512 



NATURE 



[September 29, 1S92 



two parts. The experiments start off with tha connsnly 

 occurring phenomena of combustion, and lead up to the 

 laws of chemical combination, the determination of 

 chemical equivalents, vapour densities, &c. 



Part II. consists of qualitative and quantitative ana- 

 lysis taken together, no attempt being made to separate 

 the two. The results of the experiments are here care- 

 fully withheld from the student, and are given in the Key. 

 A useful table for the detection of the positive radicles 

 is published separately, and may be used in connection 

 with this part. 



The book can be recommended as a trustworthy one, 

 and, apart from the novelty of the system adopted, 

 as a storehouse of knowledge useful to the chemist, it 

 will be appreciated by many a teacher. 



The problems are actual examples met with in the 

 laboratory, and appear to be free from the artificial 

 exercises so common in text-books. It is also noteworthy 

 that they, as well as the lectures, are concerned to a con- 

 siderable extent with the energy changes as well as with 

 the material changes which constitute chemical ph eno- 

 mena. 



In glancing at the tables of physical constants to be 

 found as answers in the Key, it is frequently noticeable 

 that these magnitudes are given to an accuracy which is 

 altogether fictitious. For example, to express heats of 

 vaporization or absorption coefficients to one part in 

 thousands of millions, or to give a boiling point such as 

 that of bromine to one thousandth of a degree Fahren- 

 heit, tends to create an erroneous idea of the accuracy 

 with which such determinations can be made. In one or 

 two instances the information is not quite up to date. 

 Hydrofluoric acid, for instance, is still formulated H^Fg, 

 and Bunsen's values for the absorption coefficients of hy- 

 drogen and oxygen are still given, although they have bee n 

 superseded by the observations of Winkler and Timo- 

 f^ef. Van der Waals's work might have been included 

 in the otherwise serviceable account of the kinetic theory 

 of gases, and it is somewhat unfortunate that the author 

 insists upon the narrow view that specific gravity has no 

 other meaning than that which is perhaps more correctly 

 attributed to relative density. 



The printing and the woodcuts are hardly up to the 

 standard usually attained in books of this kind. 



J. W. R. 



OUR BOOK SHELF. 

 Die Pflatize in ihren Beziehungen zum Eisen. Von Dr . 

 Hans Molisch. Iron in its Relations to Plant-life . 

 8vo, 119 pages, with one coloured plate. (Jena : 

 Gustav Fischer, 1892.) 



An interesting essay on the presence, function, and form 

 of iron in plants, embodying the results of previous in- 

 vestigators and of the author's experiments and researches 

 extending over several years. Though the outcome of 

 much labour. Dr. Molisch regards it as preliminary to 

 more extended inquiries, and the whole subject as being 

 yet in its infancy. He discusses the determination of the 

 presence in the vegetable cell of iron in loose combina- 

 tions and in dense combinations, or what he terms the 

 masked condition. He then describes the occurrence 

 and distribution of iron in plants in loose and dense 

 combinations, and enters somewhat fully into the de- 

 scription of a new method he claims to have discovered 



NO- I 1 96, VOL. 46] 



for proving the existence of iron in the masked condi- 

 tion, even when it is present only in infinitesimally small 

 quantities. This is done by soaking the objects one or 

 more days or weeks in saturated aqueous liquor potassae, 

 and then, after quickly washing them in pure water, sub- 

 jecting them to the usual reagents. He further claims to 

 have proved that iron is not one of the constituents of 

 chlorophyll. There is also a short chapter on healing 

 vegetable chlorosis by the use of chloride of iron, sul- 

 phate of iron, and other salts of iron. W. B. H. 



up the Niger. By Captain A. F. Mockler-Ferryman 

 (London: George Philip and Son, 1892.) 



Several years ago complaints were made about the 

 conduct of various British subjects in the territories 

 placed under the Royal Niger Company. The British 

 Government accordingly sent Major Claude Macdonald 

 to inquire into the matter. He was accompanied by 

 Captain Mockler-Ferryman, who in the present volume 

 gives a full account of the proceedings of the Mission. 

 During the entire journey, which extended over more 

 than 3000 miles, nothing "of a blood-curdling nature" 

 occurred, so that any one who is attracted to books of 

 travel mainly by the chance of finding them full of sensa- 

 tional narratives, need not trouble himself with Captain 

 Mockler- Ferryman's pages. On the other hand, those 

 who like to read about remote regions and their native 

 inhabitants, will find in this book much to interest them. 

 The author is an accurate observer, and notes in a clear 

 and unpretending style the facts by which his attention 

 has been most strongly attracted. His descriptions of 

 the native tribes of the Niger country, so far as he him- 

 self observed them, are particularly good, and will not 

 only please the general reader, but be of service to eth- 

 nologists and anthropologists. A capital chapter on 

 music and musical instruments, prepared from materials 

 collected by the members of the mission, is contributed 

 by Captain C. R. Day, and the value of the volume as a 

 whole is much increased by a map and illustrations. 



LETTERS TO THE EDITOR. 



yrhe Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. ] 



Density of Nitrogen. 



I AM much puzzled by some recent results as to the density of 

 nitrogen, and shall be obliged if any of your chemical readers 

 can offer suggestions as to the cause. According to two methods 

 of preparation I obtain quite distinct values. The relative 

 difference, amounting to about xthtc^ P^-rt, is small in itself ; 

 but it lies entirely outside the errors of experiment, and can only 

 be attributed to a variation in the character of the gas. 



In the first method the oxygen of atmospheric air is removed 

 in the ordinary way by metallic copper, itself reduced by 

 hydrogen from the oxide. The air, freed from COg by potash, 

 gives up its oxygen to copper heated in hard glass over a large 

 Bunsen, and then passes over about a foot of red-hot copper in a 

 furnace. This tube was used merely as an indicator, and the 

 copper in it remained bright throughout. The gas then passed 

 through a wash-bottle containing sulphuric acid, thence again 

 through the furnace o\Qr copper oxide, and finally over sulphuric 

 acid, potash, and phosphoric anhydride. 



In the second method of preparation, suggested to me by 

 Prof. Ramsay, everything remained unchanged, except that the 

 first tube of hot copper was replaced by a wash-bottle contain- 

 ing liquid ammonia, through which the air was allowed to 

 bubble. The ammonia method is very convenient, but the 

 nitrogen obtained by means of it was yxiW part lighter than the 

 nitrogen of the first method. The question is, to what is the 

 discrepancy due ? 



