240 



NATURE 



[July 25, 1872 



OUR BOOK SHELF 



Expt:yimni/ii/ Clwrnislrv. Founded on the work of Ur. 



J. A. Stockhardl. By C. W. Heaton, F.C.S. (London : 



Bell and Daldy.) 

 Manv students of chemistry have had reason to be grate- 

 ful to Dr. Stockhardt for his work on the Principles of 

 Chemistry. For many years it was almost the only re- 

 presentative of its class ; forit enabled students to acquire 

 a considerable and useful knowledge of chemistry by 

 teaching them to work experimentally at the subject, in- 

 stead of merely reading about it. One of the great merits 

 of his book, and which also belongs to the volume now 

 under consideration, is that, although the number of ex- 

 periments described is large and well selected, yet they do 

 not necessarily require anything but extremely simple 

 apparatus. This work, therefore, we believe will be found 

 useful to a numerous and increasing class of students, 

 who, though hindered by limited means and want of 

 opportunity, wish to acquire some knowledge of chemistry. 



The work is divided into four parts : the first treating 

 of the General Principles ; the second on the non-metallic 

 elements ; the third on the metals ; and the fourth 011 

 Organic Chemistry. With the commencement of Part 1. 

 we confessed we were rather startled. The student is at 

 once taken into a sort of half discussion as to whether 

 matter has any existence or not, and the conclusion come 

 to is that the problem will probably be for ever in dispute. 

 This to a young beginner would scarcely impress him with 

 the definite and unchangeable facts of Physical and 

 Chemical Science. 



Part I., on General Principles, is, we think, too advanced 

 and complicated for the class of students by whom it is 

 likely to be used. In fact, we should imagine that a 

 student commencing the book and working by himself 

 would find this part very up-hill work. For instance, 

 before having studied any of the properties of the elements, 

 he has to become acquainted with the various methods of 

 fixing the atomic weights, the classification by atomicity, 

 variations of atomicity, isomorphism, &c. In our opinion 

 it would be almost better for a student to commence at 

 the second part, that is, with the study of the non-metallic 

 elements, in doing this, however, some little reference 

 to Part 1. would be necessary for the explanation of the 

 meaning of symbols, &c., and he might then return to the 

 complete study of Part I. The first part contains a number 

 of definitions, several of which are not so good as they 

 might be. It is said, for instance, that in a mixture the 

 properties of the different ingredients arc always percep- 

 tible. Gunpowder is given as an instance of a mixture ; 

 but in this the yellow colour of the sulphur and the white 

 colour of the potassic nitrate are certainly not perceptible. 

 Again, the definition of an acid is the following: — "An 

 acid is composed of hydrogen with one of those radicles 

 (p. 86) which are called acid radicles. The hydrogen can 

 be replaced by metals, in which case one of the compounds 

 called salts is formed. Acids redden litmus, and are com- 

 monly sour." On referring to p. 85, the exact definition of an 

 acid radicle is not to be found ; it is, as nearly as can be ex- 

 pressed, according to the author's ideas, the residue of an 

 acid from which the hydrogen is abstracted. The de- 

 finition of an acid, then, seems to be a body that contains 

 hydrogen replaceable by metals, which is sometimes 

 sour and reddens litmus. Surely definitions of a rather 

 more definite and complete character might have been 

 selected. Further in the book (p. 29S) the author thinks 

 it is often more convenient to regard the inorganic acids 

 as hydrates, that is containing the radicle hydroxyl 

 (HO), and of course uses this radicle throughout the 

 organic acids. If the student accepts the two definitions 

 he will have a double set of radicles, which would pro- 

 bably lead to much confusion. 



The second part of the book is devoted to the non- 

 metallic elements, the properties of which are studied 



by means of simple and instructive experiments, which 

 are generally well described; the same is also the case 

 with the next part, on the metals, and we then pass to the 

 organic section of the work. 



The field of Organic Chemistry is now so large that in 

 the small space here devoted to it, a brief description only 

 can be given of some of the more important compounds. 

 It is also difficult in this section to arrange experiments 

 which can easily be performed by students. It is thus 

 necessary to confine the description of such classes ot 

 substances as the alcohols, the aldehydes, acids, haloid 

 ethers, &c., to a very few pages. The arrangement, too, 

 is peculiar, the experimental part of the organic work 

 beginning with the study of cellulin, starch, sugar, &c., 

 passing afterwards to the study of the more simple com- 

 pounds, such as ethylic alcohol, acetic acid, &c., — which 

 seems rather like reversing the order of things. In a 

 subsequent edition it would, perhaps, be bitter to adopt 

 the modern system of classification, which would pro- 

 bably give the student a far better and more comprehen- 

 sive knowledge of the subject. The book is, on the 

 whole, one which, with a little reservation, can be safely 

 recommended to students who wish to study Chemistry in 

 the experimental way rather than simply to cram it up by 

 reading. There is some room for improvement in the 

 woodcuts, which in some instances are not artistic, and 

 might be replaced by engravings of more modern and 

 convenient apparatus. 



LETTERS TO THE EDITOR 



[ The Editor docs not hold himself responsible for opinions expressed 

 by his correspondents. No notice is taken of anonymous 

 communications. ] 



Ocean Currents 



I HAVE just read Mr. Ferrel's letter (Nature, June 13), in 

 which he refers to mine of April 25, and the proof therein ad- 

 duced by me to show the physical impossibility of oceanic circu- 

 l.atioii being the result of differences of specific gravity. Unless 

 Mr. Fenel means (and I hardly think he does) that six foot- 

 pounds of energy can perform 9,025 foot-pounds of work pro- 

 vided only sufficient time be allowed in which to perform that 

 work, then I do not suppose there is any reader who may have 

 glanced over my article on the subject who will not readily admit 

 that Mr. Ferrel's reasoning has no direct bearing whatever on my 

 argument. 



The slope from the equator to latitude 60° is six feet. The 

 total amount of work which gravity can perform upon a pound 

 of water in carrying it down this slope is, of course, six foot- 

 pounds. And this holds equally true whether the pound of 

 water moves down the slope in, say one month, or takes 1,000 

 years to perform the journey ; because the amount of work per- 

 formed by gravity depends not upon the time whicli a body takes 

 in descending, but upon the distance through which the body 

 descends. In the present case six feet is the distance, conse- 

 quently six foot-pounds is the amount of work performed upon 

 tlie pound of water in its passage down the slope from the equa- 

 tor to lat. 60°. 



Mr. Ferrel assumes that the velocity of the general movement 

 of the water advocated by Dr. Carpenter does not exceed one 

 mile per day, and that consequently the resistance to motion must 

 be small. IjndLiubtedly the slower the motion the less the resist- 

 ance ; but so far as the argument under consideration is concerned, 

 it is a matter of indifference whether we suppose the velocity 

 of the water to be a mile per minute, a mile per day, or only a 

 mile in 1,000,000 years ; because it is found that when the water 

 from the equatorial regions reaches, say, lat. 60', it, as a matter 

 of fact, is not moving eastwards relatively to the earth's surface 

 with a velocity of several hundreds of feet per second, but with a 

 velocity of only a few feet per second, perhaps not more than 

 three feet at the utmost. In this case the water has lost 760 feet 

 per second of velocity which it possessed when it left the equator. 

 Kach pound of water has therefore lost 9,025 foot pounds of 

 energy. What has become of all this energy ? It has all been 

 ctiiisumed in overcoming resistance during the motion of the 

 water from the eiiuator to lat. 60°. But, be it observed, it has 



