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the latter derivatives of a dihydrobenzene, which would account in the simplest way for the comparative ease with which phenol rings are oxidized and opened. It is well-known that the analogy in the behavior of I ,~-dihydroxy-and I ,3~-trihydroxybenzenesand t h a t of I ~ - d i c a r b o n y l derivatives is even more striking. The puzzling and central fact t h a t benzene and its derivatives appear t o be more stable in the unsaturated condition (Kekule's formula) and react in most cases a s saturated compounds (in the ring) is also not without parallel in the aliphatic series; for instance, the organic acids certainly resist reduction in the unsaturated carbonyl group almost as vigorously a s do certain benzene compounds ; even when their carbonyl group absorbs certain reagents] yielding temporarily ortho derivatives, there is a rapid reversion t o the more stable unsaturated carbonyl group-@ the acid esters, amides, etc.). ,4t the same time this same unsaturated carbonyl group has a n unmistakable effect on the activity of the hydrogen of the immediately neighboring groups, e. g., such groups as CH and OH--rr.uch as the activity of the hydrogen atoms adjacent t o the unsaturated groups of the benzene nucleus is enhanced, and when we have two such neighboring unsaturated groups in aliphatic Compounds, e. g., in the ~,g-dicarbonylseries, the analogy is even rrore marked. Again, we have all degrees of gradation in such relations-the carbonyl group in aldehydes is readily reduced by hydrogen, but towards very many other reagents shows again the same tendency t o reversion t o the unsaturated condition a s a stable form. Benzene derivatives are likewise not all equally resistant t o reduction and saturation, as shown by Baeyer, Bamberger and others for the phthalic acids, the naphthalenes and similar compounds. Stability in the so-called unsaturated condition may therefore well be simply a question of peculiarities of structure and energy content, common t o all fields of chemistry. It may not be amiss to recall parallel cases of the resistance to saturation of unsaturated compounds in inorganic chemistry, a s shown by the phosphines and arsines a t ordinary temperatures, and by ammonia above 400'. The arrangement used by Noyes, treating the aromatic compounds with t h e aliphatic ones, appears to the writer therefore logical, both pedagogically and scientifically ; exhaustive studies of the relation between the two series and especially of the question of stability and reactivity of unsaturated molecules, a s made in the investigations of Baeyer, Nef and Thiele, may solve that perplexing problem of the structure of benzene in the simplest of all ways, by demonstrating that there is no real benzene problem, but a broader, greater problem of equilibrium conditions of unsaturated valences. J. STIEGLITZ. Exercises in Elementary Quantitative Analysis for Students of Agriculture. By AZARIAHTHOMASLINCOLN, PH.D., and JAMEL HENXUWALTON,JR.,
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I'H.L). Sew I'ork: The Macmiilan Co. $1.50 net.
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I hc work includes introductor?- exercise5 in gravimetric analysis, acidimetry and alkalimetry, perinanganate and dichromate titrations, iodimetry, stoichionietry, and a sectiori 011 agricultural analysis coyvr. ing the examination of milk, butter, cereals and feeding materials, itlrtilizers and soils. The book is well written and contains :I nuiiiber of good illustmtions. It will be welcomed by those beginners in agricultural analysis who have been obliged to use the methods of the -4ssociation of Official Agricultural Chemists in bulletin form in lieu of a test-book. 'Che procedures Lire clearll- and explicitly described and the c*xplandtory notes are g e i : ~I ;ill\. good. The numerical data selected to illustrate norinal coniposition could in some cases be improved, but thr 0111~.figures likely to be seriously misleading are those for starch in grain products on page IZI. The failure of the authors to make use of t h e conceptions of ionizatioii, mass action and solubility product in the discussion of inorganic reactions and the entire oniissioii of electrolytic methods are unfortunate in a textbook which is likely to represent the sole training in quantitative anal! sis of many of the students who use it. 'These, howel-er. arc oinissions which may be supplied by the teacher and which the authors will probably correct in a subsequent edition. The book will fill a real need in the cas? of the agricultural student for whom it is especially intended arid will be found useful arid sugges tive to many others. It is coniInendabl!- frre froni typographical errors and its general make-up is excellent. I_
Testing
Milk and Its Products. B y L:.IRIU,YGTON
Jlenduta Book Co. 1908. pp.
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The authors have revised their useiul book. 'I'lic present constitutrs the eighteenth edition, the first edition haying been issued over ten Tears ago. Considerable r a t t e r has been added, which includes new met hods that have come into recent use. I,. L. v. s. The Chemistry of Commerce. By KOBERTKENNEDVDUNCAN. Harper Brothers. Price, $I .50.
It is perhaps questionable whether '~Clieiuistryof Coriii~ii.rce* ' should be reviewed in a scientific journal like that of the Cheniical SocietJ-, inasInuch as the book can only be regarded as a report on certain spectacular topics, sortie of which barely lie within the broad doli ains of cheniistr!,. At the present time, anything which tends t o stiniulatc indubtriai :and applied cheiiiistr!- in tht. IJnited S;tatc.s. \vi11 lie l i a i l ~ . dTvir I: dclighr is i r i ~ J Yeycry chemist of the land. 'That a*Cheriiistr!. of Commerce tejltled t o dn t h k . i5 evident iroiii the author'>, pr L Y ~arid introduction. mThetller lie has succct-dctl in stinlulating thc :i:as in this hig11l.v ~ C C ~ J "
