436 



NA TURE 



\^April I, 1875 



and the frontier of Sikkim. The better class of teas cost at 

 Lhassa about two rupees per pound, but are seldom imported. 

 It is estimated that the annual supply of tea to Thibet amounts to 

 about six millions of pounds, producing an income of not less 

 than 300,000/. 



A NEW source of caoutchouc reaches us from Burmah, a 

 description of which has been given in a pamphlet published in 

 Rangoon. The plant yielding this caoutchouc is the Chavan- 

 nesia escnhnta, a creeper belonging to the natural order Apocy- 

 nei:e, an order which includes the Borneo rubber plant Urccola 

 dastica, the African rubber plants Laiidolphia spp., as well as 

 oiher genera yielding milky juices. The plant, which is common 

 in the Burmese forests, is said to be cultivated by the natives for 

 the sake of its fruit, which has an agreeable acid tasle. It 

 comes into season when tamarinds are not procurable, and finds 

 a ready sale at Rangoon, at an anna per bunch of ten fruits. 

 The milk is said to coagulate more readily than that of Finis 

 elisika, and to be purer and better for most purposes for which 

 rubber is used. 



Ukder the title of " Contributions to the Fossil Flora of the 

 Western Territories, U.S., Part I. The Cretaceous Flora, by 

 Prof. Lesquereux," Prof. Hayden haspirblished the sixth volume 

 of the series of final reports of the United Stales Geological 

 Survey of the Territories. The work is in quarto, and embraces 

 136 pages an 1 thirty plates. Very nuny n ew species are figured 

 and described. The work covers all the known species of the 

 Dakota group, and constitutes an important starting-point for 

 similar monographs of other divisions of the fossil plants of 

 America. Prof Lssquereux considers the surface and strati- 

 graphical distribution of the species. In accordance with Dr. 

 Ilayden's views, the author finds the group to be of marine 

 origin, as shown by the occurrence of various species of marine 

 molluscs. Prof. Lesqirereux is not prepared to commit liimself 

 ia regard to the correlaton of the flora of the Dakota group with 

 that of subsequent geological epochs and their identity, pre- 

 ferring to wait the gathering and examination of other series, 

 lie, however, states that this flora, without affinily with any 

 preceding vegetable types, without relation to the flora of the 

 Lower Tertiary of the United States, and with scarcely any forms 

 re.''erable to species known from coeval formations in Europe, 

 presents, as a whole, a renrarkable and, as yet, unexplained case 

 o! i.o'.ation. 



The cultivation of the tobacco plant in Algeria has been car- 

 ried out very successfully, the soil and climate of that country 

 being well suited to the growth of the plant. In 1874 no less 

 than 4,850,00 kilogrammes, or over 9,700,000 lbs., we.e pro- 

 duced and passed thro ugh the State warehouses. The value of 

 this crop was 141,224/., or nearly double th»t of 1S73. The 

 experiment — though it is no longer merely an exp erimcnt, but a 

 practical industry — has been carried on since 1847, and during 

 the past twenty-seven years about 140,000,000 lbs. weight of 

 tobacco has been produc ed and sold. 



It is stated that the Italian Government, foUowin g the course 

 it his already adopted on previous occasions, will gratuitously 

 distribute this year 5, coo plants of the Eiualypliis globulus, for 

 cultivation in the Agro Romano, especially in the spot infected 

 by malaria. 



The additions to the Zoological Society's Gardens during the 

 past week include an African Civet Cat ( ? Vt'tvvrt iVtr/A!), pre- 

 sented by the Karl of Harrington ; an Australian Monitor 

 (Monitor gouldi), presented by Dr. Pardee ; three Black-necked 

 Storks {Xenorliynchus australis) from Malacca, purchased ; a 

 Blue-faced Green Amazon (Cliiysolis bouqiidi) from St. Lucia; 

 two Yellow-fronted Amazons (Chrysalis ochroccphala') and a 

 Brown-throated Conure (Coimrus aniginosus) from S. America, 

 deposited. 



ACCIDENTAL EXPLOSIONS * 



T 



HE term "accident," applied in its strict sense to disasters 

 caused by explosions, would imply that these were due to 

 some circumstance, or combination of circumstances, entirely 

 unforeseen, and that they were consequently unpreventible. An 

 explosion which occurs during the prepai'ation or investigation 

 of a compound the explosive nature of which is as yet unknown 

 may be purely accidental, but if, after the properties of the sub- 

 stance have been thoroughly ascertained and made known, an 

 explosion occurs during its production, by some person who has 

 not properly made himself acquainted with or has neglected in 

 some point or other those conditions essential to its production 

 with safety, the knowledge of which is within his reach, the 

 term "accidental" can certainly not be properly applied to it, 

 although in all probability it would be so designated popularly, 

 and even by those entrusted on behalf of the public with the 

 investigation of its origin and results. 



In the present discourse the definition "accidental" is ac- 

 cepted in the loose sense in which it is popularly applied to 

 explosions, with the object of examining into the nature and 

 causes of such explosions, and, if possible, of indicating direc- 

 tions in which there may be hope of successful efforts being made 

 for reducing the frequency of their occurrence. 



The phenomena attendant upon an explosion are generally 

 due to the sudden or very rapid expansion of matter, accom- 

 panied in most instances by its change of state from solid or 

 liquid to gas or vapour. The most simple classes of explosions 

 are those caused by the sudden yielding to force, exerted from 

 within, of receptacles in which a gas is imprisoned in a highly 

 compressed condition, or a liquid has been raised to a temperature 

 greatly exceeding that at which its molecules have a tendency to 

 fly asunder or to assume the state of vapour or gas. The strength 

 or elasticity of the envelope which confines them suddenly 

 yielding to pressure, the liquid passes with gi'eat rapidity into 

 vapour, violently dispUcing by this sudden expansion the sur- 

 rounding air and any other obstacles opposed to the expanding 

 molecules. 



Similar explosive effects less simple in their origin are brought 

 about by the sudden development of chemical activity in mix- 

 tures of gases or vapours, of solids and gases, or of solids only, 

 or in chemical compounds of unstable character, the result in all 

 such instances being the development of intense heat and the 

 sudden or very rapid and great expansion of nratter. 



Examples of the most simple class of explosions are the sudden 

 failure in strength at some particular point, or generally, of the 

 material composing a vessel in which a gas has either been lique- 

 fied or highly compressed. Accidental explosions of this cha- 

 racter take place chiefly, and happily not very frequently, in the 

 laboratory or lecture-room, yet instances occasionally occur of 

 disastrous explosions resulting from such causes in manufacturing 

 ojieration:, or in the practical application of compressed air or 

 other gases. The most recent illustration of a serious accidental 

 explosion of this kind is that which occurred in the Arsenal at 

 Woolv/icH in January 1874, with the air-chanrber of a White- 

 head, or Fish torpedo, when one man lost his life and several 

 were seriously injured. In this instance some part of the soft 

 steel diaphragm closing the chamber in which the motive power 

 of this self-propellant torpedo (air) was imprisoned under a 

 pressure of about 800 lb. on the square inch, suddenly yielded to . 

 the efforts of the gas to return to its normal condition. 



Other explosions of this class, which are of more than weekly 

 occurrence, and but too frequently result not merely in destruc- 

 tion of property, but in more or less serioas loss of life, are due 

 to the bursting of boilers at factories, mines, and collieries, to 

 say nothing of those which occur in buildings, in connection 

 with heating appliances and with kitchen ranges, and bath- or 

 other heating-arrangements. The explosion of a boiler may 

 arise either from an exceptionally rapid development of steaiu 

 or from an absence, or failure in the proper operation, of appli- 

 ances for relieving the pressure in a boiler, by permitting the 

 escape of steam and giving warning when the pressure begins to 

 exceed that of safety. But by far the chief causes of boiler 

 explosions are defects in their construction or repair, and the 

 reduction in thickness of the metal in parts by corrosion or 

 oxidation, internally and externally, from long use, and neglect 

 of proper measures for periodically cleaning the boilers. 



The accidents due directly to the deposits formed from water 

 in boilers have been very greatly diminished of late years by the 



* Aljstract of a lecture delivered at the Royal Institution, March is, 

 by Prof. F. A. Abel, F.R.S. 



