690 



GREENHOUSE 



desirable to open all the ventilators in a long house with 

 one set o£ apparatus, for frequently one end will not 

 need as much ventilation as the other end, or may be 

 affected by the wind for.niug a current lengthwise of 

 the house. To avoid this a Greenhouse 200 feet long 

 should have 3 or 4 sets of apparatus, which can be ope- 

 rated separately. In all Greenhouses of considerable 

 width, it is desirable that ventilation should be provided 

 on both sides of the ridge, so that the ventilation can be 

 given on the "leeward" side, which will prevent the 

 wind from blowing directly into the house. 



Sealimj.-The success of the florist, gardener or 

 amateur in the management of a Greenhouse depends 

 largely on the satisf actorv working of the heating appa- 

 ratus. There are two systems of Greenhouse heating 

 which, when the apparatus is properly installed, are 

 economical and satisfactory; viz., hot water and steam. 

 The open-tank hot water heating has more advantage 

 in its adaptation to general use than any other, and is 

 so simple that its management is readily understood by 

 anv one It is practically automatic, and is capable ot 

 maintaining an even temperature for ten hours without 

 attention. Low pressure steam heating is well adapted 

 to large commercial ranges, and to largo conservatories 

 in parks and private places, where a night attendant can 

 be kept in charge of the fires to turn on and shut oft 

 steam from the radiating pipes as the changing outside 

 temperature may require. The heating of Greenhouses 

 to the best advantage under the varying conditions ot 

 climate and interior requirements, demands, like the 

 designing of Greenhouses, the services of an experi- 

 enced specialist in horticultural work. 



^ Lord & Bubsham Co. 



Greenhouse Glass.-The selection of glass for Green- 



ad the 



der it undesirable for such 



ture of the imperfections which ren 



are questions which 



have received much attention from horticultural writers, 

 and which huve brnu^'ht forth a variety of answers. 



^., ,1 .I'»'. ■I'-' ■' -iititil in all glass to be used in 



11^,.,.,,!,, ,,.,.,;•,,,,: iM-i , minimum of obstruction 



^',, '.!,,. I ,,■'.■ ., . h sufficient to withstand 



ti,,. liri , ■: I-, especially hail ; and 



tiiir.l 1 1 i : • :i : ■! . ■!' '■ '-I - ''■ rnlc-ring it liable tc 



I burn 



995. Details of 



I 



GREENHOUSE 



the thoroughness of the annealing. Glass is annealed 

 by passing through a series of ovens, where it is raised 

 to a high heat and then gradually cooled, whatever 

 toughness and elasticity the finished product may con- 

 tain being due to this pro- j,, 

 cess. The thickness of glass - _ 

 varies;, not only with grades 

 (single and double thick) \ 

 but also more or less within 



the grades, and even with v«%^ ' 



different parts of the same ^^ . , ' 



pane. Single thick glass is *, 



too thin for use in Green J 



houses, and in selecting anj Ji 



glass for such a purpose it 

 should be examined pane b) 

 pane, and all showing 

 marked variation in thick 

 ness, either between panes 

 or in different parts of the 

 pane, rejected. A pane of 

 varying thickness is much 

 more liable to breakage from 

 climatic changes or sudden 

 shocks than one which is 

 uniform in this regard. 

 From the foregoing state- 

 ments it will be seen that, in 

 general, the ordinary dou- '^ 



ble thick green glass is best, ggg Bumed areas on a 



as regards both tint and Begonia leaf. 



irsrf\'^lltrc\^g/int"nf than white, and the double 

 thick being the stronger grade. By green glass is meant 

 simply the ordinary sheet glass, the green color of 

 which is only noticeable when looking at a cut edge. 



The idea has long been more or less prevalent that 

 such visible defects in sheet glass as the so-called 

 "bubbles." "blisters" and " stones," produce a focusing 



N 



w 



11 I ,1 /^i ist|-ii, -1 I ;i,'t that plants thrive best under 

 I , ,11 I i 'ii !■ '!'■"! "lass, which lets through the 



'.,,!,.. a, -1 ,,-,smI.1.- V'' "tag« of ^^^ '^""''' '^^'^- '^^^^ 



rnciudcs all the solar rays, calorific or heat rays and 

 actinic or chemical rays, as well as the colorific «' 'isnt 

 rays. Clear white glass of the grade knomi as singR 

 thick " (12 panes to the inch) lets through from CO to <0 



per cent of the sun's rays, common green glass ;;^.' ",, 

 same thickness, 52 to 56 per cent, and "double thick 

 (8 panes to the inch) common green glass from 50 to 5- 

 per cent. This percentage is reduced by other colors, 

 dark blue glass letting through but 18 percent. In con- 

 nection with the matter of tint, it should be noted that 

 some glass, especially clear white glass purified with 

 arsenic acid, or that in which a large amount of potash 

 Is used in proportion to the amount of lime used m 

 manufacture, becomes .hill riftrr Ions exposure to the 

 weather, the dullness h.-U,.: .si,,,,,., by the efflo- 

 rescence of salts contain. .1 .., ili- i:!^...-. Before this dis- 

 integration has prociaMl.-.l t,". IM-. fUr crust or efflo- 

 rescence may be removi-d w,tl, ,iii,i-,atn" acid. 



The strength of glass depends upon its thickness and 



,,'■' I , ,, \ ! i |i. Sta.jp.'-'TS). In view of the 



,.,,,!,,,,,,,/,,, I ry, it is rather remarkable 



ti,.,. ,1 ; v,'ich prevalence. Nearly all 



l,,,'i, ,1, , ,imI Ih-i , ., , thinner in the middle than at 

 the pi-riphiTV, bi-ing thus concave rather than convex 

 lenses, and actually diffusing the rays of light passing 

 through them rather than producing destructive toei. 

 While it is true that sand stones or knots in glass may 

 produce foci, these points of focus scarcely ever exist 

 more than a few inches from the surface of the glass, 

 and consequently these defects can do no damage when 

 oncurring in roofs several feet distant from the grow- 

 in- plnits below. 



I ' Tilv full and complete series of experiments on 



I,. iiii'ot in this country (conducted at the Cornell 



■ ,,i,v Agricultural Experiment Station, the Physi- 



! I ,.„'atory of Cornell University, and a glass fac- 



, Ithaca, New York, but yet unpublished) shows 



,,■ cause of the burning by glass to be the 



,, in thickness of the entire pane, or por- 



: . . same, thus causing a prismatic or lens-like ef- 

 1, , t ri" 997), which causes a more or less distinct 

 t.,.u--hv^ of the sun's rays at distances varying from 

 -, ,„• i; flit to 30 feet, or even more, from the glass. 



This defect usually occurs along the side or end of 

 the pane, and is not visible to the eye, but may be 

 easily detected by the use of the micrometer caliper or 

 by testing in the sunlight. It may be found m all kinds 

 of glass, and is caused by a reduction of the upper or 

 pipl end of the cylinder from which sheet glass is made 

 by^the glass blower, to facilitate the removal of the 

 "cap" or neck end of the cylinder, by wh'ch it is at- 

 tached to the pipe while being blown. The defect, as 

 before stated, is 



and qualities of sin 

 tic manufacture, 

 ences in the thi.'K 

 imperceptible to 1 1 

 tion to materially 



be found in all grades 

 foreign and domes- 

 known that diiter- 

 • lenses, which are 

 re sufficient refrac- 

 )n of rays of light 



