June 3, 1909] 



NATURE 



595 



T/lL£JVCy. 

 The Theory of Valency. By Dr. J. Newton Friend. 

 Pp. xiv+180. (London : Longmans, Green and 

 Co., 1909.) Price 5;;. net. 



ALTHOUGH one ma}' be inclined to criticise the 

 inclusion of this volume in Sir William Ramsay's 

 well-known series of text-books of physical chemistry, 

 it is to be heartily welcomed on its own account, for 

 tliere is no English treatise, and no very recent 

 <Jcrman one, dealing- with the important subject of 

 valency. The author's exposition is careful and 

 thorough, dealing at length with the bearing of the 

 periodic law on valency, and with the numerous, and 

 in some cases fantastic, theories which profess to 

 interpret the facts of chemical combination. Dr. 

 Friend is not in a position to expound any one theory 

 of valency which commands general acceptance ; in 

 the present state of our knowledge he can only put 

 before the reader some half-dozen theories — Werner's, 

 Abegg's, Ramsay's, his own, and others — to each of 

 ■ivhich exception may be taken in one respect or 

 another. 



The theorj' of constant valency, which had difficulty 

 with the interpretation of the so-called " molecular " 

 compounds, has, of course, been abandoned, and the 

 ^authors of the newer theories vie with each other in 

 postulating valencies of all sorts and conditions — 

 *' principal," " auxiliary," " normal," " contra-," and 

 ■" latent." From the examples quoted in the book it 

 will be seen that, according to the theory adopted and 

 the particular compound under consideration, hydro- 

 gen may be regarded as mono- or di-valent, nitrogen 

 as tri-, tetra-, or penta-valent, bismuth as di-, tri-, 

 or tetra-valent, and chlorine as mono-, di-, tri-, or 

 tetra-valent. Perhaps, however, the crowning example 

 of departure from the older view of the constancy of 

 valency is found in the suggestion, which has been 

 brought forward in one quarter, that oxygen may 

 have a valency of six or even twelve! The grounds 

 on which a particular number is chosen to represent 

 the valency of a given element are, indeed, frequently 

 unconvincing, and after a perusal of Dr. Friend's 

 volume one feels how much vagueness and arbitrari- 

 ness there is about the whole subject. 



In proportion as it is found necessary to admit the 

 variability of valency, doubts arise as to the practical 

 value of a doctrine of valency. It must be borne in 

 mind that certain chemists have challenged even the 

 contention on which is based the whole structure of 

 modern organic chemistry, the contention, namely, 

 that carbon is never anything else than tetravalent. 

 The author, indeed, maintains that nothing is gained 

 hv assigning a variable valency to carbon, and prefers 

 to attribute variability to other elements, such as 

 oxygen, chlorine, and fluorine. But the argument 

 that unless the valencies of carbon and hydrogen are 

 limited to four and unity, respectively, the possibilities 

 of formulation are indefinitely multiplied is not a 

 weighty one. Equally Unconvincing is a criticism of 

 the interesting view that different grades of chemical 

 union may exist; this view is characterised, not as 

 unsound, but as " dangerous," a line of argument 



NO. 2066, VOL. 80] 



that generally bespeaks a certain weakness in the 

 defence. 



The author is probably right in concluding that the 

 solution of the valency problem is to be sought for on 

 electrical lines, but at the same time he has done well 

 to present to the reader everything which has a bear- 

 ing on the subject, as, for instance, the new theory 

 of Barlow and Pope, who regard valency from a non- 

 electrical standpoint. It is only by a full and faithful 

 presentation of conflicting facts and theories that the 

 actual state of the problem can be rightiv understood. 



J. C. P. 



ECONOMIC GEOLOGY IN BRITISH GUIANA 

 AND SOUTH AFRICA. 



(1) The Geology of the Goldfields of British Guiana. 

 By J. B. Harrison. With Historical, Geographical, 

 and other Chapters by F. Fowler and C. W. .Ander- 

 son. Pp. ix-t-320. (London : Dulau and Co., 1908.) 



(2) The Ore Deposits of South Africa. By J. P. John- 

 son. Part i.. Base Metals. Pp. iv+6i. (London : 

 Crosby Lockwood and Son, 1908.) Price 5^. net. 



(i) "T^HE history of gold mining in British Guiana 

 -L dates from 1720, when an expedition was dis- 

 patched to Berbice in quest of gold. Further unsuccess- 

 ful attempts were made at intervals, and modern min- 

 ing in the colony dates from 1863. The first important 

 success was gained in 1886, and mining regulations 

 were enacted. The efforts were again commercially 

 unprofitable, but some alluvial mining has always 

 since been carried on. Quartz mining first attracted 

 much attention in 1890, but none of the attempts was 

 then commercially successful, because, Mr. Harrison 

 tells us, the work was conducted recklessly, mills being 

 erected before the mines had been adequately pro- 

 spected. .-\t length, in 1903, more judicious manage- 

 rncnt was rewarded by success, and the mines on the 

 Puruni River added British Guiana to the profitable 

 gold-fields of the British Empire. The greatest yield 

 was 138,000 ounces, in 1893-4, since when the yield 

 has been slowly falling, until the output in 1906-7 was 

 85,000 ounces. 



The first important contribution to the geology of 

 British Guiana was the memoir by Brown and 

 Sawkins, published in 1875 by the British Geological 

 Survey. Since then various additions have been made 

 to its mining literature, and an important series of 

 contributions to its pure geology by its Government 

 geologist, Mr. J. B. Harrison. He has now issued a 

 valuable handbook to the geology of the colony, to 

 which chapters on the history and geography are con- 

 tributed by Messrs. Fowler and Anderson. 



Mr. Harrison's monograph includes a detailed ac- 

 count of the geology and petrography .of the country, 

 which consists of a foundation of .Archcean rocks, with 

 intrusive series of granites and diabases, covered by 

 a series of sandstones apparently of .Algonkian age. 

 Intrusive diabase and other basic igneous rocks are 

 widely distributed ; they are perhaps the most interest- 

 ing rocks in the country, and, according to Mr. 

 Harrison, are the source of most of the placer gold. 

 The origin of the gold is discussed in an interestinf 



