May 4, 1893] 



NA TURE 



19 



and count the cost. Representative growers agree in advising 

 me that although horticulture, under these conditions, would be 

 very interesting from a scientific point of view, it would hardly 

 be commercially desirable. The necessity for the recon- 

 struction of glass-houses upon valu.ible urban land must of 

 necessity suggest to the horticulturist the alternative of decamp- 

 ing into the country, where the cultural conditions are more 

 favourable. The enhanced value of urban sites has, apart from 

 other inducements, no doubt been a factor in determining an 

 increasing number of growers to settle well outside the suburbs. 

 If, then, any idea of reconstruction is raised, it would in all pro- 

 bability prove to be the last straw. Considerations of this sort 

 lead me, in making a few remarks upon cultural precautions, to 

 limit my suggestions to such as are possible of realisation — things 

 being as they are. 



If we could eliminate atmospheric contamination, I do not 

 think the reduction of light alone would be a very serious cause 

 of complaint. Now and then it might be so to some extent, 

 though it would hardly be a grievance of the first magnitude. 

 It is when we have superadded aerial contamination that the 

 mischief is done. Many very common injuries to flowers — 

 injuries which impress the cultivator and catch his attention — ■ 

 have no casual relation with diminished illumination. The in- 

 fiorescencesof rhododendrons, which become so characteristically 

 glued up in their bud-scales and fail to open, will expand per- 

 fectly in total darkness. So also will the flower-buds of most 

 orchids. Since, however, the application of artificial light, in a 

 manner likely to be effective, Would be an unduly heavy burden 

 on the grower, we will dismiss this aspect of the question, and 

 proceed to discuss whether atmospheric contamination can be 

 cheaply remedied. 



And, first of all, can fog be neutralised or absorbed afier it 

 has entered a plant house ? I have experimented with several 

 things, but my results do not justify me in basing any recom- 

 mendations upon them. The sluicing or syringing of liquid 

 chemicals about a house has little to recommend it, even when 

 attended with some success, To solids the objection is not so 

 great. But I have not found that carbonate of ammonia, for 

 instance, exerts any noticeably beneficial action as a neutraliser 

 of the acid vapour of fog. But fog is a complex product, and 

 anything which might neutralise one constituent would probably 

 leave the others free to do their damage. I have never felt that 

 anything could be done inside the house towards mitigating fog 

 except the taking of certain precautions as regards watering and 

 heating. And I am of this opinion still. 



The scope of this report does not extend to a discussion of the 

 big question of the abolition of fog. Even the most sanguine 

 of the present generation can hardly hope to enjoy any abatement 

 of the fog-nuisance. So that I shall be more practically dis- 

 charging my mission in discussing how fogs may be excluded 

 from plant-houses than in attacking the greater problem. Stoves, 

 within certain limits, can be covered in with sheets of canvas, 

 and this has been tried with encouraging results. I first heard 

 of this method being systematically and successfully applied from 

 Mr. C. Davies, of the Mote Park Gardens, Maidstone. Even 

 the fogs of limited duration which are experienced there are 

 sufficient to destroy the blossoms of a whole houseful of orchids. 

 But they have been successfully combated by covering in the 

 house with canvas sheets. Elsewhere I have seen this done, 

 sometimes at my suggestion, with beneficial results. Still, at the 

 best, it is but an expedient. Immunity obtained in this way is 

 only partial. Severe fogs of short duration, or longer ones of 

 only moderate density, may be filtered through canvas, so that 

 the damage caused is lessened ; but a persistent dense fog gener- 

 ally prevails in the end. 



If plant-houses were constructed rather less leaky than is the 

 case at present, something definite could no doubt be done 

 towards filtering the air. I confess to holding serious doubts as 

 to whether the admission of air to plant-houses, as in vogue just 

 now, is based on sound physiological principles — and this quite 

 apart from the fog-nuisance. During the course of my inquiries 

 into fog, a device for ventilating conservatories — the " patent fog- 

 annihilator" of Mr. Charles Toope — came prominently under 

 my notice ; and as I have been frequently asked what I think of 

 it, I will take this opportunity of stating what I know. The 

 system is as follows : A number of boxes, situated on the floor 

 I under the staging, communicate directly with the exterior by 

 means of aperatures which can be readily closed if desirable. 

 These boxes contain several open-work trays, upon which sticks 

 of charcoal are loosely placed. The air entering a box from out- 



NO. 1227. VOL. 48] 



side is led through these trays, coming into close contact with the 

 charcoal. As the air leaves the box it impinges upon the hut- 

 water pipes, and is thus warmed before it reaches the plants in 

 cultivation. The entrance of air is promoted by simple con- 

 trivances known as "exhaust-caps " placed on or near thericige 

 of the house. These caps are so constructed that practically, 

 under all conditions, an out-draught of air obtains. Should the 

 draught be too great, it can be regulated by means of valves. 

 By this system a constant circulation of air throughout the house 

 is brought about. The air enters the charcoal-box at once fnm 

 outside. It passes through this and is warmed by the hot-water 

 system of the house, and ultimately escapes by means of the 

 "exhaust-caps." Excepting for the apertures mentioned the 

 house is air-tight. It is by means of the charcoal that Mr. 

 Toope claims that the air admitted is purified. As the air cir- 

 culates between the sticks of charcoal it gives up the products 

 of coal-combustion with which it may be contaminated, as in 

 foggy weather. 



Charcoal undoubtedly possesses remarkable properties as an 

 absorbent, and Mr. Toope is by no means the first to call atten- 

 tion to its properties in this respect. Forty years ago the 

 chemist Stenhouse' made observations on these properties, and 

 it may not be without interest to call attention to what he said 

 about it. In the paper referred to, Stenhouse describes and 

 illustrates the remarkable property of charcoal as an absorbent 

 and oxidiser of the products of decomposition of organic matter. 

 He describes how the carcases of dogs were kept covered with a 

 thin layer of powdered charcoal — but otherwise exposed — 

 without any nuisance arising therefrom. He adds that he has 

 devised a respirator on this principle, to be used in districts 

 smitten with cholera or yellow fever. He found, further, that 

 with such a respirator he could breathe with impunity air con- 

 taining large amounts of ammonia, sulphurrtted hydrogen, and 

 other hurtful gases. Finally, he suggested the application of 

 charcoal for purifying the air of houses located in infected 

 districts — all air admitted to be passed through thin canvas 

 bags containining crushed charcoal. Were snch precautions 

 taken, many regions at that time fatal to Europeans could be, 

 he was sanguine, dwelt in with impunity. 



In a later papei- Stenhouse describes his experiments, show- 

 ing how the absorbent property of charcoal could be greatly 

 increased. From this paper I venture to make the following 

 extract, as charcoal seems to have fallen into desuetude as an 

 absorbent : — 



"The lighter kinds of wood charcoal, owing to the nine 

 volumes of oxygen gas contained in their pores, possess a con- 

 siderable power of oxidising the greater number of easily 

 alterable gases and vapours. The absorbent power of charcoal 

 is comparatively much greater than its capacity for inducing 

 chemical combination. In this respect charcoal presents a 

 remarkable contrast to spongy platinum, which, though inferior 

 as an absorbent for some gaseous substances — such, for instance, 

 as ammonia, of which spongy platinum absorbs only thirty 

 volumes, while charcoal absorbs ninety — is, nevertheless, 

 immensely more effective both as an oxidiser and as a promoter 

 of chemical combination generally. As it is desirable, for some 

 purposes, while retaining the absorbent power of charcoal un- 

 impaired, to increase its oxidating influences, it struck me that 

 this important object might be easily effected by combining the 

 charcoal with minutely divided platinum. In this way a com- 

 bination is produced to which I have given the name of plat- 

 inised charcoal, which possesses the good properties of both of 

 its constituents. In order to platinise charcoal, nothing more 

 is necessary than to boil the charcoal, either in coarse powder 

 or in large pieces, in a solution of bichloride of platinum, and 

 when the charcoal has become thoroughly impregnated with the 

 platinum, which seldom requires more than ten minutes or a 

 quarter of an hoar, to heat it to redness in a closed vessel — a 

 capacious platinum crucible being very well adapted for this 

 purpose. When 150 grains of charcoal were impregnated with 

 nine grains of platinum, by the process just described, the 

 charcoal was found to have undergone no change in its external 

 appearance, though its properties had been very essentially 

 altered. ... I find that two per cent, cif platinum is sufficient 



I J. Stenhouse, " Ueb. dieentfiirbenden iind disinficirenden Eigenschaften 

 der Holzkohle, nebst Ueschreibung eines Kohle-Respirators ziir Reinigung 

 der Luft durch YWxjXL^xon," Annalen derChemie itmi Pkarmacie^ Ud. xc. 

 1854, p. 186. 



-J. Stenhouse, "On Platinised Charcoal," /£?««/. Clwm. Soc. viii. 1856, 

 p. 105. 



