82 



HARDWICKE'S SCIENCE-GOSSIP. 



dancing round a Maypole, and vastly more interesting 

 and productive. This suggestion met with a ready 

 response, and in the first year of its adoption more 

 than two million trees were planted. The Arbor-Day 

 festival soon spread far beyond the place of its origin. 

 It is now formally adopted by seventeen of the 

 United States. Even in the older northern and 

 eastern states, originally over-wooded, some parts 

 are now suffering from the ravages of axe and fire. 

 School children, headed by their teachers, proceed 

 in grand procession, with music and banners, and 

 military battalions, to plant trees by hundreds of 

 thousands in suitable spots, dedicating them in some 

 instances, as in the Authors' Grove of Eden Park, to 

 favourite authors and eminent statesmen. This 

 development among the children appears to be a 

 most promising feature of the movement. 



Trees and Climate. — The effect of trees on 

 climate has formed the subject of a recent article in 

 Petermann's " Mittheilungen " by an able Russian 

 observer, M. Wocikoff. He maintains that the 

 diminution of evaporation effected by forests is not 

 due to the lower temperature known to exist under 

 their shadow, but that the most important factor is 

 the resistance to the winds by the trees. This causes 

 the air of the forest to be changed more slowly, and 

 thus the saturated air is not so largely replaced by 

 dry air, and the moisture is less rapidly carried 

 away. The vicinity of a forest increases the summer 

 rainfall considerably, but has less effect in winter. 

 The storage of rainwater in the moss, fallen leaves 

 and herbage of the woods, affords a supply to 

 ■vegetation during dry seasons. A. striking illustra- 

 tion of this is afforded by a forest on the western 

 coast of the Caspian, where the vegetation is very 

 luxuriant, although it never rains excepting in autumn 

 and winter. M. Wocikoff has observed that forests 

 lower the temperature of the country around them. 

 In Bosnia the summer is five or six degrees cooler 

 than in Herzegovina. This difference is attributed to 

 the woods. 



Properties of Pure Zinc. — All who have to do 

 with voltaic batteries are acquainted with the troubles 

 due to "local action," and the necessity for amalga- 

 mating the zinc plates to prevent it ; and students of 

 chemistry know that ordinary zinc decomposes water 

 at its boiling heat. In a paper recently communi- 

 cated to the French Academy of Science ("Comptes 

 rendus," vol. 101, p. 1153), L. l'Hote has described 

 his experiments on pure zinc prepared by mixing 

 artificial precipitated zinc oxide (instead of the natural 

 ore) with calcined lamp-black, and distilling the 

 metallic vapour downwards. He finds that the pure 

 metal does not decompose water at boiling heat, nor 

 is it attacked by dilute sulphuric acid. If however 

 the pure zinc is melted and stirred with an iron rod, 

 it takes up from 003 to 0^05 per cent, of iron, and 



the zinc, thus rendered impure with that very small 

 quantity of iron, decomposes boiling water and dis- 

 solves in dilute sulphuric acid. Very small quantities 

 of antimony or arsenic have the same effect. 



These experiments confirm the old theory of local 

 action, which attributes it to the presence of such 

 impurities establishing local voltaic couples. 



Poisonous Confectionery. — The results of the 

 investigations of Messrs. P. Caseneuve and R. Lepine, 

 described in their communication to the French 

 Academy of Sciences ("Comptes rendus," vol. 101, 

 p. 1 167) should be widely known. They made expe- 

 riments on the action of three coal-tar yellows which 

 are used somewhat largely in colouring confectionery 

 and beverages, viz. Manchester or Martins yellow 

 (dinitronaphthol yellow) ; N. S. yellow, a sulphonic 

 derivative of the Manchester yellow, and solid yel- 

 low, a sulphonic derivative of amidoazo orthotoluenc. 

 Manchester yellow, even in small doses, was found 

 to have a strong poisonous action, producing vomit- 

 ing, diarrhoea, panting respiration, and a high 

 temperature, followed by death. N. S. yellow has 

 no appreciable poisonous action, and solid yellow is 

 similarly harmless. 



Should this " meet the eye" of any manufacturer 

 of yellow goodies or drinks, he will doubtless be 

 guided accordingly in the selection of his colouring 

 ingredient, as no such manufacturer would wilfully 

 select a poisonous colour, though he may have done 

 so without knowing its properties, as these are but 

 recent investigations, and all confectioners do not 

 read the weekly issue of the "Transactions of the 

 French Academy." 



Effects of Pressure on the Respiration of 

 Plants. — Johannsen has recently made some in- 

 teresting experiments on the effect of supplying plants 

 with oxygen, first at ordinary atmospheric pressure, 

 and then at pressures of two, four, and five atmo- 

 spheres, the activity of vegetation being measured by 

 the quantity of carbonic acid evolved. At first this 

 increases as the pressure of the oxygen increases, but 

 the increase is only temporary ; the respiration 

 gradually diminishes, more and more quickly as the 

 pressure is greater, and the plants soon die. The 

 most curious result is that which follows when the 

 plant is subjected to the action of oxygen at a high 

 pressure for short periods, and the excess of pressure 

 then removed. The plant thus restored to the 

 action of ordinary pressure shows a great increase of 

 respiration, amounting to as much as 50 per cent, in 

 the case of maize. The cause of this after-action is 

 still a mystery. 



Many of my readers have doubtless heard of the 

 " Thomas-Gilchrist process." It consists in lining 

 the Bessemer converter (the vessel in which the 

 molten pig-iron is subjected to the blast of air), with 





