110 



KNOWLEDGE. 



March, 1913. 



which assume the form of lines, streams, and meandering 

 rivers, have steep banks. In certain circumstances a deeper 

 black is set up within their areas, and this black film may be 

 as little as the itrnJcTT^th of an inch in thickness. At that 

 stage one is justified in supposing that hardly more than five 

 hundred molecules are set end to end through the black film's 

 thickness. 



These divagations of the black aided by stopping and 

 starting and reversing the rotation of the drum several times, 

 are productive of a number of very beautiful patterns of 

 colour: Persian shawl patterns, spirals, and an innumerable 

 variety of groupings of colour. Perhaps nothing is more 

 striking, however, than the appearance of the surface of the 

 film when, a considerable quantity of black having been 

 allowed to grow, the drum is again rotated. The surface 

 then appears like the eye of some strange beast, with a huge 

 black pupil and a rainbow coloured iris. 



It will be comprehended, however, that beautiful qs the 

 colour patterns are they are neither the end nor the aim of 

 this instrument, which enables many striking phenomena of 



the surface tension of films, as well as of their thicknesses, to 

 be measured and examined. The black film's movements, for 

 example, provide the means by which the existence of " line 

 tension " as distinct from, surface tension of a film can be 

 made manifest. Along the margin of the black area there 

 exists a tension of the order of nrtrtrtb or Tciciith of a dyne, 

 the latter amounting roughly to the nineteenth of a grain. A 

 large number of interesting experiments illustrating the surface 

 tension can be made ; one of the most striking is that of 

 laying a loop of hair or of spun glass on the film and of then 

 treating the film within the area of the loop. The surface 

 tension immediately pulls the loop into a perfect circle. Small 

 bubbles of coal gas can be joined to the film, and in this case, 

 as in that of the spun glass hairs, the portions taken up 

 can be compared mathematically with the thicknesses of 

 the film. 



The " Rainbow Cup" is made by Messrs. John Griffin, of 

 Kingsway, to whom we are indebted for the loan of the 

 instrument from which our photograph of the film, with the 

 central black spot, was obtained. 



REVIEWS. 



CHEMISTRY. 



Leather Chemists' Pocket Book. — Edited by Professor 



H. R. Procter, M.Sc, F.I.C. 223 pages. 4 illustrations. 



6^-in. X 4j-in. 



(E. & F. N. Spon. Price 5/- net.) 



This little book is not intended to take the place of a 

 laboratory text-book, but to give in a convenient and concise 

 form outlines of analytical methods and the various data to 

 which the chemist may have occasion to refer in connection 

 with leather. Among the subjects dealt with are the analysis 

 of water, the recognition of vegetable tannins, the estimation 

 of tannin, and the analysis of oils and fats. As a rule 

 sufficient directions are given, but in some cases, where more 

 detail would have been advisable, the reader is referred to the 

 author's larger laboratory book. This is most noticeable in 

 the section dealing with oils. For example, on page 147 the 

 bromine thermal test is dismissed with the remark that it 

 conveys little information not given more satisfactorily by an 

 estimation of the iodine value. This is true ; but it omits 

 mention of the fact that the thermal method gives the result 

 in five minutes, and is applicable to most oils and fats. 



There is a useful section upon microscopical manipula- 

 tion and another upon the general methods of bacteriological 

 examination, which might with advantage be amplified. 



The book, which is well printed and excellently bound in 



leather, should be found of constant use to the class of 



chemists and students for which it is intended. „ . ., 



C. A. M. 



Radium and Radioactivity. — ByA.T. Cameron, M.A.,B.Sc. 

 185 pages. 23 illustrations. 6j-in.X5-in. 



(The Society for Promoting Christian Knowledge. Price 2/6.) 



In a book intended for readers who have little or no previous 

 chemical knowledge we look for simplicity of language and 

 clear description which assumes nothing to be known before- 

 hand. These conditions are well fulfilled in this little book, 

 which gives a most readable outline of the discovery of 

 radioactivity and the preparation and properties of radium. 

 Interesting chapters are also devoted to the production of 

 energy in radioactive changes and its bearing upon the 

 estimation of the age of the earth ; to the question of the 

 transmutation of the elements ; and to the uses of radium in 

 medicine. The book is well illustrated with photographs and 

 diagrams, and anyone who wishes to have a summary of the 

 present state of knowledge on this subject cannot do better 

 than obtain a copy. In the next edition it would be an im- 

 provement if an index were added. _ 



C. A. M. 



Lead Poisoning and Lead Absorption. — By Thomas M. 

 Legge, M.D. and Kenneth W. Goadby, M.R.C.S. (Inter- 

 national Medical Monographs). 308 pages. 4 plates and 

 numerous diagrams. 8j-in.X5j-in. 



(Edward Arnold. Price 12/6 net.) 



Though the units of the International Medical Monograph 

 series are intended chiefly for medical men and for those 

 whose work lies along the lines indicated by the titles of the 

 individual volumes, yet the subject of Lead Poisoning is one 

 of such national and international importance that the text 

 book on it by Drs. Legge and Goadby ought to find a much 

 more general audience. There is no Industrial disease which 

 has attracted so much attention to itself as lead poisoning, 

 and none in which the interests of manufacture have appeared 

 to conflict more continuously with those of the workmen. It 

 is not easy to perceive the reason of this, unless it may be 

 that in a number of the industries where lead is used women 

 are employed because the nature of the occupation does not 

 require unusual physical ability, and that the effects of lead 

 poisoning on women, who are more susceptible to it than 

 men, have shocked the philanthropic community. Otherwise 

 it would be quite easy to show that lead poisoning is the cause 

 of far fewer deaths and disabilities than arise in many other 

 occupations ; and, compared with the number of " accidents 

 of occupations," the proportion of cases of dangerous lead 

 poisoning is extremely small. The smallness of the proportion 

 becomes more marked where specific trades, such as that of 

 painting, are considered ; for, contrary to general belief, 

 painting is one of the healthiest trades. 



It is, however, when all the trades in which white lead, or 

 carbonate of lead is employed, are considered, that the number 

 of cases of lead poisoning rises ; and the reason for this is 

 largely to be assigned to the ignorance of the nature and 

 causes of lead poisoning. Dr. Goadby, who contributes the 

 bulk of the chapters relating to the pathology of the disease, 

 makes it quite clear that while lead poisoning may arise from 

 any cause by which lead is infiltrated into the system, the 

 chief danger arises when lead dust is inhaled. It is important, 

 as Dr. Legge points out, that precautions should be taken by 

 manufacturers, and should be enjoined, and as far as possible 

 made compulsory, on workmen, to prevent them swallowing 

 lead with their meals or in any other way ; but it is far more 

 important that regulations such as Dr. Legge describes and 

 prescribes for drawing off the dust by fans should be made 

 compulsory. Dr. Legge is one of H.M. Medical Inspectors 

 of factories, and it is to be hoped that the strong line he takes 

 on the necessity for the highest degree of precaution in the 

 prevention and withdrawal of lead dust by mechanical 

 processes will be emphasised by legislation. 



