

 from the extreme 

 end. From the 

 top of the boiler 

 A, a pipe commu- 

 nicates with one 

 of the divisions, 

 say at h, and from 

 the bottom of 

 the boiler another 

 pipe opens into 

 the division c. 



The first is the flow, the second is the return, and the 

 apparatus is complete. The hottest water flows by 

 the pipe inserted in the top of the boiler into the 

 tank at b ; and simultaneously its place is supplied 

 by colder water descending through the pipe 

 which enters at or near the bottom of the 

 boiler, to be. re-heated, and so maintain the circula- 

 tion. The flow and return portions may be in one 

 trough or tank, with a division along the centre, as 

 shown in the figure, or a series of tanks may be 

 carried in different directions, provided all are con- 

 structed on the same level. Various kinds of 

 materials have been employed in the construction 

 of tanks, but owing to the action of the hot water 

 it is a difficult matter to keep them sound and free 

 from leakage. Wood has answered fairly well 

 when well put together, but being perishable, it 

 does not last long. Iron is a rapid conductor, 

 moreover it is expensive. Brick, on the other hand, 

 radiates heat slowly, and on this account is perhaps 

 the best material that can be used, as the sides of the 

 tank can be raised to any convenient height, and it 

 forms the best of all foundations for a coating of good 

 Portland cement. 



Heating by Flues.— Posi^io^i of the Flue. — We 

 are indebted to the Dutch for the introduction of the 



Tank System of Heating-. 



detached brick flue, and although we do not often 

 hear of gardeners giving preference to this mode of 

 heating, there still exist many good old gardens in 

 which well-built flues are in active operation. An 

 experienced horticulturist and writer who had great 

 opportunities for testing the merits of the flue, the 

 tank, and the hot-water pipe system, says : " If well 

 built and managed, they have their advantages. 

 They are less expensive and more quickly heated 

 than steam or hot-water pipes, and therefoie useful 

 in repelling sudden attacks of frost in plant-pits and 

 green-houses. The space they occupy, and their 

 heavy appearance, militate against theii' being used 

 in green-houses of the first order-, unless they are 

 placed under the stages or plant tables as in a, or 

 under the floor as in B (Fig. 71), in which case they 

 should be carried thi-ough a chamber, the sides, 



bottom, and top of 

 which should be 

 clear of the flue 

 at least three 

 inches. The small 

 quantity of air 

 thus surrounding 

 them soon be- 

 comes heated, and 

 should be admit- 

 ted into the house 

 thi-ough neat hit- 

 and-miss brass ventilators. A similar ventilator 

 should be built in the waU of the chamber near the 

 fire-place, by which a fresh supply of air is admitted, 

 and propels the heated air in the chamber through 

 the ventilators in the pavement into the house. All 

 underground flues, however, lose much of their heat 

 by its being absorbed by the walls which surround 

 them, and they can only be recommended when it 

 becomes absolutel}' necessary that they be placed out 

 of sight." 



In A (Fig. 71) we find the flue running along the 

 front, where it is partially shut out from \dew by the 

 plant table above it, and the warm air, given'off by the 

 brickwork of which the flue is constructed, being 

 light and buoyant, taking the direction of the arrows, 

 completely cutting off the entrance of cold from 

 without. This, however, is perhaps not the best 

 mode of diffusing heat throughout a glass structure, 

 as it is a well-proved fact that the atmosphere of all 

 glass-houses is coldest near the roof on frosty nights, 

 on account of the loss of heat by radiation. More- 

 over it is doubtful if a flue running along the front 

 only would be found sufiicient for a green-house of 

 ordinary dimensions ; therefore, assuming- that there 

 is only one doorway, it would be advisable to carry 

 the flue all round the interior of the house into the 

 chimney formed in the back wall at the north-east 



