January 2, 19 13] 



NATURE 



497 



Taveau (2000 francs); the Carrier^ prize to M. 

 Gisclard; the Jerome Ponti prize to Georges Rouy, 

 for his researches in systematic botany; the Leconte 

 prize between Charles Tellier (8000 francs) and M. 

 Forest (12,000 francs); the prize founded by Mme. 

 la Marquise de Laplace to Jules Adolphe Menj ; the 

 prize founded by M. Fdlix Rivot between J. A. Menj, 

 I F. G. Daval, R. G. R. Mabilleau, and R. E. 

 "BoUack. 



THE TIN MINES OF NEW SOUTH WALES.''^ 



THE more rapid growth of the demand for tin than 

 of the supply, and the disappointing failure of 

 aluminium to replace tin for many purposes for whicli 

 it was hoped to prove an efficient substitute, have led 

 to the more careful study of the tin fields of the world 

 and to an increase in the tin production by about a 

 third in the first decade of this century. Mr. J. E. 

 Carne has added a monograph on the tin mines of 

 New South Wales to the series of valuable monographs 

 with which he has enriched the economic geology of 

 Australia. 



The monograph is careful and exhaustive, and 

 shows the author's combined caution and insight. It 

 consists mostly of detailed descriptions of the tin 

 mines and milling fields, and the economic problems 

 naturally receive greater attention than the theoretical. 

 There is, however, an interesting discussion of the 

 genesis of tin ores, and the account of the mines is 

 often enriched with suggestions of general interest. 

 Economic questions are especially important in con- 

 nection with- a metal which is subject to such violent 

 fluctuations in value, for the price of tin on the London 

 market has varied since 1905 between 120I. and its pre- 

 sent price of 230!. per ton. The association of tin with 

 pegmatite veins has led to its being often claimed as 

 one of the metals most likely to be of direct igneous 

 origin ; but Mr. Carne rejects the view that the tin 

 in some granites was a primary constituent of the 

 granite, and has been collected into veins as a direct 

 differentiation product. He lays stress on the evidence 

 which points to the deposition of the tin after the 

 complete consolidation of the granite. 



The New South Wales tin deposits are, however, 

 not of the kind for which there is most to be said for 

 the igneous theory. Mr. Carne gives a list of seventy- 

 seven tin veins in New South Wales, and in sixty- 

 nine of these the tin is associated with quartz, in 

 twenty-nine with chlorite, in twentv with felspar, and 

 in only three with tourmaline. The rarity of the 

 association with tourmaline suggests that tin in New 

 South Wales is not a pneumatolvtic product. 



The first record of tin in Australia which Mr. 

 Carne accepts as authentic was in 1S24. Actual tin- 

 mining in New South Wales onlv began in 1872. 

 Since 187s the largest field— Emmaville— has yielded 

 about 52,000 tons, and the Tingha field has yielded 

 slightly less (45,500 tons). The tin mines in New 

 South Wales include both alluvial deposits and lodes. 

 The lodes belong to a type in which the distribution 

 of the tin is sporadic and the patches of ore become 

 smaller and poorer in depth. The deepest tin mine 

 in Australia is the Vulcan Mine in North Queensland, 

 which has already attained the depth of 1400 ft. 

 The deepest in New South Wales is onlv 360 ft., and 

 Mr. Carne's account of the lodes renders this fact not 

 surprising. j. ^y. G. 



1 ''The Ti-n-miinne Industry .tnd (he Di^ltibution of Tin OroJ in New 

 South \\ .1 es.' By J. E. Carne. (New Soiith Wales Department of Mines. 

 Geological Survey, Mmeral Re-<ources No. ,4.) Pp. :)7S+xx.viii plate.s+8 

 figs.-i-i4 maps and sections + ui m.ips in portfolio. (Sydney, 1911.) 



NO. 2253, VOL. go] 



OSMOTIC PRESSURE AND THE THEORY 



OF SOLUTIONS. 



A TTENTION may be directed to a paper by Prof. 



-^^~~*- A. Findlay on osmotic pressure and the theory 



of solutions, which has recently been published in 



Scientia. It has sometimes been suggested that the 



problems of osmotic pressure were solved once for all 



by van't Hoff's discovery that the gas equation 



PV = RT could be applied to solutions by substituting 



"osmotic pressure" for "gas pressure." But the 



recent exact measurements of the Earl of Berkeley 



and Mr. Hartley in England and of Morse and his 



colleagues in America have shown clearly that this 



simple equation is so restricted that it cannot in 



practice be applied with any approach to accuracy in 



the case of any of those solutions of which the osmotic 



pressures have been exactly measured. 



As Prof. Findlay points out, the first limitation to 



the equation PV = RT, when applied to solutions, is 



that the method used in deducing it only holds good 



for very dilute solutions. For stronger solutions the 



„ RT RT , 

 equation P = -—= ^ ;ir becomes 



RTf 



I -x)\ 



ii-x) 



i " V I 



-v + i.i-2 + -. 



&c. 



where V„ is the molecular volume of the solute and x 

 is the molar ratio, i.e. the ratio of the number of 

 molecules of solute to the total number of molecules 

 present. 



This equation assumes that there is no forma- 

 tion of complex molecules, no change of energy 

 or volume on mi.xing the liquid solvent and solute, 

 and that the solution is incompressible. G. N. Lewis 

 has sho\vn that it holds good in a marvellous way 

 when applied to vapour pressure measurements in 

 mixtures of propylene bromide and ethylene bromide 

 at 85°. But even this equation fails to represent with 

 any approach to accuracy the measured osmotic pres- 

 sures of cane-sugar solutions. Better results are 

 obtained by assuming the formation of a hydrate of the 

 sugar, but it is abundantly clear that van't Hoff's 

 equation is only the beginning and not the end of the 

 quantitative study of osmotic pressure, and that direct 

 measurements of this property are still of the highest 

 importance in studying the theory of solutions. 



ENGINEERING AT THE BRITISH 

 ASSOCIATION. 



A GLANCE at the proceedings of the Mechanical 

 Science Section shows that a wide range of 

 subjects was considered by the members, and, indeed, 

 much planning was required to group the papers in 

 such a way that all could be read and adequately 

 discussed, and every moment of the available time was 

 fully occupied in carrying out the longest programme 

 of recent years. 



In the course of his presidential address on the 

 Thursday morning. Prof. Barr discussed the relation of 

 the engineer to the public, both from a utilitarian and 

 an Jesthetic point of view, and by aid of many illustra- 

 tions of modern engineering achievements he again 

 and again enforced his main argument that the main- 

 tenance of a high ideal in all engineering work was 

 necessary to obtain the highest good for the greatest 

 number. 



Such illustrations as the attainment of dustless 

 roads, smokeless factories, ships, and locomotives, and 

 the abandonment of all sham decoration of engineering 

 structures gave point to an address which was free 



