326 



THE BEE-KEEPERS' REVIEW. 



The material of which your bee house is 

 built will iutiueuce the amount of artihcial 

 veutilation ueeded. In order to give you au 

 idea of the exteut of uatural ventilation 

 through the walla of buildings, I cannot do 

 better than again quote Retieukoffer : — 



' For every square yard of wall surface, at 

 !)K° falir. ditterence of temperature, the 

 spontaneous veutilation, or passage of air 

 through the wall, amounts per hour to 



♦ 7 cubic feet, with walls of sandstone 



6.5 •* •' " •' of quarried limestone. 



7.9 ' " of brick. 



14. i " " " " of mud.' 



We prefer to build our wmtering houses of 

 earth. You will at first conclude that sand- 

 stone walls would be more porous than lime- 

 stone, but sandstone is a smoother stone and 

 does not require so much mortar. It is the 

 mortar that admits the larger part of the 

 air. There has always been a serious dis- 

 agreement between theoretical and practical 

 ventilation, until a consideration of the ex- 

 tent of natural ventilation reconciled the 

 difference. Many interesting experiments 

 are on record. With suitable apparatus, 

 candles are extinguished by air blown from 

 the mouth through solid brick walls, a foot 

 in thickness. 



Another mistake still current in some of 

 our text books on ventilation is the state- 

 ment that impure air, being heavier than 

 pure, falls to the bottom of a room and re- 

 mains there, unless provision is made for its 

 outlet at that point. These authors are igno- 

 rant of the law of the diffusion of gases. 

 Gases intermingle perfectly, no matter what 

 the variation in density. Usually there is 

 not much difference in the purity of the at- 

 mosphere in the various parts of a room, 

 unless the changes are quite rapid. 



A consideration of the moisture of the air, 

 as well as of the practical appliances for ven- 

 tilation must be deferred for the present. 

 P. H. Elwood. 



Starkville, N. Y., Feb. 1, 1878." 



After reading over the above it occurred 

 to me that if bees thus secured ventilation 

 in spite of their owners, why need there be 

 any attempt made to secure ventilation for 

 them ? I wrote Mr. Elwood saying that it 

 seemed as though a little explanation on 

 this point would make things a little more 

 satisfactory. He replied as follows : — 



OoTOBEB 18th, 1893. 

 W. Z. Hutchinson, Flint, Mich. :— 



Deab Sik : — Yours of July, also of October 

 6th, came in due time, but in a busy tin^e. 

 You refer me to an article of mine in the A. 

 B. J. for July 1878 and ask why if natural 

 ventilation is so great it ever becomes neces- 

 sary to resort to the artificial ventilation of 

 a bee cellar ? In reply permit me to say we 

 have a pasture lot of about the right size for 

 our old Guernsey. However, if we turn in a 

 pair of horses with her we shortly find that 



the pasture is over stocked. So with a bee 

 cellar having enough natural ventilation for 

 fifty swarms of bees. When five or ten times 

 that number are put in it, it is overstocked 

 unless the cellar is artificially ventilated. 

 Again, the feed in the pasture is not a con- 

 stant quantity, for in a time of drouth the 

 grasses grow very slowly if at all. So in a 

 bee cellar tlie uatural ventilation varies and 

 at times is very little. When the wind is a 

 gale and the temperature below zero, the 

 natural ventilation of our bee cellar is suf- 

 ficient for a thousand swarms. But let the 

 wind deaden to a calm, the temperature rise 

 outside to that within and the degree of 

 moisture rise to the point of saturation and 

 a million voices would scold you should you 

 depend wholly upon natural ventilation. 

 The most important factor in natural venti- 

 lation is the diffusion of gases when brought 

 in direct contact or what is practically the 

 same contact though a porous diaphragm or 

 partition. We inhale air into the passages 

 of the lungs, but diffusion causes it to pass 

 further in while the impure air passes out by 

 this process of intermingling. *' The rates 

 of diffusion of gases are inversely propor- 

 tioned to the square roots of their relative 

 weights." Temperature directly changes the 

 relative weights (besides exerting other in- 

 fluences) and thus becomes an important 

 factor in changing the rates of diffusion. 

 An ordinary room with a capacity of 2,6,50 

 cubic feet had its entire contents changed 

 once in an hour by natural ventilation when 

 the difference between the inside and out- 

 side temperature was 34 F. (66^ inside, 32° 

 outside) the doors and windows of course 

 being shut. When all openings and crevices 

 in doors and windows were pasted up and 

 rendered as thoroughly air-tight as possible, 

 there was still a change amounting to 1,0(50 

 cubic feet per hour which was owing to dif- 

 fusion through the walls. On lessening the 

 difference between the internal and external 

 temperature to 7° F. (71° in 64° out) the 

 change of air was reduced to 780 cubic feet 

 per hour, but on opening a window of eight 

 square feet, the change rose again to 1,060 

 cubic feet, showing that we may have in 

 winter better ventilation with windows 

 closed than in summer \\ ith the same open. 

 Thus it is seen that artificial ventilation is 

 most urgently called for when the temper- 

 ature outside and inside is nearly the same. 

 Yours truly, 



P. H. Elwood. 



