222 



NA TURE 



[August i i, 1923 



comprises the remainder of the country under review, 

 extending northwards to include a strip of Southern 

 Rhodesia and the southern part of Portuguese East 

 Africa. There are also chapters on the physical 

 features and climate, on methods of survey, with 

 instructions to collectors and observers, and a biblio- 

 graphy. Dr. Marloth writes on the use of the common 

 names of plants, which, though sometimes not trust- 

 worthy, may be very useful if accepted with care and 

 discretion. 



The Report of the Canadian Arctic Expedition 

 191 3-18 (vol. v., Botany, part B) by Theo. Holm 

 (*' Contributions to the Morphology, Synonymy, and 

 Geographical Distribution of Arctic Plants ") contains 

 some interesting notes on the methods of growth 

 and reproduction, manner of hibernation and other 

 characteristics, of many of the species collected by 

 the expedition. Certain biological types are absent 

 from the polar regions ; there are no climbers, no 

 saprophytes, and no true parasites. Pedicularis alone 

 represents the partial parasites. The great majority 

 of the herbs are perennial. The chapter on geo- 

 graphical distribution contains a table showing the 

 general distribution of the species collected, which 

 indicates that the vegetation of the north coast of 

 America is composed of types from various parts of 

 the northern hemisphere of both worlds, and bears out 

 the view that the present arctic flora consists to a 

 great extent of remnants of the alpine floras of the 

 tertiary period. These alpine floras were principally 

 those of the European Alps, Altai and Baikal, the 

 Rocky Mountains, and perhaps also Caucasus and 

 Scandinavia. 



Memoir 126,, issued by the Canadian Depart- 

 ment of Mines ("A Botanical Exploration of the 

 North Shore of the Gulf of St. Lawrence," by Harold 



St. John), includes an annotated list of all the flower- 

 ing plants and ferns recorded from this area, in all 

 622 species, and some discussion of the soil-relations 

 of the various ecological plant groups. A comparison 

 of the habitats of 103 species along the north shore of 

 the gulf and in other regions, especially Europe, 

 indicates an agreement the more surprising consider- 

 ing that the data have been gathered by many 

 botanists at widely separated places and times. Mr. 

 St. John also gives an account of botanical explora- 

 tion in the same area previous to his own visit in 

 1915- 



" A Flora of the Shetlands," by Dr. G. C. Druce, 

 forms a supplement to the recently issued rep>ort of 

 the Botanical Society and Exchange Club for 1921. 

 The total land surface of the islands, which number 

 more than a hundred, is rather more than that of the 

 Faroes, but the hills are lower and lack the marked 

 alpine element found in the flora of the Faroes. The 

 population of the islands since the glacial period has 

 been explained alternatively by the existence of a 

 land-bridge and immigration by means of birds, 

 ocean-currents, and wind. The latter view would 

 seem the more probable. There are practically no 

 endemic species, and many species found in the 

 islands are extremely local. The flowering plants and 

 ferns number about 500 species, 59 of which have 

 probably been introduced by man. Dr. Druce 

 remarks on the size and brilliancy of some of the 

 flowers, and suggests the feeble intensity of sunlight 

 as a cause ; clouds are absent from the sky only on 

 a few days in the year, and mists are verj' frequent. 

 There are few Lepidoptera ; many plants are self- 

 pollinated, and others never ripen seed. The flora 

 approximates most closely to that of the Faroes, and 

 is distinctly poorer than that of the Orkneys. 



The Gas Industry and Coal Conservation. 



THE annual coal output of Great Britain is about 

 300 million tons, of which approximately 20 

 million tons are carbonised annually in gasworks for 

 the production of towns' gas. The reserves of 

 British coal within 4000 feet of the surface were 

 estimated in 1915 at 197,000 million tons. In some- 

 thing like 600 years the coal measures of this country 

 will be probably exhausted, and what then ? The 

 world's scramble for oil to-day indicates that a coal age 

 will certainly not be succeeded by an oil age. Possibly 

 we shall have learnt to tap atomic sources of energy, 

 or perhaps the earth's internal heat may be available 

 to us, after the manner suggested by Sir Charles 

 Parsons. 



There are those who hold that how posterity will 

 provide itself with supplies of energy is posterity's 

 own concern and need cause us no uneasiness ; the 

 gas industry takes a wider view. Its processes are 

 continually being examined with a view to effecting 

 greater conservation of coal. In a Report to the 

 Institution of Gas Engineers in 1919, by Sir Dugald 

 Clerk, Profs. Cobb and Smithells, it is shown that the 

 thermal efficiency of the process of carbonisation of coal 

 achieved to-day in the United Kingdom is from 70 to 

 80 per cent., and that debiting gas with the whole of 

 the thermal losses of the process and allowing for 

 transmission and other losses, at least 45 per cent, of 

 the heat of the coal carbonised is delivered to the 

 consumer as inflammable gas. This is a high figure, 

 but it can be considerably improved upon if the heat 

 content of the coke produced, amounting to more than 

 10 cwt. per ton of coal carbonised, is made available to 

 the consumer by the conversion of the coke into gas. 

 The Gas Regulation Act, 1920, had this point among 

 others in view when it conferred upon individual gas 



NO. 2806, VOL. 112] 



undertakings freedom to declare the calorific value of 

 the gas each would supplj'. As there appears to be 

 considerable confusion of thought on this matter, per- 

 haps it were as well if we explained briefly the nature 

 of the component mixtures constituting towns' gas. 



" We see all sights from Pole to Pole, 

 And glance and nod and bustle by, 

 And never once possess our soul. 

 Before we die." 



Blue water gas is produced from coke by passing air 

 and steam alternately over an incandescent bed of 

 "this fuel. Its calorific value is about 300 B.Th.U. per 

 cubic foot, and its composition is approximately 

 represented by COj, 4*5 per cent. ; CO, 43 per cent. ; 

 Hj, 48 per cent. ; methane, 0-5 per cent., and nitrogen, 

 4 per cent. Sometimes this gas is mixed direct with 

 coal gas in a towns' gas supply, a customar}- propor- 

 tion being 80 per cent, of coal gas and 20 per cent, of 

 water gas, the percentage of carbon monoxide in the 

 resulting mixture being approximately 14 per cent, 

 and the resulting calorific value about 500 B.Th.U. 

 per cubic foot. More commonly, however, car- 

 buretted water gas, produced by enriching blue water 

 gas with gaseous hydrocarbons derived by " crack- « 

 ing " various oils at high temperatures, is used for " 

 this purpose. The carbon monoxide content of 

 carburetted water gas is on the average about 27 per 

 cent., and, when admixed to the extent of about 

 20 per cent, with straight coal gas, a mixture contain- 

 ing approximately 11 per cent of carbon monoxide 

 results. Straight coal gas produced by the high 

 temperature distillation of coal has a calorific value 

 of about 560 B.Th.U. per cubic foot and contains 

 about 7 per cent, of carbon monoxide. 



