198 



HEATING AS APPLIED IN HORTICULTURE. 



cheaper than metallic ones of the same 

 capacity. They are also exceedingly du- 

 rable, and give out heat best of all, next 

 to iron ones. Very elegant and durable 

 tanks may be formed of large Welsh slates 

 or Caithness pavement, which may be 

 procured of almost any size and thick- 

 ness; and we have no doubt but that 

 glass tanks will be ere long as common 

 as any at present in use. 



Where narrow tanks, or what may be 

 called the gutter mode of circulation, is 

 adopted, well-prepared fire-clay tubes, 

 perforated on their tops, may be advan- 

 tageously employed. In the construction 

 of brick tanks, we believe that too thick 

 a coat of cement has been in general 

 used. We have in practice found it bet- 

 ter to make the cement into the consis- 

 tency of thick paint, and to lay it on 

 with a common whitewash brush, one 

 coat after another, until all the pores of 

 the bricks and the joints between them 

 become completely saturated and closed. 

 This is an operation that can be done by 

 any handy labourer, and which might be 

 repeated at times when the tanks are un- 

 employed. The tanks thus finished may 

 be, with advantage, painted over with 

 two or three coats of oil. A great mis- 

 take was fallen into soon after the intro- 

 duction of the tank system of heating; 

 and we mention it here, because we know 

 the practice is continued by some who 

 know no better, by covering them over 

 with faggots or hurdles, and then with 

 turf and straw, upon which the beds to 

 be heated were formed. This was done 

 with a view, no doubt, of allowing vapour 

 to ascend, to keep the mould at the roots 

 of the plants moist. This it did to a very 

 injurious extent, rendering the whole a 

 mass of puddle, as well as choking up the 

 tanks, and ruining the boilers with the 

 sediment. When brick tanks are used, 

 the very hardest bricks should be em- 

 ployed, or composition or glazed bricks 

 would be preferable, as they would ab- 

 sorb a very limited quantity of water : 

 and hence the advantage of constructing 

 tanks of Welsh slates or Caithness pave- 

 ment, which are known to absorb the 

 smallest amount of water of all known 

 building materials. 



Rendle's mode of tank-heating. — We have 

 had an opportunity of seeing Mr Rendle's 

 mode of tank-heating in full operation, 



in the exceedingly well-managed nursery 

 of Messrs Veitch and Son, at Exeter. 

 The sketch we made at the time has been 

 mislaid'; we, however, again draw upon 

 that fertile source of information in such 

 matters, "The Gardeners' Chronicle," 

 from which the annexed figs., 254, 255, 



Fig. 254. 



256, and 257 are taken, as well as the 

 description by Mr Veitch, jun. The 

 house in which we saw it is used as a 

 propagating-house, and a better we have 

 not seen. So far as the heating is con- 

 cerned, the system may be applied to 

 houses of various descriptions. " The 

 tank is formed of brick arches worked in 

 cement, with brick sides, the whole being 

 well coated with cement. The top is of 

 slate, cemented down. The sides of the 

 bed are also formed of brickwork. The 

 material used for plunging is a clear 

 sharp sand, which we find retains the 

 heat for a considerable time. In one 

 part of the bed we have put soil, and the 

 cuttings planted out in it have rooted 

 most rapidly. We would draw your 

 attention," says Mr J. Veitch, "to the 

 simple yet efficient manner in which we 

 regulate the heated water by means of 

 the apparatus d. By this contrivance we 

 can heat only one division of the house 

 at a time, or only half of either, or both 

 divisions ; and while all can be heated at 



