20 



NATURE 



[May 4, 1893. 



to platinise charcoal for most purposes. Charcoal containing 

 this small amount of platinum causes a mixture of oxygen and 

 hydrogen to combine perfectly in about a quarter of an hour, 

 and this is the strength of platinised charcoal that seems best 

 adapted for charcoal disinfectant respirators .... Platinised 

 charcoal seems likely to admit of ■various useful applications ; 

 one of the most obvious of these is its excellent adaptability to 

 air-filters and respirators for disinfectant purposes." So much 

 lor the properties of charcoal. My colleague, Prof. Corfu Id, 

 of University College, assures me that " charcoal is now very 

 little used for the purification of foul air. It was formerly em- 

 ployed in sewer ventilation, but it was found that it soon 

 became damp and was then useless. 



I was anxious to test Mr. Toope's application, and to see how 

 far the sulphurous acid of fog might be absorbed as the foggy 

 air passed through the charcoal trays. Mr. Toope, therefore, at 

 my request, furnished me with a sample box, so arranged that 1 

 could aspirate air throught it. I was frequently in the habit of 

 aspirating fog through 25 c.c. of potassium permanganate of such 

 strength that the aspiration of 2i to 3 cubic feet of an 

 ordinary fog would decolorise the solution, whilst li to 2 cubic 

 feet sufficed in the case of very severe fogs- I have repeatedly 

 aspirated air, in all sorts of foggy weather, through the charcoal 

 box. But even in the most severe instances I have never noticed 

 anything more than a slight discoloration of the permanganate 

 after the passage of as [much as 25 cubic feet. I have also 

 placed the box in a chamber into which an atmosphere of strong 

 sulphurous acid was introduced- — an atmosphere of which -^t, 

 cubic foot sufficed to entirely decolorise the permanganate. When 

 drawn through the charcoal, however, 3 cubic feet could be 

 drawn without perceptibly affecting the colour of the fluid. 

 When kept in an atmosphere of strong sulphurous acid the 

 charcoal becomes in time charged, and, for the time being, in- 

 capable of further absorption. In this charged condition I left 

 the box for some eight or ten weeks, and found that by the ex- 

 piration of that time it was as good an absorber as ever. With 

 ordinary fogs there seems little fear of anything of this kind 

 happening ; nor have I observed any tendency in the charcoal 

 10 get choked in this way in long spells of foggy weather. That 

 other impurities are also absorbed I have no proof, though 

 I consider it most probable. 



In order to demonstrate the advantages of his system to horti- 

 culturists, Mr. Toope has constructed a small conservatory at 

 his offices in Stepney. Here he cultivates, in an unfavourable 

 atmospheric environment, a collection of orchids and other 

 -tove plants. The results I regard as distinctly favourable to 

 his system, though they were not by any means convincing. 

 This arose, not necessarily, from any defect in the filtering 

 apparatus, but rather from faulty cultural methods. Mr. Toope 

 is a busy man, and the charge of his plants falls to the lot of 

 others. Many plants very sensitive to atmospheric impurities, 

 which he obtained at my suggestion, received a severe check in 

 transit before they reached him. Others, again, which he raised 

 from seed for observation were liable to neglect from time to 

 time. So that a casual visitor unacquainted with the facts might 

 easily have carried a«ay an unfavourable impression of the 

 utility of the system. But, taking everything into consideration, 

 I incline to take a distinctly favourable view of charcoal as a 

 filter for contaminated air — so much so that I believe it might 

 be adopted with advantage by our urban cultivators. The 

 charcoal undoubtedly absorbs a very large percentage of the 

 sulphurous acid, and this can only have a beneficial result. The 

 adoption of the system to old plant-houses does not involve any 

 very serious reconstruction. The charcoal-boxes and exhaust-caps 

 are easily fixed ; whilst it is only very old and leaky houses that 

 cannot be rendered reasonably airtight. In this way the toxic 

 action of fog will, lam confident, be mitigated to an appreciable 

 extent. 



As regards cultural precautions to be observed in foggy 

 weather, experience indicates that a low temperature and a 

 moist atmosphere are conducive to the well-being of the plants, 

 though ihey, of course, afford no absolute protection. This 

 aspect of the question has been clearly put in the following note 

 from the Carchneis' Chronicle by Mr. Thiselton-Dyer, which I 

 venture to quote in extenso : — 



"The Kew practice of keeping the winter temperature of the 

 houses as low as we dare is based on the result of practical ex- 

 perience. I do not dogmatise for other people who want to 

 solve their own problems, and find out what is best for their 

 particular requirements for themselves. But, as Mr. Henslow 



NO. 1227. VOL. 48] 



has pointed out, the theory of the subject has been stated clearly 

 by Lindley ; and it may not be amiss to quote a few words from 

 his classical ' Theory and Practice of Horticulture ' on the subject. 



" The point of the whole matter is that in winter, with a low 

 external temperature and nocturnal radiation, it is practically 

 impossible, in a large glasshouse, to keep the internal atmo- 

 sphere humid with a high temperature. I quote from Lindley, 

 p. 207 : — 



" ' Another source of dryness is the coldness of the glass roof, 

 especially in cold weather, when its temperature is lowered by 

 the external air, in consequence of which the moisture of the 

 artificial atmosphere is precipitated upon the inside of the glass, 

 whence it runs down in the form of "drip." ' 



" Again, ' It is evident that the mode of preventing this dry- 

 ing of the air by the cold surface of a glass roof will be either 

 by raising the temperature of the glass, which can only be 

 effected by drawing a covering of some kind over our houses at 

 night, so as to intercept radiation, or by double glass sashes ; or 

 else by keeping the temperature of the air as low as possible, 

 consistently with the safety of the plants, and so diminishing the 

 difference between the temperature of the external and internal 

 air.' 



" In large glasshouses it is obviously impracticable to adopt 

 the expedients which Lindley suggests. The only alternative is 

 to do what we do at Kew — lower the temperature as much as 

 possible, and so secure the highest possible relative humidity, 

 with the double result of keeping the plants at rest and of check- 

 ing their desiccation." 



I hope shortly to issue a third report dealing with thii fog 

 question from its purely local aspect, including lists of plants 

 which suffer and the area around the metropolis to which these 

 special injuries are observed. 



In due lime I shall prepare a very detailed report or mono- 

 graph, illustrated from the large seiies of drawings which 1 have 

 accumulated. It will only be in such a detailed monograph 

 ihat I shall be able to justify many of ihe .';tatements which 

 occur in the bcdy of this, the second report. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — Mr. Perdlebury, of St. John's College, has 

 been reappointed a University Lecturer in Mathematics, for 

 five years, fiom Lady Day 1893. Prof. Macalisler, President of 

 the Anthropological Institute, has given three lectures this term 

 on Physical Anthropology as follows : April 27, " The Races of 

 Australia ; " April 29, "The Ancient Egyptians ; " May 2, "The 

 Prehistoric Races of Britain." 



The Professor of Pathology announces a practical course of 

 instruction in bacteriology, to be given during the ensuing long 

 vacation, by Prof. Adami, Dr. A. A. Kanthack, Dr. Wesbrook, 

 and Mr. L. Cobbett. 



Mr. J. V. Buchanan, F.R.S., will deliver the second part of 

 his course of lectures on oceanography at noon on Tuesdays 

 during the present term. 



The Sflniih's Prizes are this year awarded to three mathema- 

 ticians, who are bracketed, namely, C. E. Cullis, B.A-, of 

 Caiu.=, for an tssay "On the Motion of Perforated Solids in an 

 Incompressible Liquid"; D. B. Mair, B.A., "On the Con- 

 tinuous Deformation of Surfaces" ; and R. H. D. Mayall, 

 B.A., of Sidney, "On Certain Forms of Current Sheets." 

 Mr. Mair and Mr. Mayall were bracketed Second Wranglers, 

 and Mr. Cullis bracketed Sevenih Wrarglerin the Mathematical 

 Tripos of 1 89 1. 



SCIENTIFIC SERIAL. 

 American Meteorological Jotnnal, April. — Ice columns in 

 gravelly soil, by Prof. C. Abbe. During spring and autumn 

 little slender columns of ice are found at the surface of 

 gravelly toils in moist places after a clear cool night, and 

 the surface layer is found to be raised up an inch or two. 

 Prof. Abbe offers an explanation of the phenomenon, which 

 diffets ficm that given by Leconte and others. The subject 

 is of some importance to agiicultural soil physics. — The 

 diurnal variations of barometiic pressure, by C. J. Lyons, of 

 the Hawaiian Weather Bureau. The author takes into account 

 the ex] anticn of the air loih upwards and laterally, caused 



