28 



DISCOVERY 



tion is divided into three periods of a centurj', in each oj 

 which the development of art and literature, and the 

 particular events occurring in Uume, Milan, l-'lurcnce, and 

 Venice, ore described. 



The book is bcautiiully got up, and exceptionally well 

 illustrated. 



Introduction to Physical Chemistry. By James Walker. 

 (Macmillan &: Co., lbs. net.) 



This is tile eighth edition of a very old friend of ours, 

 and we are glad to see it in its new and up-to-date form 

 ready for the many thousands of students who are now 

 studying Physical Chemistry for the first time, or brushing 

 up their former knowledge. We know no book dealing 

 with this important subject which is more useful and 

 belptul than tliis one. To those who have never studied 

 a line of Chemistry, or done an experiment with a test- 

 tube, here is a book which opens up a new lield of reading 

 and of interest. To those who arc studying Chemistry for 

 any purpose, it is a good introduction to the physical 

 side of the subject. 



The importance of a knowledge of physical chemistry 

 in technical processes is now %videly recognized, and, as 

 a consequence, the subject is receiving more and more 

 attention both in the class-room and the laboratory, 

 and at the works. To fit workers to acquire and appreciate 

 the many important points involved, a good general 

 introduction to the whole subject is necessary, and this 

 Prof. Walker has written with the ma.ximum appeal 

 to experimental work, and the minimum to higher 

 mathematics. 



The new chapters deal with recent discoveries in 

 radio-activity, in crystal structure, and in the nature of 

 the atom, and these chapters should interest the general 

 reader most. Of one of these new pieces of work we shall 

 now give a short account. 



Until quite recently there was no special reason to 

 believe that the number of elements known to the chemist 

 was a fixed and definite one. About eighty or so different 

 elements were known, but from time to time research 

 workers announced a new element, and in some cases tiiis 

 discovery was comirmed by others. For all we knew, 

 then, there might really be a hundred or a hundred and 

 fifty elements, and the reason why we had not found 

 them all was simply that we were not clever enough. But 

 this somewhat pessimistic view is no longer tenable. 

 Hydrogen is the lightest of elements, and uranium (a rare 

 element) the heaviest, and between these two substances 

 there are ninety others only. 



The chief credit for this discovery belongs to Moseley, 

 a young O.xonian who worked in Manchester, and who was 

 killed in the war. Moseley showed, from a study of the 

 X-rays produced by different elements, that each element 

 has a number which belongs to it, and to it alone. Thus 

 the number that belongs to mercury is 80, to gold 79, 

 to platinum 78, and so on. Now, while every different 

 element has its own particular number, there are some 

 numbers for which there is no known element. There is, 

 for example, no element which, when examined by Mose- 

 ley's method, corresponds to the number 43. Here, then, 

 is an element which is still unknown, and, if Moseley's 

 work is right, the only elements which are still to be 

 discovered are those for which we have the number but 

 no corresponding substance. If hydrogen's number is 

 taken as 1, uranium's number is 92, so that there are 

 altogether 92 elements. Of course, there may be elements 

 heavier than uranium, or lighter than hydrogen ; and, 

 if so, this number 92 would be increased accordingly, but 

 until such are discovered, we may conclude there are 

 92 only. 



Of these the chemist has discovered 86, so that six alone 

 remain to be found, 'lliis is extremely creditable to the 

 chemist. Not only has he discovered nearly 94 per 

 cent, of the total number of possible elements, but 

 of the number of bodies which chemists have agreed to 

 look up)on as elements, not one was proved, by Moseley's 

 wonderful and illuminating method, to be spurious. 



Catalysis in Theory and Practice. By E. K. Rideal 

 and H. S. Taylor. (Macmillan & Co., 17s. net.) 



Catalysts are substances which change the velocity 

 of a chemical reaction without apparently themselves 

 taking part in it. Thus if a quantity of alcohol be added 

 to a quantity of acetic acid, a chemical reaction will take 

 place at a definite rate, and will continue till only a small 

 part of the original quantity of alcohol is left. By 

 repeating the experiment and adding to the mixture this 

 time a small quantity of sulphuric acid, the reaction takes 

 place at an enormously increased speed. This small 

 amount of acid has nothing to do with the cause of the 

 reaction, and no influence on the extent to which it goes. 

 Its action is simply to " speed-up " things. Such 

 accelerators, it will be realized, are of great importance 

 in industry, in the manufacture of substances, for example, 

 like indigo, ammonia, and alcohol, for there is no land 

 of chemical reaction which cannot be influenced by these 

 catalytic substances. 



The authors of this work have made a valuable compila- 

 tion of the chief phenomena associated with catalysis, 

 studied both from the practical and the theoretical side. 

 It should be a serviceable textbook for all " finished " 

 chemists. 



The World's Minerals. By L. J. Spen'CER. (Cham- 

 bers, los. 6d. net.) 

 An excellent book for the general reader by one who is 

 well qualified to write on his subject. It gives an interest- 

 ing and very readable account of the more imjiortant 

 minerals. The title rather suggests that the book deals 

 with minerals from a commercial or economic view, but 

 this is not so. The place that minerals occupy in com- 

 merce as ores of metals, as gems, and so on, is of course 

 mentioned, but the book deals chiefly with the appear- 

 ance, structure, and characteristics of the minerals them- 

 selves. More than a hundred are described. The 

 diagrams are clear, and the coloured plates, illustrating 

 the minerals, are really excellent. 



The Amaebce Living in Man. By Clifford Dobell. 

 (John Bale, Sons & Danielsson, 7s. 6d. net.) 

 This book is written by one whose chief interest in the 

 subject is from the zoological standpoint, and its appeal 

 is both to research workers in protozoology, and to doctors 

 who are making a special study of the diseases produced 

 by protozoa, especially dysentery. Knowledge concern- 

 ing the amoebaj living in man has hitherto been in a state 

 of some confusion. Mr. Dobell has set himself the task 

 of collecting the true facts of the subject, and from an 

 exhaustive study of the literature, a large personal ex- 

 perience of research, and from the exceptional oppor- 

 tunities that the war has afforded him of studying a very 

 large number of cases, he has been able to advance our 

 knowledge of these amccba: to a state approacliing 

 finality. He has put his readers on their guard against 

 many erroneous facts and conclusions which apfiear in 

 the literature and the textbooks. Medicine and Zoology 

 alike are indebted to the author for this accurate, exhaus- 

 tive, and illuminating work. It is hoped that the results 

 and conclusions given in this book by Mr. Dobell, and his 

 classification of the genera of amoebse, wiUfind a place soon 



